Study On The Preparation Technics Of Nanocrystalline Titanium Carbonitride Powders

As a kind of non-oxide ceramic materials, Ti(C,N) powder are known for their outstanding properties,such as high melting point, significant harness-toughness compromise,wear resistamce, thermal conductivity , low electrical resistivity. Therefore, they are widely used as the main raw materials of the preparation of tool materials-Ti(C,N) based cermets and applied in many fields such as machine chemical engineering, automobile manufacturing and aviation aerospace,etc. The Ti(C,N) powders characteristic affect the body materials greatly, Being the nanosize, the performance of their body materials will be improved.Therefore, research on the prepation of nanocrystalline Ti(C,N) powders and their structure and properties becomes the hotspot in the material subject currently. Based on a review of devolopment and progress on the prepration technics, titanium carbonitride powders is synthesized directly by the carbonthermal reduction-nitridation between titanium oxide and carbon black in a nitrogen atmosphere.The mechanism during the reactions and influence of the parameters,such as temperature,remain times,the pressure of N₂ has been studied systematically in this dissertation by using all kinds of apparatus such as chemistry analysis, x-ray diffractomerer (XRD),scanning electron microscope (SEM), transmission electron microscope(TEM), etc. A few quantity on the condition of industrialization production will be carried on. In this works, synthesis process of titanium carbonitride by the carbothermal-reduction-nitridation was studied. During the reaction prcoss,at first ,nanosize TiO₂ converted from the antase to the rutile in 900℃and did not react with C at this time;At 1050℃, the TiO2 and carbon black respond the born low price titanium oxide Ti3O5;While continuing to 1200℃, Ti3O5 and C, N2 responds to produce the immerate TiON, the Ti3O5 reacts completely at this time;Up to 1250℃, there has been a mount of Ti(C,N) phase, which is from part of the TiON;When the temperature rises to 1300℃,Ti(C,N) produces completely.According to the basis thermodynamics, the most suitable reaction temperature should be between 1260¹586℃. However,Ti(C,N) can be produced at 1250℃by our experiments,we think that this reason may be that using the raw material of the nanoszie which have the high ratio surface and the surface energy, the reaction could be carried on at lower temperature in the thermodynamics. The amounts of carbon in raw materials influence the N content of Ti(C1-x,Nx). When other conditions are constant, improving the content of C can lower the x value of Ti(C1-x,Nx) powders. The content of C in the raw materials which is too excessive will respond to the dissociation carbon morely and debase the quantity of the synthesized powders. Reaction temperature and the remain times are the key factors of carbothermal-reduction-nitridation. Improving the reaction temperature and the remain times are all be advantage to the reaction completely. Along with the exaltation of the temperature and the extension of the remain times, the x value of Ti(C1-x,Nx) powdrs will lower and FSSS grain size and crystalline size of the Ti(C,N) powder will grow up at the same time. The crystalline size grows up than the FSSS grain size. Enlarging the pressure of N2 in the reaction can lower the reaction temperature of Ti(C,N) powders. But under the condition which the pressure of N2 is very high, the C content of Ti(C,N) powders can hardly raise because the N element combined with the Ti element more easier than the C element. By optimizing the technics parameter,when the carbon wt% is 25% , Ti(C0.427N0.573) powders with 0.46 μm of Fsss grain size and 40 nm of crystalline size could been synthesized by the preferable technic under the condition of lab which is that reaction temperature is 1350℃, the remain times is 3 hours and thepressure of nitrogens is 0.04 MPa;When a batch is 0.5 kg,the technic parameters should be changed.In this paper,Ti(C0.379,N0.621) powders with 1.41 μm of Fsss grain size and 35 nm of crystalline size could been synthesized by the optimum parameters which are that reaction temperature is 1450℃, the remain times is 270 minutes and the nitrogen flux is 1.0 m3/h;Ti(C0.395,N0.605) powders with 1.53 μm of Fsss grain size and 40 nm of crystalline size could been synthesized by the optimum parameters which are that reaction temperature is 1600℃, the remain times is 180 minutes and the nitrogen flux is 1.0 m3/h.