A Raman spectroscopy study of cerium oxide in a cerium–5 wt.% lanthanum alloy

This paper describes a study of a cerium–5 wt.% lanthanum (Ce–5 wt.% La) alloy using Raman spectroscopy and X-ray diffraction (XRD). Examination of the alloy microstructure by optical microscopy and Raman spectroscopy revealed the presence of inclusions which were identified as cerium oxide (CeO₂). The study also highlighted the need to avoid excessive laser power during acquisition of the Raman spectra as this appeared to cause the oxidation of the region being analysed where previously no cerium oxide peak had been detected. The propensity of cerium to oxidise in air results in the formation of a CeO₂ layer on the surface of the alloy. Raman spectroscopy of the oxide layer formed on the alloy after exposure to air for 21 days found that the Raman peak denoting cerium oxide was seen at between 5 and 7 cm⁻¹ lower than the value for CeO₂ (465 cm⁻¹). This is attributed to a combination of a sub-stoichiometric oxide layer and the presence of La in the alloy.     

Thermokinetic study on the phase evolution of mechanically alloyed Ni–B powders

A combination of differential thermal analysis and detailed X-ray diffraction (XRD) analyses were used for the thermokinetic study of phase evolution during heating–cooling of the mechanically alloyed (MA-ed) Ni–15 wt% B. According to the results obtained, different phase transition sequences led to the formation of nanocrystalline Ni–B alloys comprising of Ni₂B + o-Ni₄B₃ and Ni₂B + m-Ni₄B₃ + B. Using the XRD studies, it was found that the Ni₂B is the most stable intermetallic compound in the Ni–B binary phase diagram, and its nanocrystalline nature retained unchanged even after annealing up to temperatures near the melting point. In addition, average enthalpy as well as activation energy of occurred reactions was calculated; the latter was estimated using two well-known Kissinger and Augis & Bennett methods.     

<Emphasis Type="Italic">In vitro</Emphasis> bioactivity of 70 wt.% SiO<Subscript>2</Subscript> — 30 wt.% CaO sol-gel glass,doped with 1, 3 and 5 wt.% NbF<Subscript>5</Subscript>

The 70SiO₂-30CaO (wt.%) sol-gel glasses doped with 1, 3 and 5 NbF₅ (wt.%) were prepared via polystep sol-gel route. The synthesized glasses were characterized by XRD, FTIR and SEM. Changes in 1.5 SBF solutions were measured by ICP-AES. XRD of the glasses stabilized at 700°C for 6 hours proved the presence of niocalite. FTIR was consistent with XRD data. The in vitro bioactivity study of all glasses prepared were carried out by soaking in 1.5 simulated body fluid (1.5 SBF) at 37°C for 6 and 12 days in static conditions. The FTIR reveals the formation of A-type and B-type carbonate containing hydroxyapatite (CO₃HA) layer. Changes in 1.5 SBF solutions, after 6 days of soaking, show that the Ca concentration increased significantly, compared to the initial Ca content in the 1.5 SBF solution before in vitro test. After 12 days of immersion, the Ca concentration decreased, i.e., the formation of HA phase consumed Ca from 1.5 SBF solution. For all soaking times, the concentration of P is much lower than that the used 1.5 SBF. Based on these results we suggest that Ca and P play an active role in the future of the glasses. SEM depicts that the different morphology of hydroxyapatite can be formed as a function of soaking time.     

Curing kinetics study of melamine–urea–formaldehyde resin

The influence of the preconditioning at different temperatures on the cure kinetics of melamine?Curea?Cformaldehyde resins coated on stone wool was investigated under acidic conditions using differential scanning calorimetry and thermogravimetry. The higher pre-treatment temperature was applied, to which resin-coated stone wool was exposed, the lower was the mass loss during the experiment. Kinetic model parameters were determined in two different manners, with the parameters being independent of preconditioning temperature and dependent on the latter. The apparent orders of reaction were approximately two (all of them being within the range 0.96?C2.33), which would imply that cross-linking predominantly proceeds via the bimolecular reaction of either melamine or urea and formaldehyde. Nonetheless, the apparent orders of reaction decreased as a function of preconditioning temperature. The apparent activation energies varied less with preconditioning temperature, assuming values between 64.2 and 78.5?kJ?mol^?1. The applicability of nth-order reaction kinetic models was consequently validated for two other dynamic thermal regimes.     

Comparison of mechanically alloyed and sputtered tin–cobalt–carbon as an anode material for lithium-ion batteries

High energy ball milling, vertical-axis attritor milling and co-sputtering were used to prepare Sn₃₀Co₃₀C₄₀ or Sn₃₆Co₄₁C₂₃ electrode materials. By varying the milling conditions, it was possible to obtain nanostructured materials by mechanical methods whose X-ray diffraction patterns mimicked the diffraction pattern of the co-sputtered material. Electrochemical testing showed that composite electrodes made from each of the prepared materials showed stable charge–discharge capacity for at least 100 charge–discharge cycles and stable differential capacity versus potential profiles. Although the materials appear to be similarly nanostructured, the sputtered material showed a reversible capacity near 610 mA h/g, close to the theoretical capacity of 661 mA h/g, while the best material prepared by mechanical methods attained a specific capacity near 470 mA h/g. Further experiments are required to understand the differences in the nanostructure of these materials that leads to the differences in attained specific capacity.     

The non-isothermal kinetics of mullite formation in mechanically activated kaolinite–alumina ceramic system

The non-isothermal kinetics of mullite formation from both non-activated and mechanically activated kaolinite?+?alumina ceramic system have been studied by differential thermal analysis (DTA). The mixture of kaolinite and alumina was activated mechanically in a planetary mill, while amorphization in the kaolinite and alumina structure was studied by X-ray diffraction analysis. The activation energies depending on the conversion for mullite formation have been calculated from the DTA curves by using the non-isothermal method of Coats and Redfern at heating rates of 5, 10, 15, and 20?°C?min^?1. The mechanical activation of the kaolinite and alumina mixture resulted in the decrease in activation energy values for mullite formation.     

Extended study of crystallization kinetics for Se–Te glasses

Crystallization kinetics of chosen compositions from Se–Te glassy system were studied under non-isothermal conditions depending on particle size using differential scanning calorimetry. The purpose of this article is to demonstrate the extent of information accessible by the modern kinetic analysis provided by the differential scanning calorimetry, and to suggest its importance and merit for the development of new, high-tech PCM materials. The crystallization kinetics was described in terms of the nucleation-growth Johnson–Mehl–Avrami model. Complexity of the crystallization process was in this case represented by very closely overlapping consecutive competing surface and bulk nucleation-growth mechanisms. Mutual interactions of both mechanisms as well as all other observed effects were explained in terms of thermal gradients, surface crystallization centers arising from the sample preparation treatments, and changing amount of volume nuclei originating from the combination of pre-nucleation period, and the very glass preparation phase. Accent was laid on the merits resulting from interpretations of characteristic kinetic functions. A new criterion for quick determination of the dominating crystallization mechanism—surface or bulk—was introduced.     

Microanalytical study of sub-nanoliter samples by capillary electrophoresis – mass spectrometry with 100 % injection efficiency

Microchimica Acta - A method is presented for conducting fast capillary electrophoresis (CE) with ultrasmall sample volumes (&lt;10&nbsp;nL) and subsequent determination of target analytes...     

Electrochemical behavior of passive films on Al–17Si–14Mg (wt.%) alloy in near-neutral solutions

The anodic polarization behavior of alloy Al–17Si–14Mg in borate solutions with and without 0.01 M NaCl was compared to that for pure Al. Results showed that, for the alloy, the passive current density increased but the pitting susceptibility decreased. The first effect was ascribed to a significant electrochemical activity of the Mg₂Si intermetallics and the second to improved stability of the oxide film. X-ray photoelectron spectroscopy analysis of potentiostatically formed passive film on the alloy showed that it consisted of aluminum oxyhydroxide with incorporation of silicon in its elemental and two oxidized states (+3 and +4). Mott–Schottky analysis showed that trivalent silicon ion acted as an n-type dopant in the film. The interrelationship between passive film composition, electronic properties, and pitting behavior has been discussed.     

Studies of chemical–catalytic formation of Ni–Re (Mo,W)–B alloys

The paper briefly reviews the studies of the processes of formation of Ni–Re–B, Ni–Mo–B, and Ni–W–B triple alloys using the method of chemical–catalytic reduction of metal ions and their properties.     

Preparation of nanocrystalline CuAlO<Subscript>2</Subscript> through sol–gel route

Nanocrystalline powders of CuAlO₂ were synthesized through sol–gel method using nitrate-citrate route and also through solid state reaction method. We used a new set of precursor materials for the synthesis of CuAlO₂ through sol–gel route which were not reported in the past. A little lowering of the synthesis temperature (1,000 °C) was observed in case of sol–gel process compared to the solid state reaction method (1,100 °C) and also at shorter time duration. The particle size of the synthesized powders was determined through small angle X-ray scattering. It has been observed that the particle size prepared by nitrate-citrate technique is less than the particle size prepared by the solid-state reaction method. Chemical states of the atomic species were determined by X-ray photoelectron spectroscopy. The formation of phase pure CuAlO₂ were also confirmed by Fourier transformed infrared spectroscopy. A number of solvents were also used for finding the best possible combinations for obtaining phase pure CuAlO₂ at 1,000 °C and it was observed that only the combination of nitrate salts, citric acid and ethanol resulted phase pure CuAlO₂.     

Corrosion resistance of sol–gel alumina coated Mg metal in 3.5 % NaCl solution

Journal of Sol-Gel Science and Technology - This investigation describes the potential of sol–gel derived alumina coating on the corrosion resistance of magnesium metal in 3.5&nbsp;% NaCl...     

First-principles study on the geometries,stabilities and electronic properties of yttrium–silicon clusters (Y2Si n ; 1 ≤ n ≤ 12)

Structural Chemistry - The geometries, growth patterns, relative stabilities and electronic properties of yttrium-doped silicon clusters Y2Si n (n&nbsp;=&nbsp;1–12) are systematically...     

Study of the products of radiation and thermal destruction in the extraction system of 30 vol% TBP–Isopar-M–HNO3

Journal of Radioanalytical and Nuclear Chemistry - The composition of the products of radiation and radiation-thermal destruction of the PUREX extraction organic phase of 30&nbsp;vol% TBP in...     

Electrodeposition of nano-sized nuclei of magnetic Co–Ni alloys onto n-Si (1 0 0)

Nanometer-sized nuclei of Co–Ni alloys were electrodeposited onto n-Si (1 0 0) electrodes from buffered solutions of the metallic ions. The energy levels of the interface Si/(Co(II),Ni(II))_aq were determined from Mott–Schottky plots. Electrodeposition of the alloys occurs by an anomalous mechanism and preferential deposition of Co took place at all the Co(II)/Ni(II) ratios investigated. The morphology and magnetic properties of the nuclei were studied by AFM and MFM, respectively. It is showed that nuclei of height <30 nm and low aspect ratio present a single-domain magnetic behaviour. Larger nuclei depict complex magnetic characteristics, with a progressive built-up of multi-domains.     

Thermodynamics and kinetics of hydrogen absorption–desorption of highly crystalline LaNi<Subscript>5</Subscript>

Lanthanum penta-nickel (LaNi₅) has been considered as potential candidates for hydrogen storage application at room temperature (20 °C). The intermetallic could store more than 1.36 mass % hydrogen. Substantially, work has been done on the hydrogenation–dehydrogenation kinetics and thermodynamics of LaNi₅. It has been reported that the hydrogen storage capacity reduced after single activation due to the deep trap of hydrogen. The kinetics and thermodynamics of trap hydrogen need to be quantified to understand the nature of trap and the required temperature to release the trapped hydrogen. In the current study, thermodynamics and kinetics of hydrogenation–dehydrogenation of high phase purity crystalline LaNi₅ were investigated. Sievert’s apparatus was used to investigate the pressure composition-temperature measurement to find out the cyclic hydrogen storage capacity and the thermodynamic parameters. The thermodynamic data obtained were evaluated using high-pressure differential scanning calorimetric technique. The trap hydrogen and their desorption kinetics were studied using thermogravimetric–thermal analysis–mass spectrometric techniques.     

Thermochemical behaviour of crown ethers in the mixtures of water with organic solvents. Part IX. Effect of base–acid properties of {(1 − x)AN + xH2O} on the solution enthalpy of cyclic ethers in this mixed solvent at T = 298.15 K

The enthalpies of solution of cyclic ethers: 1,4-dioxane, 12-crown-4 and 18-crown-6 in {(1 ? x)AN + xH₂O} have been measured over the whole mole fraction range at T = 298.15 K. Based on the results obtained, the effects of base–acid properties of mixed solvent and the number of –CH₂CH₂– groups in cyclic ethers molecules on the solution enthalpy of cyclic ethers in {(1 ? x)AN + xH₂O} have been analyzed.