Study on the synthesis of Spray Coating Composed of Refractory Boride Ceramics by Electrothermal Explosion of powders

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The subject of this research is to find the spraying process to produce the coating composed of refractory carbide ceramics due to electrothermal explosion of the ceramic powders. In addition, it is also expected to research a new technique suitable for the enlargement of this process.The electrothermal explosion of conductive powders has been applied to produce spray coatings of refractory boride ceramics without any additives. The powder of conductive zirconium boride was pluged in a container made of an inner insulating tube and an outer metal cylinder having a window for ejection of molten paticles. Such a container was holded between a pair of electric contacts in a vacuum chamber. The spray of the ceramics was done by the explosion caused by electrical rapid heating due to high voltage application and large current discharge. In order to obtaine dense and adhessive coatings of novel functional boride ceramics, the explosion and spray of ceramic powders was observed by Sclieren photography which was composed of a high speed camera and high power argon ion laser. It was found that high power electrical discharge caused the production of a high speed jet containing molten particles. The representaive velocity of the jet was estimated 3000m/s of more on the basis of one dimensional approximation of intense shock wave formation. The electric energy supplied to the powder was twice to three times the one needed to melt just the powder. Thus it was revealed that this spray technique is chracterized with high temperature and speed jet which have not been obtained in other techniques yet. The coatings obtained was also as unique so that it had no pore and lamella, and that it mixed with the top layr of a substrate over the range of 50mum. Thus the coatings are expected to be highly dense and adhesive. For the large-scaled spraying, the shapes of the powder container and other equipment were evaluated.