CA1136388A - Method of producing sintered ceramic articles using liquid boron-containing sintering aid - Google Patents
Method of producing sintered ceramic articles using liquid boron-containing sintering aidInfo
- Publication number
- CA1136388A CA1136388A CA000312562A CA312562A CA1136388A CA 1136388 A CA1136388 A CA 1136388A CA 000312562 A CA000312562 A CA 000312562A CA 312562 A CA312562 A CA 312562A CA 1136388 A CA1136388 A CA 1136388A
- Authority
- CA
- Canada
- Prior art keywords
- sintering aid
- aid
- liquid sintering
- liquid
- solution
- 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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Classifications
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/64—Burning or sintering processes
-
- 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
- B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
- B22F3/10—Sintering only
- B22F3/1003—Use of special medium during sintering, e.g. sintering aid
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/515—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics
- C04B35/56—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbides or oxycarbides
- C04B35/565—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbides or oxycarbides based on silicon carbide
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- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Manufacturing & Machinery (AREA)
- Ceramic Engineering (AREA)
- Materials Engineering (AREA)
- Structural Engineering (AREA)
- Organic Chemistry (AREA)
- Inorganic Chemistry (AREA)
- Mechanical Engineering (AREA)
- Ceramic Products (AREA)
- Compositions Of Oxide Ceramics (AREA)
- General Preparation And Processing Of Foods (AREA)
Abstract
ABSTRACT
The present invention relates to the use of liquid sintering aid to densify ceramic materials, for example , silicon carbide. The liquid sintering aid is selected from the group of solutions of H3BO3, B2O3, or mixtures thereof.
The sintering aid is particularly adapted to be utilized in combination with a liquid carbon source material. The sintering aid, or combination sintering aid and carbon source, is added to a formed, porous article, suitably by vacuum filling, and the article sintered between about 1900° C, and about 2200°C, to produce a hard, dense article.
The present invention relates to the use of liquid sintering aid to densify ceramic materials, for example , silicon carbide. The liquid sintering aid is selected from the group of solutions of H3BO3, B2O3, or mixtures thereof.
The sintering aid is particularly adapted to be utilized in combination with a liquid carbon source material. The sintering aid, or combination sintering aid and carbon source, is added to a formed, porous article, suitably by vacuum filling, and the article sintered between about 1900° C, and about 2200°C, to produce a hard, dense article.
Description
1~ 3,~
, 2 S BACKG~OUND 01 Tlll INVENTION
s Tlle present invention relates to the use of liqu;d sin~ering aid in processes involvin~3 sintering of ceramic materials ~o produce dense, hard articl~s having industrial uses. Altllough the present invcntion will be sl)eci-8 fically discussed in retJard to compositions con-taining silicon carbi(lc as ~lle 9 ¦ ceramic material, it will be unders~ood that other sinterable carbides, for 0 ¦ e~ample, titanium carbide, may be utilized as ~he ceraMic mat,crial. .
Silicon carbide has long been l~nown for its llardness, strentJ~h, and ¦ excellent resistance to oxidation and corrosion. Silicon carbide has a low 13 coefficient of expansion, good lleat transfer properties, and maintains hig}1 14 stren~th at eleva-led temperatures. In recent years, -the art of producing hi~h-density silicon carbide materials by sintering s~licon carbidc powders has been 6 developed. High-density silicon carbide materials find utility in the fabrica-7 tion of components for turbinesl heat exchange units, pumps, and other equipment 8 ~r tools that are exposed to severe corrosion or wear, especially in operations 19 !1carried out at high temperatures Ceramic bodies or compacts may be formed or shaped by various cas~iny 21 or molding processes~ Forming or shaping processes known in thc art, such as 22 cold pressing, isostatic forming, slip casting, extrusion, injection or transfer 23 ¦ molding or tape casting, may be utili~ed. The shaped ceramic body is subse-24 ~ quently sintered, between about 1900 C. and 2200 C., to form a dense, hard article.
26 In order to obtain high-density and high-strength silicon carbide 27 ceramic ma-terials, various additives haY~ been util~zed. ~or exa~ple, a nle~hod 28 of hot pressing s:ilicon carbide to densi-ties in order of 9~ percent of theore-29 tical by addition of aluminum and iron as densification aids is disclosed by Alliegro, et al, J. Ceram. Soc., Vol. 39, No. 11, Nov., 195~, pages 33~ to 3~9.
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:, 3~3~3 Thcy foun(1 ~ha~ a d(!r1sc silicon cnr1)i(10 coul(1 be 1)ro(1llco(1 from a p()w(1cr mixture
, 2 S BACKG~OUND 01 Tlll INVENTION
s Tlle present invention relates to the use of liqu;d sin~ering aid in processes involvin~3 sintering of ceramic materials ~o produce dense, hard articl~s having industrial uses. Altllough the present invcntion will be sl)eci-8 fically discussed in retJard to compositions con-taining silicon carbi(lc as ~lle 9 ¦ ceramic material, it will be unders~ood that other sinterable carbides, for 0 ¦ e~ample, titanium carbide, may be utilized as ~he ceraMic mat,crial. .
Silicon carbide has long been l~nown for its llardness, strentJ~h, and ¦ excellent resistance to oxidation and corrosion. Silicon carbide has a low 13 coefficient of expansion, good lleat transfer properties, and maintains hig}1 14 stren~th at eleva-led temperatures. In recent years, -the art of producing hi~h-density silicon carbide materials by sintering s~licon carbidc powders has been 6 developed. High-density silicon carbide materials find utility in the fabrica-7 tion of components for turbinesl heat exchange units, pumps, and other equipment 8 ~r tools that are exposed to severe corrosion or wear, especially in operations 19 !1carried out at high temperatures Ceramic bodies or compacts may be formed or shaped by various cas~iny 21 or molding processes~ Forming or shaping processes known in thc art, such as 22 cold pressing, isostatic forming, slip casting, extrusion, injection or transfer 23 ¦ molding or tape casting, may be utili~ed. The shaped ceramic body is subse-24 ~ quently sintered, between about 1900 C. and 2200 C., to form a dense, hard article.
26 In order to obtain high-density and high-strength silicon carbide 27 ceramic ma-terials, various additives haY~ been util~zed. ~or exa~ple, a nle~hod 28 of hot pressing s:ilicon carbide to densi-ties in order of 9~ percent of theore-29 tical by addition of aluminum and iron as densification aids is disclosed by Alliegro, et al, J. Ceram. Soc., Vol. 39, No. 11, Nov., 195~, pages 33~ to 3~9.
: -1- ' I , ~ ' ~L
:, 3~3~3 Thcy foun(1 ~ha~ a d(!r1sc silicon cnr1)i(10 coul(1 be 1)ro(1llco(1 from a p()w(1cr mixture
2 contail1in~ l percc11t by wei~ht of aluminum, I'heir product ha(1 a Modulus of
3 ru1~ture of 5~,000 psi at room -~en1perature and 70,0()0 ~si at 1371 C. ,~loro ¦ recen~ly, L~10 USO ol' boron or beryllium as s1nterintJ or dens1fication a1ds has S ¦ been developed. Such aids are usually addecl to the ceramic material powder in 6 ¦ amounts ranginy between about O.3 and about 5.0 percent by wei~Jht of boron or l beryllium. The sinterin~ aid may be in the form of elemental boron or beryllium 8 ¦ or in -the form of boron- or beryllium-containin~ compounds. Boror1 is tl1e r~re-9 ¦ ferred additive for rea,sons of handlin~ and peirformance. Boron is commonly ¦ utili~ed in the form of boron carbide. I.xamples of boron-containintJ silicon ¦ carbide powders may be found in US Patents 3,~52,099, 3,95~ 3; and 3,96U,199.
2 ¦ Sinterable powders also contain excess or uncombined carbon, Excess 13 ¦ carbon in amounts of from about l.O to abou-t ~.0 percent by wei~Jht are commonly 1~ ¦ used. The excess carbon required for sintering may be in the form of carbon ¦ remainin~ in the article from a previous processiny step or may be added in the 6 ¦ form of a carbon source material which would yield the desired amount of excess 7 carbon as the article is sintered. E~cess carbon facilitates sinterin~ and is 8 ben~eficial in reducing the amounts of various oxide impurities in ~he starting 19 ceramic material that otherwise would remain in the finished product.
i 22 In accord with the present invention, the sinterin(~ aid utilized to 23 densify ceramic materials is e~ployed in liquid form. The source of boron, or sinterin~ a-id, of the present invention is selected from solutions of ~131303, 2s ~23~ or mixtures thereof. A1thou~Jh the solvent may be any liquid in wilich 26 H3B03 or B203 are soluble, wa-ter or alcohols are preferred because of their 27 ~ availability and cost.
28 ¦ The liquid sintering aid is suitably added to a sl1aped, porous 29 ¦ ceramic body prior to sintering. In one mode of the invention, the sintering ~o ~ aid and a source of c-rbon are adde' o2ether in l:quid form. In such mode, I ., , .
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¦ thc sintcrin(J aid 11n1y bo dissolvod in ~hc carbo1l so1Jrcc, or ~i1(' sinterin(J aid 2 1 and the carbon source may be dissolvcd in a c0111mon solvcn~, for example, water 3 ¦ or alcohol.
2 ¦ Sinterable powders also contain excess or uncombined carbon, Excess 13 ¦ carbon in amounts of from about l.O to abou-t ~.0 percent by wei~Jht are commonly 1~ ¦ used. The excess carbon required for sintering may be in the form of carbon ¦ remainin~ in the article from a previous processiny step or may be added in the 6 ¦ form of a carbon source material which would yield the desired amount of excess 7 carbon as the article is sintered. E~cess carbon facilitates sinterin~ and is 8 ben~eficial in reducing the amounts of various oxide impurities in ~he starting 19 ceramic material that otherwise would remain in the finished product.
i 22 In accord with the present invention, the sinterin(~ aid utilized to 23 densify ceramic materials is e~ployed in liquid form. The source of boron, or sinterin~ a-id, of the present invention is selected from solutions of ~131303, 2s ~23~ or mixtures thereof. A1thou~Jh the solvent may be any liquid in wilich 26 H3B03 or B203 are soluble, wa-ter or alcohols are preferred because of their 27 ~ availability and cost.
28 ¦ The liquid sintering aid is suitably added to a sl1aped, porous 29 ¦ ceramic body prior to sintering. In one mode of the invention, the sintering ~o ~ aid and a source of c-rbon are adde' o2ether in l:quid form. In such mode, I ., , .
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¦ thc sintcrin(J aid 11n1y bo dissolvod in ~hc carbo1l so1Jrcc, or ~i1(' sinterin(J aid 2 1 and the carbon source may be dissolvcd in a c0111mon solvcn~, for example, water 3 ¦ or alcohol.
4 1 Tllo c~rnmi~ sLnrtln~ mntor1al i8 ln1~lnlly propnred ln ~inely dlvided ¦ form. Preferably, -the particles have an average size of fro1n about O.lO to 6 1 about 2.00 microns, with a maximum of about 5.00 microns. Althou~h sizc is a 7 ¦critical parameter, surface area is also of relevant consk1eration in deter-R ¦minin~ the suitable material. AccordincJly, the particles preferably have a 9 ¦surface area of frorn about l to about lO0 m2/g. Within this ran~e, it is more ¦preferred that the surface area of particles range betwcen about 5 and about 20 .
¦ m2~-2 1 Silicon carbide is a preferred ceramic starting material. The sili-13 ¦con carbicle may be alpha or beta phase, or may be amorphous At ~he present 14 ¦time, the alpha (non-cubic) crystalline phase of silicon carbide is most econo-S ¦mically obtained. The present compositions may contain substan~ially entirely, 6 le.g., 95 percent or more by wei~ht, silicon carbide of the alpha phase, or may 7 ¦cont`ain mixtures o the various forms of silicon carbide. For e~annple, n1ix-8 Itures which are predominantly alpha phase (~reater than 50 percent) are aptly l~ ¦suited to use. The ceramic material may contain minor amounts of impurities ¦without deleterious effect. Generally, a purity of at least about 95 percent 21 ¦is required and a higher purity desired.
22 1 In accord with the present invention^, the sinterin~ aid, or a com-23 l bination of sinterin~ aid and carbon source material, are added to a sha1-cd, 24 1 porous ceramic body af-ter baking and prior to sintering. Such bodies are pro-¦ duced by moldin~ or casting processes wherein a (~1een body is fo~m~id, bakcd, 26 1 and subsequently sintered. The addition of sintering aid or a combination of sintering aid and carbon source material after baking and just prior to sinter-28 ~ ing is particularly advantageous in injection molding and slip castin~ processes 29 In present practice, the ceramic startin~ material is initially mi~ed with a ~o , vDriety of n it;v-s, e.g., sinterin~ a~ds, carbon source material, resin ~, ' - ~ .
~' ' ' , ~ ' l3~3~!3 j I ~bill~er ma~crials, mol(l release agcnts, and ad(li~iv(s ~o lower ~ilc visc~si~y of 2 ¦ the mixLurc. l't has heen found that the sintering ai(l a~(l/or the carbon source 3 ¦ material fre~lucntly has a deletcrious erfect on the binditl(J, rclcasc, or flow ¦ ~ro~orLio~ of t~,~ mix~uro. T)lo ~limln~ltlon of ~ho sintorln~ aid, or ~he sin-¦ tering aid and the carbon source material, facilitates the ~orming process and6 ¦greatly increases -tlle number of useful binder resins and processinD additives 7 ¦ that may be utilized in such mixtures.
8 ¦ The sintering aid of the present invention is ad(~ed to the bal~ed 9 ¦ green body in amounts which will provide from about 0 3 lo about 5.0 percent by 0 ¦ weigh~ of boron, and, within ~his range, from about 0.5 to abou-t ~.0 percent .
¦ are aptly suited to use. When amoun-ts of boron below abollt 0.3 percent by ¦ weigllt are used, sintering is generally not effeotively carried out. When 13 ¦ amounts of boron above abou-t 5.0 percent by weiyht are included, dcnsification 14 ¦ is not noticeably improved and may be adversely affected by the inclusion of 1 excessive amounts of boron. The s-trength of the present solutions of sinteriny ¦ a`id is adjusted to provide a boron source substantially uniformly d-is;,ersed ¦ throu(Jhout the porous body that, upon sintering, will yield boron within the 8 ¦ foregoing ranges. The sintering aid solution may be made relativ~ly strong, 19 1 and, after sa~urating or impregnating the porous area, the excess may be allo~ed 0 1 to drain off. ;The amount of boron added may be determined by a simple weighing 21 1 of the body before and after impregnation or dispersion of the sintering aid 22 ¦ and calculating from the added weight.
23 ¦ The present invention also contemplates the usc of a combination of 24 ¦ sintering aid and a source of excess carbon in li~uid form. Suitably, the sin-¦ tering aid may be dissolved in the excess carbon source material, or both the 26 ,I sintering aid and the excess carbon source material may be dissolved in a 27 common solvent. ~xcess or combinable carbon in amounts bctween about 0.05 and 28 about 5.0 percen-t of the ceramic material are useful to facilitate sintering, and, within this range, amounts of from about 1.0 to about ~.0 percent by weig'ht are espccially uscful. The carbon source may be any carbonaceous material in _~_ .'' : ~ , .
1 ~1 3~
¦wllicll l,hc Silll.(!l'ill~l iai(l :is mis(:il)lo, wil,llnlll. nll a~lvel.~o 1-(';l~'l iOII, or wili(d~
C ¦misc.il)le .in n co1~1()r' solvel1t, wil,11 l,ho sinl,erln(J i)id. Su(lars, .su(:l1 ,3s Sll('rOS(' 3 Ian(l (I(~xl.ros(~, C()~'17 syr~l), rtlr.t'ury*alco~ ~, I.clrill)y(lror~lrl~lryJ
¦alcohl)l, p11enn:L;i(, resins, poly1l11eny:1e11c~ros1lls, an(l furai1 re,sin,s are 1,ypi(,i1J
¦use.rul carbon source m;1~erials. Usually, L11e chiar or carb()n v1.lue of carbon 6 ¦sourco mat,erlals ran~ses rro1n about lS to al)out (I() percent l)y weiql11,. lhe a1)1)ro--¦priate amoun~.s of s:interin(J aid and carbon soulce a;ater.ial 111ily Lhus l)e easily ¦calculated. It is postll1ate~ that the presenL sinl.eril1~J aid.un~1ertJoos reduc-9 ¦tion dur:i1l~ sinLer:i11(J. The amounl Or carbo11 sourco mill,erii1l 1nay bo ild,jusled l,o ¦ provi(:le both the amol1nt of carbon re~luire(l for sucll roducLion nn(l lho iam()l'nt of 11 1 exeess earbon re(111ir()(1 for sinterinU~
12 1 . . ., 3 ¦ DE'I'AILEI) DESCRIPTION Oli 'i'llE INV[~NTlON
Tl1e li~luid sinterincJ aid of the l)resenL invention may be p~epare(l by ¦ simply ~issolvin(~ 113[303, B203, or mixtmres l,h~re()r~ in an ia11pro1lrii1te solvent,.
lG l It will he un(lerstoocd 1,1lal, llle for1~ la d!~s.i~nal,iolls 1~13[303 an(l '323~ bor:ic a(,;(l : 17 ¦ and boron o~icle, shall he read to be inelusive of hy(lrlt,es of 113B03 and B203;
8 1 The solvent nlay be any liqui(l in whieh ~]3B03.,or B203 are soluhle, suitabl.y !.he 9 , ¦solvenl is water or aleo1lol. ~The sinter~n~ aiLI Or lhe pr~se1ll invenl,ion is ¦ad~iecl to a porous body to provide fro1n about 0.3 to ahoul, 5.0 percent an(.1, pre-~ 21 ¦ ferably, withln that ran(Je~ Irom abou.t 0.5 to abollt 1.0 [-ercent, by weitJht, boron ; 22 ¦to the body. Tl1e stren~Jlh of the solul;o1l of sinterin(J aid is ar1justed l,o faci-3 ¦liLate a substantially unifor1n dispers:io1l Or a boron source throu~l1ollt tlle body.
¦ The sinlerin~ aid of the present invention may be d.issolved in a ¦ source oL earbon to provide a li(luid eo~nb.ination of sint,erin(J aid an(l carbon 26 1 source malerial. Suitable sourees Or earbon useLul in this mode are those in whiel1 the sinter:in~ al(l is solubl.(. Especially suiled are aleoho1s such as 28 1 furruryl aleohol and t.etrahydrofl1rfury,l alcohol. Excess or comb:inable carbon , ~ 29 ¦ is utilized in the ran(3e of from about 0.05 to about, 5.0 percenl, by wei(JIlt, an(l, :~ 30 ~ preIerably, from aDoul l.0 to ab~ut ~.0 percenl by weivht Or ll1e porous bo(ly to ~ . I . -5-I
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o ~ ri~ ur~ y, ~,;lrl)()n;~ ; yi( ~ t l~er) ;~ IJ~
2 an(l abollt ~0 percent by weiuht fre(3 or cornbinnl)le c;lll)on ul)~)n dcs~ruc~ion by~
heating. ln this mode of the inven~ion, an apl-)ror)riate arnount Or sintering aicl 4 is dissolvo(l, suitilhly by mixinU, in an al~proprillo amollrl~ nr call)on sollrco material to provide excess carbon witllin tlle desired ranye, G The sintering aid of the present invention and the carbon source 7 ¦ material may be dissolved in a mutual solvent to Lorm a combina~ion liquid sin-tering aid and carbon source material. In this mo~e, water is aptly suited to ? I use as the mutual solvent. Examples of water-soluble carhon source materials o that may be employed are sugar, such as sucrose and dextrose, corn syrup, and alcohol, such as Lurfuryl alcohol. Alcollols may also be used as the mutual 2 solvent. Ethyl, methyl, propyl, and isopropyl alcohols are eminently use~ul.
3 11 ~'henol-ormaldehyde resins are particularly adapted to use as ~he carbon source ?4 . ¦¦ material when short chain alcohol is used as the common sqlvent. The sinterin(J
S ~aid and carbon source ma-terial are dissolved, suitably by mixing, in the common 6 jsolvent to provide a combina-tion iiquid sinterin0 aid and carbon source materia~
7 In carrying out the method of the present invenlion, the liquid sin-8 tering aid or combination liquid sintering aid and carbon source material are 9 dispersed in a baked green body, and subsequently the body is sintered to pro-duce a dense, hard ceramic srtiGle.
21 The process used to form or shape the green body is not cri~ical to 2 the present invention. Generally, in such processes, the particulale ceramic 3 starting material is initially mixed wi-th a resin binder ma~terial and other 4 appro~ te additives, for example, mold release agents, lubrican~s, viscosi~y 2s aids, and excess carbon sources. The mix-ture is then molde~ or shaped by kno~n G art processes such as col~ pressing, isostatic-formin(J, slip casting, tape27 castin~, injeetion or transfer molding. The shaped green body is baked, usually 28 at temperatures between about 500 C. and about 1000 C., ancl, more commonly, 29 between about 700 C. and about 900 C. The result of the baking step is a product having an open pore structure which is particularly adapted to be : ~: ,, . ; ~ ; : , l ~a~3~
2 l troated with thc~ liqlli(l sinterin~l aid or combin.lLion sin~trin(J ai(l an(l carbor 3 1 source material of the prcsent invention. 'rhe sintcrin(J ai(l or combination sintering aid and carbon source mater`ial may bc dispcrsctl subs~.lntially uni-l formly throu~hout the baked body by impregnatincJ the body, by applyin~y pressure, S ¦ or capillary action of the pores. The preferred method, ho~ever, is by vacuum 6 ¦ fillin~. In such method, a vacuum is drawn on the body, an(l the li(~uid sin-7 ¦ terin(~ aid or combination liquid sinterillg aid and carbon source material, is 8 I fed into the evacuated body. After dis~ersion of the sinterin(J aid, or combina-tion sintering aid and carbon source material, the iml)r~'~nated body is sintere~
lo ¦ at temperatures b~ltween abou-t 1900 C. and 2200 C. to pro~lce a ~cnsc, hard .
ll ¦ article or body.
2 ¦ It will be appreciated that the invention is not limited to the l4 I specific examples and embodiments of sintering ai~s and sinterincJ me~hods, and that various modifications may be made within the ordinary skill of the art, G without departing frgm the spirit and scope of the invention.
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¦ m2~-2 1 Silicon carbide is a preferred ceramic starting material. The sili-13 ¦con carbicle may be alpha or beta phase, or may be amorphous At ~he present 14 ¦time, the alpha (non-cubic) crystalline phase of silicon carbide is most econo-S ¦mically obtained. The present compositions may contain substan~ially entirely, 6 le.g., 95 percent or more by wei~ht, silicon carbide of the alpha phase, or may 7 ¦cont`ain mixtures o the various forms of silicon carbide. For e~annple, n1ix-8 Itures which are predominantly alpha phase (~reater than 50 percent) are aptly l~ ¦suited to use. The ceramic material may contain minor amounts of impurities ¦without deleterious effect. Generally, a purity of at least about 95 percent 21 ¦is required and a higher purity desired.
22 1 In accord with the present invention^, the sinterin~ aid, or a com-23 l bination of sinterin~ aid and carbon source material, are added to a sha1-cd, 24 1 porous ceramic body af-ter baking and prior to sintering. Such bodies are pro-¦ duced by moldin~ or casting processes wherein a (~1een body is fo~m~id, bakcd, 26 1 and subsequently sintered. The addition of sintering aid or a combination of sintering aid and carbon source material after baking and just prior to sinter-28 ~ ing is particularly advantageous in injection molding and slip castin~ processes 29 In present practice, the ceramic startin~ material is initially mi~ed with a ~o , vDriety of n it;v-s, e.g., sinterin~ a~ds, carbon source material, resin ~, ' - ~ .
~' ' ' , ~ ' l3~3~!3 j I ~bill~er ma~crials, mol(l release agcnts, and ad(li~iv(s ~o lower ~ilc visc~si~y of 2 ¦ the mixLurc. l't has heen found that the sintering ai(l a~(l/or the carbon source 3 ¦ material fre~lucntly has a deletcrious erfect on the binditl(J, rclcasc, or flow ¦ ~ro~orLio~ of t~,~ mix~uro. T)lo ~limln~ltlon of ~ho sintorln~ aid, or ~he sin-¦ tering aid and the carbon source material, facilitates the ~orming process and6 ¦greatly increases -tlle number of useful binder resins and processinD additives 7 ¦ that may be utilized in such mixtures.
8 ¦ The sintering aid of the present invention is ad(~ed to the bal~ed 9 ¦ green body in amounts which will provide from about 0 3 lo about 5.0 percent by 0 ¦ weigh~ of boron, and, within ~his range, from about 0.5 to abou-t ~.0 percent .
¦ are aptly suited to use. When amoun-ts of boron below abollt 0.3 percent by ¦ weigllt are used, sintering is generally not effeotively carried out. When 13 ¦ amounts of boron above abou-t 5.0 percent by weiyht are included, dcnsification 14 ¦ is not noticeably improved and may be adversely affected by the inclusion of 1 excessive amounts of boron. The s-trength of the present solutions of sinteriny ¦ a`id is adjusted to provide a boron source substantially uniformly d-is;,ersed ¦ throu(Jhout the porous body that, upon sintering, will yield boron within the 8 ¦ foregoing ranges. The sintering aid solution may be made relativ~ly strong, 19 1 and, after sa~urating or impregnating the porous area, the excess may be allo~ed 0 1 to drain off. ;The amount of boron added may be determined by a simple weighing 21 1 of the body before and after impregnation or dispersion of the sintering aid 22 ¦ and calculating from the added weight.
23 ¦ The present invention also contemplates the usc of a combination of 24 ¦ sintering aid and a source of excess carbon in li~uid form. Suitably, the sin-¦ tering aid may be dissolved in the excess carbon source material, or both the 26 ,I sintering aid and the excess carbon source material may be dissolved in a 27 common solvent. ~xcess or combinable carbon in amounts bctween about 0.05 and 28 about 5.0 percen-t of the ceramic material are useful to facilitate sintering, and, within this range, amounts of from about 1.0 to about ~.0 percent by weig'ht are espccially uscful. The carbon source may be any carbonaceous material in _~_ .'' : ~ , .
1 ~1 3~
¦wllicll l,hc Silll.(!l'ill~l iai(l :is mis(:il)lo, wil,llnlll. nll a~lvel.~o 1-(';l~'l iOII, or wili(d~
C ¦misc.il)le .in n co1~1()r' solvel1t, wil,11 l,ho sinl,erln(J i)id. Su(lars, .su(:l1 ,3s Sll('rOS(' 3 Ian(l (I(~xl.ros(~, C()~'17 syr~l), rtlr.t'ury*alco~ ~, I.clrill)y(lror~lrl~lryJ
¦alcohl)l, p11enn:L;i(, resins, poly1l11eny:1e11c~ros1lls, an(l furai1 re,sin,s are 1,ypi(,i1J
¦use.rul carbon source m;1~erials. Usually, L11e chiar or carb()n v1.lue of carbon 6 ¦sourco mat,erlals ran~ses rro1n about lS to al)out (I() percent l)y weiql11,. lhe a1)1)ro--¦priate amoun~.s of s:interin(J aid and carbon soulce a;ater.ial 111ily Lhus l)e easily ¦calculated. It is postll1ate~ that the presenL sinl.eril1~J aid.un~1ertJoos reduc-9 ¦tion dur:i1l~ sinLer:i11(J. The amounl Or carbo11 sourco mill,erii1l 1nay bo ild,jusled l,o ¦ provi(:le both the amol1nt of carbon re~luire(l for sucll roducLion nn(l lho iam()l'nt of 11 1 exeess earbon re(111ir()(1 for sinterinU~
12 1 . . ., 3 ¦ DE'I'AILEI) DESCRIPTION Oli 'i'llE INV[~NTlON
Tl1e li~luid sinterincJ aid of the l)resenL invention may be p~epare(l by ¦ simply ~issolvin(~ 113[303, B203, or mixtmres l,h~re()r~ in an ia11pro1lrii1te solvent,.
lG l It will he un(lerstoocd 1,1lal, llle for1~ la d!~s.i~nal,iolls 1~13[303 an(l '323~ bor:ic a(,;(l : 17 ¦ and boron o~icle, shall he read to be inelusive of hy(lrlt,es of 113B03 and B203;
8 1 The solvent nlay be any liqui(l in whieh ~]3B03.,or B203 are soluhle, suitabl.y !.he 9 , ¦solvenl is water or aleo1lol. ~The sinter~n~ aiLI Or lhe pr~se1ll invenl,ion is ¦ad~iecl to a porous body to provide fro1n about 0.3 to ahoul, 5.0 percent an(.1, pre-~ 21 ¦ ferably, withln that ran(Je~ Irom abou.t 0.5 to abollt 1.0 [-ercent, by weitJht, boron ; 22 ¦to the body. Tl1e stren~Jlh of the solul;o1l of sinterin(J aid is ar1justed l,o faci-3 ¦liLate a substantially unifor1n dispers:io1l Or a boron source throu~l1ollt tlle body.
¦ The sinlerin~ aid of the present invention may be d.issolved in a ¦ source oL earbon to provide a li(luid eo~nb.ination of sint,erin(J aid an(l carbon 26 1 source malerial. Suitable sourees Or earbon useLul in this mode are those in whiel1 the sinter:in~ al(l is solubl.(. Especially suiled are aleoho1s such as 28 1 furruryl aleohol and t.etrahydrofl1rfury,l alcohol. Excess or comb:inable carbon , ~ 29 ¦ is utilized in the ran(3e of from about 0.05 to about, 5.0 percenl, by wei(JIlt, an(l, :~ 30 ~ preIerably, from aDoul l.0 to ab~ut ~.0 percenl by weivht Or ll1e porous bo(ly to ~ . I . -5-I
~ - , , I
::
o ~ ri~ ur~ y, ~,;lrl)()n;~ ; yi( ~ t l~er) ;~ IJ~
2 an(l abollt ~0 percent by weiuht fre(3 or cornbinnl)le c;lll)on ul)~)n dcs~ruc~ion by~
heating. ln this mode of the inven~ion, an apl-)ror)riate arnount Or sintering aicl 4 is dissolvo(l, suitilhly by mixinU, in an al~proprillo amollrl~ nr call)on sollrco material to provide excess carbon witllin tlle desired ranye, G The sintering aid of the present invention and the carbon source 7 ¦ material may be dissolved in a mutual solvent to Lorm a combina~ion liquid sin-tering aid and carbon source material. In this mo~e, water is aptly suited to ? I use as the mutual solvent. Examples of water-soluble carhon source materials o that may be employed are sugar, such as sucrose and dextrose, corn syrup, and alcohol, such as Lurfuryl alcohol. Alcollols may also be used as the mutual 2 solvent. Ethyl, methyl, propyl, and isopropyl alcohols are eminently use~ul.
3 11 ~'henol-ormaldehyde resins are particularly adapted to use as ~he carbon source ?4 . ¦¦ material when short chain alcohol is used as the common sqlvent. The sinterin(J
S ~aid and carbon source ma-terial are dissolved, suitably by mixing, in the common 6 jsolvent to provide a combina-tion iiquid sinterin0 aid and carbon source materia~
7 In carrying out the method of the present invenlion, the liquid sin-8 tering aid or combination liquid sintering aid and carbon source material are 9 dispersed in a baked green body, and subsequently the body is sintered to pro-duce a dense, hard ceramic srtiGle.
21 The process used to form or shape the green body is not cri~ical to 2 the present invention. Generally, in such processes, the particulale ceramic 3 starting material is initially mixed wi-th a resin binder ma~terial and other 4 appro~ te additives, for example, mold release agents, lubrican~s, viscosi~y 2s aids, and excess carbon sources. The mix-ture is then molde~ or shaped by kno~n G art processes such as col~ pressing, isostatic-formin(J, slip casting, tape27 castin~, injeetion or transfer molding. The shaped green body is baked, usually 28 at temperatures between about 500 C. and about 1000 C., ancl, more commonly, 29 between about 700 C. and about 900 C. The result of the baking step is a product having an open pore structure which is particularly adapted to be : ~: ,, . ; ~ ; : , l ~a~3~
2 l troated with thc~ liqlli(l sinterin~l aid or combin.lLion sin~trin(J ai(l an(l carbor 3 1 source material of the prcsent invention. 'rhe sintcrin(J ai(l or combination sintering aid and carbon source mater`ial may bc dispcrsctl subs~.lntially uni-l formly throu~hout the baked body by impregnatincJ the body, by applyin~y pressure, S ¦ or capillary action of the pores. The preferred method, ho~ever, is by vacuum 6 ¦ fillin~. In such method, a vacuum is drawn on the body, an(l the li(~uid sin-7 ¦ terin(~ aid or combination liquid sinterillg aid and carbon source material, is 8 I fed into the evacuated body. After dis~ersion of the sinterin(J aid, or combina-tion sintering aid and carbon source material, the iml)r~'~nated body is sintere~
lo ¦ at temperatures b~ltween abou-t 1900 C. and 2200 C. to pro~lce a ~cnsc, hard .
ll ¦ article or body.
2 ¦ It will be appreciated that the invention is not limited to the l4 I specific examples and embodiments of sintering ai~s and sinterincJ me~hods, and that various modifications may be made within the ordinary skill of the art, G without departing frgm the spirit and scope of the invention.
17 . , .
2s . ~ I
.~ . .
: ~: ~ ' .
:' ' ' .Il .
: ~: , '`.
Claims (13)
1. The method of producing a sintered ceramic article which comprises the steps of:
a) forming a shaped green body comprised of a particulate ceramic material and a resin binder;
b) baking said green body at a temperature between about 500°C and about 1000°C to form a porous body;
c) dispersing in said baked green body a liquid sintering aid comprising a solvent and a member selected from the group con-sisting of H3BO3,B2O3, and mixtures thereof through said porous body in sufficient quantity to add between about 0.3 and about 5.0 per-cent by weight boron;
d) sintering said treated body at a temperature between about 1900°C and 2200°C to produce a sintered ceramic article.
a) forming a shaped green body comprised of a particulate ceramic material and a resin binder;
b) baking said green body at a temperature between about 500°C and about 1000°C to form a porous body;
c) dispersing in said baked green body a liquid sintering aid comprising a solvent and a member selected from the group con-sisting of H3BO3,B2O3, and mixtures thereof through said porous body in sufficient quantity to add between about 0.3 and about 5.0 per-cent by weight boron;
d) sintering said treated body at a temperature between about 1900°C and 2200°C to produce a sintered ceramic article.
2. The method of Claim 1 wherein the said ceramic material is silicon carbide.
3. The method of Claim 1 wherein a liquid sintering aid is a solution of H3BO3.
4. The method of Claim 3 wherein a liquid sintering aid is an aqueous solution of H3BO3.
5. The method of Claim 1 wherein the liquid sintering aid is an acqueous solution.
6. The method of Claim 1 wherein the liquid sintering aid is an alcohol solution.
7. The method of Claim 1 wherein the liquid sintering aid includes a source of carbon.
8. The method of Claim 1 wherein the liquid sintering aid is in solution with a source of carbon.
9. The method of Claim 8 wherein the liquid sintering aid includes a source of carbon as a solvent.
10. The method of Claim 8 wherein the solution is aqueous.
11. The method of Claim 8 wherein the solution is alcoholic.
12. The method of Claim 1 wherein the liquid sintering aid is dispersed within said green body by vacuum filling.
13. The method of Claim 1 wherein the liquid sintering aid is dipersed within said green body by capillary action.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US86786178A | 1978-01-09 | 1978-01-09 | |
| US867,861 | 1978-01-09 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1136388A true CA1136388A (en) | 1982-11-30 |
Family
ID=25350613
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000312562A Expired CA1136388A (en) | 1978-01-09 | 1978-10-03 | Method of producing sintered ceramic articles using liquid boron-containing sintering aid |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JPS54101809A (en) |
| CA (1) | CA1136388A (en) |
| DE (1) | DE2900440A1 (en) |
| FR (1) | FR2414030B1 (en) |
| GB (1) | GB2012309B (en) |
Families Citing this family (14)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5585467A (en) * | 1978-12-15 | 1980-06-27 | Hitachi Ltd | Silicon carbide sintered body and its manufacture |
| NL7907160A (en) * | 1979-09-26 | 1981-03-30 | Holec Nv | METHOD FOR MANUFACTURING MOLDED ELECTRICALLY CONDUCTIVE PREPARATIONS FROM SILICONE POWDER, AND FORMING PRODUCTS OBTAINED USING THIS METHOD |
| JPS57160970A (en) * | 1981-03-27 | 1982-10-04 | Omori Mamoru | Silicon carbide sintered formed body and manufacture |
| DE3243570C2 (en) * | 1982-11-25 | 1984-09-13 | Hutschenreuther Ag, 8672 Selb | Process for producing a dense polycrystalline molded body from SiC |
| JPS6011269A (en) * | 1983-06-27 | 1985-01-21 | 松下電器産業株式会社 | Manufacture of nitride, carbide ceramic |
| IT1215202B (en) * | 1986-12-03 | 1990-01-31 | G E V I P I A G | SEALING BODY IN HARD MATERIAL SINTERED BY A SEMI-FINISHED FORMED WITH AN ORGANIC BINDER |
| CN100564316C (en) * | 2004-04-21 | 2009-12-02 | 陶氏环球技术公司 | Strengthen porous ceramic bodies intensity method and by its ceramic body that forms |
| US20110027559A1 (en) | 2009-07-31 | 2011-02-03 | Glen Harold Kirby | Water based environmental barrier coatings for high temperature ceramic components |
| US9005717B2 (en) | 2009-07-31 | 2015-04-14 | General Electric Company | Methods for making environmental barrier coatings using sintering aids |
| US9062564B2 (en) | 2009-07-31 | 2015-06-23 | General Electric Company | Solvent based slurry compositions for making environmental barrier coatings and environmental barrier coatings comprising the same |
| US9005716B2 (en) | 2009-07-31 | 2015-04-14 | General Electric Company | Method for making solvent based environmental barrier coatings using sintering aids |
| US9023435B2 (en) * | 2009-07-31 | 2015-05-05 | General Electric Company | Methods for making water based environmental barrier coatings using sintering aids |
| US8999457B2 (en) | 2009-07-31 | 2015-04-07 | General Electric Company | Methods for making environmental barrier coatings using sintering aids |
| EA037685B1 (en) * | 2017-11-24 | 2021-05-04 | Акционерное Общество "Наука И Инновации" | Method for processing porous metal-based implants |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2938807A (en) * | 1957-08-13 | 1960-05-31 | James C Andersen | Method of making refractory bodies |
| GB1175887A (en) * | 1967-05-31 | 1970-01-01 | Gen Electric & English Elect | Improvements in or relating to the Manufacture of Articles of High Density Polycrystalline Refractory Oxide Material |
| GB1478898A (en) * | 1973-10-24 | 1977-07-06 | Gen Electric | Silicon carbide ceramic |
| JPS543682B2 (en) * | 1974-08-29 | 1979-02-26 | ||
| US4312954A (en) * | 1975-06-05 | 1982-01-26 | Kennecott Corporation | Sintered silicon carbide ceramic body |
-
1978
- 1978-10-03 CA CA000312562A patent/CA1136388A/en not_active Expired
-
1979
- 1979-01-08 GB GB7900548A patent/GB2012309B/en not_active Expired
- 1979-01-08 FR FR7900304A patent/FR2414030B1/en not_active Expired
- 1979-01-08 JP JP14279A patent/JPS54101809A/en active Granted
- 1979-01-08 DE DE19792900440 patent/DE2900440A1/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| FR2414030B1 (en) | 1985-08-09 |
| GB2012309B (en) | 1982-12-08 |
| JPS6350310B2 (en) | 1988-10-07 |
| DE2900440C2 (en) | 1987-06-25 |
| DE2900440A1 (en) | 1979-07-19 |
| JPS54101809A (en) | 1979-08-10 |
| FR2414030A1 (en) | 1979-08-03 |
| GB2012309A (en) | 1979-07-25 |
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