JPS5823346B2 - Production method of α-sialon sintered body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a high-density α-sialon sintered body.

5iAl ON-based compound or solid solution.

Generally called Sialon.

Sialon has high strength and low coefficient of thermal expansion, so
Gas turbine parts as a high-temperature heat-resistant material that replaces conventional heat-resistant alloys.

It is expected to be used in heat exchangers, etc.

It also has excellent oxidation resistance and corrosion resistance, and is also excellent as a fireproof and heat insulating material.

Recently, α-sialon having an α-8t s N4 structure was discovered as a new sialon.

This is because Al is substituted in the Si position of the α-8i3N4 structure, Al is substituted in the N position, and O is substituted in the N position, and at the same time, other metals are dissolved in the interstitial space. , general formula Mx(S i, Al)x2(0,N)t6 (however.

M represents Li, Mg, Ca, Y, a rare earth element, or a mixture thereof, and X represents 0<X<2).

In addition to its use as conventional SanoAlion, this new α-sialon has excellent electrical properties due to the solid solution of various metals between the lattices, and is expected to be used as a new electrode material.

Firstly, the present inventor developed a hot press method of firing under pressure as a method for producing a high-density α-sialon sintered body.

Although this hot pressing method can easily produce a high-density sintered body, there are problems in that the product is expensive and can only be manufactured in a simple shape.

The present invention aims to solve this problem.

The present invention provides a method for manufacturing a high-density sintered body having an arbitrary shape by simply heating it in a nitrogen stream at normal pressure without requiring pressurization.

As a result of intensive research to achieve the above object, the present inventor has found that when the raw material molded body is coated with powder containing silicon nitride and heated and fired in a nitrogen stream, the porosity is 15% or less at normal pressure. It was found that a high-density sintered body can be produced by crushing.

The present invention was completed based on this research fact.

The raw material for α-Sialon is silicon nitride.

Aluminum nitride and oxides of Li, Ca, Mg, Y, or rare earth elements, or salts that produce oxides of the metals through thermal decomposition, such as carbonates, oxalates, basic carbonates, hydroxides, etc. One or a mixture of two or more of these are used.

The mixing ratio of the raw material powders is as shown in the chemical formula below.

When using oxides of monovalent metals, Si3N4+a(3AlN+M20)-+M2a(S
i3. A13a) (Oa, N3a+4) (However, 0<
a1) When using an oxide of a divalent metal 513N4 +b (3AlN+MO) → Mb (Si3.A13b) (Ob, N3b+4) (O<b×2) When using an oxide of a trivalent metal Si3N4+c(9AlN+M2O5) → M2C(Si
3yA19c) (OscyNoc++) (however, o<
c1) After mixing the raw material powders, mold them into a predetermined shape.

Molding methods include die molding, slurry casting, isostatic pressing, and injection molding.

However, it is not limited to this.

The raw material silicon nitride and the produced α-sialon are thermally decomposed at high temperatures and hinder sintering.

In the method of the present invention, the molded body is made of silicon nitride powder alone or silicon nitride and aluminum nitride or α
- Li, Ca, and Mg dissolved in Sialon.

By sintering the α-sialon by coating it with a mixture containing Y or an oxide of a rare earth element or a metal salt thereof that produces an oxide through thermal decomposition, the sintering of the α-SiAlON produced is not hindered and can be carried out at any time. High density can be obtained by pressure.

In addition, AA'2o3. Good results are also obtained by mixing S 1o2.

Note that the amount of silicon nitride in the mixture is 5% by weight or more.

This sintering is performed in a nitrogen atmosphere.

The sintering temperature is 1600-1900°C, preferably 170°C.
The temperature is 0 to 1850°C.

At temperatures lower than 1600°C, the sintering reaction does not proceed, and 19
If the temperature exceeds 00°C, thermal decomposition of silicon nitride and α-sialon cannot be prevented.

The sintering time is 15 minutes to 3 hours, preferably 30 minutes to 1 hour.

According to the method of the present invention, no pressure is required during sintering.

Therefore, the apparatus is simple, and it has an excellent effect that a high-density α-SiAlON sintered body can be easily obtained in any shape.

Example l Silicon nitride (average particle size 0.5 μm, impurity Fe0125
% AlO, 18% 01,2% % indicates weight % rack.

(same below), aluminum nitride (average particle size 2 μm, impurity Si 0.2% 01.8%), and IJium (purity 99.9%) at a molar ratio of 5
They were mixed at a ratio of 0:27:3.

Using a mold with a diameter of L2tnm, the mixture 2I is
Primary molding was performed at a pressure of 20 olv/ffl.

Next, secondary molding was performed using a hydrostatic press at a pressure of 1.5 b/ffl to obtain a cylindrical molded product having a density of 1.8597 ctrl.

The compact was placed in a crucible made of BN sintered body with an inner diameter of 118 mm and a length of 25 wings, and was covered with silicon nitride powder.

The crucible was placed in a graphite crucible, heated by high frequency induction in a nitrogen stream, and kept at 1750°C for 1 hour.

The sintered body has an α-3i3N4 structure, and its composition is Yo,
41 (Silo, 2.A 111.B) (O
o, a.

N154).

The weight loss due to heating was 2.3% by weight, the density of the sintered body was 3.1 s E /crit, and the porosity was 85%.

Examples 2 to 6 Raw material mixtures of various compositions were molded into molded products in the same manner as in Example 1, and sintered bodies of α-SiAlON were produced under different conditions.

The results were as follows.

Claims (1)

[Claims] 1. Silicon nitride, aluminum nitride and h Lt. One or more of the oxides of Ca, Mg, Y or rare earth elements or the salts of the metals that produce oxides upon heating are combined with the general formula Mx (S i , A#)12S(0,N) 16. (However, MfjL i , Ca ,
Mg. Y also represents a rare earth element or a mixture thereof. A molded body of powders mixed in a proportion to produce α-sialon expressed as (X represents O<x×2). A method for producing an α-sialon sintered body, which comprises covering the powder with silicon nitride-containing powder and heating it in a nitrogen stream to form a sintered body. 2. The powder containing silicon nitride is silicon nitride alone or silicon nitride and aluminum nitride or Li. Oxides of Ca, Mg, Y or rare earth elements. 2. The production method according to claim 1, wherein is a mixture with one or more salts of a pre-metal which forms an oxide upon heating. 3 The heating temperature for making a sintered body is 1600 ℃ in nitrogen at 1 atm.
The manufacturing method according to claim 1, wherein the temperature is 1900°C.