Evaporation of Silicon from Molybdenum Silicides at High Temperature and in Hard Vacuum

The nature of the degradation of molybdenum disilicide coatings on molybdenum at 3110° to 4000°F in hard vacuum (10−7 torr) was investigated. Degradation occurred as a selective silicon loss by the successive transformations: MoSi2→Mo5Sia →Mo3Si →Mo. Comparison of estimated emittance values with surface composition of the coating indicated an abrupt decrease in emittance from 0.5 to 0.3 corresponding to the transformation Mo5Si3→Mo3Si.