Bulk density of small materials, heat conduction tear your eyes coefficient is generally small, but at the same time decreases in the mechanical strength, so be reasonable choice.
容重小的材料，一般导热泪盈眶系数也小，但同时机械强度也随之降低，故要合理选择。
2
The low density graphite gets higher friction coefficient and bulk worn loss than the high density graphite.
低密度石墨的摩擦系数和体积磨损量比高密度石墨材料高。
3
On the assumption that the product of volume thermal expansivity and bulk modulus based on the thermodynamic approximation theory, a new equation is presented for volume thermal expansion coefficient.