JPH0323266A - Production of silicon carbide-based starting material for sintering - Google Patents

Abstract

PURPOSE:To obtain homogeneous starting material for sintering and to produce a high density and high strength sintered body with the starting material by spray-drying a slurry contg. silicon carbide powder of a prescribed particle size, a water soluble carbon-contg. compd. and boron or a boron compd. CONSTITUTION:Silicon carbide powder of <=1mum average particle size, a water soluble carbon-contg. compd. (water soluble phenol resin) and boron or a boron compd. are prepd. These starting materials are suspended and slurried by mixing in an aq. solvent. The resulting uniformly dispersed slurry is spray-dried.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing a sintered raw material for obtaining a high-density and high-strength silicon carbide sintered body. [Prior Art] Silicon carbide has extremely excellent chemical and physical properties and is a suitable material for applications such as high-41 structural materials used under severe conditions. Pressure sintering, reaction sintering, and pressureless sintering are widely known methods for sintering silicon carbide. Among these methods, the pressure sintering method has problems in that it is difficult to manufacture complex sintered bodies and productivity is also poor. In addition, the reaction sintering method has problems such as difficulty in obtaining high-strength sintered bodies. The pressureless sintering method is a method in which a desired shape is formed at room temperature to obtain a raw shape, and then this formed body is sintered under no pressure. Carbon, boron, etc. are added as sintering aids. By doing so, these drawbacks can be overcome. For example, slurry casting, extrusion, dry pressurization, etc. are known as methods for forming a raw material in the pressureless sintering method. These forms of precepts are broadly divided into wet and dry methods depending on the liquid content during preforms, but wet methods require sufficient drying of the raw material after forming prefectures; Shrinkage must be taken into consideration, and defects such as warping and cracking are likely to occur due to drying. On the other hand, the dry method has excellent dimensional accuracy and is an advantageous molding method, but when using fine powder, the fluidity of the powder is poor, so it must be uniformly filled into the mold and processed. It is difficult to press, and the bulk density etc. of the raw or shaped body becomes non-uniform, and the sintered body sintered using this material will have defects due to this non-uniformity, and the physical properties of the sintered body will deteriorate. In particular, it reduces mechanical strength. Therefore, conventionally, when using fine powder raw materials to form raw or shaped objects, the powder is prepared in advance into granules in order to improve its fluidity. Make this powder into granules a
The tablet method, direct granulation method, spray drying method, etc. are known as means for rms, but the tablet method involves pressurizing and forming the mold, then crushing it and sieving it. It becomes liquid and has poor liquidity.
In addition, the direct granulation method has problems such as difficulty in controlling particle size and variation in particle size distribution. Spray drying is a method in which a slurry-like suspension is sprayed into a high-temperature atmosphere and granulated at the same time as drying, making it possible to obtain granules with a narrow particle size distribution, spherical shape, and excellent fluidity. be. In order to obtain a high-strength silicon carbide sintered body, it has been proposed that it is effective to include carbon and boron, and examples of carbon sources include carbon blank, tar, and various types of resin. In addition, as a boron source, boron,
Boron carbide, boric acid, and boric acid compounds are applied, but these need to be uniformly mixed with the raw material silicon carbide powder. It was common to use ITS agents such as alcohol, benzene, and cyclohexane to dissolve the resin. However, using these mt'ip agents! When carrying out spray drying using cloudy water, it is necessary to take measures to prevent agitation, which poses handling problems, requires environmental measures such as deodorization, and requires additional equipment such as collecting the solvent used. It had various problems such as necessity. [Means for Solving the Problems J The present inventors have arrived at the present invention as a result of intensive studies in view of the problems of the prior art. In other words, the present invention focuses on the average particle size! A method for producing a silicon carbide sintering raw material, which is characterized by mixing silicon carbide powder of μm or less, a water-soluble carbon-containing compound, and boron or a boron compound in an aqueous solvent, and then spray-drying the mixture. This is a method for producing a silicon carbide sintering raw material using water-soluble phenolic resin. In the present invention, silicon carbide powder has an average particle size of 1 μm.
The following fine powder is used. Average particle size is 1μ
If it exceeds m, it is difficult to obtain a dense sintered body, and the object of the present invention, which is to prepare a raw material for obtaining a high-strength sintered body, is not achieved. In the present invention, water is used as a medium for mixing and slurrying silicon carbide f/I: powder, a carbon source, and a boron source, and a water-soluble carbon-containing compound is used as a carbon source. Examples of water-soluble carbon-containing compounds include water-soluble phenolic resins, sucrose, starch, etc., but water-soluble phenolic resins are most preferred from the viewpoint of fixed carbon content and uniform dispersibility of carbon. There are two main types of phenolic resins: novolacs and resols. Among resols, those produced by reaction with excess alkali during production are water-soluble and are usually commercially available as aqueous solutions with a resin content of 40 to 60%. This aqueous solution is used in the present invention. As the boron source, boron, boron carbide, boric acid, etc. can be used, but among these, boron and boron carbide are most preferred from the viewpoint of non-volatility. The amounts of these carbon sources and boron sources are not particularly limited, but generally silicon carbide 1003
The amount of fixed carbon is set in the range of 1 to 3 parts by weight based on 131 parts, and the amount of boron is set in the range of 0.1 to 0.5 parts by weight. The conditions for slurrying these additives and silicon carbide powder in water are not particularly specific, but the slurry concentration is between 30 and 30.
A range of 60% is preferable. Below this range, it is necessary to increase the drying capacity and the density of the granules tends to decrease. Moreover, when this range is exceeded, the granule particle size tends to become large. In addition, the temperature of the hot air, the efficiency of the spraying method, etc. may be taken into consideration when selecting the appropriate amount. When making a slurry, it is preferable to disperse it more uniformly, and mixing and stirring using a ball mill or the like is recommended. When using a 411 solvent as a dispersion medium, it is easy to uniformly disperse even fine powders by selecting a suitable solvent.However, in the aqueous dispersion system of the present invention, fine particles may aggregate, but dispersion Uniform dispersion is easily possible by adjusting the pH of the body, and specifically, ammonia etc.
It is preferable to adjust it to about H10. The slurry uniformly dispersed in this way is spray-dried, but since the dispersion medium in the present invention is water, there are no particular restrictions on the drying conditions, and commonly used lightning drying conditions can be applied. In this way, the average particle size is 40~
Granules in the range of 90 μm can be obtained, and these granules uniformly contain carbon and boron, have a narrow particle size distribution, are spherical in shape, and have excellent fluidity.

The present invention will be specifically explained below with reference to Examples. Example I 100 parts by weight of β-silicon carbide powder with an average particle size of 0.6 μm (specific surface area 14.2 rrl/g) was mixed with a water-soluble phenol resin manufactured by Meiwa Kaei Co., Ltd. (MWR Ichikai, resin content 58%) as fixed carbon. 2 parts by weight, 0.3 parts by weight of boron, and distilled water were added so that the slurry concentration was 50% by weight, and after adding ammonia water so that the pH of the slurry was 10, it was heated using a ball mill for 20 hours. We performed distributed processing. This slurry was spray-dried using a rotating disk type spray dryer at a hot air inlet temperature of 220°C and an outlet temperature of 120°C. The obtained granules had an average particle size of 47 μm and an apparent specific gravity of 1.05 g/1. The granules were formed into a mold at a pressure of 150 kg/unit, and then rubber pressed at a pressure of 1.5 t/unit to obtain a raw material shape. The density of this raw material was 2.03 g/1. This one at 2000'C,
Pressureless sintering was performed for 1 hour. The density of the sintered body is 3.
It showed 1.5 g/cj (corresponding to 98.1% of the theoretical density). The three-point bending strength of this sintered body was measured in accordance with JIS-R-1601 1604. As a result, it weighs 67Kg at room temperature.
/1, It had an average strength of 79 kg/1 at 1500°C. Examples 2 to 9 Spray drying, molding and sintering of raw materials were carried out in the same manner as in Example 1 while changing various conditions. The results are shown in Table 1. Comparative example 1. 2 Using carbon black as a carbon source, 0.6 parts by weight of PV per 100 parts by weight of silicon carbide as a binder.
A was added (Comparative Example 1), and Dainippon Ink & Chemicals Co., Ltd. (J-325) was used as the non-water-soluble phenolic resin (Comparative Example 2). The shape of the body was shaped and sintered. The results are shown in Table 1. As is clear from Table 1, the sintered body using the sintered raw material powder obtained by the method of the present invention has a high density,
It shows high strength. [Effect of the invention]

Claims (2)

[Claims] (1) A method for producing a silicon carbide sintering raw material, which comprises mixing silicon carbide powder with an average particle size of 1 μm or less, a water-soluble carbon-containing compound, and boron or a boron compound in an aqueous solvent, and then spray-drying the mixture. (2) The method for producing a silicon carbide sintering raw material according to claim (1), wherein the water-soluble carbon-containing compound is a water-soluble phenol resin.