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Effects of phosphoric acid and phosphates on magnesium oxysulfate cement

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Abstract

Magnesium oxysulfate (MOS) cement is a promising material for fire-proofing and insulation applications. Here, we have studied the effects of phosphoric acid and phosphates (H3PO4, KH2PO4, K3PO4 and K2HPO4) on the setting time, mechanical strength and water resistance of MOS cement. X-ray diffraction was used to examine phase composition, and analytical reagents were used to prepare samples of the new phase found so that it would be examined by chemical and thermogravimetric analyses. Adding phosphoric acid and phosphates can extend the setting time and improve the compressive strength and water resistance of MOS cement by changing the hydration process of MgO and the phase composition. A new subsulfate phase 5Mg(OH)2·MgSO4·7H2O (517 phase) is formed, which is needle-like and insoluble in water. Phosphoric acid or phosphates ionize in solution to form H2PO4 −, HPO4 2− and/or PO4 3−, and these anions adsorb onto [Mg(OH)(H2O) x ]+ to inhibit the formation of Mg(OH)2 and further promote the generation of a new magnesium subsulfate phase, leading to the compact structure, high mechanical strength and good water resistance of MOS cement. The improvement produced by adding phosphoric acid or phosphates to MOS cement follows the order of H3PO4 = KH2PO4 ≫ K2HPO4 > K3PO4.

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Acknowledgments

Partial financial support from the One-Hundred Talent Project of the CAS granted to HFY (B0210), and the Qinghai Province Science and Technology Tackling Key Project under Grant 2008-G-158 are gratefully acknowledged; this project was also supported by the National Natural Science Foundation of China (Grant No. 51178221).

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Authors and Affiliations

  1. Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, No. 18, Xinning Road, Xining, 810008, People’s Republic of China

    Chengyou Wu, Hongfa Yu, Huifang Zhang, Jinmei Dong, Jing Wen & Yongshan Tan

  2. University of Chinese Academy of Sciences, Beijing, 100049, People’s Republic of China

    Chengyou Wu, Huifang Zhang, Jinmei Dong, Jing Wen & Yongshan Tan

  3. Department of Civil Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing, 210016, People’s Republic of China

    Hongfa Yu

  4. Department of Civil Engineering, Qinghai University, Xining, 810008, People’s Republic of China

    Hongfa Yu

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  1. Chengyou Wu
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Correspondence to Chengyou Wu.

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Wu, C., Yu, H., Zhang, H. et al. Effects of phosphoric acid and phosphates on magnesium oxysulfate cement. Mater Struct 48, 907–917 (2015). https://doi.org/10.1617/s11527-013-0202-6

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  • DOI: https://doi.org/10.1617/s11527-013-0202-6

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