Coprecipitation of Crystalline Calcium Silicates and Carbonates from the Hydrothermal Reaction of Pseudowollastonite
Coprecipitation of Crystalline Calcium Silicates and Carbonates from the Hydrothermal Reaction of Pseudowollastonite
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DOI：
10.1021/acssuschemeng.3c05110
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发表时间：
2024-01
期刊：
影响因子：
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通讯作者：
Coleman Tolliver;Suzanne Nguyen;Kimmie Mae Dela Cerna;Rachel McNamara;E. Opila;A. Clarens
中科院分区：
文献类型：
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作者：
Coleman Tolliver;Suzanne Nguyen;Kimmie Mae Dela Cerna;Rachel McNamara;E. Opila;A. Clarens
硅酸钙含量丰富，但很少溶于水，是制造低碳替代水泥的重要原料。在水热和碱性条件下，它们可以形成在罗马混凝土中丰富的结晶水合硅酸钙（CCSH）产物，或者在co2存在时形成碳酸盐。为了了解CCSH和碳酸盐相何时可能共沉淀，我们研究了模型硅酸钙、伪硅灰石（α-CaSiO3）在150°C和高pH下的水热碳酸化，研究了CO2源[CO2(g)或Na2CO3]和不同浓度的钠、氧化铝和二氧化硅的函数。我们的实验早在实验开始后1天就产生了一系列CCSH相，包括托贝莫里石- 13 Å、罗得石和胸石。在2m NaOH溶液中固化7天后，超过10%的样品已经转化为这些CCSH相。我们还观察到当碳引入我们的实验系统时，文石和方解石的CaCO3as的形成。碳源对反应产物中caco3与CCSH相的比例有影响。na2co3的可用性在CaCO3和CCSH相之间产生平衡，而CO2(g)产生更多的CaCO3，样品的碳酸盐质量超过三分之一。较高浓度的Na+增加了caco3和CCSH相的析出。在碱性反应条件下，过量的二氧化硅以溶解的硼硅酸盐玻璃的形式从我们的反应容器中存在，也促进了在一些实验中形成的CCSH相的形成。补充的Al2O3，在许多硅酸盐原料中常见的成分，也增强了CCSH的形成，可能是通过在这里测试的条件下形成铝取代相。这些化学见解可以使新型胶凝材料的配方和固化指南的设计成为可能。
Calcium silicates are abundant but sparingly soluble feedstocks of interest for making low-carbon alternative cements. Under hydrothermal and alkaline conditions, they can form crystalline calcium silicate hydrate (CCSH) products, which are abundant in Roman concrete, or they can form carbonates when CO2is present. To understand when coprecipitation of CCSH and carbonate phases is possible, we studied the hydrothermal carbonation of a model calcium silicate, pseudowollastonite (α-CaSiO3), at 150 °C and high pH as a function of CO2source [CO2(g) or Na2CO3] and different concentrations of sodium, alumina, and silica. Our experiments produced a range of CCSH phases including tobermorite–13 Å, rhodesite, and pectolite, as early as 1 day after the start of our experiments. After 7 days of curing in a 2 M NaOH solution, over 10% of the samples had been converted to these CCSH phases. We also observed the formation of CaCO3as both aragonite and calcite when carbon was introduced to our experimental system. The carbon source impacted the ratio of the CaCO3to CCSH phases in the reaction products. The availability of Na2CO3produced a balance between the CaCO3and CCSH phases, whereas CO2(g) produced more CaCO3, with samples that were over one-third carbonate by mass. Higher concentrations of Na+increased the precipitation of both the CaCO3and CCSH phases. The presence of excess silica, in the form of dissolved borosilicate glass from our reaction vessels under alkaline reaction conditions, also enhanced the formation of CCSH phases formed in some experiments. Supplemental Al2O3, a common constituent in many silicate feedstocks, also enhanced CCSH formation, likely by forming aluminum-substituted phases under the conditions tested here. These chemical insights can enable the design of formulation and curing guidelines for novel cementitious materials.