JPS6270209A - Production of readily sintered beta-sialon based fine powder - Google Patents

Abstract

PURPOSE:To produce fine, uniform and readily sintered beta-sialon based powder, by adding a solution of an aluminum compound and a sintering assistant to an Si alkoxide containing dispersed carbon powder having a specific particle diameter and heating the formed reaction precipitates under specific conditions. CONSTITUTION:Fine carbon particles having <=0.1mu particle diameter are dispersed in an Si alkoxide, e.g. methyl silicate, by ultrasonic vibration, etc., and a solution of an aluminum compound, e.g. Al(NO3)3, containing a sintering assistant, e.g. MgO, or a salt thereof, dissolved therein is added to the dispersion. The mixing ratio of the Si alkoxide to the aluminum compound is about 0.5-25 (Si/Al). The resultant reaction precipitates formed by the mixing are heated at about 400-700 deg.C to release water and then the resultant precipitates are fired in a nitrogen gas stream at 1,350-1,550 deg.C for about 0.5-50hr. Thereby, fine powder containing uniformly mixed beta-sialon based powder and sintering assistant and having about 0.3-0.5mu particle diameter is obtained and fired in a nitrogen gas stream at about 1,700-1,800 deg.C to form a sintered material.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for producing easily sinterable β-sialon fine powder. β-Sialon is a solid solution of β-8i, N4 with At in the S1 position and O in the N position as a substituted solid solution, and has the general formula 51
61A1202N8-7 (0<z stands for 4.2).

The sintered body of β-sialon has high strength at high temperatures.

Corrosion resistance? It has excellent oxidation resistance and is expected to be applied to cutting tools, metal rolling rollers, automobile engine parts, etc.

Prior Art A conventional method for producing easily sinterable β-sialon powder has been a method of simply mixing a sintering aid with β-sialon powder.

In addition, methods for producing β-sialo powder include: 1) A reduction/nitriding method in which carbon is added to natural silica-alumina minerals and heated in a nitrogen stream.

2) Adding aluminum metal to silica raw materials such as whitebait,
Method of heating in a nitrogen stream.

3) A method is known in which a coprecipitate of Al(OH)3 and silica gel is heated in an ammonia atmosphere.

However, since methods 1) and 2) use natural raw materials, they have the disadvantage of containing a large amount of impurities, and method 3) has the disadvantage that the reaction is difficult to complete and unreacted M compounds remain. there were.

The present inventors first proposed a method to overcome these drawbacks of the conventional method by hydrolyzing a silicon and aluminum alkoxide solution in which carbon powder was dispersed7 to form a precipitate consisting of a uniformly mixed fine powder. A method of heating in a nitrogen stream was developed (%Gan No. 59-2317).

However, even with this method, ceramics with high strength 1
SiAlON powder having a small amount of solid solution of Al cannot be obtained, and crushed aluminum alkoxide has the drawback of being expensive.

Purpose of the Invention The present invention was made in order to eliminate the drawbacks of the conventional method, and its purpose is to reduce the
- To provide a method for producing easily sinterable β-sialon fine powder in which a sialon powder and a sintering aid are uniformly mixed.

Structure of the Invention As a result of intensive research to achieve the above object, the present inventor has added a solution of an aluminum compound and a sintering aid to a silicon alkoxide in which carbon powder with a particle size of 0.1 micron or less is dispersed. When salts are added and the precipitate produced by the reaction is heated in a nitrogen stream, a powder is obtained in which a fine powder of β-sialon powder and a sintering aid is uniformly mixed, and this fine powder is sintered under atmospheric pressure. It was found that it could be easily obtained by sintering even if it was made of solids, and 2 was obtained. The present invention was completed based on this knowledge.

The gist of the present invention is to add an aluminum compound solution and a sintering aid solution or salts of a sintering aid to silicon alkoxide in which carbon powder with a particle size of 1 micron or less is dispersed, Precipitate in a nitrogen stream at 1350~
Easy-to-furnace β characterized by heating to 1550°C
- A method for producing sialon fine powder.

Examples of the raw material silicon alkoxide include methyl silicate, ethyl silicate, propyl silicate, and butyl silicate. Sweet, aluminum compounds include aluminum nitrate, aluminum sulfate, aluminum chloride B
Examples include Youpan and the like. However, it is not limited to this.

The mixing ratio of silicon alkoxide and aluminum compound is Si/A in atomic ratio! = preferably in the range of 0.5 to 25. When the Si/Al ratio is lower than 0.5, the amount of aluminum exceeds the solid solution WJ range of Sialon, and aluminum compounds are mixed into the powder as impurities. Also this is 2
If it exceeds 5, the reduction/nitriding reaction becomes non-uniform and uniform sialo/powder cannot be obtained.0 The aluminum compounds are ethanol and butanol.

Use alcohol such as propatool or dissolve it in water. Mg02Y2o51Zro2., a sintering aid with a particle size of 1 micron or less, is added to this solution. One or more lanthanide metal oxides are dispersed or the sulfates, chlorides, nitrates or alkoxides of these metals are dissolved. The amount of the sintering aid and its salts is such that the oxide after powder synthesis is 0.1
The content is set within the range of ~10% by weight. The amount of sintering aid is 0. If lNff is less than 1%, there will be no effect on sintering, and if it exceeds 10'3% by weight, the high temperature strength and oxidation resistance of the sintered body will decrease.

Carbon fine particles of 0.1 micron or less are dispersed in silicate alkoxide using ultrasonic vibration or the like. A solution of an aluminum compound in which the above-mentioned sintering aid is dispersed or a salt of the sintering aid is dissolved is added to this. If the aluminum compound solution is an aqueous solution, add acid or #X group after mixing,
Complete the reaction. The reaction is the hydrolysis of silicon alkoxide and the production of aluminum hydroxide from an aluminum solution.

If the sintering aid salts are dissolved in the solution, they will co-precipitate as oxides or hydroxides during the reaction.

If the solution of the aluminum compound is an organic solution, after mixing with silicon alkoxide in which carbon is dispersed,
Add 4 times as much distilled water and then add an acid or base solution to hydrolyze the silicon alkoxide and produce aluminum hydroxide.

The resulting precipitate is so fine that it is difficult to separate it from the solution by ordinary filtration. Therefore, spray dryer or force [
1. A convenient method is to evaporate the liquid using heat.

The precipitate consists of uniform particles of 0.01 to 0.1 micron and is amorphous both in X-ray and electron beams. According to chemical analysis, the atomic ratio of 5j7At matches the atomic ratio of the raw material within a range of ±2%.

When the precipitate is heated, water is released at 400 to 700° C., resulting in an amorphous silica-alumina-carbon-sintering aid mixed powder. When this powder is heated as it is or after molding in a nitrogen stream, reduction and nitriding reactions occur, resulting in a powder in which the β-sialon powder and the sintering aid are uniformly mixed.

The car punch necessary for the reduction/nitriding reaction is the Si/Si powder in the powder.
It varies depending on the Al ratio.

When Si/l = 1: 3 (25in2・A1205) + 150 +
5N2-+ 23i, A7303N5+ 15CO-=
=-Bel) S co/Al=3 case 3 (65in2・At,,o,) + 39Cj +
13N2443i4.5Al,,0. ．． 5N6.5
+39GO・-Curve (2) The amount of carbon to be dispersed in the silicon alkoxide is 1 to 1 of ■) shown in the above representative formula.
Three times the amount is the Kaburato. If the amount of carbon is less than 1 time, the reaction will not be completed and the oxide will remain as an unreacted product. When the amount of carbon exceeds three times, silicon carbide is also generated at the same time.

Heating temperature is 1350-1550℃, 1400℃ for 9 years
~1500°C. If the temperature is lower than 1350°C, it will take a long time to complete the reaction, which is not practical. When the temperature exceeds 1550°C, scattering of raw materials and generation of silicon carbide occur. Baking time is 0.5~
It takes 50 hours, but it takes a long time at low temperature.

5-20 hours at 1400℃, 1-5 hours at 1soo℃
The time is appropriate.

Most of the particles of the obtained powder are fine particles with a particle size of 0.3 to 0.5 microns, and the β-sialon powder and the sintering aid are uniformly mixed.

After molding, this powder is heated to 1700-1800℃ in a nitrogen stream.
A sintered body is obtained by heating to .

Example 1 Carbon black 67 with an average particle size of 0.05 microns was dispersed in butyl silicate 535', aluminum nitrate (nonahydrate) 252 and yttrium ethoxide 0.8
200 CC of isopropanol in which 7 was dissolved was added.

To this solution, 200 CCr of distilled water and 100 cc of aqueous ammonia solution (so%) were added dropwise. This was heated at 80° C. and maintained for 8 hours to complete the formation of a precipitate. After cooling, the pressure inside the container was reduced to 100 Torr and the liquid was removed by gradually heating it to 90°C. The obtained precipitate was a homogeneous mixture of fine particles with a particle size of 0.01 to 0.05 microns.

These powders o and sy are put into a mold with a diameter of 12 mm at a rate of 300Kf/
A force was applied to Cm2 to make a pellet. The pellets were placed in an alumina boat and heated at 1450° C. for 8 hours in a nitrogen stream. The obtained powder was fine particles with an average particle size of 0.7 microns, and consisted of a glass phase containing β-xialon and 3.2 ft% of ittria.

This was first molded in a mold with a diameter of 16 mm at a pressure of 200 K17 cm2, and then molded with a rubber press at 2 jon/'Cm2 to form a pellet. This pellet was held at 1750° C. for 1 hour in a nitrogen stream to obtain a high-density sintered body with a porosity of 066%.

Example 2゜To ethyl silicate42) in which carbon black with an average particle size of 0.05 micrometers was dispersed, an aluminum compound was dissolved in 150 cc of distilled water, and then a solution in which a sintering aid was dispersed was added to form a precipitate. was generated. The aluminum compound and its amount ↑ the sintering aid and its amount and the carbon amount are as shown in Table 1 below.

The resulting precipitate was heated in the same manner as in Example 1 at the temperature and time shown in Table 1. The obtained powder was a uniform powder with an average particle size of 1 micron or less.

Example 36 Aluminum nitrate (9
Hydrate) 222 and a specified amount of sintering aid salt with distilled water 150
Added to solution in CC. Add 30 cc of 2N hydrochloric acid aqueous solution to this mixed solution, heat at 80°C for 4 hours,
The hydrolysis of ethyl silicate and the formation of a precipitate of compounds containing aluminum and sintering aids were completed. The solution containing the precipitate was centrifuged to collect the precipitate, and this was mixed with 150% distilled water.
cc was added and centrifuged again, and this operation was repeated three times.

After drying the obtained precipitate by keeping it at 90°C for 10 hours,
It was heated in the same manner as in Example 1 to perform ÷4 sintering. The results were as shown in Table 2.

The obtained sintered body had a high density porosity of 1.2% JJT.

Table 2 Effects of the Invention According to the method of the present invention, fine and uniform raw material powder can be obtained by the reaction of silicon alkoxide in which fine carbon powder is dispersed and a solution of an aluminum compound containing a sintering aid or its salt. By heating this in a nitrogen stream, a β-sialon powder having a particle size of 1 micron or less and uniformly mixed with a sintering aid is obtained.

Therefore, even by pressureless sintering, a dense sintered body with a porosity of 2% or less can be obtained, which is an excellent effect. Moreover, since the synthesis reaction can proceed uniformly without using a β-valent aluminum alkoxide, the β-sialon powder in the region where solid solution of aluminum is small can be easily produced at low cost.11. It also has the effect of

Hair permit applicant: Fuji Ushigo, Science and Technology Agency, Musashi Materials Research Institute
Excellent

Claims (1)

[Claims] 1) An aluminum compound solution and a sintering aid or salts of a sintering aid are added to silicon alkoxide in which carbon powder with a particle size of 0.1 micron or less is dispersed, and a precipitate is produced by the reaction. A method for producing easily sinterable β-sialon fine powder, which comprises heating the above to 1,350 to 1,550°C in a nitrogen stream. 2) The method for producing easily sinterable β-sialon fine powder according to claim 1, wherein the mixing ratio of silicon alkoxide and aluminum compound is Si/Al=0.5 to 25 in atomic ratio.