Inorganic self-organized silica aragonite biomorphic composites

The precipitation of calcium carbonate in alkaline silica solutions results in the formation of complex curvilinear forms if aragonite formation is encouraged by growth at an elevated temperature (80 °C). The resulting coralline self-assembled silica-calcium carbonate particles are "biomorphs", bearing a striking resemblance to natural coral forms. These materials, comprised of calcium carbonate nanocrystals and an amorphous silica matrix, have a complex ultrastructure, made of clusters of gathered sheets of variable curvatures formed by successive curling. The nanocrystals within these "ruled surfaces" are thin, elongated, densely packed needles of aragonite. These clusters are outgrowths from central saddlelike cores that resemble developable petaloid surfaces. The size, shape, crystallography, and chemical composition of the resulting biomorphs were examined by optical microscopy, field emission scanning electron microscopy (FE-SEM), powder X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM and HRTEM), and energy dispersive X-ray analysis (EDX).