Highly constricted plasmas are an active research area because of their ability to generate high activity of plasma beams, which exhibit potential in applications of material processing and film deposition. In this study, optical emission spectroscopy was used to study the highly constricted nitrogen plasma created at low pressure. The vibrational and rotational temperatures of molecules were determined by fitting the second positive system of nitrogen molecule. Under the conditions of the power densities as high as 7 ∼ 85 W/cm3 and the pressures of 2 ∼ 200 Pa, the determined rotational temperature was found to be relatively low, increasing from 350 to 700 K and the vibrational temperature keeping at ∼ 5000 K. The analysis of dissipated power revealed that ∼ 80 % of input power is dissipated for the nitrogen molecule dissociation and the creation/loss of ions at the tube wall, producing an as high as 1012 ∼ 1013 cm−3 plasma with the nitrogen dissociation degrees of 2%∼15%. With the increase in the discharge pressure, more input power was found to be dissipated in the dissociation of nitrogen molecules instead of creation of ions, resulting in a higher density of radicals.
TiC powders have been prepared with titanium dioxide and charcoal powders as raw materials by vacuum carbothermal reduction technique. Meanwhile the as-prepared TiC powders were characterized by acid corrosion resistance test and oxidizability test. The results show as follows: the acid corrosion resistance of titanium carbide powders prepared at the optimum experiment conditions is better than that of industrial powders. It hardly dissolves in HCl, H2SO4, HNO3, HF, HClO4and aqua regia, and slightly dissolves in mixed solution HF+HNO3. The TiC powders are gradually oxidized at 352°C~917°C at air atmosphere and the product may be titanium dioxide and titanium oxides with lower valence. When the temperature rises to 546°C, a large quantity of titanium carbide powders are oxidized. And when the temperature rises to 688°C, besides the titanium carbide powders are oxidized to release heat, the free carbon is also oxidized and transformed into CO2gas to escape.
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