Fabrication of ceramic nozzle made from clay-alumina mixture

Abstract

Heat transfer from hot gases to the chamber and nozzle walls, can result in weakening the rocket casing. Thus proper and complete insulation is needed to protect the casing material from reaching melting temperature or become damaged at elevated temperature. Typical solution to this problem would be to thicken the casing walls which in effect would increase the total weight. To reduce the total weight, a new material that can withstand high temperature and is lightweight was studied. Ceramic is one of the materials that can withstand high temperature and at the same time is much lighter than normal metal. There are several developments using ceramic as a hot section component. In this study, ceramic was used as a replacement for typical metal component of rocket motor. Traditional clay called Sayong clay and refractories material, namely, alumina were used. A suitable material for rocket motor development would be one that has good mechanical strength, minimum shrinkage and low thermal conductivity. Three different composition sets were prepared and characterized according to shrinkage reduction, compressive strength and thermal conductivity. Composition A which contains only clay mixed with water as a binder shows high degree of shrinkage during drying and firing at temperature ranging from 700 oC to 1500 oC. Thus, by introducing alumina to the tune of 30% and 50%, the shrinkage of clay was reduced significantly. Furthermore, high compressive strength was achieved for the mixed composition of 50% alumina-clay (composition C) at firing temperature of 1500 oC, about 29.2 kN. Thermal conductivity test was conducted on composition C, and it was observed that as the firing temperature increases the value of thermal conductivity, k also increases due to the densification of ceramic particles. To verify the real potential of this ceramic material, Ballistic Research Motor (BRM) test was performed. Since composition C was found to be superior to others, a nozzle made from it was fabricated. The nozzle with throat measuring 30 mm in diameter was loaded into the existing rocket motor with solid propellant and combustion chamber. The firing of BRM took about 5 seconds with average chamber pressure reaching 0.124 Mpa. Calculations showed that the ceramic nozzle produced 42.47 N of thrust. The experiment proved the potential of ceramic as a suitable material for rocket motor design