Explore the vast range of titles available.

In the original publication [...]

The goal of the presented work was to find the most favorable conditions for the synthesis and stabilization of chemically pure ettringite and monosulfate. The reaction was carried out by mixing pure tricalcium aluminate (C[sub.3]A) and gypsum (CS¯H[sub.2]) in an excess amount of water. The impact of hydration time (2–7 days), C[sub.3]A:CS¯ molar ratio (1:1–1:3) and water vapor pressure of the selected drying agents (anhydrite-III and supersaturated CaCl[sub.2] solution) on the phase composition of the products was evaluated. After 7 days of hydration, either ettringite or monosulfate was obtained as the main product, depending on the C[sub.3]A:CS¯ molar ratio. The synthesis carried out at a C[sub.3]A:CS¯ molar ratio of 1:3 produced pure ettringite. In the case of the sample characterized by the ratio of 1:1 (typical of monosulfate), a considerable portion of ettringite (27.9%) was present in the final products along the AFm phase. Therefore, a different synthesis method has to be selected in order to obtain pure monosulfate. The results showed that thermal analysis, X-ray diffractometry and FTIR spectroscopy can be used to distinguish the characteristic features of ettringite and monosulfate.

This study aimed to reveal the effects of the hydration products AH[sub.3] and AFt phases on the hydration and hardening properties of calcium sulfoaluminate (CSA) cement. In addition, the effects of anhydrite (CS¯) and gypsum (CS¯H[sub.2]) on the properties of CSA cement were compared. Calcium sulfoaluminate (C[sub.4]A[sub.3]S¯) was synthesized with analytical reagents, and the C[sub.4]A[sub.3]S¯-CS¯-H[sub.2]O system with different molar ratios of CS¯ and C[sub.4]A[sub.3]S¯ was established. The phase compositions and contents of AFt and AH[sub.3] were determined by X-ray diffraction (XRD), Rietveld quantitative phase analysis, and thermogravimetric analysis (TG). The effects of pore structure and hydration product morphology on mechanical properties were analyzed by mercury intrusion porosity (MIP) and scanning electron microscopy (SEM). The results showed that the compressive strength exhibited a correlation with the AH[sub.3] content. In the case of relatively sufficient anhydrite or gypsum, C[sub.4]A[sub.3]S¯ has a high degree of hydration, and the AH[sub.3] content can be considered to contribute more to the strength of the hardened cement paste. When anhydrite was selected, the combined and interlocked AFt crystals were covered or wrapped by a large amount of AH[sub.3]. The mechanical properties of the hardened cement paste mixed with anhydrite were better than those of that mixed with gypsum.

In the original publication [...]

In recent years, there has been an urgent need for integrated solutions to synergistically manage industrial solid waste stockpiling and CO[sub.2] emissions. Single-component solid waste mineralization, such as those using only fly ash (FA) or carbide slag (CS), often encounters performance bottlenecks, typically characterized by a compressive strength of less than 2 MPa and a carbonation efficiency of under 10%. Furthermore, a systematic quantitative understanding of the synergistic interactions within multi-component systems remains absent. This study employs Response Surface Methodology to investigate the interactive effects of solid waste ratios, the water-to-solid ratio, and alkali content, aiming to elucidate the synergistic mineralization mechanism and overcome the bottlenecks of single solid waste mineralization. Under optimized conditions—specifically, 34% CS, 30% phosphogypsum (PG), a water-to-solid ratio of 0.48, and an alkali content of 27%—the system achieved a 7-day compressive strength of 3.5 MPa and a CO[sub.2] mineralization efficiency of approximately 16%, representing a significant improvement over typical single solid waste mineralization materials. Microstructural and spectroscopic analyses indicate that CS serves a dual function as both a calcium source for CaCO[sub.3] precipitation and an alkaline activator for FA. FA constructs a dense aluminosilicate network via pozzolanic reactions, while SO[sub.4] [sup.2−] released from PG promotes the formation of ettringite, facilitating efficient pore filling and early strength development. Additionally, it was observed that surface pores were filled with more products compared to the interior, forming a gradient pore structure that is dense on the outside and sparse on the inside. The AFt and silicate gel were identified as the key microstructural driver for the performance enhancement. This study not only explores the ternary synergistic mechanism of FA, CS, and PG but also provides a viable pathway for developing high-performance solid waste-based mineralization materials that combine mechanical properties with efficient CO[sub.2] sequestration.

C.sub.3A and C.sub.3S are the two fastest hydrating minerals in Portland cement, while nano-SiO.sub.2 also promotes the early hydration of Portland cement. Given the complex composition of cement, it is of more practical significance to study the optimization mechanism of nano-SiO.sub.2 in the early hydration stage of pure C.sub.3S-C.sub.3A-gypsum system and reveal the synergistic effect between various phases than to study the early induction of cement-based materials by nanomaterials. Therein, this paper carried out the research on the influence mechanism of nano-SiO.sub.2 on the very early hydration property of the C.sub.3S-C.sub.3A-gypsum composite system. Some tests have shown that nano-SiO.sub.2 hinders the dissolution of gypsum components and the generation of ettringite in the product. Furthermore, through some experimental tests, it can be found that the material properties are continuously optimized with the increase in the amount of nano-SiO.sub.2. When the nano-SiO.sub.2 is added to 1.5 mass%, the compressive strength, the hydration rate, and the total porosity improve by 12.8 MPa, 21.8, and - 8.3%. All results described and discussed in this study will contribute to the application of nano-SiO.sub.2 and the in-depth understanding of the synergistic effect mechanism between silicate monominerals.

Gypsum (CaSO4·2H2O) is the most common sulfate mineral on Earth and is also found on Mars. It is an evaporitic mineral that predominantly precipitates from brines. In addition to its precipitation in natural environments, gypsum also forms an undesired scale in many industrial processes that utilize or produce brines. Thus, better insights into gypsum formation can contribute to the understanding of natural processes, as well as improving industrial practices. Subsequently, the thermodynamics, nucleation and crystal growth mechanisms and kinetics, and how these factors shape the morphology of gypsum have been widely studied. Over the last decade, the precipitation of gypsum under saline and hypersaline conditions has been the focus of several studies. However, to date, most of the thermodynamic data are derived from experiments with artificial solutions that have limited background electrolytes and have Ca2+/SO42− ratios that are similar to the 1:1 ratio in the mineral. Moreover, direct observations of the nucleation and growth processes of gypsum are still derived from experimental settings that can be described as having low ionic strength. Thus, the mechanisms of gypsum precipitation under conditions from which the mineral precipitates in many natural environments and industrial processes are still less well known. The present review focuses on the precipitation of gypsum from a range of aspects. Special attention is given to brines. The effects of ionic strength, brine composition, and temperature on the thermodynamic settings are broadly discussed. The mechanisms and rates of gypsum nucleation and growth, and the effect the thermodynamic properties of the brine have on these processes is demonstrated by recent microscopic and macroscopic observations. The morphology and size distribution of gypsum crystals precipitation is examined in the light of the precipitation processes that shape these properties. Finally, the present review highlights discrepancies between microscopic and macroscopic observations, and studies carried out under low and high ionic strengths. The special challenges posed by experiments with brines are also discussed. Thus, while this review covers contemporary literature, it also outlines further research that is required in order to improve our understanding of gypsum precipitation in natural environments and industrial settings.