Please help...

(a) Your division head (at work) has asked you to develop a pore free dense (99.99% of theoretical density) alumina body by conventional (pressureless) solid-state sintering. Your R&D manager has told you that alumina generally densifies at 1400-1650C temperature range. You have used cold isostatic press for good compaction with highest green density. You have a regular furnace, which can reach a maximum 1750C temperature but the atmosphere of the furnace cannot be controlled. You have sintered the compact at different temperature for different dwell time. However, you found the presence of pores at the grains as well as few large grains (abnormal grain) in the microstructure of the sintered alumina of highest density. What are the strategies do you follow to solve the problem?

(b) t is reported in literature that precoarsening of alumina powder compact helps to develop uniform microstructure. Another research team reported that multistage sintering at high temperature regime (intermediate and final stages of sintering) also helps to develop uniform microstructure. Why does precoarsening is helpful for obtaining uniform (homogeneous) microstructure? Why does multistage sintering at high temperature regime also helpful for developing uniform (homogeneous) microstructure?