Black rhenium coating prepared on graphite substrate by electrodeposition in NaCl-KCl-CsCl-K2ReCl6 molten salts

A compact and continuous rhenium coating with black appearance was obtained on the surface of graphite substrate in chloride molten salts with high efficiency and low cost. The rhenium coating prepared at a cathodic current density of 50mA/cm(2) at 850 degrees C has a preferential growth orientation of < 110 > and a high deposition rate of similar to 40 mu m/h. The rhenium coating is composed of a fine equiaxed-grain zone and a spired columnar-grain zone. The surface emittance is as high as 0.73, which is comparable with black rhenium coating reported by Ultramet. The microhardness of the coating as deposited is 350 16.4 kg/mm(2). The bond strength of rhenium/graphite interface tested at room temperature is similar to 10.2 MPa and is greatly improved after heat treatment at 1200 degrees C for 3 h in vacuum.