Low pressure experiments in piston cylinder apparatus: Calibration of newly designed 25mm furnace assemblies to P=150MPa

摘要

We present new pressure calibration experiments demonstrating that the piston cylinder apparatus is suitable for experiments at pressure as low as 150MPa. Two newly designed 25mm furnace assembly have been developed and calibrated using two different calibration methods: the NaCl melting curve and the solubility of H _2O in albitic and rhyolitic melts. The NaCl calibration experiments performed in the pressure range 150-500MPa yield the pressure correction that has to be applied to the nominal pressure in order to have the equivalent (real) pressure on the sample. This correction varies as a function of the experimental pressure as follows:Pcorrection(MPa)=-0.115xPnominal(MPa)+78.23The H _2O solubility experiments in albitic and rhyolitic melts confirm the corrections determined using the NaCl calibration method. Moreover, because these experiments are performed at temperatures higher than those used for NaCl calibration, they demonstrate that the pressure correction is not affected by temperature in the range 800-1000°C. The accuracy of the pressure estimate associated with the calibration methods is ±25MPa. The major advantage of using the new assemblies is that low pressure experiments, which require rapid heating and quenching rates (e.g. volcanic and hydrothermal systems), can be performed with the same ease and precision as standard high pressure experiments for which piston cylinder is routinely used.