Measurement of the burning surface temperature in ammonium perchlorate

Abstract

There are a number of inconsistencies in the measured values reported for the burning surface temperatures of ammonium perchlorate (AP). Therefore, the temperature profile near the burning surface of pure AP was measured using microthermocouples. A pressed AP specimen was burned using a propane/air diffusion flame or by increasing initial temperature below the pressure deflagration limit of AP. Since a small cavity may exist around the thermocouple, a large AP crystal was grown around the thermocouple head, and it was also used in the temperature measurement of the burning surface. A video recording of the AP surface was also male using a charge-coupled device (CCD) camera during the combustion process. The time on videotape was synchronized with that on the record of the thermocouple measurements using a flash lamp. As a result, the time at which the thermocouple bead appeared on the burning surface was precisely identified on a temperature-time diagram, and the burning surface temperature was obtained. It was found that the surface temperature of pure AP is in the range of 450–480 ° C, and it was ascertained that the burning surface temperature is independent of the regression rate and the heating rate of the AP specimen. On the other hand, the surface temperature does depend on pressure. The slope of the logarithmic pressure versus reciprocal surface temperature was 130–160 kJ/mol. This value is slightly higher than one-half of the heat of dissociation for AP. Our results were similar to results obtained by Powling et al. with an infrared-radiation technique. However, these results are different from those measured by thermocouples in several other studies. These differences may actually reflect differences in the methods used to identify the burning surface in the measured temperature data.