Effect of borax on the hydration and setting of magnesium phosphate cements

This work unravels for the first time the concentration dependent retarding effect of borax on tri-magnesium phosphate-based cements by studying the hydration and the phases formed in the set cements, exploiting multiple characterization techniques. In the presence of borax, the hydration was found to be slower and less exothermic, leading to the formation of struvite without newberyite, with no effect on cement's strength. The observed boron species allowed us to ascribe the retardation to the complexation of NH4+ and Mg2+ by borate and polyborate anions.

Automated summary

This study explores the concentration dependent retarding effect of borax on tri-magnesium phosphate-based cements for the first time. By investigating the hydration and phases formed in the set cements using multiple characterization techniques, it was found that borax slows down the hydration process, reduces heat release, and leads to the formation of struvite instead of newberyite, without affecting the strength of the cement. The observed boron species suggest that the retardation is caused by the complexation of NH4+ and Mg2+ ions with borate and polyborate anions.