Mechanically Induced Reactivity in Boehmite (y-AlOOH)

Abstract

Boehmite (y- A100H) is widely used as a precursor material for the industrially important transition aluminas. Effect of mechanical activation on the thermal transformation of boehmite into other phases has been investigated and res-ults are presented in this paper. Boehmite samples, pre-pared from gibbsite by thermal decomposition, were mecha-nically activated (MA) up to 4 hours in a planetary mill. Thermal analysis (TG-DTA and DSC), XRD and FTIR were used as main techniques to study the transformations. X-ray diffraction patterns showed formation of no new phase. A steady decrease in peak intensities and broadening of peaks with increase in MA time indicated structural degradation. The changes in the FTIR, spectra with MA also supported this. The first endotherm in the DTA pattern, between 70 and 200°C, was found to correspond to the removal of physically adsorbed water. The peak temperature of this endotherm increased as a result of MA. Noticeable weight-loss in the temperature range 200-350°C, is associated with the condensation of equatorial A120H groups. As temperature is raised above 350°C the transition to y-A120-3-stArts with the condensation of other Al-OH groups. These two stages clearly manifested with different slopes in the TG profile, move towards a single event with increase in MA time. As a result of MA for four hours, boehmite to y-A1203 transition temperature decreased from 522°C to - 474°C. For samples which are MA for less than 1 hour, no thermal event occurred above 600 °C and up to 1200°C. Beyond 1 hour of MA, an exotherm began to emerge and evolved in to a fully developed one after 4 hours of milling. Its temperature of occurrence decreased from 1040°C for 90 min. milled sample to 1000 °C for 240 min. milled sample MA. DSC studies has been temperature at cutting stage by using an infrared based length system as shown in and put into practice.