Preparation and characterization of sulfate cancrinite, a synthetic analog of vishnevite, obtained under mild hydrothermal conditions

Vishnevite is a mineral classified within the cancrinite group of the feldspathoid family. Literature about the preparation of vishnevite synthetic analogs, recognized as sulfate cancrinite, is limited so far. Furthermore, it is well documented that the synthesis of materials from the cancrinite group exhibits certain difficulties that include structural disorder, intergrowths, and co-crystallization of the sodalite group. Thus, it is necessary to assess synthetic conditions that allow for solving these problems. In this work, a study of the influence of benzyldodecyldimethylammonium bromide (BDDAB) as a structure-directing agent (SDA) in the hydrothermal preparation of sulfate cancrinite materials, synthetic analogs of vishnevite, is presented. The materials were characterized by XRPD, FT-IR, SEM-EDX, and N₂-physisorption. A pure phase of the vishnevite-type structure was obtained in the presence of BDDAB (VIS-24G and VIS-48G samples), while traces of impurities accompanied the vishnevite-type structure in the absence of BDDAB (VIS-24W and VIS-48W samples). Synthesized materials crystallized in hexagonal unit cells with space group P6₃, as shown by the Pawley refinement of powder diffraction patterns recorded, confirming the vishnevite-type structure. SEM results showed small and irregular particles that form spherical aggregates in botryoidal habits, and the N₂-physisorption indicated low values of surface area and pore volume. In this work, synthetic analogs of pure vishnevite were obtained at lower crystallization temperatures than those previously reported using BDDAB as SDA under mild hydrothermal conditions.