An investigation of the composition dependence of the elasticity, reaction rate and porosity of orthophosphate bonded ceramics using an ultrasonic double-probe method

Abstract

An ultrasonic double-probe method has been used to monitor the setting process of phosphate-bonded, alumina filled, magnesia ceramics using commercial 2.25 MHz and 2 MHz transducers, for compressional and shear wave modes, respectively, in samples with alumina content in the range 0-60 wt.%. The elastic properties of the material were determined from the ultrasonic velocity measurements and were found to be dependent upon the filler volume fraction. The reaction rate was also investigated using the same ultrasonic data and found to increase with increasing filler volume fraction overall. The composition dependence of the elastic moduli is compared with the Hashin and Shtrikman theoretical bounds (1963) for the elastic moduli of two-phase materials. All data lie between these bounds, suggesting that the alumina particles were well dispersed and well bonded to the matrix. However, the fact that the data lie well above the lower bound suggests that the particles are not spherical and this, together with other evidence obtained from an analysis of reaction rates, indicates the predominance of plate-like grain structures. The measured elastic moduli were found to increase exponentially as porosity decreased and this effect could possibly be used to measure or estimate porosity.