Preparation Of High Density And High Strength Carbon Graphite Materials For Monocrystalline Silicon Furnace

As the global energy supply shortage increasing, solar photovoltaic power as a sustainable alternative energy source, has gotten rapid development in recent years. The development of photovoltaic industry high needs monocrystalline silicon materials. The high density and high strength carbon graphite materials has become the preferred heating material of monocrystalline silicon furnace because of its high strength, low resistivity, good thermal shock resistance, high temperature resistance, oxidation resistance, high heating efficiency, and the advantages of easy to be precision machined.The research of high density and high strength carbon graphite materials mainly focuses on the selection of raw materials and reinforcement of production technology two aspects over the world presently. Explorations and attempts were carried out in the development of high density and high strength carbon graphite materials for monocrystalline silicon furnace use in this paper, using superfine "second coke" powder and coal tar pitch as the main raw materials, coupled with some proper preparation technology.In this study, bulk density, resistivity, compressive strength, flexural strength, apparent porosity and Shore hardness were chosen as the major quality indicators of the high density and high strength carbon graphite materials. The influences of petroleum coke and coal pitch properties, particle size, molding pressure, dwell time, maximum calcination temperature, heating rate and graphitize on the structure and performance of high density and high strength carbon graphite materials have been researched. The results show that properties of the high density and high strength carbon graphite materials significantly improved by using low ash, low sulfur, low resistance, high true density and tap density superfine "second coke" powder as aggregate and coal pitch with appropriate softening point, toluene insolubles content, P resin content and coking value as binder. Appropriately increase the molding pressure and extend the dwell time can make products more compact and uniform, thus helping to improve the properties of the products. A proper low heating rate at250℃ ～ 700℃temperature range during the heating process helps increasing the coking value of the coal pitch and preventing the formation of cracks in the products. Impregnation can cover defects such as voids within the products, thus helping to improve the properties of the products. After graphitization treatment, the products have an increase in bulk density by0.05g/cm3and the resistivity was reduced by approximately70%. The study has gained some promising results. The processing conditions for preparing high density and high strength carbon graphite materials are: take superfine "second coke" powder as described in this study as aggregate coal pitch C as binder and coal pitch A as impregnating agent, molding pressure130MPa, dwell time3min, maximum calcination temperature1200℃, impregnated and then calcined for2～ 3times, and then graphitized under a high temperature of about2400℃at last. High density and high strength carbon materials prepared under this conditions have a bulk density≥1.85g/cm3, a resistivity≤12.0μ?．m, a compressive strength≥80.0MPa, a flexural strength≥40.0MPa, a apparent porosity≤14.0%, and a Shore hardness≥50.