In this work the sintering characteristics and mineral transformation behaviors of sewage sludge ash (SSA) at elevated temperatures were investigated by using ash fusion analyzer. X-ray fluorescence (XRF), X-ray diffraction (XRD) and scanning electron microscopy equipped with energy dispersive X-ray spectrometry (SEM/EDX). High initial fusion temperatures above 1100 degrees C were detected from the sewage sludge ashes (SSA 1 and SSA 2) with high Al contents. Corundum, quartz and calcium aluminum silicates were dominating crystalline phases identified from SSA 1 and SSA 2 sintered at elevated temperatures. For the SSA 3 with a high Fe content, low initial melting temperature of 994 degrees C was detected with observation of severe fusion behavior from the ash sintering tests. SEM analysis revealed that SSA 3 melted completely into a more homogeneous and continuous phase at high sintering temperatures. A significant amount of Fe bearing mineral phases and quartz (SiO2) was identified from the sintered SSA 3. Diffraction intensities of hematite (Fe2O3), quartz (SiO2) and alkali feldspar decreased with increasing sintering temperatures, suggesting interaction and re-assemblage of these mineral phases. In combining the XRD and SEM/EDX analyses, it is believed that formation of low melting temperature iron silicates is the main reason for sintering of SSA 3. (C) 2011 Elsevier B.V. All rights reserved.