JPH04119977A - Production of porous functionally gradient material - Google Patents

Abstract

PURPOSE:To improve filtration efficiency by separating solid. from liq. in a suspension while continuously changing the mixing ratio of suspended particles to the suspension to form a gradient-composition layer and then subjecting the specified suspended particles to a reaction to form pores. CONSTITUTION:A suspension A of SiC particles, etc., is injected into an agitated mixing tank 1, agitated, mixed and then introduced into a tank filter 2. The particles in the suspension A are deposited on a filter medium 21 by gravity and by the dehydration by a pump in the tank filter 2, and a suspension B of carbon particles, etc., is continuously introduced into the tank 1 at a specified flow rate when a specified thickness is obtained. The suspensions A and B are sufficiently mixed in the tank 1, the ratio of the suspension B to the mixed suspension is successively increased to control the suspension B to a specified concn. A gradient-composition layer with the composition successively changed is formed on the particle layer deposited on the upper surface of the filter medium 21 to obtain a cake 5. The cake 5 is discharged from the tank filter 2, compressed, dehydrated and then formed, and the formed body is calcined in an O2 atmosphere to obtain a porous gradient functional material with the porosity successively changed in its thickness direction is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for manufacturing a porous functionally graded material in which the pore density changes continuously in the thickness direction.

[Prior Art] Conventionally, regarding the production of functionally graded materials in which the composition, that is, the mixing ratio of a plurality of fine particle components changes continuously in the thickness direction,
Various layering methods have been proposed, including vacuum film forming techniques such as CVD and PVD, and powder scattering techniques in which raw material powder is destroyed and layered one after another.

This powder scattering technique scatters or sprays raw material powder while changing the mixing ratio from a nozzle that moves relatively in the X and Y directions above the laminated surface.

Furthermore, porous materials such as aerated concrete having a uniform pore density inside are known.

[Problem to be solved by the invention] However, the inclined layering method using vacuum film-forming technology
Although it is suitable for forming thin films on the order of m, it is impractical to form thicker films because it takes too much time.

On the other hand, although the gradient layering method using the powder scattering technique has a higher layering speed than the vacuum film forming technique, it has the following drawbacks.

First of all, the surrounding area is contaminated with raw material powder due to scattering or spraying, which deteriorates the working environment. Second, since the spray nozzle relatively moves above the laminated surface in the X and Y directions, the working efficiency is poor and the composition varies greatly in the surface direction.

Furthermore, the conventional porous materials mentioned above have uniform pore densities, so the only way to provide different functions (characteristics) between the surface and the inside is to glue multiple types of materials together. .

The present invention has been made in view of these problems, and an object to be solved is to provide a method for manufacturing a porous functional tree N1 in which the pore density changes continuously in the thickness direction. It is something.

[Means for Solving the Problems] The method for producing a porous functionally gradient material of the present invention continuously changes the mixing ratio of suspended fine particles in a suspension in which a plurality of types of suspended fine particles are suspended. a suspension step, a gradient coarse production forming step in which the suspension is solid-liquid separated to form a gradient assembly in which the composition changes continuously in the production direction; and at least one type of suspension during the production of the gradient assembly. The method is characterized by comprising a pore forming step of forming pores by reaction of turbid fine particles.

In one preferred embodiment, the pores are formed by burning off or pyrolysis of certain suspended particulates during graded assembly manufacturing.

A porous functionally graded material product formed using the production method of the present invention and having a continuously changing porosity is used, for example, as a filter medium.

The filter medium requires a filtration section having a large number of minute continuous holes for filtering fluid or particles having a predetermined diameter or less, and a support section that can withstand filtration pressure and mechanically supports the filtration section. In a conventional filter medium in which the supporting portion has the same pore density as the filtering portion, the filtering portion is constituted by the surface portion of the filtering medium that is in contact with the liquid to be filtered.

Although most of the filter medium except for the surface portion of the filter medium constitutes the support section, it is merely a resistor against filtration. According to the present invention, since the pore density can be changed continuously (or stepwise), the so-called support part inside the filter medium is integrated with the surface part of the filter medium, so-called filtration part, to support it, and also to support it during filtration. It is possible to reduce pressure loss and improve filtration efficiency.

Examples of suspended fine particles for forming pores include carbon particles and resin powder. These carbon particles and resin powder are oxidized during the sintering process in a high-pressure oxygen environment.
Forms pores. Furthermore, water-insoluble natural organic polymer substances such as starch can be used as suspended fine particles for forming pores that are thermally decomposed.

[Example] A manufacturing apparatus for carrying out the manufacturing method of the present invention will be described with reference to FIG.

This manufacturing apparatus consists of a stirring mixing tank 1, a filtration tank 2, a circulation pump 3, on-off valves 4a, 4b, 4c, 4d, and a control device 9.

Pipes 38.39 for injecting slurry A and slurry B are connected to the stirring mixing tank 1.
9 manually supplies slurries A and B from a stirring tank (not shown) for slurry formation.

Slurry A and slurry B injected into the stirring mixing tank 1 are sufficiently stirred and mixed by the stirrer 11 to form a mixed slurry with a predetermined mixing ratio, and the mixed slurry is sent to the filtration 4f72 via the on-off valve 4a.

A filter medium 21 of a predetermined thickness is installed horizontally in the center of the filtration tank 2, and a mixed slurry inlet pipe 22 and a mixed slurry discharge pipe 23 are connected to the upper part of the filtration tank 2. The lower part of the filtration WJ2 is connected to a suction part of a vacuum pump (not shown).

Here, slurry A is a suspension of 3iC (silicon carbide) powder with an average particle size of several μm in water, and slurry B is a suspension of carbon particles with an average particle size of several μm or less in water. be. The concentrations of each slurry A and B are determined as appropriate.

The control device 9 is composed of a microcomputer and controls the on-off valves 4a, 4.
b, 4C14d is opened and closed to control the flow rate of the mixed slurry and slurries A and B. The on-off valve 4b controls the supply of slurry A to the stirring mixing tank 1, the on-off valve 4C controls the supply of slurry B to the stirring mixing tank 1, and the on-off valve 4d connects the stirring mixing tank 1 to the external drain port. Control the discharge of the mixed slurry to.

The circulation pump 3 circulates the mixed slurry between the stirring mixing tank 1 and the filtration tank 2 to equalize the composition of both.

Hereinafter, a manufacturing method using this manufacturing apparatus will be explained with reference to the flowchart of FIG.

(Suspension step and gradient rough production forming step) First, open the on-off valve 4b to inject slurry A into the stirring mixing tank 1, and drive the stirrer 11 and circulation pump 3 (
SIO).

After a predetermined time T1 (S12>, the on-off valve 4b is closed and the on-off valve 4a is opened to introduce a predetermined amount of slurry A into the filtration tank 2, and at the same time a vacuum pump (not shown) is started (S
14).

The 5iC (silicon carbide) powder in the slurry A introduced into the filter tank 2 settles and accumulates on the upper surface of the filter medium 21 due to its own weight and dehydration using a vacuum pump (not shown).

After the predetermined time T2 (S16), that is, when the SiC powder layer that has settled and accumulated on the upper surface of the filter medium 21 is expected to have a predetermined thickness, the on-off valve 4C is opened to pour slurry B (carbon slurry) into the stirring mixing tank 1 to a predetermined value. Continuously inject at a flow rate of At the same time, the on-off valve 4d is opened to discharge the mixed slurry from the filtration tank 2 at a predetermined flow rate (818). the result,
The slurries A and B in the stirring mixing tank 1 are sufficiently mixed by the stirrer 11, and the proportion of slurry B in the mixed slurry in each tank 1.2 and the pipe line increases continuously, and after a predetermined time. The slurry B has a predetermined concentration.

Therefore, the SiC sedimented and accumulated on the upper surface of the filter medium 21
A mixed layer of continuously varying composition is produced on top of the powder layer, resulting in cake 5.

After the predetermined time T3 (S20>, open/close valve 4a, 4C14
d is closed, the stirrer 11 and circulation pump 3 are turned off, the mixed slurry remaining in the filtration tank 2 is dehydrated, the vacuum pump is turned off, and the cake 5 is taken out (S22).

FIG. 3 shows the composition change over time of the mixed slurry in the filter tank 2, and FIG. 4 shows the composition change in the thickness direction of the cake 5.

(Pore Formation Step) The cake 5 taken out from the filtration tank 2 is further compressed and dehydrated, then molded into a predetermined shape, dried, and sintered.

That is, the taken out cake 5 is pre-compressed and then molded into a predetermined shape or sintered as it is in the presence of high temperature and high pressure oxygen.

Note that hot pressing in an oxygen environment may be used instead of this sintering step.

In this way, the carbon particles in the cake (gradient assembly production) 5 react with oxygen and disappear under the above-mentioned high temperature and high pressure, and as a result, a SiC ceramic in which the pore density continuously changes in the thickness direction is obtained.

When using the d-flow type manufacturing equipment shown in this example,
If the injection flow rate of slurries A and B into the stirring mixing tank 1, the discharge flow rate of the mixed slurry from the filtration tank 2, and the settling and accumulation rate of the mixed slurry in the filtration tank 2 are controlled, a composition with a mountain-shaped gradient can be obtained. Functionally graded materials can also be obtained.

Hereinafter, modifications of the manufacturing apparatus of this embodiment will be explained.

The filtration tank 2 can be of a suction filtration type using a vacuum pump, a pressure filtration type, a centrifugal separation type, or a compression separation type.Of course, a fixed liquid separation means of an electrophoresis type or a slip casting type can also be used. be able to.

The filter medium 21 can also be appropriately formed into a desired product shape.

The dispersion medium for the slurry is not limited to water, and other organic solvents can be used.

The porous SiC ceramics sintered as described above can also be used as various filter media.

When used as a filter medium, it is necessary to make the internal pores continuous by increasing the carbon mixing ratio.

[Effects of the Invention] As explained above, the method for producing a porous functionally graded material of the present invention involves separating the suspension into solid and liquid while continuously changing the mixing ratio of suspended fine particles in the suspension. Since the inclined set is formed and then predetermined suspended fine particles are reacted to form pores, the following effects can be achieved.

(a) It is possible to produce a porous gradient material with small composition variations in the plane direction and excellent continuous gradient of pore density in the thickness direction.

(b) Since it does not depend on processes such as spraying and dispersion, it is possible to prevent environmental deterioration.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an example of a manufacturing apparatus for carrying out the method of the present invention, FIG. 2 is a flowchart showing the operation of the manufacturing apparatus shown in FIG. 1, and FIG. A line diagram, FIG. 4 is a diagram showing compositional changes in the thickness direction of the manufactured cake. Patent applicant Nagao Kogyo Co., Ltd.

Claims (4)

[Claims] (1) A suspension step of continuously changing the mixing ratio of the suspended fine particles in a suspension in which a plurality of types of suspended fine particles are suspended, and a solid-liquid separation of the suspension so that the composition is in the stratified direction. a gradient composition layer forming step of forming a gradient composition layer that continuously changes; and a pore formation step of forming pores by a reaction of at least one type of suspended fine particles in the gradient composition layer. Characteristic layering method for porous functionally graded materials. (2) The method for producing a porous functionally graded material according to claim 1, wherein the pore forming step is a step of generating the pores by burning out or thermally decomposing the suspended fine particles in the compositionally graded layer. (3) A porous functionally graded material product manufactured using the method according to claim 1, in which the porosity continuously changes in the thickness direction. (4) The porous functionally graded material product according to claim 3, which has continuous pores and is used as a filter medium.