JPS6272556A - Manufacture of fine polycrystal mgal2o4 spinel - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing dense polycrystalline M g A l 2O4 spinel, and more particularly, to a high temperature viewing window.

Dense polycrystalline M g A l suitable as a base material for infrared transmission windows, viewing windows for chemical engineering, high-pressure sodium discharge lamps, etc.
The present invention relates to a method for producing 2O4 spinel.

[Prior Art] In recent years, attempts have been made to make various high-melting point oxide sintered bodies transparent as heat-resistant transparent materials, and MgA12O4 spinel has been developed as a type of such translucent ceramics. There is. This translucent M g A 1 2 O 4 spinel is a cuboidal sintered body, and its light transmittance is about 70%.

By the way, in order to make ceramics into translucent bodies, methods for manufacturing translucent ceramics include high-temperature sintering, methods using sintering aids (hereinafter sometimes simply referred to as aids), or For example, the ultra-pressure sintering method is adopted.
Translucent M g A l 2O4 can be produced by sintering it at a high temperature near its melting point (about 15°C), or by adding an auxiliary powder such as CaO to the raw material powder, as shown in Figure 1. Add and mix 0.2 to 0.6% by weight, calcinate,
After pulverization and molding, after processing if necessary, calcining in an H2 furnace or vacuum furnace, then heating at 1700-1900℃ for 5-2O
Manufactured by firing for hours.

[Problem to be solved by the invention J As described above, when producing a dense M g A l 2O4 spinel with transparency without using a sintering aid, it is necessary to sinter it at an ultra-high temperature. It was industrially disadvantageous. Further, by using a sintering aid, the firing temperature can be lowered, but in this case, there is a problem in mixing the raw material powder and the aid powder. That is, these powders usually have a fine particle size of about 0.5 to IILm, and since the amount of auxiliary powder added is very small, it is difficult to uniformly mix the raw material powder and the auxiliary powder. This is extremely difficult. Moreover, since the contact area with each other is extremely small, the effect of adding the auxiliary agent may not be fully exhibited.

In addition, under ultra-fine pressure of about 1000 to 1100 Kg/cm', it is possible to obtain a dense sintered body by firing at a low temperature of about 1000 to 1300 °C; This method requires equipment, which causes problems such as increased equipment size and complicated maintenance management, and has the disadvantage that manufacturing costs are high.

[Means for Solving the Problems] As a result of various studies in order to solve the problems of the above-mentioned conventional methods, the present inventors focused on ultrafine particles produced by the alkoxide method. M obtained by baking
g A l A produced by the alkoxide method in 2O4
By adding and mixing fL2O3 as an ultrafine powder auxiliary agent, dense polycrystalline Mg can be easily formed at low temperatures and in a short time.
The present invention was completed by discovering that it is possible to produce A2O4 spinel.

That is, the present invention provides a dense molded product characterized by mixing ultrafine particles A fL2O3 obtained by an alkoxide method with a high-purity MIIA12O4 raw material, molding this mixture, and then calcining it in a vacuum or hydrogen atmosphere. Polycrystalline M 11 A l 2O4
The gist is a method for manufacturing spinel.

The present invention will be explained in detail below.

In the present invention, high purity M g A l 2 O4 is used as the MgA exchange 2 O4 raw material. High purity MgAl2O
The four raw materials are preferably highly purified products with a purity of 99.9% or more.

One such high-purity M 11 A 1 2 O 4 raw material includes M g A 1 2 O 4 obtained by calcining a coprecipitate obtained by an alkoxide coprecipitation method. this is,
The metal alkoxide solution as a raw material is hydrolyzed by a conventional method, and the resulting coprecipitate is heated at 400 to 00°C, for example.
F-grilled 1. In this case, the raw material A! L and M
g alkoxides include An and Mg methoxide;
Ethoxide, impropoxide, butoxide, etc. are used. The alkoxides used preferably have a low impurity content, and these alkoxides are dissolved and mixed in an organic solvent such as benzene, toluene, xylene or alcohol.

In the present invention, the MgA exchange 2O4 raw material has an average particle size of 0.
．． A powder of about 1 to 44 #Lm, especially about 0.5 JLm, is preferred.

In addition, in the present invention, the ultrafine particles A l 2O3 obtained by the alkoxide method used as a sintering aid are those obtained by crushing and calcining the powder obtained by hydrolyzing the alkoxide of Ai as necessary. used. The ultrafine particles Al2O:1 preferably have a particle size of 10 to 100OA.

In the present invention, first, the above A! is added to the M g A l 2O4 raw material. Add and mix the L2O3 auxiliary agent wet or dry.

The amount of the A2O3 auxiliary agent added is preferably 3 to 59% by weight, particularly 10 to 50% by weight, based on the MgA2O4 raw material.

The obtained mixture is molded by a molding method such as pressure molding, but in the case of pressure molding, the molding pressure is 700 to 1500 kg.
/Cm” is suitable.

This molded body is then fired in a vacuum or hydrogen atmosphere. This firing is preferably carried out at 1500-1800°C for about 3-10 hours, particularly preferably at 1700-1800°C for about 3-5 hours.

It is preferable to perform calcination prior to this firing.

Preferably, the calcination is carried out at 1000-1200C for 1 to 5 hours. This calcination is also preferably carried out in vacuum or in a hydrogen atmosphere, but other atmospheres may be used.

Polycrystalline MgA obtained by such a method of the present invention
The l2O4 spinel is extremely dense and has excellent translucency.

[Function] Generally, the powder obtained by the alkoxide method or the alkoxide coprecipitation method has a small particle size, one surface is active, and high purity.

For this reason, according to the present invention, high purity raw material M g is obtained by calcining a coprecipitate obtained by, for example, an alkoxide coprecipitation method.
Ultrafine particles A obtained by the alkoxide method on A l 2O4! By adding and mixing 12o3, MgA
l2O<Al2O3 of ultrafine powder between particles of raw material powder
is distributed uniformly, making it possible to obtain a uniform and dense sintered body at a low firing temperature.

Moreover, the process of the method of the present invention is as shown in route A in FIG. 1, and various operations in the middle of the conventional method can be omitted, and implementation is easy.

[Examples] The present invention will be explained in more detail by examples below.
The present invention is not limited to the following examples unless it exceeds the gist thereof.

Example 1 High purity M g A l 2O with an average particle size of 0.51 Lm
4 (purity 99.9% or higher) and 95 parts by weight of k12Oa* particles (particle size 1O~1OO) produced by the alkoxide method.
A) 5ff=ffi parts were dry mixed in a pot mill. The obtained mixed powder was press-molded at 1000 kg/crn', and the compact was placed in a hydrogen furnace.

It was calcined at 0C for 1 hour and then unfired at 1800C for 3 hours to obtain a sintered body.

When various physical property values of this sintered body were measured, they were as follows.

Density: 3.78Kg/crn" Bending strength: 40.OKg/mm' Thermal shock resistance: 260
°C quenching light transmittance: 96% From these results, it is clear that according to the present invention, M g A l 2O4 spinel that is extremely dense, has high translucency, and has excellent mechanical properties can be easily obtained in a short time. .

[Effect of the invention] As described in detail 4 above, the dense polycrystalline M g A of the present invention
The method for producing l2O4 spinel is to use high-purity MgA
l 2O4 raw material, A obtained by the alkoxide method
By adding and mixing the Al2O3 ultrafine particles, the obtained Al2O3 ultrafine particles act well as a sintering aid, so an extremely dense sintered body can be obtained in a short time by low temperature firing. Therefore, one polycrystalline M g A Jl produced according to the present invention
2O4 spinel has high translucency, excellent mechanical properties such as strength and thermal shock resistance, and excellent chemical stability, and is used for high-temperature viewing windows, infrared transmission windows, chemical engineering viewing windows, high-pressure sodium discharge lamps, etc. It is extremely useful industrially as a base material.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of a conventional manufacturing process of translucent ceramics.

Claims (4)

[Claims] (1) A method for producing dense polycrystalline MgAl_2O_4 spinel, which is characterized by mixing ultrafine particles of Al_2O_3 obtained by an alkoxide method with a high-purity MgAl_2O_4 raw material, molding this mixture, and then firing it in a vacuum or hydrogen atmosphere. (2) The method for producing dense polycrystalline MgAl_2O_4 spinel according to claim 1, wherein the MgAl_2O_4 raw material is a calcined alkoxide coprecipitate. (3) Ultrafine particle Al_ for MgAl_2O_4 raw material
The method for producing dense polycrystalline MgAl_2O_4 spinel according to claim 1 or 2, characterized in that the amount of 2O_3 added is 3 to 50% by weight. (4) The average particle size of ultrafine particles Al_2O_3 is 10 to 10
Dense polycrystalline MgA according to any one of claims 1 to 3, characterized in that the particle size is 00 Å.
Method for manufacturing l_2O_4 spinel.