Use of rice husk ash for quartz substitution in stoneware glazes

455-460Two types of rice husk ashes (RHAs) with different silica contents were used for quartz substitution in a standard opaque glaze and a crystalline glaze. One RHA (RHA1) was a waste from a brick firing process and was used as received. RHA1 (particle size, 36.55±0.26 μm) contained only 71.41% SiO₂. Other RHA (RHA2) was prepared in laboratory under a well controlled process to obtain similar silica content (95.95%) and average particle size (15.83 ±0.18 μm) to quartz. Coefficients of expansion (COE) values of opaque glazes were: RHA1 glaze >RHA2 glaze >quartz glaze. RHA1 glaze, which exhibited highest COE value, crazed with finest craze pattern. All glazes melted at approx. the same temperature and exhibited similar phase changes upon firing. When RHAs were used to replace quartz in a crystalline glaze recipe, RHA1 glaze exhibited a high number of crystals with finer size, while crystals found in the quartz were larger in size with less density

Biomass bottom ash waste and by-products of the acetylene industry as raw materials for unfired bricks

This research aims to study the feasibility of using wastes: biomass bottom ash resulting from the combustion process of a mix of pine-olive pruning in power generation plants, and Geosilex, a by-product obtained in the acetylene industry, as raw materials in the manufacture of unfired bricks. These materials were characterized physically, chemically and mineralogically. Different proportions of raw materials have been investigated; biomass bottom ash (100-20 wt %) and Geosilex (0–80 wt %). The specimens were obtained by compression at 10 MPa and cured for 28 days in water. The physical, mechanical and thermal properties of the unfired bricks have been evaluated. Optimum results have been obtained for specimens with 70–60 wt % of biomass bottom ash and 30–40 wt % of Geosilex, presenting the best mechanical properties, with compressive strength values of 52 MPa and thermal conductivity of 0.52–0.57 W/mK, respectively. These unfired bricks presented a greater quantity of hydrated calcium silicates and hydrated calcium aluminates that provide mechanical properties. This fact is due to that these specimens had the optimal amount of pozzolanic materials, Ca(OH)2 present in the cementing agent Geosilex and SiO2 and Al2O3, present in the ash. Recycling these raw materials in unfired bricks implies significant economic and environmental benefits owing to wastes are used as substitutes for natural raw materials

Thermal approach to evaluate the sintering–crystallization ability in a nepheline–forsterite-based glass-ceramics

A glass in the SiO2–Al2O3–MgO–Na2O system was formulated using a non-conventional silica source and other pure raw materials. The thermal stability and crystallization mechanism have been studied by means of differential scanning calorimetry (DSC). Besides, the glass ability to sintering–crystallization has been examined by optical dilatometry, a non-contact technique allowing the acquisition of dilatometric data in the viscoelastic temperature region. The experimental data were confirmed with theoretical equations. X-ray diffraction and field emission scanning electron microscopy were used to verify the crystallization study and electron scanning microscopy to examine the fired sample microstructures. The prevalent crystallization mechanism has been evaluated from different parameters derived from characteristic temperatures of non-isothermal DSC curves, namely the working range (ΔT TS), reduced glass transition temperature (T gr), and the dissimilarity in crystallization temperature (ΔT p) between fine (<63 µm) and coarse (fragment) glass samples.Peer reviewe