{HEAD ~ The fibrous carbon material} is then impregnated with {TAIL ~ a second thermosetting resin} containing a boron compound and, optionally, a refractory metal capable of reacting with boron to form a metal boride 
{ HEAD ~ The fibrous carbon material } is then impregnated with { TAIL ~ a second thermosetting resin } containing a boron compound and , optionally , a refractory metal capable of reacting with boron to form a metal boride
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL OTH REL REL TAIL 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