JPH0672042B2 - High strength magnesia sintered body and its manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a dense magnesia sintered body having excellent mechanical properties and a method for producing the same. More specifically, the present invention provides
Magnesia that is dense and has excellent mechanical strength, fracture toughness, heat resistance, and thermal shock resistance, and can be suitably used as a heat-resistant material such as porcelain for electronic ceramics firing, β-alumina firing crucible, and metal melting crucible. Quality sintered body and its manufacturing method.

(Prior art and its problems) Magnesia has a high melting point of 2800 ° C and is excellent in corrosion resistance against alkali metals and basic slag, and is therefore used in crucibles and refractory bricks. On the other hand, since magnesia is inferior in mechanical strength, fracture toughness, and thermal shock resistance, there is a problem that cracks and spalling occur due to repeated heating and cooling, and it is used in places where a load is applied. Is also limited.

JP-A-59-182268 and "GYPSUM &LIME" No.209,
219-224 (1987) discloses a method of adding zirconia to magnesia and sintering it to improve the mechanical properties of magnesia. The mechanical properties of the magnesia sintered body obtained according to this method cannot be said to be practically sufficient.

(Technical Means for Solving Problems) An object of the present invention is to provide a magnesia sintered body having significantly improved mechanical properties and a method for producing the same.

The above object of the present invention is to provide magnesia particles having a particle size of 3 μm or less.
This is achieved by a magnesia sintered body having 70% to 99.9% by weight and 0.1 to 30% by weight of cubic zirconia particles having a particle size of 3 μm or less and having a porosity of 1% or less.

The magnesia sintered body of the present invention has a purity of 99.9% or more, a specific surface area of 5 m ² / g or more, and magnesia powder 70-99.9% by weight composed of equiaxed primary particles, and a purity of 99.9% or more and a specific surface area of 5 m ^2.
It is obtained by molding a mixed powder of 0.1 to 30% by weight of granular zirconia powder of / g or more and sintering the compact at 1400 ° C or higher.

The magnesia powder is preferably prepared according to the method described in JP-A No. 61-122106. This method is a method for producing magnesia powder by a gas phase reaction between magnesium vapor and an oxygen-containing gas. The magnesia powder obtained by this method is composed of equiaxed primary particles and is characterized by having very little aggregation. Therefore, the magnesia powder can be mixed with the zirconia powder at the primary particle level.

Generally, magnesia powder is produced by thermally decomposing magnesium salts such as magnesium hydroxide and basic magnesium carbonate. However, the magnesia powder obtained by this pyrolysis method forms agglomerated particles due to the residual mother salt skeleton. Since the agglomerated particles remain even after mixing with the zirconia powder, the resulting magnesia sintered body has a non-uniform structure and poor mechanical properties.

The zirconia powder used in the present invention can be prepared, for example, by the alkoxide method. The zirconia powder obtained by this method has good dispersibility and can be uniformly mixed with the magnesia powder.

The magnesia powder and the zirconia powder used in the present invention both have a purity of 99.9% or more and a specific surface area of 5 m ² / g.
It is necessary to be above. Generally, the smaller the particle size in the sintered body, the better the mechanical properties of the sintered body, but if the purity of both powders is lower than the above lower limit, grain growth proceeds during the sintering of the mixed powders, Mechanical properties deteriorate. Generally, the driving force for sintering is surface energy, and the powder having a larger specific surface area has a better sinterability. However, if the specific surface area of both powders is smaller than the lower limit, the sinterability is lowered and the porosity is 1 % Or less sintered body cannot be obtained.

The ratio of the zirconia powder to the total amount of the magnesia powder and the zirconia powder is 0.1 to 30% by weight. In the present invention, zirconia has the effect of promoting the sintering of magnesia and the effect of strengthening the sintered body. When the blending ratio of the zirconia powder is less than 0.1% by weight, the magnesia sintering promoting effect is small and a dense sintered body having a porosity of 1% or less cannot be obtained.
When the blending ratio of zirconia powder is 4% by weight or more, the strengthening effect of zirconia begins to be expressed, but when the ratio exceeds 30% by weight, changes in the sintering promoting effect and the strengthening effect of the sintered body are observed. I will not be able to.

There is no particular limitation on the mixing method of the magnesia powder and the zirconia powder, a method known per se, for example, a method of dry-mixing them, a method of removing the organic solvent after wet mixing them in an organic solvent such as methanol or ethanol. Can be adopted.

There is also no particular limitation on the method for preparing a molded body from a mixed powder of magnesia powder and zirconia powder, and a method of extrusion molding or injection molding using a binder, a method of rubber press molding, or the like can be appropriately adopted.

Next, the molded body is sintered at a temperature of 1400 ° C. or higher to obtain the magnesia sintered body of the present invention.

When the sintering temperature is lower than 1400 ° C, the zirconia in the sintered body becomes tetragonal. This tetragonal zirconia is transformed into a monoclinic crystal at about 200 ° C. and expands, so that minute cracks are generated in the magnesia sintered body, which causes a decrease in mechanical strength of the sintered body. When the mixed powder is sintered at 1400 ° C. or higher, the zirconia produced becomes a cubic crystal stabilized by magnesia, which makes it difficult for phase transition. As a result, a magnesia sintered body that is thermally stable and has excellent mechanical properties can be obtained. There is no particular limitation on the maximum temperature for sintering, but if sintering is performed at an excessively high temperature, evaporation of magnesia will occur, so the maximum temperature for sintering is generally 1900 ° C.

By sintering a mixed powder of magnesia powder and zirconia powder having the purity and specific surface area specified in the present invention, 70 to 99.9% by weight of magnesia particles having a particle diameter of 3 μm or less
And a cubic zirconia particle having a particle size of 3 μm or less and 0.1 to 30% by weight, a magnesia sintered body having a porosity of 1% or less can be obtained.

(Example) Below, the Example and comparative example of this invention are shown. In the following, the bulk density of the sintered body is measured by the Archimedes method,
It is shown as a percentage of the theoretical density. The bending strength of the sintered body is
In accordance with JIS R 1601, a rod-shaped test piece of 3 x 4 x 40 mm was cut out from the sintered body, the surface was polished with a diamond grindstone, and a span of 30 mm and a crosshead speed of 0.5 mm / min. A bending test was performed and measured. The fracture toughness (K _IC ) of the sintered body was determined by the Vickers indentation method.

Examples 1 to 5 Magnesia powder composed of equiaxed primary particles having a purity of 99.98% and a specific surface area of 8.4 m ² / g and a purity of 99.95% and a specific surface area of 8.6 m ² / g
The granular zirconia powder of No. 1 was blended in the proportions shown in Table 1, mixed by a ball mill for 37 hours using an ethanol solvent, and then ethanol was removed to obtain a powder mixture.

50 g of the powder mixture was filled in a mold of 80 × 54 mm, uniaxially pressure molded at 100 kg / cm ² , and then rubber pressed at a pressure of 1.5 ton / cm ² to obtain a molded body. Next, this molded body was put into an electric furnace and sintered at 1650 ° C. for 4 hours to produce a magnesia sintered body.

The characteristics of the obtained magnesia sintered body are shown in Table 1. The crystal system of the zirconia powder in the sintered body obtained in each example was cubic.

Example 6 Magnesia powder composed of equiaxed primary particles having a purity of 99.98% and a specific surface area of 15.0 m ² / g, and a purity of 99.95% and a specific surface area of 13.7 m
Example 1 was repeated except that ² / g of granular zirconia powder was blended in a ratio of 99.9: 0.1. The results are shown in Table 1.

Comparative Example 1 Example 3 was repeated except that magnesia powder having a specific surface area of 2 m ² / g was used. The results are shown in Table 1.

Comparative Example 2 Example 3 was repeated except that zirconia powder having a specific surface area of 2 m ² / g was used. The results are shown in Table 1.
The crystal system of zirconia in the sintered bodies obtained in Comparative Examples 1 and 2 was cubic.

Comparative Example 3 Example 1 was repeated except that the sintering conditions were changed to 1350 ° C. and 4 hours. The results are shown in Table 1. The crystal system of zirconia in the obtained sintered body was tetragonal.

Claims (2)

[Claims] 1. Magnesia particles 70-99.9 having a particle size of 3 μm or less
Cubic zirconia particles with weight% and particle size of 3 μm or less 0.1 to 3
A high-strength magnesia sintered body having a porosity of 1% or less consisting of 0% by weight. 2. 70 to 99.9% by weight of magnesia powder having a purity of 99.9% or more and a specific surface area of 5 m ² / g or more and equiaxed primary particles.
And a mixture of 0.1 to 30% by weight of granular zirconia powder having a purity of 99.9% or more and a specific surface area of 5 m ² / g or more, and the formed body is sintered at 1400 ° C. or more. Manufacturing method of sintered body.