JPS6283358A - Manufacture of high purity mgo 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] [Industrial Application Field] The present invention relates to a method for manufacturing a high-purity MgO sintered body, and more specifically, a crucible for melting high-purity uranium, thorium, etc., and a vacuum melting method for iron and alloys. The present invention relates to a method for producing a high-purity MgO sintered body suitable as a base material for a commercial crucible, a crucible for metal melting in a high-frequency furnace, a crucible for firing electronic ceramics, a refractory sheath, etc.

[Prior Art] In general, sintering of ceramics is a phenomenon in which adjoining particles are brought close to each other by heating, the whole shrinks, and is baked and hardened.
The driving force for this sintering is a force that attempts to minimize the surface free energy of the system by reducing the total surface area of the particle aggregate.

In this way, sintering is a phenomenon that is driven by the surface energy of a solid and is caused by the movement of substances within the solid, so it is possible to obtain a sintered body that has a dense, fine, and uniform structure and has stable performance. In order to achieve this, the method of preparing the raw material is considered to be a fundamental and important issue. First, the raw material powder must be sufficiently finely ground, and the sintering aids and firing conditions must be selected to improve the internal structure of the particles. Measures to promote mass transfer are being considered.

For example, in the production of high-purity MgO sintered bodies.

As a method of finely pulverizing the raw material, there is a method of pulverizing the raw material using a steel ball mill or the like. However, this method has a problem in that it requires subsequent treatments such as acid treatment and water washing to remove impurities, so recently it has been pulverized using a bot mill in Sinterkolund. In this case, the raw material is ground so that the particle size of the powder is mostly less than 100 gm, with a significant portion of it being less than 10 gm.

When sintering the MgO raw material powder prepared in this manner, a trace or small amount of sintering aid is added to lower the sintering temperature or to suppress crystal growth. For MgO firing, SiO2, ZrO2, C
AO etc. are added and mixed as a sintering aid. However, since this mixture has no plasticity, it is usually mixed with 1 to 2% by weight of an organic binder, molded by a method such as rubber press or extrusion, and baked at 1300 to 2000°C.
A sintered body is obtained.

[Problem to be solved by the invention] Thus, SiO2 as a sintering aid.

According to the conventional method of adding and mixing ZrO2, CaO, etc. and firing, it is possible to obtain an MgO sintered body relatively easily. However, M obtained by such a conventional method
The gO sintered body cannot be said to be fully satisfactory in terms of density, and therefore, when used as a base material for a crucible or sheath, the sintering aids S i 02 , Z ro2 . A problem arises in that CaO and the like contaminate the high-purity molten metals such as uranium and thorium contained therein and the objects to be fired such as electronic ceramics. Furthermore, the MgO sintered body produced by the conventional method has drawbacks such as not being strong against thermal shock.

Means for Solving the Problems with L] The present inventors have made various studies to solve the problems of the above-mentioned conventional method, and as a result, the present inventors have found that
The present inventors have discovered that an extremely dense MgO sintered body can be produced at low temperatures and in a short time by adding and mixing No. 3 as an ultrafine sintering aid, thereby completing the present invention.

That is, in the present invention, ultrafine particle alkoxide A l 2 O3 is added and mixed as a sintering aid to a high-purity MgO raw material, a binder is further added and mixed, and the resulting mixture is shaped and then fired.

Note that in the present invention, alkoxide A l 2O3 refers to Al2O3 obtained by an alkoxide method. In addition, all percentages refer to percentages.

The present invention will be explained in detail below.

In the present invention, high purity MgO is used as the MgO raw material. As the high-purity MgO raw material, a high-purity product with a purity of 99.0% or more is preferable.

One example of such high-purity MgO raw materials is MgO obtained by an alkoxide method. This is obtained by hydrolyzing a raw material Mg alkoxide solution using a conventional method. In this case, Mg(7) methoxide, ethoxide, isopropoxide, butoxide, etc. are used as the raw material Mg alkoxide. . The alkoxide used preferably has a low impurity content.

In the present invention, the MgO raw material is preferably a powder with an average particle size of about 44 Bm or less, especially about 10 gm or less.

Further, in the present invention, as the Mi fine particle alkoxide A 1 2 O 3 used as a sintering aid, a powder obtained by hydrolyzing AfL alkoxide is pulverized and calcined as necessary. The average particle diameter of this ultrafine alkoxide AJ12O3 is preferably 100A.

Further, as the binder added to impart plasticity to the raw material mixture, a commonly used organic binder is used. Examples of the organic binder include methylcellulose.

In the present invention, first, the above A! is added to the MgO raw material. ;L2
Add and mix O3 sintering and auxiliary agents wet or dry. A! ;
The amount of the L2O3 sintering aid added is 0.0% relative to the MgO raw material.
It is preferable to set it as 0.005 to 1.0%. A l 2O'
After adding and mixing the 3 sintering aid, or together with the A I:L2O3 sintering aid, the binder is added and mixed. The amount of binder added is preferably 1.0 to 5.0% based on the MgO 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 500 to 2000 kg.
/crn” is preferable.

This molded body is then preferably fired in a vacuum or in a hydrogen atmosphere. This firing starts from room temperature to 400~600℃.
lOO to a predetermined temperature between 00°C (e.g. 500°C)
250℃/hr 't' temperature increase from the predetermined temperature to 1
Preferably, the final calcination temperature is 250 to 500° C. and then maintained at the final calcination temperature for 2 to 5 hours.

The MgO sintered body obtained by the method of the present invention is extremely dense and has excellent strength.

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

Therefore, according to the present invention, by adding and mixing ultrafine particles A l 2O3 obtained by the alkoxide method to a high purity MgO raw material, the A l 2O3 of the ultrafine particle powder is uniformly diffused between the particles of the MgO raw material powder. Since the particles are distributed, it becomes possible to obtain a uniform and dense sintered body at a low firing temperature.

This ultrafine alkoxide Al2O3 begins to diffuse between MgO powder particles at a temperature of about 1200°C, and at a temperature of about 1500°C.
Complete solid solution at ℃. Therefore, according to the present invention, M
The gO particles are strongly bonded by spinel pounding, and the resulting sintered body is dense and strong, resulting in excellent contamination resistance and thermal shock resistance.

[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 MgO with a purity of 99.0% was ground to a particle size of 10 JLm or less using a Sinterkold type bot mill, and the obtained raw material particles had a particle size of io~100A and a purity of 99.99.
% of ultra-high purity, ultra-fine particle alkoxide Al 2 O 3 was added in an amount of 0.4%, and further, 1% of methyl cellulose and 2% of water as an organic binder were added and mixed.

The obtained mixture was molded by a rubber press method at a molding pressure of 1500 kg/crn'. Next, the temperature of the molded product was raised from room temperature to 500°C at a rate of 200°C/hr-,
The temperature was raised to 500-1500°C at a rate of 300°C/hr, and the temperature was further raised to 1700°C and held for 3 hours to obtain an MgO sintered body. “Various physical properties of this MgO sintered body were measured and compared with commercially available MgO sintered products, and the results were as shown in Table 1 below.

Table 1 From Table 1, the present invention shows that extremely dense and high strength MgO
It is clear that a sintered body can be easily obtained in a short time.

[Effects of the Invention] As described in detail below, the method for producing a high-purity MgO sintered body of the present invention includes adding A l 2 O 3 ultrafine particles obtained by an alkoxide method and a binder to a high-purity MgO raw material. The resulting mixture is molded and fired, and because the A L; can be obtained. Therefore, the obtained Mg
The O sintered body has high durability against thermal shock, and since the Al2O3 sintering aid is completely dissolved in the sintering process, it does not remain in the sintered body, so the crucible, Object to be fired when used as a base material such as pods,
It also has excellent contamination resistance against melted materials.

The high-purity MgO sintered body manufactured by the present invention can be used as a crucible for melting high-purity uranium or thorium, a crucible for vacuum melting of iron or alloys, a crucible for melting metals in a high-frequency furnace, a crucible for firing electronic ceramics, or a refractory. It is extremely useful industrially as a base material for pods, etc.

Claims (4)

[Claims] (1) A high-purity MgO sintered body characterized by adding and mixing ultrafine particle alkoxide Al_2O_3 as a sintering aid to a high-purity MgO raw material, further adding and mixing a binder, shaping the resulting mixture, and then firing it. manufacturing method. (2) The method for producing a high-purity MgO sintered body according to claim 1, wherein the average particle diameter of the ultrafine alkoxide Al_2O_3 is 10 to 1000 Å. (3) Ultrafine alkoxide Al_ for MgO raw material
The method for producing a high-purity MgO sintered body according to claim 1 or 2, wherein the addition and mixing ratio of 2O_3 is 0.005 to 1.0% by weight. (4) Firing is performed by raising the temperature from room temperature to a predetermined temperature between 400 and 600°C at a rate of 100 to 250°C/hr, and from the predetermined temperature to a final firing temperature of between 1500 and 1900°C.
After increasing the temperature at 0 to 350°C/hr, the final firing temperature is increased by 2
The method for manufacturing a high-purity MgO sintered body according to any one of claims 1 to 3, wherein the sintered body is maintained for 5 hours.