Abstract
In recent years, there has been concerted effort towards the synthesis of cermet materials from low grade titanium ore. This is because the reserve of high grade titanium containing ore, i.e. natural rutile, is fast depleting and rutile becoming more expensive across the globe. Today, titanium containing hard ceramic powders, e.g. TiC, TiN and their solid solution TiCN powders have become important reinforcement materials due to their suitable properties. Titanium carbonitride, which is a boundary solid solution of titanium carbide and titanium nitride combines the excellent properties of both TiC and TiN in one structure of TiCN. In order to make this special material readily available, various methods have been adopted to synthesize titanium carbonitride powder. Although, the synthesis of titanium carbonitride by carbothermic reduction of titanium dioxide (rutile) with carbon under nitrogen atmosphere has been the most widely used for the commercial production of titanium carbonitride. However, this process requires the extraction and purification of titanium dioxide from its ore e.g. ilmenite, which itself is a costly process, or the use of natural rutile, which is fast depleting and becoming more expensive across the globe. Ilmenite (FeTiO3), which is a mineral source of titanium dioxide, is abundantly found in many parts of the world, most especially in South Africa. South Africa, is a leading producer of ilmenite in the world, accounting for about 37% of 6.2 million metric tons of the global production. Hence sourcing and processing of TiCN powder directly from South African ilmenite will be an added advantage. It is on this premises that the urgency for the processing of South African ilmenite to its final products, e.g. titanium containing hard ceramic products, such as TiC, TiN and/or TiCN powders or composite, and titanium metal, is being hung. Hence, this study develops a mechano-chemical processing route for the synthesis of titanium containing hard ceramic powders from ilmenite concentrate, which could be used for the production of cutting tools made of TiC and TiCN composite materials. The study also determines the possibility of sintering bulk TiCN based cermets with different metal matrices. For the synthesis of titanium carbide and titanium nitride/carbonitride powders, mixtures of ilmenite concentrate and graphite were milled in a planetary ball mill (PM 100) for different time intervals of 0, 30, 60 and 120 min, and carbo(nitro)thermally reduced under argon and nitrogen gas in a high temperature laboratory furnace (Thermal Tech., USA), respectively. These carbo(nitro)thermic reductions of mixtures of ilmenite concentrate and graphite result in the formation of Fe –TiC and Fe – TiCN powder composites in which globules of TiC and TiCN particles are embedded in the iron matrix,..
Ph.D. (Engineering Metallurgy)