JPH0230681A - Production of porous inorganic material - Google Patents

Abstract

PURPOSE:To obtain an excellent porous inorganic material by heat-treating a porous material or a material having porous part under pressure with an isotropic pressure medium, thereby decreasing closed pores while maintaining open pores. CONSTITUTION:A porous inorganic material is heated under pressure in an isotropic pressure medium to decrease the ratio of closed pore. The porous inorganic material is e.g. Al2O3, SiO2, TiO2, Si3N4 or ZrO and the porous material is preferably formed before heating under pressure in the isotropic pressure medium. The conditions of compression and heat-treatment depend upon the composition and pore diameter of the porous inorganic material to be produced and are preferably 5-3,000 atm and 500-2,200 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for manufacturing an inorganic porous body used for various sensors, catalyst carriers, biological porcelain, and the like.

<Prior art and its challenges> Conventionally, inorganic porous materials have been used for various sensors, catalyst carriers, etc. due to their large surface area, and have also been used for artificial bones, artificial teeth, etc. due to their compatibility with living tissues. It is also important as biological porcelain.

Biomedical porcelain includes high-density sintered alumina. As a necessary characteristic of living body porcelain, it is said that a porous body having a pore diameter of about 20 to 300 μm is useful in order to promote the growth of living tissue such as new bone. However, such a porous body has a drawback that it has poor mechanical strength and is easily crushed during use. In the case of a catalyst carrier, the carrier has a large surface area and a large pore volume in order to support catalytically active species. The pores are preferably pores that communicate with the outside world, that is, open pores, and pores that do not communicate with the outside world, ie, closed pores, do not participate in the reaction.

Conventionally, porous carriers have been manufactured by a method in which carrier raw material powder is prepared by a method such as hydrolysis of inorganic or organic salts, which is molded into a desired shape and then fired. Conventionally, firing has been carried out at a relatively low temperature in order to maintain open pores useful as a carrier or to maintain a small pore diameter.

Therefore, there was a problem that the mechanical strength of the obtained carrier was not sufficient. Similar problems also exist with inorganic porous materials used for various sensor applications and other applications. An object of the present invention is to solve these problems and provide a method for reducing the number of closed pores while maintaining the open pores of an inorganic porous body.

<Means for Solving the Problems> The present inventors have solved the problem by heat-treating a molded article that is porous or has a porous portion under pressure using an isotropic pressure medium.
It was discovered that closed pores can be reduced while maintaining open pores, resulting in an excellent inorganic porous material, leading to the present invention. That is, the present invention is a method for producing an inorganic porous body with reduced closed porosity, which is characterized by heating the inorganic porous body 7 under pressure in an isotropic pressure medium.

The invention will be explained in detail below. The porous body referred to in the present invention is
It is an object with open and closed pores.

Specific examples of porous bodies include Al2O, 5ift, Ti
O□, Si:+Ns,, ZrO,, C, Ca0-P
zOs series, 3CaOP2O5 series, 10Ca0 3 P
2O3MgO system, 5tO2Zr (h system, Zr02-
P2O3-H,0 system, 2Mg0 2AhOz'5SiO
z-based, Na, 0-CaO-PzOs SiO2-based,
SiO□-Alz(h MgOKzOF Bz(
h series, NazOKzOMgOCaOsto, p2
o, MgO-CaOSing PtO2 system, etc.

Further, a composite may be formed by further blending an organic substance, a metal, an inorganic substance, etc. with these porous bodies. These porous bodies are preferably formed before being heated under pressure in an isotropic pressure medium. As a molding method, a powdered inorganic material or a mixture of an inorganic material and an organic material may be pressure molded or extruded. It is also preferable to make a porous molded article by adding fibrous or particulate matter that can be removed by heat treatment during molding.

The porous body or molded body having a porous portion thus obtained is then subjected to heat treatment under pressure using an isotropic pressure medium. The isotropic pressure medium is a gas or liquid such as argon, nitrogen, etc.
Pressing) method. A molded article that is porous or has a porous portion may be produced in the pressure vessel and subsequently heat-treated under pressure in an isotropic pressure medium. The pressure and heat treatment conditions vary depending on the composition and pore diameter of the inorganic porous body to be produced, but the pressure is preferably in the range of 5 to 3000 atm and the temperature is preferably in the range of 500 to 2200°C.

The feature of the method of the present invention is that by pressurizing the isotropic pressure medium, open pores are maintained while closed pores are reduced. In other words, for open pores, the pressure acts on the inside and outside of the pore, so the open pores do not collapse, and for closed pores, the pressure acts only on the outside of the pore, so the closed pores collapse. be.

In other words, the present invention attempts to effectively apply hot isostatic pressing technology to the production of a porous body with reduced closed porosity, and is based on a novel idea that has not existed before.

The present invention will be further described below with reference to Examples.

Commercially available Al with a purity of 99.9% and an average particle size of about 0.5 μm
z(h) 0.5 wt% MgO powder was added to the powder and mixed for 20 hours using a ball mill.
Pressure preforming was carried out at l. At this time, attach a diameter of 2 mm to the end of the mold.
50 vinylon fibers with a length of 0 to 100 μm and a length of 2 to 3 ml
~60 bottles were filled.

This preformed body was pressed at 1500k using a rubber press.
Molded at g/cd. This molded body was placed in air at a temperature of 155
Preliminary sintering was performed at 0 to 1650°C for 2 hours.

The relative density of the obtained sintered body was 93%, and the closed porosity was 1.1%. The open porosity of this sintered body is 100-9
3-1.1#6%. In addition, in order to measure the bending strength of this preliminary sintered body, a width of 3 ml, a thickness of 1 crane, and a length of 1
After cutting out and polishing two fin test pieces, the three-point bending strength was measured with a span of 9 fl, and the result was 52 kg/2 cranes.

The obtained preliminary sintered body was subjected to hot isostatic pressing at a temperature of 1400 to 1500°C and a pressure of 1800 kg/cJ using argon gas as a pressure medium. The relative density of the obtained sintered body was 94%. Further, when the sintered body was evaluated by mercury intrusion method, all open pores were 100 μm or less, and the closed porosity was about 0.3%. The open porosity of this sintered body was 10094-0.3=6%, which was the same as before hot isostatic pressing. Further, the three-point bending strength of this sintered body was 76 kg/Tsuru2, which was higher than before hot isostatic pressing.

The closed porosity is calculated from the difference between the density excluding open pores measured by immersion method etc. and the theoretical density (Reference:
Ceramics Association Ceramics Handbook, page 406). Also,
The method for measuring the relative density of a sample is as follows.

The volume of the sample is vl, and the sum of the volumes of open pores in the sample is ■2
, the sum of the volumes of closed pores in the sample is 3. The true specific gravity of alumina is 81 and the specific gravity of water is 1. Since Wl is the mass of the sample, it can be written as follows.

W1=S (Vl-V2-V3) (4)
When the sample is placed in water, water enters the open pores and Vl-■
Displace 2 volumes of water. Therefore, the sample is subjected to buoyancy,
W2 is W2 = W1-1 (Vl-V2) (5) When the sample is lifted from water, water fills the open pores, so W3 is: W3 = W1+1 ・V 2
It becomes +61. The relative density of the sample is derived from the following equation.

Sr= (Wl/S・Vl)X100 (71 Also, from formula (51 f6), W 3- W 2 = V 1
(8) +71 (From formula 81, 5r=W 1 /S ・(W3-W2) X 100
(91) From equation (3), total porosity = 100-3r QO) Generally, when rubber pressing is performed, the relative density of the alumina sintered body becomes about 99%. When the relative density becomes 92% or more, all the remaining pores become closed pores, so all the pores remaining after rubber pressing become open pores. However, in the example, the relative density was as low as 93%. α [From the formula, the total porosity is 7% and the internal closed porosity is 1%. During molding, this
This means that open pores are formed by introducing vinylon fibers.

Although the closed porosity was reduced to 0.3% by HIP, the total porosity was 6%, meaning that closed pores were eliminated while open pores were maintained.

<Effects of the Invention> According to the production method of the present invention, the closed porosity of the inorganic porous body is reduced while maintaining the open pores, so the mechanical strength can be improved without impairing the functions such as biocompatibility and reaction carrier. An inorganic porous body with excellent properties can be obtained.

Claims (1)

[Claims] (1) A method for producing an inorganic porous body with reduced closed porosity, which comprises heating the inorganic porous body under pressure in an isotropic pressure medium.