Improved Carbon Thermal Reduction Preparation Of Tic Whiskers And Their Applications

Whisker is a single crystal wire with diameter ranging from 1 to 30μm. Its outstanding feature is ultra-high strength and hardness. In particular, the transitional metal carbides and nitrides have much higher strength not only at room temperature but also at high temperature. They are also corrosion resistant. Therefore, such whiskers are the ideal skeletons of the advanced composite materials. However, so far they have not found wide application because of the imperfect method of preparation.At present, there are two methods for the preparation of transitional metal carbides and nitrides, the chemical vapor deposition (CVD) method and the method of carbon thermal reduction of the oxides. By CVD high quality whiskers can be obtained, but they are low yield and expensive. On the contrary, by carbothermal reduction whiskers can be produced on a large scale, but their quality is poor. The goal of my research is to combine the advantages of the two methods while eliminating their disadvantages. Specifically speaking, I'll find a new type of carbothermal reduction for the massive production of high quality TiC whiskers.Based on a series of experiments I have finally worked out a new method of carbothermal synthesis of TiC whiskers, the so called"carbothermal reduction under the argon stream homogeneously flowing through the whole raw material stack". Here we have solved the key technological problem of how to adjust the argon stream so that the packing density throughout the stack of the raw materials roughly remains the same.Using the new method we were able to prepare quality TiC whiskers on a large scale (about 100 g or more) with high purity and high whiskers-to-particles ratio. The ratio may be as high as 90% or more. In addition, from the morphology of the whiskers we found that like in CVD, in the carbothermal synthesis process the TiC whiskers also grow by VLS mechanism.The key problem in preparing the whiskers-reinforced diamond saw blades is how to make the whiskers homogeneously distributed in the matrix of the saw blade. To this end, we first disperse the whiskers with an ultrasonator followed by ball-milling and hand stirring of the mixture of whiskers and matrix. By means of SEM examination and in-situ cutting test on a lot of diamond saw blades with different addition of TiC whiskers, we have finally found the optimum content of whiskers in the matrix of 1.5 wt%. Compared with the diamond saw blades without whisker addition, the addition of about 3～4 wt% TiC whiskers doubled the cutting length of the saw blade, which is the maximum length of the stone cut by one saw blade, while at the same time reduced the cutting time by half. Therefore, the total efficiency for cutting stone is increased four times.