Investigating sodium phosphate binders for foundry production

Abstract

The results of theoretical and practical research on the synthesis of sodium phosphates from its inorganic salts and the use of these phosphates as binders for the manufacture of molds and cores are presented.

In order to find variants of sodium phosphate synthesis, the processes of interaction of orthophosphoric acid H₃PO₄ with sodium salts of different types (Na₂CO₃ carbonate (salt of chemically weak acid), NaCl chloride (salt of chemically strong acid) and tripolyphosphate Na₅P₃O₁₀ (polyphosphoric salt)) were analyzed. The regularities of the formation of sodium phosphates in all three systems and the conversion of these phosphates when heated in the range from 20 to 1000 ^оС have been researched.

For the first time, thermodynamic parameters were established and the process of obtaining sodium phosphate through the chemical interaction of orthophosphoric acid with sodium chloride was implemented in the laboratory.

It has also been shown that the chemical interaction of sodium tripolyphosphate with orthophosphoric acid forms the strongest binder, which is a disodium pyrophosphate Na₂Н₂P₂O₇.

Synthesized sodium phosphates have an optimal set of functional properties for using in foundry technologies. They provide high strength in compositions with refractory quartz filler and have sufficient thermal stability. Experimentally established, foundry cores based on synthesized binders provide high quality cast surfaces and are easily removed from the internal cavities of cast parts.