Growth and field crystallization of anodic films on Ta–Nb alloys

The growth behavior of amorphous anodic films on Ta–Nb solid solution alloys has been investigated over a wide composition range at a constant current density of 50 A m⁻² in 0.1 mol dm⁻³ ammonium pentaborate electrolyte. The anodic films consist of two layers, comprising a thin outer Nb₂O₅ layer and an inner layer consisting of units of Ta₂O₅ and Nb₂O₅. The outer Nb₂O₅ layer is formed as a consequence of the faster outward migration of Nb⁵⁺ ions, compared with Ta⁵⁺ ions, during film growth under the high electric field. Their relative migration rates are independent of the alloy composition. The formation ratio, density, and capacitance of the films show a linear relation to the alloy composition. The susceptibility of the anodic films to field crystallization during anodizing at constant voltage increases with increasing niobium content of the alloy.     

Formation of Al2O3–BaTiO3 nanocomposite oxide films on etched aluminum foil by sol–gel coating and anodizing

Barium titanate BaTiO₃ (BT) sol was dip-coated on the etched aluminum foils by a sol–gel process. After annealed at 600 °C in air, the foils were anodized in ammonium adipate solution. The voltage–time variations during anodizing were monitored. The structure, composition, and electric properties of the anodic foils were investigated. The obtained foils were fabricated into aluminum electrolytic capacitors and the load and shelf life test were measured. It was found that the slope of the voltage–time curve of aluminum foil covered with BT films became steeper. A triple layer of Al/Al₂O₃/BT was formed after anodizing Al/BT foil. The specific capacitance and the product of specific capacitance and withstanding voltage of anodic foil with a BT coating were about 46.36% and 38.90% larger than that without a BT coating. After the load life and shelf life of 2500 h at 85 °C, two kinds of capacitors have similar behaviores and meet with Nichicon standard of Japan. From the results, BaTiO₃ is promising to be used as the dielectric of aluminum electrolytic capacitor to increase the specific capacitance.     

Thermally stimulated dielectric properties of polyvinylidenefluoride–zinc oxide nanocomposites

Thirty-micrometer thick polyvinylidenefluoride (PVDF)–zinc oxide (ZnO) nanocomposite samples in the mass ratio of ZnO (1–6% (w/w)) have been prepared by solution mixing method. The nano- and microstructures of PVDF–ZnO nanocomposite of different mass ratios were characterized by using high-resolution techniques such as atomic force microscopy (AFM) and scanning electron microscopy (SEM). The SEM and AFM images show the presence of different components such as nanoparticles, amorphous and crystalline phases in nanocomposite samples. Dielectric properties of polymer nanocomposite based on PVDF and ZnO of different mass/% compositions have been studied to understand the molecular motion at different frequencies in the temperature range from 300 to 500 K. The permittivity of the nanocomposites decreases with frequency, while increases with the increasing temperature and ZnO content. The loss peak that disappeared at higher frequency is the remarkable result of this study.     

Dependence of the mechanical characteristics of fast-quenched amorphous Zr–Cu–Al alloys on their composition

The thermal and mechanical characteristics of fast-quenched amorphous Zr–Cu–Al alloys with various concentrations of copper and aluminum are studied. It is shown that the crystallization temperature of glass-like compositions increases when copper is replaced with aluminum in concentrations of up to 10 at %, and that the hardness, Young’s modulus, and fracture stress increase only at low concentrations of aluminum (no more than 6 at %). Upon a further increase in the concentration of the alloying element, fracture stress σf decreases because σ_f the change in the fracture mechanism, despite high hardness and Young’s modulus.     

Anodic formation and properties of nanoscale oxide layers on silver–zinc alloys with different concentrations of non-equilibrium vacancies

Journal of Solid State Electrochemistry - Anodic oxidation of silver–zinc alloys with a concentration of zinc of up to 30 at.% (alpha phase) in a deaerated aqueous solution of 0.1 M...     

Improved optical and electrical properties of sol–gel-derived boron-doped zinc oxide thin films

Sol–gel spin-coating was used to grow zinc oxide (ZnO) thin films doped with 0–2.5 at.% B on quartz substrates. The structural, optical, and electrical properties of the thin films were investigated using field-emission scanning electron microscopy, X-ray diffraction (XRD), photoluminescence (PL), ultraviolet–visible spectroscopy, and van der Pauw Hall-effect measurements. All the thin films had deposited well onto the quartz substrates and exhibited granular morphology. The average crystallite size, lattice constants, residual stress, and lengths of the bonds in the crystal lattice of the thin films were calculated from the XRD data. The PL spectra showed near-band-edge (NBE) and deep-level emissions, and B doping varied the PL properties and increased the efficiency of the NBE emission. The optical transmittance spectra for the undoped ZnO and boron-doped zinc oxide (BZO) thin films show that the optical transmittance of the BZO thin films was significantly higher than that of the undoped ZnO thin films in the visible region of the spectra and that the absorption edge of the BZO thin films was blue-shifted. In addition, doping the ZnO thin films with B significantly varied the absorption coefficient, optical band gap, Urbach energy, refractive index, extinction coefficient, single-oscillator energy, dispersion energy, average oscillator strength, average oscillator wavelength, dielectric constant, and optical conductivity of the BZO thin films. The Hall-effect data suggested that B doping also improved the electrical properties such as the carrier concentration, mobility, and resistivity of the thin films.     

Microstructural properties of sintered Al–Cu–Mg–Sn alloys

A non-commercial Al4Cu0.5Mg alloy has been used for investigating the effects of the elemental Sn additions. Uniaxial die compaction response of the alloys in terms of green density was examined, and the results showed that Sn addition has no effect when compacting conducted under high pressures. In total, 93–95% green density was achieved with an applied pressure of 400 MPa. Thermal events occurring during the sintering of the emerging alloys were studied by using differential scanning calorimetry (DSC). First thermal event on the DSC analysis of the Al4Cu0.5Mg1Sn alloy is the melting of elemental Sn, whereas for Al4Cu0.5Mg alloy, it is the formation of Al–Mg liquid nearly at 450 °C. Also it is clearly seen on the DSC analysis that Sn addition led to an increase in the formation enthalpy of Al–Mg liquid phase. High Sn content and high sintering temperature (620 °C), therefore high liquid-phase content, caused decrease on the mechanical properties due to thick intergranular phases and grain coarsening. Highest transverse rupture strength and hardness values were obtained from Al4Cu0.5Mg0.1Sn alloy sintered at 600 °C and measured as 390 MPa and 73 HB, respectively.     

Influence of Ti additions on the martensitic phase transformation and mechanical properties of Cu–Al–Ni shape memory alloys

The effect of Ti additions on the microstructure and mechanical properties of Cu–Al–Ni shape memory alloys (SMA) was studied by means of a differential scanning calorimeter, field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction (XRD), a tensile test, a hardness test, and a shape memory effect test. The experimental results show that the Ti additions have an effective influence on the phase transformation behavior through generating a new phase into the microstructure, which is known as X-phase and/or controlling the grain size. The results of the XRD confirmed that the X-phase is a combination of two compounds, AlNi₂Ti and Ti₃·3Al. Nevertheless, it was found that with 0.7 mass% of Ti, the best phase transformation temperatures and mechanical properties were obtained. These improvements were due to the highest existence of the X-phase into the alloy along with a noticeable decrement of grain size. The Ti additions to the Cu–Al–Ni SMA were found to increase the ductility from 1.65 to 3.2 %, corresponding with increasing the strain recovery by the shape memory effect from 50 to 100 %; in other words, a complete recovery occurred after Ti additions.     

Study on the microstructure and liquid–solid correlation of Al–Mg alloys

Based on the available structural models and theories of electrical resistivity (ER) of liquid alloys, the structure and the liquid–solid correlation of Al _(100-x) Mg_x (x = 0, 10, 20, 30, 40, 50) alloys have been qualitatively studied by measuring the ER during the heating/cooling process using the direct-current (DC) four-probe method, as well as by characterizing the solidification morphology and testing the hardness. The result shows that the ER of Al–Mg alloys increases with the increasing temperature and the Mg content; thermal state and history have an effect on the solidification structure and properties: the ER of Al–Mg alloys exhibits a lag phenomenon of structure change during the heating/cooling process. A higher heating/cooling rate contributes to the more obvious relaxation effect of ER and the more uniform structure. Furthermore, higher pouring temperature (PT) leads the melts and solidification structure to be more homogeneous, which increases the hardness.     

Effect of sintering temperature on the structural, optical and electrical properties of sol–gel derived indium oxide thin films

Sol gel derived indium oxide, In₂O₃; films were prepared by spin coating technique. The films were dried and sintered at different sintering temperatures (300, 400, 450 and 500 °C) in air. The effect of sintering temperature on the structural, optical and electrical properties of In₂O₃ thin films was studied. The morphology and structure of the films were analyzed by scanning electron microscope and X-ray diffraction. The films showed a bcc structure that changes its 400-preferential orientation to 222 orientation as the sintering temperature increases from 300 to 500 °C. The optical behavior of the films was studied by measuring the transmission spectra in the wavelength range 200–2,500 nm. Different optical models have been proposed for fitting the transmittance data and simulate the optical constants as well as the film thickness of In₂O₃ films. The best fitting of the data was obtained by combining the classical Drude and OJL models coupled with the Bruggeman effective medium approximation. The optical parameters of Drude model (plasma frequency and damping constant) are used calculate the electrical properties of the films. The calculated values of the electrical sheet resistance were compared with those measured experimentally by four probes. The correlation between the film orientation change and its optical and electrical properties was discussed.     

Characteristics of Ti–Nb,Ti–Zr and Ti–Al containing hydrogenated carbon nitride films

Nanocomposite Me–C–N:H coatings (Me is TiNb, TiZr or TiAl), with relatively high non-metal/metal ratios, were prepared by cathodic arc method using TiNb, TiZr and TiAl alloy cathodes in a CH₄ + N₂ atmosphere. For comparison purposes, a-C–N:H films were also produced through evaporating a graphite cathode in a similar atmosphere. The films were characterized in terms of elemental and phase compositions, chemical bonds, texture, hardness, adhesion and friction behavior by GDOES, XPS, Raman spectroscopy and XRD techniques, surface profilometry, hardness and scratch adhesion measurements, and tribological tests. The nanocomposite films consisted of a mixture of crystalline metal carbonitride and amorphous carbon nitride. The non-metal/metal ratio in the films composition was found to range between 1.8 and 1.9. For the metal containing nanocomposites, grain size in the range 7–23 nm, depending on the metal nature, were determined. As compared with the a-C–N:H, the Me–C–N:H films exhibited a much higher hardness (up to about 39 GPa for Ti–Zr–C–N:H) and a better adhesion strength, while the coefficients of friction were somewhat higher (0.2–0.3 for Me–C–N:H and 0.1 for a-C–N:H).     

The influence of annealing on electrochromic properties of Al–B–NiO thin films prepared by sol–gel

Al–B–NiO thin films were prepared using the sol–gel process and deposited on Indium tin oxide (ITO)-coated glass substrates via the dip-coating technique for the purpose of developing high performance electrochromic materials. The influence of the anneal on the structural and electrochromic properties of Al–B–NiO films is reported. Thermogravimetry (TG) and differential thermal analysis (DTA), cyclic voltammetry measurements (CV), UV spectrophotometer, atomic force microscopy (AFM) and X-ray diffraction (XRD) have been used to investigate the structural and electrochromic properties. The thickness of the films was determined by spectrophotometric analysis in 350–1,000 nm wavelength. Results showed that the Al–B–NiO thin films treated at high temperature have both the excellent electrochromic properties and good reversibility. The transmittance change (ΔT) of the film treated at 500 °C reaches still ~50% at the wavelength of 550 nm. The microstructure and the surface morphology were considered to play an important role in the electrochromic properties with different temperatures.     

Formation and tribological properties of composite Langmuir–Blodgett films of stearic acid with molybdenum disulfide and amorphous carbon

The morphology and tribological properties of Langmuir–Blodgett mono- and bilayers of stearic acid with particles of molybdenum disulfide (MoS₂) and amorphous carbon (С), prepared on silicon and steel substrates by horizontal deposition (stearic acid–MoS₂ and stearic acid–С monolayers) and by the “roll” technique (stearic acid–MoS₂/stearic acid–С bilayers), were studied. Incorporation of C and MoS₂ particles into the structure of a stearic acid film enhances its wear resistance by a factor of 2.8 and 5.5, respectively. The presence of MoS₂ and С particles and of their aggregates of size from ~220 nm to 16.3 μm in stearic acid layers was confirmed by atomic force microscopy.     

Effect of cooling rate and Al content on solidification behavior and microstructure evolution of as-cast Mg–Al–Ca–Sm alloys

Journal of Thermal Analysis and Calorimetry - In the present study, the Mg–xAl–2Ca–2Sm (x = 3, 5, 9 and 15) alloys were fabricated in sand mold with stepped type, and...     

Thermodynamic properties and amorphization of Zr–Si melts

The relationship between the thermodynamic properties of Zr–Si liquid alloys and their propensity to amorphization is studied. The temperature–concentration dependences of the thermodynamic properties of melts are presented using the concept of associated solutions. It is shown that the range of amorphization coincides with the range of the predominant concentration of Zr₃Si associative groups with low formation entropy.     

Electroless deposition and properties of Co–Re–B alloys

The data on the mechanism of electroless (catalytic) deposition of Co–Re–B coatings are obtained by determining the donor capacitance of dimethylamine borane (DMAB) (CH₃)₂HN · BH₃ reductant and the oxidation level of its hydride hydrogen. From the results of the study of isotopic composition of evolved hydrogen, it is concluded that the oxidation level of DMAB hydride hydrogen depends on the catalytic activity of the alloy. The alloys containing up to 46 at % rhenium were produced by the electroless deposition.