Localized corrosion and inhibition studies using the wire beam electrode in conjunction with the electrochemical noise analysis and the scanning reference electrode techniques

Several new technical developments have been made based on the combined use of the wire beam electrode (WBE), electrochemical noise analysis (ENA) and the scanning reference electrode technique (SRET). These have included: (i) The WBE-R n method- the combined use of the WBE and the noise resistance (Rn) to map the rates and patterns of uniform or localized corrosion; (ii) The WBE-Noise Signatures method- the combined use of the WBE and the noise signature to detect the origination and propagation of localized corrosion; and (iii) The WBE-SRET method- the combined use of the WBE and SRET to investigate localized corrosion from both the metallic and electrolyte phases of a corroding metal surface. This paper presents a brief review on these novel methods and their applications for detecting general and localized corrosion, for mapping the rates of corrosion, and for studying corrosion inhibitors.

Studying and evaluating anti-corrosion coatings and inhibitors using the wire beam electrode method in conjunction with electrochemical noise analysis

Purpose – To provide a summary of research work carried out mainly in the authors' group for evaluating various protective coatings including rustproofing oils, and also for studying corrosion inhibitors using the wire beam electrode (WBE) method.

Design/methodology/approach – A range of published papers published during the past 15 years was summarised and reviewed. Recent research work in the authors' group was also included, which involved the combined use of the WBE with electrochemical noise analysis and the scanning reference electrode technique.

Findings – The WBE method has been developed into a very useful tool of evaluating the performance of coatings and inhibitors. In particular, The WBE is uniquely applicable for determining the performance of coatings and inhibitors to control localised corrosion.

Research limitations/implications – Focusing mainly on recent research.

Practical implications – A useful source of information for researchers and graduate students working in the areas of organic coating and inhibitor research.

Originality/value – The first summary or review on this research topic.

On choosing a reference redox system for electrochemical measurements: A cautionary tale

The potential of a quasi-reference electrode can be determined by introducing an internal reference redox system (IRRS) which comprises either the oxidizable or reducible form of a reversible (and, ideally, outer-sphere) redox couple and then observing the cyclic voltammetric responses. The objective is to choose the IRRS so that the cyclic voltammetric response for the simultaneously present electroactive analyte system (ANS) can be observed independently of the IRRS response. We identify three fundamental paradigms describing the relative positioning of the IRRS and ANS on the potential scale, the operative redox components for the IRRS and ANS, and the starting potential (E start), reversing potential (E rev), and ending potential (E end) for the cyclic voltammetric scan as follows: paradigm A, an optimal paradigm which can produce completely independent cyclic voltammetric responses for the IRRS or for ANS; paradigm B, a less-than-optimal paradigm which can produce an independent cyclic voltammetry (CV) response for the ANS or a mixed response for the IRRS with that response on top of the ANS response; paradigm C, a problematic paradigm that can produce an independent CV response for the IRRS or a mixed response for the ANS with that response on top of the IRRS response; and any mixed response produces a thermodynamically favored redox cross-reaction which couples the IRRS and ANS systems and which can complicate the analysis of the ANS and IRRS responses. The conclusion is that paradigm C is to be avoided.

Bi-functional oxygen electrocatalysts based on Palladium oxide-Ruthenium oxide composites

Bi-functional oxygen electrodes are an enabling component for rechargeable metal-air batteries and regenerative fuel cells, both of which are regarded as the next-generation energy devices with zero emission. Nonetheless, at the present, no single metal oxide component can catalyze both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) with high performance which leads to large overpotential between ORR and OER. This work strives to address this limitation by studying the bi-functional electrocatalytic activity of the composite of a good ORR catalyst compound (e.g. palladium oxide, PdO) and a good OER catalyst compound (e.g. ruthenium oxide, RuO2) in alkaline solution (0.1M KOH) utilizing a thin-film rotating disk electrode technique. The studied compositions include PdO, RuO2, PdO/RuO2 (25wt.%/75wt.%), PdO/RuO2 (50wt.%/50wt.%) and PdO/RuO2 (75wt.%/25wt.%). The lowest overpotential (e.g. E (2 mA cm−2) - E (-2 mA cm−2)) of 0.82 V is obtained for PdO/RuO2 (25wt.%/75wt.%) (versus Ag|AgCl (3M NaCl) reference electrode).

Preparation, characterization and dielectric properties of temperature stable SrTiO3/PEEK composites for microwave substrate applications

Poly(ether ether ketone) (PEEK) is a potential candidate for electronic applications due to its low permittivity, low loss, high melting point, better chemical resistance, excellent insulating properties and easy processibility. Present paper discusses the preparation and characterization of SrTiO3 filled PEEK composite for microwave substrate applications. The dielectric constant, dielectric loss and temperature variation of dielectric constant of the composites have been studied up to 1 MHz using an Impedance Analyzer. Different theoretical approaches have been employed to predict the effective permittivity of composite systems and the results are compared with that of the experimental data. The crystallinity of the bulk composite is studied by X-ray diffraction studies. Scanning electron microscopic technique has been employed to study the dispersion of the particulate filler in PEEK matrix. Vickers hardness of pure and filled PEEK composite has been measured using Microhardness Tester. The effect of particle size on the dielectric as well as mechanical properties of SrTiO3/PEEK composite system is also studied by incorporating micronsize and nanosize fillers. Present study shows that a temperature stable composite can be realized by judiciously selecting appropriate filler concentration in the PEEK matrix.

Comonitoring of adenosine and dopamine using the wireless instantaneous neurotransmitter concentration system : proof of principle : laboratory investigation

Object

The authors of previous studies have demonstrated that local adenosine efflux may contribute to the therapeutic mechanism of action of thalamic deep brain stimulation (DBS) for essential tremor. Real-time monitoring of the neurochemical output of DBS-targeted regions may thus advance functional neurosurgical procedures by identifying candidate neurotransmitters and neuromodulators involved in the physiological effects of DBS. This would in turn permit the development of a method of chemically guided placement of DBS electrodes in vivo. Designed in compliance with FDA-recognized standards for medical electrical device safety, the authors report on the utility of the Wireless Instantaneous Neurotransmitter Concentration System (WINCS) for real-time comonitoring of electrical stimulation–evoked adenosine and dopamine efflux in vivo, utilizing fast-scan cyclic voltammetry (FSCV) at a polyacrylonitrile-based (T-650) carbon fiber microelectrode (CFM).
Methods

The WINCS was used for FSCV, which consisted of a triangle wave scanned between −0.4 and +1.5 V at a rate of 400 V/second and applied at 10 Hz. All voltages applied to the CFM were with respect to an Ag/AgCl reference electrode. The CFM was constructed by aspirating a single T-650 carbon fiber (r = 2.5 μm) into a glass capillary and pulling to a microscopic tip using a pipette puller. The exposed carbon fiber (the sensing region) extended beyond the glass insulation by ~ 50 μm. Proof of principle tests included in vitro measurements of adenosine and dopamine, as well as in vivo measurements in urethane-anesthetized rats by monitoring adenosine and dopamine efflux in the dorsomedial caudate putamen evoked by high-frequency electrical stimulation of the ventral tegmental area and substantia nigra.
Results

The WINCS provided reliable, high-fidelity measurements of adenosine efflux. Peak oxidative currents appeared at +1.5 V and at +1.0 V for adenosine, separate from the peak oxidative current at +0.6 V for dopamine. The WINCS detected subsecond adenosine and dopamine efflux in the caudate putamen at an implanted CFM during high-frequency stimulation of the ventral tegmental area and substantia nigra. Both in vitro and in vivo testing demonstrated that WINCS can detect adenosine in the presence of other easily oxidizable neurochemicals such as dopamine comparable to the detection abilities of a conventional hardwired electrochemical system for FSCV.
Conclusions

Altogether, these results demonstrate that WINCS is well suited for wireless monitoring of high-frequency stimulation-evoked changes in brain extracellular concentrations of adenosine. Clinical applications of selective adenosine measurements may prove important to the future development of DBS technology.

Crystalline Structures and α → β and γ polymorphs transformation induced by nanoclay in PVDF-based nanocomposite

Poly(vinylidene fluoride) (PVDF) nanocomposites were prepared by melt-mixing. The dispersion of clay platelets and rheology of nanocomposites were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and rheometric mechanical spectrometer (RMS). The transformation of α to β and γ phase in PVDF was induced by the addition of nanoclay and subsequently the isothermal crystallization kinetics of neat PVDF and its nanocomposite have been investigated. The interaction between clay nanofillers and PVDF macromolecular chains induced the change of conformation from trans-gauche to all-trans crystal structure in PVDF segment. The isothermal crystallization of PVDF/clay nanocomposites was carried out by Differential Scanning Calorimetry (DSC) technique. The influence of clay platelets on nucleation crystallization rate and Avrami exponent were studied. PVDF/clay nanocomposite showed higher crystallization rate indicating that nanoclay has acted as an effective nucleation agent. This nucleation effect of nanoclay increased the Avrami exponent and decreased the degree of crystallinity. © 2014 World Scientific Publishing Company.

A multi-wavelet based technique for calculating dense 2D disparity maps from stereo

A vision based approach for calculating accurate 3D models of the objects is presented. Generally industrial visual inspection systems capable of accurate 3D depth estimation rely on extra hardware tools like laser scanners or light pattern projectors. These tools improve the accuracy of depth estimation but also make the vision system costly and cumbersome. In the proposed algorithm, depth and dimensional accuracy of the produced 3D depth model depends on the existing reference model instead of the information from extra hardware tools. The proposed algorithm is a simple and cost effective software based approach to achieve accurate 3D depth estimation with minimal hardware involvement. The matching process uses the well-known coarse to fine strategy, involving the calculation of matching points at the coarsest level with consequent refinement up to the finest level. Vector coefficients of the wavelet transform-modulus are used as matching features, where wavelet transform-modulus maxima defines the shift invariant high-level features with phase pointing to the normal of the feature surface. The technique addresses the estimation of optimal corresponding points and the corresponding 2D disparity maps leading to the creation of accurate depth perception model.

Practical application of the Delphi technique in a bicultural mental health nursing study in New Zealand

Background. Numerous studies have employed the Delphi technique to seek expert opinion about aspects of clinical practice. When researching literature on the Delphi technique, however, we discovered discrepancies in its application, and a lack of detail when reporting design, administration, and analysis methods. Such lack of specificity hinders the replicability and assessment of the clinical and cultural validity and reliability of Delphi studies.

Aim. The aim of this paper is to detail the practical application of the Delphi technique as a culturally and clinically valid means of accessing expert opinion on the importance of clinical criteria.

Methods. Reference is made to a bicultural New Zealand mental health nursing clinical indicator study that employed a three-round reactive Delphi survey. Equal proportions of Maori and non-Maori nurses (n = 20) and consumers (n = 10) rated the importance of 91 clinical indicator statements for the achievement of professional practice standards. Additional statements (n = 21) suggested by Delphi participants in round 1 were included in subsequent rounds. In round 2, participants explained the rating they applied to statements that had not reached consensus in round 1, and summarized responses were provided to participants in round 3. Consensus was considered to have been achieved if 85% of round 3 ratings lay within a 2-point bracket on the 5-point Likert-scale overall, or in one of the Maori nurse, non-Maori nurse, or consumer groups. A mean rating of 4·5 after round 3 was set as the importance threshold.

Findings. Consensus occurred overall on 75 statements, and within groups on another 24. Most statements (n = 86) reached the importance benchmark.

Conclusions. When rigorous methods of participant selection, group composition, participant feedback, and determination of consensus and importance are employed, the Delphi technique is a reliable, cost-effective means of obtaining and prioritizing experts judgements.

Development and application of a microelectrode based scanning voltammetric detector

A large part of the work presented in this thesis describes the development and use of a novel electrochemical detector designed to allow the electrochemical characterisation of compounds in flowing solution by means of cyclic voltammetry. The detector was microprocessor controlled, which provides digital generation of the potential waveform and collection of data for subsequent analysis. Microdisk working electrodes are employed to permit both thermodynamic and kinetically controlled processes to be studied under steady-state conditions in flowing solutions without the distortion or hysteresis normally encountered with larger sized electrodes. The effect of electrode size, potential scan rate, and solution flow rate are studied extensively with the oxidation of ferrocene used as an example of a thermodynamically controlled process and a series of catecholamines as examples of a kinetically controlled process. The performance of the detector was best demonstrated when used as a HPLC post-column detector. The 3-dimensional chromatovoltammograms obtained allow on-line characterisation of each fraction as it elutes from the column. The rest of the work presented in this thesis involves the study of the oxidative degradation pathway of dithranol. The oxidative pathway was shown to involve a complex free radical mechanism, dependent on the presence of both oxygen and, in particular light. The pathway is further complicated by the fact that dithranol may exist in either a keto or enol form, the enol being most susceptible to oxidation. A likely mechanism is proposed from studies performed with cyclic voltammetry and controlled potential electrolysis, then defined by subsequent kinetic studies.

Investigation of nonisothermal crystallization behaviors of poly and silica nanocomposites using differential scanning calorimetry

Nonisothermal crystallization behaviors of PVA and poly (vinyl alcohol) and Silica (PVA/SiO2) nanocomposites prepared via a self-assembly monolayer (SAM) technique are investigated in this study. Differential scanning calorimetry (DSC) is used to measure the crystallization temperature and enthalpy of PVA and nanocomposites in nitrogen at various cooling rate. The results show that the degree of crystallinity of PVA and nanocomposites decreases when the SiO₂ content increases but increases with an increasing cooling rate. The peak crystallization temperature decreases with an increasing cooling rate.

Silver sulfide as a staining agent for scanning electron microscopy of nylon 6/MXD6 blends

BACKGROUND: In transmission and scanning electron microscopy imaging, the ability to obtain sufficient contrast between the components of a blend when they are both of a similar chemical structure still remains problematic. This paper investigates the domain morphology of a polymer blend containing two polyamides, nylon 6 and the semi-aromatic polyamide poly(m-xylene adipamide) (MXD6), using scanning electron microscopy in backscattered electron imaging mode. The efficiency of three staining agents, ruthenium tetroxide, phosphotungstic acid and silver sulfide, in obtaining optimum phase contrast between the two polymers is discussed.
RESULTS: The use of silver sulfide as a staining agent was found to be a fast and reliable approach which required basic sample preparation and provided excellent compositional contrast between the phases present in the nylon 6/MXD6 blends compared to the other staining agents.
CONCLUSIONS: The technique described in this paper is believed to be a novel and versatile method that has the potential to further improve the ability to study complex polymer blends where one polymer contains an aromatic ring.