Preparation Of Ti(C,N) Powder In The Presence Of Molten Salt And The Effects Of Various Additives On Carbon Bricks' Properties

Ti(C_1-xN_x)(0≤x≤1) has many excellent advantages, such as high melting point, big hardness, relatively high thermal and electrical capability, good abrasion resistance, which make it has various applications in different areas. At present, carbothermic reduction and nitridation method is generally used to fabricate Ti(C, N) powder, however, such disadvantages as non-mixed mixtures, long reaction time and high combustion temperature existing. Molten salt method owes exclusive super-advantages in preparing ceramics powders, it can decrease initial synthesis temperature and reduce reaction time remarkably, effectively control the powder's particle size and morphology, has wide application and low cost etc. If the two methods are combined, it is likely to synthesize Ti(C, N) powder with excellent properties. Nowadays, Ti(C, N) used in refractory materials is extremely less reported. The properties of carbon brick such as strength, wear resistance, thermal shock resistance and molten iron corrosion resistance may be improved significantly when the non-oxides of titanium as Ti(C,N) is added. The work investigated contains three parts as follows:Firstly, the affection parameters in experimental procedure are investigated and the results indicate that, in the presence of molten salt and using TiO₂ (anatase type) and carbon black as raw materials, the reasonable molar ratio of C and TiO₂ determined was 2 in both atmospheres of coked condition and nitrogen gas, however, the reaction performed more completely in nitrogen gas atmosphere. Ideal yield of Ti(C, N) powder was obtained in the presence of 10wt% molten salt at 1300oC for 3h. Molten salt containing several kinds and one or more can dissolve and give out gas is favorable for the formation of Ti(C, N). The wet mixing time for the raw materials chosen was 30 min. Carbon black is as the most effective carbon source because of it' smaller particle size and high reactive ability. The possibility of mass production was identified by mid factory production.Secondly, Ti(C, N) prepared in molten salt bath shows that molten salt has a positive effect on the reaction occurrance, which effectively decreased initial reaction temperature and well controlled the particle morphology. The Ti(C, N) obtained, mean particle size was about 2⁶μm, uniform shape and less extent agglomeration. The possible reaction route was TiO₂→Ti₄O₇→Ti3O5→TiOxNy→Ti(C, N).Thirdly, effects of different kinds of additives on coked carbon brick' properties were investigated and the results show that the specimens containing TiC and TiO₂+Al as additives, have the biggest bulk density and the smallest apparent porosity, meanwhile, the specimen containing TiO₂+Al has the biggest cold compressive strength. The XRD analysis point out that metallic silicon converted into SiC,Si₂N₂O and quartz, meanwhile, TiO₂ transformed to Ti(C, N) after coking. The thermal conductivity coefficient of fired carbon brick was measured in 600oC and the results showed that the specimen adding TiO₂+Al has the biggest value of 15.03W/m.k.The value of <1μm pore volume, 78.5% in TiO₂+Al specimen was the biggest , and the pore size was mainly concentrated at about 200 nm. By comparing specimens'microstructures, it is found that the TiO₂+Al specimen has the densest structure while the TiO₂ specimen has a loose structure with many optical pores and cracks apparently. Conclusions can be drawn from the results above mentioned, TiO₂+Al can be used as the effective additive to improve the carbon brick' properties, but the ration and addition content of TiO₂ and Al should be investigated furthermore.