Precipitation of acicular hydrogoethite $(\alpha-FeOOH·xH_2O; 0.1 < x < 0.22)$ using morphology controlling cationic additives

Subbanna, GN and Sudakar, C and Kutty, TRN (2003) Precipitation of acicular hydrogoethite $(\alpha-FeOOH·xH_2O; 0.1 < x < 0.22)$ using morphology controlling cationic additives. In: Materials Chemistry and Physics, 78 (1). pp. 43-50.

 PDF Precipitation.pdf Restricted to Registered users only Download (368Kb) | Request a copy

Abstract

Acicular hydrogoethite $(\alpha-FeOOH·xH_2O; 0.1<x<0.22)$ particles of high aspect ratio of $\geq10$ and narrow size distribution with length ~0.5 μm are prepared by air oxidation of $Fe(OH)_2{\cdot}xH_2O$ (80<x<120) in presence of morphology controlling cationic additives (0.01 at.% of $Pd^{2+}$ or $Rh^{3+}$). Growth of hydrogoethite particle proceeds by the oxidation of $Fe(OH)_2{\cdot}xH_2O$ to an intermediate phase through the nucleation within the amorphous ferric oxy-hydroxide $[FeO_x(OH)_3_-_2x{\cdot}yH_2O]$ and growth of $\alpha-FeOOH·(H_2O)_x$ acicular particles with the aid of morphology controlling agents, as evidenced from X-ray diffraction (XRD) and transmission electron microscope (TEM) studies. Preferential adsorption of additives on certain crystallographic planes and thereby retarding the growth in the perpendicular direction, allows the particles to acquire acicular shape with high aspect ratio ~10. Thermal analyses of hydrogoethite samples show excess weight loss (3–4%) compared to goethite samples. Presence of $H\cdot\cdot\cdot O\cdot\cdot\cdot H$ vibrational absorptions arising from strongly coordinated water molecules in hydrogoethite and its absence in goethite is evidenced from IR spectra. $H_2O$ molecules in hydrogoethite are located in the strands of channel formed in between the double ribbons of $4FeO_6$ octahedra running parallel to c-axis of goethite, wherein the water molecules are bridging between the nearest neighbour cations.

Item Type: Journal Article Copyright of this article belongs to Elsevier. Acicular goethite (α-FeOOH);Hydrogoethite;Morphology controlling agents;Iron oxyhydroxide Division of Chemical Sciences > Materials Research Centre 31 May 2006 19 Sep 2010 04:28 http://eprints.iisc.ernet.in/id/eprint/7225