and when the amount of presence of {HEAD ~ the silicon component} exposed on {TAIL ~ the surface}, expressed in terms of silicon, with respect to the magnetite particles is designated as B, the relationship C/B≧15 is satisfied 
exposed on
and when the amount of presence of { HEAD ~ the silicon component } exposed on { TAIL ~ the surface } , expressed in terms of silicon , with respect to the magnetite particles is designated as B , the relationship C / B≧15 is satisfied
OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL 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