Thermal analysis in foundry technology

Abstract

TG–DSC thermal analysis involved two new BioCo foundry binders in the form of a composition with poly(acrylic acid) and modified polysaccharides (dextrin, sodium salt of carboxymethyl starch). Thermal analysis was conducted to determine the effect of the thermal decomposition conditions and polymer structure on the progress of degradation in terms of processes occurring in the foundry sands, when they contact with liquid metal. Thermal analysis of the composition allowed for determining the temperature range where they do not undergo degradation, by which they do not lose their binding properties. It was evidenced that the course of thermal decomposition is complex (mixed degradation mechanism). With temperature increase, physical and chemical changes occur, related to evaporation of solvent water (20–100 °C) and next release of constitution water, while finally intermolecular dehydration (100–220 °C). In this temperature range, mainly reversible processes take place. Within the temperature range of 220–300 °C, polymer chains decompose, including decomposition of side chains and glycosidic bonds. Within the temperature range of 300–500 °C, polymer compositions decompose, and gas products of destruction are generated. A part of the compound that did not decompose at the temperature of approx 550 °C can contain carbonised coal. It was evidenced that if the composition includes sodium atoms, inorganic compounds are formed which decompose at the temperature of approx 800 °C.