Rice hull ash structure and bleaching performance produced by ashing at various times and temperatures

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Abstract
Surface areas, pore sizes, and bleaching efficiencies of rice hull ashes produced under different time and temperature conditions were examined. Specific surface area and average pore diameter were measured by a surface area meter. Bleaching efficiencies were calculated based on the Lovibond color indices of sesame oil before and after bleaching by rice hull ash. Experimental results indicated that specific surface area and pore size increased with increase in ashing temperature, reached a maximum, and then decreased. Specific surface area decreased while pore size enlarged with the increase in ashing time. Both surface area and pore size were observed to reach a plateau after 30 min. Bleaching efficiency increased with increasing ashing temperature, reached a maximum, and then decreased with further increase in ashing temperature. It also increased with ashing time and then reached a plateau. Bleaching efficiency remained unaffected by specific surface area when the pore diameter was less than 50 Å but varied with specific surface area when the pore diameter was larger than 50 Å.