In the modern construction industry, large gypsum (CaSO4·2H2O) boards are manufactured through a two-step procedure, which features the heating of fine gypsum powders to form the intermediate plaster of Paris (bassanite, CaSO4·0.5H2O) followed by hydration of the intermediate phase to form the final formed product. Here, we explore a novel pathway toward the fabrication of gypsum microneedles that bypasses formation of the intermediate bassanite phase. Using in situ liquid transmission electron microscopy, the dynamic behavior of fine gypsum powders in a calcium sulfate solution is investigated at the nanoscale and in real time. An oriented-attachment mechanism is found to dominate the direct transformation of gypsum nanoparticles to gypsum microneedles, where no intermediate phases are involved. Our experimental results advance the fundamental understanding of the dynamic interactions between gypsum and water. The proposed nanoscale pathway for gypsum evolution could potentially revolutionize the construction industry rooted in gypsum board manufacturing by promising a time- and energy-efficient mass production procedure. In addition, this work can inspire research efforts associated with geology, archeology, and biology, where historical significance is frequently deduced from gypsum-related discoveries.
The formation mechanism by which gypsum nanoparticles are converted to gypsum nanoneedles was studied using liquid cell TEM. Gypsum nanoparticles dispersed in solution containing sulfate and calcium ions were observed to aggregate together, eventually forming a stable nanoneedle structure. Two mechanistic pathways were observed: a previously proposed mechanism involving nucleation and growth of an intermediate product, bassanite, and its subsequent growth into a gypsum needle, and a new mechanism, the self assembly attachment growth of the gypsum nanoparticles to form a needle structure.