A rod 5, wherein the protective layer is obtained by {HEAD ~ controlled oxidation} of the hafnium bar, for 3 to 12 hours, at a temperature in the range 820° C. to 950° C., in {TAIL ~ oxygen} diluted to a concentration of 1% to 50% in an inert gas, under low pressure 
in
A rod 5 , wherein the protective layer is obtained by { HEAD ~ controlled oxidation } of the hafnium bar , for 3 to 12 hours , at a temperature in the range 820 ° C. to 950 ° C. , in { TAIL ~ oxygen } diluted to a concentration of 1 % to 50 % in an inert gas , under low pressure
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH