Abstract
New porcelain bodies, which exhibit lightweight and relatively high-strength, were fabricated using only nonplastic raw materials, such as glass microspheres, quartz and aluminous cement. Their mechanical properties were investigated. While the α-quartz and CaAl4O7 phases did not change with hydration time in the green body, the CaAl2O4 phase diminished and, finally, disappeared after 24h hydration. A new phase, CaAl2 Si2O8. 4H2O formed but only at hydration times between 24 and 48h, which exhibits maximum green strength. Green strength decreased slightly with increasing the content of glass microspheres at a constant aluminous cement content of 20mass%. This decrease of green strength is attributed to the decreased bulk density and the relative decrease of aluminous cement volume, due to the larger volume of glass microspheres. The phases formed in the fired body were α-quartz, α-cristobalite, anorthite, glass and a small amount of α-Al2O3. The addition of larger amount of glass microspheres (60mass%) led to large pores in the fired body, due to low viscosity of glassy phase during the firing process. However, the addition of a small amount of glass microspheres, such as 20mass%, hampered vitrification and sintering in the fired body. The increased flexural strength at an intermediate composition containing 40mass% glass microspheres was attributed to a strong prestress induced by the mismatch in thermal expansion coefficient between the glass matrix and the α-quartz grains during the cooling process. Fewer fracture origins, a smaller water absorption and a higher density due to the appropriate vitrification process were also indicated as potential factors leading to the strengthening effect.
