The crystalline phases formed during microwave foaming were
characterized by X ray diffractometer (Rigaku D/max 2550PC). The
pore structure and pore morphologies were investigated by a scanning
electronic microscopy. The bulk density of samples was calculated as
the ratio of mass to volume, and the powder density was measured
with helium pycnometer. The total porosity was calculated from the
bulk density and powder density using the following equation: