Increase In Impedance Values Research Articles

Effect of combined microbial and stress corrosion on 7075 aluminum alloy in high salinity environment

The study investigates the impact of the combination of Gram-positive bacteria Bacillus subtilis (B. subtilis) and tensile stress on the surface corrosion of 7075 aluminum alloy (AA7075) in a high-salt solution environment. The change in PH value caused by the growth curve of bacteria was analyzed for corrosion factors. Scanning electron microscopy (SEM) and ultra-depth 3D microscopy (DOF) were used to compare the surface morphology, elements and corrosion of the samples. The presence of a biofilm reduces the corrosion rate by 0.005 ± 0.0004 mm/y and the application of a constant load results in an increase in the corrosion rate to 0.26 ± 0.013 mm/y. The applied stress leads to the disruption of both the biofilm and oxide film on the metal surface, causing a significant reduction in the impedance isolation effect, and resulting in an expansion of the average diameter and depth of the corrosion pit by 372.21 and 29.5 µm, respectively. In electrochemical impedance testing, there is an approximately 7.01×103 Ω increase in impedance value when exposed to B. subtilis environment; conversely, under stress conditions, there is a decrease by 4.02×103 Ω with B. subtilis present. The corrosion current density has increased fourfold to reach 9.15×10−6 (uA/cm2). This suggests that the combination of bacterial and stress can have a complex and detrimental impact on the corrosion behavior of aluminum alloys in high-salt environments.

Influence of pre-treatments on adhesion, barrier and mechanical properties of epoxy coatings: A comparison between steel, AA7075 and AA2024

In this work five independent pre-treatments – mechanical polishing, alkaline and acid etching, sol-gel primer, and anodizing – were applied on mild steel and aluminum (AA7075 and AA2024) substrates before the deposition of epoxy coatings. The results demonstrate that efficient adhesion can be achieved by simple methodologies and widely available chemicals as an alternative to toxic conversion layers or highly energetic processes. All the treatments provided higher adhesion (up to 75%, 61% and 14% on AA7075, AA2024 and steel, respectively) and better anti-corrosion performance (increase of impedance values at low frequency up to four orders of magnitude) than the polished reference. The anodizing of aluminum alloys yielded good anti-corrosion performance, but slightly lower mechanical properties compared to sol-gel primer and alkaline etching. The hydroxyls density was found to play a major role in strong adhesion prevailing over surface roughness, contact area, oxide thickness and hydrophobicity. Despite the efficient performance of hydrogen bonds from acid and alkaline etching on aluminum, these connections do not yield sufficiently stable bonds that make an impermeable barrier of epoxy coatings on steel. Covalent bonds (Me-O-Si) represent the key to achieve a significant improvement in mechanical and chemical resistance against the ingress of water and polymer chain relaxation. This makes the sol-gel primer a simple, economical, and environmentally alternative towards efficient bonding at a molecular level.

A study of crystallization behavior and magnetic property of Co-based alloy

The crystallization behavior and magnetic properties of Co-based alloy are investigated by DSC, XRD, TEM, VSM, and impedance analyzer. The results indicate that the non-isothermal crystallization of Co50Fe25Nb15B10 alloy has a significant glass transition with a supercooled liquid region of about 80 K. When the heat treatment is above crystallization temperature, some phases appear successively as the Co2B and (Co, Fe)21Nb2B6, and with the increase of annealing temperature, the values of coercivity Hc and saturation magnetic induction strength Bs increase correspondingly. After measuring the impedance effect of the Co-based alloy, it is found that the increase in impedance value is attributed to the decrease in magnetic anisotropy performance of the alloy, and the impedance curves of both amorphous and nanocrystalline alloys show a similar single peak trend. However, the crystallization phases after annealing form with a large size that hind the magnetization process resulting in a significant decrease of (ΔZ/Z)max value.

A green approach for the preparation of nanostructured zinc oxide: Characterization and promising antibacterial behaviour

In the present study, nanostructured zinc oxide (ZnO) films have been successfully synthesized using fruit extract of Viburnum opulus L. (VO) on glass slides by successive ionic layer adsorption and reaction (SILAR) procedure. The impact of VO concentrations on the structural, morphological, optical, electrical, and antibacterial attributes of ZnO films has been investigated in detail. The samples' XRD patterns present a hexagonal crystal structure with a preferential orientation along the (002) plane. The crystallite size values of ZnO samples were found to be in the ranges from 14.88 to 9.23 nm. The supplementation of VO to the synthesis solution remarkably affected the surface morphological features of the ZnO films. The optical results demonstrated that band gap energy values of the ZnO films at room temperature were decreased from 3.20 to 3.07 eV as a function of VO content in the bath solution. The films' electrical properties were determined by impedance analysis in the frequency range of 20 Hz −1 MHz. Impedance-frequency measurements showed VO insertion to ZnO thin films cause an increase in impedance value at the low frequencies. Cole-Cole plots with a single semi-circle confirmed the contribution of grain and grain boundary for the electrical conduction process. The agar disk diffusion method was used to test the antibacterial properties of ZnO/VO inserted ZnO and inhibition zones were measured. VO inserted ZnO showed a stronger inhibitory effect on gram-positive bacteria Staphylococcus aureus (ATCC 25923) and gram-negative bacteria Escherichia coli (ATCC 35218) than ampicillin antibiotic used as a control group. In line with the promising bactericidal results of a new generation, VO inserted ZnO, the nanostructured product with this study, it can also be applied in multidrug-resistant clinical isolates obtained from patients.

Influence of erbium doping on conduction behaviour of Y6-xSr4(SiO4)6F2 fluorapatite ceramic prepared by solution combustion method

This paper reports the electrical conduction mechanism of Y6-xSr4(SiO4)6F2:xEr3+ (x = 1,1.25, 1.5, 1.75 mol%) fluorapatite ceramic prepared by solution combustion method. X-ray diffraction (XRD) analysis confirms the formation of hexagonal structure with crystallite size in the nano meter range. Scanning electron microscopy (SEM) images of prepared ceramic show elongated spheroid grains with higher grain connectivity. Frequency dependent dielectric studies in the frequency range from 10 Hz to 100 KHz were done. Dielectric constant of prepared ceramic with different doping concentration decreases with increase in frequency of applied a.c field. Dielectric loss follows the same trend along with dissipation of energy. Complex impedance spectroscopy is used as a tool to investigate the change in real part of impedance (Z′), imaginary part of impedance (Z″), and a.c conductivity (σ) with the applied frequencies. Drastic increase in impedance value is being governed by aggregations of grains which is confirmed by cole-cole plots showing dielectric response of prepared ceramics. A.C conductivity shows an enhancement towards upper range i.e. dispersive region with an increase in applied frequency by giving a view on the electrical conduction behaviour of the ceramic.

A label-free electrochemical biosensor based on tubulin immobilized on gold nanoparticle/glassy carbon electrode for the determination of vinblastine.

Vinblastine (VLB) is prescribed for a wide variety of cancers. Therefore, development of sensitive methods for early diagnosis is urgently required. In this work, a highly sensitive and label-free impedimetric biosensor was fabricated for the electrochemical detection of VLB. First, the gold nanoparticles (AuNPs) were electrodeposited on the surface of a glassy carbon electrode (GCE). 3-Mercaptopropionic acid (MPA) was self-assembled over the AuNPs. Then, tubulin (TUB), as a receptor, was covalently immobilized atthe AuNPs/GCE surface via carbodiimide coupling reaction using N-(3 dimethylaminopropyl)-N'-ethyl carbodiimide (EDC) and N-hydroxy succinimide (NHS). The step-by-step modification process was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in the presence of a redox probe [Fe(CN)6]3-/4-. The VLB concentration was measured through the increase of impedance values in the corresponding specific binding of VLB and TUB. The increased electron-transfer resistance (R et) values were proportional to the value of VLB concentrations in the range of 0.4 to 65.0nmolL-1 with a detection limit of 8.4×10-2nmolL-1 (SN-1=3). The practical analytical performance of the proposed method was demonstrated by determination of VLB in plant extracts and human serum samples with satisfactory recoveries.

Development of poly(vinylcarbazole)/alumina nanocomposite coatings for corrosion protection of 316L stainless steel in 3.5% NaCl medium

ABSTRACTPoly(vinylcarbazole) (PVK) and PVK‐alumina (Al2O3) nanocomposite coatings were electrochemically coated on 316 L stainless steel (SS) substrates for corrosion protection of 316 L SS in 3.5 weight (wt) % NaCl medium. The formation of PVK and incorporation of nanoalumina particles in PVK‐Al2O3 nanocomposite coatings were confirmed from attenuated total reflectance‐infrared spectroscopy (ATR‐IR). Thermal analysis (TG) results showed enhanced thermal stability for the composites relative to PVK. Incorporation of Al2O3 nanoparticles enhanced the micro hardness of PVK coated 316 L SS. The dispersion of alumina nanoparticles was examined via scanning electron microscope (SEM) and tunneling electron microscopy (TEM) and revealed distinct features. The influence of nanoparticles on the barrier properties of PVK and PVK‐Al2O3 nanocomposites was evaluated in aqueous 3.5 wt % NaCl by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) studies. The results proved that PVK nanocomposite coatings provided better protection for 316 L SS than PVK coatings. The drastic increase in impedance values is due to the high corrosion resistance offered by the PVK nanocomposite coatings that arises due to the interaction between Al2O3 nanoparticles and PVK. The highest corrosion protection shown by the 2 wt % nano Al2O3 incorporated PVK composite coatings proved enhanced corrosion resistance compared to PVK. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44937.

Mitochondrial Membrane Studies Using Impedance Spectroscopy with Parallel pH Monitoring

A biological microelectromechanical system (BioMEMS) device was designed to study complementary mitochondrial parameters important in mitochondrial dysfunction studies. Mitochondrial dysfunction has been linked to many diseases, including diabetes, obesity, heart failure and aging, as these organelles play a critical role in energy generation, cell signaling and apoptosis. The synthesis of ATP is driven by the electrical potential across the inner mitochondrial membrane and by the pH difference due to proton flux across it. We have developed a tool to study the ionic activity of the mitochondria in parallel with dielectric measurements (impedance spectroscopy) to gain a better understanding of the properties of the mitochondrial membrane. This BioMEMS chip includes: 1) electrodes for impedance studies of mitochondria designed as two- and four-probe structures for optimized operation over a wide frequency range and 2) ion-sensitive field effect transistors for proton studies of the electron transport chain and for possible monitoring other ions such as sodium, potassium and calcium. We have used uncouplers to depolarize the mitochondrial membrane and disrupt the ionic balance. Dielectric spectroscopy responded with a corresponding increase in impedance values pointing at changes in mitochondrial membrane potential. An electrical model was used to describe mitochondrial sample’s complex impedance frequency dependencies and the contribution of the membrane to overall impedance changes. The results prove that dielectric spectroscopy can be used as a tool for membrane potential studies. It can be concluded that studies of the electrochemical parameters associated with mitochondrial bioenergetics may render significant information on various abnormalities attributable to these organelles.

A monoclonal antibody-based immunosensor for detection of Sudan I using electrochemical impedance spectroscopy

Sudan I monoclonal antibodies (Mabs) were prepared by hybridoma technique and firstly used to develop a Sudan I immunosensor by immobilizing the Mabs on a gold electrode. o-Mercaptobenzoic acid (MBA) was covalently conjugated on the gold electrode to form a self-assembled monolayer (SAM). The immobilization of Sudan I Mabs to the SAM was carried out through a stable acyl amino ester intermediate generated by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydrosuccinimide (NHS), which could condense antibodies reproducibly and densely on the SAM. The changes of the electrode behavior after each assembly step were investigated by cyclic voltammetric (CV) technique. The Sudan I concentration was measured through the increase of impedance values in the corresponding specific binding of Sudan I and Sudan I antibody. A linear relationship between the increased electron-transfer resistance (Ret) and the logarithmic value of Sudan I concentrations was found in the range of 0.05–50 ng mL −1 with the detection limit of 0.03 ng mL −1. Using hot chili as a model sample, acceptable recovery of 96.5–107.3% was obtained. The results were validated by conventional HPLC method with good correlation. The proposed method was proven to be a feasible quantitative method for Sudan I analysis with the properties of stability, highly sensitivity and selectivity.

Electrochemical Impedance Immunosensor Based on Three-Dimensionally Ordered Macroporous Gold Film

A novel label-free immunosensor for the detection of C-reactive protein (CRP) was developed based on a three-dimensional ordered macroporous (3DOM) gold film modified electrode by using the electrochemical impedance spectroscopy (EIS) technique. The electrode was electrochemically fabricated with an inverted opal template, making the surface area of the 3DOM gold film up to 14.4 times higher than that of a classical bare flat one, characterized by the cyclic voltammetric (CV) technique. The 3DOM gold film which was composed of interconnected gold nanoparticles not only has a good biocompatible microenvironment but also promotes the increase of conductivity and stability. The CRP immunosensor was developed by covalently conjugating CRP antibodies with 3-mercaptopropionic acid (MPA) on the 3DOM gold film electrode. The CRP concentration was measured through the increase of impedance values in the corresponding specific binding of CRP antigen and CRP antibody. The increased electron-transfer resistance (R(et)) values were proportional to the logarithmic value of CRP concentrations in the range of 0.1 to 20 ng mL(-1). The detection of CRP levels in three sera obtained from hospital showed acceptable accuracy.