Title: Mechanically-activated solid-state synthesis of nanoparticles of HfB₂, HfC and HfN from partially hydrated hafnium tetrachloride

Authors: E. Barraud, S. Begin-Colin, G. Le Caer, O. Barres, F. Villieras

Addresses: Laboratoire de Science et Genie des Materiaux et de Metallurgie, C.N.R.S. U.M.R. 7584, Ecole des Mines, F-54042 Nancy Cedex, France. ' Institut de Physique et Chimie des Materiaux, GMI, UMR CNRS-ULP ECPM 7504, 23, rue du Loess, BP 43, F-67034 Strasbourg Cedex, France. ' Groupe Matiere Condensee et Materiaux, U.M.R. 6626, CNRS-Universite de Rennes-I, Campus de Beaulieu, Batiment 11A, F-35042 Rennes Cedex, France. ' Laboratoire Environnement et Mineralurgie, UMR 7569, CNRS-Universite de Nancy, Ecole Nationale Superieure de Geologie de Nancy, BP 40, F-54501 Vandoeuvre-les-Nancy Cedex, France. ' Laboratoire Environnement et Mineralurgie, UMR 7569, CNRS-Universite de Nancy, Ecole Nationale Superieure de Geologie de Nancy, BP 40, F-54501 Vandoeuvre-les-Nancy Cedex, France

Abstract: Nanocrystalline hafnium diboride, carbide and nitride are synthesised by a two-step process, namely a short mechanical activation step (∼1–2 h) of powder mixtures based on partially hydrated hafnium tetrachloride, ph-HfCl₄, and on magnesium, followed by a brief annealing step (∼1 h) of the activated powders in flowing argon at 1100°C. HfCl₄ is a by-product of the carbochlorination process of extraction of zirconium from ores. Magnesium has a strong reducing capacity and is insoluble in metallic hafnium. The unsought reaction products may then be eliminated during the additional heat treatment or by further leaching. Mechanically activated powder mixtures of ph-HfCl₄ + B and of ph-HfCl₄ + B + Mg yield either facetted grains or monocrystalline rods of HfB₂ according to the composition of the initial mixtures and to the temperature and duration of the annealing treatment. The mean size of the facetted grains ranges between 100 nm and 300 nm. The growth direction of the rods is along the c-axis. Their mean diameters are around 100 nm and their mean lengths are in the range 500 nm–1 um. Hafnium carbide HfC is directly mechanosynthesised from ph-HfCl₄ + Mg + C powder mixtures. A subsequent heat treatment in flowing argon allows to better crystallise the grains of HfC (∼100 nm) and to decompose the intermediate products. Annealing of ground ph-HfCl₄ + Mg blends in flowing nitrogen for 1 h at 1100°C yields HfN nanoparticles whose size ranges between 10 nm and 30 nm. Characterisations of powders by X-ray diffraction, thermogravimetric analysis, scanning and transmission electron microscopy, Fourier Transform Infrared Spectroscopy were performed to follow the phase evolution and to clarify the reaction mechanisms.

Keywords: ceramics; borides; carbides; nitrides; hafnium tetrachloride; mechanical alloying; mechanochemical processing; nanostructures; infrared spectroscopy; thermal analysis; nanoparticles; nanotechnology; solid state synthesis; heat treatment; leaching.

DOI: 10.1504/IJNT.2008.018687

International Journal of Nanotechnology, 2008 Vol.5 No.6/7/8, pp.649 - 659

Published online: 14 Jun 2008 *

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