JPH0465351A - Mgo sintered body and production thereof - Google Patents

Abstract

PURPOSE:To improve durability to thermal shock and contamination resistance to a melt by molding and sintering a mixture of high purity starting material for MgO and fine Al2O3 powder with fine TiO2 powder. CONSTITUTION:High purity starting material for MgO having >=99.0wt.% purity and <=10mum average particle size, e.g., magnesia clinker and 0.005-1.0wt.% fine Al2O3 powder having <=0.1mum average particle size are mixed with fine TiO2 powder having <=10mum average particle size added by 0.1-2wt.% of the total amt. of the starting material and the Al2O3 powder, a binder such as polyvinyl butyral is added to the mixture by 0.5-5.0wt.% of the amt. of the starting material and they are press-molded under 500-2,000kg/cm<2> pressure to obtain a molded body. This molded body is heated from ordinary temp. to a prescribed temp. of 400-600 deg.C at 100-200 deg.C/hr heating rate, further heated from the prescribed temp. to a sintering temp. of 1,500-1,800 deg.C at 100-250 deg.C/hr heating rate and sintered by holding at the sintering temp. for 1-2 hr.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an MgO sintered body and a method for manufacturing the same, and specifically relates to a crucible for melting high-purity metals, a crucible for vacuum melting iron and alloys, and a high-frequency furnace. The present invention relates to an MgO sintered body suitable as a base material for metal melting crucibles, electronic ceramic firing crucibles, refractory sheaths, etc., and a method for manufacturing the same.

[Prior Art] Generally, sintering of ceramics refers to 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 magnesia (MgO) sintered bodies, there is a method of finely 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 Sinterkold type bot mill. In this case, the raw material is ground so that the particle size of the powder is mostly below 100 μm, of which a significant portion is below 10 μm.

When sintering the MgO raw material powder prepared in this way, a trace or small amount of sintering aid is added to lower the sintering temperature or to suppress crystal growth. For MgO firing, 5i02, ZrO2, C
AO etc. are added and mixed as a sintering aid. However, since this mixture has no plasticity, it is usually molded by adding 1 to 2% by weight of an organic binder, using a rubber press, extrusion molding, etc., and then baked at 1300 to 2000°C.
A sintered body is obtained.

[The invention tries to solve the problem! ! ! ] Thus, according to the conventional method of adding and mixing 5iO2 Zr02, CaO, etc. as a sintering aid and firing, it is possible to obtain a MgO sintered body relatively easily. However, M obtained by such a conventional method
The gO sintered body cannot be said to have sufficient density, and therefore, when used as a base material for crucibles or sheaths, sintering aids such as SiO2, ZrO2, CaO, etc. A problem arises in that the object to be fired is contaminated. Furthermore, the MgO sintered body produced by the conventional method has drawbacks such as not being strong against thermal shock.

As a result of various studies aimed at solving the problems of the above-mentioned conventional methods, the present applicant has found that Aj! 2
We discovered that by adding and mixing 03 as an ultrafine particle sintering aid, an extremely dense MgO sintered body could be produced at low temperatures and in a short time. Eight patent applications were previously filed for a method for producing a high-purity MgO sintered body by adding and mixing Al1203, further adding and mixing a binder, molding the resulting mixture, and then firing it (Japanese Patent Laid-Open No. 83358/1983).

Hereinafter referred to as "prior application". ) According to the method of the previous application, m-density, high-strength, high-purity MgO
A sintered body is provided.

The object of the present invention is to further improve the above-mentioned method, and to provide an MgO sintered body with even higher m-density, higher heat resistance strength, and higher mechanical strength, and a method for manufacturing the same.

[Means for Solving the Problems] The MgO sintered body of claim (1) contains 0.1 to 2% by weight of the high purity MgO raw material and AfL2oa fine powder, and the total weight of the MgO raw material and AIL203 fine powder. T i 02
The method for producing an MgO sintered body according to claim (2), wherein the MgO sintered body is obtained by molding and then firing a mixture containing high-purity Mg
O raw material and AIL20a fine powder, MgO raw material and Af2
0.1 to 21% Ti based on the total weight with 0s fine powder
The method is characterized in that a mixture containing O2 fine powder is molded and then fired.

The present invention will be explained in detail below.

In addition, in the following, r% indicates "wt%".

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.

In the present invention, the MgO raw material has an average particle size of 10 μm0.
Powder with a particle size of about 5 μm or less is preferable. M
If the average particle size of the gO raw material is too large, the mass transfer during sintering will not be sufficient, and not only will a dense sintered body not be obtained, but the mechanical strength will also be low. Incidentally, as the MgO raw material, light-fired or heavy-fired MgO, magnesia clinker-electrofused magnesia, etc. can be used.

As the Al1203 fine powder, it is preferable to use Aj22 o3 fine powder obtained by hydrolyzing an alkoxide. Specifically, a powder obtained by hydrolyzing the alkoxide of AJ2 is pulverized and calcined as necessary. The average particle size of the AA2 os fine powder obtained by this alkoxide method is 0.1 μm or less, especially 0.01 to 0.0 μm.
It is preferable that

Ti02t! As the powder, either rutile type or anatase type can be used, but rutile type fine particles are usually used. The TiO2 fine powder is preferably submicron particles with an average particle diameter of 10 μm or less, particularly 5 μm or less, especially 1 μm or less.

In the present invention, Al2O3 fine powder and TiO2 fine powder are added as sintering aids, and the amount added is within the following range. That is, the amount of Al1203 fine powder added is preferably 0.005 to 1.0% based on the MgO raw material. A
If the l2203 fine powder is less than 0.005%, sufficient improvement effect by the present invention cannot be obtained, and if it exceeds 1.0%, Al1
Too much 203 causes excessive precipitation of mullite, which conversely causes a decrease in strength. In addition, TiO2 fine powder is MgO
The amount is 0.1 to 2% based on the total weight of the raw materials, Al2203 fine powder and TiO2 fine powder. The proportion of TiO2 fine powder is 0.
If it is less than 1%, sufficient improvement effect by the present invention cannot be obtained,
If it exceeds 2%, the physical properties of MgO may be affected to some extent.

A binder is added to the raw material mixture of the MgO raw material, A 1120 s fine powder, and TiO2 fine powder as necessary in order to impart plasticity. As the binder, a commonly used organic binder is used. Examples of organic binders include PEG and PVB. The amount of binder added is preferably 0.5 to 5.0% based on the MgO raw material.

In the present invention, first, a predetermined amount of Al1203 fine powder is added to and mixed with the MgO raw material in a wet or dry manner, or a required amount of binder is added and mixed together with the Al203 fine powder. Then, a predetermined amount of Ti0pffa powder is further added and mixed, and the resulting mixture is molded by a molding method such as a pressure molding method. When molding is performed using a pressure molding method, the molding pressure is preferably about 500 to 2000 kg/crn'. Note that during molding, it is preferable to perform pretreatment such as granulation by spray drying in order to improve the moldability of the raw material mixture.

The obtained molded body is first fired at room temperature and then at a temperature of 400~600℃.
Loo to a predetermined temperature between 0℃ (e.g. 500℃)
Raise the temperature at 200'C/hr, and from the predetermined temperature to 1500~
Final firing temperature between 1800'C & (e.g. 1600t)
It is preferable that the final firing temperature be maintained at the final firing temperature for 1 to 2 hours after the temperature is raised to 10 to 25°C/hr.

[Action] Adding TiO2 as a third component to M g OA 12203 system
In addition to the bonding of mullite in the MgOAl2203 system, magnesium titanate due to the MgO-TiO2 system is generated at the grain boundaries, and this magnesium titanate fills the grain boundaries and increases the bond strength between crystal grains. At the same time, grain growth of MgO crystals is controlled. Therefore, a dense and heat-resistant MgO sintered body can be obtained.

By the way, it is suitable for Mg0-Al2203 system, A12o
If the amount of 3 added is large, excessive precipitation of mullite will cause a decrease in strength, but since TiO2 produces magnesium titanate that is compatible with the MgO matrix, there will be no negative effects on physical properties such as a decrease in strength. There aren't many. Therefore, even when TiO2 is added in a relatively large amount, Al
22 No problems like o3 will occur.

In addition, in the present invention, when Al120s produced by the alkoxide method is used as Al1203, the following effects are further produced.

Generally, powders obtained by the alkoxide method have small particle sizes, active surfaces, and high purity.

Therefore, by adding and mixing ultrafine particles AjZ203 obtained by the alkoxide method to a high-purity MgO raw material, the ultrafine Al of the ultrafine powder is created between the particles of the MgO raw material powder.
Since 2O3 becomes uniformly diffused and distributed, it becomes possible to obtain a uniform and dense sintered body at a low firing temperature.

This ultrafine alkoxide AjZ203 has a diameter of 1200″
'Ci degree begins to diffuse between MgO powder particles, approximately 1
Complete solid solution at 500°C. Therefore, the added alkoxide Al2O3 does not remain and the MgO particles are spinel-bonded and strongly combined, resulting in a sintered body that is denser and has higher strength, and also has excellent contamination resistance and thermal shock resistance. It will be excellent.

[Examples] The present invention will be described in more detail with reference to Examples and Comparative Examples below, but the present invention is not limited to the following Examples unless it exceeds the gist thereof.

Examples 1 and 2, Comparative Example 1 High-purity MgO with a purity of 99.0% (average particle size of 10 μm or less) was added with a particle size of 10 to 1o obtained by an alkoxide method.
oA, 0.4% high purity Al2O3 fine powder with purity of 99.9%
% and then PE01% as an organic binder.
were added and mixed.

Add TiO2 fine powder (average particle size 1 μm) to this mixture as a first
The mixture was added in the proportions shown in the table (but not added in Comparative Example 1), and the resulting mixture was molded by a rubber press method at a molding pressure of 1500 K g/cm.Then, the molded body was heated to room temperature. From 500℃ to 150℃/
Raise the temperature at 200℃/hr from 500 to 1700℃
The temperature was raised for hr, and the temperature was further maintained at 1700° C. for 1 hr to sinter, yielding an MgO sintered body. Various physical properties of this MgO sintered body were measured and the results are shown in Table 1.

Table 1 *: Ratio to theoretical values From Table 1, it is clear that the present invention produces extremely dense and high-strength MgO.
It is clear that the sintered body is easily obtained.

[Effects of the Invention] As detailed above, according to the present invention, an extremely dense and highly pure MgO sintered body is provided. Therefore, Mg of the present invention
O sintered body has high durability against thermal shock,
Moreover, the material to be fired when used as a base material for crucibles, pods, etc.
It also has excellent contamination resistance against melted materials.

The high-purity MgO sintered body produced by the present invention can be used in crucibles for melting high-purity metals, crucibles for vacuum melting iron and alloys, crucibles for melting metals in high-frequency furnaces, crucibles for firing electronic ceramics, refractory sheaths, etc. It is industrially extremely useful as a base material.

Claims (2)

[Claims] (1) High purity MgO raw material and Al_2O_3 fine powder,
An MgO sintered body, characterized in that it is obtained by molding a mixture containing TiO_2 fine powder in an amount of 0.1 to 2% by weight based on the total weight of the MgO raw material and Al_2O_3 fine powder, and then firing the mixture. (2) High purity MgO raw material and Al_2O_3 fine powder,
A method for producing an MgO sintered body, which comprises molding a mixture containing TiO_2 fine powder in an amount of 0.1 to 2% by weight based on the total weight of the MgO raw material and Al_2O_3 fine powder, and then firing the mixture.