Synthesis of phosphate-based binders from aluminum slag for heat-resistant inorganic coatings

Abstract

This study presents the synthesis and optimization of a polyaluminum phosphate (PAP) binder using aluminum slag as the primary source of Al³⁺. The binder was synthesized via acid–base reactions between aluminum slag and phosphoric acid (H₃PO₄), with varying Al/P molar ratios, temperatures, and stirring speeds. Optimal conditions were identified at 30 wt% slag and 70 wt% H₃PO₄, 60 °C, and 800 rpm, producing a homogeneous gel with a viscosity of 101 mPa·s, specific gravity of 1.46 g/cm³, and excellent adhesion. FTIR analysis confirmed the formation of Al–O–P and pyrophosphate bonds, while thermal and mechanical stability were evaluated under controlled conditions. The results indicate that aluminum slag can be effectively valorized as a raw material for high-performance inorganic binders.