ABSTRACT
In the pioneering days of space exploration, an engineer was asked to select the best material for rocket nozzles. The material must withstand exhaust gas temperatures up to 3000
°
C, must be tough and strong, and resist abrasion (due to debris coming off the exhaust). These early rockets used hydrocarbon fuels. The engineer decided to use tungsten, which appeared to satisfy all the requirements: high melting temperature (3410
°
C), tough, strong, and abrasion resistant. On the actual test stand, the nozzle material melted. Measurements during firing showed that the temperature was 3000
°
C, well below the melting temperature of tungsten. How could this have happened? Subsequent chemical analysis showed that the original tungsten was quite pure, with less than
0.1 weight percent (w/o) carbon, while the tungsten sample dripped to the ground during the firing test contained 1.5 w/o carbon. The tungsten nozzle apparently picked up some carbon impurity, most likely from hydrocarbon fuel exhaust. Could this explain the unexpected melting of tungsten?
