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 °C at a heating rate of 1 °C/min. The storage modulus of distilled water as a reference material showed a drastic decrease at 0 °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 °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 °C. The peaks at 30–51 °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 °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.