JPS59190275A - Manufacture of reaction sintered ceramics - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing /C ceramics using reactive sintering.

The reaction sintering method is a method in which, for example, a molded body containing metallic silicon is fired in a perforated air flow to obtain strong ceramics by utilizing the bonding force that occurs when the metallic silicon turns into silicon nitride. It is a self-sintering method, and it is possible to sinter at relatively low temperatures, 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 metal silicon etc. It is widely used industrially due to its advantages.

However, in the conventional method, the required amount of binder, etc. is added to the powder or granules containing metal silicon, which is then kneaded, filled into a mold, molded, and released, or extruded. 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 is also the problem of deformation of the body, and in the case of a product with a large vertical pole dimension 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 metal silicone, etc. and fired in a nitrogen stream, the sintering reaction easily takes place within the mold due to the nitrogen gas coming 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 coating material for the ceramics.

The gist of the present invention is to fill a carbonaceous mold that has poor air permeability with a metal silicon overgrowth or a powder containing a metal silicon overgrowth, and then to process the evaluation mold filled with the powder into a carbonaceous mold. Reactive firing characterized by firing in an atmosphere or in an inert atmosphere containing nitrogen (here, inert means a state in which oxidizing gases such as acid accumulation and carbon dioxide are substantially heated). It is in the manufacturing method of bonded ceramics.

The carbonaceous mold used in the present invention has a porosity of 20 to 42% because nitrogen is supplied through the mold wall.
If it is less than 20%, it becomes difficult to supply nitrogen and sintering takes a long time, and in extreme cases, metal silicon remains and a reaction sintered body cannot be obtained.
If it exceeds %, the smoothness of the mold surface in contact with the powder may not be maintained, or the powder may enter the pores, which is undesirable.

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.

Note that firing produces a large bonding force at the interface between the carbonaceous mold and the powder, so it is possible to utilize this property to obtain composite ceramics in which the mold itself is covered with a reactive sintered body. can.

On the other hand, if the reaction sintered body itself is to be made into the desired product, and it is necessary to separate the mold (it is better to use a split mold), paper may be interposed on the inner surface of the mold in contact with the powder or granules.
If you find a way to apply boron nitride powder, it will be easier to make a template, and you can reuse the mold. In addition, if the shape is complicated and difficult to carve, heating it to several hundred degrees in an oxidizing atmosphere will make it possible to
The carbonaceous type easily disappears, and a reaction sintered body is obtained in a healthy state.

The powder to be used may be silicon metal or a mixture of silicon metal and silicon carbide, silicon nitride, or alumina, and other powders may be mixed with the silicon metal depending on the purpose. In addition, their particle size and composition may be selected as appropriate 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. Since the friction between the 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, composite reactive sintered ceramics can be obtained.

The filled porridge is charged into a nitriding furnace, also known as a mold, and heated and heated in an inert atmosphere containing nitrogen or nitrogen.

Heating is relatively fast from base to 1000°G at 50~
The nitriding reaction starts at a heating rate of 150°C/hr.
Exceeding 000°G and reaching 1400°C is relatively slow5~
It is preferable to heat at a heating rate of 50°C/hr, and then maintain the maximum temperature for 10 to 200 cycles, depending on the product, to cause a sufficient nitriding reaction.

The gas fed into the nitriding furnace is an inert gas containing nitrogen, which is a reaction component.
In Germany, combustion/arm waste gas from which acid accumulation and carbon dioxide have been removed can be used.

As mentioned above, in the method of the present invention, the mold is transferred to the sintering process without being released from the mold after molding, so there is no need to take shape retention into consideration, and binders are generally not required, so the work is simplified. Productivity is improved, and a single ceramic product with good dimensional accuracy can be obtained even with complex shapes.

Hereinafter, the present invention will be explained in more detail with reference to Examples.

Examples 1 to 5 Silica metal and silicon carbide were respectively crushed and classified to prepare granules having the composition shown in Table 1, and boron nitride powder was applied to the inner surface of the powder. m
Cylindrical graphite type with a length of 300 mm (528% pore forest)
was filled using a vibration molding machine.

The molded product is placed in a firing furnace together with the mold without being used as a template, and heated at 120°C/hr up to 1000°C in a nitrogen gas atmosphere.
, 10° above 1000°C and up to 1400°C
The temperature was raised at a rate of C/hr and then maintained at that temperature for 80 hours. r) After casting, the physical properties of the obtained forest-like reaction sintered bodies were measured.

Comparative Examples 1 to 2 0.4% methyl cellulose was added as a binder to the powder and granules having the same formulation as Puco J Oil Examples 1 and 4 (in an aqueous solution)
A rod-shaped body with a diameter of 60 ml was obtained by extrusion molding.

The rod-shaped body was fired in the same manner as in Examples] to 5, and the physical properties of the obtained reaction sintered body were measured.

The following results are summarized and are also shown in No. 1122.

Below is the margin Example 6 Porosity 26%, wall thickness 5m+n, outer diameter 90i7 each
] Two graphite pipes of 111 mm and 49 mm and 400 mm in length were coated with boron nitride powder on the inner surface of the thicker one and the outer surface of the thinner one, and then straightened in double layers, and a blockage plug was installed at the bottom. The same granular material as in Example 1 was filled into the middle part of the two tubes using a vibration molding machine.

This was fired together with the mold in the same manner as in Examples 1 to 5 to obtain a reaction sintered body in the form of an inkstone and a female mold. The physical properties of this thing are
It was almost the same as Example 1.

Comparative Example 3 A cylindrical body with an outer diameter of 80 mm and a wall thickness of 20111171 mm was extruded using the same mixture as in Comparative Example 1.
It was extremely difficult to maintain the shape of the green molded body, the shape of the obtained sintered body was poor, and the compressive strength was also extremely low compared to Example 6.

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 other side of the fine graphite tube.

A cylindrical kneaded ceramic with Kurofune tube firmly bonded to the inner surface was obtained.

Patent applicant: Nippon Light Metal Co., Ltd. Agent: Patent Attorney Keiji Matsunaga

Claims (1)

[Scope of Claims] 1. Filling a carbonaceous mold with good air permeability with metal silica or powder containing metal silica, and then placing the mold filled with the powder in a nitrogen atmosphere. Alternatively, a method for producing reactive sintered ceramics characterized by firing in an inert atmosphere containing nitrogen. 2. A method for producing reactive fired wood ceramics according to claim 751, characterized in that the pores of the carbonaceous mold are 20 to 42%.