A new mechanism for cement hydration inhibition: Solid-state chemistry of calcium nitrilotris(methylene)triphosphonate
A new mechanism for cement hydration inhibition: Solid-state chemistry of calcium nitrilotris(methylene)triphosphonate
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DOI：
10.1021/cm0302431
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发表时间：
2003-08-12
影响因子：
8.6
通讯作者：
Barron, AR
中科院分区：
文献类型：
--
作者：
Bishop, M;Bott, SG;Barron, AR
水泥缓凝剂次氮基-三（亚甲基）膦酸，N [CH2PO（OH）（2）]（3）（H（6）ntmp）与氧化钙，三钙的反应。硅酸盐（C3S）、铝酸三钙（C3A）和四钙。铁铝酸盐（C4 AF）的情况下，以及在石膏存在下的C3 A的情况下，以在研究波特兰水泥的典型样品之前获得对单个矿物的影响的理解。H（6）ntmp与氧化钙反应导致可溶性[Ca（H（n）ntmp）]（（4-n）-）的初始形成，其随时间沉淀为[Ca（H（4）ntmp）（H2O）]（无穷大），其片状结构已通过单晶X射线衍射证实。在H（6）ntmp存在下C3S的水化研究表明，没有C-S-H形成，并且表面从富硅转变为富钙，并形成各种磷酸钙。在H（6）ntmp存在下，C3A的水合被严重抑制，膦酸主要与钙而不是铝反应，在C3A表面形成富Ca-P层。H（6）ntmp提高钙的溶解度，促进钙从C3A中溶解，并在石膏存在下促进钙矾石的形成。在存在H（6）ntmp的情况下，水合波特兰水泥颗粒的表面富含钙和磷，缺乏硅和铝，这与光谱上与[Ca（H（4）ntmp）（H2O）]（无穷大）相关的膦酸钙涂层的形成一致。我们提出了一种新的机制，膦酸抑制水泥水化。通过用膦酸萃取溶解钙，暴露富铝表面以增强水合作用，随后沉淀结合到水泥颗粒表面的层状膦酸钙，通过充当水的扩散屏障以及成核抑制剂来抑制进一步水合作用。样品的特征在于P-31，Al-27，和Si-29 MAS NMR光谱，扫描电子显微镜，X射线衍射，和X射线光电子能谱。
The reaction of the cement retarder nitrilo-tris(methylene)phosphonic acid, N[CH2PO(OH)(2)](3) (H(6)ntmp) with calcium oxide, tricalcium. silicate (C3S), tricalcium aluminate (C3A), and tetracalcium. aluminoferrite (C4AF) has been studied individually, and in the case of C3A in the presence of gypsum, to gain an understanding of the effect on the individual minerals prior to studying a typical sample of Portland cement. The reaction of H(6)ntmp with calcium oxide results in the initial formation of soluble[Ca(H(n)ntmp)]((4-n)-), which precipitates over time as [Ca(H(4)ntmp)(H2O)](infinity), whose sheetlike structure has been confirmed by single-crystal X-ray diffraction. The study of the hydration of C3S in the presence of H(6)ntmp indicates that no C-S-H forms, and the surface changes from silicon-rich to calcium-rich associated with the formation of various calcium phosphonates. The hydration of C3A is severely inhibited in the presence of H(6)ntmp, with the phosphonic acid reacting primarily with calcium as opposed to aluminum to form a Ca-P-rich layer at the surface of C3A. The H(6)ntmp enhances calcium solubility, promoting the dissolution of calcium from C3A and promoting, in the presence of gypsum, the formation of ettringite. In the presence of H(6)ntmp the surface of hydrated Portland cement grains is rich in calcium and phosphorus and deficient in silicon and aluminum, consistent with the formation of a calcium phosphonate coating spectroscopically related to [Ca(H(4)ntmp)(H2O)](infinity). We have proposed a new mechanism by which phosphonic acids inhibit cement hydration. Dissolution, of calcium by extraction with the phosphonic acid, exposes the aluminum-rich surface to enhance hydration, followed by precipitation of a layered calcium phosphonate that binds to the surface of the cement grains, inhibiting further hydration by acting as a diffusion barrier to water as well as a nucleation inhibitor. Samples were characterized by P-31, Al-27, and Si-29 MAS NMR spectroscopy, scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy.