Author
A.M. Posner
Bio: A.M. Posner is an academic researcher from University of Western Australia. The author has contributed to research in topics: Diffusion & Acicular. The author has an hindex of 5, co-authored 5 publications receiving 566 citations.
Papers
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TL;DR: In this article, a series of 0·5 molal Fe(III) hydroxide gels were produced by aging the gels at 60°C in the presence of excess NaOH and examined qualitatively by electron microscopy, selected area diffraction and X-ray diffractometry.
238 citations
TL;DR: The magnetite particles were present in a range of sizes and morphologies as mentioned in this paper, and the incorporation of small amounts (2+ and its ability to exhibit the Jahn-Teller effect and the larger ionic radii of Mn 2+ and Cd 2+ may be responsible for their non-uniform distribution in the magnetite crystals.
125 citations
TL;DR: The diffusion coefficients of Fe are in the range 0.8 to 2.1 × 10−15 cm2/sec and decrease with the increasing isomorphous substitution of Co, Ni and Zn for Fe(II) in the magnetite as discussed by the authors.
125 citations
TL;DR: Equations describing diffusion of the isotopic species in the solid phase are not relevant here because phosphate ions react only with the Fe(111) ions exposed at the goethite surfaces, and no measurable diffusion of phosphate ions into the bulk of the crystals was observed.
Abstract: FE(111) phosphate complexes are formed on the surfaces of goethite (α-FeOOH) crystals suspended in dilute aqueous orthophosphate solutions The rates of isotopic exchange reactions, in which phosphate ligands on the crystal surface exchange with free phosphate ions from the surrounding solution, can be readily measured by conventional techniques, using a small quantity of 32P-labelled orthophosphate solution added to the equilibrium suspension No satisfactory method is, however, available to interpret kinetic data for isotopic exchange in heterogeneous systems (two phases) Equations describing diffusion of the isotopic species in the solid phase, used when the extent of fast surface-exchanging reactions is small compared with the amount of the slower diffusion-controlled exchange involving the bulk of the solid1–3, are not relevant here because phosphate ions react only with the Fe(111) ions exposed at the goethite surfaces No measurable diffusion of phosphate ions into the bulk of the crystals was observed
55 citations
TL;DR: In this paper, the electrochemistry of apatite surfaces has not been extensively studied, and only a few studies of the surface charge characteristics of hydroxyapatite [Ca10(OH)2(PO4)6] and fluorapatites [Ca 10F2[PO4] have been conducted.
Abstract: THE crystal and solution chemistry of apatites has been studied intensively by medical, biological and earth scientists but studies of the electrochemistry of apatite surfaces have not been extensive. The few studies of the surface charge characteristics of hydroxyapatite [Ca10(OH)2(PO4)6] and fluorapatite [Ca10F2(PO4)6] show that H+ and OH− are potential determining ions, but estimates of the pH at the point of zero charge (PZC) have varied widely from 4.3 to 7.6 for hydroxyapatite1–5 and from 4 to >12 for fluorapatite6–8.
39 citations
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TL;DR: An overview of second-order kinetic expressions is described in this paper based on the solid adsorption capacity, which shows that a pseudo-second-order rate expression has been widely applied to the Adsorption of pollutants from aqueous solutions onto adsorbents.
3,458 citations
TL;DR: In this article, the As and Fe K-edges were collected from samples of two-line ferrihydrite with adsorbed (ADS) and coprecipitated (CPT) arsenate prepared over a range of conditions and arsenate surface coverages.
1,123 citations
TL;DR: Effects of Various Ions on the Aqueous Transformation of Ferrihydrite and Environmental Implications 2576.
Abstract: VII. Synthesis 2569 VIII. Adsorption and Solid Solution 2570 A. General Observations 2570 B. Adsorption of Specific Species 2571 1. Various Cations 2571 2. Various Anions 2572 3. Organic Species 2573 C. Environmental Implications 2573 IX. Transformation of Ferrihydrite 2574 A. Dry Thermal Transformation 2574 B. Aqueous Transformation 2575 C. Effects of Various Ions on the Aqueous Transformation of Ferrihydrite 2576
781 citations
01 Mar 1980
TL;DR: In this article, the formation of iron oxides by aging ferrous hydroxide gels at elevated temperatures was studied as a function of various parameters, including the nature of the anions present in the system.
Abstract: The formation of iron (hydrous) oxides by aging ferrous hydroxide gels at elevated temperatures was studied as a function of various parameters. It was found that the composition and the morphology of the resulting solids depended strongly on the nature of the anions present in the system. Spherical magnetite particles of narrow size distribution, with mean diameters ranging between 0.03 and 1.1 μm, were obtained if FeSO4 was interacted with KOH in the presence of nitrate ion and the resulting gelatinous suspension was kept at 90°C for several hours. The particle size distribution of the magnetite sol was affected by the excess concentration of Fe(II) species in equilibrium with the ferrous hydroxide precipitate. If oxygen was present in addition to nitrate ion, rodlike α-FeOOH particles crystallized along with the magnetite on aging of some ferrous hydroxide gels. A mechanism of the magnetite formation under the conditions of these experiments is offered.
610 citations
TL;DR: In this article, the effect of citrate ions on the growth of magnetite particles is investigated and the characterisation of the maghemite particles by various techniques (X-ray diffraction, transmission electron microscopy, magnetic measurements) is described.
462 citations