Properties of heat treated diatomite

The density, strength and thermal conductivity of diatomite compacts were determined after heating the specimens in the temperature range between 200 and 1050 °C. The linear dimensional change of these specimens on heating was also measured. All properties changed during heating with the increase in firing temperatures and especially above 800 °C. The reduction of density, strength and thermal conductivity of diatomite compacts on firing at up to 600 °C can be attributed to the mass loss due to decomposition of the constituents such as hydrated silica, carbonates, etc. Heating these compacts above 600 °C resulted in shrinkage with a concomitant increase in bulk density, strength and thermal conductivity. Attempts were made to evaluate the fundamental factors which may be contributing to this change of properties during heat treatment. Analyses of data have been made using a sintering model, which assumes that after decomposition diatomite particles are composed of a large number of microspheres and that the change of properties (i.e., increase in density, strength and thermal conductivity) can be attributed to the growth of interparticle contact areas (similar to neck growth during sintering) . Equations for shrinkage, thermal conductivity and strength are all related to the bulk density and weight loss of the compacts, and are given by: For shrinkage, [formula omitted] For thermal conductivity, [formula omitted] For strength, [formula omitted] The validity of these equations has been tested with the experimental data of shrinkage, bulk density, weight loss, strength and thermal conductivity of pure diatomite compacts. The good agreement between the experimental results and the equations may be indicative that it is the increase in interparticle contact areas during the heat treatment which results in the increase in strength, bulk density and thermal conductivity. The general applicability of the equations, developed in order to explain the change in properties of pure diatomite compacts, was further tested with experimental data obtained from a commercial brand of diatomite insulating bricks.Applied Science, Faculty ofMaterials Engineering, Department ofGraduat