JP2699111B2 - Translucent alumina porcelain and its manufacturing method - Google Patents

Description

The present invention relates to a translucent alumina porcelain and a method for producing the same.

[Conventional technology]

Conventionally, the arc tube of a high-pressure metal vapor lamp and the light-transmitting window of an EPROM semiconductor have been made of alumina porcelain that has translucency, high-temperature resistance, and high insulation characteristics. I have.

In such a translucent alumina porcelain, in order to obtain a high high transmittance, a raw material obtained by adding a trace amount of MgO or the like to alumina (Al ₂ O ₃ ) powder having a purity of 99.9% or more is generally used in a vacuum atmosphere or Sintering was performed at a high temperature of 1900 ° C. for 2 hours in a reducing atmosphere to uniformly grow alumina crystals. Since such alumina porcelain grows and grows with alumina crystal grains, the mechanical strength of alumina porcelain sintered by an ordinary method (generally opaque material)
About half of that. For this reason, for example, in a tubular body made of translucent alumina porcelain constituting the arc tube of the lamp, it is necessary to increase the mechanical strength and design a thicker wall to improve the durability. Could not fulfill its function.

[Means for solving the problem]

In view of the above circumstances, the present invention provides an alumina crystal having a size larger than that of the alumina crystal constituting the alumina porcelain base on the surface of the alumina porcelain base so as to have better translucency without reducing the strength. This is a porcelain with a layer of the same composition as the above, and a high-purity alumina layer of the same composition as the porcelain substrate is applied, and then fired in a vacuum furnace or a hydrogen furnace, resulting in excellent light transmission without reducing strength. To obtain alumina porcelain.

〔Example〕

 Next, the present invention will be described in detail with reference to examples.

(Example 1) Mg was added as a sintering aid to high-purity alumina powder of 99.6% or more (weight% or less) of Al ₂ O ₃ sized to an average particle size of 0.5 μm.
O added 0.05%, Fe10ppm, Si15ppm, Na40p as impurities
1.0% dispersant and 3.0% organic binder
And 35% pure water to make a slurry. This slurry was formed into a tubular body by a waste plaster casting method using a predetermined gypsum mold, and the unfired tubular body was treated with the high-purity alumina ceramic powder 10 having the same components as the tubular body.
0 (weight)%, organic binder 3%, dispersant 1%, pure water 50
%, Dried and dipped in a slurry containing 0.1% of an alumina layer having a thickness of 0.1 mm after drying, and sintered at the sintering temperature shown in Table 1; Table 1 similarly shows a comparative example in which the tubular body molded by the casting method was calcined in a vacuum furnace at each temperature for 3 hours.

Example of mold shown in Table 1 (outer diameter 12mm, wall thickness 1.0mm)
The outer surface and the inner surface of each are ground to a thickness of 50 to 100 μm and 500 to 600 μm, polished to a mirror-like surface, then etched with phosphoric acid, and observed with an electron microscope for the alumina crystal diameter of each part. Is also described.

When the bending strength of such a tubular body was measured, there was almost no change in strength, but the diffused light transmittance (%) was 1.1 to 1.1.
2.3% improvement was confirmed.

The thickness of the test piece was 1.0 mm, and the bending strength was measured by a three-point bending strength measuring method according to JIS.

(Example 2) A disk having a diameter of 24 mm and a thickness of 1 mm was prepared from the same high-purity alumina raw material used in Example 1 by dry press molding, and 10% of high-purity alumina having the same composition as the disk ( Weight) and a slurry composed of 30% of methanol and 30% of chlorofluorocarbon is applied by a spray method so that the thickness after drying becomes about 0.1 mm. After drying, the slurry is dried at a temperature shown in Table 2 in a vacuum furnace at a temperature shown in Table 2. It was baked for 3 hours.

When the bending strength of such a disc was measured, the product of the present invention in which the surface portion of alumina was formed by the spray method and the comparative product in which the alumina slurry was not applied had the same bending strength. Was. However, it can be seen that the linear light transmittance (%) has been improved to 0.6 to 4.3%.

(Example 3) A slurry obtained by adding 0.03% of MgO to a powder of 99.9% or more of alumina was applied to the surface of an alumina tubular body formed using the same composition raw material as in Example 1 with a brush, dried, and vacuumed. Firing was performed in a furnace at a temperature of 1850-1950 ° C. for 3 hours. Table 3 below shows comparative products which were not coated with the slurry and were baked under the same conditions.

Also in this case, the bending strength of the alumina ceramic tube in which the slurry was applied and the alumina ceramic tube in which the uncoated tubular body was directly baked were unchanged, but the light transmittance was improved by 0.6 to 2.6%. Porcelain was obtained.

(Example 4) An alumina tubular body was molded in the same manner as in Example 1, and after molding, a high-purity alumina (Al ₂ O
₃ 99.9% or more) by adhering were calcined for 3 hours at a hydrogen furnace. The results were as shown in Table 4.

Similarly, in Example 4, the light transmittance could be improved by 0.9 to 3.1% without lowering the bending strength of the material.

What can be said in common in the above Examples 1 to 4 is that the surface formed by adhering the slurry prepared using the raw material powder having the same composition to the particle size of the alumina crystal inside the alumina porcelain (base). Part of the alumina crystal had a larger particle size, and the ratio was at least 1.2 or more. In addition, even if it is desired to obtain alumina porcelain having the same light transmittance as a conventional product (comparative product), the firing temperature is 50 to
Since the temperature may be as low as 100 ° C., productivity and economy are excellent, and the durability of the firing furnace is also advantageous.

〔The invention's effect〕

As described above, the surface of an unsintered green body or sintered body of alumina is coated with a high-purity alumina layer having the same composition as those of the green body and the sintered body, and then fired. As compared with the alumina particle size, the alumina particle size at the surface can be made larger, and as a result, the light transmittance of the alumina porcelain can be greatly improved.

Further, when manufacturing alumina porcelain having the same light transmittance, porcelain having excellent light transmittance can be provided at a low cost, such as firing at a low temperature.

Claims (3)

(57) [Claims] 1. A light-transmitting alumina porcelain, wherein the surface portion of the alumina porcelain comprises an alumina layer having a particle diameter larger than the diameter of the alumina crystal constituting the alumina porcelain base. Alumina porcelain. 2. The translucent alumina porcelain according to claim 1, wherein the crystal grain size of the alumina porcelain base is 15 μm or more, and the crystal grain size ratio between the surface portion and the alumina porcelain base is 1.2 or more. . 3. A method for producing a translucent alumina porcelain comprising a step of attaching a high-purity alumina layer having the same composition as that of the above-mentioned base to the surface of a formed or sintered body of alumina forming a porcelain base and then firing.