High-load, high-temperature deformation apparatus for synthetic and natural silicate melts.

A unique high-load, high-temperature uniaxial press was developed to measure the rheology of silicate melts and magmatic suspensions at temperature up to 1050 degrees C. This new apparatus is designed to operate at constant stresses (up to 300 kN) or constant strain rates (approximately 10(-7) to 10(0) s(-1)) and further allows us to carry on experiments on samples with high viscosities (approximately 10(8) to 10(12) Pa s). The rheological instrument represents an advance in that it accommodates homogeneously heated samples (+/-2 degrees C) of voluminous sizes (up to 790 cm(3)) which permit the insertion of thermocouples to monitor temperature distribution evolutions during measurements. At last this setup allows for accurate measurements of viscosity of natural multiphase materials at strain rates and temperatures common to natural systems. The apparatus aspires to precisely (1) describe the onset of non-Newtonian behavior and its evolution with increasing strain rate until the point of rupture in the brittle regime, (2) constrain the effect of crystals and bubbles on the viscosity, and (3) record heating dissipated through viscous deformation. Here, we present a series of measurements on NIST standard material SRM 717a to calibrate the instrument. We couple the viscosity determined via Gent's equation with certified viscosity data of the standard material to calibrate this state-of-the-art apparatus. This work shows that we can resolve the viscosity of voluminous melt sample within 0.06 logarithmic unit and furthermore present the detection of minor viscous dissipation for a high-temperature, high strain rate experiment.