JPH03285865A - Transparent alumina ceramics and production thereof - Google Patents

Abstract

PURPOSE:To obtain Al2O3 ceramics having superior strength and light transmittance by mixing high purity Al2O3 powder with a very small amt. of MgO as a sintering aid, molding the mixture into a prescribed shape and sintering this molded body under specified conditions in a nonoxidizing atmosphere. CONSTITUTION:A powdery mixture of >99.9wt.% fine powder of high purity AL2O3 having 99.99% purity, <=1mum average particle size and 3-15m<2>/g specific surface area with <0.1wt.% fine powder of MgO as a sintering aid is press- molded into a prescribed shape. This molded body is put in a nonoxidizing heating furnace such as a hydrogen furnace or a vacuum furnace, where it is sintered at 1,650-1,750 deg.C max. temp. In this case, the molded body is heated from 1,400 deg.C to the max. temp. at a low heating rate of <=60 deg.C/hr and a sheetlike bod having 8-15mum average grain size and <=0.35mm thickness is formed by sinlering. Transparent alumina ceramics having such high transmittance as to transmit <=70% of UV having 2,537Angstrom wavelength and high strength is produced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to translucent alumina ceramics used for windows of EP-ROM packages, arc tubes of high-pressure discharge lamps, etc., and a method for manufacturing the same.

[Conventional technology]

Translucent alumina ceramics have been widely used in the past. Regarding its manufacturing method, please refer to
As shown in Japanese Patent Application No. 240, etc., an alumina raw material with a purity of 99.9% by weight or more and a particle size of 1 μm or less is mixed with 0.03~
After adding 0.5% by weight of MgO, it is molded into a predetermined shape and calcined in the air at 1000 to 1300°C, and then heated at a heating rate of 100% in a non-oxidizing atmosphere such as a hydrogen furnace or a vacuum furnace. ℃/hour, maximum firing temperature 1750-1900℃
It was supposed to be held for 0.5 to 5 hours and fired.

In this way, by firing a high-purity alumina raw material at a high temperature, the crystal grain size was grown to 20 μm or more, and it was generally made to have translucency.

[Issues with conventional technology]

However, as the crystal grain size of the ceramic for boat fishing increases, the flexural strength decreases, and the conventional translucent alumina ceramics described above have a flexural strength of 2500 Kgf/
It was only about cm2. Furthermore, in the conventional manufacturing method, the internal pores could not be completely eliminated due to the rapid temperature increase rate, and the light transmittance was also not excellent.

Therefore, it could not be used in a thin plate with a thickness of 0.5 mm or less, such as a window in a puff cage for an EP-ROM, which requires excellent strength and light transmittance.

Therefore, as shown in JP-A No. 63-242964, a method was proposed in which the firing temperature was lowered to 1450-1600°C, the crystal grain size was reduced to 8 μm or less, and the bending strength was increased. As expected, the UV transmittance of 2,537 people is 4.
It was low at 0 to 70%, making it unsuitable as a window for a puff cage for BP-ROM.

[Purpose of the invention]

The present invention was made in order to solve the above problems, and its purpose is to obtain a translucent alumina ceramic that has both excellent strength and excellent translucency, and is ideal for use as a window for a BP-ROM package. shall be.

[Means to solve the problem]

In the present invention, after forming a ceramic raw material consisting of 99.9% by weight or more of 81□03 and 0.1% by weight or less of MgO into a predetermined shape, in a non-oxidizing atmosphere such as a hydrogen furnace or a vacuum furnace, Maximum firing temperature 1650-1750℃, 14
It is characterized in that firing is performed at a rate of temperature increase from 00°C to the maximum firing temperature of 60°C/hour or less.

According to this manufacturing method, since the maximum firing temperature is low, the average crystal grain size of the sintered body can be reduced to 8 to 15 μm, and the strength can be increased to 4500 kgf/cm or more, and the heating rate can be slowed down. Since it is fired slowly, internal pores can be easily eliminated and the average pore diameter can be reduced, making it possible to obtain translucent alumina ceramics with a UV transmittance of 70% or more at a wavelength of 2537 at a thickness of 0.35 nm+m. .

In the above raw material composition, a part of MgO is solidly dissolved in the alumina crystal and acts as a grain growth inhibitor, but the remaining part forms spinel at the grain boundaries and deteriorates the light transmittance. Therefore, the amount of MgO added is 0.1% by weight or less, preferably 0.
．． A trace amount of 03 to 0.07% by weight, and during firing,
It is preferable to evaporate MgO to an extent that does not cause abnormal grain growth.

Furthermore, since the sintering aid is only the above-mentioned trace amount of MgO,
As the alumina raw material powder, it is necessary to use one having a purity of 99.99% or more, an average particle size of 1 μm or less, and a specific surface area of 3 to 15 m''/g and good activity.

Further, by setting the atmosphere during firing to a non-oxidizing atmosphere such as a hydrogen atmosphere or a vacuum atmosphere, internal pores can be easily eliminated and translucency can be improved.

Furthermore, if the maximum firing temperature is higher than 1750°C, the crystal grain size not only increases and the strength decreases, but also the thickness decreases to 0.
．． If a thin plate body of 5 w+m or less is fired, most of the MgO will evaporate and abnormal grain growth will occur. If the maximum firing temperature is lower than 1650℃, the crystal grain size will be smaller than 8μ, and the UV transmittance at a wavelength of 2537 at a thickness of 0.35mm will be lower than 70%, resulting in EP-R
It is unsuitable as a window for an OM package.

In addition, in firing alumina, 1400 to 1700℃
The grain growth of the crystals is most remarkable between 200 and 300°C, and if the temperature increase rate at this time is faster than 60°C/hour, the rate of disappearance of pores (diffusion rate) cannot keep up with the rate of grain growth, and pores remain inside. This results in a decrease in light transmittance and strength. Therefore, the temperature increase rate from 1400 DEG C. to the maximum firing temperature is 60 DEG C./hour or less, preferably 30"C/hour or less. Further, the holding time at the maximum firing temperature is required to be 3 hours or more.

〔Example〕

The present invention will be explained in detail below.

Purity 99.99%, average particle size 0.5 μm, specific surface area 5.
Add 0.035 to 0.07% by weight (7) MgO to 0 m2/g of alumina raw material powder as shown in Table 1,
After pulverization and mixing using a ball mill, a total of 4 to 7% by weight of an organic binder was added as a molding aid, and the mixture was dried and granulated using a spray dryer. Next, this granulated powder was added at a rate of 2 tons/
The material was press-molded at a pressure of cm2 or higher to have a thickness of 0.35 mm after firing, calcined in an air furnace at 1070°C to remove the binder, and then fired in a vacuum furnace.

As shown in Table 1, the maximum firing temperature and 1400℃
~The heating rate of the maximum firing temperature was varied, and the ultraviolet transmittance at a wavelength of 2573, the three-point bending strength, and the average crystal grain size were measured for each sintered body obtained. The results are shown in Table 1.

Margins below C] From Table 1, since the maximum firing temperature of floor 1 was as high as 1750°C, excessive evaporation of MgO caused abnormal grain growth. In addition, in 11h5.6, the temperature increase rate from 1400°C to the maximum firing temperature was 100°C/hour or more, which was too fast, so pores remained.
Both UV transmittance and bending strength were low. Furthermore, on the third floor,
Since the press pressure was lowered to reduce the green density to 2.20 g/cm3, both the bending strength and the ultraviolet transmittance were low.

In contrast, 11h2. which is an example of the present invention. 47.
8 and 9.10 had excellent ultraviolet transmittance of 70% or more and bending strength of 4500 kgf/cm''.

〔Effect of the invention〕

According to the invention, like soft soil, more than 99.9% by weight of A
After mixing 1zO3 and 0.1% by weight or less of MgO as a sintering aid and forming it into a predetermined shape, it is heated in a specific oxidizing atmosphere at a maximum firing temperature of 1650 to 1750°C, and from 1400°C to a maximum firing temperature. By firing at a temperature increase rate of 60°C/hour or less, the average crystal grain size is 8 to 15 μm, and the UV transmittance at a wavelength of 2,537 people at a thickness of 0.35 mm is 70% or more, both in strength and translucency. Excellent translucent alumina ceramics can be obtained, especially EP-RO
It can be suitably used as a window for an M package.

Claims (2)

[Claims] (1) Consists of 99.9% by weight or more of Al_2O_3 and 0.1% by weight or less of MgO, with an average crystal grain size of 8 to 15 μm
A translucent alumina ceramic having a UV transmittance of 70% or more at a wavelength of 2537 Å at a thickness of 0.35 mm. (2) High purity Al with a specific surface area of 3 to 15 m^2/g
After adding 0.1% by weight or less of MgO as a sintering aid to 99.9% by weight or more of _2O_3 powder and molding it into a predetermined shape, the maximum firing temperature was 165% in a non-oxidizing atmosphere.
1. A method for producing translucent alumina ceramics, which comprises firing at a temperature of 0 to 1750°C with a heating rate of 60°C/hour or less from 1400°C to a maximum firing temperature.