Colored titanium passive films preparation, characterization, applications, and surface modification

L'application de la polarisation par courant alternatif (CA) sur Ie titane dans Ie NH4BF4 aq. a permis d'obtenir des couches passives colorées brillantes et uniformes. Ces types de films révèlent une gamme de couleurs plus étendue comparativement a ceux obtenus par la technique de la passivation en phase gazeuse aux températures élevées. De plus, ces couches peuvent être formées en quelques secondes contrairement aux heures ou même aux journées nécessaires avec un traitement thermique en phase gazeuse sous atmosphère d'oxygène. Ces films démontrent de nouvelles propriétés comme protectrices et décoratives. L'influence des différents paramètres expérimentaux (ex.: Ie pH et la concentration de l'électrolyte, Ie temps de polarisation et Ie type de voltage applique) sur la coloration, l'uniformité et la brillance du film ainsi que sa morphologie a été étudiée. La comparaison avec la polarisation par courant constant (CC) était également effectuée. Les résultats expérimentaux démontrent que les couches passives colorées adhèrent bien au substrat de Ti et ne peuvent en être arrachées. Les analyses au moyen du microscope optique et du microscope a balayage électronique (MEB), confirment que la polarisation par un courant alternatif a forme des couches passives compactes ne révélant pas de fracture ou de fissure contrairement aux couches formées thermiquement en phase gazeuse. L'adhérence du film passif dépend du pré-traitement mécanique du Ti métallique avant sa formation. En général, l'adhérence est meilleure quand les films sont formés sur une surface rugueuse obtenue par décapage. Dans Ie cas d'un film formé sur une surface de Ti polie mécaniquement, l'adhérence est plus faible et Ie polissage ou Ie frottement provoque Ie détachement du film. La caractérisation par spectrométrie des photoélectrons (XPS) des couches passives colorées, révèle que la composition chimique de la surface dépend du voltage lors de la polarisation CA. Les principaux constituants de la couche passive sont Tiz+, 0 et F' (z varie de 4 a 2 selon la profondeur du film). Le fluorure dans Ie film provient de la décomposition du NH4BF4 s'accumulant a 1'interface entre Ie métal et Ie film. L'étude de la variation de la composition chimique en fonction de la profondeur nous montre que plus Ie voltage applique est élevé, plus la couche passive est épaisse.Abstract: Brightly and uniformly colored passive layers on Ti are prepared by application of AC polarization in aqueous NH4 BF4 . Such formed films reveal a wider spectrum of colors that those prepared by gas-phase techniques at elevated temperatures and can be formed within second. The influence of different experimental parameters (electrolyte pH and concentration, duration of polarization, type of applied voltage) on the coloration, uniformity, brightness, and morphology of the colored films is examined. The comparison with DC polarization was also studied. Electrochemical properties of the colored Ti passive layers are determined by recording polarization curves in the -0.8-3.2 V vs. RHE range and Tafel plots in the hydrogen evolution reaction (HER) region in 1.0 M aqueous H2 SO4 solution. Studies of morphology and electrochemical characterization of Ebonex ª are also carried out. One of the objectives of this work was the preparation of Ti-based electrode materials for Hydrogen Evolution Reaction (HER) by surface modification of colored Ti passive layers through RuO2 and/or IrO2 depositing/doping."--Résumé abrégé par UM

The effect of carbon nanotube aspect ratio and loading on the elastic modulus of electrospun poly(vinyl alcohol)-carbon nanotube hybrid fibers

The reinforcement effect of carbon nanotubes (CNTs) has been examined as a function of their loading and aspect ratio in poly(vinyl alcohol) (PVA) based hybird fibers. Lignosulfonic acid sodium salt (LSA) was used to disperse CNTs to produce consistently high CNT loaded PVA-LSA-CNT hybrid fibers using an electrospinning process. The elastic modulus of individual fibers was measured using atomic force microscopy. The presence of CNTs significantly increased the average elastic modulus of PVA-LSA-CNT fibers compared to PVA-LSA fibers. The elastic modulus, however, exhibited no fiber diameter dependency. Transmission electron microscopy (TEM) was used to determine the loading and the aspect ratio of CNTs in each hybrid fiber. The CNT loading in PVA-LSA-CNT fibers varied widely due to non-uniform CNT dispersion and displayed no relationship with the elastic modulus. Our results also demonstrated that the average value of CNT aspect ratio significantly affected the elastic modulus of the hybrid fibers. Such a result was in agreement with theoretical prediction in which the stress transfer efficiency in a composite matrix is strongly dependent on the CNT aspect ratio.NRC publication: Ye

Selective nanomolar detection of dopamine using a boron-doped diamond electrode modified with an electropolymerized sulfobutylether-\u3b2- cyclodextrin-doped poly(N-acetyltyramine) and polypyrrole composite film

N-Acetyltyramine was synthesized and electropolymerized together with a negatively charged sulfobutylether-\u3b2-cyclodextrin on a boron-doped diamond (BDD) electrode followed by the electropolymerization of pyrrole to form a stable and permselective film for selective dopamine detection. The selectivity and sensitivity of the formed layer-by-layer film was governed by the sequence of deposition and the applied potential. Raman results showed a decrease in the peak intensity at 1329 cm-1 (sp\ub3), the main feature of BDD, upon each electrodeposition step. Such a decrease was correlated well with the change of the charge-transfer resistance derived from impedance data, i.e., reflecting the formation of the layer-by-layer film. The polycrystalline BDD surface became more even with lower surface roughness as revealed by scanning electron and atomic force microscopy. The modified BDD electrode exhibited rapid response to dopamine within 1.5-2 s and a low detection limit of 4-5 nM with excellent reproducibility. Electroactive interferences caused by 4-dihydroxyphenylalanine, 3,4-dihydroxyphenylacetic acid, ascorbic acid, and uric acid were completely eliminated, whereas the signal response of epinephrine and norepinephrine was significantly suppressed by the permselective film.NRC publication: Ye

Colored titanium passive films preparation, characterization, applications, and surface modification

Brightly and uniformly colored passive layers on Ti are prepared by application of AC polarization in aqueous NH4 BF4 . Such formed films reveal a wider spectrum of colors that those prepared by gas-phase techniques at elevated temperatures and can be formed within second. The influence of different experimental parameters (electrolyte pH and concentration, duration of polarization, type of applied voltage) on the coloration, uniformity, brightness, and morphology of the colored films is examined. The comparison with DC polarization was also studied. Electrochemical properties of the colored Ti passive layers are determined by recording polarization curves in the -0.8-3.2 V vs. RHE range and Tafel plots in the hydrogen evolution reaction (HER) region in 1.0 M aqueous H2 SO4 solution. Studies of morphology and electrochemical characterization of Ebonex ª are also carried out. One of the objectives of this work was the preparation of Ti-based electrode materials for Hydrogen Evolution Reaction (HER) by surface modification of colored Ti passive layers through RuO2 and/or IrO2 depositing/doping."--Résumé abrégé par UM

Multiwall Carbon Nanotube (MWCNT) Based Electrochemical Biosensors for Mediatorless Detection of Putrescine

Y-Aminopropyltriethoxysilane (APTES)-induced solubilization of multi-wall carbon nanotube CNTs allowed for the modification of electrode surfaces. APTES also served as an immobilization matrix for putrescine oxidase (POx) to construct an amperometric biosensor. Although CNTs modified by APTES acted as semiconductors to reduce the exposed sensing surface, we reasoned that nanoscale dendrites of CNTS modified by APTES formed a network and projected outwards from the electrode surface and acted like bundled ultra-microelectrodes that allowed access to the active site and facilitated direct electron transfer to the immobilized enzyme. Our biosensor was able to efficiently monitor direct electroactivity of POx at the electrode surface. The putrescine biosensor prepared using the modified glassy carbon electrode exhibited current response within 10 s with a detection limit of 500 nM.NRC publication: Ye

Reusable platinum nanoparticle modified boron doped diamond microelectrodes for oxidative determination of arsenite

Boron doped diamond (BDD) macro- and microelectrodes were modified by electrodeposition of platinum nanoparticles using a multipotential step electrodeposition technique and used for the oxidative determination of arsenite, As(III). The formation of Pt nanoparticles was evident from cyclic voltammetry measurement, whereas AFM and SEM revealed the size and size distribution of deposited Pt nanoparticles. Raman spectroscopy illustrated a correlation between the typical BDD signature and the number of platinum deposition cycles. Linear sweep voltammetry performed with the modified BDD microelectrode outperformed its macrocounterpart and resulted in very low detecting currents with enhanced signal-to-noise ratios. With linearity up to 100 ppb and a detection limit of 0.5 ppb, the electrochemical system was applicable for processing tap and river water samples. Over 150 repetitive runs could be performed, and electrochemical etching of platinum allowed the reuse of the BDD microelectrode. The presence of copper and chloride ions, the two most severe interferents at levels commonly found in groundwater, did not interfere with the assay.NRC publication: Ye

Electrochemically-assisted deposition of oxidases on platinum nanoparticle/multi-walled carbon nanotube-modified electrodes

Platinum nanoparticles were electrodeposited by a multi-potential step technique onto a multi-walled carbon nanotube (MWCNT) film pre-casted on a glassy carbon (GC) or boron-doped diamond (BDD) electrode. The MWCNT network consisted of Pt nanoparticles with an average diameter of 120 nm after an optimization of 36 deposition cycles. The resulting electrochemical sensors were capable of detecting hydrogen peroxide as low as 25 nM. Five different enzymes: glucose, lactate, glutamate, amino acid and xanthine oxidases, respectively, were deposited by a constant current technique for 5\ufffd10 min to form a stable and active biolayer for the analysis of their corresponding analytes. The glucose oxidase-based biosensor was linear up to 10 mM glucose with a detection limit of 250 nM and a response time of 5 s. Similar response times and detection limits were observed with glutamate, lactate, and amino acid oxidase despite the fact that the linear ranges were noticeably narrower. The mechanism of deposition was attributed to the decrease of local pH, created by oxygen evolution and effected enzyme precipitation.NRC publication: Ye

Analysis of the 16 environmental protection agency priority polycyclic aromatic hydrocarbons by high performance liquid chromatography-oxidized diamond film electrodes

The capabilities of using boron-doped diamond (BDD) thin films as electrode materials for analysis of the 16 US Environmental Protection Agency (EPA) priority polyaromatic hydrocarbons (PAHs) after a liquid chromatographic separation were evaluated. The BDD electrode was able to detect all 16 PAHs with high sensitivity due to the low background current and wide potential window. The method provided detection limits ranging from 12-40 nM (3-10 ppb) and repeatable results over consecutive analysis. Calibration curves were linear up to at least 10 ?M for all PAHs. The work shows the promising use of diamond as an amperometric detector in high performance liquid chromatography (HPLC), especially for PAHs and other hydrophobic aromatic compounds.NRC publication: Ye