{HEAD ~ The bead} may optionally be converted to {TAIL ~ a phosphate} or other desired phase by hydrothermal treatment after gelation and prior to sintering 
optionally be converted to
{ HEAD ~ The bead } may optionally be converted to { TAIL ~ a phosphate } or other desired phase by hydrothermal treatment after gelation and prior to sintering
HEAD HEAD HEAD HEAD HEAD HEAD OTH REL REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH