POROUS ELECTRODE THEORY ANALYSIS OF A VARIABLE-DEPTH, FLOW-BY POROUS ELECTRODE

A comparison has been made between a variable-depth and constant-depth, flow-by porous electrode in which a single metal ion deposition occurs in parallel with proton reduction. Porous-electrode theory was applied to calculate the reactor's performance under limiting-current and below limiting-current conditions. The thickness profile of the variable-depth electrode was calculated—as first suggested by Kreysa—by constraining the solution phase potential drop across the electrode to remain constant and independent of streamwise position. For each reactor configuration, identical electrolyte and electrode properties, processing rate, reactant conversion, and inlet thickness were assumed. Under this basis of comparison, the results show: the space-time yield of the constant-depth electrode is larger, but the variable-depth electrode better utilizes the separator's and counterelectrode's surface area; the power requirement of the variable-depth electrode is greater; and, the current efficiency is parameter dependent, but for the majority of the situations likely to be found in wastewater processing, that in the constant-depth electrode is slightly higher. A simple capital-cost analysis shows that the variable-depth electrode may be less expensive if the costs associated with the separator and counterelectrode are greater than those which scale with the electrode volume.     

POROUS ELECTRODE THEORY ANALYSIS OF A VARIABLE-DEPTH, FLOW-BY POROUS ELECTRODE

A comparison has been made between a variable-depth and constant-depth, flow-by porous electrode in which a single metal ion deposition occurs in parallel with proton reduction. Porous-electrode theory was applied lo calculate the reactor's performance under limiting-current and below limiting-current conditions. The thickness profile of the variable-depth electrode was calculated—as first suggested by Kreysa—by constraining the solution phase potential drop across the electrode to remain constant and independent of streamwise position. For each reactor configuration, identical electrolyte and electrode properties, processing rate, reactant conversion, and inlet thickness were assumed. Under this basis of comparison, the results show: the space-time yield of the constant-depth electrode is larger, but the variable-depth electrode better utilizes the separator's and counterelectrode's surface area; the power requirement of the variable-depth electrode is greater; and, the current efficiency is parameter dependent, but for the majority of the situations likely to be found in wastewater processing, that in the constant-depth electrode is slightly higher. A simple capital-cost analysis shows that the variable-depth electrode may be less expensive if the costs associated with the separator and counterelectrode are greater than those which scale with the electrode volume.     

流通型碳纤维电极的电沉积行为

研究了电极构型对流通型碳纤维电极从ＡｕＣｌ－４稀溶液中电沉积金行为的影响．在顺流操作方式下，整个电极能够在极限电流条件下工作，利用电沉积分布曲线计算了传质系数与流速的关系式．逆流方式可以使电沉积分布更为均匀，从而提高整个电极的利用效率．利用数学模型对各种实验曲线进行了模拟，计算结果与实验结果相符．     

OXYGEN REDUCTION IN A CAUSTIC SOLUTION USING A GAS-FED POROUS ELECTRODE

A theoretical model is presented for a Teflon-bonded carbon porous diffusion electrode used for oxygen reduction in alkaline solution. The model is of the flooded agglomerate type and is extended to allow parameter estimation by regression analysis of polarization data. The data presented are for a Teflon-bonded carbon electrode (silver catalyst) tested in a laboratory scale cell using 3.5M (150 kg/m3) sodium hydroxide solution at 348 K with three different oxygen feed mole percents: 10, 20, and 100%. Regression indicates that the diffusion processes in both gas and liquid phases contribute significantly to polarization.     

OXYGEN REDUCTION IN A CAUSTIC SOLUTION USING A GAS-FED POROUS ELECTRODE

A theoretical model is presented for a Teflon-bonded carbon porous diffusion electrode used for oxygen reduction in alkaline solution. The model is of the flooded agglomerate type and is extended to allow parameter estimation by regression analysis of polarization data. The data presented are for a Teflon-bonded carbon electrode (silver catalyst) tested in a laboratory scale cell using 3.5M (150 kg/m3) sodium hydroxide solution at 348 K with three different oxygen feed mole percents: 10, 20, and 100%. Regression indicates that the diffusion processes in both gas and liquid phases contribute significantly to polarization.     

The anodic dissolution of 90% copper-10% nickel alloy in hydrochloric acid solutions

The anodic dissolution of the 90% copper-10% nickel alloy in hydrochloric acid solutions at the rotating disk was found to be controlled by both mass transfer and reaction in the apparent Tafel region. The kinetics of dissolution are similar to those of pure copper for the partial currents due to the dissolution of both the copper and nickel components from the alloy. A mechanism for the dissolution of the alloy is proposed. This mechanism describes the dissolution as being controlled by the dissolution of the copper from the alloy. In the limiting-current region a film of CuCl precipitates on the surface of the electrode. The reaction in the limiting-current region is controlled by mass transfer. A mechanism which describes the precipitation and dissolution of this film, and which describes the diffusion of the chloride to the surface of the electrode is proposed.     

用氧化钇掺杂氧化锆纳米粉末制备用于氧传感器的多孔铂电极(英文)

用厚膜技术制备了用于氧传感器的多孔铂电极。这种多孔铂电极浆料由纳米铂粉、银粉、氧化钇掺杂的氧化锆纳米粉末和有机载体组成。利用场发射扫描电镜研究了浆料的无机成分对烧成的铂电极微结构的影响。研究了组分对铂电极的过电位和传感器电阻的影响。结果表明:由纳米铂粉、银粉和氧化钇掺杂的氧化锆纳米粉组成的铂电极呈现疏松的海绵结构,并且过电位较低;使用同样量的三氧化二铋或硼硅酸玻璃釉代替银粉时,铂电极的电阻明显增加。使用银粉做黏结剂时,铂电极的电阻比使用同样量的三氧化铋或硼硅酸玻璃釉做黏结剂时要低。     

PREPARATION AND ELECTROCHEMICAL PROPERTIES OF NANOSCALE POROUS CARBON ELECTRODE MATERIALS BASED ON RICE PLANT SOOT

Supercapacitors are a kind of novel energy storage devices with long cycle stability and high power density. Electrode materials selection is one of the key factors that affect the properties of supercapacitors. Biomass-derived electrode materials – being low cost, renewable and environmentally friendly – are therefore attracting researchers’ attention. In this work, we adopted a simple process of carbonization and activation with rice plant soot, a common biomass material, as carbon source, and finally obtained the nanoscale porous carbon electrode (NPCE) materials. Then, the electrochemical properties of the as-prepared NPCE materials were tested in 6 M KOH, and the results indicated that the specific capacitance could reach 216?Fg^?1. Therefore, this low-cost, highly efficient technique is a significant milepost towards environmentally sustainable and commercially feasible fabrication of carbon electrode materials from biomass sources.     

The anodic dissolution of copper in hydrochloric acid solutions

The electrodissolution of copper in hydrochloric acid solutions at the rotating ring-disk electrode was found to be controlled by both mass transfer and reaction in the apparent-Tafel region in HCl concentrations of between 0.1 and 1.0 M. The proposed mechanism describes the adsorption of CuCl_ads on the corroding copper surface and the diffusion of CuCl⁻₂ from the copper surface. The reaction in the limiting-current region was found to be controlled by the diffusion of Cl⁻ to the copper surface through a porous CuCl layer that forms on the surface. The thickness of this porous layer is dependent on the stirring conditions, and independent of the Cl⁻ concentration. Cu²⁺ is also produced at the Cu surface during electrodissolution. A mechanism describing the formation of a porous film of CuCl on the surface, the diffusion of Cl⁻ through this film and the formation of Cu²⁺ has been proposed.     

TWO-SIDED DRYING OF COATINGS ON POROUS WEBS

ABSTRACT

A relatively simple spreadsheet-based model of the drying of coated webs has been extended to cover coatings on porous webs Two cases have been modeled. In one the coating is assumed to fully saturate the porous web, with the drying being completely symmetrical about the center plane except for differences in the air velocities and temperatures. The drying rate in the constant rate period is then increased, but because of the greater thickness that the coating now occupies, diffusion is much slower and the falling rate drying can be slower, even though it takes place on both sides. In the other case the coating is assumed to lie on top of the porous web, with solvent vapor diffusing through the web. Here the constant rate drying is only slightly faster than in the base case, but in the falling rate period the drying can be greatly accelerated Both models predict the temperatures and solvent levels throughout the length of the dryer.     

Simultaneous reactions at disk and porous electrodes

Advances in electrochemical engineering are reviewed, and the methodology of the analysis of electrochemical systems is outlined. Examples illustrative of current research concern simultaneous reactions for flow-through porous electrodes and the more fundamental system of a rotating disk electrode. Here the undesirable side reaction is the formation of dissolved hydrogen, and the main reaction is the deposition of copper from sulfuric acid solutions. Distributions of reaction rate, concentration, and potential describe the detailed system behavior. The side reaction is responsible for the poorly defined limiting-current plateau on the disk electrode and provides a limit for the maximum flow rate at which good recovery can be achieved with the porous electrode.     

TWO-SIDED DRYING OF COATINGS ON POROUS WEBS

A relatively simple spreadsheet-based model of the drying of coated webs has been extended to cover coatings on porous webs Two cases have been modeled. In one the coating is assumed to fully saturate the porous web, with the drying being completely symmetrical about the center plane except for differences in the air velocities and temperatures. The drying rate in the constant rate period is then increased, but because of the greater thickness that the coating now occupies, diffusion is much slower and the falling rate drying can be slower, even though it takes place on both sides. In the other case the coating is assumed to lie on top of the porous web, with solvent vapor diffusing through the web. Here the constant rate drying is only slightly faster than in the base case, but in the falling rate period the drying can be greatly accelerated Both models predict the temperatures and solvent levels throughout the length of the dryer.     

土壤腐蚀测试的一种新型电极

设计了一种用于土壤体系腐蚀测试，参比／研究电极为平面同心同材料结构的新型三电极体系。这一电极体系能很好地克服自腐蚀电位漂移的影响和有效降低ＩＲ降，为土壤体系的腐蚀测试提供了一种可靠的电极体系。     

Performance relationships in PVC–plasticizer dry blending

The phenomenon of plasticizer acceptance by poly(vinyl chloride) (PVC) in hotprocess dry blending is examined via scanning electron microscopy, mercury intrusion porosimetry, and torque rheometer measurements. The effects of granule porosity, resin molecular weight, and synthesis recipe in PVC manufacture by the suspension process are related to the rate of plasticizer acceptance. For a PVC resin to dry blend, i.e., to become a free-flowing powder when mixed with plasticizer under hot-processing conditions, the resin granules must be porous. Porosity arises from interstices between primary PVC particles. At a given granule porosity, an increase in primary particle agglomeration adversely affects dry blend performance. At constant molecular weight and for resins manufactured by a given recipe, dry-blend performance is quantitatively described by granule porosity. With an increase in resin molecular weight, a greater granule porosity is required to maintain an equivalent dry-blend time (DBT). Accordingly, for most suspending agent recipes, DBT is dependent directly upon granule porosity and inversely upon molecular weight. However, if the suspending agent used in resin manufacture is an excessively rapid film former, dry-blend performance with molecular weight variation is dependent upon the suspending agent's concentration, not upon granule porosity, which must be adequate, nor upon the resin's molecular weight. An interfacial film-forming suspending agent enhances fusion of primary PVC particles at the suspension granule—water interface, increasing the granule's “pericellular membrane” thickness. This membrane, a PVC skin, does not significantly influence dry-blend performance with low- or intermediate-viscosity plasticizers. The particle skin does impede dry-blend rates with high-viscosity, poorly solvating plasticizers, but this effect can be negated in part by increasing the diameter of pore openings in the topographical skin. Dry blending occurs below the glass transition temperature (T_g) of PVC with low-viscosity plasticizers and above the T_g with high-viscosity, poorly solvating modifiers. The influence of resin and plasticizer variables indicates the dry-blend phenomenon to be a diffusion-controlled process. The rate of dry blending is dependent upon two mechanisms: (1) the rate of pore penetration—which exposes the plasticizer to a much greater surface area than if it remained exterior, encapsulating the granule—and (2) the rate of plasticizer diffusion into the PVC matrix.     

Electron transfer reactions at film covered metal electrodes

Experimental results concerning the kinetics of electron-transfer reactions at metal electrodes covered by anodic oxide films are discussed and compared to predictions from the theory. The rate equations used in the comparison are presented assuming a n-type semiconducting film. Semi-quantitative agreement between experiment and theory is observed.At electrodes covered by very thin films, direct electron exchange between the metal and the electrolyte predominates. The exchange cd drops exponentially with film thickness. For thicknesses greater than a few nm, electron exchange preferentially occurs with the oxide film even for oxides having a large band gap. The transfer coefficients then depend on electrode potential in an often non-monotonous way, and the rate is independent of thickness.The examples of oxide covered niobium and titanium are discussed in detail considering the influences of donor density and structure of the oxide, of the potential distribution at the semiconductor—electrolyte interface, and of the reorganization energy of the redox system.     

不同Br~-浓度下铂电极上镀银层的氧化动力学

本文采用循环伏安法研究了镀银铂电极在溴化钾溶液中的成核过程及氧化动力学,结果表明:AgBr的形成包括三个步骤,首先在银表面某些吸附Br~-的特殊位置上以平面方式成核,然后经过二个三维的成核步骤。在较低浓度的KBr溶液中,AgBr的形成由溶液中的Br~-迁移控制。在较高浓度的溶液中,由于生成的AgBr膜是高度松散的,速度控制步骤转化为在膜孔内Br~-的迁移。随着AgBr的生成以及AgBr的溶解沉积作用,膜孔被堵塞,同时反应速度转化为由AgBr膜中的Ag~+迁移控制。电镜结果也支持了以上结论。     

SINGLE FLUID FLOW IN POROUS MEDIA

A comprehensive study on single fluid flow in porous media is carried out. The volume averaging technique is applied to derive the governing flow equations. Additional terms appear in the averaged governed equations related to porosity ε, tortuosity τ, shear factor F and hydraulic dispersivity D _h. These four parameters are uniquely contained in the volume averaged Navier-Stokes equation and not all of them are independent. The tortuosity can be related to porosity through the Brudgemann equation, for example, for unconsolidated porous media.

The shear factor models are reviewed and some new results are obtained concerning high porosity cases and for turbulent flows. It is known that there are four regions of flow in porous media: pre-Darcy's flow, Darcy's flow, Forchheimer flow and turbulent flow. The transitions between these regions arc smooth. The first region, the pre-Darcy's flow region represents the surface-interactive flows and hence is strongly dependent on the porous media and the flowing fluid. The other flow regions are governed by the flow strength of inertia. For Darcy's flow, the pressure gradient is found to be proportional to the flow rate. The Forchheimer flow, however, is identified by a strong inertia! effects and the pressure gradient is a parabolic function of flow rate. Turbulent flow is unstable and unsteady flow characterized by chaotic flow patterns. The pressure drop is slightly lower than that predicted using the laminar flow equation.

The hydraulic dispersivity is a property of the porous media. It may be considered as the connectivity of the pores in a porous medium. It characterizes the dispersion of mementum, heat and mass transfer. In this paper, only the dispersion of momentum is studied.

Single fluid flow through cylindrical beds of fibrous mats and spherical particles has been used to show how to solve the single fluid flow problems in porous media utilizing the knowledge developed in this communication. Both the pressure drop and axial flow velocity profiles are computed using the developed shear factor and hydraulic dispersion models. Both the predicted velocity profile and pressure drop compare fairly well with the published experimental data.     

Novel variations in the microstructure of the auxetic microporous ultra‐high molecular weight polyethylene. Part 1: Processing and microstructure

Recent publications have detailed how auxetic (negative Poisson's ratio) polymers have been fabricated by a novel thermal processing route consisting of three welldefined stages—compaction, sintering and extrusion. In this paper, the compaction stage of the processing route is omitted and the effects of this on the structural integrity, microstructure and Poisson's ratios of the extrudates examined. The effects of varying the processing parameters of the sintering and extrusion stages are studied so that a set of conditions that produce a highly fibrillar auxetic material with sufficient structural integrity to allow mechanical properties to be evaluated can be defined. Poisson's ratios as low as ?4 have been obtained.     

国产宏特针状焦生产Φ350mm超高功率石墨电极

以国产针状宏特焦为原料采用传统生产流程及国际标准流程生产Φ350mm超高功率石墨电极,并对其生产过程中的工艺进行控制。结果表明,用国产宏特针状焦为原料采用国际标准流程生产Φ350mm超高功率石墨电极,理化指标完全达到用新日铁针状焦为原料生产Φ350mm超高功率石墨电极等同类产品,通过钢厂试用,其抗热震性能、抗氧化性能、消耗性能较好,能完全满足用户的使用要求;同时实现超高功率石墨电极国际标准流程,进一步降低生产成本。     

Theory of porous electrodes—XVI. The nickel hydroxide electrode

A model of the positive plate of a nickel—cadmium accumulator is proposed, based on the known electrochemical behaviour of hydrated nickel oxides and on transport equations similar to those used previously for the cadmium electrode. The mathematical treatment of this model allows to predict the theoretical discharge characteristics, which are compared with those measured on a real electrode. A comparison of the calculated and measured discharge time suggests that the composition of the oxidised form is intermediate between NiO_1.5 and NiO_1.8.