{HEAD ~ A smooth and dense alpha alumina scale} which is free of {TAIL ~ porosity} and cracks may be formed to accomplish this purpose 
is free of
{ HEAD ~ A smooth and dense alpha alumina scale } which is free of { TAIL ~ porosity } and cracks may be formed to accomplish this purpose
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH REL REL REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH