USRE32260E - Tantalum powder and method of making the same - Google Patents
Tantalum powder and method of making the same Download PDFInfo
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- USRE32260E USRE32260E US06/634,036 US63403684A USRE32260E US RE32260 E USRE32260 E US RE32260E US 63403684 A US63403684 A US 63403684A US RE32260 E USRE32260 E US RE32260E
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- phosphorus
- tantalum
- powder
- containing material
- tantalum powder
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- GUVRBAGPIYLISA-UHFFFAOYSA-N tantalum atom Chemical compound [Ta] GUVRBAGPIYLISA-UHFFFAOYSA-N 0.000 title claims abstract description 144
- 238000004519 manufacturing process Methods 0.000 title 1
- 239000000843 powder Substances 0.000 claims abstract description 134
- 229910052698 phosphorus Inorganic materials 0.000 claims abstract description 112
- 239000011574 phosphorus Substances 0.000 claims abstract description 112
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 claims abstract description 110
- 239000000463 material Substances 0.000 claims abstract description 54
- 229910052715 tantalum Inorganic materials 0.000 claims description 39
- 238000005054 agglomeration Methods 0.000 claims description 34
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 claims description 33
- 230000002776 aggregation Effects 0.000 claims description 33
- 238000000034 method Methods 0.000 claims description 31
- 238000005245 sintering Methods 0.000 claims description 21
- QORWJWZARLRLPR-UHFFFAOYSA-H tricalcium bis(phosphate) Chemical compound [Ca+2].[Ca+2].[Ca+2].[O-]P([O-])([O-])=O.[O-]P([O-])([O-])=O QORWJWZARLRLPR-UHFFFAOYSA-H 0.000 claims description 19
- 229910000391 tricalcium phosphate Inorganic materials 0.000 claims description 19
- 235000011007 phosphoric acid Nutrition 0.000 claims description 16
- 229910000147 aluminium phosphate Inorganic materials 0.000 claims description 14
- -1 orthophosphate compound Chemical class 0.000 claims description 13
- 239000002245 particle Substances 0.000 claims description 10
- 150000001457 metallic cations Chemical class 0.000 claims description 9
- 238000003825 pressing Methods 0.000 claims description 8
- MNNHAPBLZZVQHP-UHFFFAOYSA-N diammonium hydrogen phosphate Chemical compound [NH4+].[NH4+].OP([O-])([O-])=O MNNHAPBLZZVQHP-UHFFFAOYSA-N 0.000 claims description 7
- LFVGISIMTYGQHF-UHFFFAOYSA-N ammonium dihydrogen phosphate Chemical compound [NH4+].OP(O)([O-])=O LFVGISIMTYGQHF-UHFFFAOYSA-N 0.000 claims description 5
- 230000009467 reduction Effects 0.000 claims description 3
- 238000007792 addition Methods 0.000 description 36
- 229910019142 PO4 Inorganic materials 0.000 description 24
- 235000021317 phosphate Nutrition 0.000 description 24
- 150000004678 hydrides Chemical class 0.000 description 23
- 150000001875 compounds Chemical class 0.000 description 22
- 230000006872 improvement Effects 0.000 description 22
- 239000010452 phosphate Substances 0.000 description 22
- 239000011734 sodium Substances 0.000 description 22
- 239000011575 calcium Substances 0.000 description 19
- 150000003013 phosphoric acid derivatives Chemical class 0.000 description 18
- NBIIXXVUZAFLBC-UHFFFAOYSA-K phosphate Chemical compound [O-]P([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-K 0.000 description 17
- 238000012360 testing method Methods 0.000 description 16
- 230000000694 effects Effects 0.000 description 14
- 229910052816 inorganic phosphate Inorganic materials 0.000 description 14
- 239000000654 additive Substances 0.000 description 12
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 description 11
- 229910052708 sodium Inorganic materials 0.000 description 11
- 239000002002 slurry Substances 0.000 description 9
- 238000011282 treatment Methods 0.000 description 9
- 230000015556 catabolic process Effects 0.000 description 8
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 7
- 239000000243 solution Substances 0.000 description 7
- 239000003990 capacitor Substances 0.000 description 6
- 239000000203 mixture Substances 0.000 description 6
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 description 5
- 229910052791 calcium Inorganic materials 0.000 description 5
- 238000010438 heat treatment Methods 0.000 description 5
- 150000002500 ions Chemical class 0.000 description 5
- 238000010998 test method Methods 0.000 description 5
- 230000002411 adverse Effects 0.000 description 4
- 229910052739 hydrogen Inorganic materials 0.000 description 4
- 238000010561 standard procedure Methods 0.000 description 4
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 4
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 3
- 230000000996 additive effect Effects 0.000 description 3
- 238000007743 anodising Methods 0.000 description 3
- OJMIONKXNSYLSR-UHFFFAOYSA-N phosphorous acid Chemical compound OP(O)O OJMIONKXNSYLSR-UHFFFAOYSA-N 0.000 description 3
- GNSKLFRGEWLPPA-UHFFFAOYSA-M potassium dihydrogen phosphate Chemical compound [K+].OP(O)([O-])=O GNSKLFRGEWLPPA-UHFFFAOYSA-M 0.000 description 3
- 239000002244 precipitate Substances 0.000 description 3
- 150000003839 salts Chemical class 0.000 description 3
- QTBSBXVTEAMEQO-UHFFFAOYSA-M Acetate Chemical compound CC([O-])=O QTBSBXVTEAMEQO-UHFFFAOYSA-M 0.000 description 2
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- 229910003944 H3 PO4 Inorganic materials 0.000 description 2
- 239000002253 acid Substances 0.000 description 2
- 150000007513 acids Chemical class 0.000 description 2
- 229910000318 alkali metal phosphate Inorganic materials 0.000 description 2
- 229910052788 barium Inorganic materials 0.000 description 2
- DSAJWYNOEDNPEQ-UHFFFAOYSA-N barium atom Chemical compound [Ba] DSAJWYNOEDNPEQ-UHFFFAOYSA-N 0.000 description 2
- 159000000009 barium salts Chemical class 0.000 description 2
- WAKZZMMCDILMEF-UHFFFAOYSA-H barium(2+);diphosphate Chemical compound [Ba+2].[Ba+2].[Ba+2].[O-]P([O-])([O-])=O.[O-]P([O-])([O-])=O WAKZZMMCDILMEF-UHFFFAOYSA-H 0.000 description 2
- 230000008901 benefit Effects 0.000 description 2
- 239000007795 chemical reaction product Substances 0.000 description 2
- BNIILDVGGAEEIG-UHFFFAOYSA-L disodium hydrogen phosphate Chemical compound [Na+].[Na+].OP([O-])([O-])=O BNIILDVGGAEEIG-UHFFFAOYSA-L 0.000 description 2
- LVXHNCUCBXIIPE-UHFFFAOYSA-L disodium;hydrogen phosphate;hydrate Chemical compound O.[Na+].[Na+].OP([O-])([O-])=O LVXHNCUCBXIIPE-UHFFFAOYSA-L 0.000 description 2
- 239000002019 doping agent Substances 0.000 description 2
- 238000010894 electron beam technology Methods 0.000 description 2
- 150000004820 halides Chemical class 0.000 description 2
- 239000001257 hydrogen Substances 0.000 description 2
- 239000012535 impurity Substances 0.000 description 2
- 239000007788 liquid Substances 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- GBMDVOWEEQVZKZ-UHFFFAOYSA-N methanol;hydrate Chemical compound O.OC GBMDVOWEEQVZKZ-UHFFFAOYSA-N 0.000 description 2
- 238000002360 preparation method Methods 0.000 description 2
- 238000010298 pulverizing process Methods 0.000 description 2
- 239000003870 refractory metal Substances 0.000 description 2
- BBMHARZCALWXSL-UHFFFAOYSA-M sodium dihydrogenphosphate monohydrate Chemical compound O.[Na+].OP(O)([O-])=O BBMHARZCALWXSL-UHFFFAOYSA-M 0.000 description 2
- 230000008961 swelling Effects 0.000 description 2
- KWSLGOVYXMQPPX-UHFFFAOYSA-N 5-[3-(trifluoromethyl)phenyl]-2h-tetrazole Chemical compound FC(F)(F)C1=CC=CC(C2=NNN=N2)=C1 KWSLGOVYXMQPPX-UHFFFAOYSA-N 0.000 description 1
- QGZKDVFQNNGYKY-UHFFFAOYSA-O Ammonium Chemical compound [NH4+] QGZKDVFQNNGYKY-UHFFFAOYSA-O 0.000 description 1
- GVGLGOZIDCSQPN-PVHGPHFFSA-N Heroin Chemical compound O([C@H]1[C@H](C=C[C@H]23)OC(C)=O)C4=C5[C@@]12CCN(C)[C@@H]3CC5=CC=C4OC(C)=O GVGLGOZIDCSQPN-PVHGPHFFSA-N 0.000 description 1
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- NBIIXXVUZAFLBC-UHFFFAOYSA-L Phosphate ion(2-) Chemical compound OP([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-L 0.000 description 1
- ZLMJMSJWJFRBEC-UHFFFAOYSA-N Potassium Chemical compound [K] ZLMJMSJWJFRBEC-UHFFFAOYSA-N 0.000 description 1
- ZRIUUUJAJJNDSS-UHFFFAOYSA-N ammonium phosphates Chemical class [NH4+].[NH4+].[NH4+].[O-]P([O-])([O-])=O ZRIUUUJAJJNDSS-UHFFFAOYSA-N 0.000 description 1
- 239000003125 aqueous solvent Substances 0.000 description 1
- 150000001553 barium compounds Chemical class 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- HUTDDBSSHVOYJR-UHFFFAOYSA-H bis[(2-oxo-1,3,2$l^{5},4$l^{2}-dioxaphosphaplumbetan-2-yl)oxy]lead Chemical compound [Pb+2].[Pb+2].[Pb+2].[O-]P([O-])([O-])=O.[O-]P([O-])([O-])=O HUTDDBSSHVOYJR-UHFFFAOYSA-H 0.000 description 1
- BRPQOXSCLDDYGP-UHFFFAOYSA-N calcium oxide Chemical compound [O-2].[Ca+2] BRPQOXSCLDDYGP-UHFFFAOYSA-N 0.000 description 1
- 239000000292 calcium oxide Substances 0.000 description 1
- ODINCKMPIJJUCX-UHFFFAOYSA-N calcium oxide Inorganic materials [Ca]=O ODINCKMPIJJUCX-UHFFFAOYSA-N 0.000 description 1
- 150000001768 cations Chemical class 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 230000001427 coherent effect Effects 0.000 description 1
- 239000008367 deionised water Substances 0.000 description 1
- 230000001627 detrimental effect Effects 0.000 description 1
- 229910000388 diammonium phosphate Inorganic materials 0.000 description 1
- 235000019838 diammonium phosphate Nutrition 0.000 description 1
- 239000012153 distilled water Substances 0.000 description 1
- 239000011363 dried mixture Substances 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 238000005323 electroforming Methods 0.000 description 1
- 239000003792 electrolyte Substances 0.000 description 1
- 230000008030 elimination Effects 0.000 description 1
- 238000003379 elimination reaction Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- BHEPBYXIRTUNPN-UHFFFAOYSA-N hydridophosphorus(.) (triplet) Chemical compound [PH] BHEPBYXIRTUNPN-UHFFFAOYSA-N 0.000 description 1
- 150000002431 hydrogen Chemical class 0.000 description 1
- 230000001771 impaired effect Effects 0.000 description 1
- 239000003112 inhibitor Substances 0.000 description 1
- 150000002611 lead compounds Chemical class 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 150000003017 phosphorus Chemical class 0.000 description 1
- 229910001392 phosphorus oxide Inorganic materials 0.000 description 1
- LFGREXWGYUGZLY-UHFFFAOYSA-N phosphoryl Chemical class [P]=O LFGREXWGYUGZLY-UHFFFAOYSA-N 0.000 description 1
- 239000011148 porous material Substances 0.000 description 1
- 229910052700 potassium Inorganic materials 0.000 description 1
- 239000011591 potassium Substances 0.000 description 1
- 239000002243 precursor Substances 0.000 description 1
- 239000000047 product Substances 0.000 description 1
- AJPJDKMHJJGVTQ-UHFFFAOYSA-M sodium dihydrogen phosphate Chemical compound [Na+].OP(O)([O-])=O AJPJDKMHJJGVTQ-UHFFFAOYSA-M 0.000 description 1
- 229910001379 sodium hypophosphite Inorganic materials 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 239000012085 test solution Substances 0.000 description 1
- 238000012956 testing procedure Methods 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
- H01G9/00—Electrolytic capacitors, rectifiers, detectors, switching devices, light-sensitive or temperature-sensitive devices; Processes of their manufacture
- H01G9/004—Details
- H01G9/04—Electrodes or formation of dielectric layers thereon
- H01G9/048—Electrodes or formation of dielectric layers thereon characterised by their structure
- H01G9/052—Sintered electrodes
- H01G9/0525—Powder therefor
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
- B22F1/12—Metallic powder containing non-metallic particles
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C1/00—Making non-ferrous alloys
- C22C1/04—Making non-ferrous alloys by powder metallurgy
- C22C1/045—Alloys based on refractory metals
Definitions
- This invention relates to tantalum powders and to anodes prepared therefrom, and specifically to powders capable of producing anodes improved in electrical capacitance and, in one embodiment, powders having improved flow characteristics.
- tantalum powders for the preparation of electrodes in electrolytic capacitors is well known. Such electrodes are made by pressing the tantalum powder to form a coherent compact, sintering the compact and subsequently forming a dielectric film on the sintered product.
- U.S. Pat. No. 3,418,106 discloses an agglomerated tantalum powder crushable as tantalum which when fabricated into an electrode provides enhanced specific capacity.
- the agglomerated tantalum powder described in this patent also has improved flow characteristics as compared to prior powders.
- U.S. Pat. No. 3,825,802 discloses improvements in various properties of tantalum capacitors, including specific capacity, by the addition to the tantalum of any of several "dopants", including phosphorus.
- the range of dopant disclosed is from 0.47 to 2.71 atomic percent which, for phosphorus is equivalent to from about 800 to 4600 parts per million and the improvement in specific capacity (for nitrogen, the preferred species) ranges from about 2% (at the lower end of the range) to about 6.3% (at the upper end) when the anode is sintered at 1900° C.
- a tantalum powder capable of producing capacitors of improved specific capacity is prepared by the addition of a tantalum powder of a small amount of a phosphorus-containing material, substantially less than the range disclosed in U.S. Pat. No. 3,825,802 and in the range from about 5 to about 400 parts per million, based on elemental phosphorus.
- the addition of the phosphorus-containing material is combined with the agglomeration of tantalum powder in accordance with U.S. Pat. No. 3,418,106, but the addition to an unagglomerated powder of a phosphorus-containing material in the range of from about 5 to about 400 parts per million based on elemental phosphorus also improves the specific capacity of capacitors made from such powders.
- a phosphorus-containing material be added to the tantalum powder, or to a tantalum hydride powder before reduction thereof to tantalum.
- phosphorus is present in a tantalum powder as an incidental impurity, either carried over from the original ore or introduced as an impurity in the chemicals used in the normal preparation of the tantalum powder, the results of this invention are not obtained.
- the amount of phosphorus-containing material added to the powder in accordance with this invention is, as stated above, from about 5 to about 400 parts per million based on elemental phosphorus. Within this range, higher levels of phosphorus generally produce greater improvement in specific capacity values. At phosphorus levels above about 400 parts per million, a plateau is reached and further improvement in specific capacity values are not obtained. Furthermore, phosphorus additions in excess of about 400 parts per million based on elemental phosphorus adversely affect the green strength of anodes pressed from the powder and adversely affect its sintering properties.
- the preferred phosphorus-containing materials are the inorganic phosphate salts, such as ammonium, sodium, potassium, calcium, barium and lead orthophosphates, ammonium mono-hydrogen orthophosphate, ammonium di-hydrogen orthophosphate, sodium mono-hydrogen orthophosphate, sodium di-hydrogen orthophosphate, and potassium di-hydrogen orthophosphate.
- suitable phosphorus-containing materials include elemental phosphorus, metallic phosphides, phosphorus oxides and acids, and organic phosphorus-containing materials, such as alkyl phosphates.
- Phosphate materials containing no metallic cations such as ammonium mono-hydrogen orthophosphate, ammonium dihydrogen orthophosphate and phosphoric acid, are particularly preferred because they do not introduce other metals into the tantalum powder with possible adverse effects on the d.c. leakage and breakdown voltage properties of the anodes produced therefrom.
- both the specific capacity and the flow properties of tantalum powders are improved by combining an amount of calcium orthophosphate (applied after agglomeration) which is sufficient to provide enhanced free flow properties (e.g. 20 to 80 parts per million) with an amount of a phosphorus-containing material having no metallic cations sufficient to provide a substantial boost to the specific capacity improvement provided by the calcium orthophosphate (e.g. up to a maximum total phosphorus content of about 400 parts per million).
- the phosphorus-containing material may be added to the tantalum powder in a dry state, but is preferably added in the form of a solution (in an aqueous or partially aqueous solvent) or in the form of a slurry.
- the material may be added to the tantalum powder in the desired proportion or it may be added initially in a master blend containing substantially more phosphorus than desired in the final material and thereafter blended with additional tantalum powder to produce the desired final composition.
- the tantalum powder may be agglomerated or unagglomerated at the time the phosphorus-containing material is applied thereto, and if unagglomerated, it may be thereafter agglomerated or not, as desired.
- the improvement of this invention is applicable to tantalum powders produced in different ways, such as sodium-reduced tantalum powders and tantalum powders produced from melted ingots (electron beam or arc melted).
- the tantalum powders may, if desired, be in hydride form at the time the phosphorus-containing material is added and be reduced to metallic form in subsequent treatment.
- the maximum increase in specific capacity is obtained in accordance with this invention when the pressed tantalum anodes made from the powders of this invention are sintered at a relatively low temperature (e.g. 1600° C.). Lesser increases are obtained at higher sintering temperatures (e.g. 1800° C.) and still lesser increases at high sintering temperatures (e.g. 2000° C.).
- Example 1 An agglomerated sodium-reduced tantalum powder, designated Example 1, was used as a control.
- Calcium orthophosphate was produced by adding orthophosphoric acid to calcium oxide and was washed free of acids before use. Methanol and the washed precipitate of calcium orthophosphate were added to an agglomerated sodium-reduced tantalum powder to form a slurry, and the slurry was dried in air at 90°-100° C. The dried mixture was then stirred in a V-shell blender for three minutes. The amount of calcium orthophosphate was sufficient to make a master mixture containing 800 to 1000 parts per million of the orthophosphate ion, PO 4 -3 , corresponding to about 261 to about 326 parts per million of elemental phosphorus.
- Example 2 The mixture was blended with an additional amount of the same lot of agglomerated sodium reduced tantalum powder as in Example 1 to produce a final concentration of 115 parts per million of the orthophosphate ion, corresponding to 37.5 ppm of elemental phosphorus.
- This phosphorus-containing powder is designated Example 2.
- the tantalum control powder of Example 1 was found to have a Hall flow of 46 seconds when measured in accordance with "Standard Method of Test for Flow Rate of Metal Powders," ASTM designation: B213-48 (reapproved 1965), except that the test unit was modified to vibrate the Hall flow cup, and the cup was vibrated at a frequency of 3600 cycles and an amplitude of 0.024 inch.
- the phosphorus-containing powder of Example 2 had a Hall flow of 27 seconds when measured under the same conditions.
- control powder (Example 1) and the calcium orthophosphate-containing powder (Example 2) were formed into 2-gram anodes by pressing the powder to a density of 6.45 g/cm 3 .
- the anodes were sintered either for 30 minutes at 1800° C. or for 30 minutes at 2000° C. in a cold-wall, vacuum sintering furnace (10 -5 Torr absolute pressure), and then were tested for density and specific capacity (CV/g.).
- the testing procedure involved anodizing the sintered anodes in 0.01% phosphoric acid in water. Anodizing was carried out at a current density of 35 milliamps per gram until 200 volts was reached. The anodes sintered at 1800° C. were held at 200 volts for 2 hours. The anodes sintered at 2000° C. were anodized to 270 volts but at a current density of 12 milliamps per gram. The latter anodes were held at 270 volts for 1 hour.
- the formed anodes were washed in de-ionized water and then dried in clean air at 105° C. They were then soaked in 10% phosphoric acid for 30 minutes. The capacitance was measured on the anode immersed in 10% phosphoric acid employing a type 1611B General Radio Capacitance Test Bridge with an a.c. signal of 0.5 volts and a d.c. bias of 3 volts. The results are summarized in Table I.
- inorganic phosphate compounds were utilized as additives to agglomerated sodium-reduced tantalum powder. The following list of compounds were employed:
- the calcium and barium compounds were prepared in the laboratory by a standard procedure of interacting an alkali metal phosphate with a soluble metallic halide or acetate. The precipitate formed was washed free of reaction products and was employed either as a slurry or a dried powder.
- the other phosphate compounds were commercially available.
- the appropriate phosphate was either mixed or dissolved in a 30% water-methanol solution. A sufficient amount of the phosphate-containing liquid was added to the tantalum powder to make a thick slurry. The slurry was dried at 90° C. and then thoroughly homogenized in a twin-shell blender.
- a master blend of 1000 ppm of the additive was first prepared and then blended with more tantalum powder to get final concentrations of 30-50 ppm of the PO 4 -3 ion, corresponding to about 10 to about 16 ppm of elemental phosphorus. The other salts were blended directly to the desired concentration.
- Example 3 Two-gram anodes were pressed to a density of 6.45 g/cm 3 from tantalum powder from the same lot of agglomerated sodium-reduced tantalum powder and are designated Example 3. Similar anodes were pressed from the powders containing the various phosphate compound additives and are designated Examples 4 through 9. Anodes of Examples 3 through 9 were sintered in vacuum either for 30 minutes at 1800° C. or for 30 minutes at 2000° C. and tested for specific capacitance using the sintering practice and test conditions described for Examples 1 and 2. Direct current leakage (DCL) also was measured in the electrical tests. The anodes, after anodizing, rinsing and drying, were first tested for DCL. A phosphoric acid solution was employed. The test conditions were as follows:
- the anodes were immersed in the test solution to the top of the anode and the proper voltage was applied for 2 minutes, after which the leakage was measured.
- the anodes formed to 200 volts were placed in a tray containing 10% phosphoric acid and permitted to soak 30 to 45 minutes.
- the anodes formed to 270 volts were washed for 3 to 5 minutes in running distilled water and dried 45 minutes at 105°+5° C. in air. They were then soaked in 10% phosphoric acid for 30 to 45 minutes. The capacitance was measured using the procedure described under Examples 1 and 2.
- Tantalum powder was produced from an electron beam melted high-purity tantalum ingot by embrittling the ingot by heating it in a hydrogen atmosphere then crushing and pulverizing the resulting friable ingot to yield a tantalum hydride powder.
- the tantalum hydride powder was converted to an agglomerated tantalum powder (designated hereafter as "agglomerated EB powder") by heating the tantalum hydride powder in vacuum to 1390° C., followed by pulverizing the lightly sintered cake to produce -60 mesh agglomerated tantalum powder. This agglomerated EB powder is included as a control in Example 10.
- Example 10 powder The following series of inorganic phosphate compounds were utilized as additives to agglomerated EB powder from the same lot as the control, Example 10 powder:
- the calcium, barium and lead compounds were prepared in the laboratory by a standard procedure of interacting an alkali metal phosphate with a soluble metallic halide or acetate. The precipitate formed was washed free of reaction products and was employed either as a slurry or a dried powder.
- the other phosphate compounds were commercially available.
- the appropriate phosphate was either mixed or dissolved in a 30% water-methanol solution. A sufficient amount of the phosphate-containing liquid was added to the tantalum powder to make a thick slurry. The slurry was dried at 90° C. and then thoroughly homogenized in a twin-shell blender.
- a master blend of 1000 ppm of the additive was first prepared and then blended with more tantalum powder to get final concentrations of 30-50 ppm of the PO 4 -3 ion, corresponding to about 10 to about 16 ppm of elemental phosphorus. The other salts were blended directly to the desired concentration.
- Example 10 Two-gram anodes were pressed to a density of 7.20 g/cm 3 from tantalum powder from the same lot of agglomerated EB powder and containing no added phosphorus and are designated Example 10. Similar anodes were pressed from the powders containing the various phosphate compound additives and are designated Examples 11 through 18. Anodes of Examples 10 through 18 were sintered in vacuum either for 30 minutes at 1800° C. or for 30 minutes at 2000° C. and tested for specific capacitance using the sintering practice and test conditions as described for Examples 1 and 2, and for DCL as described in Examples 3 through 9.
- Anodes prepared from each of the powders of Examples 10 to 18 were sintered for 30 minutes at 2000° C. and were measured for breakdown voltage (BDV).
- the breakdown voltage test was carried out by electroforming in an agitated 0.1% H 3 PO 4 solution at 90° ⁇ 2° C., with the forming voltage increased at a rate of 3 to 4 volts per minute until dielectric breakdown occurred.
- the point of breakdown was established when the forming current of the anode increased by 100 m.a. over the current flowing at 100 volts or when scintillation occurred.
- a mean breakdown voltage was determined after elimination of "outliers".
- outlier is one that appears to deviate markedly from other members of the set in which it occurs. Only one outlier per test lot is acceptable.
- ASTM-E-178-61T "Tentative Recommended Practice for Dealing with Outlying Observations" was followed.
- Example 19 An EB tantalum ingot hydride powder was used as a control, and is designated as Example 19.
- Hydride powder from the same lot as used in Example 19 was degassed in vacuum to remove the hydrogen, resulting in EB powder. This degassed powder was used as other controls, designated as Examples 23 and 27, according to the subsequent agglomerating treatment used.
- control hydride powder, Example 19, and the phosphate-containing hydride powders, Examples 20, 21 and 22, were converted to an agglomerated EB powder by heating these hydride powders in vacuum for 60 minutes at 1390° C.
- the EB powder control, Example 23, and the phosphate-containing EB powders, Examples 24, 25 and 26, were converted to agglomerated EB powders by heating these EB ingot powders in vacuum for 60 minutes at 1390° C.
- the EB powder control, Example 27, and phosphate-containing EB powders, Examples 28, 29 and 30, were converted to an agglomerated EB powder by heating these EB powders in vacuum for 60 minutes at 1440° C.
- Two-gram anodes were pressed to a density of 7.20 g/cm 3 from the powders of Examples 19 to 30.
- Anodes were sintered either for 30 minutes at 1800° C. or for 30 minutes at 2000° C. and tested for DCL, specific capacitance, and BDV (only on anodes sintered at 2000° C.). The same procedures were used in the electrical test procedures as described in Examples 1 through 18.
- the powder of Example 47 is an EB tantalum ingot hydride powder having an average particle size of 3.2 microns (F.S.S.S. of 3.2 ⁇ ) as determined by the procedure of ASTM-B-330-58T, "Tentative Method of Test for Average Particle Size of Refractory Metals and Compounds by Fisher Sub-Sieve Sizer". This powder was used as a control.
- the powders of Examples 47 to 51 were agglomerated at 1375° C. for 30 minutes. Two-gram anodes were pressed from the powder to a density of 7.20 g/cm 3 . Some anodes were sintered for 30 minutes at 1600° C., and others for 30 minutes at 1800° C. or 30 minutes at 2000° C. These anodes were tested for DCL, specific capacitance, and BDV (only on anodes sintered at 1800° and 2000° C.) using the same test procedures as in earlier examples.
- the hydride powders were agglomerated in one treatment for 30 minutes at 1375° C.
- the hydride powders first were subjected to a pre-agglomeration treatment for 60 minutes at 1200° C., followed by an agglomeration treatment for 30 minutes at 1375° C.
- Two-gram anodes were pressed from the powders to a density of 7.20 g/cm 3 , and then were sintered at 1600° C. (30 minutes), or at 1800° C. (30 minutes), or at 2000° C. (30 minutes), and then were tested as described in earlier examples.
- Two-gram anodes were pressed from these powders to a density of 7.20 g/cm 3 , and then were sintered either for 30 minutes at 1800° C. or 30 minutes at 2000° C. and tested for electrical characteristics using the test procedures described in earlier examples.
- the resultant agglomerated powders have a somewhat lower scott density and a particle size (F.S.S.S., in microns) of only about 60 to 70% of that of the agglomerated control powder.
- Two-gram anodes of the phosphate-containing powders were pressed to a density of 7.20 g/cm 3 and sintered for 30 minutes at 1600° C.
- the as-pressed anodes were 0.258 inches diameter and 0.323 ⁇ 0.001 inches length.
- the control anodes averaged 0.251 inches diameter and 0.314 inches length; the phosphate-containing anodes hardly showed any shrinkage, and even exhibited swelling in some cases, and they averaged 0.259 inches diameter and 0.321 inches length.
- the anodes were tested for DCL and specific capacitance. Breakdown voltage was determined on additional anodes sintered for 30 minutes at 1800° C. The test methods that were used are described in earlier examples.
- phosphorus-containing additives were various inorganic phosphate salts.
- phosphoric acid was added to either EB tantalum hydride powder (F.S.S.S. of 3.2 microns) or to agglomerated powder produced from hydride powder from the same lot.
- the powders were agglomerated for 60 minutes at 1365° C. Two-gram anodes were pressed from these powders to a density of 7.20 g/cm 3 , sintered either for 30 minutes at 1600° C. or for 30 minutes at 1800° C., and tested for DCL and specific capacitance using the procedures described in earlier examples. The results are shown in Table XI.
- An agglomerated EB tantalum powder was treated with a solution of sodium hypophosphite, NaH 2 PO 2 H 2 O to produce an added phosphorus concentration of 150 ppm.
- Two-gram anodes were pressed from the untreated control powder (Example 92) and the phosphite-treated powder (Example 93) to a density of 7.20 g/cm 3 , sintered for 30 minutes at 1600° C., and tested using the procedures described in earlier examples. The results are shown in Table XII.
- Agglomerated EB tantalum powder was treated with various inorganic phosphate salts using concentrations of 9 to 50 ppm contained phosphorus ion in a large number of experimental runs. Untreated powders from the same lots were used as controls. Two-gram anodes were pressed from these powders to a density of 7.20 g/cm 3 , sintered for 30 minutes at 2000° C., and tested for BDV. The results are shown in Table XIII.
- any of these phosphate compounds including phosphoric acid, H 3 PO 4
- the preferred additives are those which contain no metallic cations, such as the ammonium phosphate salts and phosphoric acid.
- EB tantalum ingot hydride powder with a F.S.S.S. of approximately 2 microns was used as a control in Example 102.
- An addition of (NH 4 ) 2 HPO 4 was made to another portion of EB hydride powder from the same lot.
- the amount of the compound added was 307 ppm PO 4 -3 ion, or 100 ppm of elemental phosphorus. These powders were degassed, and did not receive an agglomeration treatment.
- Two-gram anodes were pressed from the powders, sintered for 30 minutes at 1800° C. and tested for specific capacitance using the previously described procedures.
- Example 102 had a capacitance of 2700 CV/g, while the anodes made using the phosphorus-containing powder, Example 103, had a capacitance of 3608 CV/g, an increase of 33.0% over the control.
- Example 104 Sodium-reduced tantaum powder that had not received an agglomeration treatment was used as a control, Example 104. Other portions of powder from the same lot were treated with (NH 4 ) 2 HPO 4 to provide additions of 50 and 100 ppm of elemental phosphorus. Two-gram anodes were pressed from these powders to a density of 6.45 g/cm 3 , and were sintered either for 30 minutes at 1600° C. or 30 minutes at 1800° C. and then tested for DCL, specific capacitance, and BDV (on anodes sintered at 1800° C. only) using the procedures described in earlier examples.
- EB tantalum hydride powder with a F.S.S.S. of 3.2 microns was agglomerated for 30 minutes at 1365° C. and crushed to -35 mesh powder.
- Two-gram anodes were pressed from the powder to a density of 7.20 g/cm 3 .
- the anodes were divided into three groups, Examples 107 to 109.
- the average pore volume in the anodes was calculated from the density.
- a solution of amonium mono-hydrogen phosphate was applied using an eyedropper to saturate the anodes and achieve two levels of additions, plus the zero level of the control, shown in Table XV.
- the anodes were dried in air, then were sintered for 30 minutes at 1600° C. and tested for percent shrinkage during sintering and specific capacitance, using the test methods described in earlier examples. The results are shown in Table XV.
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Abstract
Tantalum powder capable of producing anodes of improved electrical capacitance is prepared by the addition of phosphorus-containing materials in amounts from about 5 to about 400 ppm based on elemental phosphorus. In one embodiment, the flow properties of the powder are also improved.
Description
This invention relates to tantalum powders and to anodes prepared therefrom, and specifically to powders capable of producing anodes improved in electrical capacitance and, in one embodiment, powders having improved flow characteristics.
The use of tantalum powders for the preparation of electrodes in electrolytic capacitors is well known. Such electrodes are made by pressing the tantalum powder to form a coherent compact, sintering the compact and subsequently forming a dielectric film on the sintered product.
In such capacitors it is desired to have as high a specific capacity CV/g. as possible. U.S. Pat. No. 3,418,106 discloses an agglomerated tantalum powder crushable as tantalum which when fabricated into an electrode provides enhanced specific capacity. The agglomerated tantalum powder described in this patent also has improved flow characteristics as compared to prior powders.
U.S. Pat. No. 3,825,802 discloses improvements in various properties of tantalum capacitors, including specific capacity, by the addition to the tantalum of any of several "dopants", including phosphorus. The range of dopant disclosed is from 0.47 to 2.71 atomic percent which, for phosphorus is equivalent to from about 800 to 4600 parts per million and the improvement in specific capacity (for nitrogen, the preferred species) ranges from about 2% (at the lower end of the range) to about 6.3% (at the upper end) when the anode is sintered at 1900° C.
In accordance with the present invention a tantalum powder, capable of producing capacitors of improved specific capacity is prepared by the addition of a tantalum powder of a small amount of a phosphorus-containing material, substantially less than the range disclosed in U.S. Pat. No. 3,825,802 and in the range from about 5 to about 400 parts per million, based on elemental phosphorus. In the preferred embodiment of this invention, the addition of the phosphorus-containing material is combined with the agglomeration of tantalum powder in accordance with U.S. Pat. No. 3,418,106, but the addition to an unagglomerated powder of a phosphorus-containing material in the range of from about 5 to about 400 parts per million based on elemental phosphorus also improves the specific capacity of capacitors made from such powders.
It is necessary, in accordance with this invention, that a phosphorus-containing material be added to the tantalum powder, or to a tantalum hydride powder before reduction thereof to tantalum. When phosphorus is present in a tantalum powder as an incidental impurity, either carried over from the original ore or introduced as an impurity in the chemicals used in the normal preparation of the tantalum powder, the results of this invention are not obtained.
Nor are the results of this invention obtained when phosphorus-containing materials are added to tantalum powder which has been pressed and sintered into anode form, as disclosed in U.S. Pat. No. 3,308,350. However, the results of this invention are obtained when a phosphorus-containing material is added to a tantalum powder which has been pressed into anode form but not sintered.
The amount of phosphorus-containing material added to the powder in accordance with this invention is, as stated above, from about 5 to about 400 parts per million based on elemental phosphorus. Within this range, higher levels of phosphorus generally produce greater improvement in specific capacity values. At phosphorus levels above about 400 parts per million, a plateau is reached and further improvement in specific capacity values are not obtained. Furthermore, phosphorus additions in excess of about 400 parts per million based on elemental phosphorus adversely affect the green strength of anodes pressed from the powder and adversely affect its sintering properties.
The preferred phosphorus-containing materials are the inorganic phosphate salts, such as ammonium, sodium, potassium, calcium, barium and lead orthophosphates, ammonium mono-hydrogen orthophosphate, ammonium di-hydrogen orthophosphate, sodium mono-hydrogen orthophosphate, sodium di-hydrogen orthophosphate, and potassium di-hydrogen orthophosphate. Other suitable phosphorus-containing materials include elemental phosphorus, metallic phosphides, phosphorus oxides and acids, and organic phosphorus-containing materials, such as alkyl phosphates.
Phosphate materials containing no metallic cations, such as ammonium mono-hydrogen orthophosphate, ammonium dihydrogen orthophosphate and phosphoric acid, are particularly preferred because they do not introduce other metals into the tantalum powder with possible adverse effects on the d.c. leakage and breakdown voltage properties of the anodes produced therefrom.
When calcium orthophosphate is added as the phosphorus-containing material and when the material is added after agglomeration, an added advantage is obtained in that the flow characteristics of the final powder are improved.
In one preferred embodiment, both the specific capacity and the flow properties of tantalum powders are improved by combining an amount of calcium orthophosphate (applied after agglomeration) which is sufficient to provide enhanced free flow properties (e.g. 20 to 80 parts per million) with an amount of a phosphorus-containing material having no metallic cations sufficient to provide a substantial boost to the specific capacity improvement provided by the calcium orthophosphate (e.g. up to a maximum total phosphorus content of about 400 parts per million).
The phosphorus-containing material may be added to the tantalum powder in a dry state, but is preferably added in the form of a solution (in an aqueous or partially aqueous solvent) or in the form of a slurry. The material may be added to the tantalum powder in the desired proportion or it may be added initially in a master blend containing substantially more phosphorus than desired in the final material and thereafter blended with additional tantalum powder to produce the desired final composition.
The tantalum powder, as stated above, may be agglomerated or unagglomerated at the time the phosphorus-containing material is applied thereto, and if unagglomerated, it may be thereafter agglomerated or not, as desired. The improvement of this invention is applicable to tantalum powders produced in different ways, such as sodium-reduced tantalum powders and tantalum powders produced from melted ingots (electron beam or arc melted). The tantalum powders, may, if desired, be in hydride form at the time the phosphorus-containing material is added and be reduced to metallic form in subsequent treatment.
The maximum increase in specific capacity is obtained in accordance with this invention when the pressed tantalum anodes made from the powders of this invention are sintered at a relatively low temperature (e.g. 1600° C.). Lesser increases are obtained at higher sintering temperatures (e.g. 1800° C.) and still lesser increases at high sintering temperatures (e.g. 2000° C.).
An agglomerated sodium-reduced tantalum powder, designated Example 1, was used as a control.
Calcium orthophosphate was produced by adding orthophosphoric acid to calcium oxide and was washed free of acids before use. Methanol and the washed precipitate of calcium orthophosphate were added to an agglomerated sodium-reduced tantalum powder to form a slurry, and the slurry was dried in air at 90°-100° C. The dried mixture was then stirred in a V-shell blender for three minutes. The amount of calcium orthophosphate was sufficient to make a master mixture containing 800 to 1000 parts per million of the orthophosphate ion, PO4 -3, corresponding to about 261 to about 326 parts per million of elemental phosphorus. The mixture was blended with an additional amount of the same lot of agglomerated sodium reduced tantalum powder as in Example 1 to produce a final concentration of 115 parts per million of the orthophosphate ion, corresponding to 37.5 ppm of elemental phosphorus. This phosphorus-containing powder is designated Example 2.
The tantalum control powder of Example 1 was found to have a Hall flow of 46 seconds when measured in accordance with "Standard Method of Test for Flow Rate of Metal Powders," ASTM designation: B213-48 (reapproved 1965), except that the test unit was modified to vibrate the Hall flow cup, and the cup was vibrated at a frequency of 3600 cycles and an amplitude of 0.024 inch. The phosphorus-containing powder of Example 2 had a Hall flow of 27 seconds when measured under the same conditions.
The control powder (Example 1) and the calcium orthophosphate-containing powder (Example 2) were formed into 2-gram anodes by pressing the powder to a density of 6.45 g/cm3. The anodes were sintered either for 30 minutes at 1800° C. or for 30 minutes at 2000° C. in a cold-wall, vacuum sintering furnace (10-5 Torr absolute pressure), and then were tested for density and specific capacity (CV/g.).
The testing procedure involved anodizing the sintered anodes in 0.01% phosphoric acid in water. Anodizing was carried out at a current density of 35 milliamps per gram until 200 volts was reached. The anodes sintered at 1800° C. were held at 200 volts for 2 hours. The anodes sintered at 2000° C. were anodized to 270 volts but at a current density of 12 milliamps per gram. The latter anodes were held at 270 volts for 1 hour.
The formed anodes were washed in de-ionized water and then dried in clean air at 105° C. They were then soaked in 10% phosphoric acid for 30 minutes. The capacitance was measured on the anode immersed in 10% phosphoric acid employing a type 1611B General Radio Capacitance Test Bridge with an a.c. signal of 0.5 volts and a d.c. bias of 3 volts. The results are summarized in Table I.
TABLE I
__________________________________________________________________________
Sintered at 1800° C.
Sintered at 2000° C.
Sintered
Capacitance
CV/g Capacitance
CV/g
Example Density
Micro-farad
Improvement
Sintered
Micro-farad
Improvement
No. Remarks g/cm.sup.3
volts/g (CV/g)
% Density
volts/g (CV/g)
%
__________________________________________________________________________
1 Control 7.31 4783 -- 8.58 3488 --
2 Ca.sub.2 (PO.sub.4).sub.2 added to
7.08 5036 5.3 8.34 3550 1.8
37.5 ppm P
__________________________________________________________________________
These results show that the addition of calcium orthophosphate to agglomerated sodium-reduced tantalum powder improved flow properties of the powder and resulted in an improvement in specific capacitance.
A series of inorganic phosphate compounds were utilized as additives to agglomerated sodium-reduced tantalum powder. The following list of compounds were employed:
______________________________________
*Ca.sub.3 (PO.sub.4).sub.2
calcium orthophosphate
*Ba.sub.3 (PO.sub.4).sub.2
barium orthophosphate
(NH.sub.4).sub.2 HPO.sub.4
ammonium mono-hydrogen orthophosphate
(NH.sub.4)H.sub.2 PO.sub.4
ammonimum di-hydrogen orthophosphate
NaH.sub.2 PO.sub.4.12H.sub.2 O
sodium di-hydrogen orthophosphate hydrate
Na.sub.2 HPO.sub.4.12H.sub.2 O
sodium mono-hydrogen orthophosphate
hydrate
KH.sub.2 PO.sub.4
potassium di-hydrogen orthophosphate
______________________________________
*Essentially insoluble in water.
The calcium and barium compounds were prepared in the laboratory by a standard procedure of interacting an alkali metal phosphate with a soluble metallic halide or acetate. The precipitate formed was washed free of reaction products and was employed either as a slurry or a dried powder. The other phosphate compounds were commercially available.
To add phosphorus to the tantalum powder, the appropriate phosphate was either mixed or dissolved in a 30% water-methanol solution. A sufficient amount of the phosphate-containing liquid was added to the tantalum powder to make a thick slurry. The slurry was dried at 90° C. and then thoroughly homogenized in a twin-shell blender. For the calcium and barium salts, a master blend of 1000 ppm of the additive was first prepared and then blended with more tantalum powder to get final concentrations of 30-50 ppm of the PO4 -3 ion, corresponding to about 10 to about 16 ppm of elemental phosphorus. The other salts were blended directly to the desired concentration.
Two-gram anodes were pressed to a density of 6.45 g/cm3 from tantalum powder from the same lot of agglomerated sodium-reduced tantalum powder and are designated Example 3. Similar anodes were pressed from the powders containing the various phosphate compound additives and are designated Examples 4 through 9. Anodes of Examples 3 through 9 were sintered in vacuum either for 30 minutes at 1800° C. or for 30 minutes at 2000° C. and tested for specific capacitance using the sintering practice and test conditions described for Examples 1 and 2. Direct current leakage (DCL) also was measured in the electrical tests. The anodes, after anodizing, rinsing and drying, were first tested for DCL. A phosphoric acid solution was employed. The test conditions were as follows:
______________________________________
Anode Formation
Test Electrolyte
Test
Voltage Concentration
Voltage
______________________________________
200 10.0% H.sub.3 PO.sub.4
140
270 0.01% H.sub.3 PO.sub.4
240
______________________________________
The anodes were immersed in the test solution to the top of the anode and the proper voltage was applied for 2 minutes, after which the leakage was measured.
After leakage measurements were completed, the anodes formed to 200 volts were placed in a tray containing 10% phosphoric acid and permitted to soak 30 to 45 minutes.
The anodes formed to 270 volts were washed for 3 to 5 minutes in running distilled water and dried 45 minutes at 105°+5° C. in air. They were then soaked in 10% phosphoric acid for 30 to 45 minutes. The capacitance was measured using the procedure described under Examples 1 and 2.
The test results are summarized in Table II. The data show that the addition of small amounts of compounds containing the PO4 -3 ion (10 to 16 ppm of elemental phosphorus) to agglomerated sodium-reduced tantalum powder will improve the capacitance of anodes sintered 30 minutes at 1800° C. by about 5 to 7%, and of anodes sintered 30 minutes at 2000° C. by about 1 to 4%. These gains in capacitance were achieved while still maintaining acceptable d.c. leakage levels.
TABLE II
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EFFECT OF INORGANIC PHOSPHATE COMPOUND ADDITIONS TO AGGLOMERATED
SODIUM-REDUCED TANTALUM POWDER ON PROPERTIES OF ANODES PRODUCED
THEREFROM
Sintered at 1800° C.
Sintered at 2000° C.
Am't Added Capacitance
CV/g Capacitance
CV/g
Example
Compound ppm DCL μfv/g
Improvement
DCL μfv/g
Improvement
No. Added PO.sub.4.sup.-3
P μa/μfv
(CV/g) % μa/μfv
(CV/g) %
__________________________________________________________________________
3 None (control)
-- -- 24 4904 -- 77 3405 --
4 Ca.sub.3 (PO.sub.4).sub.2
49 16 22 5218 6.4 100 3545 4.0
5 Ba.sub.3 (PO.sub.4).sub.2
37 12 34 5193 5.9 77 3517 3.3
6 (NH.sub.4).sub.2 HPO.sub.4
37 12 34 5203 6.1 92 3458 1.6
7 (NH.sub.4)H.sub.2 PO.sub.4
40 13 33 5168 5.4 105 3512 3.1
8 NaH.sub.2 PO.sub.4.12H.sub.2 O
34 11 25 5199 6.0 65 3470 1.9
9 Na.sub.2 HPO.sub.4.12H.sub.2 O
31 10 23 5069 5.2 113 3449 1.3
__________________________________________________________________________
Tantalum powder was produced from an electron beam melted high-purity tantalum ingot by embrittling the ingot by heating it in a hydrogen atmosphere then crushing and pulverizing the resulting friable ingot to yield a tantalum hydride powder. The tantalum hydride powder was converted to an agglomerated tantalum powder (designated hereafter as "agglomerated EB powder") by heating the tantalum hydride powder in vacuum to 1390° C., followed by pulverizing the lightly sintered cake to produce -60 mesh agglomerated tantalum powder. This agglomerated EB powder is included as a control in Example 10.
The following series of inorganic phosphate compounds were utilized as additives to agglomerated EB powder from the same lot as the control, Example 10 powder:
______________________________________
*Ca.sub.3 (PO.sub.4).sub.2
calcium orthophosphate
*Ba.sub.3 (PO.sub.4).sub.2
barium orthophosphate
(NH.sub.4).sub.2 HPO.sub.4
ammonium mono-hydrogen orthophosphate
(NH.sub.4)H.sub.2 PO.sub.4
ammonium di-hydrogen orthophosphate
NaH.sub.2 PO.sub.4.12H.sub.2 O
sodium di-hydrogen orthophosphate
hydrate
Na.sub.2 HPO.sub.4.12H.sub.2 O
sodium mono-hydrogen orthophosphate
hydrate
KH.sub.2 PO.sub.4
potassium di-hydrogen orthophosphate
*Pb.sub.3 (PO.sub.4).sub.2
lead orthophosphate
______________________________________
*Essentially insoluble in water
The calcium, barium and lead compounds were prepared in the laboratory by a standard procedure of interacting an alkali metal phosphate with a soluble metallic halide or acetate. The precipitate formed was washed free of reaction products and was employed either as a slurry or a dried powder. The other phosphate compounds were commercially available.
To add phosphorus to the tantalum powder, the appropriate phosphate was either mixed or dissolved in a 30% water-methanol solution. A sufficient amount of the phosphate-containing liquid was added to the tantalum powder to make a thick slurry. The slurry was dried at 90° C. and then thoroughly homogenized in a twin-shell blender. For the calcium and barium salts, a master blend of 1000 ppm of the additive was first prepared and then blended with more tantalum powder to get final concentrations of 30-50 ppm of the PO4 -3 ion, corresponding to about 10 to about 16 ppm of elemental phosphorus. The other salts were blended directly to the desired concentration.
Two-gram anodes were pressed to a density of 7.20 g/cm3 from tantalum powder from the same lot of agglomerated EB powder and containing no added phosphorus and are designated Example 10. Similar anodes were pressed from the powders containing the various phosphate compound additives and are designated Examples 11 through 18. Anodes of Examples 10 through 18 were sintered in vacuum either for 30 minutes at 1800° C. or for 30 minutes at 2000° C. and tested for specific capacitance using the sintering practice and test conditions as described for Examples 1 and 2, and for DCL as described in Examples 3 through 9.
Six anodes prepared from each of the powders of Examples 10 to 18 were sintered for 30 minutes at 2000° C. and were measured for breakdown voltage (BDV). The breakdown voltage test was carried out by electroforming in an agitated 0.1% H3 PO4 solution at 90°±2° C., with the forming voltage increased at a rate of 3 to 4 volts per minute until dielectric breakdown occurred. The point of breakdown was established when the forming current of the anode increased by 100 m.a. over the current flowing at 100 volts or when scintillation occurred. A mean breakdown voltage was determined after elimination of "outliers". (An outlying observation, or outlier, is one that appears to deviate markedly from other members of the set in which it occurs.) Only one outlier per test lot is acceptable. The procedure of ASTM-E-178-61T. "Tentative Recommended Practice for Dealing with Outlying Observations" was followed.
The test results are listed in Table III. These data show that the addition of small amounts of compounds containing the PO4 -3 ion (10 to 16 ppm of elemental phosphorus) to agglomerated EB tantalum ingot powder will improve the capacitance of anodes sintered 30 minutes at 1800° C. by about 5 to 9%, and of anodes sintered 30 minutes at 2000° C. by about 2 to 4%. These gains in capacitance were achieved without significantly altering the DCL. Also, the BDV of the anodes sintered at 2000° C. was not degraded.
TABLE III
__________________________________________________________________________
EFFECT OF INORGANIC PHOSPHATE COMPOUND ADDITIONS TO AGGLOMERATED
EB TANTALUM POWDER ON PROPERTIES OF ANODES PRODUCED THEREFROM
Sintered at 1800° C.
Sintered at 2000° C.
Capacitance
CV/g Capacitance
CV/g
Example
Compound Am't Added, ppm
DCL μfv/g
Improvement
DCL μfv/g
Improvement
BDV
No. Added PO.sub.4.sup.-3
P μa/μfv
(CV/g) % μa/μfv
(CV/g) % Volts
__________________________________________________________________________
10 None (control)
-- -- 16 3998 -- 67 2973 -- 226
11 Ca.sub.3 (PO.sub.4).sub.2
49 16 14 4372 9.3 65 3081 3.6 232
12 Ba.sub.3 (PO.sub.4).sub.2
31 10 16 4266 6.7 65 3085 3.8 227
13 (NH.sub.4).sub.2 HPO.sub.4
37 12 15 4206 5.2 62 3061 3.0 228
14 (NH.sub.4 H.sub.2 PO.sub.4
40 13 14 4243 6.2 53 3042 2.3 226
15 NaH.sub.2 PO.sub.4.12H.sub.2 O
34 11 20 4310 7.8 52 3072 3.3 235
16 Na.sub.2 HPO.sub.4.12H.sub.2 O
31 10 15 4249 6.3 56 3051 2.6 231
17 KH.sub.2 PO.sub.4
35 11 14 4304 7.7 64 3032 2.2 --
18 Pb.sub.3 (PO.sub.4).sub.2
47 15 16 4317 8.0 63 3078 3.7 --
__________________________________________________________________________
An EB tantalum ingot hydride powder was used as a control, and is designated as Example 19.
These inorganic phosphate compounds were utilized as additives to hydride powder from the same lot as Example 19:
______________________________________
(NH.sub.4).sub.2 HPO.sub.4
ammonium mono-hydrogen phosphate
Na.sub.2 HPO.sub.4
sodium mono-hydrogen phosphate
Ca.sub.3 (PO.sub.4).sub.2
calcium orthophosphate
______________________________________
Hydride powder from the same lot as used in Example 19 was degassed in vacuum to remove the hydrogen, resulting in EB powder. This degassed powder was used as other controls, designated as Examples 23 and 27, according to the subsequent agglomerating treatment used.
The above inorganic phosphate compounds were utilized also as additives to the degassed powder from the same lot as in Examples 23 and 27.
The method of adding phosphorus to the hydride and the EB powder followed the procedure used in Examples 3 to 9 and Examples 10 to 18. The amounts of additives used are listed in Table IV.
The control hydride powder, Example 19, and the phosphate-containing hydride powders, Examples 20, 21 and 22, were converted to an agglomerated EB powder by heating these hydride powders in vacuum for 60 minutes at 1390° C.
The EB powder control, Example 23, and the phosphate-containing EB powders, Examples 24, 25 and 26, were converted to agglomerated EB powders by heating these EB ingot powders in vacuum for 60 minutes at 1390° C.
The EB powder control, Example 27, and phosphate-containing EB powders, Examples 28, 29 and 30, were converted to an agglomerated EB powder by heating these EB powders in vacuum for 60 minutes at 1440° C.
Two-gram anodes were pressed to a density of 7.20 g/cm3 from the powders of Examples 19 to 30. Anodes were sintered either for 30 minutes at 1800° C. or for 30 minutes at 2000° C. and tested for DCL, specific capacitance, and BDV (only on anodes sintered at 2000° C.). The same procedures were used in the electrical test procedures as described in Examples 1 through 18.
The test results are listed in Table IV. Improvements in capacitance for anodes sintered for 60 minutes at 1800° C. ranged from about 17 to 25% when the phosphate compound was added to the hydride powder, and from about 11 to 15% when the addition was made to the EB powder (degassed powder) before agglomeration. For anodes sintered at 2000° C. (30 minutes), the improvement in capacitance resulting from the phosphate additions ranged from about 7 to 13% when added to the hydride powder before agglomeration, and about 4 to 7% when added to EB powder before agglomeration.
TABLE IV
__________________________________________________________________________
EFFECT OF INORGANIC PHOSPHATE COMPOUND ADDITIONS TO EB
TANTALUM HYDRIDE POWDER (EX. NOS. 20-22) AND TO DEGASSED
EB POWDER (EX. NOS. 24-26 AND 28-30) BEFORE AGGLOMERATION
ON PROPERTIES OF ANODES PRODUCED THEREFROM
Sintered at 1800° C.
Sintered at 2000° C.
Capacitance
CV/g Capacitance
CV/g
Example
Compound Am't Added, ppm
DCL μfv/g
Improvement
DCL μfv/g
Improvement
BDV
No. Added PO.sub.4.sup.-3
P μa/μfv
(CV/g) % μa/μfv
(CV/g) % Volts
__________________________________________________________________________
19 None (control)
-- -- 19 4099 -- 116 2925 -- --
20 (NH.sub.4).sub.2 HPO.sub.4
576 188 23 4925 20.2 100 3131 7.0 --
21 Na.sub.2 HPO.sub.4
500 163 33 4818 17.5 251 3067 4.9 --
22 Ca.sub.3 (PO.sub.4).sub.2
459 150 116 5107 24.6 149 3318 13.4 --
23 None (control)
-- -- 12 3892 -- 79 2958 -- 248
24 (NH.sub.4).sub.2 HPO.sub.4
230 75 13 4369 12.2 71 3147 6.4 236
25 Na.sub.2 HPO.sub.4
200 65 14 4394 12.9 86 3124 5.6 200
26 Ca.sub.3 (PO.sub.4).sub.2
99 32 22 4329 11.2 63 3110 5.1 215
27 None (control)
-- -- 24 3915 -- 62 2866 -- 225
28 (NH.sub.4).sub.2 HPO.sub.4
230 75 21 4451 13.7 62 3006 4.9 239
29 Na.sub.2 HPO.sub.4
200 65 59 4433 13.3 82 2999 4.6 202
30 Ca.sub.3 (PO.sub.4).sub.2
99 32 34 4495 14.9 52 3014 5.2 224
__________________________________________________________________________
These examples cover additions of various inorganic phosphate compounds to EB powder before agglomeration. The types and amounts of phosphate-containing compounds used are listed in Table V. The amounts of specific phosphate compounds added to the powder in these examples were considerably less than the amounts used in Examples 23 to 30. The powders were agglomerated for 60 minutes at 1390° C., then tested for DCL, specific capacitance, and BDV by the procedures described in Examples 1 through 30. The data are listed in Table V. A significant improvement in capacitance both with an 1800° C. sinter and a 2000° C. sinter compared to the controls was achieved by additions of all of the phosphate salts investigated down to and including the lowest concentrations of these compounds that were added. These improvements in capacitance were achieved without detrimental effects on d.c. leakage. In these examples, some of the metallic phosphates appeared to cause some reduction in BDV, but additions of (NH4)2 HPO4, Pb3 (PO4)2 and Ca3 (PO4).sub. 2, in one of two cases, did not impair BDV.
TABLE V
__________________________________________________________________________
EFFECT OF INORGANIC PHOSPHATE COMPOUND ADDITIONS TO EB TANTALUM POWDER
BEFORE AGGLOMERATION ON PROPERTIES OF ANODES PRODUCED THEREFROM
(POWDER AGGLOMERATED AT 1390° C. FOR 60 MIN.)
Sintered at 1800° C.
Sintered at 2000° C.
Capacitance
CV/g Capacitance
CV/g
Example
Compound Am't Added, ppm
DCL μfv/g
Improvement
DCL μfv/g
Improvement
BDV
No. Added PO.sub.4.sup.-3
P μa/μfv
(CV/g) % μa/μfv
(CV/g) % Volts
__________________________________________________________________________
31 None (control)
-- -- 16 3818 -- 40 2931 -- 221
32 (NH.sub.4).sub.2 HPO.sub.4
115 37 31 4158 8.9 38 3036 3.4 239
33 Na.sub.2 HPO.sub.4
106 35 20 4244 11.2 44 3054 4.2 204
34 Ca.sub.3 (PO.sub.4).sub.2
50 17 45 4204 10.1 38 3032 3.5 226
35 None (control)
-- -- 19 3930 -- 80 2967 -- 239
36 KH.sub.2 PO.sub.4
100 33 15 4318 9.8 86 3035 2.3 226
37 Pb.sub.3 (PO.sub.4).sub.2
100 33 13 4308 9.6 85 3039 3.8 240
38 Ba.sub.3 (PO.sub.4).sub.2
100 33 23 4450 13.2 93 3269 10.2 203
39 None (control)
-- -- 13 3946 -- 82 2835 -- 240
40 (NH.sub.4).sub.2 HPO.sub.4
57 19 11 4350 10.2 74 2888 1.9 248
41 Na.sub.2 HPO.sub.4
53 17 12 4389 11.2 87 2927 3.2 209
42 Ca.sub.3 (PO.sub.4).sub.2
25 8 17 4259 7.9 74 2914 2.8 216
43 None (control)
-- -- 16 3963 -- 83 2900 -- 240
44 KH.sub.2 PO.sub.4
50 16 15 4276 7.8 85 2967 2.3 217
45 Pb.sub.3 (PO.sub.4).sub.2
50 16 13 4269 7.7 58 2951 1.8 241
46 Ba.sub.3 (PO.sub.4).sub.2
50 16 25 4392 10.8 68 3099 6.7 209
__________________________________________________________________________
The powder of Example 47 is an EB tantalum ingot hydride powder having an average particle size of 3.2 microns (F.S.S.S. of 3.2μ) as determined by the procedure of ASTM-B-330-58T, "Tentative Method of Test for Average Particle Size of Refractory Metals and Compounds by Fisher Sub-Sieve Sizer". This powder was used as a control.
A series of progressively higher additions of (NH4)H2 PO4 were made to hydride powder from the same lot as in Example 47 to provide phosphorus additions of 20, 35, 50 and 150 ppm, and are designated as Examples 48 to 51.
The powders of Examples 47 to 51 were agglomerated at 1375° C. for 30 minutes. Two-gram anodes were pressed from the powder to a density of 7.20 g/cm3. Some anodes were sintered for 30 minutes at 1600° C., and others for 30 minutes at 1800° C. or 30 minutes at 2000° C. These anodes were tested for DCL, specific capacitance, and BDV (only on anodes sintered at 1800° and 2000° C.) using the same test procedures as in earlier examples.
The results are listed in Table VI. As may be seen from the data, an increase in capacitance of up to 35% occurred with the 1600° C. sinter, up to 23% with the 1800° C. sinter, and up to 6.5% with the 2000° C. sinter. The phosphate addition appears to act as a sintering inhibitor: the larger the quantity, the greater the effect. The BDV and DCL of the anodes sintered at 2000° C. did not appear to be adversely affected at any of the phosphorous levels, however, the BDV of anodes sintered at 1800° C. using powder with the highest phosphorus level showed some decrease.
TABLE VI
__________________________________________________________________________
EFFECT OF (NH.sub.4).sub.2 HPO.sub.4 ADDITIONS TO 3.2 MICRON TANTALUM
HYDRIDE
POWDER BEFORE AGGLOMERATION ON PROPERTIES OF ANODES PRODUCED THEREFROM
Sintered at 1600° C.
Sintered at 1800° C.
Sintered at 2000° C.
Capac- Capac- Capac-
itance
CV/g itance
CV/g itance
CV/g
Ex.
Amount P
DCL μfv/g
Improved
DCL μfv/g
Improved
BDV DCL μfv/g
Improved
BDV
No.
Added, ppm
μa/μfv
(CV/g)
% μa/μfv
(CV/g)
% Volts
μa/μfv
(CV/g)
% Volts
__________________________________________________________________________
47 None 14 5556 -- 21 4250 -- 218 -- 2832 -- 256
(control)
48 20 16 6831 22.9 20 4763 12.1 207 74 2820 -- 263
49 35 16 6932 24.8 21 4897 15.2 216 61 2921 3.1 256
50 50 14 7021 26.4 23 5003 17.7 221 60 2966 4.7 260
51 150 12 7512 35.2 15 5258 23.7 186 75 3015 6.5 262
__________________________________________________________________________
These examples are similar to Examples 47 to 51 except that data are included on EB tantalum hydride
TABLE VII
__________________________________________________________________________
EFFECT OF (NH.sub.4).sub.2 HPO.sub.4 ADDITIONS TO EB TANTALUM HYDRIDE
POWDER OF DIFFERENT PARTICLE -SIZES BEFORE AGGLOMERATION ON THE
PROPERTIES OF ANODES PRODUCED THEREFROM
Sintered at 1600° C.
Sintered at 1800° C.
Sintered at 2000°
C.
Am't of Compound
Capacitance
CV/g Capacitance
CV/g Capacitance
CV/g
Example
Hydride
added, ppm
μfv/g
Improv-
μfv/g
Improv-
DCL μfv/g
Improv-
BDV
No. FSSS. μ
PO.sub.4.sup.-3
P (CV/g) ed % (CV/g) ed % μa/μfv
(CV/g) ed
__________________________________________________________________________
% Volts
4
52 3.2 None
(control)
5630 -- 4176 -- 72 2832 -- 260
53 3.2 153 50 7426 31.9 5022 20.3 86 3003 6.0 255
54 3.2 460 150 7512 33.4 5258 25.9 75 3015 6.5 262
55 3.7 None
(control)
5455 -- 4207 -- 77 2862 -- --
56 3.7 307 100 6690 22.6 4974 18.2 65 3147 10.0 --
57 4.2 None
(control)
5200 -- 3900 -- -- 2900 -- --
58 4.2 153 50 6177 18.7 4647 19.2 87 3113 7.3 255
59 4.2 460 150 6168 18.6 4619 18.4 73 3099 6.9 248
__________________________________________________________________________
TABLE VIII
__________________________________________________________________________
EFFECT OF (NH.sub.4).sub.2 HPO.sub.4 ADDITIONS TO EB TANTALUM HYDRIDE
POWDER OF DIFFERENT PARTICLE SIZES
BEFORE PRE-AGGLOMERATION AND AGGLOMERATION ON THE PROPERTIES OF ANODES
PRODUCED
THEREFROM
Amount of
Sintered at 1600° C.
Sintered at 1800° C.
Sintered at 2000°
C.
Compound
Capacitance
CV/g Capacitance
CV/g Capacitance
CV/g
Example
Hydride
Added, ppm
μfv/g
Improv-
μfv/g
Improv-
DCL μfv/g
Improv-
BDV
No. FSSS. μ
PO.sub.4.sup.-3
P (CV/g) ed % (CV/g) ed % μa/μfv
(CV/g) ed
__________________________________________________________________________
% Volts
60 3.2 None
(control)
5630 -- 4176 -- 72 2832 -- 260
61 3.2 153 50 7483 32.9 4795 14.8 80 3079 8.7 251
62 3.2 460 150 7541 33.9 5308 27.1 72 3080 8.8 251
63 3.7 None
(control)
5526 -- 4202 -- 77 2923 -- --
64 3.7 307 100 6797 23.0 5025 19.6 65 3153 7.9 --
65 4.2 None
(control)
5200 -- 3900 -- -- 2900 -- --
66 4.2 153 50 6235 19.9 4697 20.4 89 3180 9.7 243
67 4.2 460 150 6254 20.3 4707 20.7 81 3126 7.8 241
__________________________________________________________________________
powder having F.S.S.S. values of 3.2, 3.7 and 4.2 microns. Additions of (NH4)2 HPO4 in the amounts listed in Tables VII and VIII were made to the hydride powder before the agglomeration treatments.
In Examples 52 to 59, Table VII, the hydride powders were agglomerated in one treatment for 30 minutes at 1375° C. In Examples 60 to 67, Table VIII, the hydride powders first were subjected to a pre-agglomeration treatment for 60 minutes at 1200° C., followed by an agglomeration treatment for 30 minutes at 1375° C.
Two-gram anodes were pressed from the powders to a density of 7.20 g/cm3, and then were sintered at 1600° C. (30 minutes), or at 1800° C. (30 minutes), or at 2000° C. (30 minutes), and then were tested as described in earlier examples.
The results show that the particle size of the precursor powder before either of the agglomeration treatments has a considerable bearing on the change of capacitance with the amount of phosphate added to the hydride powder before agglomeration. At a 50 ppm level of phosphorus addition, the increase in capacitance with a 1600° C. sinter over that of the control is up to 34% for a 3.2 micron powder before agglomeration and up to 20% for a 4.2 micron powder.
In these examples, additions of up to 376 ppm of phosphorus were made in the form of (NH4)H2 PO4 to EB tantalum ingot hydride powder, and also to EB hydride powder from the same lot after agglomeration for 30 minutes at 1375° C. The specific amounts of added phosphate compound in each example are listed in Table IX. Data also are included on particle size (F.S.S.S) and Scot density of the powders after agglomeration. Scott density (or apparent density) was determined by the procedure of ASTM-B-329-61, "Standard Method of Test for Apparent Density of Refractory Metals and Compounds by Scott Volumeter".
Two-gram anodes were pressed from these powders to a density of 7.20 g/cm3, and then were sintered either for 30 minutes at 1800° C. or 30 minutes at 2000° C. and tested for electrical characteristics using the test procedures described in earlier examples.
The results in Table IX show:
1. When the phosphate addition is made before agglomeration, the resultant agglomerated powders have a somewhat lower scott density and a particle size (F.S.S.S., in microns) of only about 60 to 70% of that of the agglomerated control powder.
2. These added amounts of the phosphate salt resulted in an increase in specific capacitance of up to 20% for anodes sintered at 1800° C. These additions generally did not significantly impair DCL or BDV.
TABLE IX
__________________________________________________________________________
EFFECT OF (NH.sub.4)H.sub.2 PO.sub.4 ADDITIONS TO EB TANTALUM HYDRIDE
POWDER (EX. 69-72) AND TO
THE AGGLOMERATED POWER PRODUCED THEREFROM (EX. 74-77) ON THE PROPERTIES
OF THE AGGLOMERATED POWDER AND ON THE ANODES PRODUCED THEREFROM
Agglomerated
Amount of Powder Sintered at 1800° C.
Sintered at 2000° C.
Compound Particle Scott
Capacitance
CV/g Capacitance
CV/g
Example
Added, ppm
Size Density
DCL μfv/g
Improved
DCL μfv/g
Improved
BDV
No. PO.sub.4.sup.-3
P FSSS. μ
g/in.sup.3
μa/μfv
(CV/g) % μa/μfv
(CV/g) % Volts
__________________________________________________________________________
68 None
(control)
0.3 72.6
30 4101 -- 49 3011 -- 244
69 577 188 6.1 65.5
22 4872 18.8 56 3093 2.7 243
70 721 235 6.2 67.2
21 4843 18.1 54 3035 0.8 --
71 865 282 6.6 67.9
21 4915 19.8 57 3113 3.3 246
72 1,543
376 6.7 69.2
18 4844 18.1 50 3115 3.4 222
73 None
(control)
10.3 72.6
28 4123 -- 53 3056 -- 237
74 577 188 10.5 73.5
26 4777 15.9 66 3195 4.5 256
75 721 235 10.8 73.0
21 4776 15.8 66 3170 3.7 --
76 865 282 11.0 72.5
25 4803 16.5 45 3157 3.3 239
77 1,153
376 13.5 72.9
26 4865 18.0 41 3163 3.5 237
__________________________________________________________________________
In another experiment, designated Examples 78 to 81, large additions of (NH4)2 HPO4 were made to an agglomerated EB tantalum powder. The amounts of the phosphate additions listed in Table X, covered the concentration range of 687 to 929 ppm of elemental phosphorus (0.40 to 0.54 atomic percent), a higher range than that contemplated by this invention.
Two-gram anodes of the phosphate-containing powders were pressed to a density of 7.20 g/cm3 and sintered for 30 minutes at 1600° C. The as-pressed anodes were 0.258 inches diameter and 0.323±0.001 inches length. After sintering, the control anodes averaged 0.251 inches diameter and 0.314 inches length; the phosphate-containing anodes hardly showed any shrinkage, and even exhibited swelling in some cases, and they averaged 0.259 inches diameter and 0.321 inches length.
The anodes were tested for DCL and specific capacitance. Breakdown voltage was determined on additional anodes sintered for 30 minutes at 1800° C. The test methods that were used are described in earlier examples.
The results are shown in Table X. These high phosphate additions resulted in a sizeable increase in capacitance and had no significant effect on DCL; however, the increase in capacitance was no greater than that achieved with much lower levels (<400 ppm added phosphorus). Therefore, there is no benefit attained by these large additions, and the actual swelling of the anodes during sintering is undesirable.
TABLE X
______________________________________
EFFECT OF LARGE ADDITIONS OF (NH.sub.4).sub.2 HPO.sub.4 TO
AGGLOMERATED EB TANTALUM POWDER ON THE
PROPERTIES OF ANODES PRODUCED THEREFROM
Quantity of Sintered at 1600° C.
Compound Capacitance
CV/g
Example
Added, ppm DCL μfv/g Improved
No. PO.sub.4.sup.-3
P μa/μfv
(CV/g) %
______________________________________
78 None (control)
14 4855 --
79 2107 687 16 5826 20.0
80 2462 805 17 5771 18.9
81 2850 929 16 5787 19.2
______________________________________
In earlier examples of the phosphorus-containing additives were various inorganic phosphate salts. In these examples, phosphoric acid was added to either EB tantalum hydride powder (F.S.S.S. of 3.2 microns) or to agglomerated powder produced from hydride powder from the same lot.
The powders were agglomerated for 60 minutes at 1365° C. Two-gram anodes were pressed from these powders to a density of 7.20 g/cm3, sintered either for 30 minutes at 1600° C. or for 30 minutes at 1800° C., and tested for DCL and specific capacitance using the procedures described in earlier examples. The results are shown in Table XI.
These data show that additions of phosphoric acid made either to EB hydride powder or to agglomerated EB powder resulted in a large increase in capacitance over that of the control powder. The magnitudes of the increases in capacitance were similar to those demonstrated for additions of inorganic phosphates in earlier examples. DCL was not impaired by the phosphoric acid additions.
TABLE XI
__________________________________________________________________________
EFFECT OF PHOSPHORIC ACID ADDITIONS TO EB TANTALUM HYDRIDE POWDER
(EX. 83-86) AND TO AGGLOMERATED EB POWDER PRODUCED THEREFROM (EX. 88-91)
ON THE PROPERTIES OF ANODES PRODUCED THEREFROM (POWDER
AGGLOMERATED AT 1365° C. FOR 60 MIN.)
Amount of Sintered at 1600° C.
Sintered at 1800° C.
Compound Capacitance
CV/g Capacitance
CV/g
Example
Added, ppm
DCL μfv/g
Improved
DCL μfv/g
Improved
No. PO.sub.4.sup.-3
P μa/μfv
(CV/g) % μa/μfv
(CV/g) %
__________________________________________________________________________
82 None
(control)
13 5823 -- 24 4322 --
83 31 10 14 6969 19.7 25 4857 12.4
84 92 30 13 7153 22.8 18 5048 16.8
85 184 60 14 7197 23.6 18 5194 20.2
86 307 100 27 7237 24.3 19 5258 21.7
87 None
(control)
12 5768 0 18 4426 --
88 31 10 11 6538 13.3 17 4870 10.0
89 92 30 13 6725 16.6 18 5104 15.3
90 184 60 18 6911 19.8 17 5221 18.0
91 307 100 12 7032 21.9 16 5229 18.1
__________________________________________________________________________
An agglomerated EB tantalum powder was treated with a solution of sodium hypophosphite, NaH2 PO2 H2 O to produce an added phosphorus concentration of 150 ppm. Two-gram anodes were pressed from the untreated control powder (Example 92) and the phosphite-treated powder (Example 93) to a density of 7.20 g/cm3, sintered for 30 minutes at 1600° C., and tested using the procedures described in earlier examples. The results are shown in Table XII.
TABLE XII
______________________________________
Sintered at 1600° C. (30 Min.)
Quantity of Shrinkage Capacitance
CV/g
Ex. Contained P During μfv/g Improve-
No. Added, ppm Sintering, %
(CV/g) ment %
______________________________________
92 None (control)
4.46 5327 --
93 150 0.62 6493 21.8
______________________________________
These data show that additions of the phosphite salt to tantalum powder resulted in an increase in capacitance over that of the control powder. The improvement with the phosphite addition was similar to that produced by additions of phosphate salts as shown in earlier examples.
Agglomerated EB tantalum powder was treated with various inorganic phosphate salts using concentrations of 9 to 50 ppm contained phosphorus ion in a large number of experimental runs. Untreated powders from the same lots were used as controls. Two-gram anodes were pressed from these powders to a density of 7.20 g/cm3, sintered for 30 minutes at 2000° C., and tested for BDV. The results are shown in Table XIII.
Any of these phosphate compounds including phosphoric acid, H3 PO4, can be used as an additive to tantalum capacitor powders to increase capacitance of sintered anodes, as shown in Examples 3 to 18, and in other earlier examples. However, if it is desired to simultaneously maintain highest breakdown voltage, the preferred additives are those which contain no metallic cations, such as the ammonium phosphate salts and phosphoric acid.
TABLE XIII
__________________________________________________________________________
Anodes Tested Inorganic Phosphate Salt
Sintered at 2000° C.
Example
No Anodes
Total
Added to EB Powder
BDV
No. Runs
Run Tested
Salt Cations Volts. Avg.
__________________________________________________________________________
94 11 6 66 None (control) 240
95 10 6 60 (NH.sub.4).sub.2 HPO.sub.4
2NH.sub.4.sup.+1 + H.sup.+1
244
96 2 2 12 H.sub.3 PO.sub.4
H.sup.+1
244
97 5 6 30 Pb.sub.3 (PO.sub.4).sub.2
Pb.sup.+2
240
98 9 6 54 Ca.sub.3 (PO.sub.4).sub.2
Ca.sup.+2
223
99 4 6 24 KH.sub.2 PO.sub.4
K.sup.+1 + 2H.sup.+1
220
100 10 6 60 Na.sub.2 HPO.sub.4.12H.sub.2 O
2Na.sup.+1 + H.sup.+1
209
101 5 6 30 Ba.sub.3 (PO.sub.4).sub.2
Ba.sup.+2
207
__________________________________________________________________________
EB tantalum ingot hydride powder with a F.S.S.S. of approximately 2 microns was used as a control in Example 102. An addition of (NH4)2 HPO4 was made to another portion of EB hydride powder from the same lot. The amount of the compound added was 307 ppm PO4 -3 ion, or 100 ppm of elemental phosphorus. These powders were degassed, and did not receive an agglomeration treatment. Two-gram anodes were pressed from the powders, sintered for 30 minutes at 1800° C. and tested for specific capacitance using the previously described procedures. The control anodes, Example 102, had a capacitance of 2700 CV/g, while the anodes made using the phosphorus-containing powder, Example 103, had a capacitance of 3608 CV/g, an increase of 33.0% over the control.
Sodium-reduced tantaum powder that had not received an agglomeration treatment was used as a control, Example 104. Other portions of powder from the same lot were treated with (NH4)2 HPO4 to provide additions of 50 and 100 ppm of elemental phosphorus. Two-gram anodes were pressed from these powders to a density of 6.45 g/cm3, and were sintered either for 30 minutes at 1600° C. or 30 minutes at 1800° C. and then tested for DCL, specific capacitance, and BDV (on anodes sintered at 1800° C. only) using the procedures described in earlier examples.
The results are shown in Table XIV. The addition of the phosphate compound to these sodium-reduced powders produced appreciable increases in capacitance without impairing DCL or BDV.
TABLE XIV
__________________________________________________________________________
EFFECT OF (NH.sub.4).sub.2 HPO.sub.4 ADDITIONS TO SODIUM-REDUCED
TANTALUM
POWDER ON THE PROPERTIES OF ANODES PRODUCED THEREFROM
Amount of Sintered at 1600° C.
Sintered at 1800° C.
Compound Capacitance
CV/g Capacitance
CV/g
Example
Added, ppm
DCL μfv/g
Improved
DCL μfv/g
Improved
BDV
No PO.sub.4.sup.-3
P μa/μfv
(CV/g) % μa/μfv
(CV/g) % Volts
__________________________________________________________________________
104 None
(control)
13 5953 -- 24 4900 -- 161
105 153 50 21 6512 9.4 24 5206 6.2 167
106 307 100 26 6647 11.7 22 5249 7.1 157
__________________________________________________________________________
EB tantalum hydride powder with a F.S.S.S. of 3.2 microns was agglomerated for 30 minutes at 1365° C. and crushed to -35 mesh powder. Two-gram anodes were pressed from the powder to a density of 7.20 g/cm3. The anodes were divided into three groups, Examples 107 to 109. The average pore volume in the anodes was calculated from the density. A solution of amonium mono-hydrogen phosphate was applied using an eyedropper to saturate the anodes and achieve two levels of additions, plus the zero level of the control, shown in Table XV. The anodes were dried in air, then were sintered for 30 minutes at 1600° C. and tested for percent shrinkage during sintering and specific capacitance, using the test methods described in earlier examples. The results are shown in Table XV.
TABLE XV
______________________________________
Ex- Amount of Sintered at 1600° C.
am- Compound Shrinkage Capacitance
CV/g
ple Added, ppm During μfv/g Improve-
No. PO.sub.4.sup.-3
P Sintering, %
(CV/g) ment %
______________________________________
107 None (control)
4.07 5880 --
108 460 150 1.55 7014 19.3
109 920 300 1.16 7146 21.5
______________________________________
These data show that additions of phosphate salts to as-pressed anodes before sintering resulted in significantly higher capacitance after sintering as compared to anodes similarly sintered from as-pressed anodes to which no phosphorus had been added.
It will be understood by those skilled in the art that variations and modifications of the specific embodiments described above may be employed without departing from the scope of the invention as defined in the appended claims.
Claims (12)
- agglomeration thereof..]. .[.6. A tantalum powder in accordance with claim 2 in which at least a portion of said phosphorus-containing material is calcium orthophosphate, added after agglomeration in an amount equivalent to from about 20 to about 80 parts per million of elemental phosphorus..]. .[.7. A tantalum powder in accordance with claim 1 in which the phosphorus-containing material is free of metallic cations..]. .[.8. A tantalum powder in accordance with claim 2 in which a major portion of the phosphorus in said powder is obtained by the addition of a phosphorus-containing material having no metallic cations and a minor portion is obtained by the addition of calcium orthophosphate after agglomeration in an amount not exceeding about 80 parts per million of
- elemental phosphorus..]. 9. A tantalum powder in accordance with claim .[.1.]. .Iadd.32 .Iaddend.in which at least a major portion of said phosphorus-containing material is added in the form of an orthophosphate compound of the group consisting of ammonium orthophosphate, ammonium hydrogen orthophosphate, ammonium di-hydrogen orthophosphate, and orthophosphoric acid. .[.10. A tantalum anode prepared by pressing and sintering the tantalum powder of claim 1..]. .[.11. A tantalum anode prepared by pressing tantalum powder into the shape of an anode, adding to said pressed tantalum powder a phosphorus-containing material in an amount equivalent to from about 5 to about 400 parts per million of elemental phosphorus, and thereafter sintering said pressed tantalum powder..]. .[.12. A method of improving a tantalum powder which comprises adding to said powder an amount of a phosphrous-containing material corresponding to from about 5 to about 400 parts per million of phosphorus..]. .[.13. A method in accordance with claim 1 in which said tantalum powder is agglomerated prior to the addition of said phosphorus-containing material..]. .[.14. A method in accordance with claim 12 in which said phosphorus-containing material is added to said powder prior to agglomeration..]. .[.15. A method in accordance with claim 12 in which said phosphorus-containing material comprises a minor proportion of calcium orthophosphate and a larger proportion of a phosphorus-containing material having no metallic cations, said calcium orthophosphate being added after agglomeration in an amount equivalent to from about 20 to
- about 80 parts per million of elemental phosphorus..]. 16. A method of improving a tantalum powder which comprises adding to said powder while it is in the form of tantalum hydride an amount of phosphorus-containing material corresponding to from about .[.5.]. .Iadd.37.5 to about 400 parts per million of phosphorus and thereafter converting said tantalum hydride
- to metallic tantalum. 17. A method in accordance with claim 16 in which said tantalum hydride is converted to metallic tantalum during
- agglomeration. 18. A method in accordance with claim 16 in which said tantalum hydride is converted to metallic tantalum and thereafter agglomerated. .[.19. A method of forming an improved tantalum anode which comprises pressing and sintering the tantalum powder of claim 1..]. .[.20. A method of forming an improved tantalum anode which comprises pressing a tantalum powder into the shape of an aode, adding to said pressed tantalum powder to phosphorus-containing material in an amount equivalent to from about 5 to about 400 parts per million of elemental phosphorus, and
- thereafter sintering said pressed tantalum powder..]. .Iadd.21. A method of increasing the specific capacitance of a tantalum powder which comprises adding to said powder an amount of a phosphorus-containing material sufficient to provide an improved level of specific capacitance, the amount of added phosphorus-containing material being within the range corresponding to from about 5 to about 400 parts per million of phosphorus, said phosphorus-containing material comprising a minor proportion of calcium orthophosphate and a larger proportion of a phosphorus-containing material having no metallic cations, said calcium orthophosphate being added after agglomeration in an amount equivalent to from about 20 to about 80 parts per million of elemental phosphorus..Iaddend. .Iadd.22. A tantalum powder containing an added phosphorus-containing material in an amount equivalent to from about 37.5 to about 400 parts per million of elemental phosphorus..Iaddend.
- .Iadd. A tantalum powder as in claim 22 containing an added phosphorus-containing material in an amount equivalent to at least about 50 parts per million of elemental phosphorus..Iaddend. .Iadd.24. A tantalum powder as in claim 22 containing an added phosphorus-containing material in an amount equivalent to at least 65 parts per million of elemental phosphorus..Iaddend. .Iadd.25. A tantalum anode prepared by pressing and sintering the tantalum powder of claim 22..Iaddend.
- .Iadd. A method of improving the specific capacity of tantalum powder for use in making tantalum anodes comprising adding to tantalum powder an amount of an ammonium hydrogen phosphate, within the range equivalent to from about 20 to about 400 parts per million of elemental phosphorus, sufficient to improve the specific capacity (CV/g) of the untreated tantalum by at least about 8.9% when pressed in the forms of anodes and sintered at 1800° C..Iaddend. .Iadd.27. A method of improving the specific capacity of tantalum powder for use in making tantalum anodes comprising adding to tantalum powder, which is in the form of tantalum hydride prior to reduction to metallic tantalum, an amount of phosphorus-containing material, within the range equivalent to from about 37.5 to about 400 parts per million of elemental phosphorus, sufficient to improve the specific capacity (CV/g) of the untreated tantalum by at least 5.2% when pressed in the form of anodes and sintered at 1800° C.
- .Iadd.28. A method of forming an improved tantalum anode having improved capacitance which comprises pressing a tantalum powder into the shape of an anode, adding to said pressed tantalum powder an amount of a phosphorus-containing material sufficient to provide the improved level of specific capacitance, said phosphorus-containing material being added in an amount equivalent to from about 37.5 to about 400 parts per million of elemental phosphorus and thereafter sintering said pressed tantalum powder..Iaddend. .Iadd.29. A method of improving the specific capacity of tantalum powder for use in making tantalum anodes comprising adding to tantalum powder an amount of phosphorus-containing material, within the range equivalent to from about 50 to about 400 parts per million of elemental phosphorus, sufficient to improve the specific capacity (CV/g) of the untreated tantalum by at least 5.2% when pressed in the form of
- anodes and sintered at 1800° C..Iaddend. .Iadd.30. A method as in claim 29 in which the phosphorus-containing material is present in an amount equivalent to at least about 65 parts per million of elemental phosphorus..Iaddend. .Iadd.31. A tantalum powder characterized by increased specific capacitance and improved flow characteristics containing calcium orthophosphate added after agglomeration in an amount equivalent to about 20 to about 80 parts per million of elemental phosphorus..Iaddend. .Iadd.32. A tantalum powder characterized by increased specific capacitance containing an added phosphorus-containing material which is free of metallic cations in an amount equivalent to from about 5 to about 400 parts per million of elemental phosphorus..Iaddend.
- .Iadd.33. A tantalum powder characterized by increased specific capacitance and improved flow properties containing an added phosphorus material which is comprised of a phosphorus-containing material having no metallic cations and a minor amount, not exceeding about 80 parts per million of elemental phosphorus, of calcium orthophosphate added after agglomeration, the total amount of added phosphorus-containing material being in an amount equivalent to from about 5 to about 400 parts per million of elemental phosphorus..Iaddend. .Iadd.34. A method of improving the specific capacity of tantalum powder for use in making tantalum anodes comprising adding to tantalum powder an amount of phosphorus-containing material, within the range equivalent to from about 37.5 to about 400 parts per million of elemental phosphorus, sufficient to improve the specific capacity (CV/g) of the untreated tantalum by at least about 5.2% when pressed in the form of anodes and sintered at 1800°
- C..Iaddend. .Iadd.35. A method in accordance with claim 34 in which the phosphorus-containing material is phosphoric acid..Iaddend. .Iadd.36. A method in accordance with claim 34 in which the phosphorus-containing material is added to tantalum powder which is in the form of metallic tantalum..Iaddend.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US06/634,036 USRE32260E (en) | 1975-07-14 | 1984-07-24 | Tantalum powder and method of making the same |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US05/595,569 US4009007A (en) | 1975-07-14 | 1975-07-14 | Tantalum powder and method of making the same |
| US06/634,036 USRE32260E (en) | 1975-07-14 | 1984-07-24 | Tantalum powder and method of making the same |
Related Parent Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| US05/595,569 Reissue US4009007A (en) | 1975-07-14 | 1975-07-14 | Tantalum powder and method of making the same |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| USRE32260E true USRE32260E (en) | 1986-10-07 |
Family
ID=27082311
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| US06/634,036 Expired - Lifetime USRE32260E (en) | 1975-07-14 | 1984-07-24 | Tantalum powder and method of making the same |
Country Status (1)
| Country | Link |
|---|---|
| US (1) | USRE32260E (en) |
Cited By (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5580516A (en) * | 1989-06-26 | 1996-12-03 | Cabot Corporation | Powders and products of tantalum, niobium and their alloys |
| US6193779B1 (en) * | 1997-02-19 | 2001-02-27 | H. C. Starck Gmbh & Co. Kg | Tantalum powder, method for producing same powder and sintered anodes obtained from it |
| US6679934B2 (en) | 2000-03-01 | 2004-01-20 | Cabot Corporation | Nitrided valve metals and processes for making the same |
| US7435282B2 (en) | 1994-08-01 | 2008-10-14 | International Titanium Powder, Llc | Elemental material and alloy |
| US7445658B2 (en) | 1994-08-01 | 2008-11-04 | Uchicago Argonne, Llc | Titanium and titanium alloys |
| US7621977B2 (en) | 2001-10-09 | 2009-11-24 | Cristal Us, Inc. | System and method of producing metals and alloys |
| US7632333B2 (en) | 2002-09-07 | 2009-12-15 | Cristal Us, Inc. | Process for separating TI from a TI slurry |
| US7753989B2 (en) | 2006-12-22 | 2010-07-13 | Cristal Us, Inc. | Direct passivation of metal powder |
| US8821611B2 (en) | 2005-10-06 | 2014-09-02 | Cristal Metals Inc. | Titanium boride |
| US8894738B2 (en) | 2005-07-21 | 2014-11-25 | Cristal Metals Inc. | Titanium alloy |
| US9127333B2 (en) | 2007-04-25 | 2015-09-08 | Lance Jacobsen | Liquid injection of VCL4 into superheated TiCL4 for the production of Ti-V alloy powder |
| US20180147627A1 (en) * | 2016-11-30 | 2018-05-31 | Seiko Epson Corporation | Powder for energy beam sintering, method for producing powder for energy beam sintering, and method for producing sintered body |
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| US3647415A (en) * | 1967-10-25 | 1972-03-07 | Show Denko Kk | Tantalum powder for sintered capacitors |
| US3418106A (en) * | 1968-01-31 | 1968-12-24 | Fansteel Inc | Refractory metal powder |
| US3723838A (en) * | 1972-01-14 | 1973-03-27 | Western Electric Co | Nitrogen-doped beta tantalum capacitor |
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Cited By (15)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5580516A (en) * | 1989-06-26 | 1996-12-03 | Cabot Corporation | Powders and products of tantalum, niobium and their alloys |
| US7435282B2 (en) | 1994-08-01 | 2008-10-14 | International Titanium Powder, Llc | Elemental material and alloy |
| US7445658B2 (en) | 1994-08-01 | 2008-11-04 | Uchicago Argonne, Llc | Titanium and titanium alloys |
| US6193779B1 (en) * | 1997-02-19 | 2001-02-27 | H. C. Starck Gmbh & Co. Kg | Tantalum powder, method for producing same powder and sintered anodes obtained from it |
| US20040108018A1 (en) * | 2000-03-01 | 2004-06-10 | Rao Bhamidipaty K.D.P. | Nitrided valve metals and processes for making the same |
| US7144546B2 (en) | 2000-03-01 | 2006-12-05 | Cabot Corporation | Nitrided valve metals and processes for making the same |
| US6679934B2 (en) | 2000-03-01 | 2004-01-20 | Cabot Corporation | Nitrided valve metals and processes for making the same |
| US7621977B2 (en) | 2001-10-09 | 2009-11-24 | Cristal Us, Inc. | System and method of producing metals and alloys |
| US7632333B2 (en) | 2002-09-07 | 2009-12-15 | Cristal Us, Inc. | Process for separating TI from a TI slurry |
| US8894738B2 (en) | 2005-07-21 | 2014-11-25 | Cristal Metals Inc. | Titanium alloy |
| US9630251B2 (en) | 2005-07-21 | 2017-04-25 | Cristal Metals Inc. | Titanium alloy |
| US8821611B2 (en) | 2005-10-06 | 2014-09-02 | Cristal Metals Inc. | Titanium boride |
| US7753989B2 (en) | 2006-12-22 | 2010-07-13 | Cristal Us, Inc. | Direct passivation of metal powder |
| US9127333B2 (en) | 2007-04-25 | 2015-09-08 | Lance Jacobsen | Liquid injection of VCL4 into superheated TiCL4 for the production of Ti-V alloy powder |
| US20180147627A1 (en) * | 2016-11-30 | 2018-05-31 | Seiko Epson Corporation | Powder for energy beam sintering, method for producing powder for energy beam sintering, and method for producing sintered body |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| AS | Assignment |
Owner name: TANTALUM PRODUCTION INC., A DE CORP. Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:FANSTEEL INC.;REEL/FRAME:005403/0576 Effective date: 19900726 |
|
| AS | Assignment |
Owner name: TANTALUM PRODUCTION INC., A DE CORP. Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:FANSTEEL INC., A DE CORP.;REEL/FRAME:005841/0132 Effective date: 19900726 Owner name: SIAM COMMERCIAL BANK, LTD., THE Free format text: SECURITY INTEREST;ASSIGNOR:TANTALUM PRODUCTION INC., A DE CORP.;REEL/FRAME:005841/0138 Effective date: 19910903 |