Measurements of infrared optical properties of Al2O3 rocket particles

Abstract

High temperature (1700-3000 K) optical properties of A1 2 0 3 rocket particles have been determined from mid-i.r. (1.3 to 4.5 ~~ measurements of Al z 0 3 /argon aerosols generated in a shock tube. The partIcles were collected from tile exhausts ,)f two different abminizect sol id propellant rockets and subjected to u)mprehensiv~ chemical and physical assays to determine contamination levels and particle size distributions. Observed rocket particle emissivities are low, but are nevertheless significantly greater than for pure Al z 0 3 particles. Comparison of tile rocket particle absorption indexes against pure A1 Z 0 j particles indicates that below the melt point, tl1e mld­ i.r. emission is determined by impurities, and above the melt point, it is determined by tfle bull< liquid properties of the particle material. For pure particles, this creates a jump in effective emissivities of over four orders of magnitude, whereas for contaminated particles the jump is s~aller, depending upon contamination level.