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Microstructure and Time-Dependent Behavior of STx-1b Calcium Montmorillonite Suspensions
Clays and Clay Minerals ( IF 2.0 ) Pub Date : 2022-01-27 , DOI: 10.1007/s42860-021-00170-5
Yee-Kwong Leong 1 , Pengfei Liu 1 , Pek-Ing Au 1 , Jishan Liu 1 , Peta Clode 2
Affiliation  

CaMnt is much less important than NaMnt due to its limited commercial applications. The time-dependent property of NaMnt gel has been studied extensively as it is exploited in many applications such as drilling mud and viscosity-modifier applications. In contrast, the time-dependent property of CaMnt suspension and the factors affecting it are largely unknown. The speciation of Ca2+ ions is one such factor to be evaluated. In the current study, pH and solids concentration were examined and then used to validate a recent theory on clay gel time dependency. The results supported the theory that a strong electrostatic double layer (EDL) repulsion in the 3-D network is needed to reorganize the structure and drive it toward the state of minimum free energy. The 12 wt.% CaMnt (STx-1b) gel displayed time-dependent behavior at pH 5 but not at its natural pH of 8.4. At pH 5, the interlayer Ca2+ ions became fully hydrated and desorbed from the platelet surface. This enhanced the EDL repulsion between the platelets. At pH >6.5, the positively charged hydrolysis product Ca(OH)+ began to form and was adsorbed, partially neutralizing the permanent layer charge and weakening the repulsion. However, at 19.4 wt.% solids, the gel displayed pronounced time-dependent behavior despite the high natural pH of 8. The platelets were much closer together, allowing the EDL force to operate and effect structural reorganization. The microstructure of these CaMnt gels showed high platelet concentrations interacting to form a relatively open structure. The microstructure of a kaolin (KGa-2) suspension which showed no time-dependent behavior even after 1 day of ageing revealed the importance of particle morphology and layer charge on time dependency. Its 3-D structure was formed by relatively thick, layered platelets with a low layer charge.



中文翻译:

STx-1b钙蒙脱石悬浮液的微观结构和随时间变化的行为

由于商业应用有限,CaMnt 远不如 NaMnt 重要。NaMnt 凝胶的时间依赖性特性已被广泛研究,因为它在许多应用中得到了利用,例如钻井泥浆和粘度调节剂应用。相比之下,CaMnt 悬浮液的时间依赖性以及影响它的因素在很大程度上是未知的。Ca 2+的形态离子是需要评估的因素之一。在目前的研究中,检查了 pH 值和固体浓度,然后用于验证最近关于粘土凝胶时间依赖性的理论。结果支持了这样的理论,即需要 3-D 网络中的强静电双层 (EDL) 排斥来重组结构并将其驱动到最小自由能状态。12 wt.% CaMnt (STx-1b) 凝胶在 pH 值为 5 时表现出时间依赖性行为,但在其自然 pH 值为 8.4 时则没有。在 pH 值为 5 时,层间 Ca 2+离子完全水合并从血小板表面解吸。这增强了血小板之间的 EDL 排斥力。在 pH >6.5 时,带正电荷的水解产物 Ca(OH) +开始形成并被吸附,部分中和了永久层电荷并削弱了排斥力。然而,在 19.4 wt.% 的固体含量下,尽管天然 pH 值为 8,但凝胶表现出明显的时间依赖性行为。血小板靠得更近,使 EDL 力发挥作用并实现结构重组。这些 CaMnt 凝胶的微观结构显示出高血小板浓度相互作用形成相对开放的结构。高岭土 (KGa-2) 悬浮液的微观结构即使在老化 1 天后也没有表现出时间依赖性行为,这表明颗粒形态和层电荷对时间依赖性的重要性。它的 3-D 结构是由具有低层电荷的相对较厚的层状薄片形成的。

更新日期:2022-01-27
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