Effect of mixing ratio on bactericidal action of MgO-CaO powders.

MgO-CaO powders were prepared with different molar ratios (MgO/CaO) at 1400 degrees C for 2 h in air. By using the powder samples obtained, the change in bactericidal effect as a function of MgO-CaO composition was studied by colony count method. From the XRD measurements, it was found that CaO solid solution was formed by the replacement of Mg(2+) ion with larger Ca(2+) ion. However, no formation of MgO solid solution was observed. The average particle size and the specific surface area of the samples used in this study were about 0.2 microm and 10.5 m(2)g(-1), respectively. The pH values of physiological saline containing powder samples increased with the increase of CaO content, and the value reached 12.1 in sample with the molar ratio (MgO/CaO) of 0.25. From the results of bactericidal tests for Staphylococcus aureus, it was found that the bactericidal effect increased with the increase of CaO content in the samples.