Anodic Phase Research Articles

Effect of Sn on microstructure and corrosion behaviors of Al-Mg-Si alloys

x wt% (x = 0, 0.03, 0.40) Sn addition in Al-Mg-Si alloys were prepared to investigate the effect of Sn on the performance of Al-Mg-Si alloys. Optical microscope (OM), scanning (SEM) and transmission electron microscope (TEM) were applied to observe the microstructure of these alloys. X-ray diffraction (XRD) was used to investigate the phase component among different alloys. Electrochemical polarization measurements and intergranular corrosion test were used to investigate the corrosion behaviors of these alloys. The experimental data shows that 0.03 wt% Sn can slightly enhance mechanical properties and corrosion resistance of Al-Mg-Si alloys because of the smaller precipitate free zones (PFZ) area and grain boundary refinement. Higher Sn addition (0.4 wt%) may cause detrimental effect on both mechanical properties and corrosion resistance of Al-Mg-Si alloys. Excess Sn tends to replace part of Si in Mg2Si phase and forms Mg2(Si,Sn) phase which is thought to be an anodic phase compared to Al matrix. Electrochemical measurements may not comprehensively reveal the overall corrosion processes, such as de-alloying process of Mg2(Si, Sn) phase and thus enrichment of Sn which leads to much faster dissolution of Al.

Operando X-Ray Diffraction during Battery Cycling at Low Temperatures

Lithium-ion batteries are nowadays widely used in consumer electronics and electric vehicles. However, the application in electric vehicles poses new challenges to this battery technology. High energy and power densities, a high degree of safety and a long lifetime are important to meet the requirements of the customers. To improve lithium-ion batteries, it is necessary to gain a deeper understanding of electrochemical processes occurring during battery cycling. Operando characterization techniques are used to shed light on these processes. In particular, operando X-ray diffraction (XRD) and neutron diffraction are applied for the observation of phase changes of battery materials during cycling. Thereby, the lithiation and delithiation mechanism can be investigated depending on different factors like C-rate or temperature. The gained deeper understanding of the structural behavior of battery materials under various operating conditions leads to the improvement of battery management systems by increasing the performance and reducing degradation processes of batteries. The phase changes of state-of-the-art battery materials at room temperature are well understood but the influence of temperature on the phase evolution is barely investigated. Recent studies show that the classical staging mechanism of graphite [1, 2] does not occur at higher C-rates [3, 4] and elevated or low temperatures [5, 6] and instead, several stages coexist. During a rest period after charge or discharge, these phases can equilibrate [6]. The lithiation and delithiation mechanism does not only influence the charge and discharge behavior, but also the dimensional changes concurrently with the degradation of the electrodes [5]. Therefore, a deeper understanding of the structural behavior of battery materials under various operating conditions is needed to improve the material properties and adapt battery management systems to increase the performance of the battery and reduce degradation. At DLR, a new set-up was developed to investigate with operando XRD the phase evolution of battery materials during cycling at temperatures below room temperature. This method allows a readily characterization of battery materials at various temperatures and the identification of the temperature dependent intercalation mechanisms. [1] J. Besenhard and H.P. Fritz, The Electrochemistry of Black Carbons, Angew. Chem. Int. Ed. 22 (1983) 950-975. [2] J.R. Dahn, Phase diagram of LixC6, J. Phys. Rev. B. 44 (1991) 9170-9177. [3] H. He, C. Huang, C.-W. Luo, J.-J. Liu and Z.-S. Chao, Dynamic study of Li intercalation into graphite by in situ high energy synchrotron XRD, Electrochim. Acta. 92 (2013) 148-152. [4] N. Sharma and V.K. Peterson, Current-dependent electrode lattice fluctuations and anode phase evolution in a lithium-ion battery investigated by in situ neutron diffraction, Electrochim. Acta. 101 (2013) 79-85. [5] N.A. Cañas, P. Einsiedel, O.T. Freitag, C. Heim, M. Steinhauer, D.-W. Park and K.A. Friederich, Operando X-ray diffraction during battery cycling at elevated temperatures: A quantitative analysis of lithium-graphite intercalation compounds, Carbon. 116 (2017) 255-263. [6] V. Zinth, C. von Lüders, J. Wilhelm, S.V. Erhard, M. Hofmann, S. Seidlmayer, J. Rebelo-Kornmeider, W. Gan, A. Jossen and R. Gilles, Inhomogeneity and relaxation phenomena in the graphite anode of a lithium-ion battery probed by in situ neutron diffraction, J. of Power Sources. 361 (2017) 54-60.

Operando soft X‐ray microscope study of rechargeable Zn–air battery anodes in deep eutectic solvent electrolyte

Zn–air batteries are very promising devices for energy storage at high energy density due to their intrinsic safety, environmental friendliness, and low cost, but still, there are key issues to be solved to get to the industrial scale. One of the unsolved problems is the poor cyclability of batteries based on aqueous solvents that urges to consider nonaqueous solvents. Among different possible options are deep eutectic solvents, which are cost‐effective and technologically relatively easy to implement. The present investigation reports for the first time an operando scanning soft X‐ray microscope analysis of the Zn behaviour in a choline–chloride/urea deep eutectic solvents electrolyte during the cathodic and anodic phase formation processes taking place in battery charge and discharge, providing a platform for in‐depth space–time dependent investigations of the chemistry of crystallites evolving during potential cycling. These operando measurements have been enabled by the construction of a novel wet cell, improving the design and filling protocol of earlier generation cells developed by authors.High‐resolution soft X‐ray microscope images were acquired in two modes: (a) dynamic mode at a fixed beam energy, allowing to follow morphology evolution under electrochemical control and (b) static mode for selected morphologies representative of characteristic Zn growth and dissolution steps.

Electron transfer processes occurring on platinum neural stimulating electrodes: pulsing experiments for cathodic-first, charge-imbalanced, biphasic pulses for 0.566 ⩽ k ⩽ 2.3 in rat subcutaneous tissues

Objective. Charge injection through platinum neural stimulation electrodes is often constrained by the Shannon limit (Shannon 1992 IEEE Trans. Biomed. Eng. 39 424–6) of k = 1.75. By leveraging the tools of electrochemistry to better understand the reactions at electrode-tissue interface, we endeavor to find a way to safely inject more charge than allowed if the traditional Shannon limit were followed. Approach. In previous studies on platinum electrodes using charge-balanced, cathodic-first, biphasic pulses, we noted that during the secondary anodic phase, the electrode potential moves into a range where platinum dissolution is possible when charge injection is greater than k = 1.75. Platinum dissolution products are known to be toxic to brain tissues. We hypothesize that by injecting less charge in the anodic phase than the cathodic phase, the anodic potential excursions will decrease, thereby avoiding potentials where platinum dissolution is more likely. Main results. Our findings show that using these charge-imbalanced pulses decreases the anodic potential excursions to a level where platinum oxidation and dissolution are less likely, and aligns the anodic potentials with those observed with charge-balanced stimulation at k < 1.75—a range widely accepted as safe for stimulation with platinum. Significance. From these results, we further hypothesize that charge-imbalanced biphasic stimulation would permit more charge to be safely injected through platinum electrodes than would be permitted if the dogma of charge-balanced biphasic stimuli were followed. Testing this hypothesis in cat brain in the same manner as the experiments that formed the basis for the Shannon plot could open the door for safe charge injection through platinum electrodes at levels greater than k = 1.75.

Corrosion performance of high pressure die-cast Al-Si-Mg-Zn alloys in 3.5 wt% NaCl solution

In the present investigation corrosion behavior of the Al-Si-Zn alloys with and without the addition of Mg was studied. Microstructures revealed the presence of eutectic Si and Zn phases at the grain boundaries and Mg addition led to the formation of Mg2Si phase. X-ray diffraction results clearly indicated the presence of pure Si, Mg2Si and α-Al phases. Corrosion behavior of all the alloys was investigated in 3.5 wt% NaCl solution using electrochemical and immersion corrosion techniques. Potentiodynamic polarization test results after 48 h of exposure indicated that, the corrosion resistance increased as the Zn content in the alloy was increased, while the addition of Mg decreased the corrosion resistance. Electrochemical impedance spectroscopy (EIS) results as a function of exposure time are also revealed a variation in the surface layer and charge transfer resistance values with and without Mg addition. Corrosion rates calculated from the immersion test further substantiated the electrochemical corrosion results. Corrosion morphologies after immersion test confirmed the dissolution of α-Al matrix and presence of cathodic Si phase at the grain boundaries. The presence of anodic Mg2Si phase in the Mg containing alloy could also be responsible for the decrease of corrosion resistance.

Toward an Energy-Efficient High-Voltage Compliant Visual Intracortical Multichannel Stimulator

We present, in this paper, a new multichip system aimed toward building an implantable visual intracortical stimulation device. The objective is to deliver energy-optimum pulse patterns to neural sites with needed compliance voltage across high electrode–tissue interface impedance of implantable microelectrodes. The first chip is an energy-efficient stimuli generator (SG), and the second one is a high-impedance microelectrode array driver (MED) output stage. The four-channel SG produces rectangular, half-sine, plateau-sine, and other types of current pulse with stimulation current ranging from 2.32 to 220 $\mu \text{A}$ per channel. The microelectrode array driver is able to deliver 20 V per anodic or cathodic phase across the microelectrode–tissue interface for ±13 V power supplies. The MED supplies different current levels with the maximum value of 400 $\mu \text{A}$ per input and 100 $\mu \text{A}$ per output channel simultaneously to 8–16 stimulation sites through microelectrodes, connected either in bipolar or monopolar configuration. Both chips receive power via inductive link and data through capacitive coupling. The SG and MED chips have been fabricated in 0.13- $\mu \text{m}$ CMOS and 0.8- $\mu \text{m}$ 5-/20-V CMOS/double-diffused metal-oxide-semiconductor technologies. The measured dc power budgets consumed by low- and mid-voltage chips are 2.56 and 2.1 mW consecutively. The system, modular in architecture, is interfaced with a newly developed platinum-coated pyramidal microelectrode array. In vitro test results with 0.9% phosphate buffer saline show the microelectrode impedance of 70 $\text{k}\Omega $ at 1 kHz.

Sequencing polarity-inverting microbial fuel cell for wastewater treatment

A novel sequential polarity-inverting microbial fuel cell (MFC) is developed to neutralize anodic acidification and cathodic alkalinization and treat wastewater. The same electrode sequentially experiences anaerobic anode, aerobic cathode and anoxic cathode phases like a SBR (Sequencing Batch Reactor Activated Sludge process), and such two SBR half cells with opposite electrode polarities consist of a complete MFC. The system successfully buffers electrolyte and generates electricity with a maximum power density of 623 ± 4 mW/m3. Chemical oxygen demand is completely removed. Three bacteria, Arthrobacter sp., Stenotrophomonas sp. and Sphingobacterium sp., are found on the polarity-inverting electrode, and Arthrobacter sp. is believed to be capable of transferring electrons both to and from electrode. The proof-of-principle of a polarity-inverting MFC described here may offer an opportunity of integrating MFCs into the practical wastewater treating process.

Cations Diffusion in Nafion117 Membrane of Microbial fuel cells

The effects of five kinds of cations (Na+, K+, NH4+, Mg2+, Ca2+) in the anode phase on the diffusion of hydronium ions (H3O+) in the Nafion117 membrane and at the membrane/solution interface of a microbial fuel cell are investigated by means of molecular dynamics simulations and experiments. The cation diffusion laws are elucidated by the self-diffusion coefficients and the membrane conductivities. The results show that the presence of other cations in the membrane can lower the membrane conductivity and the intramembranous diffusion coefficient of H3O+, especially Ca2+. It is found that the NH4+ diffusion is susceptible to the membrane/solution interfacial structure and the presence of other cations in the membrane. The stable metal cations diffusion law (K+>Na+>Mg2+>Ca2+) is applicative to both intramembranous and interfacial structure, as well as the complex solution containing binary and multiple cations. The main factors affecting cations diffusion are hydrated radius, hydrated degree of cations, and the interaction between cations and sulfonic acid groups (-SO3H) of Nafion side chains. In addition, the formation of large size clusters or uniform distribution of cations in the membrane is conducive to their intramembranous diffusion and the connected region is conducive to the diffusion of cations through the membrane/solution interface.

Optimization of Interphase Intervals to Enhance the Evoked Muscular Responses of Transcutaneous Neuromuscular Electrical Stimulation.

Neuromuscular electrical stimulation (NMES) is a widely used technique for clinical diagnostic, treatment, and research. Normally, it applies charge-balanced biphasic pulses, which several publications have reported to be less efficient than monophasic pulses. A good alternative is the use of interphase intervals (IPI) on biphasic pulses that allows to achieve similar responses than those evoked by monophasic stimulation. This study analyzes the enhancing mechanism of the IPI and provides guidelines on how to optimize the IPI in order to reduce secondary effects such as the electrode corrosion. The tibial nerve was excited by NMES biphasic pulses with different IPI durations and polarities. Then, the elicited responses were recorded on the soleus muscle via electromyography. When cathodic-first pulses were applied, the responses increased proportionally to the IPI until the duration of 250 µs, where the increase saturated at 30% of the original amplitude. The responses evoked during anodic-first were 6% to 30% smaller than those evoked during cathodic-first pulses and continuously increased until the IPI duration of 2500 µs, where the responses reached an increase of around 30%. The results suggest that when a cathodic-first pulse is used, the IPI could be optimized (based on the setup geometry) to allow the action potentials to travel out of the hyperpolarization zone induced by the anodic phase. When anodic-first stimuli are applied, the IPI duration allows the fiber to recover from an apparent insensitive state induced by the anodic phase. The use of IPI is a viable option to improve the efficiency of actual stimulation systems, since only small modifications are required to significantly reduce the electrical charge required and boost the stimulation efficiency.

Double Layered CeO2-Co3O4-CuO Based Anode for Direct Utilisation of Methane or Ethanol in SOFC

The present work aimed to produce an electrocatalyst suitable to be used as anode in solid oxide fuel cell that operates with hydrocarbons or alcohols as fuels. The main challenge is to avoid carbon deposition and anode depletion during operation with carbonaceous fuels. Therefore, a Cerium-Cobalt-Copper anode was developed, characterised and tested with methane or ethanol at the anode side resulting in reasonable power densities and no evidence of carbon deposition confirmed by Raman spectroscopy. SEM/EDX analysis showed the integrity of anode microstructure and phase distribution after ageing procedure.

Rare Earth Element Yttrium Modified Mg-Al-Zn Alloy: Microstructure, Degradation Properties and Hardness.

The overly-fast degradation rates of magnesium-based alloys in the biological environment have limited their applications as biodegradable bone implants. In this study, rare earth element yttrium (Y) was introduced into AZ61 magnesium alloy (Mg-6Al-1Zn wt %) to control the degradation rate by laser rapid melting. The results showed that the degradation rate of AZ61 magnesium alloy was slowed down by adding Y. This was attributed to the reduction of Mg17Al12 phase and the formation of Al2Y phase that has a more active potential, which decreased galvanic corrosion resulting from its coupling with the anodic matrix phase. Meanwhile, the hardness increased as Y contents increased due to the uniform distribution of the Al2Y and Mg17Al12 phases. However, as the Y contents increased further, the formation of excessive Al2Y phase resulted in the increasing of degradation rate and the decreasing of hardness due to its agglomeration.

Modeling electrical stimulation of retinal ganglion cell with optimizing additive noises for reducing threshold and energy consumption

BackgroundEpiretinal prosthesis is one device for the treatment of blindness, which target retinal ganglion cells (RGCs) by electrodes on retinal surface. The stimulating current of epiretinal prosthesis is an important factor that influences the safety threshold and visual perception. Stochastic resonance (SR) can be used to enhance the detection and transmission of subthreshold stimuli in neurons. Here, it was assumed that SR was a potential way to improve the performance of epiretinal prosthesis. The effect of noises on the response of RGCs to electrical stimulation and the energy of stimulating current was studied based on a RGC model.MethodsThe RGC was modeled as a multi-compartment model consisting of dendrites and its branches, soma and axon. To evoke SR, a subthreshold signal, a series of bipolar rectangular pulse sequences, plus stochastic biphasic pulse sequences as noises, were used as a stimulus to the model. The SR-type behavior in the model was characterized by a “power norm” measure. To decrease energy consumption of the stimulation waveform, the stochastic biphasic pulse sequences were only added to the cathode and anode phase of the subthreshold pulse and the noise parameters were optimized by using a genetic algorithm (GA).ResultsWhen certain intensity of noise is added to the subthreshold signal, RGC model can fire. With the noise’s RMS amplitudes increased, more spikes were elicited and the curve of power norm presents the inverted U-like graph. The larger pulse width of stochastic biphasic pulse sequences resulted in higher power norm. The energy consumption and charges of the single bipolar rectangular pulse without noise in threshold level are 468.18 pJ, 15.30 nC, and after adding optimized parameters’s noise to the subthreshold signal, they became 314.8174 pJ, 11.9281 nC and were reduced by 32.8 and 22.0%, respectively.ConclusionsThe SR exists in the RGC model and can enhance the representation of RGC model to the subthreshold signal. Adding the stochastic biphasic pulse sequences to the cathode and anode phase of the subthreshold signal helps to reduce stimulation threshold, energy consumption and charge of RGC stimulation. These may be helpful for improving the performance of epiretinal prosthesis.

Investigation of the AC Plasma Torch Working Conditions for the Plasma Chemical Applications

The presented design and parameters of a three-phase AC plasma torch with the power up to 500 kW, flow rate of air 30–50 g/s (temperature up to 5000 K) could be used in different plasma chemical processes. Range of measured plasma temperature is 3500–5000 K. The paper presents investigations of the plasma torch operation modes for its application in plasma chemical technologies. Plasma chemical technologies for various purposes (processing, destruction of various wastes, including technological and hazardous waste, conversion or production of chemicals to obtain nanoscale materials, etc.) are very promising in terms of the process efficiency. Their industrial use is difficult due to the lack of inexpensive and reliable plasma torches providing the desired level of temperature, enthalpy of the working gas and other necessary conditions for the process. This problem can be solved using a considered design of a three-phase alternating current plasma torch with power of 150–500 kW with working gas flow rate of 30–50 g/s with mass average temperature up to 5000K on the basis of which an industrial plasma chemical plant can be created. The basis of the plasma torch operation is a railgun effect that is the principle of arc movement in the field of its own current field. Thanks to single supply of power to the arc, arcs forming in the discharge chamber of the plasma torch move along the electrodes under the action of electrodynamic forces resulting from the interaction of the arc current with its own magnetic field. Under the condition of the three-phase supply voltage, arc transits from the electrode to the electrode with change in the anodic and cathodic phases with frequency of 300 Hz. A special feature of this design is the ability to organize the movement of the arc attachment along the electrode, thus ensuring an even distribution of the thermal load and thus achieve long time of continuous operation of the plasma torch. The parameters of the plasma jet of the plasma torch and the single-phase three-phase plasma injector for use in a plasma-chemical unit for production of nano-dispersed materials are described in the paper.

Mechanical and corrosion properties of biodegradable Mg-1.5Mn-1Ca-xSr alloys

The mechanical properties and corrosion mechanism of both as-cast and solution-naturally age (T4) treated Mg-1.5Mn-1Ca-xSr alloys were investigated. The results showed that Sr is helpful to decrease grain size and increase the strength. The corrosion process of alloys was mainly determined by the quantity and distribution of second phases. Mg17Sr2, α-Mn and Ca-Sr phases acted as cathodes accelerated the corrosion of Mg2Ca anodic phase and α-Mg matrix. However, continuous distributed Mg17Sr2 was beneficial to resist the happening of localized corrosion because of its barrier effect. T4 treatment could significantly improve the mechanical properties and corrosion resistance of Mg alloys because of the dissolution of Mg2Ca phase and the dispersive distribution of Mg17Sr2 and α-Mn phases.

A CMOS Current Steering Neurostimulation Array With Integrated DAC Calibration and Charge Balancing.

An 8-channel current steerable, multi-phasic neural stimulator with on-chip current DAC calibration and residue nulling for precise charge balancing is presented. Each channel consists of two sub-binary radix DACs followed by wide-swing, high output impedance current buffers providing time-multiplexed source and sink outputs for anodic and cathodic stimulation. A single integrator is shared among channels and serves to calibrate DAC coefficients and to closely match the anodic and cathodic stimulation phases. Following calibration, the differential non-linearity is within ±0.3 LSB at 8-bit resolution, and the two stimulation phases are matched within 0.3%. Individual control in digital programming of stimulation coefficients across the array allows altering the spatial profile of current stimulation for selection of stimulation targets by current steering. Combined with the self-calibration and current matching functions, the current steering capabilities integrated on-chip support use in fully implanted neural interfaces with autonomous operation for and adaptive stimulation under variations in electrode and tissue conditions. As a proof-of-concept we applied current steering stimulation through a multi-channel cuff electrode on the sciatic nerve of a rat.

Pitting corrosion of a Rare Earth Mg alloy GW93

Pitting corrosion of magnesium (Mg) alloys is greatly associated with their microstructure, especially second phases. The second phases in traditional Mg alloys such as AZ91 are electrochemically nobler than Mg matrix, while the second phases in Rare earth (RE) Mg alloy GW93 are more active than Mg matrix. As a result, the pitting corrosion mechanism of Mg alloy GW93 is different from the traditional ones. This paper aims to clarify the pitting corrosion mechanism of Mg alloy GW93 through the studies of Volta potential by Scanning Kelvin Probe Force Microscopy (SKPFM), corrosion morphology by Scanning Electron Microscope (SEM), and corrosion resistance by electrochemical tests. Results reveal that the pitting corrosion of GW93 includes three stages, first, dissolution of the second phases, followed by corrosion of Mg matrix adjacent to the dissolved second phases, and finally, propagation of corrosion pits along the depth direction of the dissolved second phases. Anodic second phases and enrichment of Cl− in the thick corrosion product films dominate the propagation of pitting corrosion.

A Mixed Wettability Pore Size Distribution Based Mathematical Model for Analyzing Two-Phase Flow in Porous Electrodes

The non-isothermal, two-phase membrane electrodes assembly numerical model previously developed in Part I [J. Electrochem. Soc., 164, 6, F530 (2017)] is validated by comparing to experimentally measured electrochemical performance data under various operating conditions. Water accumulation in catalyst layer (CL) and gas diffusion layer (GDL) are also compared to the neutron and X-ray imaging data and shown to be in agreement. Water fluxes at cathode and anode boundaries and phase change induced flow are analyzed and compared to experimental data. Simulation results indicate that when liquid water is present, reactant transport in the catalyst layer is the key factor limiting fuel cell performance. The model shows that at high relative humidity, 80°C is the optimal operating temperature in order to delay water accumulation without degrading performance due to oxygen dilution by water vapor. The impact of CL and GDL hydrophilic volume fraction, hydrophobic contact angle and pore size distribution on performance are also studied. Results suggest that when liquid water is present, GDL parameters have minimal effect on performance and a CL should have a large hydrophobic contact angle, a low hydrophilic volume fraction, and large pore radius.

Analysis of compound action potentials elicited with specific current stimulating pulses in an isolated rat sciatic nerve.

The ability to selectively stimulate Aα, Aβ-fibers and Aδ-fibers in an isolated rat sciatic nerve (SNR) was assessed. The stimulus used was a current, biphasic pulse with a quasitrapezoidal cathodic phase and rectangular anodic phase where parameters were systematically varied: intensity of the cathodic phase (ic); width of the cathodic phase (tc); width of the cathodic exponential decay (texp) and time constant of the exponential decay (τexp). A SNR was stimulated using a pair of hook electrodes while conduction velocity (CV) and compound action potentials (CAP) were measured at two sites along the SNR using another two pairs of electrodes. Results showed that the highest CAP1 (8.5-9 mV), shall be expected when parameters of the stimulus were within the following range: ic=3.8-4 mA, tc=350-400 μs and texp=330-440 μs. Results also showed that with ascending tc and texp, CV of the corresponding superficial region of the SNR was reduced in both, conduction velocity of CAP1 and conduction velocity of CAP2. It was concluded that action potentials (APs) were activated in the Aβ-fibers and Aδ-fibers along with a slight AP inhibition in the Aβ-fibers. The obtained results, could serve as a tool for developing multi-electrode systems that potentially enable fiber-type selective stimulation of nerve fibers.

Electron transfer processes occurring on platinum neural stimulating electrodes: pulsing experiments for cathodic-first/charge-balanced/biphasic pulses for 0.566 ≤ k ≥ 2.3 in oxygenated and deoxygenated sulfuric acid

The application of a train of cathodic-first/charge-balanced/biphasic pulses applied to a platinum electrode resulted in a positive creep of the anodic phase potential that increases with increasing charge injection but reaches a steady-state value before 1000 pulses have been delivered. The increase follows from the fact that charge going into irreversible reactions occurring during the anodic phase must equal the charge going into irreversible reactions during the cathodic phase for charge-balanced pulses. In an oxygenated electrolyte the drift of the measured positive potential moved into the platinum oxidation region of the i(Ve) profile when the charge injection level exceeds k = 1.75. Platinum dissolution may occur in this region and k = 1.75 defines a boundary between damaging and non-damaging levels on the Shannon Plot. In a very low oxygen environment, the positive potential remained below the platinum oxidation region for the highest charge injection values studied, k = 2.3. The results support the hypothesis that platinum dissolution is the defining factor for the Shannon limit, k = 1.75. Numerous instrumentation issues were encountered in the course of making measurements. The solutions to these issues are provided.

Comparison of Stress Corrosion Cracking Susceptibility of Laser Machined and Milled 304 L Stainless Steel

Machining of austenitic stainless steel components is known to introduce significant enhancement in their susceptibility to stress corrosion cracking. The paper compares stress corrosion cracking susceptibility of laser machined 304 L stainless steel specimens with conventionally milled counterpart in chloride environment. With respect to conventionally milled specimens, laser machined specimens displayed more than 12 times longer crack initiation time in accelerated stress corrosion cracking test in boiling magnesium chloride as per ASTM G36. Reduced stress corrosion cracking susceptibility of laser machined surface is attributed to its predominantly ferritic duplex microstructure in which anodic ferrite phase was under compressive stress with respect to cathodic austenite.