Synthesis and growth of anorthite crystal during in situ preparation of porous anorthite ceramics by foam‐gelcasting

Abstract

Pure anorthite porous ceramics have been fabricated using γ‐Al2O3, CaCO3, and SiO2 as raw materials through foam‐gelcasting method. XRD, thermal analysis, SEM, and TEM were used to study the synthesis and grain growth of anorthite during the in situ process. The results indicated that the initiator (ammonium presulfate) took part in the chemical reaction to form CaSO4, which played an effective role during synthesis of anorthite. Besides, CaO and CaSiO2 were the other intermediate phase during synthesis. Anorthite first occurred at 1050°C, and it was the only phase after it sintered over 1260°C. With sintering temperature increasing from 1300°C to 1450°C, the large sphere pore wall got denser and the anorthite grains obviously showed platelike. It was deduced that the preferential growth of anorthite crystals was parallel to the (004) plane.

Microstructure and properties of porous anorthite/mullite whiskers ceramics with high porosity

“…Therefore, developing materials with relatively high strengths and good thermal insulation properties becomes most important. However, the thermal conductivity of mullite (5.45 W/m·K) is significantly higher than that of anorthite (3.67 W/m·K) 12,19,20 . Thus, the addition of mullite usually brings the increase in thermal conductivity for porous anorthite ceramics.…”

“…anorthite (3.67 W/m•K). 12,19,20 Thus, the addition of mullite usually brings the increase in thermal conductivity for porous anorthite ceramics. And the more mullite was added, the more thermal conductivity increases.…”

Preparation and characteristics of porous anorthite ceramics with high porosity and high‐temperature strength

“…This could be caused by that the higher temperature, the less voids on the hole wall (as was shown in Figure ), and the denser hole wall made the strain smaller. The characteristics of the curves were very different from the brittle fracture of dense ceramics . Moreover, the presence of pores could passivate cracks tip and deflect the cracks propagation path.…”

“…The glass phase generated liquid phase at high temperature to fill the gap between grains . Meanwhile, the liquid phase at high temperatures could release the stress and absorb the energy caused by crack propagation . As well known, the alkali metal ions and alkaline‐earth metal ions play important role on the formation of liquid phase at high temperature through lowering eutectic point.…”

“…In past years, many researches focused on the preparation and strengthening of porous anorthite ceramics . And the researches on properties are main focus on those at room temperature …”