Thermal behavior and coloration study of silica-coated alpha-Fe2O3 and beta-FeOOH nanocapsules.

This manuscript reports characterization of the colorations and thermal behaviors of the silica-coated alpha-Fe2O3 and beta-FeOOH nanocapsules. Prepared beta-FeOOH and alpha-Fe2O3 nanoparticles were coated with silica using tetraethylorthosilicate (TEOS) and cetyltrimethyl-ammonium bromide (CTAB) as a surface modifier for the comparison of physical properties of both samples. XRD patterns of the silica-coated beta-FeOOH and alpha-Fe2O3 nanoparticles were heated to 1000 degrees C, show a hematite (alpha-Fe2O3) structure. The silica-coated beta-FeOOH nanoparticles became almost entirely hollow at 1000 degrees C due to their volume reduction. In addition, the coloration values of the transformation nano capsule alpha-Fe2O3 are lower than those of the silica-coated alpha-Fe2O3 nanostructures. On the other hand, the silica-coated alpha-Fe2O3 nanoparticles retained their colorations and shapes after being heated to 1000 degrees C. The morphologies, crystal structures and colorations of the as prepared samples were analyzed by scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction and CIE colorimeter.