Controlling the Selective Formation of Calcium Sulfate Polymorphs at Room Temperature

Abstract

Calcium sulfate is a naturally abundant and technologically important mineral with a broad scope of applications. However, controlling CaSO4 polymorphism and, with it, its final material properties still represents a major challenge, and to date there is no universal method for the selective production of the different hydrated and anhydrous forms under mild conditions. Herein we report the first successful synthesis of pure anhydrite from solution at room temperature. We precipitated calcium sulfate in alcoholic media at low water contents. Moreover, by adjusting the amount of water in the syntheses, we can switch between the distinct polymorphs and fine-tune the outcome of the reaction, yielding either any desired CaSO4 phase in pure state or binary mixtures with predefined compositions. This concept provides full control over phase selection in CaSO4 mineralization and may allow for the targeted fabrication of corresponding materials for use in various areas.

Influence of Alkyl Trimethyl Ammonium Bromides on Hydrothermal Formation of α-CaSO4·0.5H2O Whiskers with High Aspect Ratios

“…[1][2][3][4], showing excellent thermal stability and mechanical strength [5][6][7]. Calcium sulfate whiskers can be produced by preparing α-CaSO 4 ·0.5H 2 O whiskers through hydrothermal, acidification, reverse micro-emulsion, and microwave-assisted approaches [8][9][10][11][12][13] followed by calcination of the α-CaSO 4 ·0.5H 2 O whiskers above 600 • C [14,15].…”

Microscopic Studies of Calcium Sulfate Crystallization and Transformation at Aqueous–Organic Interfaces

“…This was achieved by dissolving equimolar amounts of CaCl2 and H2SO4 in dry methanol. 8,11 Similarly, we suggest that in our system the high concentration of CaSO4 within a very small volume of solvent would result in a thin interfacial fluid layer with a CaSO4:H2O ratio sufficiently high to achieve the critical value for anhydrite precipitation. This idea is also supported by noting that the equilibrium constant for the conversion of gypsum to anhydrite is highly dependent on the temperature and solvent water activity.…”

“…The discovery of simple, low-energy pathways for the growth of highly desirable and unstable polymorphs with vital industrial and biological applications is particularly important. [1][2][3][4][5][6][7][8][9][10] Numerous examples of high level control over polymorphism have been established for both organic [1][2][3] and inorganic [4][5][6][7][8] crystal systems. In particular, the calcium carbonate crystal system has been extensively studied.…”

“…Bassanite (more commonly known as plaster of Paris), is a highly valuable building material, whereas anhydrite has applications as a binder in cements and adhesives. 8 Thus, understanding and controlling the growth of these unstable hydrates under ambient conditions is of great interest.…”

“…8,11 More broadly, there are several examples where organic solvents have been exploited to study both the mechanisms and kinetics of crystallization, as well as crystal morphology. 30,31 In this paper, a two-phase, non-miscible, liquid-liquid (water-hexane or water-dodecane) system was employed, with the aqueous phase providing a source of SO4 2-and the organic phase containing a Ca 2+ source.…”