Structural and Crystallographic Evolution of Nano-POFA using XRD-Based Crystallite Analysis

Abstract

Palm oil fuel ash (POFA) is one of the main by-products of the palm oil industry, predominantly composed of silica (SiO₂) and various other metal oxides. Nano-POFA (P₁) was synthesized using a top-down approach via high-energy ball milling process at a rotational speed of 1300 rpm for 1 hour using 4 mm-diameter milling balls. The X-ray diffraction patterns revealed that the dominant crystalline phases were Quartz (SiO₂) and Mullite (Al₆Si₂O₁₃), accompanied by minor phases such as Cristobalite (SiO₂), Hematit (Fe₂O₃), Calcite (CaCO₃), CaO, and Al₂O₃. The XRD analysis results of samples P₀ (without ball milling) and P₁ (1 hour of ball milling) revealed a significant decrease in peak intensity and peak broadening after 1 hour of the milling process. This phenomenon indicates partial amorphization and crystal fragmentation. The average crystallite size decreased from 92.14 nm in sample P₀ to 47.52 nm in sample P₁. These results indicate that the high-energy ball milling process induces lattice distortion, structural disorder, and amorphization within the Si-O framework of the POFA. The Williamson-Hall analysis indicated an increase in microstrain from ԑ=3.38 x 10^-3 to ԑ=1.227 x 10^-2. The structural transformations increase surface defect density and reactivity, signifying nano-POFA’s potential as material heterogenous catalyst for related chemical processes