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