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Archive for July 6th, 2012

Synthesis and electrochemical performance of mno2/cnts–embedded carbon nanofibers nanocomposites for supercapacitors

Abstract: MnO2/carbon nanotubes (CNTs)–embedded carbon nanofibers (CNFs) nanocomposites (MnO2/CNTs–CNFs) have been prepared using electrospinning and in situ redox deposition technique. The as-prepared nanocomposites were directly employed as freestanding electrodes to evaluate the electrochemical properties. Results showed that the nanoscopic MnO2 deposits were incorporated uniformly into the CNTs–embedded CNFs network structure, which hold a great promise for high-performance supercapacitor applications. Compared to the pure CNFs substrate, the improved electric conductivity of CNTs–embedded CNFs substrate enabled a better utilization of MnO2 coating, thus resulting in higher specific capacitance (374F/g) and better rate capability (53.4%). Excellent capacitance retention of 94% of the initial capacitance after 1000cycles was achieved on the freestanding MnO2/CNTs–CNFs nanocomposites electrode. The specific capacitance was found to increase significantly with the increase in the electrolyte temperature, which offered an insight into the practical supercapacitor applications. [Copyright &y& Elsevier]

July 6, 2012 Tags: CARBON nanofibers, ELECTROCHEMICAL analysis, MANGANESE compounds -- Synthesis, NANOCOMPOSITES (Materials), OXIDATION-reduction reaction, SUPERCAPACITORS
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Study of a novel cathode tool structure for improving heat removal in electrochemical micro-machining

Abstract: In this paper, the effects of a hollow structure of cathode tool and radial flow of electrolyte on heat removal are studied using COMSOL software. A multi-physics (electrical field, flow field and heat transfer) model, which implement the bilateral interactions with customized PDE, is proposed to simulate the EMM process with a moving cathode tool. The ALE method is used to track the moving interface. The simulations show that the electrolyte flow rate and flushing time are the most important factors for the heat removal. A hollow structure of the cathode tool is proposed to improve the stability of flow rate, which will remove the heat generated during the EMM process effectively. [Copyright &y& Elsevier]

July 6, 2012 Tags: CATHODES, ELECTRIC fields, ELECTROCHEMICAL analysis, ELECTROLYTES, HEAT -- Transmission, MICROELECTROMECHANICAL systems
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Structural developments of artificial graphite scraps in further graphitization and its relationships with discharge capacity

Abstract: Petroleum coke graphite (PCG) and needle coke graphite (NCG) scraps with different aggregate and morphology were selected. The structural developments in the temperature range from 2400°C to 3000°C showed that the graphite crystallites in samples increased faster in the base plane direction (100) compared to that in the vertical direction (002). The crystallite volume of sample NCG is much bigger than the sample PCG under each condition because the former is easier to be graphitized to the latter. The discharge capacity of graphite scrap anode was mainly determined by its crystallite parameters. Although the discharge capacities of samples PCG or NCG were well fitted with their crystallite parameters separately, the correlation coefficients between the capacities and L c, L a and V of all the samples decreased. This is because big differences exist in the parameters of different samples. The discharge capacity of graphite anode still depends strongly on graphitization degree even if additional four needle coke artificial graphite scraps are introduced into the group of samples PCG and NCG. The equation obtained is D =166.9+1.8584× G, in which its correlation coefficient is as high as 0.9744. [Copyright &y& Elsevier]

July 6, 2012 Tags: CHEMICAL equations, CORRELATION (Statistics), CRYSTAL structure, GRAPHITE -- Crystallography, PETROLEUM coke, TEMPERATURE effect
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Stabilization of potassium ferrate cathodic material coated with tetraphenylporphyrin

Abstract: In this paper, K2FeO4 cathodes were coated with tetraphenylporphyrin (TPP) to improve their stability. Analyses involving a scanning electron microscope (SEM), an energy dispersive spectrometer (EDS) and Fourier transform infrared spectroscopy (FT-IR) indicated that the K2FeO4 cathodes were successfully coated with the TPP overlayer. Discharge performance tests were conducted after soaking the cathodes in a 10M KOH electrolyte for 0–6h. The discharge properties of the 8wt% TPP coated K2FeO4 cathodes indicated that they were stable, and their discharge capacity increased to 160mAhg−1 from 75mAhg−1 for the uncoated electrodes after soaking in a 10M KOH electrolyte solution for 6h. In addition, adding 5wt% sodium bismuthate (NaBiO3) to the tetraphenylporphyrin coated K2FeO4 electrode can further improve its discharge performance by increasing the discharge capacity from 275mAhg−1 to 316mAhg−1. [Copyright &y& Elsevier]

July 6, 2012 Tags: CHEMICAL stability, FOURIER transform infrared spectroscopy, METAL coating, POTASSIUM ferrate, SCANNING electron microscopy, TETRAPHENYLPORPHYRIN
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Simultaneous determination of vitamins b2, b9 and c using a heterocyclic conducting polymer modified electrode

Abstract: This paper illustrates the simultaneous determination of riboflavin (RB), ascorbic acid (AA) and folic acid (FA) at physiological pH by electrochemical method for the first time using the electropolymerized film of 3-amino-5-mercapto-1,2,4-triazole modified glassy carbon (p-AMTa) electrode. Bare GC electrode fails to show stable voltammetric signals for AA, RB and FA in a mixture due to the surface fouling caused by the oxidation products of them. In contrary, the p-AMTa electrode shows stable voltammetric signals for RB, AA and FA in a mixture with potential differences of 670mV and 530mV between RB-AA and AA-FA, respectively. Further, the p-AMTa electrode was used to selectively determine either of the vitamins individually in the presence of high concentrations of other two vitamins. When the concentration of RB was increased from 10μM to 90μM, AA was increased from 30μM to 270μM and FA was increased from 20μM to 180μM, the oxidation currents of the respective compounds increased linearly. The detection limit was found to be 4.54×10−8 M for RB, 7.14×10−7 M for AA and 2.5×10−7 M for FA (S/N=3). The practical application of the present modified electrode was demonstrated by determining the concentrations of RB, AA and FA in human plasma samples. [Copyright &y& Elsevier]

July 6, 2012 Tags: ELECTROCHEMICAL analysis, ELECTRODES, ELECTROPOLYMERIZATION, HYDROGEN-ion concentration, SIGNAL detection, VITAMIN B2, VITAMIN C
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Simulation of diffusion-induced stress using reconstructed electrodes particle structures generated by micro/nano-ct

Abstract: Lithium ion batteries experience diffusion-induced stresses during charge and discharge processes which can cause electrode failure in the form of fracture. Previous diffusion-induced stress models and simulations are mainly based on simple active material particle structures, such as spheres and ellipsoids. However, the simple structure model cannot reveal the stress development in a real complex lithium ion battery electrode. In this paper, we studied the diffusion-induced stresses numerically based on a realistic morphology of reconstructed particles during the lithium ion intercalation process. The morphology of negative and positive active materials of a lithium ion battery was determined using X-ray micro/nano computed tomography technology. Diffusion-induced stresses were simulated at different C rates under galvonostatic conditions and compared with spherical particles. The simulation results show that the intercalation stresses of particles depend on their geometric characteristics. The highest von Mises stress and Tresca stress in a real particle are several times higher than the stresses in a spherical particle with the same volume. [Copyright &y& Elsevier]

July 6, 2012 Tags: DIFFUSION, ELECTRODE failures, FRACTURE mechanics, LITHIUM-ion batteries, SIMULATION methods, STRUCTURAL analysis (Engineering)
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Separation of the isomeric long-chain aldehydes dodecanal/2-methylundecanal via layer melt crystallization

Abstract: Melt crystallization is a technically proven and selective separation method for obtaining pure isomeric compounds. Nonetheless, a separation of isomeric long-chain aldehydes has not yet been realized by melt crystallization. Existing methods often use chemical reactions or require additives. In this work, we evaluated the feasibility of the purification of dodecanal from the isomeric long-chain mixture dodecanal/2-methylundecanal (C12H24O) with melt crystallization. For this purpose, the binary solid–liquid equilibrium of dodecanal/2-methylundecanal was measured with differential scanning calorimetry. The liquidus line of the binary system can be calculated using only the melting temperature and the enthalpy of fusion of dodecanal. On the basis of the solid–liquid equilibrium, layer melt crystallization experiments under an inert gas atmosphere were conceived. Depending on the process conditions (feed concentration and cooling rate), the growth rates of the crystalline layer were measured online, and crystal purities were determined as a function of the growth rate and melt concentration. Furthermore, the efficiency of sweating as a finishing treatment was investigated. To model the crystalline layer thickness, a site-specific heat flow balance at the crystal surface and a space- and the time-dependent enthalpy balance of the crystal volume were applied. The model is able to describe the crystallization process adequately, depending on the process parameters. [Copyright &y& Elsevier]

July 6, 2012 Category: Articles No Comments

Sensitivity analysis of the magflow cellular automaton model for lava flow simulation

Abstract: MAGFLOW is a physics-based numerical model for lava flow simulations based on the Cellular Automaton approach that has been successfully used to predict the lava flow paths during the recent eruptions on Mt Etna. We carried out an extensive sensitivity analysis of the physical and rheological parameters that control the evolution function of the automaton and which are measured during eruptive events, in an effort to verify the reliability of the model and improve its applicability to scenario forecasting. The results obtained, which include Sobol” sensitivity indices computed using polynomial chaos expansion, confirm the consistency of MAGFLOW with the underlying physical model and identify water content and solidus temperature as critical parameters for the automaton. Additional tests also indicate that flux rates can have a strong influence on the emplacement of lava flows, and that to obtain more accurate simulations it is better to have continuous monitoring of the effusion rates, even if with moderate errors, rather than sparse accurate measurements. [Copyright &y& Elsevier]

July 6, 2012 Tags: CELLULAR automata, CHAOTIC behavior in systems, COMPUTER simulation, LAVA flows, MATHEMATICAL models, PARAMETER estimation, SENSITIVITY analysis, TEMPERATURE effect
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Scale-up of suspension crystallisers using a predictive model framework

Abstract: The scale-up prediction of the model framework of has been investigated on the basis of experiments at three different scales. The results show that the seeded batch experiments at 2-l scale were not useful for the estimation of a valid kinetic model of the crystallisation process. The model parameters estimated on the basis of a 75-l DT crystalliser data are capable of predicting certain extent the steady state quantiles of an 1100-l DTB crystalliser. However, fine tuning of the model parameters is still needed to get a good description of the final product quality. [Copyright &y& Elsevier]

July 6, 2012 Category: Articles No Comments

Scale-up of microbial processes: impacts, tools and open questions

Abstract: Industrial biotechnological production is developing rapidly worldwide. Consequently, more and novel bioprocesses need to perform optimally not only in small lab- but also in large production scales. This article shortly reviews typical impacts found when cells are exposed to micro environmental heterogeneities typically occurring in poorly mixed large scale production reactors. The current state-of-the-art of tool development is presented for analyzing these phenomena. Finally, still open questions are formulated and needs for future research are outlined to further support the expansion of biotech industries by successful research results. [Copyright &y& Elsevier]

July 6, 2012 Tags: BIOCHEMICAL engineering, BIOMASS, BIOTECHNOLOGY, BIOTECHNOLOGY industries, HETEROGENEITY, INDUSTRIAL microbiology, MICROBIOLOGY -- Cultures & culture media
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