Influence of phosphate, potassium, lithium, and aluminium on the anatase-rutile phase transformation

Calcination process was investigated on the laboratory scale with the use of hydrated titanium dioxide containing rutile nuclei from the industrial installation (sulfate process). The influence of temperature (750-900 degrees C) on the anatase-rutile phase transformation and on the crystallites' growth variation was determined. Phosphate, potassium, lithium, and aluminum were introduced into calcination suspension. It was found that whereas an introduction of lithium, in phosphate presence, either increased or stabilized the anatase-rutile transformation degree, the introduction of potassium significantly decreased it. The intensity of these changes depended on both the temperature of the process and on phosphate content. The introduction of aluminum, in constant phosphate presence, had an intermediate influence on the rutilization of anatase between that of either potassium and phosphate on the one hand and lithium and phosphate on the other. Similarly to potassium, aluminum intensified the influence of phosphate but to a smaller degree and only a lower temperature. The introduction of lithium, regardless of whether or not phosphate and potassium were present, increased rutilization degree. This dependence was more clearly seen at lower temperatures of the process. Aluminum, either in constant phosphate and potassium or phosphate and lithium presence, increased the anatase-rutile transformation. The degree of these changes depended on both the presence of modifying agents in their mixture and on the temperature of the process. It was found that the introduction to hydrated titanium dioxide of additives causing an increase in the surface area of TiO2, as a result of limitations of crystallite growth in the calcination process, results in elevation of temperature of the anatase-rutile phase transformation (phosphates, potassium) whereas the introduction of additives that decrease the surface area (crystallite growth) enhances the degree of transformation of anatase to rutile (lithium).