Enhanced Chemical Reactivity of Crystalline Quartz by Mechanical Grinding

Introduction: The chemical reactivity of lunar re-golith is one of the most important issues which impacts the human health and biological effects of lunar regolith. The constant micrometeorite bombardment of the lunar surface results in both comminution and shock melting of lunar regolith. In addition, radiation effects are likely to enhance the chemical reactivity of lunar regolith. With respect to chemical reactivity issues, crystalline silica is probably the most important terrestrial analog of lunar regolith. The chemical reactivity of crystalline silica can be transiently increased by mechanical grinding, a process that increases its toxicity to the lungs. In extreme situations freshly fractured crystalline silica can lead to an accelerated form of silicosis which is rapidly fatal. A tragic example of this phenomenon occurred in the Hawk's Nest Tunnel disaster in which more than 400 workers died of exposure to freshly fractured crystalline silica [1]. Laboratory examinations of the potency of freshly fractured crystalline silica in biological systems have been described by Vallyathan and colleagues at the National Institue of Occupational Safety and Health (NIOSH) [2]. The equipment used in this study for generating freshly fractured crystalline silica, however, is no longer available. The focus of this short paper is the introduction of a new technique to enhance the chemical reactivity of crystalline silica by mechanical grinding. The goal is to develop a simple method for generating " freshly fractured silica " to serve as a control material for lunar dust chemical reactivity studies. we have been using a simple chemical assay to evaluate the chemical reactivity of lunar dust, crystalline silica, and other terrestrial reference materials [3]. The assay measures the potential for surface radicals on lunar dust to generate hydroxyl radicals upon exposure to water. The assay involves the conversion of terepthalate (non-fluorescent) to hydroxyterepthalate (fluorescent), in the presence of hydroxyl radicals. Hence, simple fluo-rescence detection systems can be used as an indicator of surface radicals on lunar dust. This assay provides us with a method for evaluating different techniques of lunar dust reactivation, as well as a method for characterizing the decay (passivation) of this reactivated state. Grinding Technique: In order to reproducibly grind mineral specimens, we have been using a ball mill (Retsch MM400). The MM400 utilizes a horizontal oscillatory motion to cause repeated impacts of the balls with the top and bottom of the grinding jar in order to pulverize the material. To adapt the technique …