JPH0412063A - Production of oxynitride - Google Patents

Abstract

PURPOSE:To readily obtain oxynitride ceramic having excellent hardness, heat resistance, corrosion resistance, elasticity, etc., by hydrolyzing a silicon alkoxide, subjecting to polycondensation to give an oxide gel, drying the oxide gel under a supercritical state to give aerosol and nitriding in an ammonia flow. CONSTITUTION:A raw material comprising a silicon alkoxide (e.g. tetramethoxysilane) as a main component optionally blended with another alkoxide, etc., is hydrolyzed and subjected to polycondensation to produce an oxide gel. Then the oxide gel is dried under a supercritical state to give aerosol. Then the aerosol is burnt in an ammonia flow and nitrided to give oxynitride ceramic. The prepared oxynitride ceramic is suitably used as oxynitride glass, filter material, heat insulating material, etc.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing oxynitride ceramics, and in particular, by nitriding and firing a gel obtained by hydrolyzing a metal alkoxide, heat-resistant The present invention relates to a method for producing oxynitride ceramics containing oxynitride glass that has excellent properties such as hardness, corrosion resistance, elastic modulus, and hardness.

[Conventional technology]

Conventionally, oxynitride glass is AIN, 5i3N
A melting method is known in which nitrogen compounds such as a and BN are melted together with oxide ceramics.

Although this method is simple, it has the following problems.

■ Requires high temperature for melting and homogenization.

■ The melting atmosphere must have a low oxygen partial pressure to prevent oxidation of the glass.

■ It is necessary to select a non-reactive crucible material.

■ The types of nitrides that serve as nitrogen sources are limited, and the composition is restricted.

In recent years, a method applying the sol-gel method has been proposed as a solution to the above-mentioned problems.

This is a method in which the gel obtained by hydrolyzing metal alkoxide is nitrided and fired in an ammonia stream to form oxynitride glass. Although a large amount of nitrogen is introduced, it is not possible to increase the amount of nitrogen introduced in bulk materials such as plate-shaped and rond-shaped materials.

[Problem to be solved by the invention]

A sol with the potential for low-temperature processes with few restrictions on composition.
The purpose of this project is to develop a technology that can increase the amount of nitrogen introduced even in bulk form in a method of manufacturing oxynitride ceramics including oxynitride glass by applying the gel method.

[Means to solve the problem]

The present invention uses silicon alkoxide as a main raw material, subjects the raw material to a hydrolysis reaction, and polycondenses the resulting oxide gel, which is then dried under supercritical conditions to obtain an aerogel. The present invention is a method for producing oxynitride ceramics characterized by nitriding with nitridation, and thereby the above-mentioned problems can be solved.

The silicon alkoxide used as the main raw material in the present invention includes, in addition to the usual alkoxide represented by the general formula Si (OR) 4 (R: alkyl group), R+4
−． 1) St(OR')n (R″: alkyl group, R:
It is also possible to use alkoxides with alkyl or aryl groups (n = 1 to 3), especially in the case of a multi-component system, by keeping the nitriding temperature relatively low and introducing nitrogen before the densification of the gel. This is extremely useful.

In the above compounds, the alkyl group or aryl group represented by R and R' includes methyl, ethyl, n-propyl, i-propyl, etc.
Phenyl group is common, and specific examples of the above compounds include tetramethoxysilane, tetraethoxysilane,
Examples include methyltriethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, dimethyljethoxysilane, trimethylmethoxysilane, trimethylethoxysilane, phenyltrimethoxysilane, and phenyltriethoxysilane. One or more types may be used. Moreover, these silicon alkoxides may be oligomers that have been polycondensed in advance.

In addition to the silicon alkoxide described above, other metal alkoxides may be used as starting materials, if necessary.

The metal alkoxide used here has the formula -C M (OR
) rl (M: metal or metalloid element, R: alkyl group,
n: valence of metal or metalloid element), and R is methyl, ethyl, n-propyl, 1
so-propyl, n-butyl, sec-butyl, tert
-butyl etc. are exemplified. In addition, metals or metalloid elements include A1, Zr, Ti, B, Ge, Be,
Examples include Mg and Y. Here, semimetal means an element near the boundary with metal elements on the periodic table, and B
, Si, Ge, As, etc. are exemplified.

As starting materials, in addition to the various metal alkoxides mentioned above, it is also possible to add metal element components as a compounding process other than metal alkoxides, examples include the use of simple metals, acetates, chlorides, nitrates, etc. These may or may not be hydrolyzable, but it is preferable that components other than ceramic components remain as little as possible after firing.

It is possible to apply a known method to obtain a gel by subjecting silicon alkoxide as the main raw material to a hydrolysis reaction and polycondensation. It is preferable to carry out the reaction in the presence of an organic solvent. The organic solvent used here is preferably one that dissolves silicon alkoxide and other additive components, specifically methanol, ethanol, n-propanol, 1so-propatool, 5
Examples include alcohols such as ec-butanol, aromatic hydrocarbons such as toluene, benzene, and xylene, tetrahydrofuran, dimethylformamide, and carbon tetrachloride. Alcohols with relatively low boiling points such as methanol and ethanol are preferred from the viewpoint of supercritical drying.

Further, the amount of water used for hydrolysis is not particularly limited, and in order to obtain a gel with good reproducibility in a relatively short period of time, water is used in an amount of 2 moles or more of the metal alkoxide such as silicon alkoxide used.

In addition, to accelerate hydrolysis and polycondensation, hydrochloric acid, nitric acid,
Acids such as sulfuric acid, or bases such as ammonia, trimethylammonium, pyridine, piperidine, hydroxide, etc. may be used as catalysts.

The wet gel thus obtained is made into a dry gel, ie, an aerogel, by replacing the organic solvent contained in the gel with gas under supercritical conditions. On this occasion,
Although it is preferable to use the organic solvent used in gel synthesis as it is and dry under supercritical conditions, it may be replaced with a solvent suitable for the treatment before supercritical drying.

This supercritical drying process involves immersing the single component used or replaced in an organic solvent close to the critical temperature of that solvent in a high-pressure vessel.
A method to obtain an aerogel by removing the solvent under so-called supercritical conditions above the critical pressure, and using other low boiling point gases, such as COX.
One method is to use gas, Freon gas, etc. in combination to create a two-component system or a multi-component system, and then remove the solvent under supercritical conditions in the multi-component system to obtain an airgel, but there are no particular restrictions on this method. do not have.

Oxynitride ceramics can be converted into oxynitride ceramics by firing the obtained airgel in an ammonia stream.

The firing conditions vary depending on the composition of the airgel, but 400
A temperature range of .degree. C. or higher, preferably 500.degree. C. or higher is exemplified, and the firing time is not particularly limited, but is appropriately set depending on the required amount of nitrogen introduced and the nitriding temperature.

This ammonia can also be diluted with an inert gas such as nitrogen, helium, or argon.

Further, after firing in ammonia and nitriding, in order to eliminate remaining fine pores, firing may be performed in a gas with a fast diffusion rate such as hydrogen or helium, as is usually done in sintering ceramics.

In addition, the porous material with complete density and nitrogen introduced may be used as a filter material, a heat insulating material, a heat resistant material, and the like.

[Function] The nitriding reaction of oxide gel is basically a solid/air reaction, and the fine pores close before the temperature range where nitriding progresses.
It is thought that when the material becomes a dense material, nitridation becomes extremely difficult to proceed. Airgel obtained using silicon alkoxide as the main raw material has a high specific surface area and relatively large pore diameter, so it is thought that it has a high specific surface area even in the nitriding temperature range, making it possible to introduce a high concentration of nitrogen.

〔Example〕

Hereinafter, specific examples of the present invention will be described, but the present invention is not limited thereto.

Example 1 Oricomer-39 of tetraethoxysilane with an average degree of polymerization of 4
, 8 parts by weight, 50.0 parts by weight of ethanol, 9.7 parts by weight of water, 0.8 parts by weight of piperidine. 5 parts by weight were uniformly mixed, placed in a container, and gelatinized at 60°C.

This wet gel was aged for two weeks, the solvent was replaced with methanol, and the gel was subjected to supercritical drying. Supercritical drying is performed in a CO7-methanol system at 80°C1160 while circulating CO2.
The test was carried out under the condition of kg/cifl. The specific surface area of the obtained silica airgel was 552 rrf/g, and the BET pore size peak (direct was 180 rrf/g).

This airgel was heated at an ammonia flow rate of o, sp < i min for 12 min.
It was nitrided and fired at 00°C for 13 hours. The amount of nitrogen introduced is 21. ．．
An extremely high concentration of nitrogen was introduced at 9eytχ.

The fired product is X-ray amorphous and 31
It was a porous body having a specific surface area of 4 rrK/g.

Comparative Example 1 A wet gel was obtained in the same manner as in Example 1. The container containing this gel was covered with aluminum foil, a pinhole was made, and the container was dried at 60° C. under normal pressure for 30 days to obtain a xerogel. The BET specific surface area was 512%/g, and the liver T pore diameter peak value was 65.

This xerogel was nitrided and fired under the same conditions as in Example 1. The amount of nitrogen introduced is 1. The amount was as small as 1% by weight.

Example 2 The airgel of Example 1 was nitrided and fired at 1400° C. for 13 hours at an ammonia flow rate of 0.52/min. The amount of nitrogen introduced is 30
．． Nitrogen was introduced at an extremely high concentration of 4% by weight. Also,
The fired product is X-ray amorphous, and has a 242.8i
It was a porous body with a specific surface area of /g.

Example 3 A mixture of 2 moles of water acidified with 1N hydrochloric acid and 1 mole of ethanol was added to a mixture of 1 mole of dimethyljethoxysilane, 1 mole of tetraethoxysilane, and 4 moles of ethanol, and silicon alkoxide was partially hydrated. Disassembled.

To this, 0.2 mol of tetraethoxytitanium and 1 mol of ethanol
After adding a molar mixture and mixing uniformly, a mixture of 6 moles of water and 2 moles of ethanol, which had been acidified with 1N hydrochloric acid, was added to form a gel.

This wet gel was supercritically dried under the conditions of 80'C and 160 kg/c+fl while circulating CO□ in a CO2-ethanol system to obtain an airgel. The specific surface area of this airgel was 531 rrf/g.

This airgel was heated to 800 ml at ammonia flow rate of 0.51/min
Nitriding was performed for 13 hours. 7.2% by weight of nitrogen was introduced.

〔Effect of the invention〕

According to the present invention, oxynitride ceramics with expected properties such as hardness, strength, elastic modulus, heat resistance, and corrosion resistance can be produced by an easy method.
It becomes possible to manufacture with fewer restrictions on composition. In addition, it is possible to produce porous oxynitride bodies that could not be obtained using conventional methods, and it is also possible to make dense bodies by controlling the amount of nitrogen introduced and the heating temperature. This is an extremely useful manufacturing method.

Claims (1)

[Claims] Using silicon alkoxide as the main raw material, subjecting the raw material to a hydrolysis reaction and polycondensing it, drying the resulting oxide gel under supercritical conditions to obtain an aerogel, and nitriding the aerogel under an ammonia stream. A method for producing oxynitride ceramics characterized by: