CA1203967A - Method of making boride powder - Google Patents

Abstract

Abstract Powder of essentially diboride of Group 4b metal with particle size substantially less than 5 µm is made by:
(a) preparing a solution consisting essentially of Group 4b metal salt, soluble boron source and soluble carbon source in proportions for carbothermal reduction of the corresponding oxides of the metal and boron with carbon, (b) heating the solution to yield a dried and decomposed residue consisting essentially of very fine and intimate mixture of carbon and the oxides of the metal and boron, and (c) firing the residue up to and at temperature and for time to effect the carbothermal reaction of the residue to yield friable agglomerates primarily of the diboride which are very easily comminuted into powder of particles substantially less than 5 um size. Group 4b metal salt is replaced in part by salt of Group 5b, Group 6b and/or rare earth metal in order to yield corresponding boride of latter metal as sintering aid with Group 4b metal diboride in powder, especially as diboride solid solution. Latter complex diboride powder is suitable without hot pressing to close to theoretical density. The proportions of salt or salts, soluble boron source and soluble carbon source may be selected in additionally provide a minor boron carbon phase as sintering aid.

Description

~Ju~irika 4 .. . .

~E:TEI09 OF KING BC)RIDl~ POWDER

The ~n~ell~ior~ flee Jo the manufacture of substantially 1~3 than 5 em particle size powder of ~s~ntial}y di~30rid~ of Group 4b metal titanium,/ zirconillm and~or hafnium~, esp~c:ially such powder that can by wintered withau~ ho pressing into fin!-gr~ined coherent bodies with few poro~ y Ed re~lativ~ly close to theoretical densit:y.
Dibori~es of Group 4b metals ha been maae by 3everal typo of proce3~s. vainly they.have teen made by carboth~rmal or metalo~hermic r~duc:tion of mixture s:f the discrete ox s of thy metal and }moron with carbon or metal, bar fusion or r~a~ ive sin~ering of the petal and boron, by el~c~rolys~ of used it c:ontainirlg oxide and by vapor pha~ reae~ of ~ou~ce~ of thi3 metal and boron wever 7 5uch pr~ces~es either do Ilo~ readily produce ~ubmicron powder or are re~al~7 sly expensive to p~r~orm.
~7ery fine panda to diboride powder are believed to be essential for produeing fine grained coherent bodies with high d~n~ity" low ps:~rosîty; sul:~taIltial ~reng~h and an~ial reliance Jo ~::he~i~al cask It is knowrl thaw Croup 4b metal diboride powaers do not sin l:er into strongly cohexent dense bodies except :Ln admixture with art additi~Je a disclosed in U I, S ,. Peon

2, 984, 807 1 Whit hot prosing of Group 4b diboride powers cay yield substantially eohPrent bodies, ~h~y are generally '

3~ 7 quit porous except in admixture with an additive as disclosed in UOS. Patent 3,437,606.
39Dg~9~
It is an oboe of hi invention to provide a relatively i~expensi~e methoa of making substantially less Han 5 particle si2e powder of ~ssen~ially diboride of Group 4b petal. Such powder can be admixed with known additives for product fine-grained coherent bodies by ordinary shaping and ~in~ering or hot pressing techniques.
. It is another object of this invention to provide a simple method of making substantially lest than 5 Jim particle I powder consisting essentially of diboride of Group 4b metal in~i~a~ely as~o~iat d with a sintering aid, which powder is readily ~in~erabl~ without hot pressing into lS a fine~gxained, coh~re~, dense body.
It it a further obj ect to provide a method that can employ carboth~rmal redu tion thaw proceeds at relatively low ~empera~ures because of the intima~a contact among the , reac~an~s.
The method of the invention comprises:
pa) preparing a solution consisting essentially of first Walt or at or group 4b metal, soluble boron source and soluble carbon ~oUECe in proportions for carbothermal reduetion of the corr@sponding oxides of the metal and boron 25 with carbon to a least ~Qr~ the corresponding diboride of the meal (b) heating the solution to yield a dried and decomposed or charred residue consisting essentially of a very ~Lne and time mixture of carbon and the oxides of the metal and boron and (c) wiring the residue up Jo and at t~mperatu~e an for time to ef~ec~ the carbothermal x~a~tio.n of the residue to yield friable agglomerate primarlly of the diboride ~3~

.. . . . . . ....... .. . . . . ........ . ..... . .
which are very easily comminut~3d into powder of particle substantially less than 5 pm to This method can also be performed with proportions of the salt or salts, boris:: acid and soluble carbon source in 5 proportions to alsv ;~t upon c:arbothermal reduction, borc3n carbide as minor sintaxing aid phase in the primarily diboxide aggl~merat~ and powder.
I:n this method the solution may include second 3alt vx elk of Group 5b~ group 6b and/or rare eax~h tat alto in 10 propt~rtion wlth the aforesaid ~olu~i.on ingredierlt~ for carbo1thermal r~luc~ior~ of the c:orresponding second metal Rxide a well a the first metal oxide and boric oxide with c:arlbo~. Generally k molar ratio of Group Sb, S;roup 6b and/or rare earth metal to Group 4b metal in the solution is 15 les~3 than one. Upon iring of the residue, the boride powder will con~ai~ boride of Group 5b~ Groul? 6b or rare earth metal eOg. in diboride solid solution with Grollap 4b m~t~l diborîde 9 as a built-in sintering aid or the es~e3ltially Group 4b diboride powd2x.
Any decomposable salt of the noted metals may be employed in the method of the invention. however, especially yood felts have been :3b~ained with halide7 e.g.
chloxid~ cluding oxychlorid~), of Group 4b metal generally" ~ulfate~ are the least desired because of slower 25 d~compoaition ~u:ring drying an charring.
As used h~reirl, Group 4b metals are titaniu~n~ zircotlium and hafnium; Group 5b ~a~tals art vanadium, niobium and lanai Group 6b cat are chromium, molybdenum and tungsten; and rare earth ~etal~ are yttriuxn and the metals 30 ox the lanthanide Erie elements.

3~

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i r~etiorl Illustrative of the carbothex~;al reduction reaction takirlg place in the raethod c~ thy invention is the following molar equation ~i2 B203 t 5C q!iB2 - h series of po~der~ were made acc:ording Jo the invention r~m aqueo7l~ ~olution~ ox ba~:h menials a isdicated it T~lç~ he ~olu~ion for each powder was heated at lOO'~C in art oven UIl'i tl a dried and decomposed or charred residue way wormed, which was a very fine and in~i~a~e ~ix~ure of Tiû2~ ~322~ carbon and in all bul:
po~r~ers 1 alld 3 t a I:hird oxide of the metal from the addit:ioIlal lesser batch material. Rome combustion lost of carbon appears to occu:r durlrlg heatialg a 100~ ach residue was therl fired a 1400Qc for 2 hours it argon to yield primarily boride aggl~meratss which wer@ very friable.
Those agglomerate were separately milled in a pl netary mill for abQ111: 10-15 minute to yiela the powder. The intended Gompo~i~ions ox those powder3 are set forth it 20 Tale 2. ~3[o~ever, the ac:t~al fired powdP.r~ probably contalned very small amount ox oxygen and carbon teach less than 1 wt . 96 in addition to the diboride ., ` 1. ;

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Table 1 ~L~L~
Bateh Material A B C D
___ _ _ _ _ TiCl,L solution in I::e 59 o l 40 0 4 56 .1 56 .1 5 ( laes: 4 0 5 gram TiO~
Borie ae~ d in gram 41. 250 0 0 41. 2 41. 7 Suero~e in gray 47 o 512 2 0 71~ 371 n 3 Ziree~slium oxyehlorid~
hydrate ZrOa;2 8E~201 -; 8 -no 10 in graJn~ -Ch:Eomium nitrate irk 6~,7 ~ra~ let (~0~ 3 a 9~ ;~0) F G
15 TiC14 ~oluti on ira ce56 o l56 .1 56 .1 56 .1 c - I., 5 a iO 2) BQris: ac:id in gram~41. 7 41. 7 41,, 7 410 7 Suero~e in grams 71. 3 71. 3 71. 3 71. 3 Yt1:xium elate on gr~l~ 5 . 7 20 (Y ~2~32~ 2 ' ~23 C:~ric: a~nonium suïa~e - 10 0 7 -- -in graun~
V21~5 (~is~lvea lCl~
gr2lms I- - lo 54 ~~
25 I.a~hama~n titrate - .
grams 7 I, 3 ` ~2~3~7 .. `... ; . .. , .. .- .-. . ., .. . .. , ., .. . `, .~.. .. . . . . ., . ,.. . ,., .:
Table X
Powder TiB2 B O g TiB2 .1 ZrB2 solid solution C TiB2 - with excess carbon D 0 . 95 TiE12 + 0 O OS CrB2 solid solution E 0 9 95 TiB2 05 YB2 solid solution F O 95 TiB2 * 05 CeB2 solid solution O 95 TiB2 . 05 ~2 ;~ ss~lid ~oïution Ei 0 . 95 T1B2 + . 05 LaB2 solid solutio To demon~;~ra~e the inning ability of the preceding powd~r~, whey were pr2ssed into bars and fired at 2000~C
n argorl for 0 u 5 laours O The properties of the fired bars 15 end the particle size of the diboride powderR of whic:h tl~ey were foxed are shc3wn irl Table 3. Powders 5 and 7 sintered close Jo t~eoreti~al density of their compo~ition~ duo to the presence ox thy ~iboride ~in~ering aids. Powders 4 exhibited a us ~an~ial ~in~ering ability, although nsk as 20gaod as that of Po~aer~ 5 and 7. Powders 2, 3, 6 and showea l~it~d ~lntering ability, while powder 1 essentially lacked sir~eri~g~ y. Of course, powders ï~3 Gould be admix~3d with ss:n~e pre~r.iollsly noted sirtering aid or additive Jo as Jo re~dex them sint~rable unto e-grained bodies 25 The x-ray ph~e~ wound in these prosed and fired powder bar S sot forth it Table 4.
Table 3 ~7olume % ESlac~rical particle %l Ilear Density Open . resistivity Power my ohm - cm 1 . 9 B 3 . 12 1. 9 40-50 0 .17 C 2.û 13 2.0 40- 50 0.14 3~'7 ~7_ .. . ,~ . . . .

D . 1. 3 19 3 . 5 17 0 .16 E . 1.5 25 3 / 8 5 0~15 F 2 . 9 8 2, 540-50 . 30 I; 1.1 2~ 4.~ 0,.1~
El . 15 ~,DB. Dew y o T~B2 4~38-4.56 gm/cc, as repoxted lit~ratlare - .
- . Tile 4 minor 2ha3e A TiB~2 TiC
B T~B2 B~C
C TiB;~ TiC Tilt Traces o:E unid~n~i~ied peaks D TiB2 TiC
E Til32 TiC
TiE~2 TiC + TiN Traces of unidentified p~alks G TîB2 TiC Trace of unidentified peaks Ti}S2 TlC Tree of - unid~n tied peaks other ~raria~30n of thy saethod ox thy inven~iorl, titanium ~iboride p~der way pr~par~a Tom a~eoll~ solutions in which the earbon source way ~uriEural mixed with a small 25 quantity o etha~olO boric acid solutions were fond ir.
three different way: ~23 di~olved in hot water, in ho ethans:~l, and in ho glycerol each about 9S O The glycerol ~olutis:~n ~acte~ t:o fonn glycer~nQ borate ai~ol~r~d in ~Jater. ~po~ drying thaw borate acted to maintain 30 excellent dl~p~r~io~ oiE t~a~3 insredient~ in the r~idue~ The furfu~al and ethanol mixture way added Jo ~ac~ boric acid ~lt3~3~ ;7 .

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solutiorl., Titanium oxychloride aqueous solution way added last to each of these solutions. In each solution, the propor1:iosls of titarl1~un, boron and carbon were substantially stoichiometric with r~spec:~ to the earlier molar equation.
S Those separa~ solutions were heaved at lOaC it an oven Jo yield a dried arld de~:o~nposed residues of intimate i2 B203 and carbon . Each residue was hen fired at 145û~C or 00 5 hour to yield predomi~ ly TiB2 agglom~ral:ed powêler~ of particle sizes ~u~3tantially 10 less than 5 pIQ. In thy fag the powder re ul~ing from the ~olutior~ ~ar~i~g with B203 dissolved in glycerol had particle sizing generally in the range ox SOO-1000 and it contained a very small amount (e., g. lass than 1 wt. %) o TiC. The othe:r two powder s:ontained very small a~no~nts 15 (e.g,. let than 1 wt.. % ea .h) of both TiC and Ti 203 .
It Jill be appreciated that similar powdars of ZrE32 and ~fB2 wit anal without built in intering .aids, ca2l be prepared f the same manner as the foregoing TiB2 powaers.
For examE~le, on the precedi3lg example employing glycerine 20 borate dissol~red irl Nat r, oxychloxide of zirconium was subs~ltu~2d for what ot ~i~anium. The résultan~ powder also had par le sizing g~neraily in k range of 500-1000 I,

Claims (12)

CLAIMS:

1. The method of making substantially less than 5 µm particle size powder of essentially diboride of Group 4b metal comprising:

(a) preparing a solution consisting essentially of first salt or salts of Group 4b metal, soluble boron source and soluble carbon source in proportions for carbothermal reduction of the corresponding oxides of the metal and boron with carbon to at least form the corresponding diboride of the metal, (b) heating the solution to yield a dried and decomposed residue consisting essentially of a very fine and intimate mixture of carbon and the oxides of the metal and boron, and (c) firing the residue up to and at temperature and for time to effect the carbothermal reaction of the residue to yield friable agglomerates primarily of the diboride which are very easily comminuted into powder of particles substantially less than 5 µm size.

2. The method of claim 1 wherein the proportions of salt or salts, soluble boron source and soluble carbon source are sufficient to form, upon carbothermal reduction thereof, boron carbide as a minor phase in the primarily diboride agglomerates.

3. The method of claim 1 wherein the solution includes second salt or salts of group 5b, Group 6b and/or rare earth metal in proportions with the first salt or salts, soluble boron source and carbon source for carbothermal reduction of the corresponding oxides of the metals and boron with carbon.

4. The method of claim 3 wherein the molar ratio of Group 5b, Group 6b and/or rare earch metal to Group 4b metal in the solution is less than one.

5. The method of claim 4 wherein the molar ratio is sufficient to yield, upon fixing of the residue, at least about 5 mole percent of boride of Group 5b, Group 5b and/or rare earth metal in the boride powder.

6. The method of claim 5 wherein, upon firing of the residue, the boride powder comprises a solid solution of diboride of Group 5b, Group 6b and/or rare earth metal in diboride of Group 4b metal.

7. The method of claim 1 wherein the first salt is halide.

8. The method of claim 7 wherein the halide is chloride.

9. The method of claim 8 wherein the group 4b metal is titanium.

10. The method of claim 3 wherein the first salt is of titanium and the second salt is of vanadium.

11. The method of claim 3 wherein the first salt is of titanium and the second salt is of chromium.

12. The method of claim 3 wherein the first salt is of titanium and the second salt is of yttrium.