Production of Sintered α-Alumina by Explosive Compaction from Low Temperature Calcinated Aluminum-Rich Sludge

Abstract

Up to now the studies performed on alumina nanocrystalline powders using explosive compaction were restricted to the powders produced by specific industrial processes. The research work concerning other sources of alumina, like sludge from industries of aluminum anodizing, only regards to alpha-alumina. This is resulting from a previous heat treatment to high temperatures for which the phase transformation γ → α occurs. In present research is evaluated the possibility to use sludge having, before consolidation, as main phase γ-alumina, that means lower maximum temperature during preliminary calcination. After dried at 110 °C and heat treated at 800 °C during 1 h having as the major phase γ-alumina, the sludge was processed by explosive compaction followed by sintering at 1,200 and 1,650 °C (holding time = 1 h). During shock compaction the γ-alumina was transformed into α-alumina. The role of phase transformation during the explosive compaction followed by sintering is highlighted by the mechanical properties of the bulk material after sintering. The bulk material has hardness values close to α-alumina produced by conventional powder technology. Moreover, it was detected that the sulfur content of 4.5 % (w/w) measured in sludge previously calcinated was further reduced to 0.04 % (w/w), after explosive compaction. This study opens a sustainable possibility to recovery of Al-rich sludge to produce bulk alpha-alumina components/devices.