Increase In Charge Transfer Resistance Research Articles

Identification of Lithium Plating in Lithium-Ion Batteries using Nonlinear Frequency Response Analysis (NFRA)

Nonlinear Frequency Response Analysis (NFRA) is a novel dynamic analysis method for Lithium-ion batteries. In contrast to the most commonly applied Electrochemical Impedance Spectroscopy (EIS), NFRA is not limited to the linear response of the system, as it uses higher sinusoidal excitation currents IAC of approximately 1.5 C. Higher harmonic response signals Yn with n2 are analysed. Thereby, additional dynamic information about the system is accessible. Here, the authors evaluate the potential of NFRA to detect the safety critical ageing process of Lithium plating. NFRA results are analysed and compared to EIS for cells aged at −10∘C with plating occurence and for cells without plating aged at 25∘C. A proof of concept for detection of Lithium plating with NFRA is presented. The third harmonic, Y3, is strongly sensitive to plated Lithium at time constants characteristic for electrochemical reactions for the analysed cells. Here, Lithium plating causes an increase of charge transfer resistance between the anode and the electrolyte, which affects the nonlinear behaviour. Ex-situ analysis validated that plating occurs only for the cells aged at −10∘C, but not for the cells aged at 25∘C. Further, it is presented that Y1, analysed with EIS, is not sufficient for the diagnosis of this ageing process. Therefore, NFRA is suggested as a new, reliable method for the identification of Lithium plating in Lithium-ion batteries.

Anti-corrosion performance of an epoxy ester coating filled with a new generation of hybrid green organic/inorganic inhibitive pigment; electrochemical and surface characterizations

In this study the effect of a hybrid organic/inorganic pigment based on zinc acetate-Cichorium intybus L. leaf extract on the corrosion protection properties of an epoxy ester coating were studied. Results of electrochemical impedance spectroscopy (EIS) revealed that the mild steel corrosion was significantly inhibited in the chloride solution in the presence of hybrid pigment extract. Results exhibited that with the increase in immersion time up to 24 h the corrosion inhibition efficiency significantly increased and reached the maximum value of 94%. Results obtained from the scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and energy dispersive spectroscopy (EDS) techniques confirmed the deposition of inhibitive films on the mild steel surface. Results showed that in the presence of hybrid pigment not only the barrier but also the active inhibition properties of the epoxy ester coating were effectively enhanced. The low frequency impedance value of the epoxy ester coating was increased in the presence of hybrid pigment, indicating the role of pigment on the coating barrier action enhancement. The increase in charge transfer resistance of the epoxy ester coating with artificial scratch depicted the active inhibition role of the hybrid pigment.

Unraveling the capacity fading mechanisms of LiNi0.6Co0.2Mn0.2O2 at elevated temperatures

LiNixCoyMnzO2 cathode materials play a vital role in next-generation lithium-ion batteries because of their high energy density, but they suffer capacity decay at elevated temperatures. Improving the cycling stability of LiNixCoyMnzO2 requires a basic comprehension of its capacity fade mechanisms. Here, we investigate the electrochemical performance of LiNi0.6Co0.2Mn0.2O2 at 55 °C under various cutoff voltages and examine the corresponding degradation mechanisms. The discharge capacity of LiNi0.6Co0.2Mn0.2O2 increases from 176.0 mAh g−1 to 218.1 mAh g−1 at 1 C as the cutoff voltage increases from 4.3 V to 4.7 V, whereas the capacity retention decreases from 96.3% to 78.9% after 50 cycles, respectively. Ex situ analyses via high-resolution transmission electron microscopy illuminate structural transformations of cathode materials after electrochemical cycling. This accounts for the increase in charge transfer resistance and capacity loss. In addition, X-ray photoelectron spectroscopy analyses highlight the correlations between the electrochemical performance and interfacial compositions of the cathode/electrolyte interface. These data provide another explanation for the capacity degradation. Our results underscore the value of improving the surface structural stability of cathode materials and reducing the charge transfer resistance of the electrode/electrolyte interface.

An ultrasensitive and selective electrochemical aptasensor based on rGO-MWCNTs/Chitosan/carbon quantum dot for the detection of lysozyme

An aptamer-based method is described for the electrochemical determination of lysozyme. A glassy carbon electrode was modified with a nanocomposite composed of reduced graphene oxide (rGO), multi-walled carbon nanotubes (MWCNTs), chitosan (CS), and a synthesized carbon quantum dot (CQD) from CS. The composition of the nanocomposite (rGO-MWCNT/CS/CQD) warrants a high surface-to-volume ratio, high conductivity, high stability, and great electrocatalytic activity. This nanocomposite provides a suitable site for better immobilization of aptamers due to the existence of many amino and carboxyl functional groups, and remaining oxygen-related defects properties in rGO. In addition, this nanocomposite allows considerable enhancement of the electrochemical signal and contributes to improving sensitivity. The amino-linked lysozyme aptamers were immobilized on the nanocomposite through covalent coupling between the amino groups of the aptamer and the amino groups of the nanocomposite using glutaraldehyde (GLA) linker. The modified electrode was characterized by electrochemical methods including differential pulse voltammetry (DPV), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). In the presence of lysozyme, the immobilized aptamer selectively caught the target lysozyme on the electrode interface that leads to a decrease in the DPV peak current and an increase in Charge Transfer Resistance (Rct) in EIS as an analytical signal. Using the obtained data from DPV and EIS techniques, two calibration curves were drawn. The anti-lysozyme aptasensor proposed has two very low LODs. These measures are 3.7 and 1.9 fmol L−1 within the wide detection ranges of 20 fmol L−1 to 10 nmol L−1, and 10 fmol L−1 to 100 nmol L−1 for DPV and EIS calibration curves, respectively. The GCE/rGO-MWCNT/CS/CQD showed sensitivity, high reproducibility, specificity and rapid response for lysozyme which can be used in biomedical fields.

An impedimetric biosensor for DNA damage detection and study of the protective effect of deferoxamine against DNA damage

The detection and inhibition of DNA damage are of great importance in the prevention and treatment of diseases. Developing a simple and sensitive tool for this purpose would be a chance to monitor the DNA damage and could be helpful in introducing some drugs which can prevent this phenomenon. Here, we report a novel and sensitive electrochemical biosensor based on DNA/Au nanoparticles (AuNPs) modified screen printed gold electrode (DNA/AuNPs/SPGE) to investigate the DNA damage process and also to study the protective behavior of deferoxamine (DFO). The proposed biosensor was fabricated by electrodeposition of AuNPs onto SPGE, followed by chemical immobilisation of thiol-terminated DNA. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) have been used to characterise this biosensor. Hydroxyl radical (OH), which is generated during the Fenton reaction, is responsible for the induced damage to DNA. EIS technique was applied to monitor the DNA damage, and the increase in charge transfer resistance (Rct) following the DNA damage, was considered as an indicator. Furthermore, the ability of the electrochemical screening system was proved by the investigation of the antioxidant effect of DFO in prohibiting the DNA damage.

A universal and label-free impedimetric biosensing platform for discrimination of single nucleotide substitutions in long nucleic acid strands

We report a label-free universal biosensing platform for highly selective detection of long nucleic acid strands. The sensor consists of an electrode-immobilized universal stem-loop (USL) probe and two adaptor strands that form a 4J structure in the presence of a specific DNA/RNA analyte. The sensor was characterized by electrochemical impedance spectroscopy (EIS) using K3[Fe(CN)6]/K4[Fe(CN)6] redox couple in solution. An increase in charge transfer resistance (RCT) was observed upon 4J structure formation, the value of which depends on the analyte length. Cyclic voltammetry (CV) was used to further characterize the sensor and monitor the electrochemical reaction in conjunction with thickness measurements of the mixed DNA monolayer obtained using spectroscopic ellipsometry. In addition, the electron transfer was calculated at the electrode/electrolyte interface using a rotating disk electrode. Limits of detection in the femtomolar range were achieved for nucleic acid targets of different lengths (22 nt, 60 nt, 200 nt). The sensor produced only a background signal in the presence of single base mismatched analytes, even in hundred times excess in concentration. This label-free and highly selective biosensing platform is versatile and can be used for universal detection of nucleic acids of varied lengths which could revolutionize point of care diagnostics for applications such as bacterial or cancer screening.

Aging induced structural and electrochemical corrosion behaviour of Sn-1.0Ag-0.5Cu and Sn-3.8Ag-0.7Cu solder alloys

The electrochemical corrosion behaviour of Sn-1.0Ag-0.5Cu (SAC105) and Sn-3.8Ag-0.7Cu (SAC387) solder alloys, isothermally aged at 120 °C for two different time periods of 4 h and 72 h, has been investigated in 0.5 M NaCl solution using potentiodynamic polarization measurements and electrochemical impedance spectroscopy. The aging of SAC105 and SAC387 results in significant changes in morphology, size and distribution of intermetallic compounds Cu6Sn5 and Ag3Sn. This study reveals that SAC387 has more corrosion resistance than SAC105 for both aging time periods of 4 hrs and 72 h. SAC105 solder alloy after aging for 72 h became significantly more corrosion resistant than SAC387 aged for 4 hrs. SAC105 and SAC387 aged for 72 hrs exhibit increased charge transfer resistance (Rct), the impedance value, and maximum bode phase angle. This study signifies that an aging process combined with Ag content in SAC solder alloys can be exploited to enhance the corrosion resistance making them suitable for electronic devices used in harsh environments.

SOLVENTS EFFECT ON THERMAL STABILITY AND ELECTROCHEMICAL BEHAVIOUR OF GRIFFONIA SIMPLICIFOLIA EXTRACTS AS STEEL CORROSION INHIBITOR IN ACIDIC ENVIRONMENT

Different solvents were used to extract Griffonia simplicifolia and tested corrosion inhibitors for as X80 steel in 1 M HCl solution. The corrosion tests were conducted by thermo-gravimetric analyses (TGA), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) while the surface morphologies were checked by scanning electron microscopy (SEM). The essence was to investigate the effects of the solvents on the yield, phytochemical profile, corrosion inhibition properties and thermal stability of the extracts. The highest yields of 63.24 g kg -1 and 51.63 g kg -1 were obtained with seeds (SEGS) and leaves (LEGS) extracts respectively in ethanol-water (1:1) system. Acetone extract showed presence of all the tested phytochemicals namely alkaloids, tannins, saponins, glycosides, steroids and terpenoids. The highest inhibition efficiencies of 95.86 % (SEGS) and 82.14 % (LEGS) were obtained with acetone extracts. Acetone extract was also most thermally stable being 66.4 % (SEGS) and 50.05 % (LEGS) efficient at 90 °C, followed by ethanol extract while methanol extract was least stable and least efficient. Inhibitors act as mixed type and their addition increased charge transfer resistance and decreased corrosion current density with respect to the free acid solution. Micrographs of the steel surface in some systems show evidence of slight surface protection by the inhibitors. It has been inferred from this study that both acetone and ethanol are better solvents for extraction of Griffonia simplicifolia based corrosion inhibitors.

Mechanisms of the decrease in low-temperature electrochemical performance of Li4Ti5O12-based anode materials

The electrochemical performances of Li4Ti5O12 (LTO) and Li4Ti5O12-rutile TiO2 (LTO–RTO) composite electrodes at low temperatures were evaluated. The electrochemical performance of both electrodes decreased at low temperatures; regardless, the LTO–RTO electrode performed better than the LTO electrode. First, high viscosity and low ion conductivity of liquid electrolytes at low temperatures significantly reduce electrochemical performance. Second, cycling at low temperatures changes the crystal structure of LTO–based electrodes, impeding lithium ion diffusion and even causing the diffusion path to change from easy to difficult. However, changes in the crystal structure of the LTO–RTO electrode were not sufficient to change this path; thus, diffusion continued along the 8a-16c-8a pathway. Finally, from the perspective of dynamics, aggravation of a side reaction, increase in charge transfer resistance and polarization, and decrease in lithium ion diffusion at low temperatures reduce the electrochemical performance of LTO–based anode materials. However, the activation energy based on lithium ion diffusion is lower in the LTO–RTO electrode than the LTO electrode. The results confirmed that the electrochemical performance of the LTO–RTO electrode was better than that of the LTO electrode at low temperatures.

Lithium ion batteries (NMC/graphite) cycling at 80 °C: Different electrolytes and related degradation mechanism

A comprehensive study on high temperature cycling (80 °C) of industrial manufactured Li-ion pouch cells (NMC-111/Graphite) filled with different electrolytes is introduced. Ageing processes such as capacity fade, resistance increase and gas generation are reduced by the choice of appropriate electrolyte formulations. However, even by using additive formulations designed for elevated temperatures a large resistance increase is observed after 200 cycles and more (which does not happen at 55 °C). Symmetrical EIS (Electrochemical Impedance Spectroscopy) shows that the cathodic charge transfer resistance is the main reason for this behaviour. Nonetheless most of the active Li is still available when cycling with suitable additives. No change of the cathode crystalline structure or a growth of the cathodic surface reconstruction layer is observed post cycling at 80 °C. Therefore a disintegration of NMC secondary particles is believed to be the main reason of the cell failure. A separation of single grains is leading to new decomposition and reconstruction layers between primary particles and an increased charge transfer resistance. Further approaches to improve the high temperature cycle stability of NMC based materials should therefore be aimed at the cathode particles morphology in combination with similar electrolyte formulations as used in this study.

Highly Sensitivein vitroBiosensor for EnterotoxigenicEscherichia coliDetection Based on ssDNA Anchored on PtNPs‐Chitosan Nanocomposite

AbstractDetection of EnterotoxigenicEscherichia coliin various biological samples has tremendous importance in human health. In this direction, we have designed a label free electrochemical biosensor for highly selective detection ofEscherichia colithrough detecting ST gene. The ability of sensor probe to detect STGwas confirmed using polymerase chain reaction. The biosensor was fabricated based on STGspecific probes immobilized on platinum nanoparticles chitosan nanocomposite on screen printed carbon electrode, which was characterized by cyclic voltammetry, transmission electron microscopy, and fourier transform infrared spectroscopy. A highly sensitive label free sensing was achieved by analyzing STGhybridization using electrochemical impedance spectroscopy (EIS) technique. The EIS analysis showed a significant increase in charge transfer resistance after STGinteraction with the highly selective ssDNA probe immobilized on the nanocomposite film. The increase in charge transfer resistance was evaluated for varying concentrations of STG, which shows a dynamic range between 1.0×10−12and 1.0×10−4with the detection limit of 3.6×10−14 M (RSD<4.5 %). The regeneration of sensor probe was also studied and interference due to non‐target sequences was evaluated to ensure the selectivity of the designed sensor. The practical applicability of sensor probe was also analyzed by detecting the STGfrom the bacteria present in surface water.

Antibacterial effects, biocompatibility and electrochemical behavior of zinc incorporated niobium oxide coating on 316L SS for biomedical applications

Abstract In the present study, Nb2O5 (NZ0) composite coatings with various concentrations of zinc (NZ2, NZ4 & NZ6) are produced on 316L SS by sol-gel method with the aim of improving its antibacterial activity, bone formability and corrosion resistance properties. This work studied the surface characterization of NZ0, NZ2, NZ4 & NZ6 coated 316L SS by ATR-FTIR, XRD, HR-SEM with EDAX. The synthesized coatings were different in the morphological aspects, NZ0 shows mesoporous morphology whereas irregular cluster like morphology was observed for the zinc incorporated coatings. The chemical composition of the NZ0 and NZ4 composite coatings were studied by XPS and the results revealed that the zinc exist as ZnO and Nb as Nb2O5 in the coatings. The increase in the concentration of zinc in Nb2O5 increases the hydrophilic nature identified by water contact angle studies. The potentiodynamic polarization studies in simulated body fluid reveals the increase in polarization resistance with decrease in current density (icorr) and electrochemical impedance spectroscopic studies with increase in charge transfer resistance (Rct) and double layer capacitance (Qdl) were observed for NZ4 coated 316L SS. The inhibition of Staphylococcus aureus and Escherichia coli bacteria were identified for NZ4 coated 316L SS by bacterial viability studies. The NZ4 coated 316L SS showed better Osseo-integration by spreading the MG 63 osteoblast cells. The study results imply that zinc incorporated Nb2O5 (NZ4) composite coating exhibits antibacterial activity and also enhance the corrosion resistance and biocompatibility of the 316L SS.

Corrosion inhibition performance of tannins for mild steel in hydrochloric acid solution

The corrosion inhibition behavior of commercial hydrolysable tannin (tara tannin), condensed tannin (black wattle tannin) and complex tannin (bayberry tannin) for mild steel in hydrochloric acid were investigated by means of gravimetric and electrochemical measurements. The inhibition efficiency increased with the increase of tannin concentration, and the inhibition performance of tannin followed hydrolysable tannin > complex tannin > condensed tannin. The pH of bulk solution has a significant impact on the inhibition behavior of tannin. Tannins exhibited high inhibition performance at low pH (0.3), but the corrosion rate slightly increased with a pH ≥ 2 for hydrolysable tannin and a pH > 3 for condensed tannin and complex tannin. Surface analysis revealed the formation of a protective compact inhibition film at pH 0.3, whereas a loose cracked film at pH 5.0 was revealed on the mild steel surface. The loose cracked film was deposition of ferric-tannates characterized by FTIR. Polarization experiments showed tannins act as mixed-type inhibitors with predominant anodic depression for hydrolysable tannin and cathodic depression for condensed tannin and complex tannin. EIS results indicated the increase of charge transfer resistance in the presence of tannins in 0.5 M HCl, supporting the formation of a protective film on a mild steel surface. Quantum chemical calculations predicted the higher inhibition performance of hydrolysable tannin based on the electronic properties of the molecular model. Molecular dynamic simulation revealed a nearly flat configuration for the hydrolysable tannin model molecule on a metal surface with more negative adsorption energies, as confirmed by the experiments.

Chitosan: A macromolecule as green corrosion inhibitor for mild steel in sulfamic acid useful for sugar industry

The present investigation aims at investigation of low cost nontoxic carbohydrate biopolymer chitosan as corrosion inhibitor alone and in combination with KI for mild steel in 1M sulfamic acid medium using gravimetric, electrochemical and surface analysis techniques. It is found that chitosan alone exhibits inhibition efficiency of 73.8% at 200ppm concentration. However, in combination with KI (5ppm), it gave more than 90% inhibition efficiency. The significant increase in the inhibition performance of chitosan has been explained by the synergistic mechanism. The results of Potentiodynamic polarization study shows that chitosan and its blend with KI decreases both anodic and cathodic reactions occurring at mild steel surface in 1M sulfamic acid medium by blocking active sites of the metal and acts as mixed type inhibitor. EIS study reveals that the polarization resistance increases with increase in the concentration of inhibitors which increases charge transfer resistance across the metal/solution interface. The adsorption of chitosan followed the Langmuir adsorption isotherm. The formation of inhibitor film on metal surface was supported by scanning electron microscopy (SEM) and atomic force microscopy (AFM) surface studies.

Investigation of electrolyte leaching in the performance degradation of phosphoric acid-doped polybenzimidazole membrane-based high temperature fuel cells

Precise monitoring of electrolyte leaching in high-temperature polymer electrolyte membrane fuel cell (HT-PEMFC) devices during lifetime tests is helpful in making a diagnosis of their quality changes and analyzing their electrochemical performance degradation. Here, we investigate electrolyte leaching in the performance degradation of phosphoric acid (PA)-doped polybenzimidazole (PBI) membrane-based HT-PEMFCs. We first perform quantitative analyses to measure PA leakage during cell operation by spectrophotometric means, and a higher PA leakage rate is detected when the current density is elevated in the cell. Second, long-term degradation tests under various current densities of the cells and electrochemical impedance spectroscopy (EIS) analysis are performed to examine the influence of PA loss on the membrane and electrodes during cell performance degradation. The combined results indicate that PA leakage affect cell performance durability, mostly due to an increase in charge transfer resistance and a decrease in the electrochemical surface area (ECSA) of the electrodes. Additionally, a three-dimensional (3-D) HT-PEMFC model is applied to a real-scale experimental cell, and is successfully validated against the polarization curves measured during various long-term experiments. The simulation results highlight that the PA loss from the cathode catalyst layer (CL) is a significant contributor to overall performance degradation.

Mechanism for capacity fading of 18650 cylindrical lithium ion batteries

The mechanism for capacity fading of 18650 lithium ion full cells under room-temperature (RT) is discussed systematically. The capacity loss of 18650 cells is about 12.91% after 500 cycles. The cells after cycles are analyzed by XRD, SEM, EIS and CV. Impedance measurement shows an overall increase in the cell resistance upon cycling. Moreover, it also presents an increased charge-transfer resistance (Rct) for the cell cycled at RT. CV test shows that the reversibility of lithium ion insertion/extraction reaction is reduced. The capacity fading for the cells cycled can be explained by taking into account the repeated film formation over the surface of anode and the side reactions. The products of side reactions deposited on separator are able to reduce the porosity of separator. As a result, the migration resistance of lithium ion between the cathode and anode would be increased, leading the fading of capacity and potential.

What Limits the Rate Capability of Li-S Batteries during Discharge: Charge Transfer or Mass Transfer?

Li-S batteries exhibit poor rate capability under lean electrolyte conditions required for achieving high practical energy densities. In this contribution, we argue that the rate capability of commercially-viable Li-S batteries is mainly limited by mass transfer rather than charge transfer during discharge. We first present experimental evidence showing that the charge-transfer resistance of Li-S batteries and hence the cathode surface covered by Li2S are proportional to the state-of-charge (SoC) and not to the current, directly contradicting previous theories. We further demonstrate that the observed Li-S behaviors for different discharge rates are qualitatively captured by a zero-dimensional Li-S model with transport-limited reaction currents. This is the first Li-S model to also reproduce the characteristic overshoot in voltage at the beginning of charge, suggesting its cause is the increase in charge transfer resistance brought by Li2S precipitation.

Nanostructured magnesium silicide Mg2Si and its electrochemical performance as an anode of a lithium ion battery

Nano-crystalline Mg2Si (Mg67Si33) and its Si-rich eutectic (Mg47Si53) composition were synthesized by hydrogen desorption-recombination process, casting and rapid solidification techniques. The synthesis of Mg2Si meets experimental challenges due to a significant difference in the melting temperatures of Mg (650 °C) and Si (1414 °C) and due to easy vaporization of magnesium metal. As cast alloys were obtained by induction melting the precursors, Mg and Si, followed by the casting and water quenching. These alloys were rapidly solidified using a chill block melt spinning which produces ribbons with fine dendritic morphology and a grain size close to 100 nm. Hydrogen desorption-recombination process of MgH2-Si mixture resulted in a release of ∼4.67 wt % H and formation of Mg2Si. The microstructure of the alloys has been studied using Scanning Electron Microscopy and the relationship between microstructure and electrochemical properties as anodes of the lithium ion batteries was characterised. The electrochemical tests indicate that Si rich eutectic electrode shows a higher charge-discharge capacity than the Mg2Si intermetallic. Rapidly solidified Mg2Si and Mg2Si + Si alloys showed the highest initial discharge capacities of 989 mAh/g and 1283 mAh/g, respectively, superior to the alloys prepared by hydrogen desorption-recombination process and casting. The presence of electrolyte additives FEC (5%) and VC (1%) resulted in the formation of the stable SEI layer and enhanced the cycling capacity of the electrodes. Electrochemical Impedance Spectroscopy (EIS) was used to characterize the anode electrodes on cycling. A mathematical model for accounting the impedance response was utilised. The EIS response showed an increased overall resistance for the Mg2Si eutectic Si-containing alloy electrodes when compared to the electrodes based on a stoichiometric Mg2Si. Long-term cycling resulted in increased charge transfer resistance, which slowed down the electrochemical processes at the surface of the electrodes.

A study of the interactions of Hg(II) with T-T mispair containing hairpin loops

This manuscript describes the result of a series of electrochemical, spectroscopic and thermodynamic studies into oligonucleotide hairpin structures equipped with T-T mispairs and investigates their interaction with Hg(II). For this purpose, three hairpin DNAs were designed, in which the stem-region remains constant and loop region contains increasing T-T mispairs (5ʹ-HO-(CH2)6-S-S-(CH2)6-TGTAGTTCCTTCTACA-3ʹ, 5ʹ-HO-(CH2)6-S-S-(CH2)6-TGTAGTTTTCCTTTTCTACA-3ʹ; 5ʹ-HO-(CH2)6-S-S-(CH2)6-TGTAGTTTTTTCCTTTTTTCTACA-3ʹ). Various techniques such as electrochemical impedance spectroscopy (EIS), circular dichroism (CD), UV-visible and isothermal titration calorimetry (ITC) were employed to get a systematic evaluation of the need for multiple T-T mispairs for enhanced Hg(II) binding. EIS shows an increase in charge transfer resistance (ΔRCT) due to structural changes within the thin film caused by Hg(II) binding. The CD studies indicate the Hg(II) induced changes in CD signals of hairpin DNAs from right-handed to left handed structures. Highest cooperative binding was observed with DNA having maximum T-T mispairs which was supplemented by detailed UV-visible thermal analysis of DNA-Hg(II) structures. These findings were further supported by detailed measurements of the thermochemistry of the interaction by ITC. Our studies show that the number of T-T mispairs are critical for maximizing nucleobase-Hg(II) interactions.

Electrophoretic deposition of 3YSZ coating on AZ91D using an aluminum interlayer

The zirconia stabilized by 3 mol % Y2O3 (3YSZ) was applied onto the surface of the magnesium alloy AZ91D using electrophoretic deposition (EPD) from a non- aqueous solvent. An interlayer of aluminum between the substrate and YSZ coating was also prepared by EPD. The preparation, microstructure and corrosion resistance of the coatings were investigated. The surface morphologies of the coatings were studied by scanning electron microscopy (SEM) and their compositions were determined by X-ray diffraction (XRD). The corrosion resistance of the coatings was evaluated by electrochemical impedance spectroscopy (EIS) in 3.5% NaCl solution. The results indicate that the aluminum interlayer has a favorable effect on the densification of the coating by formation of aluminum oxide. In addition, the corrosion resistance of coated AZ91D alloy in chloride solution is significantly improved because of the aluminum interlayer and an increase in charge-transfer resistance of the AZ91D surface in chloride solution was observed which was attributed to YSZ.