Thermodynamic data for magnesium (potassium) phosphates
Thermodynamic data for magnesium (potassium) phosphates
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DOI：
10.1016/j.apgeochem.2019.104450
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发表时间：
2019-12-01
影响因子：
3.4
通讯作者：
Winnefeld, Frank
中科院分区：
文献类型：
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作者：
Lothenbach, Barbara;Xu, Biwan;Winnefeld, Frank
磷酸钾镁（MKP）水泥具有凝结快、早期强度高的特点。由于磷酸二氢钾（KH 2 PO 4）与氧化镁（MgO）反应，导致主要形成钾鸟粪石（MgKPO 4中心点6 H（2）O），MKP水泥在水存在下硬化。在水化过程中，还形成了水化中间相新铍石、磷镁矾、钙钛矿和Mg 2KH（PO 4）（2）中心点15 H（2）O。本文根据对水镁矾、磷镁矾、磷镁矾、Mg-3（PO 4）（2）中心点4 H（2）O、水镁矾、钙镁矾、钾鸟粪石、KMgPO 4中心点H2 O的溶解度测定，和Mg 2KH（PO 4）（2）中心点15 H（2）发现不同水合物的形成受pH值的强烈影响。磷沸石和Mg 2KH（PO 4）（2）中心点15 H（2）O是中间相，其在低pH下形成，典型地在非常早的水合时间。随着pH值的升高，水镁矾和钙镁矾可以稳定，而在高pH值下形成钾-鸟粪石。形成的相也强烈地受温度的影响。
Magnesium potassium phosphate (MKP) cements show fast setting and high early strength. MKP cements harden in the presence of water due to the reaction of potassium dihydrogen phosphate (KH2PO4) with magnesia (MgO) resulting in the formation of mainly K-struvite (MgKPO4 center dot 6H(2)O). Other hydrates, newberyite, phosphorrosslerite, cattiite and Mg2KH(PO4)(2)center dot 15H(2)O are formed as intermediate phases during hydration. This paper presents a consistent thermodynamic database for magnesium phosphate hydrates based on solubility measurements for newberyite, phosphorrosslerite, farringtonite, Mg-3(PO4)(2)center dot 4H(2)O, bobierrite, cattiite, K-struvite, KMgPO4 center dot H2O, and Mg2KH(PO4)(2)center dot 15H(2)O carried at different temperature.It was found that the formation of the different hydrates is strongly influenced by pH. Newberyite, phosphorrosslerite and Mg2KH(PO4)(2)center dot 15H(2)O are intermediate phases, which form at low pH as typical at very early hydration times. As pH rises, bobierrite and cattiite may be stabilised, while at high pH K-struvite forms. The phases formed are also strongly influenced by the temperature.