J. An ceran.Soc,830]2584-9202000) urna Morphology and Stacking Faults of B-Silicon Carbide Whisker Synthesized by carbothermal Reduction Won-Seon Seo and Kunihito Koumoto* Department of Applied Chemistry, Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Jap MV Electron Microscopy Laboratory, Center for Integrated Research in Science and Engineering, Nagoya University Nagoya 464-8603, Japan The main formation reaction for whisker that has been losely related to the formation reactions and the reaction rate. synthesized from SiO2 and carbon black(CB)in a hydrogen- Thus, to be successful in forming specially shaped whiskers, the gas atmosphere was a solid-gas reaction between Sio and CB. insertion directions of the stacking faults and the whisker growth The synthesized whiskers were classified into three types, in rate each must be controlled terms of the morphology, growth direction, and stacking-fault In the present study, as the first step in our attempt to make bent planes:(i)type A, which has a relatively flat surface and the whiskers with different stacking-fault layers, we have investigated stacking-fault planes are perpendicular to the growth direc- several factors, using various sample-preparation methods. These tion;(ii)type B, which has a rough surface and the stacking Factors include the whisker formation reaction the whisker mor- fault planes are inclined at an angle of 35 to the growth phology and growth direction, and stacking-fault insertion of the direction; and (iii)type C, which has a rough sawtooth surface synthesized whisker. and the stacking faults exist concurrently in three (111 planes. The observed angles in the deflect branched whiskers were125°,70°,and109°. These m were composed of mixtures of type A and type B, type A only, Il. Experimental Procedures or parallel growth by two pairs of type A and type B whiskers. (1) Synthesis The whisker deflection was closely related to the difference in B-Sic powder was synthesized via carbothermal the growth speed of each type of whisker using carbon black(CB)powder and silica(SiO2)po L. Introduction theoretically needed was added to the sio, powder, and the SiLcoN ARBIDE (SiC) whiskers provide an effective means for polet ers were mixed via ball milling, using a-SiC balls in a The use of the naturally stacked powder bed of because of their good mechanical properties. The morphology and CB and Sio,(with CB positioned on the top), with a thickness of stacking faults of SiC whiskers are considered to be important, in 7mm, also was used as one of the methods for whisker synthesis regard to the mechanical properties of Sic whiskers themselves to provide a continuous supply of silicon monoxide (Sio) gas. The and whisker-reinforced composites. -4 To obtain good mechanical mixed powders(Fig. I(a), stacked powders(Fig. 1(b),and properties of the SiC-reinforced composite materials, most re- separated powder stacks( Fig. I(c)and(d)were annealed at a marchers are concerned about the interface between the matrix and mperature of 1420.C for 0. 1-3 h in a hydrogen atmosphere the whiskers, in addition to the homogeneous distribution of sic under vacuum( the latter condition is depicted in Fig. I(e)). The whiskers in the matrix 3,5 - However, only a few researchers have heating rate from room temperature to 1000C was 15C/min, and tried to improve the mechanical properties through a change in the that from 1000oC to 1420oC was 10 C/min. The flow rate of morphology of the Sic whiskers and control of the insertion hydrogen gas during heating was 0. 15 cm/s. The carbon layer in direction of stacking faults in Sic whiskers Moreover. because the stacked layers was separated physically from the SiO2 layer the grain growth and stacking-fault annihilation occur at high after the reaction run. The whisker that was formed in the cb layer temperatures in SiC, it is important that the final product that the during the reaction had sufficient handling strength to allow the Sic whisker morphology and the stacking-fault density be con- CB layer to be separated from the SiOz layer. The weight los trolled during the synthesis process. B-SiC whiskers generally the Sio, layer after the reaction was measured. The reactant of the(111) planes; hence, a stacking fault easily can be inserted into additional heating at 700C for 3 h in air, to eliminate excess the 111) planes that are perpendicular to the growth direc carbon xidation, and the weights of the synthesized Sic acking faults in B-SiC also are well-known to be powders were measured N. S. Jacobson--contributing editor Table I. Properties of Starting No. 189998. Received July 27, 1998; approved March 31, 2000 material n, Science and Culture(No. 1 1650857) 0.8 Carbon black 0.04-0.1 Institute of Ceramic Engineering and Technology, Seoul, Korea n Center,Korean tResidual after ignition.Morphology and Stacking Faults of b-Silicon Carbide Whisker Synthesized by Carbothermal Reduction Won-Seon Seo† and Kunihito Koumoto* Department of Applied Chemistry, Graduate School of Engineering, Nagoya University, Nagoya 464–8603, Japan Shigeo Aria 1MV Electron Microscopy Laboratory, Center for Integrated Research in Science and Engineering, Nagoya University, Nagoya 464–8603, Japan The main formation reaction for whisker that has been synthesized from SiO2 and carbon black (CB) in a hydrogen￾gas atmosphere was a solid–gas reaction between SiO and CB. The synthesized whiskers were classified into three types, in terms of the morphology, growth direction, and stacking-fault planes: (i) type A, which has a relatively flat surface and the stacking-fault planes are perpendicular to the growth direc￾tion; (ii) type B, which has a rough surface and the stacking￾fault planes are inclined at an angle of 35° to the growth direction; and (iii) type C, which has a rough sawtooth surface and the stacking faults exist concurrently in three different {111} planes. The observed angles in the deflected and branched whiskers were 125°, 70°, and 109°. These whiskers were composed of mixtures of type A and type B, type A only, or parallel growth by two pairs of type A and type B whiskers. The whisker deflection was closely related to the difference in the growth speed of each type of whisker. I. Introduction SILICON CARBIDE (SiC) whiskers provide an effective means for the reinforcement of metal and ceramic-matrix composites, because of their good mechanical properties. The morphology and stacking faults of SiC whiskers are considered to be important, in regard to the mechanical properties of SiC whiskers themselves and whisker-reinforced composites.1–4 To obtain good mechanical properties of the SiC-reinforced composite materials, most re￾searchers are concerned about the interface between the matrix and the whiskers, in addition to the homogeneous distribution of SiC whiskers in the matrix.3,5–7 However, only a few researchers have tried to improve the mechanical properties through a change in the morphology of the SiC whiskers and control of the insertion direction of stacking faults in SiC whiskers.8 Moreover, because the grain growth and stacking-fault annihilation occur at high temperatures in SiC, it is important that the final product that the SiC whisker morphology and the stacking-fault density be con￾trolled during the synthesis process.9,10 b-SiC whiskers generally grow in the [111] direction, because of the low surface energy of the {111} planes; hence, a stacking fault easily can be inserted into the {111} planes that are perpendicular to the growth direc￾tion.11–15 Stacking faults in b-SiC also are well-known to be closely related to the formation reactions and the reaction rate.11–13 Thus, to be successful in forming specially shaped whiskers, the insertion directions of the stacking faults and the whisker growth rate each must be controlled. In the present study, as the first step in our attempt to make bent whiskers with different stacking-fault layers, we have investigated several factors, using various sample-preparation methods. These factors include the whisker formation reaction, the whisker mor￾phology and growth direction, and stacking-fault insertion of the synthesized whisker. II. Experimental Procedures (1) Synthesis b-SiC powder was synthesized via carbothermal reduction, using carbon black (CB) powder and silica (SiO2) powder. The properties of the starting powder are listed in Table I. To increase the efficiency of b-SiC formation, twice as much carbon powder as theoretically needed was added to the SiO2 powder, and the powders were mixed via ball milling, using a-SiC balls in a polyethylene jar. The use of the naturally stacked powder bed of CB and SiO2 (with CB positioned on the top), with a thickness of 7 mm, also was used as one of the methods for whisker synthesis, to provide a continuous supply of silicon monoxide (SiO) gas. The mixed powders (Fig. 1(a)), stacked powders (Fig. 1(b)), and separated powder stacks (Fig. 1(c) and (d)) were annealed at a temperature of 1420°C for 0.1–3 h in a hydrogen atmosphere and under vacuum (the latter condition is depicted in Fig. 1(e)). The heating rate from room temperature to 1000°C was 15°C/min, and that from 1000°C to 1420°C was 10°C/min. The flow rate of hydrogen gas during heating was 0.15 cm/s. The carbon layer in the stacked layers was separated physically from the SiO2 layer after the reaction run. The whisker that was formed in the CB layer during the reaction had sufficient handling strength to allow the CB layer to be separated from the SiO2 layer. The weight loss of the SiO2 layer after the reaction was measured. The reactant mixtures, which contained synthesized whiskers, were subjected to additional heating at 700°C for 3 h in air, to eliminate excess carbon via oxidation, and the weights of the synthesized SiC powders were measured. N. S. Jacobson—contributing editor Manuscript No. 189998. Received July 27, 1998; approved March 31, 2000. This work was supported by a Grant-in-Aid for Scientific Research from the Japanese Ministry of Education, Science and Culture (No. 11650857). *Member, American Ceramic Society. † Currently at Advanced Materials Analysis and Evaluation Center, Korean Institute of Ceramic Engineering and Technology, Seoul, Korea. Table I. Properties of Starting Source Powders Starting material Purity (%) Particle size (mm) SiO2 99.9 0.8 Carbon black ,2† 0.04–0.1 † Residual after ignition. J. Am. Ceram. Soc., 83 [10] 2584–92 (2000) 2584 journal