Patent ID: 8518536

Claim:
A magnesium oxide particle aggregate consisting of: magnesium oxide particles±each of the magnesium oxide particles consisting essentially of magnesium oxide, wherein the magnesium oxide particles have an average particle size of 1 micron or less, and have Si, Al, Ca, Fe, V, Cr, Mn, Ni, Zr, B and Zn as impurities in their respective amounts of 10 ppm by mass or less; wherein the total amount ratio of the impurities is 100 ppm by mass or less; the magnesium oxide particle aggregate has a particle size of 10 microns or more; the magnesium oxide particle aggregate has a spherical shape; and the magnesium oxide particle aggregate has a first mode size and a second mode size larger than the first mode size in the pore distribution measured by mercury intrusion porosimetry, wherein the first mode size is 0.1 to 1 micron and the second mode size is 8 to 20 microns.