JPS58122016A - Production of silicon carbide filter - Google Patents

Abstract

PURPOSE:To realize a filter that can burn away deposits by having not only high temp. heat resistance but self-exothermic characteristic. CONSTITUTION:High polymer foam is immersed in silicon carbide slurry to fill and impregnate said slurry into the pores. If necessary, the foam is subjected to impregnating and drying again after drying, whereby skeleton of a desired thickness is formed and is later subjected to sintering, whereby a porous sintered body of silicon carbide (filter) is obtained. The high polymer foam material (impregnation) impregnated with the silicon carbide slurry is first dried, then the impregnation is treated under heating to annihilate the high polymer foam material, whereby a body with skeleton construction is obtained. The body with silicon carbide construction (uncalcined) is then subjected to primary sintering for about 30min -3hr at about 1,900-2,300 deg.C in Ar flow, whereby a porous sintered body is obtained. Said body is subjected to secondary calcination in a high pressure gaseous nitrogen atmosphere of about 1,600-2,100 deg.C and 1-200atm.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a porous silicon carbide sintered shard capable of generating heat when energized;
That is, it relates to a method of manufacturing a silicon carbide filter.

Conventionally, heat-resistant filters are required to remove combustible particulate matter such as particulate cargo contained in high-temperature gases such as exhaust gas from internal combustion engines, especially diesel engine exhaust gas. Mere heat resistance would result in clogging tb, etc., resulting in a short service life and the hassle of cleaning or replacement, which would pose problems in practice. In response, it has been desired to realize a filter that not only has high temperature resistance but also has self-heating properties and can burn off deposits.

Since such a filter is installed in the exhaust pipe of a diesel engine, it must have strength and vibration resistance, and must also have high temperature strength, oxidation resistance, and corrosion resistance.

As such a filter material, a material such as silicon carbide that can self-heat by being energized can be considered, but until now it has not been easy to manufacture a material that is excellent both as a filter and as a self-heating material.

It is an object of the present invention to solve the difficulties of these conventional methods and to make it possible to manufacture a silicon carbide filter that can generate heat when energized. That is, the method of manufacturing a silicon carbide filter capable of generating electricity through electricity according to the present invention involves impregnating a polymeric foam material with silicon carbide matrix slurry, and eliminating the polymeric foam material by heat treatment to form a silicon carbide matrix skeleton structure. death,
The structure e is first fired in argon at a temperature of 1900 to 2300°C, then secondarily fired in nitrogen gas of 1 to 200 atm at a temperature of 1600 to 2100°C, and then heat-resistant electrodes are attached to both ends. It can be formed and energized.

The present invention will be explained in detail below.

First, a porous sintered body of silicon carbide is selected as the filter material. By using silicon carbide, high temperature (1000°
C or higher) corrosion resistance and oxidation resistance are improved. Due to its porous nature, in the present invention a polymeric foam, ie porous and with open pores, is used as a means of skeleton formation. As the polymeric foam, known ones can be used, particularly polyurethane foam, flexible polyethylene foam, polyvinyl formal foam, urea foam, and the like.

This polymer foam is immersed in silicon carbide slurry to fill and impregnate its pores with the slurry, and if necessary, after drying, it is re-impregnated and the drying process is repeated to form a skeleton with a desired thickness. A porous silicon carbide sintered body (filter) is obtained by sintering.

As a polymeric foam suitable for this purpose, for example, in the case of a polyurethane foam, one having a porosity of at least about 50% and an average pore diameter of 0.5 to 5% can be used, and can be prepared by known methods. Note that the porosity, pore diameter, etc. of the polymer foam are selected depending on the filter design.

A conventional silicon carbide slurry may be used. That is, approximately 0.3~
In general, 1.0μ fine particles of β-type silicon carbide (or a sintering aid, etc.) are dispersed in an organic solvent such as acetone or ethyl alcohol, and an organic binder such as a phenolic resin (the dry strength of the skeleton structure is maintained when heated). (which can maintain as much bonding strength as possible during the process). Furthermore, a water-soluble or water-based (emulsion type, etc.) organic binder can also be used, and in that case, it can also be made into an aqueous slurry. For example, it can be made by adding and mixing a sintering aid, a binder, and a dispersant to β-type silicon carbide.

The concentration of the slurry is selected mainly based on the viscosity so as to be suitable for impregnation, and is usually adjusted to about 10 to 50 centipoise (at room temperature).

In the present invention, silicon carbide refers to silicon carbide that is substantially recognized as a sintered body of silicon carbide in addition to pure silicon carbide, such as B4C, B, AIN, carden, or silicon carbide as a known sintering aid. This includes those that partially contain remaining organic resins. For example, a starting material containing 0.5 parts of 84C and 6 parts of a phenol resin can be used.

The polymeric foam material (impregnated body) impregnated with the silicon carbide slurry is first dried, and then the impregnated body is heat treated to eliminate the polymeric foam material and form a skeleton structure. This heat treatment is preferably carried out by gradually increasing the temperature in a vacuum to about 40%
0-1. OOO1'C, preferably about 3 to 800°C
The polymeric foam material is completely dissipated by holding for 0 minutes to 3 hours, preferably about 1 hour. At this time, care must be taken to gradually eliminate the organic material while preventing rapid heating and combustion.

The silicon carbide structure thus obtained (unfired) is then heated in an Ar gas flow at approximately 1900 to 2300°C, preferably 1950 to 2100°C, for approximately 30 minutes to 3 hours.
Preferably, it is fired for about 1 hour to perform primary sintering to form a porous sintered body. Next, secondary firing is performed at a temperature of approximately 1600 to 2100°C, preferably 1800 to 2000°C, and a high pressure nitrogen gas atmosphere at 11 to 200 atm. In this way, the specific resistance of the sintered body at room temperature becomes 10Ω or less.

The current carrying resistance characteristic is a specific resistance of 0.01 to 1Ω (100
0°C) is preferable as the heating element.

Heat-resistant electrodes are further formed at both ends of the filter to enable electricity to flow. This electrode can be used, for example, for the formation of metallized surfaces,
Although other known methods may be used, it is particularly preferable to use a silicon carbide sintered body having a metallized surface as disclosed by the applicant in Japanese Patent Application No. 184793/1983.

That is, a composition consisting of 5ilO to 90% by weight, the balance being Fe, and a mixture of at least two or more of Ni+Co was
The metallized surface is sintered in a non-oxidizing atmosphere at a temperature of ~1800°C. Other methods include spraying metallized aluminum or other metals such as Ni, 'l'i
Thermal spraying or vapor deposition and sintering after vapor deposition, so-called baking after coating of silver, platinum, or ruthenium, etc., etc.

Note that the surface of the silicon carbide filter other than the electrode portions is preferably subjected to a known auxiliary treatment for the purpose of preventing oxidation, increasing corrosion resistance, preventing strength deterioration, and the like. That is, as disclosed in Japanese Patent Application No. 54-96998 filed by the present applicant, it is useful to form a siliceous glass layer with a thickness of about 0.1 to 20 microns. In this case, the filter is
Heat treatment in an oxidizing atmosphere of about 1,300°C or more (preferably about 1,500°C) for about 1 hour or more (usually after metallizing the electrodes and taking protective measures as necessary) By doing so, a siliceous glass layer is formed.

The oxidizing atmosphere may be air, preferably wet hydrogen or wet inert gas.

By forming this siliceous glass layer coating, the specific resistance of the filter increases by up to about 5% compared to before treatment, and this is thought to be because the siliceous glass layer forms an insulating layer.

This filter thus has a high porosity (30-60%)
It has sufficient strength (both room temperature and high temperature), good heat resistance, and low electrical resistance, so it can be used at low voltage (12 to 24
v) It is a self-cleaning filter that generates heat when energized, raises the temperature to 1000°C or more when energized for a short period of time, and can completely burn off carbon deposits such as diesel engine exhaust gas.

According to the present invention, a filter made of a self-heating silicon carbide sintered body, which can be used as a filter for porous and fine substances, can be replaced, and the oxidation strength deterioration due to the heat generated by energization can be avoided. Can be effectively prevented.

The heat generated by energization of this filter can be maintained for a long time at about 1200°C, and can be heated up to about 1300°C for a short time, and the spalling resistance does not deteriorate even if the filter is repeatedly energized and heated.

Therefore, this filter can be advantageously used to remove carbon (soot) etc. from diesel engine exhaust gas, and can also be used as any other high-temperature filter (self-cleaning), and can also be used as a support for reaction catalysts, etc. It is clear that it is useful as a

Examples of the present invention will be shown below.

Example 1 A commercially available polyurethane foam with a porosity of 60%, an average pore diameter of 3 uL, a length of 120 cm x a width of 120 cm (XX height of 240 cWL) was impregnated with the following slurry, and the slurry was allowed to adhere to the inside of the foam and dried. The drying process was repeated 3 to 6 times.After being left in the air for 24 hours, it was dried in an infrared radiation dryer for 100°QX 2 hours.

Sludge Weight part β-8iC (
Average particle size 0.3μ) io.

B, C (1/) 0.5 Phenol resin (liquid) solid content 6 Ethyl alcohol
100 This mixture was mixed in a ball mill for 3 hours, and ethyl alcohol was added to reduce the viscosity of the slurry to 30.
Poise.

The impregnated body thus obtained was heated in vacuum at a heating rate of 10°C per minute and held at 800°C for 1 hour to completely eliminate organic matter, and the resulting porous silicon carbide body was heated in an Ar gas stream. After sintering at 2,000 to 2,100° CX for 60 minutes, gas was replaced, secondary sintering was performed at 1,800 to 2,000° C. for 3 hours in N2 gas at 14 hours of atmospheric pressure, and the mixture was allowed to cool.

Next, in terms of weight ratio, 5i was 66%, the balance was Fe17, and N1
A paste made by adding 2% organic binder and 100% solvent (acetone) to a mixture of 10% Cr and 7% Cr was applied to the opposite sides of the sintered body and heated at 1500° in a vacuum atmosphere of 10-8 torr. C×30 minutes of firing to form an electrode having a distance of 200 ffLjlL between the metallized surface and the blank fired surface.

The filter was treated in wet hydrogen at 1500°C (wetter temperature 50", H2/N2 = 3A) to form a siliceous glass layer on the surface of the silicon carbide layer. As a result, the specific resistance was 2.
~10% increase. 10,000 coated filters
Although it was heated continuously in the air for Qx1000 hours, no change in resistance value was observed, and no deterioration in strength was observed. When electricity was applied between the filter electrodes at 2.4V x 60^, the temperature rose to 800°C in 3 minutes.

Example 2 A silicon carbide filter obtained in the same manner as in Example 1 with a passage length of 50 x width of 3QQll x height of 300B was set in the conduit of a diesel engine exhaust pipe, and a silicon carbide filter obtained in the same manner as in Example 1 was made to be energized at 24V. Using a 5000cc (direct injection type) 6-cylinder engine, we conducted a 100 km drawing test according to the Ministry of Transport's 6 modes, and as a result of continuous testing by energizing for 2 minutes every hour, no deterioration in filter performance was observed even after the test. I couldn't.

When the smoke concentration of carbon in the mixed gas was measured using a Bosch smoke densitometer, it was 3 before passing through the filter and 2 after passing through the filter.

Applicant: NGK SPARK PLUG CO., LTD. Agent: Patent Attorney Asami Kafuji

Claims (1)

[Claims] 1) A polymeric foam material is impregnated with a silicon carbide matrix slurry, and the polymeric foam material is completely heat-treated to be completely eliminated to form a silicon carbide matrix skeleton structure, and the structure is heated from 1900 to
Firstly fired in argon at a temperature of 2300°C, then secondarily fired in nitrogen gas at 1 to 200 atm at a temperature of 1600 to 2100°C, after which heat-resistant electrodes are formed on both ends to enable electricity to flow. A method for manufacturing a silicon carbide filter that can generate heat when energized.