JP3251937B2 - Manufacturing method of sintered ceramic compact - Google Patents

Description

The present invention relates to a method for forming a ceramic.

Ceramic materials are very important for many high temperature, high performance applications such as, for example, engine components and gas turbines. These applications require a specific combination of properties such as, for example, high specific strength, retention of mechanical properties at elevated temperatures, low heat and electrical conductivity, hardness and wear resistance, and chemical inertness. However, the inability to produce complex shapes with high dimensional accuracy and sufficient strength using economical manufacturing methods has prevented ceramic materials from fulfilling their potential for these applications.

Several processes have been used to attempt to form ceramic bodies. Such processes include compression molding of a ceramic powder into a green body, followed by sintering or hot pressing, and subsequent molding or machining of the sintered body to produce a finished product. Another method is slip casting, in which the ceramic particles are dispersed in water, the slurry is placed in a mold, and the water is removed to form a green or green body. Compression molding methods have proven inadequate for forming ceramic articles of complex shapes, which must meet certain design specifications. The slip casting process is time consuming and does not form a green body of sufficient strength. In view of the problems associated with the prior art, the use of injection molding methods for molding ceramic articles is increasing. Injection molding is a process of pressing a moldable composition into a mold or die. Injection molding facilitates rapid, repetitive molding of multiple compacts having precise dimensional tolerances. Injection molding minimizes the amount of molding or machining required to produce the finished product.

U.S. Pat.No. 4,906,424 discloses a reaction injection molding process in which an unheated liquid mixture of a binder and ceramic is injected into a heated mold and reacted there. The advantages over the conventional injection molding method of cooling and solidifying are described. U.S. Patent 4,
Although the reaction injection molding method described in 904,424 is an improvement over conventional injection molding of ceramics, this method still requires a binder removal step after removal of the cured molding from the mold.

There remains a need for a reaction injection molding process that eliminates the need to remove the binder in the firing step. Such a method avoids the adverse effect on the high-temperature strength of the sintered ceramic compact in which residual carbon and impurities have been formed.

According to the present invention, a mixture of a liquid binder and ceramic and / or metal powder is poured into a heated mold, the mixture is cured, a compact is produced, and then the compact is sintered to a desired density. (A) using a curable ceramic precursor that is liquid below the curing temperature as a binder; (b) curing the ceramic precursor; and (c) Prior to sintering, the method comprises heating the reinforced compact to a temperature sufficient to convert the cured ceramic precursor to ceramic under a suitable atmosphere.

The method according to the present invention involves the reaction injection molding of ceramic and metal powders to form a tough and strong green body, which is then fired without the time consuming and energy consuming binder removal step. A method for obtaining a sintered product is provided.

Any ceramic powder can be used in the method of the present invention. Silicon nitride, silicon carbide and alumina are preferred. Suitable metal powders include, for example, silicon, aluminum, transition metals. The ceramic and / or metal powder is at least 40% by volume of the mixture, especially at least 50%
It is preferred that The volume percentage varies depending on the density of the filler. Although the physical state of the metal and ceramic is referred to throughout this specification as "powder", it should be understood that the ceramic or metal can also exist in various other forms, such as, for example, fibers, whiskers or small pieces. .

The ceramic precursor used in the method of the present invention is liquid at temperatures below its curing temperature, and has a large amount of ceramic and / or
Alternatively, the metal powder can be dispersed, but the mixture of the ceramic powder and the ceramic precursor still has such a low viscosity that it is fluid. It is preferred that the precursor have a low molecular weight so that the mixture of the powder and the precursor is not swellable, ie, does not increase in viscosity when shearing the material.

Ceramic precursors are monomers or polymers,
For example, polysilazane, polyurea silazane, polythiourea silazane, polycarbosilazane, polysiloxane. These precursors contain alkenyl, alkynyl, epoxy, acrylate or methacrylate substituents,
It is preferred to facilitate curing by free radical or ionic mechanisms. Special examples of ceramic precursors include:
Poly (acryloxypropylmethyl) siloxane, glycidoxypropylmethyldimethylsiloxane copolymer, polyvinylmethylsiloxane, poly (methylvinyl) silazane, 1,3,5-trimethyl-1,3,5-trivinyltrisilazane, 3,5,7-tetravinyltetra-1,3,5,7
-Tetravinyltetrasilazane, 1,3,5,7-tetravinyltetramethylcyclotetrasiloxane, tris (vinyldimethylsiloxy) methylsilane and trivinylmethylsilane.

The ceramic precursor and the ceramic and / or metal powder can be mixed by milling or can be mixed without milling. Processing aids such as, for example, dispersants, rheology modifiers, sintering aids, lubricants can also be added to the mixture.

The ceramic precursor is cured in the mold by methods well known in the art, for example, by heating or by irradiation with ultraviolet, electron beam or gamma radiation. The time required for curing is generally less than 5 minutes, and in some cases less than 1 minute. The time and method required for curing depends on the type of precursor used, but is readily determined by one skilled in the art. When curing by heating, the mixture of ceramic precursor and ceramic and / or metal powders,
Depending on the type of precursor used, a free radical generator, a curing agent or a catalyst can also be included. The green body formed by curing the polysilazane ceramic precursor has unusual toughness and toughness, i.e., the green body does not cause visible damage when thrown against a concrete floor. The flexural strength of the green body is generally greater than 1.0 MPa as measured by the four-point bending method on thin bar samples.

After the ceramic precursor is cured, the compact is removed from the mold and heated in a suitable atmosphere to convert the ceramic precursor to ceramic, and then sufficient to densify the compact in a suitable atmosphere. Heat to temperature. The densified compacts retain their net shape after firing. The term densified is meant to include solid phase sintering, liquid phase sintering, and reaction bonding. The atmosphere selected for each of these steps is the same or a different atmosphere, depending on the type of ceramic preferred in the final product. For example, if a silicon nitride product is desired, to maximize ceramic yield,
Polysilazane is thermally decomposed in an ammonia atmosphere, and is sintered under a nitrogen atmosphere, which is less expensive than ammonia and has a low risk of use. Alternatively, the silicon carbide product is obtained by using a polysilazane ceramic precursor and treating both steps under an argon atmosphere. As another example, the silicon dioxide product is obtained by using a polysilazane ceramic precursor and treating in both steps under an atmosphere of air or oxygen.

The silicon nitride product is obtained by thermally decomposing polysilazane in ammonia from a mixture of silicon metal and a polysilazane ceramic precursor and then nitriding the silicon metal in an atmosphere consisting of a mixture of hydrogen, helium and nitrogen, and compacting the compact. It can also be obtained by

Example 1 Poly (methylvinyl) silazane is prepared as follows.

A 5-neck flask is equipped with an overhead mechanical stirrer, a dry ice / acetone cooler (-78 ° C), an ammonia / nitrogen supply tube and a thermometer. This apparatus was sparged with nitrogen, and hexane (1760 ml, dried on a 4A molecular sieve) and methyldichlorosilane (209 ml, 230.9 g, 2.0
Mol) and vinylmethyldichlorosilane (64 ml, 69.6 g,
0.5 mol). Ammonia is added at a rate of 3.5 / min (9.37 mol) over 1 hour. During the addition, the reaction rate increases from 25 ° C to 69 ° C. After 1 hour, the ammonia flow is stopped and the reaction mixture is cooled to room temperature. The reaction mixture is passed through a glass filter to remove the precipitated ammonium chloride. The hexane was removed from the liquid under reduced pressure (28 mmHg, 60 ° C.) to give a clear oil (150.76 g, 2.34 mol, 9
(CH ₃ SiHNH) _0.8 (CH ₃ SiCH = CH ₂ NH)
_0.2 is obtained. The oil had a viscosity of 43 cps at 25 ° C and 56
It has a molecular weight of 0 g / mol.

80 g of silicon powder, 25 g of poly (methylvinyl) silazane,
A mixture of 0.15 g of dicumyl peroxide and 100 ml of 1,1,1-trichloroethane is mixed in a jacketed resin reactor by means of a stirring blade. The solvent is stripped under reduced pressure by the heat of steam. The blend is injection molded into a steel die using 800 psi (56 kg / cm ² ) pressure on an injection ram. Next, the filled die is heated to 150 ° C. to cure the polysilazane. After removing from the die, even if the molded part is strongly thrown on the concrete floor,
No visible damage occurs. The part is heated in a mixed nitrogen-hydrogen atmosphere at 55 ° C./hour to 1000 ° C. and at 100 ° C./hour to 1350 ° C. to convert the poly (methylvinyl) silazane to silicon nitride and densify the compact. After densification, the net shape of the compact is retained.

Example 2 Vibration mill using 454 g of silicon nitride powder, 23 g of alumina powder, 23 g of yttria powder, 5 g of poly (methylvinyl) silazane prepared as described in Example 1 and 1,1,1-trichloroethane using a silicon nitride grinding medium. Crush in. Strip the solvent from the mixture. A portion (380 g) of the mixture is blended with 145 g of poly (methylvinyl) silazane, 1 g of dicumyl peroxide, 1.0 g of glycerol monooleate and 250 ml of 1,1,1-trichloroethane. Strip solvent and blend at 6 ° C on die with 150 ° C die temperature.
Injection molding using 00 psi (42 kg / cm ² ). The molded part is heated up to 1000 ° C at 55 ° C / hour in a nitrogen atmosphere, then to 100 ° C / hour.
In some cases, heating to 1600 ° C. converts poly (methylvinyl) silazane to silicon nitride and densifies the compact. The net shape of the compact remains after densification.

Example 3 52 g of silicon powder are mixed with 30 g of silicon nitride. To a portion of 78 g of this mixture, 30 g of poly (methylvinyl) silazane prepared as described in Example 1, 0.2 g of dicumyl peroxide,
And 100 ml of 1,1,1-trichloroethane. After stripping the solvent, the blend is injection molded and cured using 800 psi (56 kg / cm ² ) pressure on a ram and a die temperature of 150 ° C. A tough and strong green body is obtained. The molded part is heated under a nitrogen atmosphere to a temperature above 1000 ° C., sufficient to convert the poly (methylvinyl) silazane to a silicon nitride-containing ceramic, thereby densifying the molded body. After densification, the net shape of the compact is retained.

Example 4 A mixture of 50 g of silicon carbide powder, 50 g of poly (methylvinyl) silazane prepared as described in Example 1, 0.4 g of dicumyl peroxide and 100 ml of 1,1,1-trichloroethane is reacted in a jacketed resin reactor. I do. The solvent is stripped, the mixture is injection molded and then cured at 150 ° C. The molded part is heated to 1600 ° C. under an argon atmosphere to convert the poly (methyl vinyl) silazane to silicon carbide. The net shape of the compact is retained.

Example 5 4.5 g of silicon carbide whiskers are mixed with 6.7 g of poly (methylvinyl) silazane prepared as described in Example 1 and 0.05 g of dicumyl peroxide. Injection molding the mixture, 1
Cures at 50 ° C. Molded parts under argon atmosphere
Heat to 1600 ° C. to convert poly (methylvinyl) silazane to silicon carbide. The net shape of the compact is retained.

Example 6 A jar was equipped with a stirring bar, and 1.5 g of silicon nitride powder, 1,
5.0 g of 3,5,7-tetramethyltetravinylcyclotetrasiloxane and 0.01 g of dicumyl peroxide are charged.
After thorough mixing, the reaction mixture is injection molded and then 15
Heat to 170 ° C. for minutes. At 170 ° C., the fluid mixture cures to a solid compact. It is easy to handle after cooling to room temperature. The compact, heated to a temperature above 1000 ° C., is densified enough to convert the cyclosiloxane into a ceramic.

Example 7 A polyureasilazane is prepared as follows.

A 100 ml one-necked flask is equipped with a stir bar and septum and sparged with nitrogen. The flask is then charged with poly (methylvinyl) silazane prepared as described in Example 1 and 0.1% by weight of phenylisocyanate. Stirring the reactor /
Place in the oil path on the hot plate and use a water condenser with a septum at the top instead of a septum. Insert the nitrogen supply needle and oil bubbler outlet into the septum. The reaction mixture
Heat to 110 ° C for 20 minutes. A yellow viscous oil having a viscosity of 1298 cps is obtained.

5.0 g of the polyureasilazane prepared as described above is stirred with 0.05 g of dicumyl peroxide, 15.0 g of silicon nitride powder and 15.0 ml of methylene chloride until a homogeneous mixture is obtained. Strip the solvent under nitrogen. The resulting mixture is injection molded and cured at 150 ° C. to obtain a strong and hard green body. The molded part is heated to a temperature above 1000 ° C., sufficient to convert the polyurea silazane to ceramic, to densify the molded body.

Example 8 A jar equipped with a stir bar, 2.06 g of silicon nitride powder,
1,3,5-trimethyltrivinylcyclotrisilazane and 1,
4.01 g of a mixture of 3,5,7-tetramethyltetravinylcyclotetrasilazane (70:30 molar ratio, prepared by ammonolysis of methylvinyldichlorosilane) and 0.01 g of dicumyl peroxide are charged. The reaction mixture is injection molded and then heated to 185 ° C. for 30 minutes. At 185 ° C., the fluid slurry hardens into a solid compact, which after cooling to room temperature, becomes easier to handle. Sufficient to convert the cyclosilazane to a silicon nitride-containing ceramic,
The molded part is heated under a nitrogen atmosphere to a temperature higher than 1000 ° C. to densify the molded body.

Example 9 50 g of alumina powder, 15.0 g of poly (methylvinyl) silazane prepared as described in Example 1, 0.2 g of dicumyl peroxide and 75 g of 1,1,1-trichloroethane are mixed and the solvent is stripped. The resulting mixture is injection molded and 150
Heat to ° C. The cured molded part is heated in air at 60 ° C./hour up to 1600 ° C. to convert the poly (methylvinyl) silazane to silica and obtain an alumina / silica containing ceramic material.

────────────────────────────────────────────────── ─── Continued on the front page (73) Patent holder 594142403 1300 Marrows Road, New work, Delaware 19714-6077, United States of America (72) Inventor Alexander Lukax the Third Wilmington, Delaware, USA City Marklin Court 5 (56) References JP-A-61-203135 (JP, A) JP-A-1-317169 (JP, A) JP-A-3-52287 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C04B 35/622-35/64

Claims (11)

(57) [Claims] 1. A mixture of a liquid binder and a source of free radicals and a ceramic and / or metal powder is poured into a heated mold, the mixture is cured and a molded body is obtained, and the molded body is then cooled to a desired density. (A) using a radically curable ceramic precursor that is liquid below its curing temperature as a binder; and (b) using the ceramic precursor as a binder. Curing; and prior to sintering, (c) heating the cured compact in a suitable atmosphere to a temperature sufficient to convert the cured ceramic precursor to ceramic. 2. The method of claim 1 wherein the powder is present in an amount of at least 40% by volume. 3. The method according to claim 1, further comprising curing the ceramic precursor by heating. 4. The method according to claim 1, wherein the ceramic powder is silicon nitride. 5. The method according to claim 1, wherein the powder is silicon metal and silicon nitride. 6. The method according to claim 1, wherein the ceramic powder is silicon carbide. 7. The method according to claim 1, wherein the ceramic powder is alumina. 8. The method according to claim 1, wherein the powder is silicon metal, and the atmosphere used in the step (c) and the sintering step is a nitrogen-containing atmosphere. 9. The ceramic precursor is poly (methyl vinyl).
The method according to any one of claims 1 to 8, further comprising silazane. 10. The method according to claim 1, wherein the ceramic precursor is polyureasilazane or polythioureasilazane. 11. The method according to claim 1, wherein the ceramic precursor is a non-dilatant liquid.