【発明の詳細な説明】[Detailed description of the invention]
本発明はSiC焼結体の製造法に関するものであ
る。
SiC焼結体は近年ホツトプレス法を使用せず、
無加圧で焼成できるようになり、その優れた熱的
性質、化学的性質、耐摩耗性等からエンジニアリ
ングセラミツクスとして脚光をあびている。この
ようなSiC焼結体は通常サブミクロンのSiC粉に
Ｂ・Al・Be・Ｃやそれらの化合物からなる焼結
助剤とバインダー等の添加物を加えた成形体を不
活性雰囲気中1900〜2500℃で焼成して得られる。
この焼成は高温であるので焼成炉の高温部分には
通常黒鉛材料が用いられ、この成形体は黒鉛製台
の上に載せて焼成される。この成形体の焼成によ
る線収縮率は18〜20％である。焼結体は焼成中黒
鉛製台の上をすべり、焼成体と黒鉛製台の間には
摩擦が生じる。特にリング状の成形体では摩擦の
大きいところと小さいところが生じるため均一に
収縮せず、真円度の良い焼結体が得られず、変形
が生じる。このような現象はSiC焼結体のみでな
く一般のセラミツクスでも起こる。従来からこの
ような変形防止の対策として同一材質の板状の成
形体を敷く（通常トモトチと称する）ことにより
変形を防止する方法が知られている。しかもトモ
トチを用いる方法は通常のセラミツクスのように
安い原料を用い、大きな炉で比較的低温（1800℃
以下）で焼成する場合にはあまり問題がなくと
も、SiC焼結体ではトモトチを用いることは極め
て不経済である。
本発明はこのような従来の問題点を解決し、安
価で変形のないSiC焼結体の製造法を提供するこ
とを目的とするものである。
本発明はトモトチに替わるものについて研究を
重ねた結果、トモトチの替わりに天然黒鉛粒子を
用いることにより変形せずにSiC焼結体を製造で
きることを見い出した。
本発明はSiC粉、焼結助剤及びその他の添加物
からなる成形体を焼成してSiC焼結体を得る場合
に、成形体と成形体を載せる台との間に扁平な鱗
状の天然黒鉛粒子を配置するSiC焼結体の製造法
に関する。
本発明で使用する天然黒鉛粒子は焼成で成形体
が収縮する場合に成形体と成形体を載せる台の間
のすべりを良くし、均一に収縮させ、真円を保つ
たまま焼結させ、変形を防止する働きをする。こ
のため天然黒鉛粒子は潤滑性の良い扁平な鱗状黒
鉛の粒子を使用する。人造黒鉛や炭素は不適であ
る。SiC焼結体の組成、成形法等は公知のものを
使用する。
以下、実施例により本発明を詳細に説明する。
実施例
コークス粉とケイ石粉とを反応させ粉砕して得
た平均粒径0.8μｍのα−SiC粉100重量部に平均
粒径２μｍのB4C粉１重量部、ノボラツクフエノ
ールレジン（三菱ガス化学製、商品名SM−Ｐ、
107A）６重量部、アセトン10重量部を添加して
混合し、乾燥後、ポリビニルアルコール（株式会
社クラレ製、商品名ポバール）水溶液を固形分で
１重量部加えて造粒し、外径225mm、内径202mm、
高さ13mmの成形体を得た。この成形体をAr雰囲
気中で第１図のように黒鉛製台３の上に載せて毎
時100℃で昇温し、2300℃で１時間焼成した。
第１図においてａは炉内の黒鉛製台３と成形体
１との間にJIS Ｒ 6001における粒度＃100の
SiC粒子２を置いた場合（比較例１）、ｂは黒鉛
製台３と成形体１との間に厚さ13mmのトモトチ４
を置いた場合（比較例２）及びｃは黒鉛製台３と
成形体１との間に平均150μｍの鱗状黒鉛粒子５
（日本黒鉛工業KK製、商品名CB−100）を置いた
場合（実施例１）である。
この場合、焼結体の密度はいずれの方法でも
3.15ｇ/cm3であつた。また焼成後の方法は変形を
考慮して平均すると外径は180mmで約20％の収縮
率であつた。上記三通りの方法による変形量を最
大値及び最小値の差から測定し、第１表に示し
た。
The present invention relates to a method for manufacturing a SiC sintered body. SiC sintered bodies do not use the hot pressing method in recent years,
It is now possible to fire without pressure, and it is attracting attention as an engineering ceramic due to its excellent thermal properties, chemical properties, and wear resistance. Such SiC sintered bodies are usually made by adding additives such as sintering aids made of B, Al, Be, C and their compounds to submicron SiC powder, binders, etc. in an inert atmosphere for 1900 ~ Obtained by firing at 2500℃.
Since this firing is performed at a high temperature, graphite material is usually used in the high temperature part of the firing furnace, and the molded body is placed on a graphite stand and fired. The linear shrinkage rate of this molded body upon firing is 18 to 20%. The sintered body slides on the graphite table during firing, and friction occurs between the fired body and the graphite table. In particular, in a ring-shaped compact, there are areas where the friction is high and areas where the friction is low, so it does not shrink uniformly, making it impossible to obtain a sintered body with good roundness and causing deformation. This phenomenon occurs not only in SiC sintered bodies but also in general ceramics. Conventionally, as a measure to prevent such deformation, a method has been known in which deformation is prevented by laying a plate-shaped molded body made of the same material (usually referred to as tomotochi). Moreover, the method using Tomotochi uses cheap raw materials like ordinary ceramics, and uses a large furnace at a relatively low temperature (1800℃).
Although there are no problems when firing with the following), it is extremely uneconomical to use Tomotochi for SiC sintered bodies. It is an object of the present invention to solve these conventional problems and provide a method for manufacturing a SiC sintered body that is inexpensive and free from deformation. As a result of repeated research into alternatives to tomotochi, the present invention has discovered that a SiC sintered body can be manufactured without deformation by using natural graphite particles instead of tomotochi. In the present invention, when obtaining a SiC sintered body by firing a shaped body made of SiC powder, a sintering aid, and other additives, flat scale-like natural graphite is placed between the shaped body and a table on which the shaped body is placed. This article relates to a method for manufacturing a SiC sintered body in which particles are arranged. When the molded body shrinks during firing, the natural graphite particles used in the present invention improve the sliding between the molded body and the table on which it is placed, shrink uniformly, and sinter while maintaining a perfect circle, resulting in deformation. It works to prevent For this reason, flat scale graphite particles with good lubricity are used as the natural graphite particles. Artificial graphite and carbon are not suitable. The composition, molding method, etc. of the SiC sintered body are known. Hereinafter, the present invention will be explained in detail with reference to Examples. Example 100 parts by weight of α-SiC powder with an average particle size of 0.8 μm obtained by reacting and pulverizing coke powder and silica powder, 1 part by weight of B 4 C powder with an average particle size of 2 μm, Novolac phenol resin (Mitsubishi Gas Made by Kagaku, product name SM-P,
107A) 6 parts by weight and 10 parts by weight of acetone were added and mixed, and after drying, 1 part by weight of solid content of polyvinyl alcohol (manufactured by Kuraray Co., Ltd., trade name Poval) aqueous solution was added and granulated. Inner diameter 202mm,
A molded body with a height of 13 mm was obtained. This molded body was placed on a graphite stand 3 as shown in FIG. 1 in an Ar atmosphere, heated at 100°C per hour, and fired at 2300°C for 1 hour. In Fig. 1, a indicates a particle size of #100 according to JIS R 6001 between the graphite table 3 and the compact 1 in the furnace.
When SiC particles 2 are placed (comparative example 1), b is a tomotochi 4 with a thickness of 13 mm between the graphite base 3 and the molded body 1.
(Comparative Example 2) and c are cases in which scaly graphite particles 5 with an average size of 150 μm are placed between the graphite table 3 and the molded body 1.
(manufactured by Nippon Graphite Industries KK, trade name CB-100) (Example 1). In this case, the density of the sintered body is
It was 3.15g/ cm3 . In addition, in the post-firing method, the outer diameter was 180 mm and the shrinkage rate was about 20% on average, taking deformation into account. The amount of deformation by the above three methods was measured from the difference between the maximum value and the minimum value, and is shown in Table 1.
【表】
本発明の天然黒鉛粒子を用いる方法は被焼成物
と同様のSiC粒子を用いるよりはるかに変形防止
効果があり、またトモトチを用いる方法と比較し
て変形防止効果はそれほど変わらないが、トモト
チを用いない点で原料コストが低く、焼成炉内の
スペースを有効に使用できる。[Table] The method using natural graphite particles of the present invention has a much more effective deformation prevention effect than the use of SiC particles similar to those to be fired, and the deformation prevention effect is not significantly different from the method using Tomotochi, but Since it does not use tomotochi, the cost of raw materials is low, and the space in the kiln can be used effectively.
【図面の簡単な説明】[Brief explanation of the drawing]
第１図は成形体を黒鉛製台の上に載せて製造す
る状態を示す断面図である。
符号の説明、１……成形体、２……SiC粒子、
３……黒鉛製台、４……トモトチ、５……鱗状黒
鉛粒子。
FIG. 1 is a sectional view showing a state in which a molded body is manufactured by placing it on a graphite stand. Explanation of symbols, 1... Molded object, 2... SiC particles,
3... Graphite base, 4... Tomotochi, 5... Scale-like graphite particles.