锂离子蓄电池正极材料LiFePO4研究进展

锂离子电池正极材料正在向着高比能量、长寿命、低成本、环境友好的方向发展，而具有橄榄石结构的LiFePO4正极材料以其结构稳定、成本低、无污染等优点成为21世纪最理想的绿色电源，但自身也存在缺点。综述了锂离子电池正极材料LiFePO4的研究进展。系统地阐述了LiFePO4的晶体结构特征及性能、多种合成方法以及掺杂多种导电材料和控制晶体生长制备纳米粉体对材料性能的影响。对该材料的应用前景进行了展望，并提出了下一步可能的研究趋势。     

Low temperature crystallization behavior of TiO<Subscript>2</Subscript> derived from a sol–gel process

TiO₂ nanoparticles are widely used for many applications and an understanding of the crystallization behavior of TiO₂ is essential, so that heat treatment conditions can be optimized for particular applications. The effect of sol–gel synthesis conditions on the crystallization behavior of TiO₂ has, therefore, been investigated. Complete crystallization to the anatase phase (determined by XRD and TEM analysis) was achieved during drying of the synthesis product at 95 °C. The nanoparticles grew during heat treatment, reaching ∼10–15 nm in diameter with a heat treatment at 450 °C. Explanations are offered for the observed differences in the crystallization and particle growth behavior of TiO₂ synthesized under various conditions.     

Fe mineralogy of rocks from the Vredefort impact structure investigated with Mössbauer spectroscopy

The Vredefort impact structure in South Africa is the largest and oldest remnant impact structure on Earth. Observations from above the crater reveal lower than average magnetic field intensities, but the rocks in the crater have been shown to possess much higher magnetic intensities than the regional average that varies on a centimeter scale. Various mechanisms, including the presence of single domain magnetite structures, have been proposed for this anomaly. Mössbauer spectroscopy has been applied to study the Fe-mineralogy of samples from near the centre of the Vredefort crater. Transmission Mössbauer measurements on bulk and microtomics sections of samples showed that the magnetic minerals were magnetite and hematite, and we suggest that oxidation of olivine during the impact is responsible for the magnetic properties of the rocks.     

Control of Aharonov–Bohm oscillations in a AlGaAs/GaAs ring by asymmetric and symmetric gate biasing

The control of the Aharonov–Bohm effect on a AlGaAs/GaAs ring structure is studied by employing two in-plane-gates. By applying a gate voltage to one of the gates, a change of the oscillation pattern due to the additional potential induced in one branch of the ring is observed. The change of the oscillation frequency as well as the phase is attributed to the multi-channel transport. In case of a symmetric biasing, where both gates are biased simultaneously, a larger voltage is required to change the oscillation pattern than for the case when only one gate is used. This effect is explained by a partial compensation of the phase difference between both branches of the ring.     

Determination of flunitrazepam and nitrazepam in beverage samples by liquid chromatography with dual electrode detection using a carbon fibre veil electrode

Both nitrazepam and flunitrazepam have been determined by high-performance liquid chromatography dual electrode detection (LC-DED) in the reductive–reductive mode, using a carbon fibre veil electrode (CFVE) in conjugation with a glassy carbon electrode. Initial studies were made to optimise the chromatographic conditions. These were found to be 45% acetonitrile-55% acetate buffer (50 mM, pH 4.1) at a flow rate of 1.0 ml/min, employing a Hypersil C18, 5 μm, 250 mm × 4.6 mm column. Cyclic voltammetric studies performed to ascertain the redox behaviour of nitrazepam and flunitrazepam at a CFVE in the optimised mobile phase. Studies showed that similar voltammetric behaviour was obtained to that report at Hg or glassy carbon based electrodes. Further studies were then carried out to identify the optimum conditions required for the LC-DED determination of nitrazepam and flunitrazepam in beverage samples. Hydrodynamic voltammetry was used to optimise the applied potential at the generator and detector cells; these were identified to be −2.40 and −0.25 V, respectively. A linear range of 2.0 to 100 μg ml⁻¹, with a detection limit of 20 ng ml⁻¹ was obtained. A convenient and rapid method for the determination of both nitrazepam and flunitrazepam in beverage sample was developed. Following a simple sample extraction procedure, extracts were examined using the optimised LC-DED procedure. An average percentage recovery of 95.5% (%CV = 4.5%) for nitrazepam and 78.0% (%CV = 8.8%) was achieved for a sample of “Pepsi Max” spiked at 1.0 μg ml⁻¹ nitrazepam, 1.47 μg ml⁻¹ flunitrazepam. Presented at the 4th Annual Meeting of the Great Western Electrochemistry Group, 8th June 2005, University of the West of England, Bristol, UK.     

Susceptibility to basal cell carcinoma is associated with high dermal mast cell prevalence in non-sun-exposed skin for an Australian populations

In a Danish population, basal cell carcinoma (BCC) patients have a higher dermal mast cell prevalence in buttock skin than controls. This finding was supported by a functional link in mice between histamine-staining dermal mast cells and the extent of susceptibility to UV-B-induced systemic immunomodulation. It was important to confirm that this association was maintained in an Australian population with very different ancestry and sun exposure patterns. Australian BCC patients (n = 26) had significantly higher densities of mast cells in the dermis of buttock skin than control subjects (n = 25) (P = 0.0003, Mann-Whitney U-test). However, this correlation was lost at the sun-exposed site of the hand (P = 0.547, Mann-Whitney U-test). To further evaluate whether a relationship exists between dermal mast cell prevalence in sun-exposed skin and incidence of BCC in a larger study, biopsies of dorsal hand skin were obtained from an age-stratified random sample of 166 Queensland subjects, together with the 51 South Australian subjects, and dermal mast cell prevalence was quantified. Older subjects (over the median age of 42 years) had a greater incidence of BCC development (P = 0.0001, chi-square test) and significantly higher mast cell densities in hand skin (P = 0.0001, chi-square test) than younger subjects. However, mast cell density in sun-exposed hand skin was not significantly associated with BCC incidence. Finally, cellular expression of c-kit correlated with mast cell prevalence in non-sun-exposed skin, thereby implicating the stem cell factor-c-kit axis in the intrinsic mechanisms that regulate prevalence. These results show that high prevalence of dermal mast cells in buttock skin but not hand is associated with BCC development in an Australian population.     

Development of algorithms for automated elucidation of spectral feature/substructure relationships in tandem mass spectrometry

A pattern-recognition/artificial-intelligence program, referred to as MAPS (method for analyzing patterns in spectra), is described for the identification of relationships that exist between the presence of substructures in molecules and the characteristic features they produce in mass spectrometry (MS) and MS/MS data. The MAPS algorithm discovers these relationships by intelligent analysis of a data base of MS and MS/MS spectra. The relationships found are expressed as rules, which may then be used to identify characterized substructures in “unknowns”. No prior knowledge of fragmentation pathways or rearrangements is assumed in the rule-generation process. While MAPS currently uses MS and MS/MS data, the approach (and much of the software) is equally suited to multiple-stage mass spectrometric data.     

Measurement of thiol-containing amino acids and phytochelatin (PC2) via capillary electrophoresis with laser-induced fluorescence detection

An analytical method for determining thiols and phytochelatins using high-performance capillary electrophoresis coupled with laser-induced fluorescence detection is presented. The technique utilizes the labeling of thiols with the fluorescent reagent 5-bromomethylfluorescein (5-BMF), which is excited by a 488 nm argon ion laser and fluoresces at 515 nm. The paper describes the determination of the optimal conditions for reaction of 5-BMF with thiols as well as the parameters for electrophoresis runs that produce optimal electropherogram peaks. The technique is shown to be very sensitive for cysteine, cysteinyl-glycine, gamma-glutamyl-cysteine, glutathione and (gamma-glutamylcysteinyl)2-glycine (PC2). Concentrations as low as 25 nmol/L and amounts as low as 1 fmol were detected for glutathione. Sensitivity for detection of PC2 was somewhat lower. The method was shown to be simple, rapid and accurate and should facilitate measurement of thiol-containing amino acids, peptides and phytochelatin (PC2) in small volumes of extracts obtained from biological tissue.