Pressure derivatives of elastic constants of monoclinic M(NO3)3·9H2O (M=Al, Fe, Cr) and third-order elastic constants of Al(NO3)3·9H2O

Research paper by E. Behnke, S. Haussühl

Indexed on: 01 Jun '89Published on: 01 Jun '89Published in: Journal of Materials Science


The elastic constants and their pressure and temperature derivatives of monoclinic M(NO3)3·9H2O (M=Al, Fe, Cr) have been determined from ultrasonic resonance frequencies of thick plates and from their temperature- and pressure-induced shifts. In addition, the complete third-order elasticity tensor of Al(NO3)3·9H2O has been evaluated from a combination of measurements of shifts of ultrasonic resonance frequencies produced by hydrostatic pressure and uniaxial stresses in various directions. The elasticity tensors of the three isotypic salts and their temperature and pressure derivatives are almost identical. The elasticity tensor exhibits a distinct anisotropy as well as the tensor of thermal expansion. The thermoelastic constants behave quite normally, whereas the pressure derivatives show anomalous features, i.e. some of them are negative similar to the situation in cubic Ba(NO3)2 and α-ammonium or α-selenate alums. These effects are accompanied by a very small, even negative, thermal expansion. The third-order elastic constants of Al(NO3)3·9H2O also reflect this anomalous behaviour.