JPS62260766A - Alumina sintered body - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Industrial applications The present invention relates to an alumina sintered body.

BACKGROUND OF THE INVENTION Alumina sintered bodies are widely used in various fields because they are transparent and have excellent electrical properties such as electrical insulation and dielectric constant. However, these characteristics are roughly improved by increasing the density.

For example, high-density alumina sintered bodies are
Engineering”, Volume 30, No. 4, No. 37-43
(1985) and [Magazine [Ceramics], Vol. 12, No. 1, No. 12-23M (1977), the hot press method is used for manufacturing. It is. In this method, alumina powder is placed in a graphite die, heated and sintered under a reducing atmosphere such as a window element atmosphere under a pressure of several hundred atmospheres. However, according to this method, during sintering, impurities contained in the raw materials in the form of compounds are reduced, and carbon etc. enter from the die, causing the sintered body to darken and lose its transparency. descend. Also,
If carbon, etc. are present, when used at high temperatures, it will turn into carbon dioxide gas and evaporate, creating pores, resulting in a decrease in strength A.
bThe Weibull coefficient decreases. In general, the presence of carbon etc.
Also lower the electrical characteristics.

On the other hand, there is a method called pressureless sintering method. This is a method in which a molded product formed by isostatic pressing or molding is heated at 1600 to 1150'C in a deep chamber or in a hydrogen atmosphere to sinter it. This method is as follows: Since the obstinacy is carried out under normal pressure, the degree of activity is set high to increase the density.
Therefore, there is a problem that the growth of the standing seed is large and the mechanical strength and Weibull coefficient are low.

Problems to be Solved by the Invention The purpose of the present invention is to solve the above-mentioned drawbacks of conventional alumina sintered bodies, and to achieve not only a very high density and excellent optical and electrical properties, but also to improve their optical and electrical properties. An object of the present invention is to provide an alumina sintered body with little variation in properties and almost no decrease in strength even when used at high temperatures.

Means for Solving the Problems In order to achieve the above objects, the present invention provides a material that contains substantially no carbon, has a porosity of 0.6% or less, and has a pore size of 0.1 μm or less. Provided is an alumina sintered body characterized in that pores are mainly present at triple points of refined grain boundaries.

Hereinafter, the alumina sintered body of the present invention will be explained in detail along with its preferred manufacturing method.

In this invention, first, an aqueous solution of aluminum chloride with a purity of 99.9% or more and magnesium chloride as a sintering aid is prepared. The amount of magnesium chloride as magnesia in a'3 in the raw material powder to be described later is 0.5% by weight or less, preferably 0.1 to 0.25% by weight. Aluminum nitrate can be used instead of aluminum chloride, and magnesium fluoride can be used instead of magnesium chloride.

Next, from the above aqueous solution, using a coprecipitation method with a circumference of 9.0, a hydrolysis method, a thermal decomposition method, a metal alkoxide method, a sol-gel method, a gas phase method, etc., the average particle size is 0.3 μm or less. A raw material powder in which magnesia is dissolved in alumina is obtained. In this step, calcination is performed at 800 to 1000'C. The temperature increase rate is 100-300°C/hour. The calcined powder is preferably crushed using a ball mill lined with a rubber or urethane resin cylinder, using balls of the same quality as the powder.

Next, the raw material 61 powder is molded into a desired shape using a molding method such as a rubber press method, an injection molding method, a mold molding method, an extrusion molding method, etc., and the molded product is heated once. .

Next, the above molded body is placed in a heating furnace at a rate of 50-100'C/hour up to about 900'C, and at a rate of 30-50'C/hour above that.
Warm the stomach to 1500-1800'C at a rate of °C/hour,
After being held at that time for several hours, it is cooled to obtain a pre-sintered body having a key density of 95% or more of the theoretical density, preferably 97.5% or more. In the process of 71', hot and cold inlets, the alumina takes on the shape of α-alumina. The crystal grain size and density of the pre-sintered body are determined by the activity of the raw material powder, the sintering temperature, etc.

Next, the preliminary sintered body is subjected to so-called main sintering using a hot isostatic pressing method (HIP method) in an oxidizing atmosphere. That is, the preheated sintered body '1 was heated under a pressure of 1000 to 2000 KCJ/Cm for 14 hours in a controlled oxygen atmosphere, that is, an oxidizing atmosphere.
Number from 00 to 1700'C! Heat for 111 minutes, then 20
A sintered body is obtained by cooling at a rate of 0 to 500'C/hour. H
The oxygen concentration used in the IP method must be between 10oopm and 25% by volume.

11000pp wood): 51" means the oxygen concentration is too low,
One sintered piece is reduced to the residue released from the furnace, and carbon etc. remain in the sintered body.Also, if the amount exceeds 25% by volume In such a high-concentration oxygen atmosphere, the ignition point of the members constituting the processing furnace will be significantly lowered, and the life of the furnace will be shortened, making it impractical.

By the way, there are two methods for processing using the HIP method.

One method is to place the raw material powder or compact into a glass or metal container (capsule) and subject it to treatment, and the other method is to prepare a pre-sintered body with a key density of 95% or more of the theoretical density, as described above. This is a method for processing 1q of yen.

The former has the advantage that a dense sintered body can be obtained even at a relatively low temperature. However, due to the container used, it may be complicated. It is not suitable for manufacturing a sintered body having a shape of 1. Although the latter does not have such shape restrictions, it is necessary that the pores of the preliminary sintered body be closed pores rather than open pores because of pressurization with gas. In this respect, most of the pores in the antagonists whose key density is 95% or more of the theoretical density are closed pores, and there is no problem. For example, the bonds between crystal grains are strengthened, and a dense sintered body can be obtained even at low temperatures.

As mentioned above, the HIP method needs to be performed in an oxidizing atmosphere. This is because the TO+IP method uses a heater made of carbon or the like and is generally carried out in an inert atmosphere such as an argon atmosphere, but in this case a small amount of carbon or carbon monoxide remains in the sintered body. It becomes like this. However, if carbon or the like remains in the sintered body, it will darken and the translucency and electrical load will decrease. In addition, when used at high temperatures of 600'C or higher, residual carbon and carbon monoxide spontaneously turn into carbon dioxide gas, creating pores in the sintered body, resulting in a significant decrease in strength and Weibull coefficient. Resulting in.

As mentioned above, the normina sintered body of this invention is
Carbon, which causes a decrease in strength when exposed to temperatures above 0°C, is 71%
Not included. Here, the sintered body that does not substantially contain carbon is defined as follows.

In other words, to analyze the amount of carbon in the sintered body, combustion infrared method,
Various methods are used, such as secondary ion mass spectrometry called SIMS and laser Raman spectroscopy.
In a'3 of this invention, laser Raman spectroscopy is used to measure the sintered body using an argon laser at a wavelength of 488.
The presence of carbon, which is detected as alpha carbon when excited with light of 0.5, 13, and 4579 degrees, is considered to be essentially absent when the presence of carbon is not fully absorbed. Define.

In this invention, a'3 requires that the porosity of the sintered body be 0.6% or less, and that the pore size be 0.1 μm or less. Here, pore IP (%) is
It is defined by the formula, P=[1-(kazadensity/theoretical density)]X100. In other words, the strength, strength, and variation of the sintered body are largely influenced by the porosity, but also by the size of the pores. If pores are present, stress will be concentrated in those areas. Deterioration or unevenness in strength, translucency, and electrical properties [;Although it is not so bad if the porosity is low and the pores are small, if the porosity exceeds 0.6%,
Moreover, when the size of the pores exceeds 0.1 μm, the size of the pores increases rapidly.

Therefore, in the present invention, in order to prevent such problems from occurring, the porosity is set to 0.6% or less, and the total pore size is limited to 0.1 μm or less. The preferred porosity is 0.3% or less.

Note that the Weibull coefficient is an index that statistically represents the variation in strength. The larger the Weibull coefficient, the less variation there is, and the higher the reliability and quality. Furthermore, a large Weibull coefficient tJl means that the material is homogeneous and has few pores and foreign matter, which necessarily means that the optical and electrical properties are also uniform and have little variation.

In the sintered body of the present invention, IJ3 exists mainly at triple points of pores or grain boundaries of alumina. That is, in general, pores appear within refined grains of alumina or at one boundary, and when they appear at a grain boundary, they appear at a portion where two crystal grains touch, that is, at a three-sided point. However, pores in the inner grains and boundaries between two crystal grains appear when the growth of crystal grains, sintering, and densification of the viscous material are not sufficient, and are the cause of a noticeable decrease in the strength of the sintered body. become. The pores filled in the three points also cause a decrease in strength (although they do, the extent of the decrease does not significantly reduce the bond between grains, so the pores between the two grains (intragrain) The one that appears in 11 I
J.No.

The sintered body of the present invention as described above can be sintered at relatively low humidity, so grain boundaries (there are virtually no holes, the diameter of the pores is extremely small, and the pores are present only at 3,000 points). The light transmittance of the object is 95% or more (4j). Here, the light transmittance (:1.) is fixed as follows.

In other words, using a spectrometer and an integrating sphere (60 cm in diameter),
From the ratio of the amount of direct light and the amount of light that has passed through a sintered body (grindstone) with a thickness of 1rl'1m, for wavelengths of 400 to 700nm: Determine the spectral transmittance of the book (λ (%)), and calculate it using the following formula. use

Tm=1/300. /',,,TλdλTm: Average light transmission・ki 1%) 43 above, try i! '20 is 1.05 mm
Thickness//) I)',: l', l'i Polish both sides of the body with Maza #400 emery paper and roughen R200.
Finish with Gouya Endo paste to give it a mirror finish and a thickness of 1mm. In addition, when the sintered body has a color due to the addition of a coloring agent, which will be described later, a spectral distribution of transmittance is formed, so it is necessary to compare the transmittance in a wavelength range corresponding to the color.

If the sintered body contains 0.001 to 2% of various oxides as colorants, the color tone will be improved. for example,
A sintered body containing nickel oxide, chromium oxide, copper oxide, titanium oxide, etc. has a brown or green color. Also, pink color is erbium oxide, yellow color is vanadium oxide,
Cerium oxide and cobalt oxide are effective for purple, neodymium oxide and cobalt oxide are effective for orange, iron oxide is effective for orange, and cobalt oxide and nickel oxide are effective for blue. Two or more types can also be used in combination. These colorants may be added to the raw material powder in the form of hydrochloride or nitrate in the culm, or may be added to the raw material powder in the form of oxide.

Example i Aluminum chloride with 99.95% purity and 99% purity
．． An aqueous solution was prepared by mixing 5% magnesium chloride in a sintered body so that the concentration as magnesia was O+ 21%.

Next, a raw material powder was prepared by a hydrolysis method.

That is, the above aqueous solution is gradually heated to about 100'C, held at that temperature for about 150 hours to evaporate the water, and further heated to about aoo'C at a rate of about 100'C/hour. The calcined powder was held for about 3 hours and then put into a ball mill lined with urethane and ground using an alumina pole to obtain raw powder with an average particle size of about 0.05 μm. I got it.

Next, the raw material powder is molded using a rubber press method,
A molded body was obtained. Pressure force during molding is approximately 2000 K C1
/ Cm 2 t:.

Next, the above molded body was placed in a heating furnace, and the temperature was increased to about 1700'C at a rate of about 50'C/hour up to about 900'C, and at a rate of about 40'C/hour thereafter. , the pre-sintered body is held at that temperature for about 2 hours and the bulk density is about 98% of the theoretical density.

Next, the preliminary sintered body was main sintered using the HIP method.

That is, using a platinum heater, the pre-sintered body is brought to a temperature of about 1600'C at a rate of about 40'C/hour in an oxidizing ↑1 atmosphere containing about 3% oxygen and the balance being argon gas,
At the same time, a back pressure was applied so that the pressure became 2000 KCI/Cm2, and this was maintained for about 1.5 hours, and then cooled at a rate of about 400'C/hour to obtain a sintered body.

Regarding the above sintered body, the porosity, the size of the pores, the position difference of the pores, the absence of carbon, the bending strength, the Weibull coefficient, and the 1000'C'C''100 in air. The bending strength (hereinafter referred to as "temperature strength") and light transmittance after holding for a time were measured.The pore size and phase difference were measured using electron microchains.The bending strength was also measured. JIS-R1
According to 601. Weibull coefficient [calculated with 510 number as 20]. The measurement results are shown below.

Porosity: 0.4% Pore size: 0.04 μm Pore (I placement: Mainly 3-point carbon: Detectionless bending strength Near 50 MPa Weibull coefficient: 14 High temperature strength Near 40 MPa Light transmittance: 97% Invention Effects The alumina sintered body of this invention has a porosity of 0.6% or less, a pore size of 0.1 μm or less, and pores mainly exist at the 3A points of the grain boundaries. from,
Excellent electrical and special characteristics. In addition, since it does not substantially contain carbon, the light transmittance is high and the strength does not decrease even when used at high temperatures.
It can be used for various purposes. An example is shown below.

A. Electrical applications such as circuit boards.

B. Optical applications such as lamp outer tubes.

Heat-resistant applications such as C1 insulation materials and heat-resistant substrates.

D. Nuclear reactor-related applications such as moderators.

Biochemical uses such as snakes, artificial teeth, catalyst carriers, etc.

``, artificial jewelry, seals, tie pins, cowl buttons,
For decoration of special training parts, etc., and as a substitute for Song stone.

G, Go stone, i-] Sponge of thread vise, used for regille.

1-1. For use in tableware such as spoons, spoons, and spoons.

1. For writing instruments such as ballpoint pen balls and pen nibs.

J. Balls for crushing, various mechanical seals, various valves, various bearings, various l-rues, various pumps, impellers, screws, various sleeves, orifices, tiles,
Product 2, such as threading guides, is used as machine parts.

Claims (1)

[Claims] It is characterized by substantially not containing carbon, having a porosity of 0.6% or less, a pore size of 0.1 μm or less, and pores mainly existing at triple points of grain boundaries. Alumina sintered body.