DE3700659A1 - FINE-GRAINED PROBLEM TANTALO WIRE - Google Patents

Description

The present invention relates to metal alloys Tantalum base, more precisely made from such alloys Wires.

Electrolytic capacitors and components of high temperature vacuum furnaces are the main areas of application for tantalum. For these applications, tantalum becomes a preferred material primarily due to the following properties: high melting point, high dielectric constant in the tantalum oxide film produced by anodizing, good electrical conductivity, excellent manufacturability and ductility and availability in manifestations of high purity. Other desirable properties of tantalum for these applications are:
Resistance to embrittlement, fine grain size and resistance to grain growth as well as good weldability including connections with dissimilar materials.

It is known that tantalum becomes brittle when it such as oxygen, carbon monoxide and carbon dioxide, over short periods at temperatures of about 315 ° C and above. Such and other contaminating gases are products or Reaction elements of many physical and chemical Reactions in which tantalum products are either direct or used indirectly, such as in the electronics, metal and chemical industries. In the case of "embrittlement", the corresponding item loses Material the ability to look at the desired application (at or almost at room temperature) bend without breaking while doing so is due to the fact that tantalum is at high temperatures unwanted negative or contaminating Is exposed to gases and vapors. The lack of Ability to look after pollution at low Bending temperatures without breaking leads to serious problems when made from tantalum Parts that have been contaminated, then vibrations, Impact loads and static loads or almost at room temperature during use or suspended in their manufacture.  

One of the main difficulties when using Tantalum in electrolytic capacitors is that the tantalum lead wires during the sintering of Tantalum smelting anodes by pressing and sintering Tantalum powder with embedded in the powder lump Tantalum wire can be made, very brittle. It is known that the extent of embrittlement is larger when such tantalum lead wires in Tantalum powder are embedded, which is a relative have a high oxygen content, for example more than 1600 ppm, and in powder, which is at temperatures of 1800 ° C or more are sintered. The embrittlement of tantalum lead wires poses a serious problem when handling anodes that are compatible with the Anodizing used frame are welded. The Embrittlement is particularly large where the tantalum wire is embedded in the tantalum powder lump is. The maximum embrittlement takes place at the exit point of the wire from the sintered anode instead where the oxygen content in the wire is high and the Wire is not stored. The embrittlement of Tantalum lead wires are also essential Importance in terms of the ability to further manufacture and handling operations in capacitor manufacturing endure. A corresponding solution regarding the embrittlement problem of the tantalum lead wires has a strong impact on the ability  To produce capacitors in an economical manner.

In addition, the embrittlement of drawn Tantalum parts in the high-temperature furnace or others High temperature inserts the life of the parts adversely affect. Tantalum materials in high temperature applications are adversely affected as a "catcher" for contaminating Gases, for example carbon monoxide, carbon dioxide, Oxygen and nitrogen. The grain growth at elevated temperatures also sets significant problem. Coarse grains tend to to promote embrittlement and cracking when they are contaminated with relatively small amounts of oxygen will. The exchange of tantalum parts due to embrittlement and mistakes can take a long time Effect idle times and at considerable replacement costs to lead. Essential economic Advantages can be achieved if the usable Lifetime of such tantalum parts can be increased can.

A way to overcome these difficulties consists of the surface of the tantalum lead wire with carbon or a carbon-containing one Treat material. The carbon coating tends to occur during the subsequent high temperature sintering process  with oxygen in the tantalum powder react so that the bendability of the lead wire is maintained because the oxygen with the Carbon coating has reacted and not in the Tantalum lead wire has been absorbed. It prepares however, difficulties in applying Carbon to get reproducible Control properties and the desired flexibility of the lead wire. Furthermore, the carbon on the surface of the Wire adverse effects on the electrical Properties of tantalum because of an undesirable increase of DC leakage through the dielectric Tantalum oxide film of the resulting capacitor becomes.

Another method of reducing the extent of Embrittlement of a tantalum wire exists therein, a grain size tantalum lead wire to use, d. H. a tantalum wire, who has a grain size that is the Sinters of the anode used elevated temperatures does not increase significantly. An Indian However, grain size controlled lead wire has in many cases still not the one you want Resistance to embrittlement, especially in such Cases where the grain size controlled Tantalum wire in a lump of tantalum powder  is embedded with a high oxygen content, and especially when the oxygen content of the tantalum powder Is 1600 ppm or more.

According to U.S. Patents 40 62 679, 41 28 421 and 42 35 629 is achieved by adding a sufficient amount of silicon about 50 to 700 ppm relatively evenly distributed in the metal embrittlement of tantalum and alloys Lowered tantalum base. The silicon containing Tantalum compositions are made by powder metallurgical Pressing and sintering are made by first silicon in a relatively high master alloy mix Silicon content is mixed in and then the main alloy mixture added to the total composition becomes. The final mix is pressed and sintered to make one to produce dense bars, which then in the desired Way is fabricated. In the preparation of of tantalum wire is the ingot of a variety of Cold rolling steps and then a variety of wire drawing steps subjected to a wire with the desired Diameter is obtained.

According to US-PS 32 68 328 10 to 1000 ppm Elements with the ordinal numbers 39 (yttrium) and 57 to 71 (lanthanum rare earths) added to ductile drawn tantalum and tantalum alloy products with to obtain fine grain size compared to a Grain coarsening resistant at elevated temperatures  are. The US-PS 34 97 402 proposes a method to produce a cold worked tempered Tantalum alloy that is between about 10 and Contains 1000 ppm yttrium and after heating up 2038 ° C over one hour has a grain size that is less than ASTM # 3. Good ductility and good strength properties are also used for the materials containing yttrium are claimed.

There are also other additives drawn metal products been added to a fine grain size, an increased recrystallization temperature and increased resistance to grain growth to get at elevated temperatures. Thorium oxide and zirconium oxide, which are very high-melting Oxides, remain in tungsten products about high temperature sintering and restrict the grain growth during the heating of a Lamp thread to the operating temperature like this in "Tungsten Sources. Metallurgy, Properties and Applications "by Jih, S. W. H. and C. T. Wang, Plenum Press, New York, 1979. Thorium oxide and zirconium oxide are called nitrate or chloride added to yellow, blue or brown tungsten oxide, depending on the reduction process used. The amount up to 4 or 5% of thorium oxide or zirconium oxide of the calculated final weight to be reduced Tungsten metal powder. After mixing  the tungsten oxide is air dried and in a hydrogen oven reduced. The reduced product is sieved and mixed with pure tungsten powder to make a powder to get with 1 or 2% of the high-melting oxide.

Good weldability is achieved with tantalum and tantalum alloys required for many purposes. At Tantalum lead wires for electrolytic tantalum capacitors good weldability may be required to seal the wire to the capacitor case, or around the wire with another tantalum wire or a metal wire, such as nickel, connect to.

The prior art wires do not have all of the properties required for the requirements of capacitors on, especially in relation to the combination good embrittlement resistance, maintenance a fine grain size across all manufacturing steps and their weldability.

The object of the invention is to achieve this based on these disadvantages of the prior art to overcome. More precisely, the invention aims the creation of an improved molding process of products based on tantalum with an improved Resistance to embrittlement, an increased resistance to Grain growth and improved weldability compared to the state of the art. Beyond that corresponding products available through the invention  be put.

The above object is achieved according to the invention solved in that silicon in combination with a or several metal oxides that are high in own free educational energies and therefore relative to Tantalum are thermodynamically very stable, the tantalum products is added. The metal oxide is separate Phase dispersed in tantalum, d. H. does not go in Solution, and serves to stabilize the tantalum grain boundaries. Thorium oxide is preferred.

The silicon addition to the tantalum material compositions according to the invention is made by powder metallurgical Process according to the aforementioned U.S. Patents 40 62 679, 41 28 421 and 42 35 629. Typically becomes finely divided silicon powder with a finely divided Tantalum powder mixed in an amount to make one nominal silicon concentration between 1 to 5 wt .-% in to get a main mix. This main mix will then with further finely divided tantalum powder in portions mixed to achieve a nominal silicon content, which is about 2 to 3 times the size you want Silicon content in the final material. This is done because a significant portion of the silicon during this High temperature treatment due to evaporation is lost.  

The thorium addition is carried out in the form of a stable thorium compound, for example thorium nitrate, which can be dispersed relatively evenly in the tantalum powder mixture. Typically, a thorium nitrate solution is prepared that contains the amount of thorium desired in the final material. This solution is mixed into the final tantalum and silicon powder mixture and then dried at a temperature of about 65 ° C. The resulting dried powder mixture is compressed and sintered under high vacuum (typically less than 10 ^-5 torr) to produce a dense ingot which is then processed in the desired manner. For the manufacture of wire, the billet is subjected to a series of cold rolling steps, followed by a series of wire drawing steps until the desired wire diameter is reached.

The improved ones achieved by adding silicon and thorium Properties go from the exemplary embodiments and figures, of which show:

Figure 1 is a representation of the average grain size of a tantalum wire, depending on the thorium content at 2 levels of silicon, wherein the wire at 2000 ° C was vacuum-annealed for 30 min. and

Fig. 2 is a representation of the mixing ratio of the tantalum wire as a function of the thorium content at 3 levels of silicon.

Example 1:

A mother tantalum-silicon mixture was prepared by three parts by weight of a powder of elemental silicon with a grain size corresponding to a mesh size of 0.074 mm (200 mesh) with 97 parts by weight of highly pure tantalum powder with a mesh size of 0.044 mm (-325 mesh). appropriate grain size were mixed. The mixture was degassed under vacuum at 1325 ° C. for 3 hours, crushed, ground and sieved to a particle size of 0.044 mm (-325 mesh). This mother mix was then mixed with additional high purity tantalum powder to obtain a powder mix containing 125 ppm silicon. Furthermore, 50 ppm of thorium were mixed into the mixture in the form of an aqueous solution of thorium nitrate Th (NO ₃ ) ₄ . The powder was then mixed in a rotary dryer and dried. An amount of about 4,988 kg of the powder mixture was pressed isostatically with a compaction pressure of 2756 bar to an ingot of 22.22 mm × 22.22 mm with a length of about 38.1 cm. The compacted ingot was brought to a temperature of 2380 ° C. by vacuum resistance self-heating for 3.5 h under vacuum (less than 10 ^-5 torr), cooled under vacuum, isostatically pressed again to 5512 bar in order to increase the density of the ingot DC resistance heating brought back to a temperature of 2400 ° C. over 3.5 h under vacuum and cooled under vacuum. The resulting double sintered wire bar was analyzed as follows: 21 ppm Cb, 44 ppm Fe, 50 ppm Ni, less than 50 ppm W, less than 10 ppm Cr, less than 10 ppm C, 102 ppm O ₂ , 14 ppm N ₂ , less than 10 ppm each of Ca, Mg and Mn, 120 ppm Si by emission spectroscopy and less than 100 ppm Th (lower limit of detection) by optical plasma emission.

Corresponding bars were produced in which the The amount of silicon added was also 125 ppm, however, the amount of thorium added as thorium nitrate was 100, 200 and 400 ppm, respectively. Samples of these bars revealed about 125 ppm Si after sintering by emission spectroscopy in all cases and less than 100, approximately 100 and about 200 ppm thorium by optical plasma emission. Another group of ingots was created in corresponding Made wise, except that none Silicon was added, the amount of as thorium nitrate added thorium was 50, 100, 200 and 400 ppm. Optical plasma emission analysis of samples of these After sintering, ingots yielded less than 10 ppm Si in all cases and less than 100, about 100 and about 200 ppm thorium. Another ingot was also used the same amount of tantalum powder as the  ingots described above, except that no silicon or thorium was added. This bar and the wire made from it afterwards are hereinafter referred to as "undoped control sample".

Each square, twice sintered wire bar with a length of 22.22 mm was cold-rolled onto a bar with a square cross-section with rounded corners with a side length of 11.18 mm, degreased in perchlorethylene, pickled in a nitric acid-hydrofluoric acid-sulfuric acid solution by one Obtain chemically pure surface, and annealed for 60 minutes under vacuum (10 ^-4 Torr) at 1300 ° C. Each annealed 11.18 mm ingot was then cold rolled to a square cross-section with rounded corners and a side length of 3.73 mm and coiled to this size. The winding was cleaned by degreasing and subsequent acid pickling in the manner described above and again annealed under vacuum at 1300 ° C for 60 minutes. Each 3.73 mm wire was then rolled to a square cross-section with rounded corners and a side length of 2.26 mm using square roll passes, which cross section was then rounded to a 2.11 mm diameter in rolls with a semicircular cross-section . This 2.11 mm diameter wire was cleaned by degreasing and acid pickling and annealed under vacuum as described above. It was finally drawn to the final wire size with a diameter of 0.48 mm. The final diameter wire was lightly pickled in a solution of 1300 ml of 48% hydrofluoric acid, 450 ml of 70% nitric acid, 600 ml of 98% sulfuric acid and 2500 ml of deionized water. The wire was then annealed in vacuo at 1300 ° C for 60 minutes.

The wire was spooled and checked for surface quality at 10X magnification to find possible defects such as silver particles, flaking, pits, or other defects that could be detrimental to the quality of the wire. Wire samples of each composition were annealed in vacuo (less than 10 ^-5 torr) at 2000 ° C for 30 minutes. The microstructure of each sample across and parallel to the wire axis was examined. All of the wires were completely recrystallized. The average ASTM grain size numbers were plotted against the amount of thorium added for the two silicon levels (0 and 125 ppm) in FIG. 1. These data show that the addition of silicon gave a finer grain size of approximately one grain size number over the entire range of thorium added from 0 to 400 ppm. Thorium had a strong effect on grain size, which resulted in a finer size of about 4 grain sizes with 400 ppm of thorium added with any silicon added. The synergistic effect of 125 ppm silicon added and 400 ppm thorium added resulted in an ASTM grain size number of 10 compared to a grain size number of 5 for the undoped control sample.

In order to determine the embrittlement strength of the wire samples in a capacitor anode, an investigation was carried out under conditions that simulated the embrittlement of tantalum wire, which can occur under the toughest conditions. A total of five samples of each wire of different diameters were cut to lengths of about 19.05 mm and the wires were pressed into cylindrical pellets of tantalum powder with an average particle size of about 10 µm containing about 2400 to 2500 ppm oxygen. The wires were embedded to a depth of 3.18 mm in the anodes, which had a diameter of 6.55 mm, a height of 8.89 mm +/- 0.25 mm and a weight of 2.0 +/- Owned 0.1 g. A non-doped standard wire (which contained no additives), the behavior of which had previously been determined by tests, was included in the test for comparison purposes. The anodes made of tantalum powder were pressed to a density of 7.5 g / cm ³ without added binder. The pressed anodes with the embedded lead wires were applied symmetrically from sintered shells. Each batch of sinter, along with the anodes containing the test wires, contained anodes made with the standard wire. The anodes were sintered in an oven with cold walls at an absolute pressure of 10 ^-5 Torr for 30 minutes at an optical temperature of 2000 ° C +/- 10 ° C.

After sintering, the anodes were anodized with the test wires and control wire at 35 milliamperes / g in 0.01% phosphoric acid at 90 +/- 2 ° C until 100 V was reached and then to 100 for one hour V held. The anodized anodes were washed thoroughly and then dried in a circulation oven at 125 ° C for one hour. The dried anodes were sintered again in an oven with cold walls under vacuum (10 ^-5 Torr) for 30 minutes at an optical temperature of 2000 +/- 10 ° C.

The lead wires in the sintered anodes were repeated at a point that is 3.18 mm above the exit point the anode was bent. A stamp of a thickness of 3.18 mm with a hole in the middle was over the Lead wire slid to control the spot too where the bend occurred in the bending test. The wires were over the 3.18 mm thick stamp except for one Bent 90 ° and then back into the vertical Position bent back. This overall movement was called defines a bend in the wire. Consecutive Bends were made in a similar manner, with however between successive bends  Force application direction was rotated by 60 °. The number of Bends before the wires failed due to breaking certainly. A bending ratio became from these results calculates that the number of bends up to Failure for the test wire and that for the control wire with the same diameter, which among the same Conditions had been tested (for a satisfactory test should be the one for the control wire number of bends received on average in range from 1-5). For these comparisons the number of bends for the control wire (none Additives) to a bend ratio value of 1.0.

Figure 2 shows the least squares curves for the bend ratio data of these tests relative to the amount of thorium added for the two levels of 0 and 125 ppm silicon. The addition of 125 ppm silicon alone with no added thorium resulted in an increase of approximately 16% (bending ratio 1.6 compared to 1.0 for the undoped control sample). The addition of thorium up to 400 ppm alone resulted in an increase of about 40% in the bending ratio. The combined addition of 125 ppm silicon and 400 ppm thorium caused an increase in the bending ratio of approximately 100%.

Example 2:

Additional doped tantalum wires were made as described in Example 1, except that 300 ppm silicon and no thorium in one case and 300 ppm silicon and 400 ppm thorium in another case were added. The bend ratio data is also shown in FIG. 2. The addition of 300 ppm silicon resulted in a bending ratio of 1.8 (80% increase compared to the undoped control sample). The addition of 300 ppm silicon and 400 ppm thorium resulted in a bending ratio of approximately 2.2, ie a 120% increase compared to the undoped control sample.

Example 3:

Samples of the doped and undoped wires of the example 1 were in a T-connection with non-alloyed Spot welded nickel wire. Train examinations on each other connected tantalum nickel wires revealed that in a satisfactory strength of the connection in all cases was present.

All of the data presented above indicate that by the combined addition of silicon and thorium to a tantalum wire a finer grain size and an improved Resistance to grain growth at very high Temperatures is reached. Furthermore, an improved Resistance to embrittlement during sintering of tantalum powder anodes  achieved. These properties are compared to wires achieved without any addition or with an addition alone. The addition of these elements to tantalum creates a drawn one Tantalum product created that a unique combination has desirable properties.

In the previous examples, the thorium in the form of a thorium nitrate solution was added as an example. During the subsequent treatment of the tantalum bars, the thorium nitrate dissociates, and the thorium remains in the tantalum in the form of fine, relatively evenly distributed thorium oxide particles (ThO ₂ ). Thorium oxide particles dispersed in substantially the same manner can also be obtained by using the thorium in the form of other soluble salts (ie thorium carbonate) or as a thorium oxide sol or as an insoluble or low-solubility salt (thorium oxalate) which is used as a slurry in an aqueous or organic solution is added.

The thorium oxide particles once formed prove to be thermodynamically stable during the processing of the tantalum ingot and wire. This is due to the fact that thorium oxide (ThO ₂ ) has significantly more free negative formation energy than tantalum oxide (Ta ₂ O ₅ ) (Reed, "Free Energy of Formation of Binary Compounds, an Atlas of Charts for High-Temperature Chemical Calculations, MIT, In addition, the melting point of thorium oxide is 3220 +/- 50 ° C. (Handbook of Chemistry and Physics, Physical Constants of Inorganic Compounds, 60th Edition, by RC Weast, Chemical Rubber Co., 1979), which is above the temperature of 2400 ° C, which is used when sintering the tantalum bars.

Certain other metal oxides related to tantalum are thermodynamically stable and have a melting point above Can have 2400 ° C as alternatives to thorium oxide Find use. These metal oxides and their melting points are:

Metal oxide melting point ° C

ThO ₂ 3220 MgO2800 HfO ₂ 2758 +/- 25 ZrO ₂ 2715 CeO ₂ 2600 CaO2580 BeO2530 +/- 30 Y ₂ O ₃ 2410

These metal oxides can have tantalum in the following forms are added: As a fine metal powder, the can then be oxidized in situ, for example by a reaction with the tantalum-associated oxygen, as Metal oxide powder, either as a dry powder or in in the form of a sol or porridge or as soluble or  insoluble salt of the metal in an aqueous or dissolved or slurried organic solvent or carrier is, and then to produce the metal oxide thermally decomposed. The metal oxides can be used individually or used in combination with one another or with thorium will. The preferred silicon content is one Range from about 70 to 200 ppm, though through this Adding benefits emerged over a wider range of about 10 to 1000 ppm were observed. The most preferred The range is about 100 to 500 ppm silicon. Beneficial Effects by the further addition of a metal oxide producing species were from about 10 to 1000 ppm observed on the basis of the contained metal, whereby 50 to 500 ppm are preferred.

The by the addition of silicon and a permanent Metal oxide benefits were demonstrated in the examples described in connection with non-alloyed tantalum. The term "unalloyed tantalum" refers to normal, commercially available pure tantalum metal, d. H. Tantalum, which is the usual small amount of impurities contains, for example that of Example 1. Benefits by adding silicon and a permanent Metal oxide can also be used in alloys can be achieved on a tantalum basis. An example of this is a manufactured by Fansteel Inc. and under the name Tantaloy "61" sold tantalum 7.5% - Tungsten alloy. This alloy is made by a powder metallurgical  Process prepared according to the Example 1 for the non-alloyed tantalum corresponds. For the production Tantaloy "61" becomes tantalum and tungsten powder mixed with fine particle size (92.5% Ta and 7.5% W). Silicon and thorium nitrate can be added to this mixture be, and the resulting doped powder mixture is treated, sintered and to wire or any other desired Factory product processed.

The advantages of adding silicon and a permanent Metal oxide to tantalum and tantalum alloys can also for other metals in group V of the periodic table of the elements can be achieved, namely with niobium, columbium and vanadium and alloys of these metals.

Claims (18)

1. Forged product based on tantalum, characterized in that it contains about 10 to about 1000 ppm silicon in combination with about 10 to about 1000 ppm of one or more metals in oxide form with a high free energy of formation compared to tantalum and an oxide melting temperature above 2400 ° C having. 2. Product according to claim 1, characterized in that the one or more metal Metals selected from the group consisting of thorium, Magnesium, hafnium, zircon, cerium, calcium, beryllium and yttrium. 3. Product according to claim 1 or 2, characterized in that that the product tantalum based, apart from the inclusions, um essentially pure unalloyed tantalum.   4. Product according to claim 3, characterized in that the one or more metal Metals are made of thorium. 5. Product according to claim 4, characterized in that there is silicon in an amount of about 70 to 700 ppm and thorium in an amount of contains about 50 to 500 ppm. 6. Product according to claim 5, characterized in that there is silicon in a range of contains about 100 to 500 ppm. 7. tantalum wire, characterized in that it is made of essentially pure unalloyed tantalum, which is about 10 to 1000 ppm silicon combined with about 10 to 1000 ppm of one or more metal oxides with one Melting point of at least 2400 ° C and a larger one negative free formation energy as tantalum oxide contains up to at least 2400 ° C. 8. tantalum wire according to claim 7, characterized in that that's a metal oxide or the multiple metal oxides from that from the oxides of thorium, magnesium, hafnium, zircon, cerium, Calcium, beryllium and yttrium existing group are selected.   9. tantalum wire according to claim 7 or 8, characterized characterized in that it contains silicon in a Contains amount of about 70 to 700 ppm. 10. tantalum wire according to claim 9, characterized in that he's silicon in one Contains amount of about 100 to 500 ppm. 11. tantalum wire according to claim 10, characterized in that he's the one metal oxide or the plurality of metal oxides in an amount of about Contains 50 to 500 ppm in total. 12. tantalum wire according to claim 8, characterized in that he's the one metal oxide or the plurality of metal oxides in an amount of about Contains 50 to 500 ppm in total. 13. tantalum wire according to claim 12, characterized in that that the one Metal oxide or one of the several metal oxides is the only metal oxide that comes from the above Group is selected. 14. tantalum wire according to claim 13, characterized in that the metal oxide thorium oxide is.   15. Metal-based product, characterized in that it is from a base metal that from tantalum, niobium, columbium, vanadium and Alloys of these metals existing group selected is 10 to 1000 ppm silicon and 10 to 1000 ppm in total consists of one or more metal oxides, which have a melting point of at least 2400 ° C possess and a greater negative free educational energy have as the oxide of the base metal to up to at least 2400 ° C. 16. Product according to claim 15, characterized in that that that's a metal oxide or the multiple metal oxides from that from the oxides of thorium, magnesium, hafnium, zircon, cerium, Calcium, beryllium and yttrium existing group are selected. 17. Product according to claim 16, characterized in that that the metal oxide thorium oxide is. 18. Product according to claim 17, characterized in that that there is silicon in one Amount from about 70 to 700 ppm and thorium in one Contains amount of about 50 to 500 ppm.