JP2005082444A - Production method for silicon nitride reaction sintered compact - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a production method for a silicon nitride reaction sintered compact whereby nitriding reaction is accelerated by a simple method. <P>SOLUTION: In the production method for a silicon nitride reaction sintered compact, a metallic silicon powder is mixed with an aqueous solution or an alcohol solution of a water-soluble compound having a nitriding acceleration element and molded; and the resultant molded product is reaction sintered in a non-oxidative atmosphere containing a nitrogen gas. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing a silicon nitride reaction sintered body that promotes a nitriding reaction.

  Japanese Patent Laid-Open No. 59-30767 discloses 100 parts by weight of metallic silicon having a maximum particle size of 20 μm or less as a method for producing a highly dense silicon nitride reaction sintered body having high mechanical strength and excellent oxidation resistance. After forming a mixed powder containing 0.5 to 2 parts by weight of powdered chromium oxide to a molded body, the molded body was subjected to 1350 in a non-oxidizing atmosphere containing nitrogen gas or nitrogen gas without pre-sintering. A manufacturing method in which reactive sintering is performed at 1450 ° C. is disclosed.

  Japanese Patent Application Laid-Open No. 57-188465 discloses that a silicon powder containing a specific amount of a nitriding accelerator such as iron, cobalt, or nickel is molded and inactive at a temperature of 1100 ° C. or higher and lower than the melting point of silicon. A method for producing a high-density silicon nitride reactive sintered body is disclosed in which nitrogen is applied to a silicon pre-sintered body obtained by sintering in an atmosphere or a vacuum at a temperature of 1100 to 1500 ° C. for nitriding.

  In JP-A-63-85052, as a method for accelerating nitriding and improving the quality of a sintered body to be produced, a metal nitriding accelerator such as iron or chromium dioxide is blended and molded. A production method is disclosed in which the pressure in the nitrogen atmosphere is 10 atm or higher when the formed body is reactively sintered in a nitrogen atmosphere at 1200 to 1500 ° C.

JP-A-5-330921 discloses a method for producing a silicon nitride reaction sintered body having a high nitriding rate, a high density and a high strength as a metal silicon powder having a specific particle size distribution as a metal powder for nitriding promotion. A step of forming a molded body using a raw material powder in which a specific proportion of nickel powder is blended, a step of performing a primary reaction sintering process in which the molded body and nitrogen gas are reacted to obtain an intermediate containing synthetic silicon nitride, Nitriding that sequentially performs a step of subjecting the intermediate to an acid cleaning treatment to elute the nickel component from the intermediate, and a step of performing a second reaction sintering process for synthesizing silicon nitride by reacting the intermediate with nitrogen gas A method for producing a silicon reaction sintered body is disclosed. In this method, since the pores formed by elution of the nickel component by acid cleaning serve as a gas intrusion path into the intermediate body in the secondary reaction sintering process, the nitriding rate can be increased.
JP 59-30767 (Claim 1) JP-A-57-188465 (Claim 1) JP-A-63-85052 (Claim 1) JP-A-5-330921 (Claim 1)

  However, although the conventional method for producing a silicon nitride reaction sintered body adds nitriding accelerators such as iron and chromium dioxide to metal silicon powder, the nitriding reaction is promoted, but the effect is not yet sufficient. Depending on the particle size of the silicon powder, the shape and density of the molded body, a heating process requiring a long time that cannot be said to be practical beyond 80 hours including the temperature raising and lowering time is required. Further, in the conventional method for producing a silicon nitride reaction sintered body, there is a problem that expensive equipment such as a pressure furnace is required and the process is complicated in order to promote the nitriding reaction.

  Accordingly, an object of the present invention is to provide a method for producing a silicon nitride reaction sintered body that promotes the nitriding reaction by a simple method.

  In such a situation, the present inventors have intensively studied, and as a result, when the metal silicon powder and the nitriding accelerator are mixed and molded, the nitriding accelerator is used as an aqueous solution of a water-soluble compound having a nitriding accelerator. Surprisingly, it has been found that the nitriding reaction is remarkably accelerated by a simple method, and the present invention has been completed.

  That is, the present invention mixes and molds metallic silicon powder and an aqueous solution or alcohol solution of a water-soluble compound having a nitriding promoting element, and the molded body is in nitrogen gas or in a non-oxidizing atmosphere containing nitrogen gas. The present invention provides a method for producing a silicon nitride reactive sintered body characterized by performing reactive sintering.

  According to the present invention, the nitriding reaction can be significantly accelerated by a simple method. For this reason, a heating process can be shortened and manufacturing cost can be reduced.

  In the method for producing a silicon nitride reaction sintered body of the present invention, metallic silicon powder and an aqueous solution or alcohol solution of a water-soluble compound having a nitriding promoting element are mixed and molded, and the molded body is nitrogen gas or nitrogen gas. Reactive sintering is carried out in a non-oxidizing atmosphere containing

  Although it does not restrict | limit especially as a metal silicon powder, For example, a thing with a largest particle size of 1-100 micrometers is preferable. When the maximum particle size is less than 1 μm, it is easily scattered and difficult to handle, and when the maximum particle size exceeds 100 μm, a sufficient nitriding reaction promoting effect cannot be obtained even if the method of the present invention is used. Absent.

  In an aqueous solution or an alcohol solution of a water-soluble compound having a nitriding promotion element (hereinafter, also simply referred to as “nitriding promoting element-containing solution”), examples of the nitriding promoting element include nickel, cobalt, copper, and iron. Examples of the water-soluble compounds having these nitriding promoting elements include acetates, nitrates, sulfates, carbonates or chlorides of these nitriding promoting elements. Specifically, nickel nitrate, nickel sulfate, nickel chloride, nickel acetate, nickel carbonate and other nickel compounds, cobalt nitrate, cobalt sulfate, cobalt chloride, cobalt acetate, cobalt carbonate and other cobalt compounds, copper nitrate, cuprous chloride And copper compounds such as cupric chloride, copper acetate and copper carbonate, and iron compounds such as ferrous chloride, ferric chloride and ferrous sulfate.

  Examples of the nitriding promoting element-containing solution include a solution obtained by dissolving a water-soluble compound having these nitriding promoting elements in water, alcohol, or a mixture of water and alcohol. Examples of the alcohol include ethanol. The amount of the water-soluble compound in the aqueous solution or alcohol solution is not particularly limited, and is appropriately determined depending on the type of the water-soluble compound, the mixed form of the metal silicon powder and the aqueous solution, and the like. These nitriding promotion element-containing solutions can be used singly or in combination of two or more. Among these, an aqueous solution in which nickel nitrate hexahydrate is dissolved in water is preferable because nickel nitrate hexahydrate has high solubility in water.

  In the present invention, the method for mixing the metal silicon powder and the nitriding accelerating element-containing solution is not particularly limited. For example, in a molding method in which water or alcohol is blended, such as casting molding or extrusion molding, the blended water is preliminarily used. And a method of forming by mixing with metal silicon powder using a nitriding promoting element-containing solution. If the molding method requires only a small amount of water, such as isostatic pressing, after mixing the metal silicon powder and the nitriding promoting element-containing solution in advance, the liquid component is removed by drying, and the resulting dried product is removed. Examples of the method include molding.

  As a method of mixing the metal silicon powder and the nitriding promoting element-containing solution in advance, for example, a water-soluble compound having a predetermined amount of nitriding promoting element is added to and dissolved in a predetermined amount of water or alcohol to obtain a nitriding promoting element-containing solution. Then, a method in which a predetermined amount of metal silicon powder and the nitriding promoting element-containing solution obtained by the above method are charged into a mixing apparatus such as a planetary mixer and mixed for several tens of minutes can be mentioned. The drying method performed after the mixing is not particularly limited, and may be a condition in which the obtained dried body can be molded and a reaction sintered body having a uniform composition can be obtained.

  It is preferable that an organic binder is blended in an appropriate blending amount in the mixture of the metal silicon powder and the nitriding promoting element-containing solution or the dried product thereof. By blending an organic binder, a strong molded body can be obtained. Examples of the organic binder include cellulose derivatives and acrylic derivatives.

  In the mixture of the metal silicon powder and the nitriding promoting element-containing solution, the compounding amount of the nitriding promoting element is 0.05 to 10 parts by weight, preferably 0.5 to 5 parts by weight as an element with respect to 100 parts by weight of the metal silicon powder. is there. If the blending amount of the nitriding accelerating element is less than 0.05 parts by weight with respect to 100 parts by weight of the metal silicon powder, it is not preferable in that a sufficient nitriding accelerating effect cannot be obtained. The above nitriding promotion effect cannot be obtained, and impurities in the obtained sintered body increase, which is not preferable in terms of strength and corrosion resistance.

  By mixing the metal silicon powder and the nitriding accelerating element-containing solution by the above-described method and drying the mixed solution, the nitriding accelerating element is uniformly supported in a minute size on the surface of the dried metal silicon powder. In the nitriding reaction in the next step, the adsorption of nitrogen to the nitriding promoting element supported on the surface of the metal silicon powder is promoted, and as a result, the nitriding reaction is promoted.

  In the present invention, the sintering temperature is 1200 to 1500 ° C, preferably 1300 to 1400 ° C. If the sintering temperature is less than 1200 ° C., the nitriding reaction is slow, and the effects of the present invention cannot be obtained sufficiently. This is not preferable, and a temperature exceeding the sintering temperature of 1500 ° C. is unnecessary as a sintering temperature and wastes energy. Therefore, it is not preferable.

Reaction sintering is performed under known reaction sintering conditions in nitrogen gas or in a non-oxidizing atmosphere containing nitrogen gas. The non-oxidizing atmosphere containing nitrogen gas means a gas atmosphere containing nitrogen gas such as hydrogen gas or helium gas in the nitrogen gas. Moreover, it does not restrict | limit especially as a pressure in nitrogen gas or the non-oxidizing atmosphere containing nitrogen gas, An atmospheric pressure like 1 * 10 < ⁵ > Pa (1 atmosphere) may be sufficient. Since the reactive sintering of the present invention can promote the nitriding reaction without applying pressure, expensive equipment such as a pressure furnace is not required.

In the present invention, the reaction sintering time is not particularly limited, but for example, a sintered body of 100 mm × 100 mm × 10 mm and bulk density of 1.2 to 1.4 g / cm ³ made of metal silicon powder having a maximum particle size of 30 to 50 μm. In this case, 15 to 20 hours is sufficient in a nitriding atmosphere at 1350 to 1400 ° C. Even with such a short reaction sintering, a nitride ratio of 85% or more, preferably 90% or more can be obtained with certainty. Since the reaction sintering time in the conventional method for producing a silicon nitride reaction sintered body is actually 30 to 40 hours, according to the method for producing a silicon nitride reaction sintered body of the present invention, the heating process is greatly increased. It can be shortened.

  In the method for producing a silicon nitride reaction sintered body of the present invention, the nitriding reaction is remarkably accelerated because the nitriding accelerating element is uniformly supported on the surface of the metal silicon powder of the compact. For this reason, in the nitriding reaction, the adsorption of nitrogen to the nitriding promoting element supported on the surface of the metal silicon powder is promoted, and this large amount of adsorbed nitrogen is further adsorbed to the metallic silicon, which is presumed to promote the nitriding reaction. The

Nickel nitrate hexahydrate was added in an amount of 1 part by weight as nickel atoms to 50 parts by weight of ethanol and dissolved sufficiently to obtain a nitriding promotion element-containing solution. Next, the entire amount of the nitriding promotion element-containing solution, 100 parts by weight of metal silicon powder having a maximum particle size of 30 μm, and 1 part by weight of an acrylic derivative serving as a binder were put into a planetary mixer and mixed and stirred for 30 minutes. Next, this mixture was poured into a casting mold made of stainless steel and then dried at 120 ° C. for 5 hours to obtain a plate-like molded body having a size of 100 mm × 100 mm × 10 mm and a density of 1.4 g / cm ² . Next, the obtained molded body was subjected to nitriding treatment in a nitrogen gas atmosphere of 1 × 10 ⁵ Pa (1 atm) at 1400 ° C. for 20 hours to obtain a silicon nitride reaction sintered body having a nitriding rate of 98%. Obtained. The nitriding rate is expressed as a percentage by dividing the actual weight increase by the theoretical weight increase in the nitriding reaction.

An amount of cuprous chloride to be 1 part by weight as copper atoms was added to 50 parts by weight of water and dissolved sufficiently to obtain a nitriding promotion element-containing solution. Next, the entire amount of the nitriding promotion element-containing solution and 100 parts by weight of metal silicon powder having a maximum particle size of 30 μm were put into a planetary mixer, mixed and stirred for 30 minutes, and then heated to 100 ° C. to dry and remove moisture. Next, the total amount of the metal silicon powder after drying, 7 parts by weight of water and 1 part by weight of a cellulose derivative as a binder were put into a planetary mixer, mixed and stirred for 30 minutes, and then the mixture was 100 mm × 100 mm × 10 mm, density 1 It was press-molded into a 4 g / cm ² plate. The obtained molded body was dried at 120 ° C. for 5 hours, and then subjected to nitriding treatment at 1400 ° C. for 20 hours in a nitrogen gas atmosphere of 1 × 10 ⁵ Pa (1 atm). A sintered body was obtained.

  A silicon nitride reaction sintered body having a nitriding rate of 91% was obtained when the same method as in Example 1 was used except that cobalt sulfate heptahydrate was used instead of nickel nitrate hexahydrate. .

A silicon nitride reaction sintered body having a nitriding rate of 92% was obtained by the same method as in Example 1 except that iron chloride hexahydrate was used instead of nickel nitrate hexahydrate. .
Comparative Example 1
A silicon nitride reaction sintered body having a nitriding rate of 43% was obtained by the same method as in Example 1 except that nickel nitrate hexahydrate was not added.
Comparative Example 2
A silicon nitride reaction sintered body having a nitriding rate of 52% was obtained in the same manner as in Example 1 except that metallic nickel powder having a maximum particle size of 3 μm was used instead of nickel nitrate hexahydrate. Obtained.

Claims (4)

  Metal silicon powder and an aqueous solution or alcohol solution of a water-soluble compound having a nitriding promoting element are mixed and molded, and the molded body is subjected to reactive sintering in nitrogen gas or in a non-oxidizing atmosphere containing nitrogen gas. A method for producing a silicon nitride reaction sintered body.   The method for producing a silicon nitride reactive sintered body according to claim 1, wherein the nitriding promotion element is one or more selected from nickel, cobalt, copper and iron.   The method for producing a silicon nitride reaction sintered body according to claim 1 or 2, wherein the water-soluble compound of the nitriding accelerating element is acetate, nitrate, sulfate, carbonate or chloride.   The method for producing a silicon nitride reactive sintered body according to any one of claims 1 to 3, wherein the reactive sintering is performed in a temperature range of 1300 to 1400 ° C.