Low-temperature Processing Routes for Fabrication of Open-cell Mullite Foams by Silica Nanoparticles Derived from Rice Husk

In this study, rice husk (RH) upcycled as silica nanoparticles (nSiO(2)), was used as one of the raw materials for fabrication of open-cell mullite foams. To synthesis of nSiO(2), RH was environmentally pre-treated by immersing in a natural enzyme solution for 7 days. The treated RH was washed and calcined at 650 degrees C for 6 h. Four compositions of mullite powders (3Al(2)O(3)center dot 2SiO(2)) were formulated by mixing a commercial alumina (alpha-Al2O3) powder with two sources of SiO2 powders (a commercial SiO2 and nSiO(2)) and alternatively added with a fix amount of activated carbon (AC). The mixture powders were finally sintered at 1350, 1400 and 1450 and 1500 degrees C to monitor the mullitization related to sintering temperatures. The green mixture powders were used for fabricating open-cell mullite foams via a replica technique and sintered at 1500 degrees C. Experimental results revealed that the mullitization was formed at lower sintering temperature for both sintered powders and foams using nSiO(2) as the starting raw materials. The foam strengths were relied on the mullite phase contents and porosities. nSiO(2) used as the starting raw material affected decreasing the sintering temperature and influencing on the enhancement of the foam properties.