CA2014482A1 - Production of alpha-al 0 sintered bodies - Google Patents
Production of alpha-al 0 sintered bodiesInfo
- Publication number
- CA2014482A1 CA2014482A1 CA 2014482 CA2014482A CA2014482A1 CA 2014482 A1 CA2014482 A1 CA 2014482A1 CA 2014482 CA2014482 CA 2014482 CA 2014482 A CA2014482 A CA 2014482A CA 2014482 A1 CA2014482 A1 CA 2014482A1
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- Canada
- Prior art keywords
- sintering
- process according
- al2o3
- alpha
- precursor
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Abstract
-ABSTRACT OF THE DISCLOSURE
Production of abrasive grade alpha-Al2O3 by hydrothermal treatment of chi-Al2O3 in the presence of catalytic amounts of acid and fine particles of certain metal oxides and/or alpha-Al2O3, drying, pressing, calcining, and sintering. The sintering is enhanced by use of particulate sintering additives added no later than the pressing step.
The end product alpha-Al2O3 is over ninety five percent theoretical density and has a hardness of 16-22 GPa and submicron crystallite structure.
Production of abrasive grade alpha-Al2O3 by hydrothermal treatment of chi-Al2O3 in the presence of catalytic amounts of acid and fine particles of certain metal oxides and/or alpha-Al2O3, drying, pressing, calcining, and sintering. The sintering is enhanced by use of particulate sintering additives added no later than the pressing step.
The end product alpha-Al2O3 is over ninety five percent theoretical density and has a hardness of 16-22 GPa and submicron crystallite structure.
Description
21~144~
CCTIoN OF Alpba-Aa203 SINTSRED
FIELD OF THE INVENTIoN
The present invention relates to a process for the production of alp a-A1203 sintered bcdies, in whidh an A1203 starting material is subjected to a hydro*herJol treatment and the product thus cbtained is dried, calcined and sintered.
A preferred application of alpha-A1203 sintered bodies is their use as abrasives.
EALi~ROLWD OF T9E INvENTIoN
~esides fused corundum abrasives, sintered abrasive materials have already been kncwn for about fifty years. More recently, sintered abrasivee based on aapha-Aa203 have beoome kncwn, whose microcrystalline ~tructure has brcught speciaa adNantages for abrasion tedhnology.
Ihus, U.S. Patent ~USP) 4,314,827 describes a microcrystaaline 15 abraglve material which i5 prepared by the ~ol-gel technique at si~tering te~perat w o~ about 1,400 C. As a sintering aid a modifying oomQorYnt 6uch ae HfO2, ZrO2, M~O, ZnD, Cco, Nio, etc., is addbd.
Eurcpean Patent Ccnvention Application ~Eæ'A~ 0 152 768 discloses 20 an abrasive materLal which ie al60 Frcduced by sint2ring an aluminum oxide hydrate gel. Extremely fino alpha-A1203 particlee are a~dQl here a~ nucleati~g agente to reduce the traneition temperature of gamma-A12O3 into alpha-A1203. CryEtal growth inhibitors such as MigO, SiO2, cr203, Fe203, ZrO2 can be addbd. Similar procesCPa and swb~tdncce as 2o1448~
described in West German application tDæ-A) O 024 099, DE-A-3 219 607, USP 4,518,397, USP 4,574,003, USP 4,623,364, EP-A 0 168 606, Eæ-A 0 200 487, EP-A 0 228 856, EP'A 0 209 084 and Eæ-A 0 263 810.
All the above- entiQned pdccesses have the common feature that they are carried out by a sol-gel process with extremely finely dlRperse~ aluminu~ oxide ~Irohydrate of the baehmitç tAlO(OH)~ type.
Ihe relatively expensive raw matçri lg, which for example are Qbtained by the hydrolysis of aluminum~organic ccrpouGds, and their e~pensive prooess technology ca1~C~ the costs of the sol-gel alpha-A1203 tsynthetic 10 ccrurdum) to rise to many times that of the oonventional alpha-A12O3.
In Wbst German patçnt ~DE-C) 3 604 848 a prooess is described for grinding a dispersion of alumina-cont3dn1ng raw ~aterials, silicio-acid-conkainlng ocr}ounds and further additives (oarpounds o~ the metals Co, Ni, Cr, Zr, Zn, Si, T1 or Ni) to a ~inkÆrable 51ip, from whidh by 15 stepwi~e drying and sintering at temperatures up to 1,700 C, an abra~ive can be produoed who6e ccrundum czy~tal~ have a diameter o~ less than 5 microns. Thus, the expenslve raw material is certa~nly avoided, ~ut lt ~ ~tlll neoe~sary to rely on very expens~ve grinding processes and h~gh ~inkerin~ temperatuxe3 in order to arrive at the ~cired 20 ~dclccry~ta111ne abrasive.
Ths prcduct oo ob~ain~d also containe about tWD percent sillcates (which are valuele~s à~ to abrasive power as lndlcated by their b~2dneLses, ranging up ~o 14 GPa, comp~red to 18 to 23 GPa ~or alumina) and has a czyEtalllte size less than five microns, l.e., well ~hort o~
25 the standard set in the ~ine struc*ure of a subst~nce whldh has been 2~44~
obtained by the sol-gel method (crystallite 6ize less than 0.4 microns).
m e princip21 cbject of the invention is to provide for the production from an inexpensive raw material of a sintered micIocrystJ1line alpha-A1203 sintered bo~y of submicron crystallite strLcture and of good abrasive gyalities, which does not have the above-described disadvantages of the process of the state of the art.
SUMM~RY OF 19E INVENTICN
It has ncw been found that the recu1rements, stated in the above cb~ect, are met if chi-A1203 is used as starting material, particularly in the manner described below. The present invention includes a process for the ~ ction of alp a-A1203 sintered bodies, in which an A1203 etarting material i5 sNk~ected to a hydrot`uIr~ul treatment, in the pYe~ence o~ catalytic ancunts of acid, and the pm duct so cbtained is drled, calcined and ~i ~ d, in which dhi-A1203 iB used as A1203 ~tarting materiaa and ~intering additives are added to the product cbtained by the hydrothermal treatm~nt.
Pre~errably the dhi-A12O3 used according to the inventian is produced in ao~ordbnD~ with ~E-C 2 059 946. A~oording to this, the chi-A1203 is prcduced by ahodk heating in the ~o,called Sdhcppe chamber from alumlnNm trihydrate (hydrargyllite). Ihe active oxide ~o cbtained i~
ess~ntially cc~pletely boehmite-free and h2s a surfaoe area o~ 200-400m2/gL~.l (usually about 300 m2/gram) via 2runauer-Emmet~Teller method (EEr) (measured by the one-point nitm gen eobod~ment of EEr method). It is preferrably converted as an aqueous nitric acid suspension in an autoclave to a high-viscosity mass after the hy~rother~zl treatment.
Especially good results are achieved if the hydrcthermol treatment is carried out at temperatures between 150 and 250 C for one half to five hours. The resNltant nass is dried. lhe drying step is preferably followed by a grinding of the dried mass. m e ground p rticles can be calcined and sintered. me grinding, if use, can be to a coarse end size or very fine. Grinding to a coarse particle size (0.1 ~ 3.0 mm) does not necessarily compromise abrasive utility; self sharpening mech3r1E~ of abrasive particles are well kncwn per se. If fine grinding i9 done, it must be followed by a molding step.
Parti~l æly good abrasive use results æe achieved for fine or coarse particles if before calcinstion a pressing cperation is carried out. Ihe additlon o~ sintering additives aocording to ths invw,tion is, Fr~errably carried out, at the latest, be~cre thls pressing cperaticn.
Such additian nay occur: (a) in the Euspension pricr to hyor~her~l treatment, (b) when drying or grinding subseqpcnt to such treatment, or (c) ~ust prior to pressing.
Aercedlnq to pre~erred practice o~ the inventicn the amount o~ the 6intering ~A~tives is 0.2 to 10 w~i~ht percent (ratio o~ additives to A12O3), and mcre pre~errably 0.5 to 2 wei~ht percent. Sintering additives U~e~ in this inventicn ars pre~errably nekal cxides, an~/or pre~erably 6pinel6 or n`etal compcunde ~orming 6pinele under the sin~er ~Z~3L448~:
reaction conditions. Ihere are at present several kncwn ~etal oxides in the latter category. Apprcpriate sintering additives are disclosed e.g., in EP'A 0 200 487.
In an also-preferred variant of the process according to the lnvention, alpha-A1203 nuclei are added as sinter additives.
Cbmbinations of the above sinter additives can also be used.
Nitric acid (HN03) is especially suitable as acid during the hyc~cehIrn~l treatment. Other sinilar acids (as to low pH andyor volatility) can be emplcyed. Ihe final sintering of the prcduct is 10 carried out according to pre~erred rbod1~erts of the invention at temperatures between 1,200 and l,600 C, re preferably frcm 1,300 to 1,380 C. It is preferred fbrthencore to carry out the sintering and the calcination in one step. According to the process of the invention, alpha-A1203 sintered bodies can be prcduced wi~h a density greater than 15 95 percent of the theoretical dnsity and with a h2rdness in the range o~ 16 to 22 Gpa, and having a crystallite struoture in the submlcron range.
In the ~ollowing detailed descripkicn, preferred mbodlmcnt9 of practice of the process o~ the inventicn are illustrated ky ex~mples, but the in~ention is not limited thereto.
EXample ~
750 grams of chi-A1203 was ~tirred in three liters o~ distilled watçr with 150 ml o2 cohcentr~ted nitrlc acid (15~ ~or one hour in an autoclave at 200 C and 20 bar. The high visoosity ub tzno ~ormed wa~
2t~ L448~:
dried in a drying oven at 80 C, then ground, mixed with seven grams of alpha-A1203 particles (particle size <1 micr~n) as 8intering aid, and pressed into tablets. Ihe pressings were heated within six hours to 1,350 C and calcined/sintered at ~h;~ temperature for about five hcurs.
The end-product sNbst~ncc had the following prcperties:
H~rdness: 21 GPa Density: 98% of theoretical Crystallite size: less than 1 micron Example _ m e processing of Example 1 was repeated except that the pressings were first calcined at temperatures up to 700 C, next c c inuted and then sintered at 1,350 C.
Properties of the end-prcduct sub~t~nae were:
Hardneee: 20 GPa Deneity: 98.2% of theoretieal Another preferred e~tYdlment of the invention involves adding the ~inter aid partlcle~ at the beginning or in the ccurse of hydrcthcrmal treatment.
Example _ 750 grams of chi-A1203 are stirred in three litres of dietilled water with 150 ml o~ corccrtrated nitric acid ~15k~ and 14 grame of M~(N03)2 ~or thirty ninute5 in ~n autoclave at 20 bar and 200 C. The gel i~ extruded with a vacuum prese and dried in the drying oven at 80 C. lhe dry gel is he~ted stepwise over six hours to 600 C, during 20144~3~
which the residual water and nitrous gases are evolved. Ihe resulting calcined A12O3 is then sintered for five hcurs at 1,350 C.
The swbet~nco cktained has the following prcperties:
H2rdness: 21 Gæa Density: 98.8% of theoretical CXystallite size: less than one micran EXample 4 As in Example 3 except that 7 grams of alpha-A1203 is used as sintering aid.
qhe ~ts~anc obkained had the following proFerties:
Hardness: 21 GPa Density: 99.0% of theoretical Crystallite size: less than one microns Ihe materials produced through use of the process of the present lnventlon can alBo be uBed in other conventional alpha-A1203 appllcations, el.g. as refractory liners, shapes, 6tructures, as ~pecialty electrical and cpkical materials, as catalyst carri 0 and as ccrF~ne~ts of ccmposites for 6uch purposes.
Ihe praotice of the invention can ~e modified in several ways, consistent wi~h the broadest socpe of the invention, including - without limitatlon - mixing al ~ -A1203 with c~her high power abrasives (e.g., silicon carbide) or i ~ ing other qualities as describel herein to the produoed alpha-A1203. Larger Al203 crystallltes than mentioned above, e.g., abaut 30 mlcrcns, can be employe(d.
A further alternative to preferred sets o~ prcess 5teps outlined 20~L4482 above in Examples 3 and 4 is to dry the gel product of hb~roehermal treatment, calcine and 6inter and corodnube. The sintering aid (if any) wculd then be added prior to or during aukcclaving. The cc inutlon would be after drying, calcining or 6intering.
It will now be apparent to thcee skilled in the art that other cbodimenks, i~prcvemenks, details, and uses can be nade consistent with the letter and spirit of the foregoing disclocure and within the socpe of this patent, which i8 linited only by the following claims, ccrstrued in accordance with the patent law, including the doctrine of equivalents.
What is clained i8:
CCTIoN OF Alpba-Aa203 SINTSRED
FIELD OF THE INVENTIoN
The present invention relates to a process for the production of alp a-A1203 sintered bcdies, in whidh an A1203 starting material is subjected to a hydro*herJol treatment and the product thus cbtained is dried, calcined and sintered.
A preferred application of alpha-A1203 sintered bodies is their use as abrasives.
EALi~ROLWD OF T9E INvENTIoN
~esides fused corundum abrasives, sintered abrasive materials have already been kncwn for about fifty years. More recently, sintered abrasivee based on aapha-Aa203 have beoome kncwn, whose microcrystalline ~tructure has brcught speciaa adNantages for abrasion tedhnology.
Ihus, U.S. Patent ~USP) 4,314,827 describes a microcrystaaline 15 abraglve material which i5 prepared by the ~ol-gel technique at si~tering te~perat w o~ about 1,400 C. As a sintering aid a modifying oomQorYnt 6uch ae HfO2, ZrO2, M~O, ZnD, Cco, Nio, etc., is addbd.
Eurcpean Patent Ccnvention Application ~Eæ'A~ 0 152 768 discloses 20 an abrasive materLal which ie al60 Frcduced by sint2ring an aluminum oxide hydrate gel. Extremely fino alpha-A1203 particlee are a~dQl here a~ nucleati~g agente to reduce the traneition temperature of gamma-A12O3 into alpha-A1203. CryEtal growth inhibitors such as MigO, SiO2, cr203, Fe203, ZrO2 can be addbd. Similar procesCPa and swb~tdncce as 2o1448~
described in West German application tDæ-A) O 024 099, DE-A-3 219 607, USP 4,518,397, USP 4,574,003, USP 4,623,364, EP-A 0 168 606, Eæ-A 0 200 487, EP-A 0 228 856, EP'A 0 209 084 and Eæ-A 0 263 810.
All the above- entiQned pdccesses have the common feature that they are carried out by a sol-gel process with extremely finely dlRperse~ aluminu~ oxide ~Irohydrate of the baehmitç tAlO(OH)~ type.
Ihe relatively expensive raw matçri lg, which for example are Qbtained by the hydrolysis of aluminum~organic ccrpouGds, and their e~pensive prooess technology ca1~C~ the costs of the sol-gel alpha-A1203 tsynthetic 10 ccrurdum) to rise to many times that of the oonventional alpha-A12O3.
In Wbst German patçnt ~DE-C) 3 604 848 a prooess is described for grinding a dispersion of alumina-cont3dn1ng raw ~aterials, silicio-acid-conkainlng ocr}ounds and further additives (oarpounds o~ the metals Co, Ni, Cr, Zr, Zn, Si, T1 or Ni) to a ~inkÆrable 51ip, from whidh by 15 stepwi~e drying and sintering at temperatures up to 1,700 C, an abra~ive can be produoed who6e ccrundum czy~tal~ have a diameter o~ less than 5 microns. Thus, the expenslve raw material is certa~nly avoided, ~ut lt ~ ~tlll neoe~sary to rely on very expens~ve grinding processes and h~gh ~inkerin~ temperatuxe3 in order to arrive at the ~cired 20 ~dclccry~ta111ne abrasive.
Ths prcduct oo ob~ain~d also containe about tWD percent sillcates (which are valuele~s à~ to abrasive power as lndlcated by their b~2dneLses, ranging up ~o 14 GPa, comp~red to 18 to 23 GPa ~or alumina) and has a czyEtalllte size less than five microns, l.e., well ~hort o~
25 the standard set in the ~ine struc*ure of a subst~nce whldh has been 2~44~
obtained by the sol-gel method (crystallite 6ize less than 0.4 microns).
m e princip21 cbject of the invention is to provide for the production from an inexpensive raw material of a sintered micIocrystJ1line alpha-A1203 sintered bo~y of submicron crystallite strLcture and of good abrasive gyalities, which does not have the above-described disadvantages of the process of the state of the art.
SUMM~RY OF 19E INVENTICN
It has ncw been found that the recu1rements, stated in the above cb~ect, are met if chi-A1203 is used as starting material, particularly in the manner described below. The present invention includes a process for the ~ ction of alp a-A1203 sintered bodies, in which an A1203 etarting material i5 sNk~ected to a hydrot`uIr~ul treatment, in the pYe~ence o~ catalytic ancunts of acid, and the pm duct so cbtained is drled, calcined and ~i ~ d, in which dhi-A1203 iB used as A1203 ~tarting materiaa and ~intering additives are added to the product cbtained by the hydrothermal treatm~nt.
Pre~errably the dhi-A12O3 used according to the inventian is produced in ao~ordbnD~ with ~E-C 2 059 946. A~oording to this, the chi-A1203 is prcduced by ahodk heating in the ~o,called Sdhcppe chamber from alumlnNm trihydrate (hydrargyllite). Ihe active oxide ~o cbtained i~
ess~ntially cc~pletely boehmite-free and h2s a surfaoe area o~ 200-400m2/gL~.l (usually about 300 m2/gram) via 2runauer-Emmet~Teller method (EEr) (measured by the one-point nitm gen eobod~ment of EEr method). It is preferrably converted as an aqueous nitric acid suspension in an autoclave to a high-viscosity mass after the hy~rother~zl treatment.
Especially good results are achieved if the hydrcthermol treatment is carried out at temperatures between 150 and 250 C for one half to five hours. The resNltant nass is dried. lhe drying step is preferably followed by a grinding of the dried mass. m e ground p rticles can be calcined and sintered. me grinding, if use, can be to a coarse end size or very fine. Grinding to a coarse particle size (0.1 ~ 3.0 mm) does not necessarily compromise abrasive utility; self sharpening mech3r1E~ of abrasive particles are well kncwn per se. If fine grinding i9 done, it must be followed by a molding step.
Parti~l æly good abrasive use results æe achieved for fine or coarse particles if before calcinstion a pressing cperation is carried out. Ihe additlon o~ sintering additives aocording to ths invw,tion is, Fr~errably carried out, at the latest, be~cre thls pressing cperaticn.
Such additian nay occur: (a) in the Euspension pricr to hyor~her~l treatment, (b) when drying or grinding subseqpcnt to such treatment, or (c) ~ust prior to pressing.
Aercedlnq to pre~erred practice o~ the inventicn the amount o~ the 6intering ~A~tives is 0.2 to 10 w~i~ht percent (ratio o~ additives to A12O3), and mcre pre~errably 0.5 to 2 wei~ht percent. Sintering additives U~e~ in this inventicn ars pre~errably nekal cxides, an~/or pre~erably 6pinel6 or n`etal compcunde ~orming 6pinele under the sin~er ~Z~3L448~:
reaction conditions. Ihere are at present several kncwn ~etal oxides in the latter category. Apprcpriate sintering additives are disclosed e.g., in EP'A 0 200 487.
In an also-preferred variant of the process according to the lnvention, alpha-A1203 nuclei are added as sinter additives.
Cbmbinations of the above sinter additives can also be used.
Nitric acid (HN03) is especially suitable as acid during the hyc~cehIrn~l treatment. Other sinilar acids (as to low pH andyor volatility) can be emplcyed. Ihe final sintering of the prcduct is 10 carried out according to pre~erred rbod1~erts of the invention at temperatures between 1,200 and l,600 C, re preferably frcm 1,300 to 1,380 C. It is preferred fbrthencore to carry out the sintering and the calcination in one step. According to the process of the invention, alpha-A1203 sintered bodies can be prcduced wi~h a density greater than 15 95 percent of the theoretical dnsity and with a h2rdness in the range o~ 16 to 22 Gpa, and having a crystallite struoture in the submlcron range.
In the ~ollowing detailed descripkicn, preferred mbodlmcnt9 of practice of the process o~ the inventicn are illustrated ky ex~mples, but the in~ention is not limited thereto.
EXample ~
750 grams of chi-A1203 was ~tirred in three liters o~ distilled watçr with 150 ml o2 cohcentr~ted nitrlc acid (15~ ~or one hour in an autoclave at 200 C and 20 bar. The high visoosity ub tzno ~ormed wa~
2t~ L448~:
dried in a drying oven at 80 C, then ground, mixed with seven grams of alpha-A1203 particles (particle size <1 micr~n) as 8intering aid, and pressed into tablets. Ihe pressings were heated within six hours to 1,350 C and calcined/sintered at ~h;~ temperature for about five hcurs.
The end-product sNbst~ncc had the following prcperties:
H~rdness: 21 GPa Density: 98% of theoretical Crystallite size: less than 1 micron Example _ m e processing of Example 1 was repeated except that the pressings were first calcined at temperatures up to 700 C, next c c inuted and then sintered at 1,350 C.
Properties of the end-prcduct sub~t~nae were:
Hardneee: 20 GPa Deneity: 98.2% of theoretieal Another preferred e~tYdlment of the invention involves adding the ~inter aid partlcle~ at the beginning or in the ccurse of hydrcthcrmal treatment.
Example _ 750 grams of chi-A1203 are stirred in three litres of dietilled water with 150 ml o~ corccrtrated nitric acid ~15k~ and 14 grame of M~(N03)2 ~or thirty ninute5 in ~n autoclave at 20 bar and 200 C. The gel i~ extruded with a vacuum prese and dried in the drying oven at 80 C. lhe dry gel is he~ted stepwise over six hours to 600 C, during 20144~3~
which the residual water and nitrous gases are evolved. Ihe resulting calcined A12O3 is then sintered for five hcurs at 1,350 C.
The swbet~nco cktained has the following prcperties:
H2rdness: 21 Gæa Density: 98.8% of theoretical CXystallite size: less than one micran EXample 4 As in Example 3 except that 7 grams of alpha-A1203 is used as sintering aid.
qhe ~ts~anc obkained had the following proFerties:
Hardness: 21 GPa Density: 99.0% of theoretical Crystallite size: less than one microns Ihe materials produced through use of the process of the present lnventlon can alBo be uBed in other conventional alpha-A1203 appllcations, el.g. as refractory liners, shapes, 6tructures, as ~pecialty electrical and cpkical materials, as catalyst carri 0 and as ccrF~ne~ts of ccmposites for 6uch purposes.
Ihe praotice of the invention can ~e modified in several ways, consistent wi~h the broadest socpe of the invention, including - without limitatlon - mixing al ~ -A1203 with c~her high power abrasives (e.g., silicon carbide) or i ~ ing other qualities as describel herein to the produoed alpha-A1203. Larger Al203 crystallltes than mentioned above, e.g., abaut 30 mlcrcns, can be employe(d.
A further alternative to preferred sets o~ prcess 5teps outlined 20~L4482 above in Examples 3 and 4 is to dry the gel product of hb~roehermal treatment, calcine and 6inter and corodnube. The sintering aid (if any) wculd then be added prior to or during aukcclaving. The cc inutlon would be after drying, calcining or 6intering.
It will now be apparent to thcee skilled in the art that other cbodimenks, i~prcvemenks, details, and uses can be nade consistent with the letter and spirit of the foregoing disclocure and within the socpe of this patent, which i8 linited only by the following claims, ccrstrued in accordance with the patent law, including the doctrine of equivalents.
What is clained i8:
Claims (46)
1. Process for production of alpha-Al2O3 at 95-100% theoretical density and as a high abrasive power material comprising hydrothermal processing of a precursor material comprising chi-Al2O3 as a principal ingredient and then subjecting the hydrothermal treatment material to sintering-like process conditions whereby a alpha-Al2O3 is formed to high density and high hardness hardness with sub-micron size crystallites without use of expensive starting materials or process conditions.
2. Process according to claim 1 wherein the precursor is in fact sintered.
3. Process according to claim 2 wherein sintering-aid additives are incorporated into the material prior to sintering.
4. Process according to claim 3 wherein the sintering aids are selected from the class consisting of metal oxides and alpha-Al2O3.
5. Process according to claim 4 wherein the sintering additive is alpha-Al2O3.
6. Process according to claim 3 wherein the metal oxides are of initial spinel crystalline structure or of a character to form such structure under the sintering conditions.
7. Process according to any of claims 3, 4 or 6 wherein the sintering is carried out at a temperature in the range of 1,200 to 1,800° C to effect sintering.
8. Process according to either of claims 4 or 5 wherein the sintering is carried out at a temperature in the range of 1,300 to 1,380° C.
9. Process according to claim 2 wherein the sintering step is also utilized as a calcining step follow-up of the hydrothermal processing.
10. Process according to claim 1 wherein the hydrothermal processing comprises high pressure and heating treatment of a water suspension of the chi-Al2O3 in the presence of catalytic acid.
11. Process a according to claim 10 wherein the hydrothermal processing temperature/time range matrix is 150--250° C/0.5 -- 5 hours.
12. Process according to either of claims 1 or 10 wherein the precursor material is formed to sub-micron size within, or post-hydrothermal process treatment and wherein such material is subsequently sintered.
13. Process according to claim 12 wherein sintering-aid additives are incorporated into the material prior to sintering.
14, Process according to claim 13 wherein the sintering aids are selected from the class consisting of metal oxides and alpha-Al2O3.
15. Process according to claim 14 wherein the sintering additive is alpha-Al2O3,
16. Process according to claim 13 wherein the additives are of initial spinel crystalline structure or of a character to form such structure under the sintering conditions.
17. Process according to either of claims 14 or 16 wherein the sintering is carried out at a temperature in the range of 1,200 to 1,800° C to effect sintering.
18. Process according to either of claims 14 or 16 wherein the sintering is carried out at a temperature in the range of 1,300 to 1,380 ° C.
19. Process according to claim 12 wherein the sintering step is also utilized as a calcining step conclusion of the hydrothermal processing.
20. Process according to either of claims 1 or 10 wherein the hydrothermal processed precursor is pressed and calcined.
21. Process according to claim 20 wherein a sintering additive is embedded in the material prior to such pressing and the material is then calcined and sintered.
22. Process according to claim 21 wherein the amount of added sinter additive is in a range of 0.2 to 10 weight percent compared to the weight of precursor chi-Al2O3.
23. Process according to claim 22 wherein said range is 0.5 - 2 weight percent.
24. An abrasive alumina material as made by the process of claim 1, including usage of the precursor material recited therein, and further characterized by over 95% theoretical density and a sub-micron crystallite size.
25. Process according to claim 1 wherein the hydrothermal processing is carried out using catalytic means.
26. Process according to claim 25 wherein the catalytic means are selected from the class consisting of (a) an adjusted acid amount and type used in such processing, (b) fine particles used therein and (c) a combination of (a) and (b).
27. Process according to claim 26 with catalytic artifact selected from the class consisting of (a) and (¢) wherein the acid comprises nitric acid.
28. Process according to claim 26 with the catalytic artifact selected from the class consisting of (b) and (c) where the particles are selected from the class consisting of metal oxides and alpha-Al2O3.
29. Process according to claim 28 wherein the particles are added in a range of 0.2 to 10 weight percent compared to weight of precursor chi-Al2O3.
30. Process according to claim 29 wherein said additive range is 0.5 - 2 weight percent.
31. In the process of production of alpha-Al2O3 by hydrothermal treatment of a precursor, and drying, calcining and sintering the product of such treatment, the improvement wherein chi-Al2O3 is used as the precursor.
32. Process according to claim 31 wherein the material is pressed prior to calcining and sintering.
33. Process according to claim 32 wherein sintering-aid additives are incorporated into the material prior to sintering.
34. Process according to claim 33 wherein the sintering aids are selected from the class consisting of metal oxides and alpha- Al2O3.
35. Process according to claim 35 wherein the sintering additive is alpha-Al2O3.
36. Process according to claim 34 wherein the metal of oxides of initial spinel crystalline structure or of a character to form such structure under the sintering conditions.
37. Process according to either of claims 34 or 36, wherein the sintering 15 carried out at a temperature in the range of 1,200 to 1,800° C to effect sintering.
38. Process according to claim 37 wherein the sintering is carried cut at a temperature in the range of 1,300 to 1,380°C.
39. Process according to claim 32 wherein the sintering step is also utilized as a calcining step conclusion of the hydrothermal processing.
40. Process for production of alpha-Al2O3 at 95-100% theoretical density and as a high abrasive power material comprising hydrothermal processing of a precursor material comprising chi-Al2O3 as a principal ingredient and then subjecting the hydrothermal treatment material to sintering-like process conditions whereby a alpha-Al2O3 is formed to high density and high hardness without use of expensive starting materials or process conditions.
41. Process according to claim 40 wherein the precursor is in fact sintered.
42. Process according to claim 41 wherein sintering-aid additives are incorporated into the material prior to sintering.
43. Process according to claim 42 wherein the sintering aids are selected from the class consisting of metal oxides and alpha-Al2O3.
44. Process according to claim 43 wherein the sintering additive is alpha-Al2O3.
45. Process according to claim 42 wherein the metal oxides are of initial spinel crystalline structure or of a character to form such structure under the sintering conditions.
46. An abrasive alumina material as made by the process of claim 40, including usage of the precursor naterial recited therein, and further characterized by over 95% theoretical density and a sub-micron crystallite size.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| EP89106819A EP0394500B1 (en) | 1989-04-17 | 1989-04-17 | Process for the production of sintered alpha-alumina bodies |
| EP89106820A EP0394501B1 (en) | 1989-04-17 | 1989-04-17 | Process for the production of alpha alumina sintered bodies |
| EP89106820.7 | 1989-04-17 | ||
| EP89106819.9 | 1989-04-17 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2014482A1 true CA2014482A1 (en) | 1990-10-17 |
Family
ID=26120100
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2014482 Abandoned CA2014482A1 (en) | 1989-04-17 | 1990-04-12 | Production of alpha-al 0 sintered bodies |
Country Status (2)
| Country | Link |
|---|---|
| JP (1) | JPH02293371A (en) |
| CA (1) | CA2014482A1 (en) |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5611829A (en) * | 1995-06-20 | 1997-03-18 | Minnesota Mining And Manufacturing Company | Alpha alumina-based abrasive grain containing silica and iron oxide |
| US5645619A (en) * | 1995-06-20 | 1997-07-08 | Minnesota Mining And Manufacturing Company | Method of making alpha alumina-based abrasive grain containing silica and iron oxide |
| US6277161B1 (en) | 1999-09-28 | 2001-08-21 | 3M Innovative Properties Company | Abrasive grain, abrasive articles, and methods of making and using the same |
| US6287353B1 (en) | 1999-09-28 | 2001-09-11 | 3M Innovative Properties Company | Abrasive grain, abrasive articles, and methods of making and using the same |
| WO2009048573A2 (en) * | 2007-10-10 | 2009-04-16 | Massachusetts Institute Of Technology | Densification of metal oxides |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2001056926A1 (en) * | 2000-02-04 | 2001-08-09 | Goro Sato | Alumina composition and method for preparing the same |
| EP2981378B1 (en) * | 2013-04-05 | 2021-06-30 | 3M Innovative Properties Company | Sintered abrasive particles, method of making the same, and abrasive articles including the same |
-
1990
- 1990-04-12 CA CA 2014482 patent/CA2014482A1/en not_active Abandoned
- 1990-04-13 JP JP2096643A patent/JPH02293371A/en active Pending
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5611829A (en) * | 1995-06-20 | 1997-03-18 | Minnesota Mining And Manufacturing Company | Alpha alumina-based abrasive grain containing silica and iron oxide |
| US5645619A (en) * | 1995-06-20 | 1997-07-08 | Minnesota Mining And Manufacturing Company | Method of making alpha alumina-based abrasive grain containing silica and iron oxide |
| US6277161B1 (en) | 1999-09-28 | 2001-08-21 | 3M Innovative Properties Company | Abrasive grain, abrasive articles, and methods of making and using the same |
| US6287353B1 (en) | 1999-09-28 | 2001-09-11 | 3M Innovative Properties Company | Abrasive grain, abrasive articles, and methods of making and using the same |
| WO2009048573A2 (en) * | 2007-10-10 | 2009-04-16 | Massachusetts Institute Of Technology | Densification of metal oxides |
| WO2009048573A3 (en) * | 2007-10-10 | 2009-07-23 | Massachusetts Inst Technology | Densification of metal oxides |
Also Published As
| Publication number | Publication date |
|---|---|
| JPH02293371A (en) | 1990-12-04 |
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