The microstructure, phase transformation and sinterability of desert sand

Desert sand has been widely used to manufacture paving materials, concrete, cement clinker, ceramics, glass, and bulk materials. It has different effects on the processing and properties of the materials from that of quartz sand, clay, and aggregates; however, the physicochemical characteristics of desert sand have not been deeply realized in term of the materialogy, bringing about much confusion in the manufacturing. In the present study, desert-sand samples were collected at different locations in the Hobq desert, a typical desert in China, their microstructure, phase composition, phase transformation, and sinterability were examined using X-ray diffraction (XRD), scanning electronic microscope (SEM), transmission electronic microscope (TEM), differential scanning calorimeter (DSC) techniques, as well as a sintering test. Results show that the sampling location had a little influence on the characteristics. Desert-sand granules were not uniform, which displayed variety of morphology and microstructure and some microcracks existed inside. They had a phase composition of alpha-quartz, amorphous SiO2, glass phase, and feldspars, some of them were with nano and submicron sizes. alpha-quartz was a dominant phase and had distorted crystal lattices. Four phase transformations successively occurred upon heating: alpha-quartz to beta-quartz and further to beta-tridymite, low-melting substances melt, and amorphous SiO2 and beta-tridymite to beta-cristobalite. Desert-sand powder compacts had an excellent self-sinterability, the densest bodies and the highest mechanical properties occurred when sintered at 1100 degrees C for 2 h. This information is beneficial to understand the mechanism and control the synthesis and properties of desert-sand materials.