Kinetics of SiC formation during high P–T reaction between diamond and silicon Cristian Pantea a,b, * , Georgiy A. Voronin a , T. Waldek Zerda a , Jianzhong Zhang b , Liping Wang c , Yanbin Wang d , Takeyuki Uchida d , Yusheng Zhao b, * a Department of Physics and Astronomy, TCU, Fort Worth, TX 76129, USA b LANSCE-12, Los Alamos National Laboratory, Los Alamos, NM 87545, USA c Mineral Physics Institute, State University of New York at Stony Brook, Stony Brook, NY 11794-2100, USA d Consortium for Advanced Radiation Sources, The University of Chicago, Chicago, IL 60637, USA Received 1 April 2005; accepted 26 April 2005 Available online 1 June 2005 Abstract Time-resolved in situ X-ray diffraction at simultaneous high pressures (P) and high temperatures (T) was used to monitor kinetics of the reaction between diamond and silicon. Analysis of the data indicated that the reaction was diffusion controlled, and the diffusion was taking place through grain boundaries. For the nm size diamond the activation energy (170 kJ/mol) was smaller than that for Am size diamond (260 kJ/mol), and the reaction started at a temperature below the melting point of silicon. These effects are attributed to nanocrystalline structure and strained bonds within grain boundaries. Published by Elsevier B.V. Keywords: High pressure; High temperature; SiC formation; Diffusion; Nanocrystalline diamond 1. Introduction Diamond composites are a class of hard-materials with a huge variety of applications in diverse fields, such as mining, grinding, cutting, machining, drilling, engineering components, and heat sinks for electronic equipment [1–3]. Several different techniques have been used for diamond – SiC composites manufacturing, among them the most common is the high pressure –high temperature reactive infiltration technique [4]. Recent developments in the manufacturing process, such as addition of nanosize diamonds and silicon and structure engineering of grain boundaries, renewed interest in investigation of the process and mechanical properties of the product [5–8]. However, information on the kinetics of formation of diamond–SiC composites is limited. It is generally accepted that the reaction between diamond and liquid silicon starts on the surface of diamond crystals, near the surface defects [9]. The surface defects that are promoting the reaction between diamond and melted silicon are of microscopic level and consist of growth steps, surface dislocations and/or places of increased roughness [10]. It has been observed that the reaction proceeds faster for diamond crystals of smaller sizes and when the temperature is increased. In the last 25 years several studies on the kinetics of SiC formation at high temperature from different precursors were reported [11–14]. In general, there is an agreement that the controlling step of the reaction is the diffusion of carbon atoms through the newly formed SiC layer, with activation energies of 100–400 kJ/mol. Many authors have studied self-diffusion of carbon and silicon in h-SiC [15- 18]. Despite numerous efforts over the past 25 years that process is still not fully understood. Although different authors provided different values of activation energies for diffusion, ranging from 600 to 900 kJ/mol, they all agreed 0925-9635/$ - see front matter. Published by Elsevier B.V. doi:10.1016/j.diamond.2005.04.013 * Corresponding authors. Cristian Pantea is to be contacted at LANSCE- 12, Los Alamos National Laboratory, Los Alamos, NM 87545, USA. E-mail addresses: pantea@lanl.gov (C. Pantea), yzhao@lanl.gov (Y. Zhao). Diamond & Related Materials 14 (2005) 1611 – 1615 www.elsevier.com/locate/diamond