Corrosion characteristics of aluminum alloy in bio-ethanol blended gasoline fuel: Part 2. The effects of dissolved oxygen in the fuel

This study examined the effects of dissolved oxygen on the corrosion properties of aluminum cast alloy, A384, in bio-ethanol blended gasoline fuel at 100 °C. Oxygen enhanced the corrosion resistance of the alloy by forming a protective hydrous oxide film. The acetic acid and water produced by ethanol oxidation in the fuel had a corrosive and protective effect, respectively. However, the protective hydrous oxide film enhanced by the water suppressed the corrosiveness of the acetic acid in the fuel when the two by-products coexisted. Therefore, the water formed by dissolved oxygen in the bio-ethanol blended gasoline fuel enhanced the corrosion resistance of the aluminum alloy by promoting the formation of a protective surface film.     

Pitting corrosion of friction stir welded aluminum alloy thick plate in alkaline chloride solution

The pitting corrosion of different positions (Top, Middle and Bottom) of weld nugget zone (WNZ) along thickness plate in friction stir welded 2219-O aluminum alloy in alkaline chloride solution was investigated by using open circuit potential, cyclic polarization, scanning electron microscopy and atomic force microscope. The results indicate that the material presents significant passivation, the top has highest corrosion potential, pitting potential and re-passivation potential compared with the bottom and base material. With the increase of traverse speed from 60 to 100 mm/min or rotary speed from 500 to 600 rpm, the corrosion resistance decreases.     

Evaluation of galvanic corrosion of a Zn alloy in alcohol fuel

Galvanic corrosion of zamak was evaluated in alcohol fuel and in some alcoholic solutions that contained ionic impurities. Also, the effect of corrosive process on the quality parameters of ethanol was investigated. The results showed that corrosion of zamak mainly occurred in solutions with high levels of water and impurities. After the assays, the increasing of both pH and conductivity of the alcohols was observed. Therefore, the results showed that the contact between zamak and some materials must be avoided and the quality control of alcohol fuel must be assured as a way of avoiding damages on engines and storage-transportation fuels systems.     

铝在高压直流输电系统中高电压高温下的腐蚀行为研究

高压直流输电换流阀的内冷水系统中,铝散热器在高压高温下会腐蚀进而引起均压电极发生氢氧化铝结垢,导致生产异常。此状态下的铝的腐蚀行为少有报道。本文研究了与散热器相同材质的铝电极在高电压、高温下于蒸馏水和弱碱性溶液中的腐蚀行为及其电化学反应规律。理清了铝的电化学腐蚀行为,建立铝在中性溶液中失去电子的反应的模型。建立了铝电极的腐蚀反应的等效电路,计算了各历程的阻抗,发现腐蚀的控制步骤为OH^-穿过沉淀层。研究表明,在3.35mmol/L氨水溶液中具有最低的腐蚀趋势,其腐蚀电位为-0.731 V,腐蚀电流密度为7.667×10^-7 A/cm²,塔菲尔斜率为5.328。此时电化学反应的阻抗最大,其腐蚀速度最低。铝电极表面会覆盖氢氧化铝等腐蚀产物,其限制离子的扩散,减缓腐蚀趋势。由此建议在保证低电导率的前提下调整内冷水的pH,来改善换流阀内冷水系统的防腐能力。     

Mechanistic aspects of electrochemical corrosion of aluminum alloy in ethylene glycol–water solution

The electrochemical corrosion behavior of 3003 aluminum (Al) alloy in ethylene glycol–water solutions was studied by electrochemical measurements and surface analysis techniques through an impingement jet system. Al corrosion in aerated, stationary solution is a mixed-controlled process, i.e., both activation and mass-transfer steps control the corrosion reaction. Upon flowing of solution, no matter if sand particles are contained, Al corrosion is an activation-controlled process. In addition to Al oxide film, a layer of Al-alcohol film will also be formed on the electrode surface in ethylene glycol–water solution, contributing to inhibition of anodic dissolution of Al. In the absence of oxygen, a stable passivity could also be achieved on Al alloy. The main cathodic reaction is either reduction of water or reduction of ethylene glycol. However, the reduction of water and ethylene glycol would not be as significant as that of oxygen. As a consequence, the resultant film is not as stable as that formed in the presence of oxygen, as shown in polarization measurements. Al corrosion reaction in mixed-controlled by activation step and mass-transfer step through the anodic surface film. The coverage of the adsorbed intermediate product on Al electrode surface is expected to be very small under the impingement of fluid and sand particles, which results in the generation of an inductive loop in Nyquist diagrams measured on Al electrode in ethylene glycol–water solution.     

Cathodic reaction kinetics and its implication on flow-assisted corrosion of aluminum alloy in aqueous ethylene glycol solution

The cathodic reaction kinetics and anodic behavior of Al alloy 3003 in aerated ethylene glycol–water solution, under well-controlled hydrodynamic conditions, were investigated by various measurements using a rotating disk electrode (RDE). The transport and electrochemical parameters for cathodic oxygen reduction were fitted and determined. The results demonstrate that the cathodic reaction is a purely diffusion-controlled process within a certain potential region. The experimentally fitted value of diffusion coefficient of oxygen is 3.0 × 10⁻⁸ cm² s⁻¹. The dependence of cathodic current on rotation speed was in quantitative agreement with Levich equation. At potentials more positive than the diffusion controlled region, the cathodic process was controlled by both diffusion and electrochemical kinetics. The electrochemical reaction rate constant, k ₀, was determined to be 1.1 × 10⁻⁹ cm s⁻¹. There is little effect of electrode rotation on anodic behavior of Al alloy during stable pitting. However, fluid hydrodynamics play a significant role in formation of the oxide film and the Al alloy passivity. An enhanced electrode rotation would increase the mass-transfer rate of solution, and thus the oxygen diffusion towards the electrode surface for reduction reaction. The generated hydroxide ions are favorable to the formation of Al oxide film on electrode surface.     

High temperature corrosion of boiler waterwalls induced by chlorides and bromides. Part 1: Occurrence of the corrosive ash forming elements in a fluidised bed boiler co-firing solid recovered fuel

In waste fired boilers high temperature corrosion has often been attributed to zinc and lead chlorides. In addition, bromine induced high temperature corrosion has been earlier observed in a bubbling fluidised bed (BFB) boiler co-firing solid recovered fuel (SRF) with bark and wastewater sludge. In Part 1 of this work a measurement campaign was undertaken to determine the occurrence of Cl, Br, Zn and Pb in the fuel, in the combustion gases as well as in the deposits on the boiler waterwalls. It was observed that Cl, Br, Zn and Pb originate to a large extent from the SRF, they are vaporised in the furnace, and may form waterwall deposits. This, complemented by fluctuations between oxidising and reducing atmosphere resulted in rapid corrosion of the waterwall tubes. Concentrations of Cl, Br, Zn and Pb in the fuel, in the furnace vapours and in the deposits are reported in this work. As there is lack of published data on the bromine induced high temperature corrosion, laboratory scale corrosion tests were carried out to determine the relative corrosiveness of chlorine and bromine and these results will be reported in Part 2 of this work. Furthermore, the forms of Cl, Br, Zn and Pb in the combustion gases as well as in the waterwall deposits were estimated by means of thermodynamic equilibrium modelling and these results will also be discussed in Part 2.     

The effect of platinum on carbon corrosion behavior in polymer electrolyte fuel cells

To assess the catalytic effect of platinum on the corrosion of the high surface area carbon support, single triangular potential sweeps with various upper and lower limits were applied to fuel cells comprising electrodes having different Pt/C compositions. Carbon loss rates in H₂/N₂ and air/air mode were determined by integration of the resulting CO₂ concentration peaks in the exhaust gas of the positive electrode. Generally, the contribution of platinum catalyzed carbon corrosion to total CO₂ evolution was found to decrease with increasing upper potential limit. Similar carbon loss rates obtained for Pt/C and pure carbon electrodes in case of lower potential limits of 1.0 V indicate that the catalytic activity of platinum is substantially lowered by the formation of a passivating oxide layer on the platinum particles. Changes in corrosion behavior in the potential range below 0.6 V, which cannot be attributed to platinum effects, are suggested to originate from modifications in carbon surface oxide composition. Due to the high oxygen equilibrium potential of approximately 1 V, carbon corrosion in air/air mode is significantly influenced by platinum oxide formation. However, the polarization of the negative electrode and the influence of platinum oxidation on the equilibrium potential results in a passivating effect that is less pronounced than expected from measurements in H₂/N₂ mode.     

Fundamental studies of aluminum corrosion in acidic and basic environments: Theoretical predictions and experimental observations

Using quantum electrochemical approaches based on density functional theory and cluster/polarized continuum model, we investigated the corrosion behavior of aluminum in HCl and NaOH media containing phenol inhibitor. In this regard, we determined the geometry and electronic structure of the species at metal/solution interface. The investigations revealed that the interaction energies of hydroxide corrosive agents with aluminum surface should be more negative than those of chloride ones. The inhibitor adsorption in acid is more likely to have a physical nature while it appears as though to be chemical in basic media. To verify these predictions, using Tafel plots, we studied the phenomena from experimental viewpoint. The studies confirmed that the rate of corrosion in alkaline solution is substantially greater than in HCl media. Moreover, phenol is a potential-molecule having mixed-type inhibition mechanism. The relationship between inhibitory action and molecular parameters was discussed and the activity in alkaline media was also theoretically anticipated. This prediction was in accord with experiment.     

Electrochemical characteristics of Al-Mg alloy in seawater for leisure ship: Stress corrosion cracking and hydrogen embrittlement

We investigated the mechanical and electrochemical properties of aluminum alloys. Aluminum alloys do not corrode due to the formation of an anti-corrosive passive film, such as Al₂O₃ or Al₂O₃ · 3H₂O, which resists corrosion in neutral solutions. In seawater, however, Cl⁻ ions destroy this passive film. The current density in the first passivity range during the application of anodic protection had a similar value as that for concentration polarization by dissolved oxygen during the application of cathodic protection. The current density in the first passivity range had the lowest value overall. The lowest current densities in the potentiostatic and galvanostatic tests occurred at potentials of −1.4 to −0.7 V and −0.9 to −0.7 V, respectively.     

The influence of activated carbon as an additive in anode materials for low temperature solid oxide fuel cells

The effects of activated carbon (AC) as an additive in multi-oxide nano composite LiNiCuZn–O for application as anode in solid oxide fuel cell (SOFC) is reported. The composite was synthesized using solid state reactions method with varying content of AC in range 0.1%–0.9% for use as anode in the cell. The cell was composed of the synthesized composite as anode, LiNiCuZn–O as cathode and Samaria doped ceria (SDC) as electrolyte. The prepared composites were characterized for morphology and crystal structure by scanning electron microscope (SEM) and x-ray diffraction (XRD) respectively. Furthermore, the crystallite sizes of LiNiCuZn–O and LiNiCuZn–O with AC as an additive have been found in the range from 50 nm to 70 nm. The prepared composite materials were observed porous and the porosity of the sample having 0.5% additive was found highest. The conductivity and power density of the SOFC were studied at temperature of 600 °C. The maximum value of conductivity was found as 4.79 S/cm for the composite containing 0.5% AC as measured by using 4-probe method. The maximum value of power density of the fuel cell with anode comprising of 0.5% AC along with the mentioned cathode and the electrolyte was 455 mW/cm². Therefore, out of the compositions studied, the composite comprising of LiNiCuZn–O with 0.5% AC offered best performance for anode in the cell. This oxide composite is reported as a potential candidate for use as anode in low temperature SOFCs.     

Long‐term testing of a high temperature polymer electrolyte membrane fuel cell: The effect of reactant gases

The investigations have been conducted with different oxidants and fuels with the aim of determining the state‐of‐the‐art of commercially available high temperature polymer electrolyte fuel cells based on polybenzimidazole for its application in combined heat and power generation systems. The fuel cell test performed with synthetic reformate (?63 μV/h) showed an increase of anode charge and mass transfer resistances. This behavior has suggested that CO may be generated from the CO₂ included in the synthetic reformate via reverse water gas shift reaction. The fuel cell test performed with pure O₂ developed the highest degradation rates (?70 μV/h) due to fast oxidative degradation of membrane electrode assembly materials such as cathode catalyst and membrane. Fuel cell operation with H₂/air exhibited the lowest degradation rates (?57 μV/h) and it requires longer investigating times to identify the different degradation mechanisms. Moreover, fuel cell tests performed with air suggested longer break‐in procedures to complete catalyst activation and redistribution of electrolyte. © 2015 American Institute of Chemical Engineers AIChE J, 62: 217–227, 2016     

Effects of dissolved calcium and magnesium ions on lead-induced stress corrosion cracking susceptibility of nuclear steam generator tubing alloy in high temperature crevice solutions

The effects of Ca²⁺ and Mg²⁺ ions on the stress corrosion cracking (SCC) susceptibility of UNS N08800 are investigated using constant extension rate tensile (CERT) tests at 300 °C in simulated crevice chemistries. The presence of lead contamination in the crevice chemistries increases significantly the SCC susceptibility of the alloy. The lead-assisted SCC (PbSCC) susceptibility is reduced markedly by the addition of Ca²⁺ and Mg²⁺ ions into the solution and this mitigating effect is enhanced by increasing the total concentration of Ca²⁺ + Mg²⁺. The CERT test results are consistent with the types of fracture surfaces shown by Scanning Electron Microscopy (SEM). There is a reasonable correlation between the SCC susceptibility and the donor densities in the anodic films in accord with the role of lead-induced passivity degradation in PbSCC.     

Corrosion of Si3N4-ceramics in aqueous solutions Part I: Characterisation of starting materials and corrosion in 1 N H2SO4

The corrosion behaviour of silicon nitride materials in acids strongly depends on the composition and amount of the grain boundary. But there exist no systematic investigations of the relation between the corrosion behaviour and the composition and amount of the grain-boundary phase. The aim of the series of these papers is the systematic investigation of these relations. In the first part the methods of determination of the amorphous grain-boundary phases are described in detail. Additionally, the correlation between the corrosion behaviour and the composition of the grain-boundary phases are given. The structural reasons and the mechanisms behind the observed changes in the corrosion behaviour will be given in part II of this paper.     

The characteristics of X1 type Y2SiO5:Tb phosphor particles prepared by high temperature spray pyrolysis

The X1 type Y₂SiO₅:Tb phosphor particles with high brightness were prepared by spray pyrolysis from spray solution with NH₄F flux material. The phosphor particles prepared by spray pyrolysis at high preparation temperature had spherical shape, fine size and dense morphology. The mean sizes of the phosphor particles prepared at 900 and 1650 °C were 1.3 and 0.9 μm. The emission spectrum of the phosphor particles prepared by spray pyrolysis at 1650^oC had the characteristics of X1 type Y₂SiO₅:Tb phosphor. The photoluminescence intensity of the phosphor particles directly prepared by spray pyrolysis from spray solution with 20 wt.% NH₄F flux of the product at temperature of 1650 °C was 127 and 184% of the X1 and X2 type Y₂SiO₅:Tb phosphor particles post-treated at 1100 and 1300 °C, respectively. The Y₂SiO₅:Tb phosphor particles prepared by spray pyrolysis at 1650 °C had X1 type crystal structure because of short residence time of particles inside hot wall reactor of 0.4 s.     

Modeling of solid fuels combustion in oxygen-enriched atmosphere in circulating fluidized bed boiler: Part 1. The mathematical model of fuel combustion in oxygen-enriched CFB environment

The paper is focused on the idea of large-scale CFB boiler operation with oxygen/CO₂-modified atmosphere inside combustion chamber. The following main advantages can be found for this technology: reduction of pollutant emissions, possibility of high efficiency separation of CO₂ from the exhaust gases that results from increased CO₂ concentration, lower chimney loss due to the reduction of flue gases in a volume, limitation of the combustion chamber dimensions etc. The paper presents a model of coal combustion in oxygen-enriched CFB environment, where air staging, desulfurization process, NO_x formation and reduction as well as a stationary dense phase of coarse particles in the bottom part of combustion chamber and a circulating dilute phase in the upper part are included.     

A comprehensive evaluation of mimosa extract as a corrosion inhibitor on AA6060 alloy in acid rain solution: part I. Electrochemical AC methods

The inhibition effect of mimosa extract on the corrosion of AA6060 aluminum alloy in acid rain solution was investigated by electrochemical impedance spectroscopy and dynamic electrochemical impedance spectroscopy (DEIS). All the studied electrochemical parameters showed good corrosion inhibitive characteristics with respect to the aluminum alloy in the tested solution. Inhibitor efficiency increased with the concentration and attained 45% at 2750 ppm. The advantage of DEIS as a tool for the investigation of corrosion inhibitor influence was discussed.     

Electron-transfer coupling in microbial fuel cells: 1. comparison of redox-mediator reduction rates and respiratory rates of bacteria

Redox mediators promote electron transfer in microbial fuel cells. The reduction of a range of redox mediators by bacteria was studied in some detail in order to identify effective mediator—organism combinations. Rates of reduction of mediator dyes by bacteria were measured spectrophotometrically at 30°C under anaerobic conditions for standardised concentrations of organism, substrate and dye. The kinetics of dye reduction showed two general patterns: a simple, exponential curve or a complex curve with an initial linear rate followed by a faster exponential rate of reduction. Dye-reduction rates were greater than rates of oxygen consumption (Q_O2) for several combinations of organism and redox dye. Thionine, brilliant cresyl blue, methylene blue and benzyl viologen were tested in combination with Alcaligenes eutrophus, Azotobacter chroococcum, Bacillus subtilis, Escherichia coli, Proteus vulgaris, Pseudomonas aeruginosa and Pseudomonas putida, using glucose and succinate as substrates. Rates of reduction of alizarin brilliant blue, 2,6-dichlorophenolindophenol, gallocyanine, new methylene blue, N,N-dimethyl-disulphonated thionine, phenazine ethosulphate, resorufin, safranine-O, phenothiazinone and toluidine blue-O were also measured with Pr. vulgaris only. For E. coli, both Q_O2 and the rate of thionine reduction increased with increasing temperature in the range 25 to 37°C, but for Pr. vulgaris thionine reduction rates did not correlate with temperature in this way. Dye-reduction rates and Q_O2 for Az. chroococcum were dependent on the components of the washing solution and/or the temperature at which cell suspensions were prepared. The results are discussed in relation to the use of these dyes as electron-transfer mediators in microbial fuel cells.     

A fundamental study on the control of the HCCI combustion and emissions by fuel design concept combined with controllable EGR. Part 1. The basic characteristics of HCCI combustion

This article investigates the basic combustion parameters including start of the ignition timing, burn duration, cycle-to-cycle variation, and carbon monoxide (CO), unburned hydrocarbon (UHC), and nitric oxide (NO_x) emissions of homogeneous charge compression ignition (HCCI) engines fueled with primary reference fuels (PRFs) and their mixtures. Two primary reference fuels, n-heptane and iso-octane, and their blends with RON25, RON50, RON75, and RON90 were evaluated. The experimental results show that, in the first-stage combustion, the start of ignition retards, the maximum heat release rate decreases, and the pressure rising and the temperature rising during the first-stage combustion decrease with the increase of the research octane number (RON). Furthermore, the cumulative heat release in the first-stage combustion is strongly dependent on the concentration of n-heptane in the mixture. The start of ignition of the second-stage combustion is linear with the start of ignition of the first-stage. The combustion duration of the second-stage combustion decreases with the increase of the equivalence ration and the decrease of the octane number. The cycle-to-cycle variation improved with the decrease of the octane number.     

Water sorption characteristics in moderately hydrophilic polymers,Part 1: Effect of polar groups concentration and temperature in water sorption in aromatic polysulfones

The water equilibrium concentration has been determined for three aromatic polysulfones differentiated essentially by the sulfone concentration, in the 0–0.9 activity range, at temperatures of 50, 60, and 70°C, using a dynamic vapor sorption apparatus. In all the cases, Henry's law was obeyed. The corresponding solubility S and heat of dissolution H_s were determined and their relationships with structure were investigated. The fact that S increases nonlinearly with the sulfone concentration and that H_s is also an increasing function of the latter leads one to abandon classical approaches to polymer–water interactions and propose a model in which water is doubly bonded. Then, S depends on the distribution of distances between polar groups, characterized by a function P(r) and H_s depends on both P(r) and the hydrogen bond potential U(r). © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008