JPS5950068A - Manufacture of high minuteness magnesia sintered body - 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 The present invention relates to a method for producing a highly dense magnesia sintered body that can easily produce a sintered body with a high density.

Magnesia has excellent base resistance at high temperatures of 7,300℃, low dielectric loss at high frequencies, relatively large coefficient of thermal expansion and thermal conductivity, high transmittance of infrared and visible light, and is inexpensive. be.

(1) Therefore, it is widely used as a high-temperature heat-resistant material, a high-temperature insulating material, a high-temperature lighting material, etc., and has also recently attracted attention as a fine ceramic material. In addition, magnesia sintered bodies are dense and have high hot strength for high-temperature heat resistance, hydration resistance and high insulation resistance for high-temperature insulation, and highly dense and light-resistant for high-temperature lighting. It is required to have high transmittance and hydration resistance.

Since magnesia has a high melting point (stood C.), it has been difficult to obtain a highly dense sintered body close to the theoretical density. Especially for high-purity magnesia (more than 99% by weight), it is necessary to obtain a bulk density of about 9S% of the theoretical value.
To obtain a temperature of 00℃ or higher and a bulk density of about 99%, λ
It was necessary to bake at a high temperature of 100° C. or higher for a long time. For this reason, highly dense sintered bodies have been produced in a relatively low temperature range by using the hot press method or sintering aids.

In the hot press method, for example, LiF, NaF, MgF2.
A small amount of fluoride 1 such as HF was added and hot pressed under vacuum. However, this method not only makes it difficult to produce a sintered body of large size or complicated shape, but also requires high-temperature heat treatment after sintering, and has drawbacks such as low productivity and high cost.

Further, as a method of using a sintering aid, magnesia powder or a magnesium compound that generates magnesia by heating, for example, BeO, LiF.

It was fired at temperatures above ℃. In these methods, special care must be taken when preparing B20 due to its significant toxicity. The evaporation of B2O3 over LiF is extremely large, which not only contaminates the inside of the furnace, but also causes the microstructure to become nonuniform because the distribution of additives is not uniform.
C203, Yb2O3, and GeO each have drawbacks such as being relatively expensive. In addition, both require a large amount to be added, which has the disadvantage that the inherent properties of magnesia, such as hot strength, fire resistance, and transparency, are impaired.

1.゛--1.1 The purpose of the present invention is to create a high-purity material that has a bulk density close to the theoretical value and can be used for high-temperature heat-resistant materials, high-temperature insulating materials, high-temperature lighting materials, fine ceramic materials, etc., without the drawbacks of conventional methods. The present invention provides a method for manufacturing a magnesia sintered body.

In the present invention, magnesia powder is added to a solution 1' of a magnesium compound that produces magnesia by heating.
0.003 to 3.3% by weight of aluminum compound (
However, it is added (as Al2O5 to MgOK), and in the air [7! The gist of the present invention is a method for producing a highly dense magnesia sintered body, which is characterized by heat treatment or calcining at 0 to 100°C, followed by shaping and firing at 12so°C or higher.

The magnesia powder used in the present invention or the magnesium compound that produces magnesia by heating is 99.9% by weight.
, preferably with a purity of 99.99% by weight or more. If the purity is low, a glass phase will be formed at the grain boundaries, resulting in disadvantages such as deterioration of the inherent properties of magnesia, such as hot strength, fire resistance, transparency, etc. Particularly, for example, 5in2. OaOI B2
It is important that compounds such as O3, Fe2O, etc. are not included as impurities.

Magnesium carbonate and magnesium carbonate, which produce magnesia when heated, are mentioned. Examples of the solution-form aluminum compound used in the present invention include aluminum chloride, aluminum sulfate, aluminum nitrate, ammonium alum, potassium alum, aluminum alcoholade, etc. can be mentioned. Among these, aluminum chloride and aluminum sulfate are preferable because they provide a high bulk density, can be obtained by lowering the sintering temperature, have a uniform microstructure, and have good translucency.

(j) However, the present invention is not limited to the above-mentioned exemplified compounds; any aluminum compound may be used as long as it is in the form of a solution and supplies alumina by heating.

As a method of adding an aluminum compound in solution form, (1)
Magnesium salts for precipitation reactions, such as magnesium chloride,
A method of adding it to a solution of magnesium sulfate, magnesium nitrate, etc. (For example, when using aluminum chloride, aluminum sulfate, aluminum nitrate, ammonium alum, potassium alum), (2) Method of adding during the progress of the precipitation reaction.

(-For example, when using aluminum Alcolade)
(5) A method of adding magnesia powder or a magnesium compound that produces magnesia by heating into a dispersion medium. (For example, when using aluminum chloride, aluminum sulfate, aluminum nitrate, ammonium alum, or potassium alum). Among these methods, method (1) is the most preferred because it provides uniform dispersion and can yield a translucent magnesia sintered body with a uniform microstructure.

The amount of aluminum compound added is 0.003 to 3.3 parts (
t) The amount ranges from %° (Al2O3 to MgO). 3. If the amount added is less than 0.003% by weight, the effect of the addition is strong. If it exceeds j@wt%, free alumina components will accumulate at grain boundaries, making it impossible to obtain a highly dense product. In this case, the range of O,S to 3.5% by weight provides good density, but the particle size becomes coarse (more than Sθμ) and the strength decreases, so the preferred addition amount is 0.003 to O,S.
is within the range of

When an aluminum compound in solution form is added in the method (1) above, it is baked in a range of 0.003 to 0.3% by weight. , good quality, o, oor-o, o-21% (7)
Transparency pi='4 is the best in the range. Also, (2) and (
When added by method 3), o, os-o, s weight%
It is preferable that it is in the range of .

Heat treatment or calcining of magnesia powder added with an aluminum compound or a magnesium compound that produces magnesia by heating, in air or oxygen atmosphere, 73
It is necessary to carry out at 0-1iooC. When using a magnesium compound, it is preferable to dehydrate it completely at 300 to aOO°C. If the temperature is lower than 730°C, the thermal decomposition will not be sufficient, and if the temperature exceeds 100°C, strong secondary particles will be formed, making it impossible to achieve the object of the present invention.

In this case, basic magnesium carbonate or magnesium carbonate must be calcined and must be heated in air or in an oxygen atmosphere in order to prevent free carbon from remaining. Pressure molding after heat treatment or calcining. This pressure molding may be carried out by a method using an ordinary mold, but it is preferable to further hydrostatic press this.

Molding pressure using metal joints can be applied as long as the molded object does not break.←
It is desirable to be small, and it is desirable for the hydrostatic press to be as large as possible.

Firing after pressure molding may be performed in any of oxidizing, neutral, and reducing atmospheres. However, it is preferable to use it in a vacuum (/θ-3 torr or more) because it has excellent light transmittance. Furthermore, if it is necessary to reduce the particle size, it is preferable to carry out the process in an oxygen atmosphere. The firing temperature is /2! ; at 0°C or higher for 2 hours or more, preferably at 100°C or higher. /
2! ; If the temperature is lower than 0°C, the purpose of firing cannot be achieved. As the sintering method, the industrially simplest method of cold pressing and sintering is sufficient; however, it is more preferable to use an improved sintering method such as vacuum hot pressing or HIP. ' According to the method of the present invention, (1) the firing temperature is 2 times lower than that of the conventional method;
Even though the temperature is as low as jO~3jO<0>C, a magnesia sintered body having a high bulk density, a uniform microstructure, and good translucency can be obtained. (2) Since the sintering temperature can be low, it is economically extremely advantageous in terms of simplification of the material of the sintering furnace, simplification of the furnace structure, energy saving, etc. (5) cvK'A is an inexpensive and safe sintering aid that can be obtained without changing the normal manufacturing process and can be produced using equipment as is. .

A highly dense magnesia sintered body close to the theoretical value can be obtained without sacrificing properties. (5) By changing the amount of the sintering aid added, it has excellent effects such as being able to control the particle size over a wide range without reducing the bulk density of the sintered body.

Example 1 (9) ・MgO in a magnesium chloride solution of Q,≠14/l
ni', vs. le Al2O5 as o, oor v amount % (g
o ppm). /M amount% aluminum chloride solution is added, and this is reduced to 0. The reaction was carried out by addition to QM/l of sodium carbonate solution, and the resulting precipitate was heated at 35°C for 24 hours.
After aging for a period of time, it was sufficiently hydrolyzed. The obtained basic magnesium carbonate was calcined in an oxygen atmosphere at qoo°C for tg hours. This 0.32 was molded in a mold at 1OOKeI/crn2, and then hydrostatically pressed at λton/my2.

The molded body is placed in vacuum (/θ-5 torr) to °C/mi
It was heated at a constant rate of temperature increase of n and baked at 7300° C. for 2 hours.

The obtained i-tagnesia sintered body has a bulk density of 3. stq 1
It had a particle size of 7 cm3 (99.5% of the theoretical value) 9/rμ, a uniform microstructure, and was transparent.

Example 2 In the method of Example 1, the amounts of the aluminum chloride solution added were o, oos wt% and O,S weight%, respectively. Example 1 Magnesium sulfate was used instead of magnesium chloride in Example 1, and A magnesia sintered body was produced in the same manner as tl, using aluminum sulfate instead. Its bulk density is 3! 36 f/crn'
(99.3% of the theoretical value), the microstructure was uniform and transparent.

This was then evaporated to dryness. This powder was heat treated at 900° C. for 2% of the time, and molded and fired in the same manner as in Example 1. The bulk density of the obtained magnesia sintered body is 3, IIaq
y/an5 (9≦2% of the theoretical value).

Example 5

Claims (1)

[Claims] 1. Add 0.0% of a solution of aluminum compound to magnesia powder or a compound that produces magnesia by heating.
03 to 3.5% by weight (However, Al2O3 to MgO
71 in air or oxygen atmosphere.
After heat treatment or calcining at 0-1100°C, pressure molding is performed, /2! ; A method for producing a highly dense magnesia sintered body, which is characterized by firing at a temperature of 0°C or higher.