JPS6114171A - Manufacture of silicon carbide structure - 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 [Field of Application of the Invention] The present invention relates to a method for producing a porous structure of silicon carbide having a skeleton structure of an organic polymer foam.

[Prior art]

Using organic polymer foam, especially polyurethane foam,
Ceramic products that have a network structure of their skeletal structure have attracted particular attention in recent years. Typical examples include ceramic foam structures made by immersing breathable polyurethane foam in a slurry of ceramics such as cordierite, alumina, or mullite, and firing this. Industrial applications such as media carriers and heat transfer elements are expanding.

On the other hand, as their uses have expanded, there has been a demand for structures that can withstand use at higher temperatures. Naturally, the types of ceramics used as raw materials for automobiles have been carefully examined, and the possibility of manufacturing silicon carbide using the same process as above is being considered.

However, among ceramics, silicon carbide is generally classified as difficult to sinter, and it has been difficult to prepare high-strength samples without using specific sintering methods such as hot pressing and hot isostatic nibbling. However, due to the selection of a low sintering aid and the selection of sintering conditions, it has been difficult to obtain a satisfactory product with good reproducibility using the atmospheric pressure sintering method in which sintering is performed after depositing the slurry.

[Purpose of the invention]

The present invention provides a new method for manufacturing a silicon carbide porous structure that is different from the above methods.

[Structure of the invention]

That is, 1. the present invention is a carbonaceous porous structure obtained by carbonizing an organic polymer foam, particularly an organic polymer foam containing a phenol formaldehyde resin, in an inert gas atmosphere, in a vacuum or in an inert gas atmosphere. ,(
a) treatment with silicon vapor or a gaseous silicon compound at a temperature of 1400° C. or higher; or (b) immersion in a liquid silicon compound or silicon melt to impregnate the silicon component;
Processing in a temperature range of 1400°C or higher, or (c)
The present invention relates to a method of manufacturing a silicon carbide structure by coating it with silicon powder and treating it in a temperature range of 1400° C. or higher.

The present invention will be described in detail below.

Examples of organic polymer foams used in the present invention include foams of polyurethane, polyethylene, polyolefins, polyvinyl compounds, furan resins, and the like. Among these, polyurethane foam is preferred. Moreover, among the above resins, those containing 7 enol-formaldehyde resin are preferable. In this case, a mixture of 7 enol-formaldehyde resins among the above resins may be used, or a mixture of the resins may be crosslinked with each other.
In other words, taking polyurethane foam as an example of an organic foam, phenol-formaldehyde resin powder is mixed with its raw materials (polyether polyols or polyester polyols, diisocyanate compounds, catalysts, blowing agents, stabilizers, etc.) and foamed. Alternatively, after foaming polyurethane, the phenol-formaldehyde resin is dispersed or partially solubilized in a polyvinyl alcohol or polyvinyl butyral aqueous solution or alcohol solution (0.5 to 10% by weight liquid). The material before carbonization is obtained by impregnating the material in a solution (preferably containing phenol formaldehyde resin of 5 to 900% by weight), removing the excess impregnation solution by centrifugation, etc., and drying it.

Furthermore, by making the material before carbonization contain 0.1 to 2% by weight of boron or aluminum compound,
A more preferable silicon carbide structure is obtained. Examples of the boron or aluminum compound used here include boron nitrogen, boron carbide, boric acid, aluminum nitride, alumina, and aluminum carbide. Methods for containing these include mixing in the raw material stage before foaming, and mixing in the phenol-formaldehyde resin after foaming, etc.

The phenol-formaldehyde resin used here preferably contains 2 to 10% by weight of methylol groups. Moreover, it is preferable that the particle size of the powder is 1 to 50 IL.

The above organic polymer foam is carbonized under vacuum or in an inert gas atmosphere at a temperature of 700 to 1300°C, preferably 1000°C or higher.The carbonaceous structure obtained here is It is a carbon material having a skeleton structure, and although it is not necessarily structurally strong, the present invention provides a method of obtaining a strong carbon-silicon porous structure by further silicifying it. As the silicon source for siliconization used here, solid or liquid silicon, liquid silicon compounds, silicon-containing gases such as silicon tetrachloride and silicon hydride can be used.

(a) When siliconizing using a solid or liquid silicon source, in the presence of a carbonaceous structure, in vacuum or in an inert gas atmosphere, 1400" or more, preferably 1400" or more
This is done by heating to a temperature in the range of 1 aoo"c to generate silicon vapor.

Alternatively, a silicon-containing gas such as silicon tetrachloride, trichlorosilane, dichlorosilane 1, monochlorosilane, silicon tetrafluoride, silicon hydride, monosilane, disilane, and trisilane is reacted with the carbonaceous structure.

(b) When using a liquid silicon compound or molten silicon, impregnating a carbonaceous structure into these liquids,
After shaking off the excess liquid by centrifugation or the like, siliconization is carried out by heating at 1400°C or higher.

Here, liquid silicon compounds include silicon alkoxides such as tetraethyl silicate, siloxane type polymers such as dimethylpolysiloxane, polycarbosilane, organic compounds with OH groups, silicic acid esters, hydrolyzable silicic acid, etc. Examples include esters of compounds and organic compounds or organometallic compounds, such as ethyl silicate, which is synthesized by the reaction of silicon tetrachloride and ethanol. Among them, ethyl silicate polymer is preferred.

Or (c) siliconization is carried out by spraying and coating the above-mentioned carbonaceous structure with silicon powder and heat-treating it at a temperature of 1400° C. or higher in vacuum or in an inert gas atmosphere.

The siliconized structure as described above can be put to practical use as it is, or the skeletal structure may be further densified by further heating and sintering the above-mentioned treated product at a temperature of 1800° C. or higher.

The silicon carbide structure thus obtained can be stably used in the same applications as cordierite ceramic porous bodies or even in higher temperature ranges.

For example, various heat exchange elements, in-furnace heat transfer conversion elements, catalyst carriers, exhaust gas purifiers, sound absorbing materials, various electronic materials, beds for immobilized enzymes, heat-resistant filters, fluid mixers, molten metal filters, catalytic reaction fillers. , etc. It has a wide range of uses.

[Embodiments of the invention]

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

Example 1 ′!
Poly(oxypropylene) triol (molecular weight 3000
, hydroxyl value 56)'too parts, tolylene diisocyanate (TDIma105) 80 parts, granular phenol resin (methylol residue 9% by weight, granular 20JL) 15 parts, water 4.8 parts, silicone foam stabilizer 2. 0 parts, 0.48 parts of stannous 2-toate, io parts of monofluorotrichloromethane, amine catalyst (1,8-diaza-bicyclo[
A phenolic resin-containing polyurethane foam was prepared using 0.1 part of 5,4,0]phenol salt of undecene-7.

Next, after preheating this foam at 1.50°C for 30 minutes, it was placed in an electric furnace, the atmosphere was replaced with nitrogen, and the temperature was raised while a small amount of nitrogen gas was flowed to 1000°C in about 4 hours. After maintaining this temperature for 60 minutes, the foam was allowed to cool to carbonize. The weight of the carbonaceous structure obtained here was measured, and the carbon yield was calculated to be about 53%.

On the other hand, metal silicon was placed at the bottom of a heat-resistant crucible, the carbonaceous structure was placed through a perforated plate, and a lid with ventilation holes was placed on top.
Placed in an electric furnace and heated to 1650℃ while maintaining vacuum.
The temperature was maintained at this temperature for about 3 hours, and then allowed to cool.

The resulting structure was a strong porous structure that maintained the shape of polyurethane foam. Crush the end and
Line analysis revealed that the structure was essentially made of silicon carbide. (See Figure 1) Example 2 A phenolic resin-containing polyurethane foam was prepared in the same manner as in Example 1, and a carbonaceous structure was obtained under the same conditions.

After immersing this in an ethyl silicate polymer (Colcoat Co., Ltd., trade name: Ethyl Silicoat 40) and pulling it up,
1 in a crucible under an argon atmosphere in the same manner as in Example 1.
As a result of firing at 700° C. for 30 minutes, it was found that the skeleton structure was substantially composed of silicon carbide.

〔Effect of the invention〕

The silicon carbide structure of the present invention has at least the surface portion of its skeleton substantially made of silicon carbide, and has extremely excellent heat resistance and oxidation resistance. Furthermore, there is no deposition of extra ceramic layers other than forming a skeletal structure, as is often the case with slurry impregnation methods, and therefore no clogging is observed.

Therefore, the air permeability is good, and the pressure loss due to ventilation is extremely small. Further, it is possible to easily create any mesh structure from large to small, and any shape from large to small.

[Brief explanation of drawings]

FIG. 1 is an X-ray analysis diagram of the silicon carbide structure obtained in Example 1.

Claims (2)

[Claims] (1) A carbonaceous porous structure obtained by carbonizing an organic polymer foam in a vacuum or an inert gas atmosphere is heated under a vacuum or an inert gas atmosphere to (a) 140
(b) immersion in a liquid silicon compound or silicon melt to impregnate silicon components and treatment at a temperature of 1400°C or higher; c) A method for producing a silicon carbide structure by coating with silicon powder, treating at a temperature of 1400° C. or higher, and silicifying. (2) The manufacturing method according to claim 1, wherein the organic polymer foam is a polyurethane foam containing a phenol-formaldehyde resin.