Y. Yuan, J. Pan/Journal of Crystal Growth 193(1998)585-591 with alumina matrix [3-5]. Therefore, in It describes this modified CVD method with empha years, many experiments have been made on the sis on the effect of vapor phase on the growth of preparation and properties of the TiC whiskers TiC whiskers [6-8] iC whiskers are usually prepared by the CVD method in a horizontal reaction tube in which the 2. Experimental procedure iCl-CH4-H2-and / or Ar)gas mixture was used as reactant and pure nickel as substrate. In the The schematic diagram of the experimental ap- early 1990s, our group began to prepare TiC paratus is shown in Fig. 1. It is composed of two whiskers and develop their applications. As the parts, a gas-flow system and a reactor system. In conventional CVD method, an apparatus made of stead of the horizontal reaction tube used in our a horizontal alumina reaction tube was used to previous works [9, 10], the modified CVD method prepare TiC whiskers in our previous work [9, 10]. uses a vertical graphite tube of 30 mm in inner The TiC whiskers prepared by the CVD method diameter heated by a nickel-chromium alloy coil usually have high purity and fewer defects resulting The inner diameter of the gas inlet is reduced great to better mechanical properties as well as desirable ly, so that the flow rate increases significantly. The geometric characteristics such as shape, size, aspect TiCl4-CH4-H2-Ar gas mixture is used as the reac- ratio, surface smoothness which are closely related tant and a pure hollow nickel cylinder as the sub- drawback associated with the conventional CVD is inner reaction tube wall the gas inlet around the to the toughening of CMCs. However, a serious strate which is placed near the gas inlet around the the low yield and, consequently, the high cost of The temperature is measured with a Pt/Pt-Ph whiskers. To overcome this drawback, a modified thermocouple. The temperature of the TiCla evap- CVD method is presented, by which quality Tic orator is ma aintained at 60C. The gas flow rate whiskers with high yield are obtained. This pap measured with the flow meter. The morphologies of alumina tube nickel subtrate- Fig. 1. Schematic diagram of the whisker deposition apparatusFig. 1. Schematic diagram of the whisker deposition apparatus. with alumina matrix [3—5]. Therefore, in recent years, many experiments have been made on the preparation and properties of the TiC whiskers [6—8] TiC whiskers are usually prepared by the CVD method in a horizontal reaction tube in which the TiCl4 —CH4 —H2 —(and/or Ar) gas mixture was used as reactant and pure nickel as substrate. In the early 1990s, our group began to prepare TiC whiskers and develop their applications. As the conventional CVD method, an apparatus made of a horizontal alumina reaction tube was used to prepare TiC whiskers in our previous work [9,10]. The TiC whiskers prepared by the CVD method usually have high purity and fewer defects resulting to better mechanical properties as well as desirable geometric characteristics such as shape, size, aspect ratio, surface smoothness which are closely related to the toughening of CMCs. However, a serious drawback associated with the conventional CVD is the low yield and, consequently, the high cost of whiskers. To overcome this drawback, a modified CVD method is presented, by which quality TiC whiskers with high yield are obtained. This paper describes this modified CVD method with empha￾sis on the effect of vapor phase on the growth of TiC whiskers. 2. Experimental procedure The schematic diagram of the experimental ap￾paratus is shown in Fig. 1. It is composed of two parts, a gas-flow system and a reactor system. In￾stead of the horizontal reaction tube used in our previous works [9,10], the modified CVD method uses a vertical graphite tube of 30 mm in inner diameter heated by a nickel—chromium alloy coil. The inner diameter of the gas inlet is reduced great￾ly, so that the flow rate increases significantly. The TiCl4 —CH4 —H2 —Ar gas mixture is used as the reac￾tant and a pure hollow nickel cylinder as the sub￾strate which is placed near the gas inlet around the inner reaction tube wall. The temperature is measured with a Pt/Pt—Ph thermocouple. The temperature of the TiCl4 evap￾orator is maintained at 60°C. The gas flow rate is measured with the flow meter. The morphologies of 586 Y. Yuan, J. Pan / Journal of Crystal Growth 193 (1998) 585–591