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一、引言对于电弧炉应用和宇航应用来说,要求多晶石墨具有低的膨胀系数,以便具有良好的抗热冲击性能。块石墨的热膨胀系数直接依赖于焦炭的种类和处理情况。由针状焦制备的石墨,热膨胀系数最低。一般块石墨的体积热膨胀系数比单晶石墨的低得多,这主要归因于晶体的择优取向程度和晶体间空隙容纳晶体C向膨胀的能力。择优取向程度取决于原料焦炭的结构和制造工艺方法。晶间的空隙和显微裂纹是因热处理而形成的。White指出,容纳晶体C向热膨胀能力并不是由于石墨化冷却产生的晶间裂纹,而是由于生焦初始热处理产生的晶微裂纹。
I. INTRODUCTION For electric arc furnace applications and aerospace applications, polycrystalline graphite is required to have a low coefficient of expansion in order to have good thermal shock resistance. The thermal expansion coefficient of block graphite directly depends on the type of coke and handling. Graphite prepared from needle coke has the lowest thermal expansion coefficient. The bulk thermal expansion coefficient of bulk graphite is much lower than that of single-crystal graphite due to the degree of preferred orientation of the crystals and the ability of the interstices between crystals to accommodate the expansion of crystal C. The degree of preferred orientation depends on the structure of the raw coke and the manufacturing process. Intergranular voids and microcracks are formed by heat treatment. White points out that the thermal expansion of crystal C is not caused by the intergranular cracking caused by graphitization but rather by microcracking due to the initial heat treatment of green coke.