Preparation and characterization of sintered ceramics made with spent foundry olivine sand and clay

Two different types of clay (a yellow and a red clay) were used to prepare two sets of materials containing spent foundry olivine sand. They were blended by attrition milling in varying proportions to obtain powders of different composition. All mixtures were dried, sieved, uniaxially pressed into specimens and air sintered for 1 h at temperatures ranging from 900 to 1140 °C. The resulting materials were characterized by density, water absorption, shrinkage, crystallographic composition, microstructure and physico-mechanical properties. Mechanical and crystallographic properties were determined on samples fired at 1040 °C in order to compare materials with similar characteristics. It was observed that, after sintering, all compositions show the presence of the glassy phase which surrounds the crystalline grains and the set of materials prepared using the red clay displayed best overall behaviour. XRD analysis performed on the free surface of the fired samples did not show the presence of compounds containing heavy metals present in the starting materials.