Electrodeposition of metallic molybdenum films in ZnCl2-NaCl-KCl-MoCl3 systems at 250 °C

Molybdenum metal film has been electrodeposited in ZnCl₂-NaCl-KCl (0.60:0.20:0.20, in mole fraction) melt containing MoCl₃ at 250 °C. In this melt, a dense film was obtained by potentiostatic electrolysis at 0.15 V versus Zn(II)/Zn for 3 h. However, the film had a thickness of smaller than 0.5 μm and was not adhesive. On the other hand, addition of 4 mol% of KF to the melt led to larger cathodic current in cyclic voltammogram, and gave a dense, adhesive and thicker metal film of ca. 3 μm thickness in the same electrolysis condition as above. The present process is promising as a new method for molybdenum coating at low temperatures.     

Drying of latex films and coatings: Reconsidering the fundamental mechanisms

The two existing theories describing drying of latex films or coatings are reconsidered. Subsequently, a novel mathematical drying model is presented, the simulations of which can match and explain experimental drying rate data of two previous investigations with latex films. In contrast to previous model studies, but in agreement with observations, simulations suggest that during the falling rate period of the drying process of a latex film, a porous skin of partly coalesced latex particles is indeed formed, which limits transport of water vapour from the receding air–liquid interphase to the surface of the film. The value of the effective diffusion coefficient of water vapour in the dry and partly coalesced layer (7 × 10⁻⁷ m²/s at 19–24 °C), the adjustable parameter of the model for the falling rate period, was found to be independent of initial wet film thickness (89–1322 μm), latex particle size (500–600 nm), initial polymer volume concentration (19–47 vol.%), and molecular weight of latex polymer (not quantified). Simulations also demonstrate that the transition from a constant to a falling drying rate in all cases takes place when the polymer volume concentration of the latex film is equal to that of hexagonal closest packed monodisperse spheres (74 vol.%). Consequently, the model has predictive properties and model inputs are only needed on the specific experimental (or field) conditions of interest. The effects on drying time of variations in relative humidity, wet film thickness, initial polymer volume concentration, and air flow velocity are simulated and analysed using the new model.     

Phase separation and dewetting in polystyrene/poly(vinyl methyl ether) blend thin films in a wide thickness range

Phase separation and dewetting processes of blend thin films of polystyrene (PS) and poly(vinyl methyl ether) (PVME) in two phase region have been studied in a wide film thickness range from 65 μm to 42 nm (∼2.5R_g, R_g being radius of gyration of a polymer) using optical microscope (OM), atomic force microscope (AFM) and small-angle light scattering (LS). It was found that both phase separation and dewetting processes depend on the film thickness and were classified into four thickness regions. In the first region above ∼15 μm the spinodal decomposition (SD) type phase separation occurs in a similar manner to bulk and no dewetting is observed. This region can be regarded as bulk. In the second region between ∼15 and ∼1 μm, the SD type phase separation proceeds in the early stage while the characteristic wavelength of the SD decreases with the film thickness. In the late stage dewetting is induced by the phase separation. In the third region between ∼1 μm and ∼200 nm the dewetting is observed even in the early stage. The dewetting morphology is very irregular and no definite characteristic wavelength is observed. It is expected that the irregular morphology is induced by mixing up the characteristic wavelengths of the phase separation and the dewetting. In the fourth region below ∼200 nm the dewetting occurs after a long incubation time with a characteristic wavelength, which decreases with the film thickness. It is considered that the layered structure is formed in the thin film during the incubation period and triggers the dewetting through the capillary fluctuation mechanism or the composition fluctuation one.     

Assembly of 8YSZ nanoparticles into gas-tight 1-2 μm thick 8YSZ electrolyte layers using wet coating methods

The application of a thin film electrolyte layer with a thickness in the micrometer range could greatly improve current solid oxide fuel cells (SOFCs) in terms of operating temperature and power output. Since the achievable minimal layer thickness with conventional powder coating methods is limited to ∼5 μm, a variety of thin film methods have been studied, but results on regular large-scale anode substrates are still lacking in the literature. In this paper, a wet coating process is presented for fabricating gas-tight 1-2 μm thick 8YSZ electrolyte layers on a regular NiO/8YSZ substrate, with a rough surface, a high porosity and a large pore size. These layers were deposited in a similar way as conventional suspension based layers, but the essential difference includes the use of coating liquids (nano-dispersion, sol) with a considerably smaller particle size (85 nm, 60 nm, 35 nm, 6 nm). Successful deposition of such layers was accomplished by means of an innovative coating process, which involves the preparation of a hybrid polyvinyl alcohol/8YSZ membrane by dip-coating or spin-coating and subsequently burning out the polymer part at 500 °C. Results from He leak tests confirmed that the sintered layers posses a very low number of defects and with values in the range 10⁻⁴-10⁻⁶ (hPa dm³)/(s cm²) the gas-tightness of the thin film layers is satisfactory for fuel cell operation. Moreover, preliminary results have also indicated a potential reduction of the sintering temperature from 1400 °C to the range 1200-1300 °C, using the presented coating process.     

Formation of porous anodic titanium oxide films in hot phosphate/glycerol electrolyte

The present study reveals the formation of porous anodic films on titanium at an increased growth rate in hot phosphate/glycerol electrolyte by reducing the water content. A porous titanium oxide film of 12 μm thickness, with a relatively low content of phosphorus species, is developed after anodizing at 5 V for 3.6 ks in 0.6 mol dm⁻³ K₂HPO₄ + 0.2 mol dm⁻³ K₃PO₄/glycerol electrolyte containing only 0.04% water at 433 K. The growth efficiency is reduced by increasing the formation voltage to 20 V, due to formation of crystalline oxide, which induces gas generation during anodizing. The film formed at 20 V consists of two layers, with an increased concentration of phosphorus species in the inner layer. The outer layer, comprising approximately 25% of the film thickness, is developed at low formation voltages, of less than 10 V, during the initial anodizing at a constant current density of 250 A m⁻². The pore diameter is not significantly dependent upon the formation voltage, being ∼10 nm.     

Towards the conception of an amperometric sensor of l-tyrosine based on Hemin/PAMAM/MWCNT modified glassy carbon electrode

A novel amperometric sensor was fabricated based on the immobilization of hemin onto the poly (amidoamine)/multi-walled carbon nanotube (PAMAM/MWCNT) nanocomposite film modified glassy carbon electrode (GCE). Electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and ultraviolet visible (UV-vis) adsorption spectroscopy were used to investigate the possible state and electrochemical activity of the immobilized hemin. In the Hemin/PAMAM/MWCNT nanocomposite film, MWCNT layer possessed excellent inherent conductivity to enhance the electron transfer rate, while the layer of PAMAM greatly enlarged the surface average concentration of hemin (Γ) on the modified electrode. Therefore, the nanocomposite film showed enhanced electrocatalytical activity towards the oxidation of l-tyrosine. The kinetic parameters of the modified electrode were investigated. In pH 7.0 phosphate buffer solution (PBS), the sensor exhibits a wide linear range from 0.1 μM to 28.8 μM l-tyrosine with a detection limit of 0.01 μM and a high sensitivity of 0.31 μA μM⁻¹ cm⁻². In addition, the response time of the l-tyrosine sensor is less than 5 s. The excellent performance of the sensor is largely attributed to the electro-generated high reactive oxoiron (IV) porphyrin (O = Fe^IV-P) which effectively catalyzed the oxidation of l-tyrosine. A mechanism was herein proposed for the catalytic oxidation of l-tyrosine by oxoiron (IV) porphyrin complexes.     

Electrochemical formation of AlN in molten LiCl-KCl-Li3N systems

Electrochemical formation of aluminum nitride was investigated in molten LiCl-KCl-Li₃N systems at 723 K. When Al was anodically polarized at 1.0 V (versus Li⁺/Li), oxidation of nitride ions proceeded to form adsorbed nitrogen atoms, which reacted with the surface to form AlN film. The obtained nitrided film had a thickness of sub-micron order. The obtained nitrided layer consisted of two regions; the outer layer involving AlN and aluminum oxynitride and the inner layer involving metallic Al and AlN. When Al electrode was anodically polarized at 2.0 V, anodic dissolution of Al electrode occurred to give aluminum ions, which reacted with nitride ions in the melt to produce AlN particles (1-5 μm of diameter) of wurtzite structure.     

Effect of UV aging on electrochemical behavior of an anticorrosion paint

The effect of the photochemical artificial ageing (UVA) on the electrochemical behavior of an anticorrosion paint has been studied by electrochemical impedance spectroscopy (EIS). Two types of coatings have been tested: a formulated tri coat system (FS) formed by a primer (epoxy), an intermediate coat (epoxy) and a topcoat (alkyd) which presents a total film thickness of 240 μm and, on the other hand, a non-formulated varnish (NFV) which presents a total film thickness of 70 μm. Panels have been aged in a QUV chamber and the maximal exposure's time was about 1000 h. EIS testing were carried out with a naturally aerated 3% NaCl solution.     

Mechanical properties of MWPECVD diamond coatings on Si substrate via nanoindentation

The mechanical properties of polycrystalline diamond coatings with thickness varying from 0.92 to 44.65 μm have been analysed. The tested samples have been grown on silicon substrates via microwave plasma enhanced chemical vapour deposition from highly diluted gas mixtures CH₄-H₂ (1% CH₄ in H₂). Reliable hardness and elastic modulus values have been assessed on lightly polished surface of polycrystalline diamond films.The effect of the coating thickness on mechanical, morphological and chemical-structural properties is presented and discussed. In particular, the hardness increases from a value of about 52 to 95 GPa and the elastic modulus from 438 to 768 GPa by varying the coating thickness from 0.92 to 4.85 μm, while the values closer to those of natural diamond (H = 103 GPa and E = 1200 GPa) are reached for thicker films (> 5 μm). Additionally, the different thickness of the diamond coatings permits to select the significance of results and to highlight when the soft silicon substrate may affect the measured mechanical data. Thus, the nanoindentation experiments were made within the range from 0.65% to 10% of the film thickness by varying the maximum load from 3 to 80 mN.     

A novel and facile route of ink-jet printing to thin film SnO2 anode for rechargeable lithium ion batteries

Thin film SnO₂ electrode has been prepared for the first time by using a novel facile and low-cost ink-jet printing technique. Wet ball-milling was employed to stabilize SnO₂ nano particles and conducting agent acetylene black (AB) using two kinds of polymeric hyperdispersants CH10B and CH12B, respectively, to prepare the stable colloid as “ink”. The morphology, structure, composition and electrochemical performance of SnO₂ thin film electrodes were investigated in detail by SEM, TEM, XRD, EDX, cyclic voltammograms (CV) and galvanostatic charge-discharge measurements. SEM images show uniform distribution of as-printed SnO₂ thin film electrodes. The thickness of monolayer thin film electrode was about 770-780 nm by TEM observation. The thickness of SnO₂ thin film could be increased by repeating the printing procedure on the Cu foil substrate. The average thickness of 10-layer SnO₂ thin-film electrode after compression for electrochemical measurement was about 2.3 μm. High initial discharge capacity about 812.7 mAh/g was observed at a constant discharge current density of 33 μA/cm² in a potential range of 0.05-1.2 V. It is expected that ink-jet printing is a very feasible, simple, convenient and inexpensive way to prepare thin film electrode for lithium ion batteries.     

Deproteinised natural rubber used as a controlling layer membrane in reservoir-type nicotine transdermal patches

Reservoir-type nicotine transdermal patches (NTPs), composed of a concentrated nicotine solution embedded between a backing layer and a controlling layer membrane, were constructed by a heat-sealing technique. The aim of this research was the preparation of a novel controlling layer membrane from deproteinised natural rubber latex (DNRL). The ultimate tensile strength and percentage of elongation at breakage of the DNRL membrane were 0.23 ± 0.04 MPa and 604.46 ± 95.38%, respectively. The DNRL membrane existed as an amorphous phase and was poorly hygroscopic and dense. FT-IR and DSC analysis demonstrated that the membrane consisted almost entirely of isoprene functional groups with a T_g of −64.79 °C. The effects of the DNRL membrane thickness (100–300 μm) and different nicotine concentrations in the reservoir (1.75–4.25 mg/cm²) on the nicotine release rate and nicotine permeation through a pig skin membrane were studied in vitro. The in vitro nicotine release rate and skin permeation rate increased with decreasing membrane thickness and increasing nicotine content in the reservoir. The release and permeation profiles followed first- and zero-order kinetics, respectively. The release and permeation performance was similar to a commercially available Nicotinell TTS-20 patch. The newly developed NTPs were stable under storage in a tightly sealed container at 4 °C or at ambient temperature for up to 3 months. Thus, DNRL is suitable for use as a controlling layer membrane in NTPs in transdermal drug delivery systems.     

Electrochemical behavior and voltammetric determination of 4-aminophenol based on graphene-chitosan composite film modified glassy carbon electrode

The graphene-chitosan composite film modified glassy carbon electrode (GCE) was fabricated and used to determine 4-aminophenol (4-AP). In 0.1 M pH 6.3 phosphate buffer solution, the redox peak currents of 4-AP increased significantly and the peak-to-peak separation decreased greatly at graphene-chitosan composite film modified GCE compared with bare GCE and chitosan modified GCE, indicating that graphene possessed electrocatalytic activity towards 4-AP. The experimental conditions were optimized and the kinetic parameters were investigated. The oxidation mechanism was discussed. Under the optimal experimental conditions, the oxidation peak current was proportional to 4-AP concentration in the range from 0.2 to 550 μM with the correlation coefficient of 0.9930. The detection limit was 0.057 μM (S/N = 3). Using the proposed method, 4-AP was successfully determined in water samples and paracetamol tablets with standard addition method, suggesting that this method can be applied to determine 4-AP in environments and pharmaceuticals.     

Diamond-like carbon film deposited on nitrided 316L stainless steel substrate: A hardness depth-profile modeling

Adhesion and hardness of Diamond-Like Carbon films are improved by nitriding of the steel substrate prior to PVD deposition. Since the mechanical properties of the nitrided steel layer are not homogeneous, i.e. a significant hardness decrease is observed in the upper nitrided layer close to the surface, an outer surface layer of ~ 15 μm is removed prior to the film deposition. In the present work, a 316L stainless steel substrate is nitrided in a cyanide-cyanate solution at 570 °C during 3 h. The coated system involved the deposition of a hydrogenated, amorphous carbon (a-C:H) solid lubricant of ~ 2 μm including a chromium carbide interlayer. The comparison between the hardness behavior of the DLC/steel and the DLC/nitrided steel systems reveals the existence of a very important hardness gap, which highlights the benefit of the nitriding treatment prior to coating deposition. In addition, the microhardness-depth profile is determined from a load-depth curve, by applying a simple hardness model. The predicted change in hardness is found to be in a very good agreement with the experimental profile, which allows the hardness determination both in the white layer and in the diffusion zone over ~ 30 μm in total depth. However, only the composite hardness modeling allows the accurate determination of the intrinsic hardness of the film.     

Physical aging of thin glassy polymer films monitored by gas permeability

The physical aging at 35 °C of three glassy polymers, polysulfone, a polyimide and poly(2,6-dimethyl-1,4-phenylene oxide), has been tracked by measurement of the permeation of three gases, O₂, N₂, and CH₄, for over 200 days. Several techniques were used to accurately determine the thickness of films (∼400 nm-62 μm) in order to obtain absolute permeability coefficients and to study the effects of film thickness on the rate of physical aging. Each film was heated above the polymer T_g to set the aging clock to time zero; ellipsometry revealed that this procedure leads to isotropic films having initial characteristics independent of film thickness. A substantial pronounced aging response, attributed to a decrease in polymer free volume, was observed at temperatures more than 150 °C below T_g for thin films of each polymer compared to what is observed for the bulk polymers. The films with thicknesses of approximately 400 nm of the three polymers exhibit an oxygen permeability decrease by as much as two-fold or more and about 14-15% increase in O₂/N₂ selectivity at an aging time of 1000 h. The results obtained in this study were compared with prior work on thickness dependent aging. The effects of crystallinity on physical aging were examined briefly.     

EIS analysis on low temperature fabrication of TiO2 porous films for dye-sensitized solar cells

A low temperature (<150 °C) fabrication method for preparation of TiO₂ porous films with high efficiency in dye-sensitized solar cells (DSSCs) has been developed. The Ti(IV) tetraisopropoxide (TTIP) was added to the paste of TiO₂ nanoparticles to interconnect the TiO₂ particles. The electrochemical impedance spectroscopy (EIS) technique was employed to quantify the charge transport resistance at the TiO₂/dye/electrolyte interface (R_ct2) and electron lifetime in the TiO₂ film (τ_e) under different molar ratios of TTIP/TiO₂ and also at various TiO₂ thicknesses. It was found that the R_ct2 decreased as the molar ratio increased from 0.02 to 0.08, however, it increased at a molar ratio of 0.2 due to the reduction in surface area for dye adsorption. In addition, the characteristic frequency peak shifted to lower frequency at a molar ratio of 0.08, indicating the longer electron lifetime. As for the thickness effect, TiO₂ film with a thickness around 17 μm achieved the best cell efficiency. EIS study also confirmed that, under illumination, the smallest R_ct2 was associated with a TiO₂ thickness of 17 μm, with the R_ct2 increased as the thickness of TiO₂ film increased. In the Bode plots, the characteristic frequency peaks shifted to higher frequency when the thickness of TiO₂ increased from 17.2 to 48.2 μm, indicating the electron recombination increases as the thickness of the TiO₂ electrode increases.Finally, to make better use of longer wavelength light, 30 wt% of larger TiO₂ particle (300 nm) was mixed with P25 TiO₂ as light scattering particles. It effectively increased the short-circuit current density and cell conversion efficiency from 7.44 to 8.80 mA cm⁻² and 3.75 to 4.20%, respectively.     

Synthesis and characterisation of surface gradient thin conversion films on zinc coated steel

Surface gradient layers on hot-dip galvanised steel were synthesised in order to determine the barrier properties and corrosion resistance of thin amorphous conversion coatings as a function of layer thickness and processing time. For this purpose, a dip coating procedure was established that yields well-defined gradient layers. As a model system for conversion film formation on zinc coated steel, a zirconium based bath chemistry was used. The synthesised zirconium oxyhydroxide gradient films were characterised by localised electrochemical techniques, such as Scanning Kelvin Probe (SKP) and electrochemical impedance spectroscopy using an electrochemical capillary cell. Microscopic infrared reflection absorption spectroscopy (μ-FT-IRRAS) measurements and small-spot X-ray photo electron spectroscopy (XPS) were used as complementary surface analytical techniques. The applied analysing techniques provide a spatial resolution of 100-1600 μm. Thereby, a complete variation of thin film properties, such as thickness, barrier properties, corrosion resistance and chemical composition can be measured as function of the time of film growth on a sample with a length of a few centimetres. This approach allows a precise and accurate determination of structure-to-property relationships of thin conversion films. Moreover, it could be shown that a surface gradient film analysis significantly rationalises experimental time and increases the reliability of the experimental results.     

Separability of hydrogen from hydrogen-carbon dioxide mixture across silica-silicalite-1 film

Colloidal silica particles, grown on a mesoporous silica layer using macroporous alumina substrate as a support, were used to separate hydrogen from carbon dioxide. The particles transformed into rectangular interlocking silicalite-1 structures with size approximately 8 × 4 × 4 μm, oriented epitaxially with film thickness of ca. 22 μm. The silicalite-1 particles grew in size due to the effect of structure directing agent (SDA), Oswald ripening and hydrothermal synthesis that promoted the growth of the colloidal particles into crystals. Permeation experiment using silicalite-1 showed that CO₂ flux decreased and H₂ flux increased with increase in temperature. The separability of H₂ that was unity at the lower temperature became increased in value as the temperature was raised.     

Electrochemical characterization of poly(eriochrome black T) modified glassy carbon electrode and its application to simultaneous determination of dopamine, ascorbic acid and uric acid

A polymerized film of eriochrome black T (EBT) was prepared on the surface of a glassy carbon (GC) electrode in alkaline solution by cyclic voltammetry (CV). The redox response of the poly(EBT) film at the GC electrode appeared in a couple of redox peak in 0.1 M hydrochloride and the pH dependent peak potential was −55.1 mV/pH which was close to the Nernst behavior. The poly(EBT) film-coated GC electrode exhibited excellent electrocatalytic activity towards the oxidations of dopamine (DA), ascorbic acid (AA) and uric acid (UA) in 0.05 mM phosphate buffer solution (pH 4.0) and lowered the overpotential for oxidation of DA. The polymer film modified GC electrode conspicuously enhanced the redox currents of DA, AA and UA, and could sensitively and separately determine DA at its low concentration (0.1 μM) in the presence of 4000 and 700 times higher concentrations of AA and UA, respectively. The separations of anodic peak potentials of DA-AA and UA-DA reached 210 mV and 170 mV, respectively, by cyclic voltammetry. Using differential pulse voltammetry, the calibration curves for DA, AA and UA were obtained over the range of 0.1-200 μM, 0.15-1 mM and 10-130 μM, respectively. With good selectivity and sensitivity, the present method provides a simple method for selective detection of DA, AA and UA in biological samples.     

Characterization of gas diffusion layers for PEMFC

A carbon-filled gas diffusion layer (CFGDL), which is in the configuration similar to conventional carbon cloth gas diffusion layer (GDL) coated with carbon layer on both faces, was investigated and compared with conventional carbon paper-based single-layer and dual-layer GDLs. Like the carbon cloth GDL, CFGDL has presented superior performances over the single-layer or dual-layer GDL in all three polarization (activation, ohmic and concentration) controlled regions under electrochemical characterizations (steady-state polarization and electrochemical impedance spectra). The results from SEM showed that CFGDL has the same thickness of 0.11 mm as that of single-layer GDL, while dual-layer GDL has a thickness of 0.18 mm. The fully filled carbon paper with carbon/PTFE filler, as seen in the SEM image, displayed good support for the catalyst layer and electrolyte phase, allowing good electrical contact between the GDL/catalyst/membrane and GDL/flow field plate to be achieved. From porosimetry analysis, CFGDL presented a lower porosity of 67% and a much smaller average pore diameter of 4.7 μm compared to the single-layer GDL (porosity of 77% and pore diameter of 35.8 μm) and dual-layer GDL (porosity of 73% and pore diameter of 25.5 μm); however, it also gave the largest limiting current density, which reflects the improvement in mass transportation. This phenomenon is likely attributed to the fast removal of micro-water droplets formed in the CFGDL structure of the electrode.     

Formation of gold nanoparticles on multiwalled carbon nanotubes by thermal evaporation

Multiwalled carbon nanotubes (MWCNTs) were grown on W substrates by chemical vapor deposition and modified with Au nanoparticles by thermal evaporation. The resulting hybrid structures were investigated by TEM to determine the effects of evaporation rate, nominal film thickness, and substrate temperature on the nanoparticle size and distribution. The results demonstrate that as-grown MWCNTs can be used as a support for well distributed Au nanoparticles, with the size and distribution on the carbon nanotubes being primarily influenced by the nominal film thickness. The observed structures ranged from small 4 nm diameter spherical particles to 150 nm long wire-like structures. Depositions with substrates at 25 °C and 400 °C resulted in similar particle structures, except for the highest amount of deposited Au.