JPH0226846A - Production of crystallized glass - Google Patents

Abstract

PURPOSE:To uniformly crystallize glass in a short time and to obtain high strength crystallized glass suitable for use as a dental material, etc., by crystallizing the glass in a vessel made of a material having a prescribed high heat conductivity. CONSTITUTION:A vessel is made of a material having a high heat conductivity of >=20W/m.K, i.e., a metal such as Au or Ag, ceramics such as SiC or a mixture of them. A molded body of glass such as calcium phosphate-based glass contg. Li2O, etc., is put in the vessel and powder having a high heat conductivity of >=20W/m.K, e.g., SiC powder is densely filled into the gap between the glass molded body and the vessel. The vessel is then heated at about 300 deg.C/hr heating rate and held at 550-650 deg.C for about 10 hr to crystallize the glass and to produce crystallized glass such as calcium phosphate-based glass.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method of crystallizing mother glass when producing crystallized glass, and particularly relates to a method of crystallizing a mother glass when producing crystallized glass, and is particularly suitable for high-strength dental materials or biomaterials such as artificial bones. The present invention relates to a method for producing crystallized glass.

[Conventional technology]

Crystallized glass is obtained by reheating a glass body of a predetermined composition to uniformly precipitate and grow a large number of microcrystals within the glass. In the manufacturing process of crystallized glass, the heating method for crystallization is particularly important, and it is required to precisely control a crystallization furnace with a uniform temperature distribution within the furnace.

Obtaining uniform crystals contributes to improving the strength of the crystal and reducing morphological distortion. However, it is very difficult to maintain a uniform temperature distribution within the furnace. In order to solve this problem, a method has been adopted in which the glass body is heated at a very slow temperature increase rate so that no temperature difference occurs inside the glass body.

Further, since a crystalline body generally has a higher specific gravity than a glass body, volumetric contraction occurs during crystallization.

Taking this volumetric shrinkage into consideration, the glass body is enlarged in advance and crystallized, but if a temperature distribution occurs at this time as well, it will not shrink uniformly and crystal distortion will occur, and defects such as bores will occur inside. In order to prevent this, a method is being used to reduce the heat transfer by crystallizing the refractory in a sheath.

[Problem to be solved by the invention]

As mentioned above, various methods have been adopted to reduce temperature distribution, but there are so-called surface devitrification types, in which crystallization progresses from the surface of the glass toward the inside, such as calcium phosphate crystallized glass. Crystallized glass produced by the crystallization mechanism is particularly sensitive to temperature distribution, and if it is small in shape, it is possible to obtain a very uniform crystallized product by slowly heating it over time, but if it is in a large shape, a very uniform crystallized product can be obtained. When crystallizing a glass body or multiple glass bodies at once, it is almost impossible to achieve uniform crystallization using normal methods.Also, crystallization is performed by placing the glass in a refractory pod. Even with this method, refractories generally have low thermal conductivity, and although it is possible to moderate the way heat is transmitted, it is not possible to achieve a uniform temperature distribution.

In order to achieve uniform crystallization when heating and crystallizing a glass body in this way, it is necessary to achieve a uniform temperature distribution.

[Means to solve the problem]

In heating furnaces generally used for crystallization, heat transfer to the glass body is based on radiation and convection, so the distance between each part of the glass body and the heating element and whether each part of the glass body directly faces the heating element are important. This inevitably results in a temperature distribution inside the glass body.

Therefore, heating may be performed by conduction heat transfer.

In order to achieve this, the present invention, when crystallizing glass, either places the mother glass in a container made of a highly thermally conductive material, fills the void inside the container with highly thermally conductive powder, or uses a combination of both. It is characterized by crystallization.

[Structure of the invention]

The highly thermally conductive material or powder used in the present invention is metal, ceramics, or a combination of both, and the thermal conductivity of the container or powder must be 20 W/m・K or higher; Uniform crystals cannot be formed in the surface devitrification type. Metals include Aut ag, Cu,
Alt Ir, Mo, W, Cr, Ni, F
e, Pd.

Pt, Rh, Si, etc. or alloys mainly composed of these pass through, and ceramics include SiC+ Bed,
Suitable materials are Al2O31MgO and ceramic mixtures based on these. In the case of metal materials, it is also possible to apply a surface coating using methods such as plating, vapor deposition, and thermal spraying to prevent oxidation and corrosion at high temperatures. Ceramic materials are preferred from the viewpoint of preventing oxidation and corrosion at high temperatures. Also suitable are composite materials such as those in which a metal material such as Si is injected into the pores of a ceramic material such as SiC, a ceramic material dispersed in a metal material, and a mixture of a metal material and a ceramic material.

The container made of highly thermally conductive material may be in the shape of an ordinary box, but in order to enhance the effect of conductive heat transfer, which is the objective of the present invention, the container wall and glass body that match the shape of the object to be heated should be placed as close as possible. It is preferable to use a container in the form of, for example, a block with perforations.

From the viewpoint of improving heat uniformity, it is preferable that the container be thicker and denser, but it may be a molten body or a sintered body. In addition, when filling high thermal conductive powder, it may be in the form of lumps, fibers, etc., or a mixture of these in addition to powder, but it is more efficient to fill it as densely as possible, such as using a powder material with a blended particle size. The method is better.

In the present invention, only a container made of a highly thermally conductive material is used, and the gap between the container and the glass body is left as is, but it may be filled with any powder or the like. Alternatively, the container can be made of any material and the voids filled with highly thermally conductive powder. However, the most preferable method is to use a container made of a highly thermally conductive material and fill the gap between the container and the glass body with highly thermally conductive powder at a high density.

Furthermore, the method of the present invention is naturally effective when - number of glass bodies are crystallized, but it is also effective when a plurality of glass bodies are crystallized simultaneously. In that case, a plurality of glass bodies may be embedded in the powder filled in the container, or a plurality of holes may be made in the block body. In particular, when a plurality of glass bodies are crystallized at the same time, they are in the same crystallized state, so there is an advantage that glass bodies with uniform properties such as strength can be obtained.

〔Effect of the invention〕

According to the method of crystallizing the glass of the present invention, the mother glass is placed in a container made of a highly thermally conductive material, or the void in the container is filled with a highly thermally conductive powder, or a combination of both is used for crystallization. Since heat transfer to the glass body becomes uniform, there is no temperature distribution, and ideal uniform crystallization can be achieved. In particular, its characteristics are exhibited in the crystallization of surface-devitrified glass-ceramics, which are sensitive to temperature distribution, and among them, calcium phosphate-based crystallized glass, which is used as artificial tooth crowns and artificial bone materials.

Furthermore, it is possible to crystallize a plurality of glass bodies at the same time so that they are in the same crystallized state, which has been difficult in the past.

Furthermore, by using a highly thermally conductive material, there is no need to raise the temperature very slowly over a long period of time during crystallization, as is the case with conventional methods, and rapid temperature rise is also possible, significantly shortening the time required for the crystallization operation. Ru.

〔Example〕

Example 1 A SiC container is filled with SiC powder with a particle size of 149 μm or less, and 4.3 L i 20 ・38.5 Ca
O・9. I Al2O3・48. IP 20 e Null composition: 5 pieces of calcium phosphate glass molded bodies were embedded, and the temperature was raised at a heating rate of 300°C/hr to 550-650°C.
The mixture was heated and crystallized at ℃ for 10 hours to obtain calcium phosphate crystallized glass. All five of the obtained crystallized glasses showed the same uniform crystallization state regardless of their position in the container, and their bending strength was as high as 1820 to 1980 kg/cm2.
The variation was also small.

Example 2 Five holes with a diameter of 25 mm and a depth of 25 mm were bored in a copper block with approximate dimensions of 90 x 65 x 30 mm, and the same calcium phosphate system as in Example 1 was filled in each hole with SiC powder having a particle size of 149 μm or less. Embed the glass molding and cover with a copper plate (5 mm thick) of the same quality.
It was heated and crystallized under the same conditions as in Example 1 to obtain a calcium phosphate crystallized glass. In this case as well, all five crystallized glasses obtained showed the same uniform crystallization state regardless of their position in the container, and their bending strength was 1890 to 1990 kg.
/c-.

Example 3 Calcium phosphate was prepared in the same manner as in Example 1 using a SiC container filled with quartz powder with a particle size of 149 μm or less and an alumina-silica refractory brick container filled with SiC powder with a particle size of 149 μm or less. A system crystallized glass was obtained. The obtained crystallized glass exhibited a similar crystallization state regardless of its position in the container. The measured value of the strength is 1610~1 for a SiC container.
790kg/cm2, 124 in alumina-silica container
Although it was high at 0 to 1560 kg/c- and the variation was relatively small, it was not as good as Example 1.

Comparative Example 1 Five pieces of the same calcium phosphate glass moldings as in Example 1 were placed on an alumina-silica fireproof insulation brick board, and the conditions were the same as in Example except that the heating rate was very slow at 60°C/hr. The mixture was heated and crystallized to obtain calcium phosphate crystallized glass. The five crystallized glasses obtained show different crystallization states depending on their set position on the fireproof insulation brick board, and each crystallized glass itself has different crystallization states between the upper and lower bricks, which are exposed to the heating element at a closer distance. The crystallization state differed depending on the contact area. Strength is also 560
~980 kg/cWI2, which varied greatly depending on the setting position, and the strength was also small due to differences in crystallization depending on the individual site.

Comparative Example 2 Particle size 149 μm in alumina-silica refractory brick container
A calcium phosphate crystallized glass was obtained by heating and crystallizing in the same manner as in Example 1, except that 12 L of quartz powder was filled and five pieces of calcium phosphate glass were embedded, and the heating rate was 60° C./hr. Although there was little difference in the crystallization state within each of the obtained crystallized glasses, there were differences in the crystallization state among the five crystallized glasses depending on the set position in the container, and Correspondingly, the strength was also 770 to 1030 kg/cyI2.

The thermal conductivity of the material used is -/m・K in units of SiC
The container is 120, an alumina-silica refractory brick container and 2.
5. The alumina-silica fireproof insulation brick board has a rating of 0.3, the copper block has a rating of 350, and both powders are filled with Si.
C was about 50, 0.1 like quartz.

Claims (3)

[Claims] (1) A method for producing crystallized glass, which comprises crystallizing the mother glass in a container made of a highly thermally conductive material having a thermal conductivity of 20 W/m·K or more. (2) A method for producing crystallized glass, which comprises filling the periphery of the base glass with highly thermally conductive powder having a thermal conductivity of 20 W/m·K or more and crystallizing the glass. (3) When crystallizing glass, place the mother glass in a container made of a highly thermally conductive material with a thermal conductivity of 20 W/m・K or more, and fill the void inside the container with a thermal conductivity of 20 W/m・K.
A method for producing crystallized glass, characterized by filling the powder with the above highly thermally conductive powder and crystallizing it.