JPS6235995B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing ceramics using reactive sintering. The reaction sintering method is a method for obtaining strong ceramics by firing a compact containing metallic silicon particles in a nitrogen stream and utilizing the bonding force generated when metallic silicon turns into silicon nitride. Unlike the self-sintering method, it is possible to sinter at a relatively low temperature, it can withstand use even at temperatures higher than the firing temperature, and products with various properties can be obtained by changing the particle size of silicon metal etc. It is widely used industrially due to its advantages such as: However, in the conventional method, the required amount of binder etc. is added to metal silicon particles or powder containing metal silicon particles and kneaded, which is then filled into a mold, molded and released, or by extrusion method. The so-called green molded body is formed by molding, and this is then subjected to reaction sintering, but not only is it difficult to manufacture products with complex shapes, but the green molded body may be deformed or sintered due to inherent distortion. There are also problems such as deformation of the body, and furthermore, in the case of a material having a large aspect ratio, there is a drawback that sufficient strength cannot be obtained. The inventors of the present application have found that when a breathable carbonaceous mold is filled with metallic silicon particles and the like is fired in a nitrogen stream, a sintering reaction easily takes place within the mold due to the nitrogen gas from the pores of the mold. The present invention was completed based on this discovery. One object of the present invention is to provide a method for efficiently manufacturing a reaction sintered body having high dimensional accuracy and strength even when the shape is particularly complex or the size ratio is large. The object of the present invention is to provide a method for manufacturing composite ceramics in which the mold itself functions as a covering material for ceramics. The gist of the present invention is to fill an air-permeable carbonaceous mold with metal silicon particles or powder containing metal silicon particles, and then place the mold filled with the powder in a nitrogen atmosphere or under nitrogen. A method for producing reactive sintered ceramics characterized by firing in an inert atmosphere (here, inert refers to a state substantially free of oxidizing gases such as oxygen and carbon dioxide) containing . In the carbonaceous mold used in the present invention, since nitrogen is supplied through the mold wall, the porosity of the mold is preferably in the range of 20 to 42%, and if it is less than 20%, nitrogen cannot be supplied. It becomes difficult to sinter, requiring a long time to sinter, and in extreme cases, metallic silicon remains, making it impossible to obtain a reactive sintered body, and if it exceeds 42%, the smoothness of the mold surface in contact with the powder cannot be maintained. This is undesirable as it may run out or particles may enter the pores. Among carbonaceous materials, graphite has particularly good workability, so it has the advantage that molds of arbitrary shapes with high dimensional accuracy can be easily obtained. Furthermore, since a large bonding force is generated by firing at the interface between the carbonaceous mold and the granular material used, it is possible to utilize this property to obtain composite ceramics using the mold itself as a covering material for the reaction sintered body. can. On the other hand, if it is necessary to separate the mold (a split mold may be used if necessary) in order to make the reaction sintered body into the desired product, paper may be interposed on the inner surface of the mold in contact with the powder, or nitrided If a method such as applying boron powder is used, the mold can be easily released and the mold can be reused. If the shape is complex and it is difficult to release from the mold, the carbonaceous type can be easily eliminated by heating to several hundred degrees in an oxidizing atmosphere, and a reaction sintered body can be obtained in a healthy state. The powder to be used may be a single metal silicon, or a mixture of metal silicon and silicon carbide, nitrogen silicon, or alumina, and other powders may be mixed with metal silicon depending on the purpose. Further, their particle size, blending amount, etc. may be appropriately selected to suit the properties of the intended product. When filling a mold with powder or granules, various methods can be used, but it is preferable to use the vibration molding method for molds with complex shapes. This is particularly advantageous in such cases since the friction between the two is small. If a ceramic molded body of the same type or a different type is inserted into the mold before or during the filling of the powder, various composite reaction sintered ceramics can be obtained. After filling, the mold is placed in a nitriding furnace and heated to a high temperature in nitrogen or a nitrogen-containing inert atmosphere. Heating is relatively fast from room temperature to 1000℃ 50~
The nitriding reaction starts at a heating rate of 150℃/hr.
Relatively slow 5-50 above 1000℃ and up to 1400℃
It is preferable to heat at a rate of temperature increase of °C/hr, and then maintain the maximum temperature for 10 to 200 hours, depending on the product, to cause a sufficient nitriding reaction. The gas fed into the nitriding furnace is an inert gas containing nitrogen as a reaction component, and nitrogen gas alone, combustion waste gas from which oxygen and carbon dioxide have been removed, etc. can be used. As described above, according to the method of the present invention, the sintering process is carried out without releasing the mold after molding, so there is no need to take shape retention into account, and binders are generally not required, simplifying the work and production. In addition to improving the properties, ceramic molded products with good dimensional accuracy can be obtained even in complex shapes. Hereinafter, the present invention will be specifically explained with reference to Examples. Examples 1 to 5 Metal silicon grains and silicon carbide grains were crushed and classified, respectively, and powders with the composition shown in Table 1 were prepared, and boron nitride powder was coated on the inner surface of the powder with an inner diameter of 600 mm.
Cylindrical graphite type with outer diameter 100mm and length 300mm (porosity 28
%) using a vibration molding machine. The molded product is charged into a firing furnace together with the mold without being released from the mold, and heated at 120°C up to 1000°C in a nitrogen gas atmosphere.
The temperature was increased at a rate of 10°C/hr from 1000°C to 1400°C, and then held at that temperature for 80 hours.
After cooling, the mold was released, and the physical properties of the obtained rod-shaped reaction sintered body were measured. Comparative Examples 1 to 2 To the powder and granules having the same composition as in Examples 1 and 4, 0.4% by weight of methyl cellulose was added as a binder (in an aqueous solution), kneaded, and extruded to form a diameter of 60 mm.
A rod-shaped body was obtained. The rod-shaped body was fired in the same manner as in Examples 1 to 5,
The physical properties of the obtained reaction sintered body were measured. The above results are summarized and also shown in Table 1.

[Table] Example 6 Porosity: 26%, wall thickness: 5 mm, outer diameter: 90 mm.
Prepare two graphite tubes with a length of 40 mm and a length of 400 mm, apply boron nitride powder to the inner surface of the thicker one and the outer surface of the thinner one, stand them upright twice, and install a plug at the bottom to connect the two tubes. The same powder as in Example 1 was filled into the middle part using a vibration molding machine. This was fired together with a mold in the same manner as in Examples 1 to 5, and then released from the mold to obtain a cylindrical reaction sintered body. The physical properties of this product were almost the same as in Example 1. Comparative Example 3 A cylindrical body with an outer diameter of 80 mm and a wall thickness of 20 mm was extruded using the same mixture as in Comparative Example 1, but it was extremely difficult to maintain the shape of the green molded body, and the resulting sintered body The shape is poor and the compressive strength is similar to Example 6.
It was extremely low compared to Example 7 Molding and firing were carried out in the same manner as in Example 6, except that boron nitride powder was not applied to the outer surface of the thinner graphite tube. A cylindrical composite ceramic with graphite tubes firmly bonded to the inner surface was obtained.

Claims (1)

[Scope of Claims] 1. A carbonaceous mold having air permeability is filled with metal silicon grains or a powder material containing metal silicon grains, and then the mold filled with the powder material is placed in a nitrogen atmosphere or in a nitrogen atmosphere. A method for producing reactive sintered ceramics characterized by firing in an inert atmosphere containing. 2. The method for producing reactive sintered ceramics according to claim 1, wherein the carbonaceous mold has a porosity of 20 to 42%.