CA1125316A - Sinterable powders and methods of producing sintered ceramic products using such powders - Google Patents
Sinterable powders and methods of producing sintered ceramic products using such powdersInfo
- Publication number
- CA1125316A CA1125316A CA312,663A CA312663A CA1125316A CA 1125316 A CA1125316 A CA 1125316A CA 312663 A CA312663 A CA 312663A CA 1125316 A CA1125316 A CA 1125316A
- Authority
- CA
- Canada
- Prior art keywords
- carbon source
- sintering aid
- powder
- powders
- source material
- 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.)
- Expired
Links
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
- C04B35/645—Pressure sintering
-
- 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
Abstract
ABSTRACT
Sinterable powders of ceramic material, suitably silicon carbide, and methods of producing sintered articles from the powders are described. The particulate ceramic material which comprises the powders has a substantially uniform coating of the residue of a liquid sintering aid (source of boron) selected from solutions of H3BO3, B2O3, or mixtures thereof. The powders also include a carbon source material. Preferably, the particulate material is sub-stantially uniformly c???ed with a combination residue from liquid sintering aid and liquid carbon source material. The resulting powders may be shaped into articles and sintered to produce hard, dense articles.
Sinterable powders of ceramic material, suitably silicon carbide, and methods of producing sintered articles from the powders are described. The particulate ceramic material which comprises the powders has a substantially uniform coating of the residue of a liquid sintering aid (source of boron) selected from solutions of H3BO3, B2O3, or mixtures thereof. The powders also include a carbon source material. Preferably, the particulate material is sub-stantially uniformly c???ed with a combination residue from liquid sintering aid and liquid carbon source material. The resulting powders may be shaped into articles and sintered to produce hard, dense articles.
Description
~5~6 N3-16 Canaaa SINTERABLE POWDERS AND METHODS OF PRODUCING SINTERED
CERAMIC PRODUCTS USING SUCH POWDERS
BACRGROUND OF THE INVENTION
The present invention relates to the use of liquid sintering aids in processes involving sintering of particulate eeramic materials to produce dense, hard articles having industrial uses. Although the present invention will be specifically discussed in regard to powder compositions containing silicon carbide as the ceramic material, it will be understood that other sinterable carbides, for example, titanium carbide, may be utilized as the ceramic material.
Silicon carbide has long been known for its hard ness, strength, and excellent resistance to oxidation and corrosion. Silicon carbide has a low coefficient of expansion, good heat transfer properties, and maintains high strength at elevated temperatures. In recent years, the art of producing high-density silicon carbide materials by sintering silicon carbide powders has been developed.
High-density silicon carbide materials find utility in the fabrication of components for turbines, heat exchange units, pumps, and other equipment or tools that are exposed to severe corrosion or wear, especially in operations carried out at high temperatures.
Ceramic bodies or eompacts may be formed or shaped from particulate ceramic materials by various casting or molding processes. Forming or shaping processes known in the art such as hot or cold pressing, isostatic .~
forming, slip casting, extrusion, injection or transfer molding or tape casting, may be utilized. The shaped ceramic body is subsequently sintered, between about 1900C. and 2200C., to form a dense, hard article.
In order to obtain high-density and high-strength silicon carbide ceramic materials, various additives have been utilized as sintering or densification aids.
For example, a method of hot pressing silicon carbide to densities in order of 98 percent of theoretical by the addition of aluminum and iron as densification aids is disclosed by Alliegro, et al, J. Ceram. Soc., Vol. 39, No. 11, Nov., 1956, pages 386 to 389. They found that a dense silicon carbide could be produced from a powder mixture containing 1 percent by weight of aluminum.
lheir product had a modulus of rupture of 54,000 psi at room temperature and 70,000 psi at 1371~C. More recently, the use of boron or beryllium as sintering or densification aids has been developed. Such aids are usually added to the ceramic material powder in amounts ranging between about 0.3 and about 5.0 percent by weight of boron or beryllium. The sintering aid may be in the form of elemental boron or beryllium or in the form of boron- or beryllium-containing compounds. Boron is the preferred additive for reasons of handling and per-formance. Boron is commonly utilized in the form of boron carbide. Examples of boron-containing silicon carbide powders may be found in US Patents 3,852,099;
3,954,483; and 3,968,194.
Sinterable ceramic powders also contain excess or uncombined carbon. Excess carbon in amounts of from about 1.0 to about 4.0 percent by weight are commonly
CERAMIC PRODUCTS USING SUCH POWDERS
BACRGROUND OF THE INVENTION
The present invention relates to the use of liquid sintering aids in processes involving sintering of particulate eeramic materials to produce dense, hard articles having industrial uses. Although the present invention will be specifically discussed in regard to powder compositions containing silicon carbide as the ceramic material, it will be understood that other sinterable carbides, for example, titanium carbide, may be utilized as the ceramic material.
Silicon carbide has long been known for its hard ness, strength, and excellent resistance to oxidation and corrosion. Silicon carbide has a low coefficient of expansion, good heat transfer properties, and maintains high strength at elevated temperatures. In recent years, the art of producing high-density silicon carbide materials by sintering silicon carbide powders has been developed.
High-density silicon carbide materials find utility in the fabrication of components for turbines, heat exchange units, pumps, and other equipment or tools that are exposed to severe corrosion or wear, especially in operations carried out at high temperatures.
Ceramic bodies or eompacts may be formed or shaped from particulate ceramic materials by various casting or molding processes. Forming or shaping processes known in the art such as hot or cold pressing, isostatic .~
forming, slip casting, extrusion, injection or transfer molding or tape casting, may be utilized. The shaped ceramic body is subsequently sintered, between about 1900C. and 2200C., to form a dense, hard article.
In order to obtain high-density and high-strength silicon carbide ceramic materials, various additives have been utilized as sintering or densification aids.
For example, a method of hot pressing silicon carbide to densities in order of 98 percent of theoretical by the addition of aluminum and iron as densification aids is disclosed by Alliegro, et al, J. Ceram. Soc., Vol. 39, No. 11, Nov., 1956, pages 386 to 389. They found that a dense silicon carbide could be produced from a powder mixture containing 1 percent by weight of aluminum.
lheir product had a modulus of rupture of 54,000 psi at room temperature and 70,000 psi at 1371~C. More recently, the use of boron or beryllium as sintering or densification aids has been developed. Such aids are usually added to the ceramic material powder in amounts ranging between about 0.3 and about 5.0 percent by weight of boron or beryllium. The sintering aid may be in the form of elemental boron or beryllium or in the form of boron- or beryllium-containing compounds. Boron is the preferred additive for reasons of handling and per-formance. Boron is commonly utilized in the form of boron carbide. Examples of boron-containing silicon carbide powders may be found in US Patents 3,852,099;
3,954,483; and 3,968,194.
Sinterable ceramic powders also contain excess or uncombined carbon. Excess carbon in amounts of from about 1.0 to about 4.0 percent by weight are commonly
- 2 -5~
used. The excess carbon required for sintering may be in the form of carbon remaining in the article from a previous processing step or may be added in the form of a carbon source material which would yield the desired amount of excess carbon after the article is sintered.
Excess carbon facilitates sintering and is beneficial in reducing the amounts of various oxide impurities in the starting ceramic material that otherwise would remain in the finished product.
At the present time, the ceramic material and the sintering aid, both in finely divided form, are mixed, usually by milling, over a period of from several hours to several days. Even with prolonged mixing, it is difficult to obtain a mixture having a uniform distribution of sintering aid.
GENERAL DESCRIPTION OF THE INVENTION
In accord with the present invention, the sintering aid utilized to densify ceramic materials is employed in liquid form. The boron source, or sintering aid, of the present invention is selected from solutions of H3BO3, B203, or mixtures thereof. Although the solvent may be any liquid in which H3BO3 or B203 are soluble, water or alcohols such as ethyl, methyl, propyl, or butyl, are preferred because of their availability and relatively low cost.
The liquid sintering aid is mixed with the initial powder form of the ceramic material by any suitable means, ~- 3 -5~
such as slurrying, milling, or simple mixing. In one mode of the invention, the sintering aid and the source of excess carbon are added together in liquid form. In such mode, the sintering aid may be dissolved in the excess carbon source, or the sintering aid and the excess carbon source may be dissolved in a common solvent, for example, water or alcohol.
The ceramic starting material is initially prepared in finely dlvided or powder form. Preferably, the particles have an average size of from about 0.10 to about 2.00 microns, with a maximum of about 5.00 microns.
Although size is a critical parameter, surface area is also of relevant consideration in determining the suitable material. Accordingly, the particles preferably have a surface area of frbm about 1 to about 100 m2/g. Within this range, it is more preferred that the surface area of particles range between about 5 and about 20 m2/g.
Silicon carbide is a preferred ceramic starting material. The silicon carbide may be alpha or beta phase or may be amorphous. At the present time, the alpha (non-cubic) crystalline phase of silicon carbide is most economically obtained. The present compositions may contain substantially entirely, e.g.~ 95 percent or more by weight, silicon carbide o the alpha phase, or may contain mixtures of the various forms of silicon carbide.
For example, mixtures which are predominantly alpha phase (greater than 50 percent) are aptly suited to use. The ceramic material may contain minor amounts of impurities without deleterious effect. Generally, a purity of at least about 95 percent is required and a higher purity desired.
~. "~, The sintering aid of the present invention is added to the ceramic material in amounts which will provide from about 0.3 to about 5.0 percent by weight of boron, based upon the weight of the ceramic material, and, within that range, from about 0.5 to about 4.0 percent is aptly suited to use. When the amounts of boron below about 0.3 percent by weight are used, sintering is generally not effectively carried out. When amounts of boron above about 5.0 percent by weight are included, densification is no-t noticeably improved and may be adversely affected by excessive amounts of boron. The strength of the present solutions is adjusted to provide a boron source substantially uniformly dispersed through-out the particulate material so that during subsequent sintering will yield boron within the foregoing ranges.
The solution is mixed with the particulate material, suitably by simple mixing or by milling, to substankially coat the individual particles. Subsequent removal of the solvent, suitably by drying, leaves the particles with a residue of the liquid sintering aid. The amount of boron added may be determined by a simple weighing of the particulate ceramic material before and after treat-ment with the liquid sintaring aid and calculating the amount of boron from the added weight.
The present invention also contemplates the use of a combination of sintering aid and a source of excess carbon in liquid form. Suitably, the sintering aid may be dissolved in the excess carbon source material, or both the sintering aid and the excess carbon source ~`
material may be dissolved in a common solvent. Excess or combinable carbon in amounts between about 0.05 and .
5.0 percent of the ceramic material are useful to facilitate sintering, and, within this range, amounts of from about l.0 to about 4.0 percent by weight are especially useful. The carbon source may be any carbon-aceous material in which the sintering aid is miscible, without an adverse reaction, or which is miscible in a common solvent with the sintering aid. Sugars, such as sucrose and dextrose, corn syrup, furfural, furfuryl alcohol, tetrahydrofurfuryl alcohol, phenolic resins, polyphenylene resins, and furan resins are typical useful carbon source materials. Usually, the char or carbon value of carbon source materials ranges from about 15 to about 80 percent by weight.
It is postulated that the following reactions occur during the sintering operation that have an effect on the amount of carbon source material utilized with the present sintering aid:
4 H3BO3 ~ 2 B2O3 + 6 H2O
23 C ~ B4C ~ 6 CO
Thus it will be appreciated that some additional carbon will be required for the reduction of the present sintering aids during the sintering operation. U.S. patent 3/379,647 issued to P. A. Smudski describes the production of boron carbide from sugar and H3BO3.
In accord with the present invention, a liquid sinter-ing aid, or a combination liquid sintering aid and carbon source material, is mixed with a particulate ceramic starting material to form a coated powder. Various other additives, for example, mold release agents, lubricants, viscosity aids, and, if required, additional carbon, may be simultaneously or sequentially mixed with the particu-late ceramic material. The mixture, in the form of ~ri ~ 6 -either a wet or dry powder, is then shaped into the desired artic]e shape by any suitable method, for example, cold pressing, molding, or casting, to form a green body. The green body is then sintered at tempera-tures between about 1900C. and 2200C. to produce a hard, dense article. ~lternatively, the powder mixture may be hot pressed, i.e~, sintered under high pressure to form a final, dense product.
DETAILED DESCRIPTION OF THE INVENTION
The liquid sintering aid of the present invention may be prepared by simply dissolving H3BO3, B2O3, or mixtures thereof, in an appropriate solvent. It will be under-stood that the formula designation H3BO3 and B2O3 shall be interpreted to be inclusive of hydrates of H3BO3 and B2O3. The solvent may be any liquid in which H3BO3 or B2O3 are soluble; suitably the solvent is water or alcohol. The sintering aid may be dissolved in a carbon source material, for example, furfuryl alcohol, to yield a combination liquid sintering aid and caxbon source.
The sintering aid and the carbon source may be dissolved in a common solvent, for example, a solution of sintering aid and sugar in water or a solution of sintering aid and phenolic resin in alcohol, to provide a combination liquid sintering aid and carbon source.
The sintering aid is added to the ceramic material in amounts that will provide from about 0. 3 to about 5.0 percent by weight boron, and, preferably, within that range, from about 0.5 to about 4.0 percent. The strength of the H3BO3 or B2O3 solution is adjusted to be dilute enough that there is sufficient solution to coat the particulate ceramic material.
The sinterable powders of the present invention are produced by mixi.ng a particulate ceramic material, for example, silicon carbide, with a liquid sintering aid selected from the group of solutions of H3BO3, B2O3, or mixtures thereof, and a carbon source material. The present invention also contemplates the use of a com-bination liquid sintering aid and excess carbon source material. The solvent from the liquid sintering aid, or liquid combination sintering aid and excess carbon source material, is removed, suitably by spray drying, leaving a particulate ceramic material coated with a residue from the sintering aid solution, or from the combination sintering aid carbon source solution.
The sinterable powders of the present invention may be in the form of particulate mixtures of ceramic materials and excess carbon source material coated with residue from the liquid sintering aids, or, preferably, such powders may be in the form of particulate ceramic material coated with residue from a combination liquid sintering aid and excess carbon source material.
The present sinterable powders are suited to use in hot pressing processes wherein the powder is molded and sintered at temperatures between about 1900C. and about 2200C. at pressures between about 1,000 psi and about 10,000 psi to form a hard, dense article.
The present sinterable powders are suited to use as a component of moldable mixtures which may be cold pressed or mixtures which include a binder material which -~I
~ 8 -facilitates warm compression molding, for example, a thermoplastic resin, and may include release agents, lubricants, and viscosity aids. The mixture is formed into a green body having the shape of an article, by known processes, for example, by molding or casting.
If desired, the green body may be baked, prior to sintering. Baking temperatures usually range between about 500C. and 1000C. The formed article is subsequently sintered, by known sintering techniques, at temperatures between about 1900C. and 2200C. to produce a hard, dense article. Densities above about 85 percent of theoretical are eminently useful and densities above about 90 percent of theoretical are desirable and obtainable.
EXAMPLE
100 g of particulate silicon carbide having an average size ranging from about 0.10 to about 2.00 microns and a surface area ranging between about 5 and about 20 m2/g was mixed with a solution of methyl alcohol containing about Z.3 g H3BO3 and about 7.6 g of a phenol-formaldehyde resin (having a char yield of about 50 percent). The H3BO3 component was calculated to yield about 0.51 percent by weight boron based upon the weight of the silicon carbide as a subsequent sintering aid. The phenol-formaldehyde resin component was calculated to yield sufficient carbon for the reduction o the H3BO3 component and provide an excess of about 3 percent by weight of the silicon carbide. The components were mixed by ball milling for one hour. The slurry was partially dried by mixing in a Hobart mixer to ~r .~ _ 9 _ evaporate the alcohol. The mix was then removed from the mixer and pan dried in open air. The resulting dried lumps were crushed and passed through a 35 USS mesh screen to produce a coated powcler having a residue of the solution substantially uniformly distributed on the particles.
The coated powder was then formed into the shape of an article by warm compression molding utilizing a pressure of about 4,000 psi. The molded article was sintered at 2150C. in an inert atmosphere. The hard, dense, sintered article was found to have a density of 94 percent o~ theoretical.
It will be appreciated that the present invention is not limited to the specific examples of sinterable powders and sintering methods, and that various modifi-cations may be made by one of ordinary skill in the art, without departing from the spirit and scope of the invention.
used. The excess carbon required for sintering may be in the form of carbon remaining in the article from a previous processing step or may be added in the form of a carbon source material which would yield the desired amount of excess carbon after the article is sintered.
Excess carbon facilitates sintering and is beneficial in reducing the amounts of various oxide impurities in the starting ceramic material that otherwise would remain in the finished product.
At the present time, the ceramic material and the sintering aid, both in finely divided form, are mixed, usually by milling, over a period of from several hours to several days. Even with prolonged mixing, it is difficult to obtain a mixture having a uniform distribution of sintering aid.
GENERAL DESCRIPTION OF THE INVENTION
In accord with the present invention, the sintering aid utilized to densify ceramic materials is employed in liquid form. The boron source, or sintering aid, of the present invention is selected from solutions of H3BO3, B203, or mixtures thereof. Although the solvent may be any liquid in which H3BO3 or B203 are soluble, water or alcohols such as ethyl, methyl, propyl, or butyl, are preferred because of their availability and relatively low cost.
The liquid sintering aid is mixed with the initial powder form of the ceramic material by any suitable means, ~- 3 -5~
such as slurrying, milling, or simple mixing. In one mode of the invention, the sintering aid and the source of excess carbon are added together in liquid form. In such mode, the sintering aid may be dissolved in the excess carbon source, or the sintering aid and the excess carbon source may be dissolved in a common solvent, for example, water or alcohol.
The ceramic starting material is initially prepared in finely dlvided or powder form. Preferably, the particles have an average size of from about 0.10 to about 2.00 microns, with a maximum of about 5.00 microns.
Although size is a critical parameter, surface area is also of relevant consideration in determining the suitable material. Accordingly, the particles preferably have a surface area of frbm about 1 to about 100 m2/g. Within this range, it is more preferred that the surface area of particles range between about 5 and about 20 m2/g.
Silicon carbide is a preferred ceramic starting material. The silicon carbide may be alpha or beta phase or may be amorphous. At the present time, the alpha (non-cubic) crystalline phase of silicon carbide is most economically obtained. The present compositions may contain substantially entirely, e.g.~ 95 percent or more by weight, silicon carbide o the alpha phase, or may contain mixtures of the various forms of silicon carbide.
For example, mixtures which are predominantly alpha phase (greater than 50 percent) are aptly suited to use. The ceramic material may contain minor amounts of impurities without deleterious effect. Generally, a purity of at least about 95 percent is required and a higher purity desired.
~. "~, The sintering aid of the present invention is added to the ceramic material in amounts which will provide from about 0.3 to about 5.0 percent by weight of boron, based upon the weight of the ceramic material, and, within that range, from about 0.5 to about 4.0 percent is aptly suited to use. When the amounts of boron below about 0.3 percent by weight are used, sintering is generally not effectively carried out. When amounts of boron above about 5.0 percent by weight are included, densification is no-t noticeably improved and may be adversely affected by excessive amounts of boron. The strength of the present solutions is adjusted to provide a boron source substantially uniformly dispersed through-out the particulate material so that during subsequent sintering will yield boron within the foregoing ranges.
The solution is mixed with the particulate material, suitably by simple mixing or by milling, to substankially coat the individual particles. Subsequent removal of the solvent, suitably by drying, leaves the particles with a residue of the liquid sintering aid. The amount of boron added may be determined by a simple weighing of the particulate ceramic material before and after treat-ment with the liquid sintaring aid and calculating the amount of boron from the added weight.
The present invention also contemplates the use of a combination of sintering aid and a source of excess carbon in liquid form. Suitably, the sintering aid may be dissolved in the excess carbon source material, or both the sintering aid and the excess carbon source ~`
material may be dissolved in a common solvent. Excess or combinable carbon in amounts between about 0.05 and .
5.0 percent of the ceramic material are useful to facilitate sintering, and, within this range, amounts of from about l.0 to about 4.0 percent by weight are especially useful. The carbon source may be any carbon-aceous material in which the sintering aid is miscible, without an adverse reaction, or which is miscible in a common solvent with the sintering aid. Sugars, such as sucrose and dextrose, corn syrup, furfural, furfuryl alcohol, tetrahydrofurfuryl alcohol, phenolic resins, polyphenylene resins, and furan resins are typical useful carbon source materials. Usually, the char or carbon value of carbon source materials ranges from about 15 to about 80 percent by weight.
It is postulated that the following reactions occur during the sintering operation that have an effect on the amount of carbon source material utilized with the present sintering aid:
4 H3BO3 ~ 2 B2O3 + 6 H2O
23 C ~ B4C ~ 6 CO
Thus it will be appreciated that some additional carbon will be required for the reduction of the present sintering aids during the sintering operation. U.S. patent 3/379,647 issued to P. A. Smudski describes the production of boron carbide from sugar and H3BO3.
In accord with the present invention, a liquid sinter-ing aid, or a combination liquid sintering aid and carbon source material, is mixed with a particulate ceramic starting material to form a coated powder. Various other additives, for example, mold release agents, lubricants, viscosity aids, and, if required, additional carbon, may be simultaneously or sequentially mixed with the particu-late ceramic material. The mixture, in the form of ~ri ~ 6 -either a wet or dry powder, is then shaped into the desired artic]e shape by any suitable method, for example, cold pressing, molding, or casting, to form a green body. The green body is then sintered at tempera-tures between about 1900C. and 2200C. to produce a hard, dense article. ~lternatively, the powder mixture may be hot pressed, i.e~, sintered under high pressure to form a final, dense product.
DETAILED DESCRIPTION OF THE INVENTION
The liquid sintering aid of the present invention may be prepared by simply dissolving H3BO3, B2O3, or mixtures thereof, in an appropriate solvent. It will be under-stood that the formula designation H3BO3 and B2O3 shall be interpreted to be inclusive of hydrates of H3BO3 and B2O3. The solvent may be any liquid in which H3BO3 or B2O3 are soluble; suitably the solvent is water or alcohol. The sintering aid may be dissolved in a carbon source material, for example, furfuryl alcohol, to yield a combination liquid sintering aid and caxbon source.
The sintering aid and the carbon source may be dissolved in a common solvent, for example, a solution of sintering aid and sugar in water or a solution of sintering aid and phenolic resin in alcohol, to provide a combination liquid sintering aid and carbon source.
The sintering aid is added to the ceramic material in amounts that will provide from about 0. 3 to about 5.0 percent by weight boron, and, preferably, within that range, from about 0.5 to about 4.0 percent. The strength of the H3BO3 or B2O3 solution is adjusted to be dilute enough that there is sufficient solution to coat the particulate ceramic material.
The sinterable powders of the present invention are produced by mixi.ng a particulate ceramic material, for example, silicon carbide, with a liquid sintering aid selected from the group of solutions of H3BO3, B2O3, or mixtures thereof, and a carbon source material. The present invention also contemplates the use of a com-bination liquid sintering aid and excess carbon source material. The solvent from the liquid sintering aid, or liquid combination sintering aid and excess carbon source material, is removed, suitably by spray drying, leaving a particulate ceramic material coated with a residue from the sintering aid solution, or from the combination sintering aid carbon source solution.
The sinterable powders of the present invention may be in the form of particulate mixtures of ceramic materials and excess carbon source material coated with residue from the liquid sintering aids, or, preferably, such powders may be in the form of particulate ceramic material coated with residue from a combination liquid sintering aid and excess carbon source material.
The present sinterable powders are suited to use in hot pressing processes wherein the powder is molded and sintered at temperatures between about 1900C. and about 2200C. at pressures between about 1,000 psi and about 10,000 psi to form a hard, dense article.
The present sinterable powders are suited to use as a component of moldable mixtures which may be cold pressed or mixtures which include a binder material which -~I
~ 8 -facilitates warm compression molding, for example, a thermoplastic resin, and may include release agents, lubricants, and viscosity aids. The mixture is formed into a green body having the shape of an article, by known processes, for example, by molding or casting.
If desired, the green body may be baked, prior to sintering. Baking temperatures usually range between about 500C. and 1000C. The formed article is subsequently sintered, by known sintering techniques, at temperatures between about 1900C. and 2200C. to produce a hard, dense article. Densities above about 85 percent of theoretical are eminently useful and densities above about 90 percent of theoretical are desirable and obtainable.
EXAMPLE
100 g of particulate silicon carbide having an average size ranging from about 0.10 to about 2.00 microns and a surface area ranging between about 5 and about 20 m2/g was mixed with a solution of methyl alcohol containing about Z.3 g H3BO3 and about 7.6 g of a phenol-formaldehyde resin (having a char yield of about 50 percent). The H3BO3 component was calculated to yield about 0.51 percent by weight boron based upon the weight of the silicon carbide as a subsequent sintering aid. The phenol-formaldehyde resin component was calculated to yield sufficient carbon for the reduction o the H3BO3 component and provide an excess of about 3 percent by weight of the silicon carbide. The components were mixed by ball milling for one hour. The slurry was partially dried by mixing in a Hobart mixer to ~r .~ _ 9 _ evaporate the alcohol. The mix was then removed from the mixer and pan dried in open air. The resulting dried lumps were crushed and passed through a 35 USS mesh screen to produce a coated powcler having a residue of the solution substantially uniformly distributed on the particles.
The coated powder was then formed into the shape of an article by warm compression molding utilizing a pressure of about 4,000 psi. The molded article was sintered at 2150C. in an inert atmosphere. The hard, dense, sintered article was found to have a density of 94 percent o~ theoretical.
It will be appreciated that the present invention is not limited to the specific examples of sinterable powders and sintering methods, and that various modifi-cations may be made by one of ordinary skill in the art, without departing from the spirit and scope of the invention.
Claims (22)
1. A sinterable powder comprising:
a). a particulate ceramic material having an average particle size ranging from about 0.10 to about 2.00 microns and a surface area between about 5 and about 20 m2/g, b). a carbon source material which will provide between about 1.0 and about 4.0 percent by weight of said ceramic material during sintering, and c). a residue from a solution of H3B03, B203, or mixtures thereof, substantially uniformly distributed over the particulate portion of said powder to provide from about 0.3 to about 5.0 percent by weight of boron based on the weight of said ceramic material during sintering.
a). a particulate ceramic material having an average particle size ranging from about 0.10 to about 2.00 microns and a surface area between about 5 and about 20 m2/g, b). a carbon source material which will provide between about 1.0 and about 4.0 percent by weight of said ceramic material during sintering, and c). a residue from a solution of H3B03, B203, or mixtures thereof, substantially uniformly distributed over the particulate portion of said powder to provide from about 0.3 to about 5.0 percent by weight of boron based on the weight of said ceramic material during sintering.
2. The powder of Claim 1 wherein the carbon source material is a residue substantially uniformly distributed over the particulate portion of said powder.
3. The powder of Claim 1 wherein the ceramic material is silicon carbide.
4. The powder of Claim 1 wherein the residue in c). is from a solution of H3B03.
5. The powder of Claim 1 wherein the carbon source material is a phenolic resin.
6. A method of producing a sintered ceramic article which comprises the steps of:
a). forming a powder according to Claim 1 into the shape of an article, and b). sintering the formed shape at a temperature between about 1900°C and about 2200°C to produce a hard, dense sintered article.
a). forming a powder according to Claim 1 into the shape of an article, and b). sintering the formed shape at a temperature between about 1900°C and about 2200°C to produce a hard, dense sintered article.
7. The method of Claim 6 wherein the ceramic material is silicon carbide.
8. The method of Claim 6 wherein the sintering aid is a solution of H3BO3.
9. The method of Claim 8 wherein the solution is an aqueous solution.
10. The method of Claim 8 wherein the solution is an alcohol solution.
11. The method of Claim 6 wherein forming is by cold pressing.
12. The method of Claim 6 wherein forming is by hot pressing.
13. The method of Claim 6 wherein a binder material is included in a). and forming is by means of molding.
14. The method of Claim 6 wherein forming is by casting.
15. The method of Claim 6 wherein the formed article is baked.
16. The method of Claim 6 wherein the carbon source material is liquid.
17. The method of Claim 6 wherein the sintering aid is dissolved in the carbon source material.
18. The method of Claim 6 wherein the sintering aid and the carbon source material are dissolved in a common solvent.
19. The method of Claim 18 wherein the solvent is water.
20. The method of Claim 19 wherein the sintering aid is H3BO3 and the carbon source material is sugar.
21. The method of Claim 18 wherein the solvent is an alcohol.
22. The method of Claim 21 wherein the sintering aid is H3BO3 and the carbon source material is a phenol-formaldehyde resin.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US86786078A | 1978-01-09 | 1978-01-09 | |
| US867,860 | 1986-05-28 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1125316A true CA1125316A (en) | 1982-06-08 |
Family
ID=25350610
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA312,663A Expired CA1125316A (en) | 1978-01-09 | 1978-10-04 | Sinterable powders and methods of producing sintered ceramic products using such powders |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JPS54101813A (en) |
| CA (1) | CA1125316A (en) |
| DE (1) | DE2856593A1 (en) |
| FR (1) | FR2414029B1 (en) |
| GB (1) | GB2011879B (en) |
Families Citing this family (15)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4795673A (en) * | 1978-01-09 | 1989-01-03 | Stemcor Corporation | Composite material of discontinuous silicon carbide particles and continuous silicon matrix and method of producing same |
| FR2462404A1 (en) * | 1979-07-26 | 1981-02-13 | Nippon Crucible Co | Sintered silicon carbide body - formed without sintering aid, prepd. from silicon carbide powder contg. boron component |
| DE2930847C2 (en) * | 1979-07-30 | 1983-04-21 | Nippon Crucible Co., Ltd., Tokyo | Process for making a silicon carbide sintered product |
| JPS57179075A (en) * | 1981-04-30 | 1982-11-04 | Hitachi Ltd | Mixture for electric insulating silicon carbide sintering material and manufacture of sintering material |
| JPS58125667A (en) * | 1982-01-21 | 1983-07-26 | 大森 守 | Composite carborundum sintered shape and its manufacture |
| JPS59224306A (en) * | 1983-05-13 | 1984-12-17 | 日本碍子株式会社 | Manufacture of ceramic part |
| JPS61168568A (en) * | 1985-01-23 | 1986-07-30 | 日産自動車株式会社 | Manufacture of silicon carbide sintered body |
| WO1986005482A1 (en) * | 1985-03-12 | 1986-09-25 | Kitamura Valve Co., Ltd. | Valve having valve body of ceramic compound |
| JP2558688B2 (en) * | 1987-04-15 | 1996-11-27 | 株式会社東芝 | Method for manufacturing silicon carbide sintered body |
| DE3823882A1 (en) * | 1988-07-14 | 1990-01-18 | Feldmuehle Ag | SLOT SUCTION |
| DE3834325A1 (en) * | 1988-10-08 | 1990-04-12 | Bayer Ag | SIC POWDER, METHOD FOR THE PRODUCTION AND THE USE THEREOF AND THE CORRESPONDING SIC SINTER BODY |
| DE3909978A1 (en) * | 1989-03-25 | 1990-09-27 | Hoechst Ag | SINTERABLE CERAMIC POWDER, METHOD FOR THE PRODUCTION THEREOF, SILICON NITRIDE CERAMIC PRODUCED THEREOF, METHOD FOR THE PRODUCTION AND THE USE THEREOF |
| DE19505912C1 (en) * | 1995-02-21 | 1996-08-29 | Forschungszentrum Juelich Gmbh | Process for the production of ceramic, metallic or ceramic-metallic shaped bodies and layers |
| US5925405A (en) * | 1995-02-21 | 1999-07-20 | Ali-Khan; Imran | Method of manufacturing ceramic, metallic or ceramo-metallic, shaped bodies and layers |
| DE19718672C1 (en) * | 1997-05-02 | 1998-09-24 | Zschimmer & Schwarz Gmbh & Co | Use of a sugar |
Family Cites Families (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3379647A (en) * | 1966-05-04 | 1968-04-23 | Carborundum Co | Metal carbide and boride production |
| US3852099A (en) * | 1972-11-27 | 1974-12-03 | Gen Electric | Dense silicon carbide ceramic and method of making same |
| DE2351162C3 (en) * | 1973-10-11 | 1978-05-11 | Annawerk Keramische Betriebe Gmbh, 8633 Roedental | Process for reducing the porosity of molded parts made of reaction-sintered silicon nitride |
| GB1478898A (en) * | 1973-10-24 | 1977-07-06 | Gen Electric | Silicon carbide ceramic |
| US3968194A (en) * | 1974-01-08 | 1976-07-06 | General Electric Company | Dense polycrystalline silicon carbide |
| US3954483A (en) * | 1974-01-08 | 1976-05-04 | General Electric Company | Dense polycrystalline silicon carbide |
| JPS543682B2 (en) * | 1974-08-29 | 1979-02-26 | ||
| US4312954A (en) * | 1975-06-05 | 1982-01-26 | Kennecott Corporation | Sintered silicon carbide ceramic body |
| JPS606908B2 (en) * | 1977-08-04 | 1985-02-21 | 日本坩堝株式会社 | Method for producing active silicon carbide powder containing boron component |
-
1978
- 1978-10-04 CA CA312,663A patent/CA1125316A/en not_active Expired
- 1978-12-29 DE DE19782856593 patent/DE2856593A1/en active Granted
-
1979
- 1979-01-08 FR FR7900360A patent/FR2414029B1/en not_active Expired
- 1979-01-08 JP JP14379A patent/JPS54101813A/en active Granted
- 1979-01-08 GB GB7900549A patent/GB2011879B/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| FR2414029B1 (en) | 1985-08-09 |
| DE2856593C2 (en) | 1987-09-24 |
| JPS54101813A (en) | 1979-08-10 |
| DE2856593A1 (en) | 1979-07-19 |
| GB2011879B (en) | 1982-05-12 |
| GB2011879A (en) | 1979-07-18 |
| JPS6350311B2 (en) | 1988-10-07 |
| FR2414029A1 (en) | 1979-08-03 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CA1125316A (en) | Sinterable powders and methods of producing sintered ceramic products using such powders | |
| US4124667A (en) | Process for producing sintered silicon carbide ceramic body | |
| JP4236285B2 (en) | Process for producing molded articles from ceramic and metal powders | |
| CA1096408A (en) | Method of producing hign density silicon carbide product | |
| JPS6141868B2 (en) | ||
| EP0135839B1 (en) | Method of manufacturing sintered ceramic body | |
| US4063954A (en) | Fluoride-type with heat sink for casting molten reactive and refractory metals | |
| JPS6136167A (en) | Manufacture of injection-molding refractory products and composition | |
| JPS6350310B2 (en) | ||
| CN115894041A (en) | Preparation method of powder extrusion 3D printing molding reaction sintering silicon carbide ceramic | |
| US3442668A (en) | Method of manufacturing ceramics | |
| EP0178753B1 (en) | Process for producing a sintered silicon carbide/carbon composite ceramic body having ultrafine grain microstructure | |
| US5320989A (en) | Boron nitride-containing bodies and method of making the same | |
| JPH04130065A (en) | Method of forming high-density metal boride complex | |
| US3252809A (en) | Dry grinding of ceramics | |
| JPH05194037A (en) | Water extrusion of silicon nitride | |
| CA1125447A (en) | Ceramic cement and method of making composite ceramic articles | |
| Zanghi et al. | Sinterable powders | |
| JPS6253473B2 (en) | ||
| JPS5891065A (en) | Manufacture of silicon carbide ceramic sintered body | |
| Lawler | Boric oxide or boric acid sintering aid for sintering ceramics | |
| JPS61201662A (en) | Manufacture of composite ceramics | |
| JPS61158403A (en) | Method of molding ceramic | |
| JPH0210790B2 (en) | ||
| JPS5860675A (en) | Silicon nitride sintered body and manufacture |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |