TEMPERATURE-GRADIENTS IN LARGE COLD-SEAL PRESSURE-VESSELS

Radial and longitudinal temperature gradients within cold-seal pressur e vessels can contribute significantly to the total temperature uncert ainty in any one experiment and it is important to calibrate such grad ients before experiments are undertaken. We have measured temperature gradients in vertically mounted large cold-seal vessels at 1 atm and 1 kbar and in the temperature range 500-800 degrees C. Radial gradients were measured with the vessel at various positions within the furnace by recording the temperature difference between a thermocouple in the internal bore of the vessel and one in a well in the top of the vesse l. We find that when the vessel is at a certain position in the furnac e, the temperatures read by these two thermocouples are equivalent to within 1 degrees C. The contribution of radial gradients to temperatur e uncertainty can be thus be substantially minimized if experiments ar e undertaken with the vessel in this position. Longitudinal gradients of 2.8 degrees C/cm at 500 degrees C and 3 degrees C/cm at 800 degrees C were recorded at 1 kbar. These profiles are significantly steeper t han those recorded at 1 atm. Not to calibrate temperature gradients at the experimental conditions or failure to calibrate vessels at all co uld lead to large temperature uncertainties.