Frank J. Berry

Cation distribution and magnetic structure of the ferrimagnetic spinel NiCo2O4

The compound NiCo2O4, with spinel-related structure, has been prepared by thermal decomposition of metal nitrates and its bulk structural properties examined by means of magnetic measurements, neutron diffraction, X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). The results suggest a delocalised electron distribution on the octahedral sites with average oxidation states of +3.5 and +2.5 for nickel and cobalt, respectively, and lead to a cation distribution for NiCo2O4 of {Ni3+0.1Co2+0.9}tet[Ni3.5+0.9Co2.5+1.1]octO4. This electronic configuration is consistent with magnetisation measurements if applied magnetic fields cause a charge redistribution on the octahedral sites to favour Co3+ and Ni3+. The surface of NiCo2O4 was examined by X-ray photoelectron spectroscopy (XPS) and found to have a different composition containing Co2+, Co3+, Ni2+, Ni3+ and, probably, Ni4+.

Synthesis and Characterization of Nanometric Iron and Iron-Titanium Oxides by Mechanical Milling: Electrochemical Properties as Anodic Materials in Lithium Cells

Nanometric mixed iron-titanium oxides were prepared by mechanical milling with a view to determining their ability to act as anodic materials in lithium cells. At a TiO2/Fe2O3 mole ratio of 0.4, a solid-state reaction occurs that leads to the formation of Fe5TiO8, which possesses a spinel-like structure; at lower ratios, however, the structure retains the hematite framework. Li/g-Fe2O3 cells exhibit poor electrochemical reversibility; by contrast, Ti-containing electrodes possess improved cycling properties. Changes in the electrodes upon cycling were examined by X-ray photoelectron spectroscopy (XPS). XPS data confirm the participation of electrolyte in the electrochemical reaction and the different type of electrochemical reversibility exhibited by samples. Both processes were influenced by the presence of titanium. Titanium dioxide, in the presence of iron oxides, seems to be inactive to the electrochemical process. Based on the step potential electrochemical spectroscopy (SPES) curves and photoelectron spectra obtained, the presence of Ti increases the reversibility of the redox reactions undergone by the electrolyte during discharge/charge processes. The increased active-material/electrolyte/inactive-material interaction which is reported here offers new perspectives for the use of well-known transition oxides as anode materials in Li-ion batteries.

Climate and rock weathering: A study of terrestrial age dated ordinary chondritic meteorites from hot desert regions

Abstract Ordinary chondrites (OC) recovered from the desert areas of Roosevelt County, New Mexico, the Nullarbor Region of Western Australia, and the Algerian and Libyan Sahara, for which 14C terrestrial ages have been determined, were examined by 57Fe Mossbauer spectroscopy. OC were chosen as a standard sample to investigate weathering processes as their well constrained trace and bulk element chemistry, normative mineralogy and isotopic composition define a known, pre-weathering, starting composition. Given that terrestrial ages are known, it is possible to compare (initially very similar) samples that have been subsequently weathered in a range of climatic regimes from the present day to > 44 ka BP. In addition, recently fallen equilibrated OC contain iron only as Fe0 and Fe2+, thus the abundance of ferric iron is directly related to the level of terrestrial weathering. Mossbauer spectroscopy identifies two broad types of ferric alteration: paramagnetic phases (akaganeite, lepidocrocite, and goethite), and magnetically ordered (principally magnetite and maghemite). OC finds show a range in the percentage of total Fe existing as Fe3+ from zero to over 80%. However, oxidation is comparable between fragments of the same OC separated since their time of fall (i.e., paired meteorites). Our results indicate several features of meteorite weathering that may result from climatic or geomorphologic conditions at the accumulation site: (1) Saharan samples are, overall, less weathered than non-Saharan samples, which may be related to the relatively recent age (ca. 20 ka) of the Saharan accumulation surface; (2) broad differences between sites in the rate of weathering, arising from regional differences in climate; (3) consistent differences in the weathering products between samples that fell during humid periods and those that fell during more arid periods (those falling during humid periods contain a higher proportion of magnetically ordered ferric oxides); (4) one region (the Nullarbor) that shows a variation in the total amount of ferric species that closely matches the climatic record for this area of Australia for the last 30 ka. Points (3) and (4) may be related to the identification of a rapid initial weathering phase: the majority of weathering occurs in the first few hundred years after fall, followed by passivation of weathering by porosity reduction. Porosity reduction, and the associated restriction in the ability of water to penetrate the sample, appears to be the mechanism whereby a weathering assemblage formed during the brief initial period of oxidation is preserved through subsequent climatic cycles over the terrestrial lifetime of the sample.

Microwave heating during catalyst preparation : influence on the hydrodechlorination activity of alumina-supported palladium-iron bimetallic catalysts

Abstract Alumina-supported Pd–Fe mono- and bimetallic catalysts have been prepared by microwave irradiation and by conventional calcination methods. The catalysts were characterised by powder X-ray diffraction (XRD), temperature-programmed reduction (TPR) and nitrogen adsorption measurements. Hydrogen chemisorption measurements were performed after low- and high-temperature reduction (LTR and HTR) of the catalyst. Hydrodechlorination of chlorobenzene was carried out on the reduced catalysts. Microwave heating changed the crystallite size and the susceptibility of the catalysts to alloy formation, with a resultant increase in the activity of the reduced catalysts for the hydrodechlorination of chlorobenzene.

Magnetic structure evolution in mechanically milled nanostructured ZnFe2O4 particles

Nanostructured partially-inverted ZnFe2O4 particles have been prepared from bulk ZnFe2O4 by high-energy ball milling in an open container. The grain size reduction, cation site distributions, and the evolution of magnetic structures have been studied by x-ray diffraction with Rietveld structure refinements, transmission electron microscopy, and Mossbauer spectroscopy. It is found that a change of magnetic structure from an antiferromagnetic to a ferrimagnetic (or ferromagnetic) structure occurs in the milled samples. This change is correlated with the redistribution of the cations, Zn and Fe, in the A and B sublattices.

Mössbauer spectroscopic examination of a single crystal of

Mossbauer spectra have been recorded in fields of up to 13 T from a single crystal of cut perpendicular to the [111] axis. The spectra were best fitted with five magnetic components complementing studies on a crystal cut normal to a [100] axis. One component corresponds to situated on the tetrahedral A sites of the inverse spinel-related structure whilst the other four correspond to and on two non-equivalent octahedral sites.

The flux of meteorites to the Earth and weathering in hot desert ordinary chondrite finds

The abundance of ferric iron, produced by weathering in ordinary chondrites collected from hot desert regions, is related to their terrestrial age, enabling a variety of processes involved in meteorite weathering to be deduced. Fe0/Fe2+/Fe3+ content was measured quantitatively by 57Fe Mossbauer spectroscopy. It is observed that meteorites from different regions are oxidised at different rates. We also propose the tentative hypothesis that one source of scatter in total oxidation versus terrestrial age for a region is climatic change. A mechanism to explain the variable response to climatic conditions involves the high initial porosity of samples being reduced as ferric oxides and other alteration products are produced. Reliable recovery data from a meteorite accumulation site (Roosevelt County, New Mexico, USA) and a quantitative measure of weathering and terrestrial age permit an estimate of the flux of meteorites to the Earths surface. Having established a decay constant for meteorites, and accounting for the area of searches and pairing, we estimate an accumulation rate of 159 falls of mass greater than 20 g per 106 km2 per yr. This calculation is distinct from, but in broad agreement with, previous estimates from camera observations, suggesting that the accumulation rate of meteorite falls to the Earths surface has remained essentially unchanged over the last 50,000 years at between 59 and 159 falls of mass exceeding 20 g per 106 km2 per yr. The error for both methods is approximately a factor of 2.

Synthesis, structural, and magnetic characterisation of magnesium-doped lithium ferrite of composition Li0.5Fe2.5O4

Abstract Spinel-related magnesium-doped Li 0.5 Fe 2.5 O 4 has been synthesised by heating magnesium-substituted corundum-related α-Fe 2 O 3 with Li 2 CO 3 at 600°C which is ca. 600°C lower than the temperature normally used to prepare metal-doped Li 0.5 Fe 2.5 O 4 by conventional sintering methods. Rietveld structure refinement of the X-ray powder diffraction data shows that the Mg 2+ ions substitute for Fe 3+ ions on the tetrahedral sites whilst the Li + ions are located on the octahedral sites. The 57 Fe Mossbauer spectrum and magnetic measurements are consistent with this structural model.

Synthesis of chromium-containing pigments from chromium recovered from leather waste.

Cobalt-chromite green and chrome-tin pink pigments have been prepared from chromium extracted from leather shavings produced as a waste product of the leather-tanning industry. The alkaline agent (NaOH, CaO, MgO, NH4OH) used in the extraction process influences the nature of the final product. The effect of the NH4OH:CaO ratio on the final product in the case of cobalt-chromite green was examined. The pigments obtained were characterized by FT-IR and X-ray diffraction (XRD). Colour measurements were compared with those recorded from materials prepared from pure Cr2O3. The leaching of Cr(VI) from the materials was examined by UV spectroscopy.

Studies on magnesia supported mono- and bimetallic Pd-Fe catalysts prepared by microwave irradiation method

Magnesia supported mono- and bimetallic Pd-Fe catalysts were prepared by conventional and microwave irradiation method. The prepared catalysts were characterised by N2 adsorption, temperature programmed reduction, selective hydrogen chemisorption and X-ray diffraction (XRD). The conventionally prepared catalysts after high temperature reduction (HTR) showed the formation of Pd-Fe alloy. In the case of microwave irradiated catalysts the formation of Pd-Fe alloy is limited during HTR reduction. These catalysts activity was tested in hydrodechlorination (HDC) of chlorobenzene. The catalysts prepared by microwave irradiation method are more active compared to conventionally prepared ones. The microwave irradiation leads to different morphology of the bimetallic catalysts. The HDC activity results are discussed in terms of structural differences between the catalysts prepared by conventional and microwave irradiation.