A comparison of freshly ground crystalline quartz and naturally occurring crystalline quartz in ball clays

The physical characteristics of crystalline quartz presented in a variety of as mined ball clay and freshly ground quartz have been investigated. Microstructures of ground quartz and geologically aged quartz in ball clay have been examined to understand morphological differences of quartz. Scanning electron micrograph showed that freshly ground quartz (Min-U-Sil) particles have sharp edges. In contrast, much of quartz found in ball clay appeared, under microscope, as well rounded and subangular grains typical of sedimentary deposit. Semi-quantitative x-ray diffraction method for measuring quartz crystallinity was carried out on ground quartz and ball clays. It was found that the average crystallinity index (CI) value of freshly ground quartz was 9.6 in the range of 1–10, whereas, CI of ball clays were varying between 7.5 and 9.0 in terms of types of ball clays.; The index of crystallinity was examined to observe the effect of processing conditions including grinding, various temperature, and size fraction on crystallinity of different types of ball clays. It was shown that the CI value of quartz was changed in the presence of physical absorbed water and amount of surface hydroxyl. When the crude ball clays were fired up to 200°C for 2 hours, the CI values were diminished. However, the airfloated ball clays' crystallinity increased with the temperature. The relation between particle size and CI was observed by collecting samples in the range of +44 μm, −44 μm, and 5 μm size. CI of −44 μm particles was greater than +44 μm particles. Grinding and aging effects on index of quartz crystallinity was determined. The result showed that crystallinity of quartz decreased with aging after grinding.; A new semi-quantitative method was proposed by using diffuse reflectance infrared spectroscopy to obtain crystallinity index value of quartz. The ratio of bands at 800–780 cm−1 was used to measure crystallinity of quartz. A correlation (R2 = 0.82) between CI results from x-ray diffraction and results from diffuse reflectance infrared spectroscopy was found.