Effect of gravity on dimensional change during sintering—I. Shrinkage anisotropy

The effects of gravity on sintering shrinkage and dimensional uniformity are analyzed using a continuum theory of sintering. Shape change caused by gravity during sintering is described both analytically and numerically. For a cylindrical sample shape, analytical approximations to characterize gravity-induced nonuniformities in shrinkage and compact aspect ratio are shown. As an illustration of the concept, analysis is performed for the solid-phase sintering of a copper powder cylindrical specimen to replicate earlier experiments reported by Lenel et al. (Trans. Am. Inst. Min. Engrs, 1963, 227, 640) and Exner (Rev. Powder. Metall. Phys. Ceram. Soc., 1968, 51, 604). The intensity of shrinkage anisotropy is compared for viscous and diffusional mechanisms of sintering. An algorithm is introduced for minimization of gravity-induced shrinkage anisotropy, suggesting an asymptotic approach to the peak temperature for best dimensional uniformity.