MAGNESIA PHOSPHATE CEMENT BINDERS

5) Aluminum chlorophosphate hydrate decomposes on heating to form AIPO4. It can be used with the addition of MgO in formulations designed to set at ambient temperatures. 

These cements are based on the chemical reaction of solid basic magnesia powder and an aqueous acidic ammonium phosphate solution.The acid-base reactions that occur on mixing lead to the formation of insoluble magnesium ammonium phosphate hydrates, the primary binding material in the hardened product. Commercial products generally contain inert fillers and a set retarder to facilitate control of the exothermic setting process. 

The principal reaction product in the system based on magnesia and ammonium dihydrogen orthophosphate is magnesium ammonium phosphate hexahydrate (struvite)  

reportthatMgNH4P04 H20 (dittmorite) and Mg(NH4 2 (HP04)2 4H20 (schertelite) can form when the water content is too low to ensure complete reaction of NH4H2P04.[ Abdelrazigt reports the presence of schertelite as a primary intermediate reaction product  

The formation of magnesium ammonium phosphate monohydrate, MgNH4P04 H20 at low water contents was reported by Popovics, et al. t The use of excess water in magnesia-phosphate cement systems has been found to lead to increased porosity and strength reduction. 

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