Epitaxial overgrowth of goethite on hematite synthesized in phosphate media; a scanning force and transmission electron microscopy study

Other| December 01, 1997 Epitaxial overgrowth of goethite on hematite synthesized in phosphate media; a scanning force and transmission electron microscopy study Vidal Barron; Vidal Barron Universidad de Cordoba, Departamento de Ciencias y Recursos Agricolas y Forestales, Cordoba, Spain Search for other works by this author on: GSW Google Scholar Natividad Galvez; Natividad Galvez Search for other works by this author on: GSW Google Scholar Michael F. Hochella; Michael F. Hochella Search for other works by this author on: GSW Google Scholar Jose Torrent Jose Torrent Search for other works by this author on: GSW Google Scholar American Mineralogist (1997) 82 (11-12): 1091–1100. https://doi.org/10.2138/am-1997-11-1206 Article history first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Vidal Barron, Natividad Galvez, Michael F. Hochella, Jose Torrent; Epitaxial overgrowth of goethite on hematite synthesized in phosphate media; a scanning force and transmission electron microscopy study. American Mineralogist 1997;; 82 (11-12): 1091–1100. doi: https://doi.org/10.2138/am-1997-11-1206 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyAmerican Mineralogist Search Advanced Search Abstract We used X-ray diffraction (XRD), scanning force microscopy (SFM), transmission electron microscopy (TEM), and color to investigate the effect of phosphate on the crystallization rate, nature, and morphology of iron oxides prepared from ferrihydrite in the laboratory. Synthesis was performed at two temperatures (323 and 373 K) and two pH values (9 and 12) from ferric nitrate, for P/Fe atomic ratios ranging from 0 to 2.5%. The presence of phosphate retarded crystallization, tended to favor hematite over goethite, and markedly influenced the morphology of the goethite crystals formed at high pH. Application of SFM in the deflection mode was useful to investigate the morphology of the small goethite crystals, with careful attention paid to operating conditions; in particular, sharp silicon probes were found to produce fewer artifacts than coarser silicon nitride ones. At low P/Fe ratios (<0.2%), the goethite crystals were thin, elongated, multidomain laths; at high P/Fe ratios (>1.5%), star-shaped, twinned crystals were produced. All the theoretical shapes, derived from the assumption that star-shaped crystals result from the epitaxial growth of goethite on a hematite core, were observed by SFM and TEM. The presence of such hematite nuclei was supported by XRD, selected-area electron diffraction, color, and preferential dissolution of the samples in HCl, because it is known that hematite dissolves faster than goethite in acid. With increasing P/Fe ratio, the arms of the star-shaped crystals became shorter. This was likely due to the higher density of P-adsorbing pairs of singly coodinated OH groups on terminal {021} faces relative to prismatic {110} arm faces. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.