JPS60260407A - Manufacture of alpha-silicon nitride - Google Patents

Abstract

PURPOSE:To obtain fine alpha-silicon nitride powder of high grade in a high yield by mixing silicon oxide powder with specified amounts of carbon powder and beryllium or the like and heat treating the mixture in an atmosphere contg. nitrogen to reduce and nitride the silicon oxide. CONSTITUTION:To 1pt.wt. of silicon oxide powder are added 0.4-4pts. carbon powder and at least one kind component selected among Be, Sr, Sn, Ge, Ti, Hf and compounds thereof as a catalyst by 0.001-0.1pt. (expressed in terms of Be, Sr, Sn, Ge, Ti and Hf). The mixture is heat treated at about 1,300-1,500 deg.C in an atmosphere contg. nitrogen to manufacture alpha-silicon nitride by reduction and nitriding. In order to remove the remaining carbon, the reaction product is preferably heat treated at about 600-800 deg.C in an oxidizing atmosphere.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing α-type silicon nitride (α-5i3N4) fine powder, and provides a manufacturing method for obtaining high-grade, fine α-type silicon nitride fine powder with high yield. .

Silicon nitride has excellent heat resistance and high-temperature strength, and as a sintered body, it can be used as a high-strength heat-resistant material and a high-precision wear-resistant material, making it possible to achieve higher temperatures, lighter weight, and higher efficiency in heat engines such as diesels and gas turbines. It is expected to be used as a material. The thermal and mechanical properties of these sintered bodies largely depend on the properties of the raw materials for the sintered bodies. Supply is desired.

Synthesis methods for silicon nitride include (1) Direct nitridation of metal silicon BSi+2N2→5i3N4 (11) Reductive nitridation of silicon oxide 88 i0z+6c+2N2-5i3? t4+6CO) Gas phase synthesis method using silane or silicon tetrachloride 8 S 1) 14+4NH3"Si3N4+ 12H2
8S ic#4+16NHa-=Si3N4+12NH
4C10V) Thermal decomposition method of silicon diimide, silicon tetraamide, etc. 8 Si (NHh-8rs〆4+2NH38S i
(NHz)4-5i3N4+8NH3 and the like are known.

However, method (1) generates a lot of heat in the direct reaction between metal silicon powder and nitrogen gas, making it difficult to control the reaction, and the nitriding reaction proceeds from the metal silicon surface, so it is difficult to synthesize fine silicon nitride powder. There are drawbacks such as the need to use finely powdered silicon metal as a raw material or, in some cases, to pulverize the generated silicon nitride powder (!ii).The OV method uses high-purity fine powder. However, the powder obtained is generally a very fine amorphous silicon nitride powder with a grain size of 100 to 200 years, and it is difficult to use it as a raw material for a sintered body. Furthermore, crystallization is performed by heat treatment at a temperature of 1,300 to 1,500°C in a nitrogen-containing gas atmosphere, but it is difficult to obtain powder with a high ratio of α-type silicon nitride, and it is difficult to control the particle shape. However, method (11) has disadvantages such as high cost.Among these methods, the raw materials can be obtained relatively cheaply.The reaction operation is relatively easy, and there is no risk of corrosion of the equipment or explosion. Do not use dangerous raw materials such as
This is an industrially useful method because silicon nitride with a high type silicon nitride ratio can be easily obtained. However, even if this method uses carefully selected silicon oxide fine powder and carbon powder as raw materials, if the carbon/silicon oxide ratio in the raw materials is small, the nitriding reaction rate is low and unreacted silicon oxide remains. There is a problem, which becomes more pronounced as silicon oxide powder with a larger particle size is used, and is a major obstacle to obtaining α-type silicon nitride at a lower cost.

In the reduction/nitridation reaction of silicon oxide, it is possible to use coarse-grained silicon oxide powder as the raw material, which can be obtained at a lower cost, and to perform the reduction/nitridation reaction under conditions where the carbon/silicon oxide ratio is close to the reaction equivalent. Cheap silicon nitride powder can be synthesized. Therefore, it promotes the nitriding reaction and.

It is important to search for a catalyst that can control the silicon nitride powder, particle size, and shape of the particles produced. The catalyst used in the reaction is preferably a substance that does not remain in the produced silicon nitride powder, or a substance that, even if it remains, acts as an aid during sintering or does not deteriorate the strength of the sintered body.

The inventors of the present invention have been aware of this situation and have carried out various studies, and have found that beryllium, strontium, germanium, tin,
The present invention was accomplished by discovering that by adding titanium, hafnium, or a compound thereof, α-type silicon nitride powder with a high nitridation rate can be obtained in good yield regardless of the particle size of the silicon oxide used.

That is, 1 the present invention includes 1 part by weight of silicon oxide powder, 0.4 to 4 parts by weight of carbon powder, and at least one of beryllium, strontium, germanium, tin, titanium, hafnium, or a compound thereof as a catalyst.
．． 001 to 0.1 heavy part (in terms of beryllium, strontium, germanium, tin, titanium, hafnium elements) is heated in a nitrogen-containing atmosphere to cause a reduction/nitriding reaction of silicon oxide. A method for producing all-silicon nitride (α-3i3N4) fine powder is provided.

The present invention will be explained in detail below.

In the present invention, if the amount of carbon powder added to one weight tS of silicon oxide powder is less than 0.4 parts by weight, the reduction/nitridation reaction formula 8SiO2+6C+2N2→-8isN4+6CO will be less than the amount of reaction, and unreacted 5i02 will remain. On the other hand, if more than 4 parts by weight is added, the reaction yield will decrease and unreacted carbon will increase, making it difficult to remove.
Moreover, the cost is also high. Generally speaking, the amount of carbon powder added is preferably 0.4 to 4 parts by weight, more preferably 0.6 to 1.2 parts by weight.

Beryllium metal, as beryllium or its compounds;
Beryllium oxide, beryllium hydroxide, beryllium fluoride, beryllium chloride, basic beryllium carbonate, beryllium nitrate, beryllium sulfate, beryllium nitride, etc., strontium or metal strontium as its compounds,
Strontium oxide, strontium hydroxide, strontium fluoride% Strontium chloride, strontium carbonate, strontium nitrate, strontium sulfate, strontium isopropoxide, strontium nitride, etc.J Germanium or its compounds include metal germanium, germanium oxide, germanium sulfide, fluoride, etc. Germanium oxide, germanium chloride, germanium ethoxide, germanium nitride, germanium carbide, etc. as tin compounds, tin metal, tin oxide, tin chloride, tin bromide, tin iodide, tin hydroxide, strontium stannate, etc., titanium or its compounds Titanium metal, titanium oxide, titanium chloride,
Titanium hydride, titanium sulfate, titanyl sulfate, titanium fluoride, strontium titanate, titanium nitride, titanium carbide, etc., metal hafnium, hafnium chloride, hafnium carbide, hafnium nitride, etc. can be used as hafnium or its compound.5 Usually, Raw material silicon oxide powder,
Carbon powder and beryllium, strontium, germanium, tin, titanium, hafnium, or their compounds as catalysts are often mixed in a wet ball mill with water added to make the mixture more uniform. Among germanium, tin, titanium, hafnium, and their compounds, it is more suitable to use water-soluble aluminum compounds, strontium compounds, germanium compounds, tin compounds, titanium compounds, and hafnium compounds.

In addition, the substances listed above may be added alone or in combination of two or more, but the amount of addition is based on the heavy state of beryllium, strontium, germanium, tin, titanium, and lithium oxide. It is desirable that the amount is in the range of ~01 parts by weight per part of silicon powder. Addition of less than 0.001 parts by weight has little effect on promoting the nitriding reaction and atomization of the generated α-5i:+N4, while adding more than 0.01 parts by weight reduces the amount of α-5i3N4 produced.
Among them are Be and Sr.

Large amounts of Ge, Sn, 'l'i, Hf, etc. are contained. A more preferable addition amount is 000
The range is from 5 to 0.08 parts by weight.

Along with these catalysts, magnesium, calcium,
Even if zirconium or a compound thereof coexists, the effects of the present invention are not hindered.

These mixtures are heat-treated in an atmosphere containing nitrogen to cause reduction and nitriding reactions, but the atmosphere contains N2, N
A reaction gas system containing nitrogen such as H3*N2-N2, N2-Ar can be used. The heat treatment temperature is 1.800 to 1,500°C, preferably 1,850 to 1.
．． A range of 450°C can be selected. Below 1,300°C, the nitriding reaction does not proceed sufficiently, and above 1,500°C, β-5i
As the ratio of 3Nt increases, the formation of SiC also occurs, which is not a good idea.

Further, it is preferable to perform heat treatment in an oxidizing atmosphere for the purpose of removing residual carbon, and the temperature is generally in the range of 600 to 800°C.

As described above, the present invention uses silicon oxide powder, carbon powder, beryllium, and strontium.

Kermanium, tin, titanium, hafnium, or their compounds are added and mixed, and the resulting mixture is heat-treated in an atmosphere containing nitrogen. Regardless of the particle size of the silicon oxide powder used by this method, When the carbon/silicon oxide ratio is in the range of 04 to 4, it is possible to obtain α-type silicon nitride powder with a high nitrogen content and α-5i 3N4 content. According to the present invention, it is possible to industrially advantageously produce IfA powder rice powder for tLf co-silicon nitride sintered bodies with high heat resistance and high-temperature strength. The present invention is not limited to this.

Example 1 Commercially available silicic anhydride (center particle size 1.7) as silicon oxide powder
μm, BET specific surface area 03I? +'/y) was used. Acetylene black granules were used as the carbon powder. , i, and the catalysts were Be(NO3)2118HzO, Sr(
NO3)2” 4H20, GeO2, 51102.

Ti05O4 and Hf0z were used. Table 1 shows these powders.
After mixing using a wet whole mill in the composition ratio shown in
5102 was dried and heat treated at temperatures of 1,400°C and 1,450°C for 4 to 6 hours while flowing N2 gas.
was reduced and nitrided.

The obtained powder was further heat-treated in air at 800° C. for 4 hours, and unreacted C was burned off to obtain Si3N4 powder. The N content and α5izNi content (determined from the X-ray diffraction diagram) of each of the 513N4 powders synthesized in this manner were measured, and the values are shown in Table 1.

Example 2 The same powder as used in Example 1 was used, except that Nippon Aerosil 200 (center particle size 12 μm, BE′l” specific surface 49200−/y) was used as the silicon oxide powder.
Si3N4 powder was synthesized according to the procedure. For each powder, the N content rate and α-8i3N4 content rate were 5!
21.

Comparative Example 1 Using the same powder as used in Example 1 C), Si3N4 powder was synthesized according to the procedure of Example 1 without adding any catalyst. N content of the obtained powder.

The α-5i3N4 content is also shown in Table 1.

Comparative Example 2 Using the same powder as used in Example 2, the procedure of Example 1 was carried out without adding a catalyst (ζ Therefore, Si3N4 powder was synthesized. The N content and α-5i3N4 content of the obtained powder were It is also shown in Table 1.

Claims (1)

[Claims] (1 part by weight of silicon oxide powder, 0.4 to 4 parts by weight of carbon powder)
At least one of beryllium, strontium, tin, germanium, titanium, hafnium or their compounds is added to the weight part of beryllium, strontium, tin, germanium, titanium, hafnium element, 0 to silicon oxide in terms of elementary weight. .001~0.1
1. A method for producing α-type silicon nitride, which comprises heat-treating a mixture containing parts by weight in an atmosphere containing nitrogen to cause reduction and nitridation of silicon oxide. (To 21) The IJlium compound is one or two selected from beryllium oxide, lithium, beryllium hydroxide, beryllium fluoride, salt, beryllium chloride, basic beryllium carbonate, beryllium nitrate, beryllium sulfate, and beryllium nitride. A method for producing α-type di-silicon nitride according to claim 1, which is the above compound. (3) The strontium compound is strontium oxide,
Claims are one or more compounds selected from strontium hydroxide, strontium chloride, strontium chloride, strontium carbonate, strontium nitrate, strontium sulfate, strontium isopropoxide, and strontium nitride, 2. A method for producing α-type silicon nitride according to item 1. (4i '7' Ruvnium compound is oxidized del manila,
The α-type silicon nitride according to claim 1, which is one or more compounds selected from germanium bersulfide, germanium fluoride, germanium chloride, germanium ethoxide, germanium nitride, and germanium carbide. Manufacturing method. (5) Claims in which the tin compound is one or more compounds selected from tin oxide, tin chloride, tin bromide, tin iodide, tin hydroxide, and strontium stannate. The method for producing α-type silicon nitride according to item 1. (6) The titanium compound is selected from titanium oxide, titanium chloride, titanium hydride, titanium sulfate, titanyl sulfate, titanium fluoride, strontium titanate, titanium nitride, and titanium carbide. The method for producing α-type silicon nitride according to claim 1, wherein the hafnide iJ is selected from hafnium oxide, hafnium chloride, hafnium carbide, and hafnium nitride. The method for producing α-type silicon nitride according to claim 1, wherein the α-type silicon nitride is a compound having one or more properties.