Focus Raw Material: Sibelco - Sand 8

At its Colombara facility at Monte San Pietro (province of Bologna, Italy), Sibelco Italia extracts and processes a feldspathic sand known as Sand 8, which has excellent characteristics for the production of vitrified tiles, particularly glazed and unglazed porcelain tile. Sand 8 contains a high percentage of clay minerals. The mineralogical analysis (XRD) reveals the presence of 7% Mica with a high content of Illite, a fairly plastic clay mineral, and 1% Chlorite which is a highly plastic clay mineral that has a very strong influence on rheology and flexural breaking load. It also has a 36% feldspar content in which the potassium component is certainly predominant. To understand the technological advantages offered by Sand 8 for a glazed porcelain tile body, two bodies were formulated, one with 20% of Sand 8 and the other with the same quantity of a sand commonly found in the Tusco-Emilian Apennine mountains. The two bodies were treated in the laboratory in the same conditions of wet grinding, powder humidification and pressing so as to simulate industrial production. A comparison between the two ceramic formulations demonstrates that Sand 8 considerably improves the mechanical properties of the dried body prior to firing. Modulus of rupture (MOR, kg/cm2) increases by 7.5% and elastic deformation (ε%) by 30%.
Furthermore, if we plot MOR against elastic deformation on a graph using Hooke’s Law (σ= εE), the area below the curve represents flexural toughness (the energy that the test specimen can absorb before breaking). It is therefore clear that due to the presence of a natural mix of clay minerals such as illite and chlorite, Sand 8 (blue line) considerably increases the mechanical characteristics of the body and guarantees greater strength of the unfired tile as it travels along the glazing line. The high degree of natural fineness of this sand together with the high content of feldspathic component makes this material highly fusible, so for the same grinding residue it allows water absorption to be reduced without affecting linear shrinkage.