Effect of Holding time on Binder Burnout, Density and Strength of Green and Sintered Alumina Samples

Abstract

The present work deals with the effect of holding time on the binder burnout, bulk density and strength of the sintered alumina bodies. Binders provide better green strength to the ceramic bodies and their efficient removal from the system during sintering plays a crucial role in bulk density and strength of sintered bodies. The sintered bodies in this project were alumina samples which were prepared by dry pressing of granules. These granules were prepared by mixing reactive alumina (-75 micron) with binders solution of 3 and 4 weight percent. The thermal decomposition characteristics of the binders namely (Poly Vinyl Alcohol (PVA), Dextrin and starch) was carried out. On the basis of these studies, the binder burnout temperature was found to be 450 0C.Accordingly during sintering of the pellets a hold time was given at 450 0C. In order to see the effect of holding time on binder removal rate, the holding time was varied between- no holding (0 minute), 30 minute holding time, 60 minutes holding time. The samples were sintered at 1600 0C for one hour and the sintered samples were characterized for bulk density, apparent porosity, compressive strength and shrinkage. It was observed that Starch (3 %) added samples showed highest compressive strength and also had a high bulk density. It was observed that effective binder burnout could enhance strength of sintered bodies and incomplete removal may lead to defects like cracking, black coring, bloating and formation of closed pores which adversely affect the properties of the sintered bodies.