When {HEAD ~ Al contents} increased above {TAIL ~ about 2 wt %}, it was necessary to heat rapidly in order to achieve high density 
increased above
When { HEAD ~ Al contents } increased above { TAIL ~ about 2 wt % } , it was necessary to heat rapidly in order to achieve high density
OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH