X-Ray micro-tomography of freeze dried nickel alginate beads and transformation into NiO nanopowders

A generic ion-exchange mediated sol-gel method has been developed for the production of high purity nickel and other metal oxide nanopowders using sodium alginate precursor. X-Ray micro-tomography (XMT) shows that the nickel ions have been uniformly cross-linked in the alginate structure and remained stable after freeze drying as evidenced by the bright green color of the freeze dried beads. The freeze dried nickel alginate beads exhibit a porous foam-like structure composing of a thin nickel alginate film and a dominant fraction of voids. The porous nickel alginate beads when calcined at 700 °C for 1 h in ambient air yielded spherical nickel oxide nanoparticles of ∼50 nm in size. Powder X-ray diffraction (XRD) confirms that the sample is single phase cubic NiO powders with no trace of impurity. The mean crystallite sizes calculated from XRD analysis using the Rietveld refinement method agree with the morphological features observed by transmission electron microscopy (TEM).