Abstract:In melt foaming method, the thermal stability and foaming speed of blowing agent significantly affect the pore structure, pore size and porosity of metal foams. To retard the foaming speed and increase thermal stability, Na₂O·nSiO₂ and dilute hydrochloric acid were used to coat SiO₂ passive layer on the surface of CaCO₃ which is the blowing agent of Mg foams. Thermal stability and microstructure of the SiO₂ passive layer were studied by thermo gravimetric analyzer-differential thermal analysis (TGA-DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that the thermal stability of coated CaCO₃ is improved. The SiO₂ layer is amorphous with reticular structure. Contrasting experiments reveal that the coated CaCO₃ can foam placidly. Moreover, large size and homogeneous Mg foams were prepared without protective gas with the ignition- proof by alloying. And the porosity of the Mg foams is 60%-70%.

Key words: melt foaming; close-cell Mg foam; foaming agent; SiO₂ coating; CaCO₃