The Hollow Corundum Microspheres (HCM) are made of aluminum oxide with purity of 99.6%, has a round shape with wide surface, particle size from 5 to 180 microns, density from 0.8 to 2.0 gram per cm3, refractoriness 1800 °C and cold crushing strength from 40 to 120 MPa. In the photos taken by an optic and an electron microscope is visible a wide surface of HCM, a particle size and the crashing walls of the HCM.
