• PDF / 696,977 Bytes
• 6 Pages / 612 x 792 pts (letter) Page_size
• 94 Downloads / 264 Views

DOWNLOAD

REPORT

---

J.H. Ahn Division of Chemical & Materials Engineering, Ajou University, Kyoungki 441-749, Korea

B.K. Kim Nano P/M Group, Korea Institute of Machinery and Materials (KIMM), Kyungnam 641-010, Korea (Received 21 May 2004; accepted 3 January 2005)

Nanostructured titanium carbonitride (TiC0.5N0.5) powders were synthesized by a Mg-thermal reduction process. The evaporated liquid solution made from TiCl4 + 1⁄4C Cl reacted with liquid magnesium protected with nitrogen gas. The extremely 2 4 fine titanium carbonitride particles of about 50 nm were successfully produced by the reaction of Ti and C atoms released from chloride reduction with liquid magnesium and nitrogen gas. After the reduction process, the residual phases of MgCl2 and the excess Mg were removed by mechanical vacuum conditions. To obtain the maximized stoichiometry of product, the process optimization with thermodynamic study was performed with various experimental parameters such as reaction temperatures and solution feeding rates.

I. INTRODUCTION

Titanium carbonitride powders have been widely used as raw materials for production of various ceramic tools.1–3 Because of its high melting point of about 3373 K, the production of bulk parts containing the TiCN component has been made possible by powder mixing and consolidation processes only. In general, the finer titanium carbonitride powder particles with stoichiometry and lower quantity of impurity have enhanced the hardness and toughness of consolidated tool materials. There are several methods for synthesizing titanium carbonitride powders: (i) solid state-methods, such as carbothermal reduction of titanium dioxide or titanium hydride by carbon, nitrogen and ammonia,4–6 direct reaction of TiC with TiN or Ti with C, N,7,8 and self propagating high-temperature synthesis (SHS);9 (ii) gaseous phase reaction;10 and (iii) liquid-phase reaction such as the sol-gel process.11 However, these processes have demonstrated many drawbacks. For example, the carbothermal reduction of TiO2 has to be processed under considerably high reaction temperatures (2000–2500 K) because of the high thermal stability of titanium dioxide. Thus, it causes a pre-sintered coarse structure, and consequently, many hours of post-milling are required to produce fine powders.

http://journals.cambridge.org

II. EXPERIMENTAL

A solution composed of TiCl4 (OTT-O, 99.99%) and C2Cl4 (TVS, 99.96) was fed vertically to an isolated cylindrical chamber made of mild steel with an inner

DOI: 10.1557/JMR.2005.0118 844

Moreover, the size of milled powders has been limited to about several microns. Nowadays, these powders are commercialized. The other processes have also been flawed by at least one or more of the following weaknesses: (i) easy oxidation during the process results in the formation of oxycarbonitride with a significant oxygen content in sol-gel process, (ii) expensive initial titanium powder with high purity required in the direct carburization and SHS process, and (iii) low productivity in the gas-phase reaction. Previously, we introd