JPH03261611A - Production of silicon nitride composite powder - Google Patents

Abstract

PURPOSE:To obtain a raw material for high-strength silicon nitride composite material by heating a mixture of Si powder and carbonaceous powder in a nitrogen-containing inert gas atmosphere and causing carbonization reaction of Si and nitriding reaction at the same time. CONSTITUTION:Metal Si powder is blended with carbonaceous powder to give a powder mixture. The mixture is heated to <=1,400 deg.C in a nitrogen-containing inert gas atmosphere. Carbonization reaction of the Si powder and nitriding reaction are effected at the same time. The synthesized silicon.carbide silicon.nitride composite powder has uniformly dispersed silicon carbide and composite ceramics produced from the powder has both excellent strength and fracture toughness.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing silicon nitride composite powder, and more specifically, silicon nitride composite powder that is a raw material for a silicon nitride yarn composite sintered body having high strength. The present invention relates to a manufacturing method.

[Conventional technology] Silicon nitride thread ceramics are attracting attention as structural ceramic materials for various refractory materials and engine parts because of their excellent high-temperature strength and wear resistance. Because of its low fracture toughness, attempts have been made to improve its fracture toughness by combining it with silicon carbide.

As a method for compositing with silicon carbide, a method is used in which silicon carbide powder and silicon nitride thread powder are mixed and then sintered.

[Problem to be Solved by the Invention 1] However, by mixing silicon carbide powder and silicon nitride powder using a conventional method such as a ball mill, it is difficult to obtain a mixed powder in which both powders are completely and uniformly dispersed. Therefore, the fracture toughness value of the sintered body using the mixed powder has only a slight property improvement effect compared to that of the single silicon nitride thread sintered body, and the uneven mixed part When it is made into a sintered body, it causes defects, which causes a decrease in strength.

[Means for Solving the Problems] The present inventors investigated various methods for uniformly dispersing silicon carbide powder and silicon nitride powder, and as a result, they synthesized silicon carbide powder and silicon nitride powder simultaneously. By doing this, we were able to obtain a composite powder in which both were uniformly dispersed, and it was confirmed that the composite crystal obtained by sintering this composite powder has superior fracture toughness and strength to sintered bodies produced using conventional techniques. This discovery led to the completion of the present invention.

That is, in the present invention, a metal Si powder and a carbonaceous powder are mixed, and the mixture is heated in a nitrogen-containing inert gas atmosphere.
This is a method for producing a silicon nitride composite powder, which is characterized in that it is heated at a temperature of 00° C. or lower to simultaneously perform a carbonization reaction and a nitridation reaction of metal Si powder.

[Operation] According to the method of the present invention, metal Si powder and carbonaceous powder react to generate silicon carbide at the same time.

Metallic Si powder and nitrogen gas produce silicon nitride powder, and a composite powder in which silicon carbide powder and silicon nitride powder are uniformly dispersed in the reaction stage is synthesized, resulting in a so-called nanocomposite having a dispersed phase of no+ order. A mixed powder is obtained.

Furthermore, the carbonaceous powder has a function of suppressing the solidification of metal Si during the reaction, so that the reaction proceeds more uniformly.

The present invention will be explained in detail below.

(Starting Materials) As the starting materials used in the present invention, such as metal Si powder and carbonaceous powder, commonly used ones can be used.

The metal Si powder is ordinary metal silicon, and its purity is 9
It is 5% or more5, preferably 98% or more.

Carbonaceous powder is blended as a carbon source for silicon carbide, and includes amorphous carbon such as carbon black, as well as carbon precursors such as phenol resin and Yuria resin, which are produced by decomposing carbon when heated.

Although the fineness of each of the above-mentioned raw material powders is not particularly limited, it is preferable to use metal Si powder with an average particle size of 10 um or less, and carbonaceous powder with an average particle size of 5 um or less.

(Blending Ratio) In the raw material blending for synthesizing the silicon nitride composite powder of the present invention using the above starting materials, the blending amount of the carbonaceous powder may be controlled depending on the desired silicon carbide composition.

For example, when manufacturing a composite powder containing silicon carbide at IO% by volume, the carbon equivalent amount is 0.03 per mole of silicon metal.
6 mol (1/28 mol) of carbonaceous powder is blended. Further, when a material with high density and high strength is required as a sintered body, it is preferable that the molar ratio of C/Si is 0.5 or less. If it exceeds 0.5, the density of the sintered body will not increase when pressureless sintered, resulting in a porous sintered body and its strength will decrease. However, in the case of pressure sintering using a hot press or the like, densification progresses during sintering, so a good sintered body can be obtained without being particular about the above blending range.

(Mixing) In any of the above formulations, each raw material is mixed using a conventional device to obtain a blended raw material.

In this case, in order to accelerate the reaction of each raw material and make a more uniform composite powder, use ceramic balls or beads and a mill (pot mill, bead mill, etc.) to mix and grind the raw materials. This is extremely effective. Examples of materials for such ceramic balls, beads, and mills include alumina, zirconia, silicon nitride, silicon carbide, and sialon. In particular, in the case of the present invention, silicon nitride, silicon carbide, and sialon are used. preferable.

The particle size after pulverization is not particularly limited, but it is desirable that the average particle size is 511!1 or less, especially an average particle size of 3.
It is preferable to use raw material powder with a particle size of μm or less.

(Calcination) Next, the process of reacting the blended raw materials and synthesizing the composite powder will be described.

The apparatus used for reacting the raw materials in the present invention may be any conventional atmosphere furnace (e.g., rotary kiln, fluidized bed calcining furnace, pusher furnace, etc.), but the apparatus may be any one of the following: In terms of.

A fluidized bed kiln is preferred.

In the present invention, it is necessary to react the blended raw materials in a nitrogen-containing inert gas atmosphere to simultaneously advance the carbonization and nitridation of gold[Si, and it is important to control the synthesis temperature.

Such a temperature is 1250 to 1420°C; at a temperature exceeding this range, the metal S1 will melt and the desired composite powder will not be obtained, and at a temperature below the above range, the metal Si will be carbonized and Nitriding does not progress. Among the above-mentioned temperature ranges, the preferred temperature is 1300-1400°C because the reaction can easily proceed and the temperature can be easily controlled.

The reaction time varies depending on the firing temperature.

The standard time is about 2 to 10 hours; if the time is shorter than this, unreacted metal Si tends to remain, and if it is held for longer than this range, the reaction has already been completed, which is economically disadvantageous. Become.

(Composite Powder) The composite powder of the present invention obtained as described above becomes a so-called nanocomposite in which carbides and nitrides are extremely uniformly dispersed and has a dispersed phase on the order of nanometers, and when made into a sintered body, the strength is Fracture toughness is significantly improved.

[Example 1 The present invention will be explained below with reference to Examples.

Example 1 Metallic silicon powder (rHisi-600S manufactured by Yamaishi Metal)
J.

Average particle size: 5.5 IIm) For 100 parts by weight, carbon powder (rMA200RBJ manufactured by Mitsubishi Kasei ■)
1.5 parts by weight was blended, mixed using a resin ball and a bot mill, and then fired under the conditions shown in Table 1 to obtain a silicon carbide/silicon nitride composite powder.

xI of the obtained composite powder! Table 1 shows the SiC:5iJ4 production ratio determined from the diffraction peak ratio of the diffraction results.

In addition, YJ3 and Al were added to the obtained composite powder as sintering aids.
2O2 was added at 5% each, mixed with water using silicon nitride beads and a bot mill, dried, press-molded, and sintered under normal pressure at 1780°C for 3 hours in nitrogen. Table 1 shows the results of the bending test strength measured according to JIS R1601 and the fracture toughness value measured by the indentation method for the compact.

Example 2 Table 1 shows the results of composite powder obtained by changing the blending ratio and firing conditions of Example 1 as shown in Table 1.

Example 3 The same raw materials and formulation as in Example 1 were used, mixed and ground using silicon nitride beads and a bot mill to obtain a mixed powder with an average particle size of 3 um.

Table 1 shows the results for the composite powder obtained by firing under the conditions shown in Table 1.

Example 4 In Example 3, mixed pulverization was performed using Sialon beads and a bead mill to obtain a mixed powder with an average particle size of 2 μm.

Table 1 shows the results for the composite powder obtained by firing under the conditions shown in Table 1.

Example 5 In Example 3, mixed pulverization was performed using zirconia beads and a resin mill to obtain a mixed powder with an average particle size of 4 μm.

Table 1 shows the results for the composite powder obtained by firing under the conditions shown in Table 1.

Comparative Example 1.2 Silicon carbide (“Beta Random Ultra Fine” manufactured by Ibiden) and silicon nitride (rKs manufactured by Shin-Etsu Chemical)
s-10MJ) and their blending ratios are as in Example 1.
and 2 were mixed in the same proportions as in the firing results, and mixed in a pot mill in the same manner as in Example 1. After blending with a sintering aid, molding and sintering were carried out in the same manner as in Example 1. The results for the sintered body are shown in Table 1.

[Effects of the Invention] The silicon carbide/silicon nitride composite powder synthesized by the method of the present invention is a powder in which silicon carbide is extremely uniformly dispersed. Compared to composite ceramics manufactured from conventional mixed powders, both strength and fracture toughness are significantly improved.
It is an excellent engineering ceramic material.

Claims (1)

[Claims] (1) Mixing metal Si powder and carbonaceous powder and heating the mixture at a temperature of 1400°C or less in a nitrogen-containing inert gas atmosphere to simultaneously perform a carbonization reaction and a nitridation reaction of the metal Si powder. A method for producing silicon nitride composite powder characterized by: