JPH0535102B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing dense polycrystalline MgAl ₂ O ₄ spinel, and specifically relates to a high temperature viewing window, an infrared transmitting window, a viewing window for chemical engineering, This invention relates to a method for producing dense polycrystalline MgAl ₂ O ₄ spinel, which is suitable as a base material for high-pressure sodium discharge lamps and the like.

[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 MgAl ₂ O ₄ spinel has been developed as a type of such translucent ceramics. . This transparent MgAl ₂ O ₄
Spinel is a cubic sintered body with a light transmittance of 70
It is about %.

By the way, in order to make ceramics into a transparent material, it is necessary to sinter it extremely densely, so methods for producing transparent ceramics include high-temperature sintering and the use of sintering aids (hereinafter simply referred to as aids). ) or a superpressure sintering method is adopted. For example, methods for manufacturing translucent MgAl ₂ O ₄ include sintering at a high temperature near its melting point (approximately 2015°C), or adding an auxiliary agent such as CaO to the raw material powder as shown in Figure 1. powder 0.2~0.6
After adding weight% and mixing, calcining, crushing, and forming, after processing if necessary, calcining in an _H2 furnace or vacuum furnace,
It is then produced by main firing at 1700 to 1900°C for 5 to 20 hours.

[Problems to be Solved by the Invention] As described above, when producing dense MgAl ₂ O ₄ spinel with transparency without using a sintering aid, firing at an ultra-high temperature is required. , which 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
It is extremely difficult to uniformly mix the raw material powder and the auxiliary powder because the particle size is as small as about 1 μm and the amount of the auxiliary powder added is very small. 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 super pressurization of about 1000 to 1100Kg/ ^cm2 ,
By firing at a low temperature of about 1000-1300℃,
It is possible to obtain a dense sintered body, but in this case, super pressurized equipment is required, leading to problems such as larger equipment and more complicated maintenance management, which increases manufacturing costs. There is.

[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. By adding and mixing Al ₂ O ₃ produced by the alkoxide method as an ultrafine powder auxiliary to MgAl ₂ O ₄ obtained by sintering, dense polycrystalline MgAl ₂ can be easily produced at low temperatures and in a short time. The present invention was completed by discovering that O ₄ spinel can be produced.

That is, the present invention provides high-purity products obtained by calcining an alkoxide coprecipitate.
Dense polycrystalline MgAl ₂ O ₄ spinel is produced by mixing ultrafine Al ₂ O ₃ particles obtained by the alkoxide method with the MgAl ₂ O ₄ raw material, molding this mixture, and then firing it in a vacuum or hydrogen atmosphere. The gist is the manufacturing method.

The present invention will be explained in detail below.

In the present invention, high purity MgAl ₂ O ₄ is used as the MgAl ₂ O ₄ raw material. As the high-purity MgAl ₂ O ₄ raw material, a high-purity product with a purity of 99.9% or more is preferable.

Such high purity used in the present invention
The MgAl ₂ O ₄ raw material is produced by calcining a coprecipitate obtained by an alkoxide coprecipitation method. Specifically, a metal alkoxide solution as a raw material is hydrolyzed by a conventional method, and the resulting coprecipitate is heated at, for example, 400 to 800°C.
It is calcined to a certain degree. In this case, the raw material
As Al and Mg alkoxides, Al and Mg methoxide, ethoxide, isopropoxide, butoxide, etc. are used. The alkoxide used preferably has a low impurity content. These alkoxides are dissolved and mixed in an organic solvent such as benzene, toluene, xylene or alcohol.

In the present invention, the MgAl ₂ O ₄ raw material is preferably a powder with an average particle size of about 0.1 to 44 μm, particularly about 0.5 μm.

In addition, in the present invention, the ultrafine particles Al ₂ O ₃ obtained by the alkoxide method used as a sintering aid are those obtained by crushing and calcining the powder obtained by hydrolyzing Al alkoxide as necessary. is used. This ultrafine particle Al ₂ O ₃ has a particle size of 10 to 1000 Å
Ultrafine particles are preferred.

In the present invention, first, the above-mentioned MgAl ₂ O ₄ raw material is added.
Add and mix Al ₂ O ₃ auxiliary agent wet or dry.
The amount of Al ₂ O ₃ auxiliary added is 3 to MgAl ₂ O ₄ raw material.
~50% by weight, especially 10-50% by weight.

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~
Approximately 1500Kg/cm ² is suitable.

This molded body is then fired in a vacuum or hydrogen atmosphere. This firing is preferably carried out at 1500 to 1800°C for about 3 to 10 hours, particularly preferably at 1700 to 1800°C for about 3 to 5 hours. Note that it is preferable to perform calcination prior to this firing. Calcination at 1000-1200℃
It is preferable to carry out the heating for about 1 to 5 hours. This calcination is also preferably carried out in vacuum or in a hydrogen atmosphere, but other atmospheres may be used.

Polycrystals obtained by such a method of the present invention
MgAl ₂ O ₄ 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, an active surface, and high purity.

Therefore, according to the present invention, a high-purity raw material is obtained by calcining a coprecipitate obtained by an alkoxide coprecipitation method.
By adding and mixing ultrafine particles of Al ₂ O ₃ obtained by the alkoxide method to MgAl ₂ O ₄ ,
There are ultrafine powder particles between the particles of MgAl ₂ O ₄ raw material powder.
Since Al ₂ O ₃ becomes uniformly distributed, it becomes possible to obtain a uniform and dense sintered body at a low firing temperature.

Further, 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, making it easy to implement.

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

Example 1 High purity MgAl ₂ O ₄ obtained by calcining a coprecipitate obtained by an alkoxide coprecipitation method with an average particle size of 0.5 μm
(purity 99.9% or more) 95 parts by weight and Al ₂ O ₃ fine particles (particle size 10-100 Å) produced by the alkoxide method
5 parts by weight were dry mixed in a pot mill. The obtained mixed powder was press-molded at 1000Kg/ ^cm2 , and this compact was calcined in a hydrogen furnace at 1000℃ for 1 hour, and further heated at 1800℃.
The main firing was carried out for 3 hours to obtain a sintered body.

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

Density: 3.78Kg/cm ³ Bending strength: 40.0Kg/mm ² Thermal shock resistance: Rapid cooling at 260°C Light transmittance: 96% From these results, the present invention shows that the present invention has been made extremely dense, has high translucency, and has good mechanical properties. It is clear that excellent MgAl ₂ O ₄ spinel can be easily obtained in a short time.

[Effect of the invention] As detailed above, the dense polycrystal of the present invention
The method for producing MgAl ₂ O ₄ spinel is to add and mix Al ₂ O ₃ ultrafine particles obtained by the alkoxide method to high-purity MgAl ₂ O ₄ raw material obtained by calcining an alkoxide coprecipitate. The mixture is molded and fired, and since the Al ₂ O ₃ ultrafine particles work well as a sintering aid, an extremely dense sintered body can be obtained in a short time by firing at a low temperature. However,
The polycrystalline MgAl ₂ O ₄ spinel produced by the present invention has high translucency, excellent mechanical properties such as strength and thermal shock resistance, and excellent chemical stability, and can be used as a high-temperature observation window, an infrared transmission window, It is extremely useful industrially as a base material for chemical engineering viewing windows, high-pressure sodium discharge lamps, etc.

[Brief explanation of the drawing]

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

Claims (1)

[Claims] 1 Ultrafine particles of Al ₂ O ₃ obtained by the alkoxide method are mixed with a high-purity MgAl ₂ O ₄ raw material obtained by calcining an alkoxide coprecipitate, and this mixture is molded and then vacuum Or, a method for producing dense polycrystalline MgAl ₂ O ₄ spinel, characterized by firing in a hydrogen atmosphere. 2. Dense polycrystalline MgAl ₂ O ₄ according to _claim 1, characterized in that the amount of ultrafine particles Al ₂ O ₃ added to the MgAl 2 O ₄ raw material is 3 to 50% by weight.
How to make spinel. 3. The method for producing dense polycrystalline MgAl ₂ O ₄ spinel according to claim 1 or 2, characterized in that the average particle size of the ultrafine particles Al ₂ O ₃ is 10 to 1000 Å.