Application of microwave radiation for crosslinking of sodium polyacry-late/silica gel system used as a binder in foundry sands

Abstract

It was proved experimentally that microwave radiation caused crosslinking of sodium polyacrylate (PAS) / silica gel system, treated in this work as a model molding sand of the type poly aery late (polymeric binder) / quartz sand (loose matrix). The results of Raman and FT-IR spectroscopic measurements are the base of proposed mechanism of the crosslinking process investigated. According to it, chemical adsorption activated with microwaves plays a significant role. The chemical adsorption leads to formation of strong hydrogen bonds [see equation (1)] or covalent ones [of anhydride type or -C (O)-O-Si, see equations (2) and (3)] PAS -silica. It favors an improvement in tensile properties in comparison with the properties of molding sands hardened traditionally with Ca(OH)2 and CO2. Additional advantages of the hardening method described, with use of microwaves, are short time (90 s) and relatively low temperature (150 °C) of the process.