Preparation Process Of Phosphate Inorganic Binder

Phosphate binder is a binder prepared by the reaction of alkali metal oxide or hydroxide with phosphoric acid,which has been valued because of its non-toxic,odorless,pollution-free and good high-temperature performance.Phosphate binders have been widely used in the preparation of high-temperature composite materials and bonding heat-resistant materials such as ceramics,glass and metals.In this paper,the aluminum phosphate and chromium aluminum phosphate binders were synthesized by the constant temperature water bath method,and the phase transition process in thermoforming of the two binders was explored.The aluminum phosphate binder is doped with different oxides,and the influence of the curing agent on the binder phase transition process is analyzed.Using phosphoric acid（85%H₃PO₄）and aluminum hydroxide（Al（OH）₃）as reaction raw materials to synthesize aluminum phosphate binder,the binder is baked at different temperatures,and using X-ray diffractometer,scanning electron microscope,comprehensive thermal analyzersand other instruments are used to characterize the structure and morphology of the calcined products.The research results show that at low temperature,the aluminum phosphate binder cannot be cured to form a film,and a large amount of free water is adsorbed.As the temperature increases,the dehydration condensation reaction occurs between the aluminum phosphate molecules,forming aluminum tripolyphosphate crystal hydration thing.When the temperature rises to 500℃,the tripolyphosphate hydrate dehydrates and condenses to monoclinic Al2P6O18（B-type Al（PO₃）₃）,and the aluminum phosphate binder solidifies to form a film.When the temperature continued to rise to 1050℃,the monoclinic B-type aluminum metaphosphate(Al₂P₆O₁₈)was transformed into cubic aluminum metaphosphate（Al（PO₃）₃）.The addition of Cr³⁺accelerates the dehydration of the aluminum phosphate binder,improves the water absorption of the binder at low temperatures,and makes the aluminum phosphate binder more densely structured and better in adhesion at high temperatures.Taking aluminum phosphate binder as the matrix,adding 10%Al₂O₃ and 5%MgO as curing agents respectively,the following conclusions can be drawn by analyzing the phase transition process of aluminum phosphate-alumina system and magnesium oxide-aluminum phosphate system:The higher the reactivity of the oxide,the greater the influence on the phase transition process of the aluminum phosphate binder,which can greatly promote the low-temperature curing and dehydration of the binder and the formation of the network macromolecular structure,but due to the high reactivity,it causes stickthe curing shrinkage of the binder is serious,the structure is not dense,and the high temperature resistance is weakened.