JPH07115968B2 - Method for producing porous SiC whisker pellets - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a porous SiC useful as a catalyst carrier, a filter, etc.
The present invention relates to a method for manufacturing whisker pellets.

[Conventional technology]

For a SiC-based porous body, a method of reacting Si with carbon or a SiC and SiC compact (Japanese Patent Laid-Open No. 61-52107, etc.) is used, and β-SiC ultrafine powder is mixed with polycrystalline SiC and baked. (Japanese Patent Laid-Open No. 61-53163) and a method of forming a cellular skeleton structure of SiC using an organic polymer foam (Japanese Patent Laid-Open No. 6-53163).
Although many proposals have been made, such as Japanese Patent No. 1-257217),
None of them have a porosity exceeding 50%.
In this regard, it is expected that the composition of fine whisker SiC whiskers will structurally increase the porosity.

Conventionally, as a method for producing a porous body made of SiC whiskers, as a means for obtaining a porous molded body having a structure in which SiC whiskers are entwined with each other, Si ₃ N ₄ in an airtight container is used.
Powder and carbon powder are filled so as to have a SiC composition ratio, and the mixture is heated to 1400 to 1900 ° C. in the atmosphere (Japanese Patent Laid-Open No. 61-191574).
No. publication) is known. However, the SiC porous molded body obtained by the above method has a drawback that the skeleton strength is weak and it is easily damaged.

In order to eliminate this drawback, the SiC whiskers are used as a means for producing a porous SiC body in which an inner layer portion made of entangled SiC whiskers is integrally formed by a strong surface layer portion made of particulate SiC, and as a means for producing the same. The thermosetting resin is impregnated into the molded body of No. 1, heated to 800 to 1200 ° C in a non-oxidizing atmosphere to carbonize the thermosetting resin, and then 800 ° C in an oxidizing atmosphere.
A method of burning and removing the carbon in the surface layer by heating to below, followed by heat treatment at 1800 to 2200 ° C. in a non-oxidizing atmosphere, and then heating to 800 ° C. or less in an oxidizing atmosphere to burn off the free carbon of the porous body. (Japanese Patent Laid-Open No. 64-3083) has been developed.

[Problems to be Solved by the Invention]

According to the method for producing a SiC porous body described above, it is possible to impart high porosity of more than 80% and excellent strength characteristics, but the production process is complicated and necessary as a catalyst carrier or the like. There is a drawback that it cannot be formed into pellets.

In particular, when it is used as a catalyst carrier, grain strength that can withstand handling is required, and normally, a crushing load of at least 1 kg is required.

An object of the present invention is to provide a method for producing a porous SiC whisker pellet which can be adjusted to a desired porosity under a high level of 60% or more, and has a crushing load of 1 kg or more of grain strength. It is in.

[Means for Solving the Problems]

In the method for producing porous SiC whisker pellets according to the present invention to achieve the above object, the mixing ratio of the silicon source raw material and the carbonaceous material is set in the range of 1: 3 to 6 as the molar ratio of SiO ₂ : C. Molding process in which the raw material components of the composition are kneaded with an inorganic and / or organic binder and molded into pellets, the molded pellets are heated to a temperature of 1300 to 1800 ° C in a non-oxidizing atmosphere to form SiC whiskers in the pellet structure. A structural feature that consists of a reaction process to generate, and an incineration process to heat the pellets after SiC whisker generation to a temperature of 600 ° C or higher in an oxygen-containing atmosphere to burn off the carbonaceous material components remaining in the structure Is.

The present invention will be described below step by step.

(1) Molding process As the silicon source material, silica, silica, silk gel,
Si-containing substances such as rice husk ash and SiC powder are used, and carbon black is preferably used as the carbonaceous material. The mixing ratio of the silicon source material and the carbonaceous material is 1: 3 to 6 as a molar ratio of SiO ₂ : C.
The composition is set within the range. If the composition of C is less than 3 mol, a high porosity cannot be obtained, and if it exceeds 6 mol, the shape retention of the pellet is lowered, and at the same time, the crushing load becomes less than 1 kg, and the engagement is increased.

In these raw material components, if necessary, a substance selected from salts such as Fe, Co, Ni, Ca, K, Mg, and Na is used as a production catalyst for promoting the production of SiC whiskers.
It can be added in the range of 20% by weight.

The raw material component is then blended with an inorganic binder, an organic binder, or a binder component that is a combination of two or more of these. Suitable types of binder components include colloidal silica or water glass as the inorganic binder, and methyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, lignin-based substances, pitch-based substances, phenol resins, furan resins and the like as the organic binders. These binder components are used in a solution state, and the compounding amount thereof is set within the range of 5 to 70% by weight in consideration of the composition of the raw material components.

The mixture of the raw material components and the binder is subjected to a sufficient kneading treatment using an appropriate kneading device, and then a method of molding into a linear body by an extrusion molding machine and cutting into a short length or a method of directly molding by a pricket machine It is formed into a desired pellet shape by, for example,

(2) Reaction process The molded pellets are filled in a sealed reaction vessel made of a heat-resistant material such as graphite and stored in an electric furnace kept in a non-oxidizing atmosphere at 1300 to 1800 ° C, preferably 1500 to 1700 ° C. A SiC whisker is formed inside the tissue by heating at a temperature.

(3) Incineration process After the SiC whiskers have been formed, the pellets are heated in air or other oxygen-containing atmosphere at a temperature of 600 ° C or higher to remove unnecessary components such as carbonaceous materials converted from the carbonaceous material and organic binder in the pellet structure. It is completely burned out, and if necessary, acid pickling or water washing is performed to remove surface deposits such as metal impurities.

Porous SiC whisker pellets with a porosity of more than 80% are produced through the above steps, but in order to reduce the porosity level, SiC whiskers or powders are added and mixed in advance as raw material components. The method of putting it is an effective means. The amount of these SiC components mixed is set according to the desired degree of porosity, but the addition of this component effectively functions to improve the crushing load and shape retention of the pellets.

To further increase the crushing load, the porous SiC whisker pellets obtained in the above step are colloidal silica,
It is possible to employ a method in which surface treatment is performed using an inorganic binder solution such as water glass and heating is performed at a temperature of 800 ° C or higher. As the surface treatment means, a method of immersing the pellets of the porous SiC whiskers in an inorganic binder solution, or coating or spraying the inorganic binder solution on the surface of the pellets is applied.

[Work]

The SiC whisker formation reaction between the silicon source material and the carbonaceous material proceeds according to the following reaction formula.

_{SiO 2 + 3C → SiC w +} 2CO Thus, the stoichiometric required amount C3 mole of SiO ₂ 1 mole, mole ratio of carbonaceous material in the present invention is in the range of excess. This excess amount of carbonaceous material remains and is uniformly distributed in the pellet structure after the reaction, and a high porosity is formed due to the burnout effect in the incineration process. Therefore, the porosity can be adjusted in the range of about 90 to 95% by controlling the blending molar ratio of the carbonaceous material. When an organic binder is used, this binder component is finally burned and removed to participate in the formation of pores, but the contribution effect is not large.

The high porosity level can be reduced and adjusted to a value in the range of 50 to 90% by adding a predetermined amount of SiC whiskers or powder to the raw material component. Also works to improve.

Furthermore, surface treatment of the obtained porous SiC whisker pellets with an inorganic binder solution brings about the effect of effectively improving the crushing load and shape retention of the pellets.

Through these various adjusting functions, it becomes possible to manufacture porous SiC whisker pellets having a desired porosity of 60% or more and a desired crushing load of more than 1 kg.

〔Example〕

 Hereinafter, the present invention will be described based on examples.

Example 1 (1) Molding process 300 g of silk gel powder was used as carbon material for carbon black [Tokai Carbon Co., Ltd., "SEAST 5H"] 180-360 g (SiO ₂
/ C molar ratio 1: 3 to 6) and CoCl ₂ · 6H ₂ O 11g (SiO ₂
2% by weight as CoCl ₂ ) and mixed with this raw material component 2% calcium lignin sulfonate, 1% methylcellulose
%, And 95% by weight of an organic binder aqueous solution of 100% was added and kneaded sufficiently. Then, the kneaded product was placed in a container of an extrusion molding apparatus, extruded into a column shape from a nozzle having a diameter of 5 mm at a molding pressure of 100 kg / cm ² , and this was cut into a length of about 5 mm to form pellets.

(2) Reaction process After the molded pellets are dried, they are packed in a graphite reaction container and heated to 1600 ° C in a nitrogen atmosphere to form the pellet structure.
A SiC whisker was created.

(3) Incineration step The pellets were taken out from the reaction vessel, washed with water, and then treated at a temperature of 600 ° C. for 3 hours in the atmosphere to completely burn off and remove residual carbonaceous material components from the pellet structure.

(4) Characteristic evaluation The porosity, crushing load, shape retention, etc. of the porous SiC whisker pellets obtained in the above steps were measured and shown in Table 1 in comparison with the raw material composition.

The crushing load is the load when crushing a cylindrical pellet (diameter 5 mm, length 5 mm) with both ends cut in parallel with a metal plate with a smooth surface, and the shape retention rate is that of a normal pellet after the incineration process. The yield is shown.

90% in the case of raw material components with a SiO ₂ : C molar ratio of 1: 3 to 6
The high level porosity and the crushing load value with a lower limit of about 1 kg were shown, but when the molar ratio was 1: 2, the generation rate of SiC whiskers deteriorated and the porosity and crushing strength were lowered, and 1: In Example 9, the crushing load and the shape retention rate were significantly reduced.

Example 2 The same organic binder as the raw material component having a SiO ₂ : C molar ratio of 1: 3 in Example 1 and SiC whiskers as a porosity adjusting material were added and mixed in the range of 100 to 400 g. Using this raw material system, porous SiC whisker pellets were produced by the same molding, reaction and incineration steps as in Example 1.

The properties of the obtained pellets are shown in Table 2 in comparison with the compounding amount of the porosity adjusting material (SiC whiskers).

From the results shown in Table 2, it is possible to adjust the porosity at a level of 60% or more by adding SiC whiskers to the raw material components, and also to improve the crushing load.

Example 3 Instead of the SiC whiskers of Example 2, S having an average particle size of 3 μm was used.
Porous SiC whisker pellets were produced by the same process as in Example 2 except that iC powder was used as the porosity adjusting material.

Table 3 shows the characteristics of the obtained pellets in comparison with the amount of the porosity adjusting material used.

Also in this case, the same result as in Example 2 was obtained.

Example 4 Porous S produced in Example 1 with a SiO ₂ : C molar ratio of 1: 3.0
The iC whisker pellets were surface-treated with an inorganic binder solution as follows.

(1) Spray treatment The surface of the pellet is evenly sprayed with a 10% aqueous colloidal silica solution in an amount equal to the weight of the pellet and dried.
It heat-processed at the temperature of 00 degreeC for 1 hour.

Furthermore, this operation was repeated twice.

(2) Immersion treatment The pellet was immersed in a 20% and 40% concentration colloidal silica aqueous solution, impregnated in a vacuum, and returned to normal pressure after 30 minutes.
This was dried at 150 ° C. and then heat-treated at a temperature of 1000 ° C. for 1 hour.

The characteristics of the porous SiC whisker pellets subjected to the above surface treatment are shown in Table 4 in comparison with the treatment method.

From the results of Table 4, it is recognized that the crushing load can be significantly increased by applying the surface treatment without significantly reducing the porosity.

[Effects of the Invention] As described above, according to the present invention, it is possible to produce porous SiC whisker pellets with a high porosity of 60 to 95% that can be adjusted to a desired level and that has a crushing load in a practical range with a high yield. Is possible. In addition, since the porous structure is composed of SiC whiskers that are highly heat and chemically stable, it can be suitably used in fields of application where heat resistance / corrosion resistance and high porosity are required, including catalyst carriers and filter media.

Claims (3)

[Claims] 1. A pellet obtained by kneading a raw material composition having a composition ratio of a silicon source raw material and a carbonaceous material set to a range of 1: 3 to 6 as a molar ratio of SiO ₂ : C with an inorganic and / or organic binder. Forming step of forming into a shape, a reaction step of heating the formed pellets to a temperature of 1300 to 1800 ° C in a non-oxidizing atmosphere to generate SiC whiskers in the pellet structure, S
60 pellets after iC whisker formation in oxygen-containing atmosphere
A method for producing porous whisker pellets, which comprises an incineration step of heating to a temperature of 0 ° C. or higher to burn off carbonaceous material components remaining in the structure. 2. The method for producing porous whisker pellets according to claim 1, wherein whiskers or powder of SiC as a porosity adjusting material is added to the raw material components. 3. A method for producing porous whisker pellets, which comprises subjecting the porous whisker pellets produced according to claim 1 or 2 to surface treatment with an inorganic binder solution and then heating at a temperature of 800 ° C. or higher.