Numerical Simulation of a Novel Method for PVT Growth of SiC by Adding a Graphite Block

SiC crystal is an excellent substrate material for high power electronic devices and high-frequency electronic devices. Being cost-effective and defect-free are the two biggest challenges at present. For the physical vapor transport (PVT) growth of a SiC single crystal, SiC powder is used as the source material, which determines the cost and the quality of the crystal. In this paper, we propose a new design in which graphite blocks are substituted for the non-sublimated SiC powder. Temperature distribution in the SiC powder, the evolution of the SiC powder, and the vapor transport are investigated by using finite element calculations. With the addition of graphite blocks, the utilization and sublimation rate of SiC powder is higher. In addition, the reverse vapor transport above the SiC powder is eliminated. This design provides a new idea to reduce the cost of SiC crystals in industrialization.

Phenomenon of Gaseous Adiabatic Compression of Powder in Explosive Compaction

This paper introducesan explosion experiment, in which the powder can be recollected100%. Based on the observations inside the recollected powder case,it can be confirmed that the very small amount of air in the space within the powderis concentrated in the bottom of the powder case,and consequently results in adiabatic compression. The compression energy of air gives rise tothe extra high powder temperature. A theoretical approach to the adiabatic mechanism was discussed and a rough estimationwas provided onthe degree of the increased temperature.

Measurement on Temperature Distribution of Metal Powder Stream in Laser Fabricating

In order to study temperature distribution of metal powder stream in laser fabricating, its thermal radiation in visible region was detected by CCD. Based on Planck’s radiation law, the relation between molten powder temperature and its visible thermal radiation could be set up. The thermal radiation image signal of powder stream was transformed to digital signal which was used to analyzing its temperature distribution. It was shown that crosswise dimension of molten powder was about 2.5mm in diameter at the distance of 5mm from power nozzle. The powder out from powder nozzle was heated rapidly by laser. Temperature of powder in central axis regions was the highest which was nearly 2000K at the power of 1100w. The temperature gradient of powder at the edge of laser stream was greatly. The measurement results could be used to optimize the design of powder nozzle and processing parameters of laser fabricating.

Digital Image Processing of CCD Measuring Temperature Field in Coaxial Powder Stream of Laser Cladding

In this paper, the theory of the powder temperature measurement using radiation is briefly illustrated, and the measurement system on temperature field in coaxial powder stream of laser cladding by applying color CCD and digital image processing technology is designed. The experimental result indicates that this measurement system can test the distribution of temperature field.