Physical and Chemical Fundamentals of Sodium Phosphate Use in Foundry Production

M.V Tyshkovets,R.V Liutyi,O.I Sheiko,D.V Liuta

doi:10.15330/pcss.21.4.756-763

Abstract

The technology of synthesis of inorganic binder material based on sodium tripolyphosphate Na5P3O10 and orthophosphoric acid has been developed. The sequence of physicochemical transformations in this system, as well as the optimal mass ratio of orthophosphoric acid and sodium tripolyphosphate are established. The research uses methods of quantitative and qualitative X-ray phase analysis, differential thermal analysis, standard methods of testing samples for compressive strength. The ratios of the atomic radii of the cation (Na) and the anion (P2O7), as well as the presence of hydrogen bonds, provide a significant increase in the binding potential compared to other sodium phosphates. It was found that the strengthening of mixtures with 2…8 mass parts including sodium pyrophosphate, the filler of which is quartz-based sand, occurs as intensely as possible when heated to 150°C. A further increase in temperature above 250 °C leads to the conversion of sodium pyrophosphate to ordinary (non-polymeric) metaphosphate NaPO3, which exists without changes in chemical structure up to 1000°C. The developed binder material, given the global trends of decarbonization and resource conservation, is a competitive alternative to widely used synthetic resins and other organic materials. It does not contain harmful substances and does not emit dangerous products when heated.

Highlights

Phosphates are inorganic salts of ortho-(H3PO4), pyro-(H4P2O7), metaphosphoric (HPO3) and polyacidstripolyphosphate H5P3O10 and hexametaphosphate H6P4O13
The aim of our research is to develop a technology for the synthesis of sodium phosphate binder with a high level of strength and thermal stability for the needs of foundry production and the study of its composition, structure and properties
The peculiarities of structure formation in the composition of sodium tripolyphosphate with orthophosphoric acid have been studied. Established that their interaction at about 200 °C leads to the formation of a new compound – disubstituted sodium pyro-phosphate Na2H2P2O7, which has additional hydrogen bonds, resulting in increasing adhesion to refractory filler and provides a significant increase in strength molding and core mixtures compared to sodium tripolyphosphate

Summary

Introduction

Phosphates are inorganic salts of ortho-(H3PO4), pyro-(H4P2O7), metaphosphoric (HPO3) and polyacidstripolyphosphate H5P3O10 and hexametaphosphate H6P4O13. All of these acids are polymorphic species. They turn into each other under certain thermal conditions. Their salts behave in the same way [1]. Phosphate-based materials occupy leading positions in terms of use in various fields of technology. This is due to their availability, prevalence, simplicity of production methods. Phosphate materials are widely used: mineral fertilizers (90% of the total volume), food additives (orthophosphoric acid is registered as an additive E338, sodium tripolyphosphate Na5P3O10 – E451, sodium metaphosphate (NaPO3)n – E452, therapeutic and prophylactic industry, refractory paints, active components in industrial and household detergents (water softener) [1,2,3,4,5,6]

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