Selection of additives for reducing the toxicity of quartz in ceramic compositions

The inhalation of crystalline silica, for example in the form of quartz, produces the well-known pathological reaction called silicosis. Traditional ceramic industries use quartz-containing raw materials such as clays, sands, and separate quartz. Consequently, the occupational environments of this type of company can contain appreciable quantities of this pollutant. However, quartz cannot be replaced in ceramic compositions because of the major role it plays in the ceramic process. The toxicity of particulate toxic agents, in contrast to that of molecular toxic agents, is not wholly determined by their chemical formula. Instead, their reactivity largely depends on factors such as the chemical, thermal, and mechanical history of the particles. Numerous studies suggest that the toxicity of quartz is conditioned by the surface chemistry of the quartz particles and, in particular, by the density and abundance of silanol groups. Blocking these groups so that they do not interact with cellular membranes would theoretically be possible in order to reduce or even to eliminate the toxic effect. This postulate has been repeatedly verified by various researchers who, on treating quartz with different substances, managed to reduce its toxicity. The mechanism by which these substances act consists of the formation of a surface coating on the quartz so that its silanol groups are no longer accessible for interaction in biological media. The present study examines the incorporation into ceramic compositions of certain additives to coat the surface of the quartz contained in the compositions, thus reducing quartz toxicity. The selected substances were nano-alumina, aluminium lactate, and organosilanes. Organosilanes are a very extensive family of compounds that simultaneously enable quartz toxicity to be reduced and the quartz surface to be functionalised, providing it with various properties. In this study, the incorporation of these compounds was conceived such that no substantial alteration of the ceramic process would be required. In addition, compounds were selected that would not adversely affect product behaviour during the process.