Pressure dependence of phase transitions in CsHSO4 studied with differential scanning calorimetry

The pressure dependence of three solid-solid and solid-liquid phase transitions in CsHSO4 has been investigated with differential scanning calorimetry at pressures up to 0.9 GPa with gaseous argon as the pressure-transmitting medium. The transitions that at ambient pressure occur at 333 K and 375 K seem to coincide at a pressure of about 0.15 MPa and probably exhibit above 0.1 GPa a solid-solid critical point. The ΔV value of the phase transition that occurs at 333 K (at ambient pressure) is calculated from the measured ΔH values and the constant dT/dp slope and is compared with rontgenographic determinations. The phase transition that occurs at 415 K (at ambient pressure) exhibits a linear temperature increase up to about 0.55 GPa and a flat maximum at about 0.6 GPa. The melting curve was determined up to 0.7 GPa and is described by Simon's equation.