Pyrolytic Carbon Coating of Zircaloy-4 Clads at Relatively Low Temperatures

Abstract

A new technique has been developed to apply pyrolytic carbon coating to the inner surface of Zircaloy-4 cladding tubes at relatively low temperatures. The coating gas was a mixture of commercial butane, as a source for carbon, and argon as a carrier gas. The rate of the coating process was found to depend on the coating temperature and the concentration of butane in the coating gas mixture. The average deposition rate of pyrolytic carbon coating increased from 0.385 to 4.315 x 10-3 mg/(cm2/min) over the temperature range 250-450 degrees C and butane flow rate 50-90 cm3/min. The reported coating efficiency ranged from 1.16 to 11.11% over the temperature and the butane flow ranges of the study, whereas the activation energy of the coating process was estimated to be 8.9kcal/mol. Tensile tests and microhardness measurements performed on samples prepared from the coated tubes indicated that the coating process has insignificant effect on the mechanical properties of the sheath.