Calcium aluminate cements in fly ash/calcium aluminate blend phosphate cement systems: Their role in inhibiting carbonation and acid corrosion at a low hydrothermal temperature of 90°C
Calcium aluminate cements in fly ash/calcium aluminate blend phosphate cement systems: Their role in inhibiting carbonation and acid corrosion at a low hydrothermal temperature of 90°C
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粉煤灰/铝酸钙共混磷酸盐水泥体系中的铝酸钙水泥：在 90°C 的低水热温度下抑制碳化和酸腐蚀的作用
DOI：
10.1023/a:1016158328024
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发表时间：
2002
影响因子：
4.5
通讯作者：
L. Weber
中科院分区：
文献类型：
--
作者：
T. Sugama;L. E. Brothers;L. Weber
研究了多聚磷酸钠改性粉煤灰/铝酸钙（SFCB）地热井水泥的抗碳化和抗酸腐蚀性能。在90°C的低水热温度下，为了改善这些性能，我们研究了各种铝酸钙水泥（CAC）反应物在最小化碳酸化速率和减轻H2SO 4（pH = 1.6）侵蚀方面的有效性。我们发现，最有效的CAC有两个主要阶段，铝酸一钙（CA）和二铝酸钙（CA 2），和一个中等的CaO/Al 2 O3比为0.4。多磷酸钠（NaP）与CA或CA 2在室温下反应，CA和CA 2脱钙生成无定形水合磷酸氢钙和阴离子氢氧化铝。当用该CAC制成的SFCB水泥在90°C下暴露于4%NaHCO3负载的水中时，水泥发生一些碳酸化，形成易于与H2SO 4反应的方解石。该反应导致石膏凝胶垢作为酸腐蚀产物沉积在水泥表面上。附着在水泥上的水垢层保护它免受进一步的腐蚀。在此保护下，在酸性溶液中完成了无定形水合磷酸氢钙→结晶羟基磷灰石和阴离子氢氧化铝→结晶勃姆石的相变。同时，NaP与粉煤灰进一步发生化学反应和水化反应，形成了更多的Na-P型沸石晶相。因此，我们建议，钝化的水泥表面的石膏沉积，形成这些反应产物，这是相对惰性的酸，是SFCB水泥的酸腐蚀抑制机制。
Study was focused upon formulating sodium polyphosphate-modified fly ash/calcium aluminate blend (SFCB) geothermal well cements with advanced anti-carbonation and anti-acid corrosive properties. At a low hydrothermal temperature of 90°C, to improve these properties, we investigated the effectiveness of various calcium aluminate cement (CAC) reactants in minimizing the rate of carbonation and in abating the attack of H2SO4 (pH ∼ 1.6). We found that the most effective CAC had two major phases, monocalcium aluminate (CA) and calcium bialuminate (CA2), and a moderate CaO/Al2O3 ratio of 0.4. The reaction between sodium polyphosphate (NaP) and CA or CA2 at room temperature led to the formation of amorphous dibasic calcium phosphate hydrate and anionic aluminum hydroxide caused by the decalcification of CA and CA2. When SFCB cement made with this CAC was exposed to 4% NaHCO3-laden water at 90°C, some carbonation of the cement occurred, forming calcite that was susceptible to the reaction with H2SO4. This reaction resulted in the deposition of gypsum gel scales as the acid corrosion product on the cement surfaces. The scale layer clinging to the cement protected it from further corrosion. Under such protection, the amorphous dibasic calcium phosphate hydrate → crystal hydroxyapatite and anionic aluminum hydroxide → crystal boehmite phase transitions were completed in acid solution. Meanwhile, the further chemical and hydration reactions of NaP with fly ash led to the formation of additional crystalline Na-P type zeolite phases. Thus, we propose that passivation of the surface of the cement by deposition of gypsum, following the formation of these reaction products, which are relatively inert to acid, are the acid corrosion-inhibiting mechanisms of the SFCB cements.