Investigation of silica from rice husk ash wastes as an alternative material for microwave absorbers

• Main Authors: Sudiana, I. Nyoman, Mitsudo, Seitaro, Firihu, Muhammad Zamrun, Aba, La, Ngkoimani, La Ode, Arsana, Made Widana, Aripin, Haji
• Format: Conference Proceeding
• Language: English
• Subjects: Absorbers; Agricultural wastes; Aluminum oxide; Ashes; Composition; Cristobalite; Degree of crystallinity; Glass ceramics; Microwave absorbers; Mullite; Reflection; Silica glass; Silicon dioxide; Sintering
• ISSN: 0094-243X; 1551-7616
• DOI: 10.1063/1.4973092

An attempt was made to produce silica from an agricultural waste, i.e. rice husk ash (RHA), for a microwave absorber. The high percentage of silica content from RHA was used as a silica source for sodium silica solutions. Different heating temperatures, times and acid treatments were studied for silica extractions. The composite was characterized and its microwave properties were investigated after sintering from 400 to 1200 °C. The results showed that the existing phases in all compositions at 1200 °C were mullite, cristobalite and Al2O3. The intensities of cristobalite peaks gradually decreased with increased compositions of Al2O3, while the intensities of mullite peaks increased with the increased compositions of Al2O3. Compositions with higher amounts of amorphous silica xerogel showed a lower degree of Al2O3 peaks when compared to other compositions, while the peaks of cristobalite were found to be with greater intensities. A correlation between the structural changes and the microwave properties of the samples in frequencies ranging from 8.2 to 12.4 GHz has been found and discussed. The calculated values showed that the reflection losses decreased as t he sintering temperatures were increased up to 1200 °C. The increasing degree of crystallinity was identified as the main reason for the decrease of the reflection losses since the silica xerogel glass ceramic becomes more transparent to microwaves.