Increase In Average Thickness Research Articles

Surface Treatment of Zn-Mn-Mg Alloys by Micro-Arc Oxidation in Silicate-Based Solutions with Different NaF Concentrations.

Newly developed Zn-Mn-Mg alloys can be invoked as biomedical materials because of their excellent mechanical properties. However, the corrosion behavior of Zn-Mn-Mg alloys was still lacking in research. It had grown to be a hot research topic to improve the corrosion behavior of Zn alloys by surface treatment to meet the application of degradable Zn alloys in biomedical applications. Micro arc oxidation (MAO) is a simple and effective method to improve the corrosion behavior of the alloy. MAO coatings were successfully prepared on the surface of Zn-Mn-Mg alloys by MAO in silicate-based solutions with different NaF concentrations. The microstructure and phase composition of MAO coatings prepared on Zn-Mn-Mg alloys with different NaF concentrations in the electrolyte was examined by a scanning electron microscope and X-ray diffraction. The results showed that the MAO coatings are porous and mainly composed of ZnO. With the increasing NaF concentration in the electrolyte, the average thickness increases. The distribution of the micro/nanopores was uniform, and the pore size ranged from the submicron scale to several micrometers after MAO treatment in the electrolyte containing different concentrations of NaF. Potential dynamic polarization curves and electrochemical impedance spectroscopy were employed to assess the corrosion behavior of MAO coatings in Hank’s solution. The highest corrosion rate can be achieved after MAO treatment, with an electrolyte concentration of 1.5 g/L NaF in Hank’s solution. These results indicated that MAO coating can accelerate the corrosion resistance of a Zn-Mn-Mg alloy.

Epithelium-off versus epithelium-on corneal collagen cross-linking with accelerated UV − a protocol for treatment of keratoconus

Purpose Our purpose was to compare the efficacy of ‘epithelium-off’ and ‘epithelium-on’ cross-linking (CXL) in treatment of progressive keratoconus. Patients and methods This study included 48 eyes of 26 patients who met our inclusion criteria. The Epi-Off CXL group included 32 eyes of 17 patients, and the Epi-On CXL group included 16 eyes of nine patients. Preoperative assessments of uncorrected and best-corrected visual acuities, refractive errors, keratometry, and corneal tomography including pachymetry, were compared with the postoperative values. Results Preoperatively, there was a statistically nonsignificant difference between the two groups in all studied variables except for the pachymetry at thinnest location. In the Epi-Off group, there was a significant improvement of uncorrected visual acuity, best-corrected visual acuity, Kmax, and inferior–superior value at the 12-month visit. There was late significant worsening of the back elevation and spherical equivalent at the 12-month visit and also significant thinning of pachymetry at thinnest location associated with significant worsening of the average thickness increase. All other variables showed nonsignificant change (stabilization) at both postoperative visits. In the Epi-On group, there was significant thinning of pachymetry at thinnest location and stabilization of uncorrected corrected visual acuity, best-corrected visual acuity, K1, Kmax, (inferior–superior), Y-coordinate, and front elevation at both postoperative visits, and early stabilization with late worsening of all of other variables. Conclusion The Epi-Off CXL was found to be more superior to Epi-On CXL in terms of stabilization of progressive keratoconus but was inevitably associated with complications related to epithelial debridement.

Surface State Trapping and Mobility Revealed by Junction Electrochemistry of Nano-Cr2O3

Hydrous chromium oxide nanoparticles (~15 nm diameter) are assembled from a colloidal solution onto tin-doped indium oxide (ITO) substrates by layer-by-layer electrostatic deposition with aqueous carboxymethyl-cellulose sodium salt binder. Calcination produces purely inorganic mesoporous films (average thickness increase per layer of 1 nm) of chromia Cr2O3. When immersed in aqueous carbonate buffer at pH 10 and investigated by cyclic voltammetry, a chemically reversible oxidation is observed because of a conductive layer at the chromia surface (formed during initial potential cycling). This is attributed to a surface CrIII/IV process. At more positive potentials higher oxidation states are accessible before film dissolution. The effects of film thickness and pH on voltammetric responses are studied. X-Ray photoelectron spectroscopy (XPS) evidence for higher chromium oxidation states is obtained. ITO junction experiments are employed to reveal surface conduction by CrIII/IV and CrIV/V ‘mobile surface states’ and an estimate is obtained for the apparent CrIII/IV charge surface diffusion coefficient Dapp = 10–13 m2 s–1. The junction experiment distinguishes mobile surface redox sites from energetically distinct deeper-sitting ‘trapped states’.

Binding site control in a layer-by-layer deposited chitosan–carbon nanoparticle film electrode

Thin chitosan–carbon nanoparticle films (ca. 2 nm average thickness increase per layer) are assembled onto tin-doped indium oxide (ITO) electrode substrates in a layer-by-layer deposition process employing carbon nanoparticles of ca. 8 nm average diameter and an aqueous solution of chitosan (poly-D-glucosamine, low molecular weight, 75–85% deacetylated). Chitosan introduces amine/ammonium functionalities which are employed for the immobilization of redox systems (i) via physisorption of indigo carmine and (ii) via chemisorption of 2-methyleneanthraquinone. The number of binding sites within the chitosan–carbon nanoparticle film is controlled by changing the thickness of the film deposit or by changing the chitosan content, which is varied by changing the chitosan concentration during layer-by-layer deposition. Voltammetric characteristics and stability of the chemisorbed and physisorbed redox systems are reported as a function of pH. The physisorbed redox system is expelled from the film at a pH consistent with the pKA of chitosan (approximately 6.5). However, the 2-methyleneanthraquinone redox system remains stable even in alkaline media and only a minor inflection in the plot of midpoint potentials vs. pH indicates the film deprotonation process at the pKA of chitosan.

Multilayers of 4-methylbenzenethiol functionalized gold nanoparticles fabricated by Langmuir–Blodgett and Langmuir–Schaefer deposition

Langmuir films of gold nanoparticles functionalized by 4-methylbenzenethiol on a water subphase were studied. Multilayers on Si and glass substrates were successfully fabricated by both the Langmuir–Blodgett (LB) and Langmuir–Schaefer (LS) deposition techniques. The multilayers were characterized by UV–vis spectroscopy, X-ray photoelectron spectra (XPS), spectroscopic ellipsometry and tapping mode AFM. Thickness measurements by XPS and ellipsometry showed that the multilayers formed from both techniques displayed a linear increase of film thickness with the number of layers, indicating a reproducible deposition process. However, it is found that the average thickness increase after each LS stroke is about double of that in the LB transfer, indicating two monolayers were deposited in one LS stroke. AFM data revealed that the films deposited at different surface pressures exhibit different morphology. The films generally showed less defects and larger domain size at higher surface pressure. It is also found that films prepared using LS technique are more uniform and smoother than the LB films prepared under similar conditions. The possible nanoparticle deposition mechanisms of LB and LS techniques have been discussed.

Structural Characterization of AlP/GaP Disordered Superlattice by Dynamical Simulation of X-Ray Diffraction

Dynamical simulation of X-ray diffraction is used to characterize structural properties of (AlP)m/(GaP)n (m, n=h, k, l) disordered superlattices (d-SLs). Many small diffraction peaks appear around the main peak, and peak intensities become weaker as the deviation from the average thickness increases. The observed diffraction patterns can be interpreted if the repetition of random series in the superlattice is taken into account. It is found that the total number of monolayers (MLs) of the 6 constituent layers or the average number of MLs of a d-SL can be precisely determined from the smallest peak separation or the angular distance between the main peak and the 0th-order diffraction peak.

Microstructure of Frankfurters Extended with Wheat Germ Proteins

ABSTRACTTransmission electron microscopy was utilized to study the microsctructure of frankfurters extended with wheat germ protein flour (WGPF) at 3.5, 5.0, and 7.0%. Samples with 3.5% WGPF showed a denser matrix than the control. They also had a uniform interfacial protein film (IPF) with a slight increase in average thickness. At WGPF >3.5%, no further effects on IPF were observed. At 7.0% WGPF, an increase in added water, and the resultant dilution of meat and fat components, resulted in fewer fat globules, some with incomplete IPFs. Proteins in the WGPF contributed to IPF formation up to a specific level. Nonprotein components also were important in batter stability by absorbing water.

Anodic Oxide Films as Barriers to Charge Transfer in O 2 Evolution at Pt in Acid Solutions

The kinetics of oxygen evolution reaction at platinum anodes in acid solutions with different pH's is examined, and possible reaction mechanisms are discussed. The activity of the reaction at initially prereduced electrodes brought to a constant potential, or kept at a constant current density, decreases with time. Only at the electrodes initially subjected for a given time either to a high potential, or to a high anodic current density, it is possible to observe in “run down,” or subsequent “run up” experiments a linear relationship for over several decades of current density with a slope close to 115 mV. The positions, but not the slopes of Tafel lines, are affected by time or conditions of pretreatments of electrodes (various or ). The decrease in the activity is attributed to the increase in average thickness of anodically formed surface oxide films. Only when it is assured that the film thickness remains practically unaltered during the measurements, meaningful kinetic parameters for the oxygen evolution reaction are obtained. The reaction order with respect to H+ is then found to be negative and fractional according to the over‐all rate equationA model is suggested according to which a surface oxide film forms a barrier to charge transfer in series with the double‐layer barrier. The fractional reaction order is accounted for with this model. A chemical step that follows a charge transfer step is rate determining. It is suggested that oxygen atoms in the surface oxide films participate in the oxygen evolution reaction.