Solar thermal, decomposition kinetics of zinc sulfate at high heating rates

This paper describes the experimental and analytical methods required to study decomposition of zinc sulfate in a simulated solar environment. Experiments were conducted at sample heating rates greater than 2 K/s and temperatures in excess of 1400 K in a specially designed thermogravimetric system which employed a 30-kWe/2-kWth downward-facing beam, arc-image furnace. The zinc sulfate decomposition took place almost exclusively through the high-temperature ZnSO4β phase under experimental conditions of this study. The kinetic parameters were determined from the thermogravimetric data by using a nonlinear least-squares optimization algorithm. An apparent activation energy, E, between 210 and 250 kJ/mol and an apparent reaction order, n, between 0 and 0.3 were obtained for β-phase ZnSO4decomposition reaction. The comparison of these results with those from lower temperature and lower heating rate zinc sulfate decomposition tends to suggest a change in reaction mechanism at the high heating rates expected in a concentrated solar environment.