Influence of mechanical properties on milling of amorphous and crystalline silica-based solids

Milling is an important and energy-intensive operation for preparing particulate solids to required specifications. It has been studied extensively to improve the rate of milling, energy utilisation and control of milling operations. With development of new materials and application of new milling systems, understanding the underlying science of milling is highly desirable for efficient and predictable size reduction. In the glass industry, silicate glasses have been developed with very special attributes, but the size reduction still poses many challenges. In this work, breakability and grindability of silicate materials in both crystalline and amorphous forms are investigated and correlations for their milling rate and energy utilisation as a function of material properties are developed. This involves physical and mechanical characterisation of the selected materials along with the analysis of milling rate in a single ball mill to develop a better understanding of the milling process. The breakability index, as described by the ratio of hardness to the square of toughness, describes well the milling rate of the crystalline form undergoing semi-brittle failure. The amorphous form of the test materials does not show a strong dependence on the breakability index, as the failure mode is brittle and dominated by pre-existing flaws.