JPH10316466A - Light-transmissible alumina ceramic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a light-transmissible alumina ceramic having a sufficient light transmissibility for light-transmissible members by reducing its sulfur content to a specified level or below. SOLUTION: This light-transmissible alumina ceramic contains sulfur at 100 ppm or less. Its total light permeability is preferably above 95%, more preferably 96% or above. Light transmissibility of an alumina ceramic is adversely affected by impurities, e.g. sulfur, iron, chromium and vanadium, and depends greatly on sulfur content. Content of each of iron, chromium and vanadium is preferably 5 ppm or below, and total content of these impurities is preferably 10 ppm or below. The alumina stock powder for the light-transmissible alumina ceramic containing sulfur at 100 ppm or less is obtained by firing aluminum ammonium sulfate [Al(NH4 )(SO4 )2 .12H2 O] at 800 deg.C or above and milling the resultant ceramic.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a translucent alumina ceramic.

[0002]

2. Description of the Related Art Translucent alumina is widely used as an arc tube for high-pressure sodium lamps and a plasma-transmitting window material because it transmits light well and has excellent chemical resistance and plasma resistance. .

Japanese Patent Application Laid-Open Nos. 61-256962, 4-356922, and 6-157132 show translucent high-purity alumina ceramic members.

The translucent alumina tube described in Japanese Patent Application Laid-Open No. 61-256962 has a diffuse transmittance of 95% or more by setting the average particle size to 20 to 40 μm and the variation of the particles to 4.0 or less. It is configured to obtain.

Japanese Patent Application Laid-Open No. 4-356922 discloses a plasma discharge member used as an electromagnetic wave transmission window. This plasma discharge member has an Al ₂ O _{3 of} 99.9 wt.
% Or more of high-purity polycrystalline alumina or high-purity single-crystal alumina.

JP-A-6-157132 discloses a high-purity alumina ceramic having a magnesia content of 1000 ppm or less and an alkali metal oxide content of 50 ppm or less.

[0007]

Generally, it is known that the properties of translucent alumina are affected by optical scattering factors such as particle size, porosity, pore size, birefringence, and grain boundary segregation layer. I have. Further, depending on the use of the light-transmitting alumina member, mechanical strength and corrosion resistance may be regarded as important as in the case of transmittance.

[0008] Of the above-mentioned prior art, Japanese Patent Application Laid-Open No. 61-25 / 1986
The transmittance of the alumina ceramic disclosed in Japanese Patent No. 6962 is improved by adjusting the average particle size and the variation of the particle size.

The alumina for plasma discharge disclosed in Japanese Patent Application Laid-Open No. 4-356922 has improved corrosion resistance in a plasma discharge atmosphere by reducing the amount of alkali metal contained in the alumina.

The alumina ceramic disclosed in Japanese Patent Application Laid-Open No. Hei 6-157132 contains 50 ppm of an alkali metal element.
By suppressing the content to below, the amount of magnesia added to the abnormal particle growth suppressing material is set to 1000 ppm or less, thereby achieving high purity.

On the other hand, the existence of a transition metal element is known as a factor that affects the light transmission. That is, iron (Fe), chromium (Cr), vanadium (V)
If a small amount of metal impurities such as is present, coloring such as black or red occurs, and the transmittance of visible light is reduced.

For this reason, in conventional translucent alumina ceramics, care has been taken to minimize the concentration of these metal impurities.

However, even if the content of these metal impurities is suppressed to the above-mentioned range, a sufficient transmittance as a light transmitting member may not be obtained.

In view of such problems of the prior art, an object of the present invention is to provide a translucent alumina ceramic having a sufficient transmittance as a translucent member.

[0015]

The gist of the present invention is a translucent alumina ceramic having a sulfur content of 100 ppm or less.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have conducted intensive studies,
In addition to iron, chromium, and vanadium, sulfur (S) is an impurity that adversely affects the light transmission of alumina ceramics.
Have been found, and that the sulfur content has a great effect on the translucency of the alumina ceramics, and have completed the present invention.

That is, the translucent alumina ceramic of the present invention is characterized in that the sulfur content is 100 ppm or less. The more preferable sulfur content of the translucent alumina ceramic is 50 ppm or less.

Of course, it is also important to reduce the contents of iron, chromium and vanadium. The contents of iron, chromium, and vanadium are each set to 5 ppm or less, and the total content thereof is desirably suppressed to 10 ppm or less.

The total light transmittance of the translucent alumina ceramic of the present invention preferably exceeds 95%. A more preferred total transmittance is 96% or more.

An example of a method for producing a translucent alumina ceramic having a sulfur content of 100 ppm or less will be described.

The starting material of the alumina raw material is aluminum ammonium sulfate (Al (NH ₄ ) (SO ₄ ) _2.
12H ₂ O), which is fired at 800 ° C. or higher,
By pulverizing, alumina raw material powder is obtained. Aluminum sulfate generated during the decomposition process of ammonium aluminum sulfate is decomposed at 770 ° C, and ammonium sulfate is decomposed at 513 ° C. Since sulfur generates various elements and compounds as a sulfuric acid compound, the remaining amount varies depending on the impurity element of the raw material and its content. As a furnace used for firing, a furnace in which volatilization of SOx is promoted to reduce the sulfur content is used.

[0022]

EXAMPLES First, alumina raw material powders were produced by using the same starting materials and changing the firing temperature, and the relationship between the firing temperature and the sulfur content was examined. As a result, the sulfur content was 800 ° C.
150 ppm at 900 ° C, 90 ppm at 950 ° C, 6 ppm at 950 ° C
It became 20 ppm at 0 ppm and 1150 ° C.

Next, translucent alumina ceramics having different sulfur contents were manufactured using alumina raw material powder having an iron content of 5 ppm or less. Hereinafter, the manufacturing procedure of the translucent alumina ceramics will be described in detail.

100 parts of alumina raw material powder prepared by changing the temperature of the sintered body, 0.5 part of magnesium sulfate heptahydrate, and PVA (polyvinyl alcohol) as a binder
One part is mixed to make a slip. Then, it is dried and granulated with a spray drier. The granulated powder is formed into a pipe by isostatic pressing at a pressure of, for example, 1 ton / cm ² . This is ground into a predetermined shape. After calcining the processed body at 1100 ° C. to scatter the binder, it is fired in a hydrogen atmosphere at 1850 ° C. for 6 hours to obtain a pipe-shaped high-purity polycrystalline alumina ceramic.

The total transmittance of the alumina ceramic thus obtained and the sulfur content in the fired product were measured, and the correlation between the two is shown in FIG.

As shown in FIG. 1, a clear correlation was observed between the total transmittance and the sulfur content.

The total transmittance is 100 to 110 pp sulfur content.
m in the region of m.
When it exceeds ppm, it was confirmed that only an insufficient transmittance of about 94% or less was obtained.

[0028] Sulfur is considered to exist in the form of aluminum sulfide in alumina ceramics, but when its content exceeds the critical value of 100 ppm, the transmittance of the translucent alumina is significantly reduced.

Finally, a method for analyzing sulfur in this embodiment will be described. The analysis of sulfur in alumina ceramics was performed by first leaching a sample with a sodium carbonate solution in a pressurized vessel by heating, and thereafter using an ion exchange chromatograph. The procedure of the analysis is shown below. 1) Preparation of a sample of about 1 g. 2) In a 23 ml PFA jar, add Na ₂ CO ₃ (2%) 1
Insert with 20 ml of pure water and 20 ml of pure water. 3) Heat at 230 ° C. for 16 hours using a pressure vessel. 4) Centrifugation at 12000 rpm for 30 minutes 5) 1.8 mM Na ₂ CO ₃ as eluent and 1.7
The supernatant was subjected to ion chromatography measurement using mM-NaHCO ₃ .
For ion chromatography measurement, 2020 manufactured by Dionex was used.
i (trade name) was used.

[0030]

The translucent alumina ceramic of the present invention has a sufficient transmissivity as a translucent member and is industrially useful.

In particular, translucent alumina ceramics having a total transmittance exceeding 95% are very useful as arc tubes for high-pressure sodium lamps and the like and plasma transmission window materials.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the total transmittance of an alumina ceramic according to an example of the present invention and the sulfur content in a fired product.

Claims (2)

[Claims] 1. A translucent alumina ceramic having a sulfur content of 100 ppm or less. 2. The translucent alumina ceramic according to claim 1, wherein the total light transmittance exceeds 95%.