Combustion Synthesis of TiN Induced by High-energy Ball Milling of Ti Under Nitrogen Atmosphere
- PDF / 410,511 Bytes
- 9 Pages / 612 x 792 pts (letter) Page_size
- 95 Downloads / 204 Views
A planetary ball-mill device that enables one to perform solid-gas reactions at constant pressure was developed. Titanium powders were ball milled under nitrogen at a spinning rate of 960 rpm. The influence of the nitrogen pressure on the mechanochemical reactivity of titanium was analyzed at 1.5 and 11 bars. A spontaneous combustion took place during the grinding process, leading to a high yield of TiN for short milling times. The conversion of titanium into titanium nitride was facilitated by increasing the nitrogen pressure. At 11 bars, full conversion was reached for grinding times shorter than 5 h. Titanium nitride obtained in this way exhibited a high sintering activity.
I. INTRODUCTION
Titanium nitride (TiN) is considered an advanced ceramic material because of its high-temperature strength, thermal shock resistance, hardness, and thermal conductivity. TiN has also good resistance to oxidation and exhibits excellent corrosion resistance for various acid solutions. TiN is a very promising material for hightemperature technological applications due to the good combination of mechanical, thermal, and thermochemical intrinsic properties. However, TiN is generally used in cermets and as coating material (on machining tools or on jewelry) rather than as a monolithic or composite ceramic material. Applications of TiN ceramics are limited for the low sintering activity of powders obtained by current conventional production techniques. Conventional TiN powders require temperatures of about 2000 °C for considerable densification. The major synthesis method for TiN involves the direct reaction of Ti powders with nitrogen at high temperatures.1 Titanium nitride is also synthesized by carbothermal reduction of TiO2 in a nitrogen atmosphere,2,3 but it does not produce a highly pure product. Synthesis of small TiN particles has been reported using a vapor phase reaction between titanium chloride, ammonia and hydrogen.4 However, the removal of large amounts of hydrogen chloride (simultaneously obtained as a by-product) causes an important problem of device corrosion. The need for further improvement in the mechanical properties of TiN sintered ceramics has led to many studies focused on the fabrication of powders with a fine microstructure (generally nanostructured) and a J. Mater. Res., Vol. 17, No. 7, Jul 2002
http://journals.cambridge.org
Downloaded: 13 Mar 2015
uniform chemical composition.5–9 However, these new synthetic routes are comparatively very expensive, which limits a hypothetical large-scale use. In recent decades, mechanical milling has stimulated a growing interest because it has been shown to be a powerful technique for the synthesis of a great number of novel materials such as amorphous phases,10 supersaturated solid solutions,11 metastable phases,12 intermetallic compounds,13 composites,14 and ceramic materials.15 Mechanical milling has been generally applied to solidsolid reactions; however, it can also be used for gas-solid reactions. The small number of publications concerning to solid-gas reaction
Data Loading...
