Effects of microstructure on mechanical strength of selected clays from Uganda

Abstract

This thesis presents results of a study of the dependence of modulus of rupture (MOR), Young's modulus, {.E), and flexural rigidity,{ DJ, of sintered clay specimens on microstructure, average particle size and production variables. The production variables considered were sintering time, sintering temperature, and compaction pressure. The study shows that the MOR, Young's modulus and flexural rigidity of the clay product increase as compaction pressure, sintering temperature and sintering time are increased, but decrease as the particle size increases for all the processing conditions. The microstructure of clay specimens of higher strength are such that, the pores are well rounded and fewer in number. The grain boundaries are also thin and well defined with glassy phase being dominant as compared to liquid and pore phases. Higher strength of the clay specimens is also associated with formation of mullite which forms needle-shaped crystals with an interlocking network that gives high stability at elevated temperatures. The variation between MOR and sintering time, t, can be described by a relation of the form MOR = ot2 + /3t + 9 where a, /3 and 9 are constants with some of their mean values for samples compacted at 49.584MPa and sintered at 12oooc are: a = -0 .37±0.16MPas2, /3 =4.93x0.87MPas·1 and 9 = 21.05±7.26MPa