Creation of binders for casting cores from orthophosphoric acid and aluminosilicate fillers

The article presents the results of the research of aluminophosphate binders, which were obtained as a result of the chemical interaction of orthophosphoric acid with dust-like aluminosilicates. The subjects of the research are the phase and chemical composition, the dynamics of thermal transformations of the binders, as well as the properties of core mixtures with them. In the experiments, it was established that due to the chemical interaction of dust-like pyrophyllite Al2(OH)2[Si4O10] or dystensillimanite Al2O[SiO4] with orthophosphoric acid after heating to 300 ºC, strong and thermally stable binders are formed, which are crystalline and amorphous aluminum orthophosphates. These phases provide strong bonding of the refractory filler and high strength of the core mixture. X-ray phase and differential thermogravimetric analyzes were used in the work to determine the structure and properties of binders. To determine the composition of the core mixture, the compositional planning of the experiment with appropriate data processing was applied. For the first time, the structure of aluminum phosphate binders, which were obtained from refractory fillers common in foundry production, was investigated. The conditions for the formation of crystalline phases were analyzed for the first time. It was established that as a result of the interaction of orthophosphoric acid with dysten-sillimanite, a larger specific amount of aluminum orthophosphate and a smaller amount of residual quartz is formed than when the acid interacts with pyrophyllite. This ensures a higher strength of the core mixture, for the formation of the binder in which orthophosphoric acid and dystensillimanite are used. Mass ratios are taken into account for the complete realization of the chemical reaction of the formation of the aluminum phosphate binder. The composition of a core mixture based on quartz sand with orthophosphoric acid and dysten-sillimanite was developed, which hardens after heating to 300 ºC and has a compressive strength of at least 2.0 MPa.