Corrosion Behavior of Coated Low Carbon Steel in a Simulated PEMFC Environment.

Here, potential metallic bipolar plate (BP) materials were manufactured by laser coating NiCr-based alloys with different Ti additions on low carbon steel substrates. The titanium content within the coating varied between 1.5 and 12.5 wt%. Our present study focussed on electrochemically testing the laser cladded samples in a milder solution. The electrolyte used for all of the electrochemical tests consisted of a 0.1 M Na2SO4 solution (acidulated with H2SO4 at pH = 5) with the addition of 0.1 ppm F-. The corrosion resistance properties of the laser-cladded samples was evaluated using an electrochemical protocol, which consisted of the open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) measurements, and potentiodynamic polarization, followed by potentiostatic polarization under simulated proton exchange membrane fuel cell (PEMFC) anodic and cathodic environments for 6 h each. After the samples were subjected to potentiostatic polarization, the EIS measurements and potentiodynamic polarization were repeated. The microstructure and chemical composition of the laser cladded samples were investigated by scanning electron microscopy (SEM) combined with energy-dispersive X-ray spectroscopy (EDX) analysis.

Functional Surfaces via Laser Processing in Nickel Acetate Solution.

This study presents a novel laser processing technique in a liquid media to enhance the surface mechanical properties of a material, by thermal impact and micro-alloying at the subsurface level. An aqueous solution of nickel acetate (15% wt.) was used as liquid media for laser processing of C45E steel. A pulsed laser TRUMPH Truepulse 556 coupled to a PRECITEC 200 mm focal length optical system, manipulated by a robotic arm, was employed for the under-liquid micro-processing. The study's novelty lies in the diffusion of nickel in the C45E steel samples, resulting from the addition of nickel acetate to the liquid media. Micro-alloying and phase transformation were achieved up to a 30 µm depth from the surface. The laser micro-processed surface morphology was analysed using optical and scanning electron microscopy. Energy dispersive spectroscopy and X-ray diffraction were used to determine the chemical composition and structural development, respectively. The microstructure refinement was observed, along with the development of nickel-rich compounds at the subsurface level, contributing to an improvement of the micro and nanoscale hardness and elastic modulus (230 GPa). The laser-treated surface exhibited an enhancement of microhardness from 250 to 660 HV0.03 and an improvement of more than 50% in corrosion rate.

Modulated Laser Cladding of Implant-Type Coatings by Bovine-Bone-Derived Hydroxyapatite Powder Injection on Ti6Al4V Substrates-Part I: Fabrication and Physico-Chemical Characterization.

The surface physico-chemistry of metallic implants governs their successful long-term functionality for orthopedic and dentistry applications. Here, we investigated the feasibility of harmoniously combining two of the star materials currently employed in bone treatment/restoration, namely, calcium-phosphate-based bioceramics (in the form of coatings that have the capacity to enhance osseointegration) and titanium alloys (used as bulk implant materials due to their mechanical performance and lack of systemic toxicity). For the first time, bovine-bone-derived hydroxyapatite (BHA) was layered on top of Ti6Al4V substrates using powder injection laser cladding technology, and then subjected, in this first stage of the research, to an array of physical-chemical analyses. The laser processing set-up involved the conjoined modulation of the BHA-to-Ti ratio (100 wt.% and 50 wt.%) and beam power range (500-1000 W). As such, on each metallic substrate, several overlapped strips were produced and the external surface of the cladded coatings was further investigated. The morphological and compositional (SEM/EDS) evaluations exposed fully covered metallic surfaces with ceramic-based materials, without any fragmentation and with a strong metallurgical bond. The structural (XRD, micro-Raman) analyses showed the formation of calcium titanate as the main phase up to maximum 800 W, accompanied by partial BHA decomposition and the consequential advent of tetracalcium phosphate (markedly above 600 W), independent of the BHA ratio. In addition, the hydrophilic behavior of the coatings was outlined, being linked to the varied surface textures and phase dynamism that emerged due to laser power increment for both of the employed BHA ratios. Hence, this research delineates a series of optimal laser cladding technological parameters for the adequate deposition of bioceramic layers with customized functionality.

Electrochemical Evaluation of Protective Coatings with Ti Additions on Mild Steel Substrate with Potential Application for PEM Fuel Cells.

In this work, the corrosion behavior of NiCr(Ti) protective coatings deposited on mild steel substrates through laser cladding technology is studied as an alternative new material for metallic bipolar plates used in PEMFC applications. For electrochemical testing, a solution consisting of 0.5 M H2SO4 + 2 ppm F- at room temperature is used as an electrolyte. The fluoride ions are added to simulate the conditions in the PEM fuel cell due to degradation of the proton exchange membrane and fluoride release. A saturated calomel electrode (SCE) is used as a reference electrode and a platinum mesh as the counter electrode. Scanning electron microscopy (SEM) and optical microscopy (OM) are used for studying the morphology of the protective coatings and the effect of Ti addition. The electrochemical evaluation consisted of measuring the open circuit potential (OCP), followed by electrochemical impedance spectroscopy measurements (EIS) and potentiodynamic polarization. It is found that the coatings with 5% Ti, 7% Ti and 10% Ti addition comply with the conditions of the US DOE regarding corrosion performance to be used as materials for the manufacture of the bipolar plates.

Morphological Analysis of Laser Surface Texturing Effect on AISI 430 Stainless Steel.

Laser surface texturing (LST) is a method to obtain micro-structures on the material's surface for improving tribological performances, wetting tuning, surface treatment, and increasing adhesion. The material selected for LST is AISI 430 ferritic stainless steel, distinguished by the low cost in manufacturing, corrosion resistance, and high strength at elevated temperature. The present study addresses the morphology of new pattern designs (crater array, ellipse, and octagonal shapes). The patterns are applied on the stainless-steel surface by a non-contact method with high quality and precision nanosecond pulsed laser equipment. The investigation of laser parameter influence on thermal affected area and micro-structures is accomplished by morphological and elemental analysis (SEM + EDX). The parameters of the laser micro-patterning have a marked influence on the morphology, creating groove-type sections with different depths and recast material features. From the SEM characterization, the highest level of recast material is observed for concentric octagon LST design. Its application is more recommended for the preparation of the metal surface before hybrid welding. Additionally, the lack of the oxygen element in the case of this design suggests the possible use of the pattern in hybrid joining.

Wettability and Surface Roughness Analysis of Laser Surface Texturing of AISI 430 Stainless Steel.

Due to its wide applicability in industry, devising microstructures on the surface of materials can be easily implemented and automated in technological processes. Laser Surface Texturing (LST) is applied to modify the chemical composition, morphology, and roughness of surfaces (wettability), cleaning (remove contaminants), reducing internal stresses of metals (hardening, tempering), surface energy (polymers, metals), increasing the adhesion (hybrid joining, bioengineering) and decreasing the growth of pathogenic bacteria (bioengineering). This paper is a continuation and extension of our previous studies in laser-assisted texturing of surfaces. Three different patterns (crater array-type C, two ellipses at 90° overlapping with its mirror-type B and 3 concentric octagons-type A) were applied with a nanosecond pulsed laser (active medium Nd: Fiber Diode-pumped) on the surface of a ferritic stainless steel (AISI 430). Micro texturing the surface of a material can modify its wettability behavior. A hydrophobic surface (contact angle greater than 90°) was obtained with different variations depending on the parameters. The analysis performed in this research (surface roughness, wettability) is critical for assessing the surface functionality, characteristics and properties of the stainless steel surface after the LST process. The values of the surface roughness and the contact angle are directly proportional to the number of repetitions and inversely proportional to the speed. Recommendations for the use of different texturing pattern designs are also made.

Influence of the Laser Cladding Parameters on the Morphology, Wear and Corrosion Resistance of WC-Co/NiCrBSi Composite Coatings.

To enhance the sliding wear and corrosion behavior of steels with low carbon content, cermet composite coatings are usually deposited on their surface by various deposition processes. Laser cladding, compared to other deposition techniques such as electroplating, arc welding, and thermal spraying, has numerous advantages to produce such protective coatings. The paper presents the optimization of laser cladding deposition speed versus energy density in order to obtain WC-Co/NiCrBSi coatings with Ni-Al addition free of defects and reduced porosity deposited on low carbon steel substrate. The microstructure and chemical composition were investigated by SEM combined with EDX analysis while XRD was performed in order to examinate the phases within the coatings. In order to investigate the cladding speed influence on the coatings, hardness measurements, POD (pin on disk) wear tests and corrosion tests in 3.5% NaCl solution were carried out. The results showed that an optimal cladding speed has a crucial impact on the microstructure, composition, and hardness. It was found out that optimizing the cladding deposition speed proved to be effective in enhancing the sliding wear resistance and corrosion behavior by controlling the iron content within the coatings.

Diffusion and Controlled Release in Physically Crosslinked Poly (Vinyl Alcohol)/Iota-Carrageenan Hydrogel Blends.

This paper reports the obtaining of poly (vinyl alcohol) and i-carrageenan blend hydrogels by physical crosslinking (consecutive freeze-thaw cycles). The two polymers were completely miscible in the weight ratio interval used in this study, as determined by solution viscometry data. Strong interactions through hydrogen bonding and forming of mixed interpolymer crystalline domains were observed, which are responsible for the formation of stable drug release-tunable matrices. The release profiles of three model antibiotic drugs (amoxicillin, tetracycline hydrochloride, and gentamicin sulfate) were assessed in a pH interval between 3 and 7.3. They were found to be strongly dependent on the drug chemistry, mesh size of the hydrogels, swelling mechanism, and pH of the release medium. A decrease of up to 40% in the release rates and up to 10% in the diffusion coefficients of the model drugs was registered with the increase in i-carrageenan content.

Protein reactivity with singlet oxygen: Influence of the solvent exposure of the reactive amino acid residues.

The singlet oxygen quenching rate constants were measured for three model proteins, bovine serum albumin, ß-lactoglobulin and lysozyme. The results were analyzed by comparing them with the corresponding singlet oxygen quenching rate constants for a series of tripeptides with the basic formula GlyAAGly where the central amino acid (AA) was the oxidizable amino acid, tryptophan, tyrosine, methionine and histidine. It was found that the reaction rate constant in proteins can be satisfactorily modelled by the sum of the individual contributions of the oxidizable AA residues corrected for the solvent accessible surface area (SASA) effects. The best results were obtained when the SASA of the AA residues were determined by averaging over molecular dynamics simulated trajectories of the proteins. The limits of this geometrical correction of the AA residue reactivity are also discussed.

Characterization of mixtures of compounds produced in chlorpromazine aqueous solutions by ultraviolet laser irradiation: their applications in antimicrobial assays.

The study reports an investigation of the photoproducts obtained by exposure of chlorpromazine hydrochloride in ultrapure water (concentration 2 mg/mL) to a 266-nm laser beam obtained by fourth harmonic generation from a Nd:YAG laser (6-ns full time width at half maximum, 10-Hz pulse repetition rate). The photoproducts were analyzed by steady-state UV-Vis absorption, laser-induced fluorescence, Fourier transform infrared spectroscopy, and liquid chromatography-tandem time-of-flight mass spectroscopy. Two figures showing pathways that take place during irradiation for obtaining the final products are shown. The quantum yield of singlet oxygen generation by chlorpromazine (CPZ) was determined relative to standard Zn-phthalocyanine in dimethyl sulfoxide. To outline the role of fluorescence in photoproducts formation rates, fluorescence quantum yield of CPZ during exposure to 355-nm radiation (third harmonic of the fundamental beam of Nd:YAG laser) was investigated relative to standard Coumarin 1 in ethanol. The CPZ solutions exposed 60 and 240 min to 266-nm laser beam, respectively, were tested against Staphylococcus aureus ATCC 25923 strain. For 25 µL of CPZ samples irradiated 240 min, a higher diameter of inhibition has obtained against the tested strain than for the 60-min exposed ones.

Effects and tolerability of betahistine in patients with vestibular vertigo: results from the Romanian contingent of the OSVaLD study.

BACKGROUND AND METHODS: An efficacy population of 245 patients with vertigo of peripheral vestibular origin was recruited in Romania as part of a 3-month multinational, post-marketing surveillance study of open-label betahistine 48 mg/day (OSVaLD). Endpoints were changes in the Dizziness Handicap Index (primary endpoint), Medical Outcome Study Short-Form 36 (SF-36v2(®)), and the Hospital Anxiety and Depression Scale. RESULTS: During treatment, the total Dizziness Handicap Index score improved by 41 points (on a 100-point scale). Statistically significant improvements of 12-14 points were recorded in all three domains of the Dizziness Handicap Index scale (P<0.0001). Betahistine therapy was also accompanied by progressive improvements in mean Hospital Anxiety and Depression anxiety and depression scores (P<0.0001) and significant improvements in both the physical and mental component summary of the SF-36v2 (P<0.0001). Betahistine was well tolerated, with only one suspected adverse drug reaction recorded in the Romanian safety population (n=259). CONCLUSION: Betahistine 48 mg/day was associated with improvements in multiple measures of health-related quality of life and had a good tolerability profile in these Romanian patients with recurrent peripheral vestibular vertigo.

Development of the A§E test battery for assessment of pitch perception in speech.

OBJECTIVES: The auditory speech sounds evaluation 2009 test battery for assessment of speech pitch perception is presented. It was designed to (a) assess perception of pitch in linguistic contexts without the confounds of secondary acoustic cues, (b) be usable with listeners from different language backgrounds, and (c) be suitable for use in a clinical setting. The need for this test battery arises from increased awareness of the importance of prosody in clinical practice, and the development of methods for improving pitch perception in listeners with profound hearing losses. METHODS: Identification and discrimination tasks based on linguistic contexts were developed to establish listeners' just noticeable differences (JNDs) for pitch changes. Stimuli were pseudosentences and pseudowords based on speech from a female speaker, overlain with stylized pitch contours. Target pitch excursions were varied from the 200 Hz baseline to a maximum of 349 Hz. Ninety normal-hearing listeners participated in test validation that assessed goals (a)-(c), established test-retest reliability, and gathered normative data. RESULTS: The JNDs on non-linguistic, control tasks were lower than on linguistic ones, showing that non-linguistic tasks may overestimate pitch perception in speech. Listeners from different language backgrounds scored comparably on most linguistic tasks, and test-retest differences were non-significant. Test usability as evidenced by task duration and subject experience seemed satisfactory for clinical use.

Clinical assessment of pitch perception.

OBJECTIVE: The perception of pitch has recently gained attention. At present, clinical audiologic tests to assess this are hardly available. This article reports on the development of a clinical test using harmonic intonation (HI) and disharmonic intonation (DI). STUDY DESIGN: Prospective collection of normative data and pilot study in hearing-impaired subjects. SETTING: Tertiary referral center. PATIENTS: Normative data were collected from 90 normal-hearing subjects recruited from 3 different language backgrounds. The pilot study was conducted on 18 hearing-impaired individuals who were selected into 3 pathologic groups: high-frequency hearing loss (HF), low-frequency hearing loss (LF), and cochlear implant users (CI). INTERVENTION(S): Normative data collection and exploratory diagnostics by means of the newly constructed HI/DI tests using intonation patterns to find the just noticeable difference (JND) for pitch discrimination in low-frequency harmonic complex sounds presented in a same-different task. MAIN OUTCOME MEASURE(S): JND for pitch discrimination using HI/DI tests in the hearing population and pathologic groups. RESULTS: Normative data are presented in 5 parameter statistics and box-and-whisker plots showing median JNDs of 2 (HI) and 3 Hz (DI). The results on both tests are statistically abnormal in LF and CI subjects, whereas they are not significantly abnormal in the HF group. CONCLUSION: The HI and DI tests allow the clinical assessment of low-frequency pitch perception. The data obtained in this study define the normal zone for both tests. Preliminary results indicate possible abnormal TFS perception in some hearing-impaired subjects.

Direct modification of bioactive phenothiazines by exposure to laser radiation.

Whereas exposure of combinations of a phenothiazine and bacterium to incoherent UV increases the activity of the phenothiazine, exposure of the phenothiazine alone does not yield an increase of its activity. Because the laser beam energy is greater than that produced by the incoherent UV sources, exposure of phenothiazines to specific lasers may yield molecules with altered activities over that of the unexposed parent. Chlorpromazine, thioridazine and promethazine active against bacteria were exposed to two distinct lasers for varying periods of time. Absorption and fluorescence spectra were conducted prior to and post-exposure and the products of laser exposure evaluated for activity against a Staphylococcus aureus ATCC strain via a disk susceptibility assay. Exposure to lasers alters the absorption/fluorescence spectra of the phenothiazines; reduces the activity of thioridazine against the test bacterium; produces a highly active chlorpromazine compound against the test organism. Exposure of phenothiazines to lasers alters their structure that results in altered activity against a bacterium. This is the first report that lasers can alter the physico-chemico characteristics to the extent that altered bioactivity results. Exposure to lasers is expected to yield compounds that are difficult to make via chemical manipulation methods. A survey of selected patents of interest, even co-lateral for the subject of this article is shortly made.

Laser-induced autofluorescence measurements on brain tissues.

It was demonstrated that comparison of the autofluorescence spectra induced with laser radiation in ultraviolet and visible allows the identification of brain tumor tissues and normal tissues as well as the difference between them. The measurements were performed on homogenates to ensure an optimal reproducibility of the results. We conclude that the autofluorescence spectra of the tumor samples are close to those measured for normal tissues, but there are differences between them that allow distinguishing the tumor from the normal tissue. One difference is that for each pair of tumor/normal tissue samples, the peak autofluorescence for the normal tissue is shifted with respect to that for the tumor-typically between 10 and 20 nm; overall autofluorescence intensity is also different for the components of the same pair, the difference being in the range 15%-30%. A parameter that can also be used is the variation of the ratio of some fluorescence intensity peaks between normal and tumor tissue samples. Measurements of this parameter yielded variations ranging between 10% and 40%. Another conclusion of the study is that in vitro experiments show that it is mandatory to use pairs of samples (normal/tumor tissue) taken from the same patient. The results show that, after further experimental in vitro tests, the method may be adapted to real-time intraoperative conditions by measuring the autofluorescence of the tumor and of the adjacent normal tissue.