Highly temperature dependent mass-transport parameters for ORR in Nafion® 211

Nafion® 211 differs from previous versions of Nafion in that the membrane is cast from a dispersion rather than being melt-extruded. As such, the water sorption properties are different, as is the rate of increase in water content with temperature. Kinetic and mass-transport parameters for dispersion-cast Nafion® 211 were determined using solid-state electrochemistry in the temperature range 30–70 °C, 100% relative humidity, and 30 psi oxygen pressure. Exchange current densities, Tafel slopes, and transfer coefficients for ORR in Nafion® 211, are similar to those observed in Nafion® 117; mass-transport parameters are not. At 30 °C and 100% RH oxygen solubility and the diffusion coefficient is determined to be 1.16 × 10⁻⁵ mol cm⁻³ and 1.13 × 10⁻⁶ cm² s⁻¹, respectively. Oxygen permeability at 30 °C (1.28 × 10⁻¹¹ mol cm⁻¹ s⁻¹) is lower than in Nafion® 117 (5.31 × 10⁻¹¹ mol cm⁻¹ s⁻¹) by factor of 4, while at T > 60 °C the permeability of Nafion® 211 increases significantly to values higher than Nafion® 117, and is correlated with the increase in water content and hydration number (λ) with temperature.     

Speciation of Fe in Fe-modified zeolite catalysts

Fe-modified zeolites (ferrierite and MFI) were prepared by four impregnation methods followed by calcination and tested as catalysts in oxidative dehydrogenation of ethane by nitrous oxide at 350 °C. The Fe cationic and Fe oxidic species were identified by combination of UV–Vis spectroscopy and voltammetry. Monomeric or dimeric Fe ions have only UV absorption bands and some of them evolve voltammetrically identifiable [Fe(OH)_x]^(3−x)+ ions in contact with acetic acid-sodium acetate buffer. Fe oxide nanoclusters characterised by UV band at about 28,000 cm⁻¹ are not detected by voltammetry under chosen conditions because they are situated inside the zeolite channels. Amorphous, nanocrystalline, and crystalline Fe(III) oxides were distinguished sensitively by their specific voltammetric reduction peaks at potentials −0.1 to −0.8 V/SCE in acetate buffer (pH 4.7) and by phase-specific electron pair transitions responsible for Vis absorption band centred at 17,500–21,000 cm⁻¹. The proposed method to differentiation between these ferric oxides is novel in materials analysis and solid state speciation. The monomeric and dimeric ferric ions are active in oxidative dehydrogenation of ethane to ethene with selectivity about 40–60% under used conditions, while Fe oxide nanoclusters are too active and over-oxidise ethane and/or ethene to C, CO and CO₂. Oppositely to general expectations, ferric oxides are indifferent in the catalytic reaction and do not decrease reaction selectivity.     

Synthesis and electrochemical characterizations of nano size Ce doped LiMn2O4 cathode materials for rechargeable lithium batteries

LiCe_xMn_2−xO₄ (x = 0.00–0.10) cathode materials for rechargeable lithium-ion batteries were synthesized by simple sol–gel technique using aqueous solutions of metal nitrates and succinic acid as the chelating agent. The gel precursors of metal succinates were dried in vacuum oven for 10 h at 120 °C. After drying, the gel precursors were ground and heated at 900 °C. The structural characterization was carried out by X-ray powder diffraction and X-ray photoelectron spectroscopy to identify the valence state of Mn and Ce in the synthesized materials. The sample exhibited a well defined spinel structure and the lattice parameter linearly increased with increasing the cerium contents in LiCe_xMn_2−xO₄. Surface morphology and particle size of the synthesized materials were determined by scanning electron microscopy and transmittance electron microscopy respectively. Electrochemical properties were characterized for assembled Li/LiCe_xMn_2−xO₄ coin type cells using galvanostatic charge/discharge studies at 0.5C rate and cyclic voltammetry in the potential range between 2.75 and 4.5 V at a scan rate of 0.1 mV s⁻¹. Among them cerium doped spinel LiCe_0.05Mn_1.90O₄ has improved structural stability, high reversible capacity and excellent electrochemical performance of rechargeable lithium batteries.     

Oxygen reduction reaction selectivity of RuxSey in formic acid solutions

Carbon-supported and non-supported cluster-like Ru_xSe_y were synthesized in aqueous media. The structure and morphology were analyzed by XRD and TEM, respectively. Particles dispersed uniformly on the support with an averaged size of 2.1 nm were obtained. The oxygen reduction reaction (ORR) in presence of HCOOH was investigated by means of rotating disk electrode at 25 °C on Ru_xSe_y nanoclusters. The kinetics of HCOOH oxidation for non-supported and carbon-supported Ru_xSe_y catalysts was analyzed. A reaction order of 1/1.4 and 1/1.6 was determined for Ru_xSe_y and Ru_xSe_y/C, respectively. This reaction order indicates that the reaction mechanism is similar to Pt/C. The chalcogenide catalyst showed a high tolerance and selectivity towards the ORR in electrolytes containing up to 0.1 M HCOOH. At the highest formic acid concentration (5 M) the potential, at e.g. current density of 0.2 mA cm⁻², shifts to negative for non-supported and carbon-supported Ru_xSe_y by 0.24 V and 0.28 V, respectively. The results reported in this work are the basis for overcoming the negative impact of fuel cross-over in microfluidic formic acid fuel cells that currently use Pt as cathode catalyst.     

Non-platinum oxygen reduction electrocatalysts based on carbon-supported metal–polythiophene composites

A series of carbon-supported metal–polythiophene composite (M–PTh/C) electrocatalysts are synthesized based on seven different non-Pt metals (M = Ir, Ru, Pd, Co, Fe, Ni, Sn) using chemical polymerization method. The electrocatalytic activity toward the oxygen reduction reaction (ORR) is characterized in acidic condition using rotating disk electrode voltammetry. Ir-, Ru-, and Pd-PTh/C show far more positive (ca. 700 mV) ORR onset potentials than Co-, Fe-, Ni-, and Sn-PTh/C. Further studies on the ORR kinetics are carried out for the three superior catalysts, Ir-, Ru-, Pd-PTh/C, using Koutecky–Levich and Tafel plots. The number of electrons (n) transferred in the ORR is ∼4 for these three catalysts, suggesting 4-electron transfer ORR is dominant. Considering all the obtained factors (such as the onset potential, n value, and exchange current density), Ir- and Ru-PTh/C catalysts are concluded to have relatively excellent ORR catalytic activity.     

Electrodeposited indigotetrasulfonate film onto glutaraldehyde-cross-linked poly-l-lysine modified glassy carbon electrode for detection of dissolved oxygen

The nano composited film of indigotetrasulfonate (ITS) electrodeposited onto poly-l-lysine (PLL)–glutaraldehyde (GA) (ITS/PLL–GA) was modified on glassy carbon electrode (GCE) by multiple scan cyclic voltammetry. Composited of the proposed film was characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), electrochemical quartz crystal microbalance (EQCM), electrochemical impedance spectroscopy (EIS), and UV–vis spectrum for the absorption at λ_max at 566 nm. For the electrocatalytic reduction of dissolved oxygen, ITS/PLL–GA film modified electrodes was determined in 0.1 M acetate buffer solution (pH 5.6) by cyclic voltammetry and rotating disk electrode voltammetry. This dissolved oxygen electrochemical sensor exhibited a linear response range (from 0 to 178.4 μM, R² = 0.9949), lowest detection limit (2.2 μM), lowest overpotential at −0.09 V, high sensitivity (906 μA mM⁻¹) and relative standard deviation (RSD) for determining dissolved oxygen (n = 3) was 4.2%. In addition, the ITS/PLL–GA/GCE was advantageous in terms of its simple preparation, specificity, stability and the ability of regeneration.     

Determination of trace vanadium(V) by adsorptive anodic stripping voltammetry on an acetylene black paste electrode in the presence of alizarin violet

A sensitive and simplified voltammetric method is developed for the determination of trace amounts of vanadium(V) by adsorptive anodic stripping voltammetry using an acetylene black (AB) paste electrode. The method is based on the preconcentration of the V(V)–alizarin violet (AV) complex at open circuit while stirring the solution for 90 s in 0.15 mol dm⁻³ hexamethylenetetraamine–hydrochloric acid buffer (pH 4.4), the adsorbed complex is then oxidized, producing a response with a peak potential of 564 mV when scanning linearly from 0 to 1000 mV. For voltammetric determination of V(V), the parameters influencing the peak current have been optimized. Under the selected conditions, the peak current and concentration of V(V) accorded with linear relationship in the range of 8.0 × 10⁻¹⁰ mol dm⁻³–1.0 × 10⁻⁷ mol dm⁻³ (c_AV = 2.0 × 10⁻⁶ mol dm⁻³) and 1.0 × 10⁻⁷ mol dm⁻³–8.0 × 10⁻⁶ mol dm⁻³ (c_AV = 2.0 × 10⁻⁵ mol dm⁻³), the detection limit (three times signal to noise) was estimated to be 6.0 × 10⁻¹⁰ mol dm⁻³ for 90 s accumulation. The relative standard deviation (RSD) is 1.9% and 2.3% for V(V) concentrations of 1.0 × 10⁻⁷ mol dm⁻³ and 1.0 × 10⁻⁸ mol dm⁻³ respectively. Finally, this proposed method was successfully applied to the determination of V(V) in natural water samples.     

Application of surfactant modified zeolite membrane electrode towards potentiometric determination of perchlorate

Potentiometric electrodes based on the incorporation of surfactant-modified zeolite Y (SMZ) particles into poly vinyl chloride (PVC) membranes were described. The electrode characteristics were evaluated regarding the response towards perchlorate ions. PVC membranes plasticized with dioctyl phthalate and without lipophilic additives (co-exchanger) are used throughout this study. The influence of membrane composition on the electrode response was studied. The electrode exhibited a Nernstian response towards perchlorate in the concentration range of 7.9 × 10⁻⁶–8.0 × 10⁻² M with a slope of 59.7 ± 0.9 mV per decade of perchlorate concentration with a working pH range of 1.7–9.5 with a fast response time of ≤10 s. The lower and upper detection limits were 4.07 × 10⁻⁷ and 0.13 M, respectively. The electrode response to perchlorate remains constant in the temperature range of 20–40 °C and in the presence of 2.5 × 10⁻⁶–1 × 10⁻² M NaNO₃. The selectivity coefficients for perchlorate anion as test species with respect to other anions were determined. The proposed modified zeolite-PVC electrode can be used for at least 30 days without any considerable divergence in potential. It was applied as indicator electrode in water samples with satisfactory results. The results of this study and our previous work show HDTMA plays different roles according to the zeolite type and matrix, as HDTMA-zeolite Y in a carbon paste matrix showed a good Nernstian behavior towards phosphate anion.     

Pitzer and Pitzer–Simonson–Clegg modeling approaches: Ternary HCl + ethanol + water electrolyte system

We report in this work, for the first time, the results obtained from both Pitzer, Pitzer–Simonson–Clegg (PSC) and an extended PSC ion-interaction approaches for modeling the non-ideal behavior of HCl electrolyte in the mixed ethanol + water solvent systems. In this context, a review of literature shows that the use of an exact and complete form of PSC ion-interaction approach for modeling electrolyte in mixed solvent systems was only limited to the works of two research groups. In this work, the modeling purposes were achieved based on the experimental potentiometric data of a galvanic cell containing a pH glass membrane and Ag/AgCl electrodes. The measurements were achieved over the HCl electrolyte molality ranging from 0.02 up to about 5 mol kg⁻¹ in mixed ethanol (x%) + water (100 − x%) solvent with different solvent mass fractions percent (x% = 10%, 20%, 30%, 40% and 50%), at 298.15 ± 0.05 K.     

Preparation of poly N,N-dimethylaniline/ferrocyanide film modified carbon paste electrode: Application to electrocatalytic oxidation of l-cysteine

Functionalized poly N,N-dimethylaniline film was prepared by adsorption of ferrocyanide onto the polymer forming at the surface of carbon paste electrode (CPE) in aqueous solution. The electrocatalytic ability of poly N,N-dimethylaniline/ferrocyanide film modified carbon paste electrode (PDMA/FMCPE) was demonstrated by oxidation of l-cysteine. Cyclic voltammetry and chronoamperometry techniques were used to investigate this ability. In the optimum pH (6.00), the electrocatalytic ability about 480 mV and the catalytic reaction rate constant, (k_h), can be seen 3.08 × 10³ M⁻¹ s⁻¹. The catalytic oxidation peak current determined by cyclic voltammetry method was linearly dependent on the l-cysteine concentration and the linearity range obtained was 8.00 × 10⁻⁵ –2.25 × 10⁻³ M. Detection limit of this method was determined as 6.17 × 10⁻⁵ M (2σ). At a fixed potential under hydrodynamic conditions (stirred solution), the calibration plot was linear over the l-cysteine concentration range 7.40 × 10⁻⁶ M–1.38 × 10⁻⁴ M. The detection limit of the method was 6.38 × 10⁻⁶ M (2σ).     

Electroanalytical determination of sildenafil in Viagra tablets using screen-printed and conventional carbon paste electrodes

This work compares the electroactivity of a conventional carbon-paste electrodes and screen-printed carbon electrodes. Potentiometric sensors responsive to sildenafil citrate (SILC) drug (the active component of Viagra) are described, characterized, compared and used for drug assessment. The proposed carbon paste electrode is fully characterized in terms of plasticizer type, response time, life span, soaking time, titrant, pH and temperature. The electrodes exhibited linear response with a Nernstian slope of 58.20 ± 1 and 58.82 ± 0.5 mV decade⁻¹ for SILC in the concentration range from 1.0 × 10⁻⁷ to 1.0 × 10⁻² and 5.30 × 10⁻⁷ to 1.0 × 10⁻² mol L⁻¹ with good reproducibility for CPE and SPE, respectively. Both CPE and SPE could be used in the pH range 3.0–5.0 and the isothermal coefficient is found to be 0.98 and 0.85 mV/°C, respectively. The limit of detection was found to be 9.0 × 10⁻⁸ and 3.5 × 10⁻⁷ mol L⁻¹ for CPE and SPE, respectively. They were applied to potentiometric determination of SILC in pure state and pharmaceutical preparation under batch conditions. The CPE and SPE sensors display good selectivity for SILC drug over large number of inorganic cations, sugars and amino acids commonly used in drug formulations. The CPE and SPE show high selectivity for the drug under investigation. The results obtained using the fabricated CPE is compared with those obtained by SPE for spiked pharmaceutical samples.     

Voltammetric sensor based on ordered mesoporous carbon for folic acid determination

With ordered mesoporous carbon (OMC) as the modifier, a voltammetric sensor for folic acid (FA) was constructed on a glassy carbon electrode (GCE). Due to the good characteristics of OMC, FA exhibited an enhanced electrochemical response and lower reduction potential in the neutral solution. In addition, the experimental parameters such as pH values, accumulation time and potential were optimized. Using the differential pulse voltammetry (DPV) measurement, the peak current was found to be linear with FA concentration in the range from 5.0 × 10⁻¹⁰ to 1.0 × 10⁻⁷ M with a lower detection limit of 6.0 × 10⁻¹¹ M (S/N = 3). Also, in real samples analysis, the as-prepared sensor successfully gives satisfying results.     

Direct electrochemistry of cholesterol oxidase on MWCNTs

The direct electrochemistry of cholesterol oxidase (ChOx) was achieved on the surface of graphite electrode by immobilizing positively charged ChOx and negatively charged multi walled carbon nanotubes through electrostatic interaction using layer-by-layer technique. Two sets of well defined redox peaks were observed in cyclic voltammogram of the modified graphite electrode in phosphate buffer solution of pH 7. These peaks are corresponding to direct electron transfer of FAD/FADH₂ of ChOx and carboxylic groups of multi walled nanotubes. The modified electrode is characterized using cyclic voltammetry and electrochemical impedance spectroscopy. ChOx modified electrode was used for the determination of cholesterol. The reduction current of oxygen at the modified electrode decreases linearly with the addition of cholesterol in the concentration range of 0.2–1 mM with the lower detection limit of 30 × 10⁻⁶ M. Some common interferents like glucose, ascorbic acid, uric acid and acetaminophen did not cause any interference due to the use of a low operating potential.     

Simultaneous determination of adenine and guanine utilizing PbO2-carbon nanotubes-ionic liquid composite film modified glassy carbon electrode

A novel and reliable electrochemical sensor based on PbO₂-carbon nanotubes-room temperature ionic liquid (i.e., 1-butyl-3-methylimidazolium hexafluorophosphate, BMIMPF6) composite film modified glassy carbon electrode (GCE) (PbO₂–MWNT–RTIL/GCE) was proposed for simultaneous and individual determination of guanine and adenine. The guanine and adenine oxidation responses were monitored by differential pulse voltammetric (DPV) measurement. Compared with the bare electrode, the PbO₂–MWNT–RTIL/GCE not only significantly enhanced the oxidation peak currents of guanine and adenine, but also lowered their oxidation overpotentials, suggesting that the synergistic effect of PbO₂, MWNT and RTIL could dramatically improve the determining sensitivity of guanine and adenine. The PbO₂–MWNT–RTIL/GCE showed good stability, high accumulation efficiency and enhanced electrocatalytic ability for the detection of guanine and adenine. Besides, the modified electrode also exhibited good behaviors in the simultaneous detection of adenine and guanine with the peak separation of 0.29 V in 0.1 M pH 7.0 phosphate buffer solution (PBS). Under the optimal conditions, the detection limit for individual determination of guanine and adenine was 6.0 × 10⁻⁹ M and 3.0 × 10⁻⁸ M (S/N = 3), respectively. The proposed method for the measurements of guanine and adenine in herring sperm DNA was successfully applied with satisfactory results.     

Rheological properties of resin composites according to variations in composition and temperature

Objective

To study the effect of compositional variables and temperature (25 °C and 37 °C) on the rheological properties of contemporary resin composites.

Methods

Fourteen commercial resin composites with different resin matrices of Bis-GMA and TEGDMA, different filler loading (41–65, v/v) and particle sizes (ranging 5 nm to 20 μm) were studied using a parallel plate rheometer. Shear sweep measurements were made to determine each composite's viscosity over the angular frequency range of ω = 10⁻⁴–10² rad/s. Data were analyzed using one way ANOVA, Bonferroni post hoc and t-independent tests (p < 0.05).

Results

All composites exhibited viscosity reducing with shear rate (pseudoplasticity). Viscosity averages were calculated over the shear rate range. These viscosities increased as the percentage of filler loading (by volume) increased ranging between 0.05–349.33 kPa s at 25 °C and 0.03–132.00 kPa s at 37 °C. Filtek Supreme XTE exhibited the highest viscosity at both temperatures (p < 0.05). Filtek Bulk Fill on the other hand, showed the lowest viscosity at both temperatures (p < 0.05). Viscosity significantly decreased with the increase in the temperatures for all materials (p < 0.05). The reduction ranged from 40.8% (for Venus Diamond Flow) to 92.2% (for Spectrum TPH3).

Significances

There was a considerable variation in the resin composite viscosities measured at 25 °C as an average value for shear-rate sweep. The factor between the least and highest viscosities was about 7000.The formulation differences that led to such a great variation were primarily: (i) volume fraction of fillers and (ii) particle size, the latter influencing total particle surface area.Rheological properties such as viscosity are key parameters influencing perceived differences in handling behavior of resin composites.     

A differential pulse voltammetric method for simultaneous determination of ascorbic acid,dopamine, and uric acid using poly (3-(5-chloro-2-hydroxyphenylazo)-4,5-dihydroxynaphthalene-2,7-disulfonic acid) film modified glassy carbon electrode

A stable modified glassy carbon electrode based on the poly 3-(5-chloro-2-hydroxyphenylazo)-4,5-dihydroxynaphthalene-2,7-disulfonic acid (CDDA) film was prepared by electrochemical polymerization technique to investigate its electrochemical behavior by cyclic voltammetry. The properties of the electrodeposited films, during preparation under different conditions, and their stability were examined. The homogeneous rate constant, k_s, for the electron transfer between CDDA and glassy carbon electrode was calculated as 5.25(±0.20) × 10² cm s⁻¹. The modified electrode showed electrocatalytic activity toward ascorbic acid (AA), dopamine (DA), and uric acid (UA) oxidation in a buffer solution (pH 4.0) with a diminution of their overpotential of about 0.12, 0.35, and 0.50 V for AA, DA, and UA, respectively. An increase could also be observed in their peak currents. The modified glassy carbon electrode was applied to the electrocatalytic oxidation of DA, AA, and UA, which resolved the overlapping of the anodic peaks of DA, AA, and UA into three well-defined voltammetric peaks in differential pulse voltammetry (DPV). This modified electrode was quite effective not only for detecting DA, AA, and UA, but also for simultaneous determination of these species in a mixture. The separation of the oxidation peak potentials for ascorbic acid–dopamine and dopamine–uric acid were about 0.16 V and 0.17 V, respectively. The final DPV peaks potential of AA, DA and UA were 0.28, 0.44, and 0.61 V, respectively. The calibration curves for DA, AA, and UA were linear for a wide range of concentrations of each species including 5.0–240 μmol L⁻¹ AA, 5.0–280 μmol L⁻¹ DA, and 0.1–18.0 μmol L⁻¹ UA. Detection limits of 1.43 μmol L⁻¹ AA, 0.29 μmol L⁻¹ DA and 0.016 μmol L⁻¹ UA were observed at pH 4. Interference studies showed that the modified electrode exhibits excellent selectivity toward AA, DA, and UA.     

Electron transfer kinetics and morphology of cytochrome c at the biomimetic phospholipid layers

Electrochemistry of cytochrome c (cyt c) at biomimetic phospholipid layers was studied in a phosphate buffer solution, which were formed with dilauroyl phosphatidic acid (DLPA, C12:0), dipalmitoyl phosphatidic acid (DPPA, C16:0), distearoyl phosphatidic acid (DSPA, C18:0), and palmitoyl–oleoyl phosphatidic acid (POPA, C16:0–18:1). The lipid-layers formed firstly at the air/water interface were immediately transferred onto the electrode surface using the Langmuir–Blodgett (LB) technique. The electrochemical properties of cyt c at the lipid covered electrodes depended on the orientation, number of layers of phospholipids, tail (or head) group down, and vice versa. Atomic force microscopy (AFM) images of cyt c adsorbed on the POPA monolayer (showing the head group diameter of POPA to be ca. 0.7 nm) formed on highly oriented pyrolytic graphite (HOPG) displayed uniform surface morphology of lipid layer and clumps of aggregated cyt c molecules with a minimum size corresponding to four cyt c molecules. The heterogeneous electron transfer rate constants, k⁰ values, of cyt c were determined to be 1.02 × 10⁻³, 0.98 × 10⁻³, and 0.67 × 10⁻³ cm/s for the lipid monolayer in the tail down orientation (X-type) of POPA, DLPA, and DPPA, and 0.67 × 10⁻³ and 0.50 × 10⁻³ cm/s for the head down orientation (Z-type) of POPA and DLPA monolayers, respectively.     

Exposure of Porphyromonas gingivalis to cortisol increases bacterial growth

Objective

Psychological stress is considered as a risk factor for periodontal diseases. The stress-related hormone, cortisol is one of the main molecules released during human stress response and is found in plasma and gingival crevicular fluid. This hormone has been suggested to modify composition of subgingival biofilms. The aim of this study was to investigate the effect of exposure to cortisol on Porphyromonas gingivalis (P. gingivalis) growth.

Materials and methods

P. gingivalis ATCC strain 33277 was cultured under strict anaerobic conditions at 37 °C in Brain Heart Infusion medium supplemented with hemin (5 μg ml⁻¹) and menadione (1 μg ml⁻¹). Bacterial cultures were incubated with or without hydrocortisone (0.04–10 μg ml⁻¹) at 37 °C for 12, 24 and 48 h and bacterial growth was evaluated by spectrophotometric method (OD_600 nm). Cortisol consumption has been followed by HPLC.

Results

Cortisol significantly increased P. gingivalis growth in the first 24 h peaking at 12 h but this increase was not related to the concentration used. During the time period, no consumption of cortisol was observed.

Conclusions

This study provides further support for the idea that stress-induced hormone; cortisol may influence the growth of P. gingivalis. This specific effect may be involved in the relationship between stress and periodontal diseases.     

Electrochemistry of magnolol and interaction with DNA

The electrochemical behaviors of magnolol have been studied at glassy carbon electrode using cyclic voltammetry, linear sweep voltammetry and chronocoulometry. Moreover, its interaction with DNA was investigated in solution by electrochemical methods and ultraviolet–visible spectroscopy. The experiment results indicated that the electrochemical oxidation of magnolol was an irreversible process with one proton and one electron transfer. The electron transfer coefficient (α) was calculated to be 0.441 ± 0.001. At the scan rate from 100 mV/s to 450 mV/s, the electrode process was controlled by the adsorption step and at the range of 600–950 mV/s the electrochemical oxidation was diffusion controlled process. The corresponding electrochemical rate constant (k_s) was 0.0760 ± 0.0001 s⁻¹. Through chronocoulometry experiment, the diffusion coefficient (D) and the surface concentration (Γ) were obtained as (3.76 ± 0.01) × 10⁻⁷ cm²/s and (2.98 ± 0.01) × 10⁻¹⁰ mol/cm². In addition, the interaction of magnolol and DNA was ascribed to be electrostatic interaction and the calculated association constant (β) and Hill coefficient (m) were 1.14 × 10⁵ M⁻¹ and 0.973. At last a sensitive and convenient electrochemical method was proposed for the determination of magnolol.     

Surface characteristics and corrosion properties of selective laser melted Co–Cr dental alloy after porcelain firing

Objective

We examined the surface characteristics and corrosion properties of selective laser melted (SLM) cobalt–chromium (Co–Cr) dental alloys before and after porcelain-fused-to-metal (PFM) firing.

Methods

Samples were manufactured utilizing SLM techniques and control specimens were fabricated using traditional casting methods. The microstructure and surface composition were examined using metallographic microscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Corrosion properties were evaluated using electrochemical impedance spectroscopy. Student's t-test was used to evaluate differences in numerical results of electrochemical corrosion tests between SLM and cast specimens before or after PFM firing. The results of electrochemical corrosion tests of the SLM and cast samples before and after firing were analyzed using one-way ANOVA.

Results

Although PFM firing altered the microstructure of the SLM specimens, they still exhibited a compact and homogeneous structure, and XPS analysis indicated that there were no significant differences in the surface composition of the specimens after firing. In artificial saliva at pH 5, the R_p value of the SLM specimens was 6.21 MΩ cm⁻² before firing and 2.84 MΩ cm⁻² after firing, suggesting there was no significant difference in electrochemical corrosion properties (P > 0.05). In artificial saliva at pH 2.5, the R_p value of the SLM group was 4.80 MΩ cm⁻² before firing and 2.88 MΩ cm⁻² after firing, again indicating no significant difference in electrochemical corrosion properties (P > 0.05). At pH 2.5, there was a significant difference in corrosion behavior between the cast and SLM groups, with the R_p value of the cast group being 0.78 MΩ cm⁻² vs. 2.88 MΩ cm⁻² for the SLM group.

Significance

The improved post-firing corrosion resistance of SLM specimens provides further support for their use in prosthodontic applications, as the oral environment may become temporarily acidic following meals.