Study of composition and structure of aluminum phosphate binder

In this article, theoretical analysis and different testing techniques were used to study the reaction pathways and synthesized products of phosphoric acid and aluminum hydroxide at different Al/P molar ratios. The results show that: (a) When the molar ratio of phosphoric acid/aluminum hydroxide is 1:3, the reaction will produce stoichiometric aluminum dihydrogen phosphate (Al(H2PO4)(3)); (b) when Al(OH)(3) is excessive, an intermediate, monohydroxy aluminum dihydrogen phospate (HO-Al-(H2PO4)(2)), will appear, which is unstable and will continue to react according to two reaction pathways, one is intramolecular dehydration to form phosphoric acid hydrogen-dihydrogen aluminum diphosphate (H2PO4)Al(HPO4); the other is intermolecular dehydration cross-linking to form a polymeric macromolecular aluminum phosphate H-((HPO4)(H2PO4)Al-O-HPO4-Al(H2PO4)-O)-H-n. The ratio of the two pathways is affected by the excess of Al(OH)(3). When the excess of Al(OH)(3) continues to increase, the ratio of the second reaction path begins to increase and the viscosity of the product gradually increases. Adhesion experiments show that the aluminum dihydrogen phosphate has the best bonding performance benefiting from its lower viscosity.