Melting properties of volcanic ash

Abstract

Volcanic ash from eastern Aleutian volcanoes is composed of rhyolitic glass, minerals, and rock fragments. Melting temperatures of the glasses, estimated from liquidus phase relations in the system SiO2-KAlSi3O8-NaAlSi3O8, range from 1000°C to 1300°C, whereas minerals begin melting at about 1100°C. Volcanic ash that is ingested into operating turbofan engines will partially melt. The molten ash is then deposited on high-temperature parts of the turbine - this can result in engine shutdown. Reduction of engine operating conditions to idle settings lowers the engine temperatures below the melting point of volcanic glass (below 1000°C), thus preventing the melting of ingested volcanic ash. However, at idle conditions, engines still operate at temperatures in excess of the glass transition temperature (700°-860°C), and annealing of glass particles to hot parts of the turbine may still be a problem. -from Authors