Temperature dependence of dynamic moduli of alumina suspensions and alumina powder compacts

The complex moduli of 10-30 vol% aqueous suspensions of alumina particles of median size of 310 nm were measured at 1 Hz of applied frequency in a temperature range of -100 to 100 degrees C at a heating rate of 1 degrees C/min. The storage modulus of distilled water as a reference material showed a drastic decrease at 0 degrees C, where a phase transition occurred from solid ice to liquid water. The loss tangent of water showed a sharp peak associated with the phase transition at 0 degrees C. In 10 vol% alumina suspensions at pH 3, 5 and 7, more additional peaks of storage modulus and loss tangent appeared at 7-51 degrees C. The peaks at 30-51 degrees C represent the phase transition of colloidal suspension from a dispersed state to a flocculated state. When the alumina content of the suspension was increased to 30 vol%, little change of storage modulus and loss tangent were measured in the wide temperature range of -100 to 100 degrees C, reflecting little change of dense packing structure of alumina particles after the melt of solid ice with increasing temperature. A similar dependence of storage modulus and loss tangent on heating temperature was measured in the calcined alumina porous compact infiltrated with water in the open pores. (C) 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved.