High-Emittance Coatings

Ultramet produces textured high-emittance coatings that radiate heat at elevated temperatures and improve heat transfer. Although usually applied to hot objects that need to be kept cool, the coatings can also be applied to cool objects that need to be radiatively heated.

The emittance of Ultramet’s black rhenium coating is 0.82 at 1292ºF (700ºC) and increases to 1.00 at 3632ºF (2000ºC). Even after partial oxidation, high emittance is achieved.

Measured emittance of black rhenium coating in as-deposited state and after partial oxidation at 2372ºF (1300ºC)

Emittance

Temperature (C)

By varying the chemical vapor deposition conditions for rhenium, Ultramet can form pyramidal dendrites, which result in a black appearance and yield high emittance. This high surface area black rhenium coating significantly increases heat transfer into or away from the coated surface.

The emittance of Ultramet’s black rhenium coating is 0.82 at 1292ºF (700ºC)
and increases to 1.00 at 3632ºF (2000ºC).

Emissivity vs Exposure Time

Emissitivy

Total Exposure Time-Seconds

Emissivity data generated during arcjet testing at NASA Johnson for a carbon/silicon carbide composite coated with Ultramet’s layered hafnium carbide/silicon carbide

Coatings with similar morphologies can be generated by chemical vapor deposition of tungsten (melting point 6165ºF [3407ºC]), but because tungsten dendrites are finer, the emissivity is slightly reduced.