C K‐edge NEXAFS study of fluorocarbon formation on carbon anodes in molten NaF–AlF3–CaF2

Operational instability from processes occurring at the anode during the production of aluminum in the commercial Hall‐Héroult process may lead to an increase in undesirable fluorocarbon emissions, higher energy use, and shorter plant life. One contribution to this instability may be the possible formation of a fluorocarbon film at the electrode interface. Here, the surface composition of graphite anodes after electrolysis in molten NaF–AlF₃–CaF₂ at 990 °C is investigated for evidence of fluorocarbon formation using C K‐edge near edge X‐ray absorption fine structure. Fluorocarbon is identified on an anode surface after prolonged anode effect (very high overpotential with increased cell resistance) and also on an anode surface after normal electrolysis without anode effect. This provides evidence that fluorocarbon formation may occur prior to anode effect lowering the surface tension of the anode and therefore resulting in dewetting to contribute to the onset of the anode effect. Confirmation that such compounds form furthers our understanding of electrochemical reactions of graphite with fluoride and of the fundamental processes that occur in an aluminum smelter cell. Copyright © 2013 John Wiley & Sons, Ltd.     

Corrugated single-layer graphite sheet as a model of stepped surface of a crystal

Electronic structure calculations have been performed for flat graphite sheets and periodically distorted sheets with different values of deformation angle and hydrogen adsorption. These characteristics do not all behave monotonically with increasing deformation angle. At small deformation angles, the electrons pass from the atoms of terraces to those of edges, while at larger angles the reverse pattern is observed. The position of the Fermi level also varies nonmonotonically. The binding energy of hydrogen depends significantly on the adsorption site, and the difference can be doubled. Based on the ata obtained, it was concluded that a priori statements derived from the “general concepts” on the difference in the physicochemical properties of, for example, terrace and edge atoms on high-index facets are unreliable.     

蒙脱石-石墨-聚氯乙烯复合电极测定制药废水中苯酚

报道了当制药废水PH8．0时，用蒙脱石－石墨－聚氯乙烯复合电极可以直接测定苯酚的含量而不受水杨酸存在的干扰，苯酚浓度在1．0μg/mL-25.0μg/mL范围内峰电流与浓度有良好的线性关系，I＝1．262c-0.046，相关系数r=0.998，检出限为0．1μg/mL，用该方法测定模拟制药废水中苯酚，其平均回收率为101．7％。     

抗癌药物的电化学研究(Ⅱ)道诺霉素在DNA修饰石墨粉末微电极上的电化学行为及分析应用

研究了道诺霉素 ( DNM)在石墨粉末微电极和 DNA修饰石墨粉末微电极上的电化学行为 ,并分析了产生差别的原因。在此基础上 ,提出了测定微量 DNM的方法 ,DNM浓度在 1 .0× 1 0 - 7～ 1 .0× 1 0 - 5mol/L之间其微分脉冲伏安 ( DPV)峰电流与浓度有良好的线性关系 ,检出限为 5 .0× 1 0 - 8mol/L。采用标准加入法测定了模拟样品中的 DNM,回收率在 94%～ 1 0 8%之间 ,结果令人满意     

Microstructure and surface roughness of graphite‐like carbon films deposited on silicon substrate by molecular dynamic simulation

Molecular dynamics simulations are performed on the atomic origin of the growth process of graphite‐like carbon film on silicon substrate. The microstructure, mass density, and internal stress of as‐deposited films are investigated systematically. A strong energy dependence of microstructure and stress is revealed by varying the impact energy of the incident atoms (in the range 1–120 eV). As the impact energy is increased, the film internal stress converts from tensile stress to compressive stress, which is in agreement with the experimental results, and the bonding of C‐Si in the film is also increased for more substrate atoms are sputtered into the grown film. At the incident energy 40 eV, a densification of the deposited material is observed and the properties such as density, sp³ fraction, and compressive stress all reach their maximums. In addition, the effect of impact energy on the surface roughness is also studied. The surface morphology of the film exhibits different characteristics with different incident energy. When the energy is low (<40 eV), the surface roughness is reduced with the increasing of incident energy, and it reaches the minimum at 50 eV. Copyright © 2012 John Wiley & Sons, Ltd.     

The Determination Of Thallium In Human Hair By Graphite Furnace Atomic Absorption Spectrophotometry

Abstract

An atomic absorption spectrophotometric procedure is des-scribed for the rapid determination of thallium in human hair. Samples of 500 μg are dissolved in nitric acid and treated with hydrogen peroxide. Aliquots of 10 μL are then analyzed using electrothermal atomization in a graphite tube furnace. The characteristic concentration for the method is 1 mg Tl kg^?1 which is adequate for forensic investigation. The relative standard deviation for a series of signals from a hair sample spiked to contain 32 mg Tl^?1 kg was 3 per cent.     

A Simple and Fast Method for Manganese Determination in Antihypertensive Drugs by Slurry Sampling Graphite Furnace Atomic Absorption Spectrometry

Abstract

A simple and rapid procedure for the determination of manganese in anti‐hypertensive drugs is proposed. The samples were treated with dilute nitric acid (1.2% v/v) with stirring using a vortex stirrer to yield a slurry. To determine the best conditions for analysis by graphite furnace atomic absorption spectrometry (GF AAS), a planning factorial was initially employed that demonstrated that the non‐use of chemical modifiers and the use of lower pyrolysis temperatures were more appropriate. Next, the pyrolysis and atomization temperature curves were obtained. The best pyrolysis and atomization temperatures encountered were 500 and 2200°C, respectively. Calibration was performed by matrix matching. The characteristic mass was 0.70±0.14 pg (the recommended mass was 0.60 pg); the limits of detection and quantification were 0.23 and 0.77 µg l^?1, respectively. The precision obtained in the intra‐ and inter‐assay studies of the drug spiked with 0.5, 1.0 and 1.5 µg l^?1 of Mn did not exceed 11% (n=7). Recovery studies of the drug spiked with three levels (n=7) of Mn yielded results between 101.0±4.5 and 116.3±9.7%. The results of an analysis of a certified urine sample (two levels of Mn) agreed at a 95% level of confidence. Forty‐eight antihypertensive drug samples were analyzed, and the results varied from 2.9 ng to 1.9 µg of Mn per capsule^?1.     

Kinetics of Central Ion Electroreduction in Cerium (IV)-Decatungstate

A general characteristics is given to the kinetics of electroreduction of cerium-decatugstate anions on mercury, polycrystalline gold, and the pyrolytic-graphite basis plane in acetate buffer solutions (pH 3.5-6.0). Based on the analysis of UV absorption spectra, the ratio of two reactant forms differing in the protonation degree in solutions under study is estimated. At a negatively charged mercury electrode, the reduction of the Ce(IV) central ion is shown to proceed as an outer-sphere process with classical manifestations of the psi-prime effect (polarization curves reveal a current minimum which deepens with supporting electrolyte dilution and an increase in the reactant negative charge). On the positively charged surface, the current is observed to increase with an increase in the supporting electrolyte concentration, which is interpreted in terms of the strong adsorption of the reactant and its coadsorption with cations. The gold electrode demonstrates pronounced effects of strong chemisorption. Adsorption complications observed on pyrolytic graphite are shown to become strongther for surfaces with more pronounced nonideal behavior. For low concentrations of atomar steps (apparently, for low coverages of pyrolytic-graphite surface with the adsorbed reactant), the quasireversible electron transfer with the rate increasing with increasing pH is observed.     

高效石墨浮选剂的合成

高效石墨浮选剂的合成金婵，薛玉，汪进，刘欣荣，秦英海（哈尔滨工业大学应用化学系哈尔滨１５０００１）（大庆石化总公司大庆）关键词石墨，浮选剂，合成，混合烃由于石墨具有良好的力学性能、导电、高熔点等性质，广泛用于原子能、宇航和民用工业。隐晶质石墨属于微晶...     

A Comparison of Electron Transfer Kinetics of Three Common Carbon Electrode Surfaces in Acetonitrile and in Room Temperature Ionic Liquid 1‐Butyl‐3‐Methylimidiazonium Hexafluorophosphate: Correlation to Surface Structure and the Limit of the Diffusion Domain Approximation

We report the comparison of electron transfer kinetic parameters of the ferrocene redox couple in both acetonitrile and in room temperature ionic liquid (RTIL) 1‐butyl‐3‐methylimidiazonium hexafluorophosphate ([C₄mim] [PF₆]), using edge plane pyrolytic graphite (EPPG), basal plane pyrolytic graphite (BPPG) and glassy carbon (GC) electrodes. Each electrode surface was characterized using SEM and AFM and the surface morphology was analyzed in terms of surface heterogeneity including the distribution of edge plane defects. The experimental data were modeled using both one and two dimensional simulations to correlate the electron transfer parameters obtained with the different surface structure of each electrode. Furthermore, we show that the diffusion domain approximation (commonly used to accurately simulate electron transfer kinetics at graphitic surfaces) breaks down when a BPPG electrode is used in RTIL and demonstrate the near impossibility of assigning rate constant to the basal plane surface.