Potentiodynamic examination of electrode kinetics for electroactive adsorbed species: applications to the reduction of noble metal surface oxides

1969 ◽  
Vol 310 (1503) ◽  
pp. 541-563 ◽  
Keyword(s):  
Noble Metals ◽  
Reaction Rate ◽  
Substrate Surface ◽  
Intrinsic Property ◽  
Surface Heterogeneity ◽  
Surface Oxide ◽  
Rate Equations ◽  
Quasi Equilibrium ◽  
Linear Potential ◽  
Reaction Velocity

The relation between reaction rate and potential (or time) for electrochemical surface processes occurring under potentiodynamic control (linear potential-time programme) has been investigated with particular reference to the behaviour of thin surface oxide films on noble metals. The kinetics of processes involving adsorbed electroactive species are treated for several model cases; the rate equations are developed for mechanisms involving various reaction orders or for processes involving adsorbed reactant interactions and surface heterogeneity effects. By examination of the dependence of the reaction rate (current) with time and the effect of potential scan rate, v , on the maximum reaction velocity and the potential at which it occurs, the models may be distinguished. In this manner, the inter­dependence of v and the reaction velocity constants k a and k c for the anodic oxidation and the cathodic reduction processes respectively, can be quantitatively established. The relation between quasi-equilibrium situations where the reverse reaction is significant and irreversible situations where it is not can be demonstrated. Heterogeneity terms introduced into the kinetic relations express deviations from Langmuir adsorption behaviour and may be an intrinsic property of the substrate surface or a property of the adsorbed reactant (induced heterogeneity). Applications of the treatment are made to reduction of surface oxide species at the noble metals and the significance of hysteresis and time effects in the processes of electrochemical formation and reduction of surface oxide at platinum, rhodium, iridium and palladium is investigated.

Kinetic Studies on the Synthesis of Hydroxyapatite Nanowires by Solvothermal Methods

2007 ◽  
Vol 60 (2) ◽  
pp. 99 ◽  
Author(s):  
Shiying Zhang ◽  
Chen Lai ◽  
Kun Wei ◽  
Yingjun Wang
Keyword(s):  
Activation Energy ◽  
Reaction Rate ◽  
Kinetic Studies ◽  
Axial Ratio ◽  
Reaction Rate Constant ◽  
Rate Equations ◽  
Solvothermal Reaction ◽  
Growth Order ◽  
Constant Diffusion ◽  
Solvothermal Methods

Hydroxyapatite nanowires with a high axial ratio have been synthesized in reverse micelle solutions that consist of cetyltrimethylammonium bromide (CTAB), n-pentanol, cyclohexane, and the reactant solution by solvothermal methods. This paper focusses on the kinetic studies of the solvothermal reaction and the linear growth of hydroxyapatite nanowires. When the reaction was carried out at low temperatures (65°C), the experimental results showed that the reaction rate was of zero order since the whole reaction was diffusion controlled with constant diffusion coefficients. In the middle to high temperature range (130–200°C), the kinetics were characterized by second order reaction kinetics. Since the controlling factor was activation energy and the apparent activation energy was large, the reaction rate was more sensitive to the temperature. Therefore, the exponent of the reaction rate constant increased by two when the temperature was increased from 130 to 200°C. By calculating the yields of products and the specific surface areas at different times, the linear and overall growth rate equations of the hydroxyapatite nanowires could be obtained. The experimental effective growth order of the crystals was 11. The larger growth order indicated that the crystal could grow more effectively in one direction because of the induction of the surfactant in the experiment system.

scholarly journals An investigation of the combustion of platinum

1929 ◽  
Vol 123 (791) ◽  
pp. 202-216 ◽  
Keyword(s):  
Metal Surface ◽  
Electron Emission ◽  
Reaction Rate ◽  
Surface Combustion ◽  
Reaction Velocity ◽  
Combustion Of Gases ◽  
Work Functions ◽  
Humphry Davy ◽  
Products Of Reaction ◽  
Low Pressures

The attack of metal surfaces by gases at low pressures under conditions suet that the products of reaction volatilise too rapidly to affect the reaction velocity is one of the simplest heterogeneous actions and presents many analogies to a simple catalytic action at a surface. Langmuir studied the rate of attack of tungsten by oxygen under these conditions and in this communication the interaction of platinum with oxygen is described. This element was chosen, not only on account of the importance of reactions involving the "clean up" of gases in contact with hot filaments, but also because the electron work functions of both tungsten and platinum are known, so that their relation ship to the reaction rate could be studied. That some connection may exist between the reactivity of a surface and the ease of electron emission has been suggested previously and is to be noted particularly in the investigations of Sir Humphry Davy on the oxidation on zinc and copper, of Langmuir, and of Thompson, Bone, Thomas, and Brine on the surface combustion of gases. From a somewhat different standpoint others, notably Brewer, and Finch and Stimson, suggest that surface reactions take place only after formation of ions on the surface has occurred, the former postulating that ions are formed by molecules entering the intrinsic field of the metal surface and react only after emergence from the field.

Modeling of Gas Turbine Combustors—A Convenient Reaction Rate Equation

1972 ◽  
Vol 94 (3) ◽  
pp. 173-180 ◽  
Author(s):  
D. Kretschmer ◽  
J. Odgers
Keyword(s):  
Rate Equation ◽  
Reaction Rate ◽  
Reaction Order ◽  
Bimolecular Reaction ◽  
Rate Equations ◽  
Combustion System ◽  
Wide Range ◽  
Simple Mass ◽  
Rich Mixtures ◽  
Reaction Rate Equation

In order to model a practical combustion system successfully, it is necessary to develop one or more reaction rate equations which will describe performance over a wide range of conditions. The equations should be kept as simple as possible and commensurate with the accuracy needed. In this paper a bimolecular reaction is assumed, based upon a simple mass balance. Temperatures derived from the latter are related to measured practical ones such that, if required, an evaluation of the partly burned product composition can be made. A convenient reaction rate equation is given which describes a wide range of blow-out data for spherical reactors at weak mixture conditions. NVP2φ={1.29×1010(m+1)[5(1−yε)]φ[φ−yε]φe−C/(Ti+εΔT)}/{0.082062φyε[5(m+1)+φ+yε]2φ[Ti+εΔT]2φ−0.5} Analysis of the components used in the above equation (especially the variation of activation energy) clearly shows its empirical nature but does not detract from its engineering value. Rich mixtures are considered also, but lack of data precludes a reliable analysis. One of the major results obtained is the variation of the reaction order (n) with equivalence ratio (φ): weak mixtures, n = 2φ; rich mixtures, n = 2/φ. Some support for this variation has been noticed in published literature of other workers.

Tunneling Injection Quantum-Dot Lasers

2005 ◽  
Vol 891 ◽  
Author(s):  
Shun Lien Chuang ◽  
Jungho Kim ◽  
Peter K. Kondratko ◽  
Gabriel Walter ◽  
Nick Holonyak ◽  
...  
Keyword(s):  
Quantum Dot ◽  
Injection Current ◽  
Stimulated Emission ◽  
Rate Equations ◽  
Quasi Equilibrium ◽  
Modal Gain ◽  
Gain Narrowing ◽  
Tunneling Injection ◽  
Gain Spectra ◽  
Evolution Behavior

ABSTRACTWe investigate a tunneling injection InP quantum-dot (QD) laser theoretically and experimentally. The device consists of a single compressively strained InP QD layer coupled closely to two tensile strained InGaP quantum wells (QWs). While most tensile strained QW lasers in this wavelength (red) range lase in the transverse-magnetic (TM) polarization, our QD laser lases in the transverse-electric (TE) polarization from the first excited state of the compressively strained QDs, which is coupled to the ground state of the tensile-strained InGaP QWs. When we measure TE and TM modal gain spectra, a typical QW gain evolution behavior is observed at low injection currents, which can be theoretically explained by the quasi-equilibrium of carrier distribution. When the injection current is increased near threshold, a TE gain narrowing and a simultaneous TM gain pinning are observed in the measured modal gain spectra, which cannot be explained via the quasi-equilibrium model. We propose a polarization-dependent photon-mediated carrier re-distribution in the QD-coupled-QW structure to explain this TE and TM gain evolution behavior. When the injection current is just below threshold, the strong carrier depletion via stimulated emission due to coupling between the InP QD and InGaP QW states plays an important role in carrier re-distribution, which depends on the optical transition energy and polarization. This polarization-dependent photon-mediated carrier re-distribution explains the TE gain narrowing and TM gain pinning behavior. To quantitatively demonstrate the photon-mediated carrier re-distribution near the threshold current, a set of coupled rate equations are solved taking into account the polarization-dependent stimulated emission processes. The calculated polarization power ratio based on the coupled rate equations explains the experimental observations.

The Dynamic and Leaching Study of Gold in Treated Sludge from Nonferrous Metal Smelting Waste Water

2011 ◽  
Vol 281 ◽  
pp. 228-232
Author(s):  
Hong Liang Guan ◽  
Xun Min Yu ◽  
Qing Xin Li
Keyword(s):  
Waste Water ◽  
Activation Energy ◽  
Dynamic Behavior ◽  
Noble Metals ◽  
Nonferrous Metal ◽  
Copper Anode ◽  
Rare Metals ◽  
Reaction Velocity ◽  
Secondary Sludge ◽  
Leaching Efficiency

Copper anode sludge was a byproduct produced during the refinery of copper. The sludge contained amount of noble metals and rare metals, and also was an important resources for recovering noble metals. In this paper, ammonium thiocyante was used as leaching reagent for extracting gold from arsenic-free anode sludge (secondary sludge). Under the optical conditions, the leaching efficiency was up to 85.1%, while the dynamic behavior of gold leaching was studied, the activation energy of the system Eα=20.093kJ•mol-1, and reaction velocity constant k=4.084e-20093/RT. The treatment of copper sludge could greatly reduce the potential contamination to the environment.

Relaxation Processes in NQR Multiple-Pulse Spin-Locking

1986 ◽  
Vol 41 (1-2) ◽  
pp. 366-369 ◽  
Author(s):  
N. E. Ainbinder ◽  
G. B. Furman ◽  
G. E. Kibrik ◽  
A. Yu. Poljakov ◽  
I. G. Shaposhnikov
Keyword(s):  
Time Constant ◽  
Pulse Sequence ◽  
Spin Echo ◽  
Rate Equations ◽  
Relaxation Processes ◽  
Quasi Equilibrium ◽  
Multiple Pulse ◽  
Spin Lattice ◽  
Kinetic Coefficients ◽  
Spin Locking

A theory of the spin-lattice and spin-spin relaxation processes in quadrupole spin systems with I > 1/2 in the situation of the multiple-pulse NQR spin locking is proposed for the pulse sequence MW-4. The theory is based on the assumption that for t ≳ T2 the change of the spin system is a quasi-equilibrium process. Rate equations for inverse generalized temperatures are obtained and the kinetic coefficients calculated for the case o f exponential correlation functions. The above assumption was confirmed for some substances containing the 35Cl and 123Sb, and the time constant T1e characterizing the spin echo signal decay was investigated and compared with the time constant T1q, in the case of continuous spin locking.

Transient rates of gas sorption. II. Rate equations for transport and adsorption in porous adsorbents

1953 ◽  
Vol 6 (3) ◽  
pp. 234 ◽  
Author(s):  
KL Sutherland ◽  
ME Winfield
Keyword(s):  
Rate Constant ◽  
Rate Constants ◽  
Reaction Rate ◽  
Reaction Rate Constant ◽  
Rate Equations ◽  
Limiting Factor ◽  
Gas Sorption ◽  
Gas Uptake ◽  
Knudsen Flow ◽  
Factor Ii

Equations are derived to describe the rate at which gas passes into a bed of adsorbent under conditions of constant volume and diminishing pressure. Of the processes which may be responsible for the observed rate of gas uptake, the following three are considered : (i) Knudsen flow within the bed, or within the granules of which it is composed, with simultaneous adsorption that is too fast to be a limiting factor ; (ii) chemisorption which is controlled by the rate of Knudsen flow ; (iii) unrestricted chemisorption.It is shown how the rate constants used in the equations are related to the overall reaction rate constant in a catalyst pore.

scholarly journals Analytical application of acidic victoria blue 4R mixture with KBrO3 for the kinetic determination of traces of antimony(III) by spectrophotometry

2012 ◽  
Vol 31 (1) ◽  
pp. 29
Author(s):  
Violeta Mitić ◽  
Snežana Nikolić-Mandić ◽  
Vesna Stankov-Jovanović
Keyword(s):  
Reaction Rate ◽  
Kinetic Method ◽  
Operating Conditions ◽  
Rate Equations ◽  
Optimum Operating ◽  
Acid Media ◽  
Kinetic Determination ◽  
Hydrochloric Acid Media ◽  
Optimized Conditions

The present paper describes a simple, selective and sensitive kinetic method for the determination of trace amounts of Sb(III) in the presence of Sb(V) based on its inhibition effect on the redox reaction between bromate and Victoria blue 4R (V.B. 4-R) in hydrochloric acid media. The reaction was followed spectrophotometrically by measuring the decrease in the absorbance of V.B. 4-R at 596.3 nm. Optimum operating conditions regarding reagent concentrations were established. The optimized conditions yielded a theoretical detection limit of 1.30·10‒8 g cm–3 Sb(III) based on the 3S0 criterion. The method allows the determination of Sb(III) in the range of 5·10‒8 ‒ 1.1·10‒6 g cm–3. The effects of certain foreign ions the reaction rate were determined for an assessment of the selectivity of the method. The kinetic parameters of the reaction were reported, and the rate equations were suggested. The results were validated statistically and through recovery studies. The proposed method has been successfully applied to the determination of Sb(III) in various model and real samples.

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