Formation Of Bronze Research Articles

Sol-Gel Pt-VO2 Films as Selective Chemoresistive and Optical H2 Gas Sensors.

In this work, VO2 (M1/R) thin films were exploited as H2 gas sensors. A flat film morphology, obtained by furnace annealing, was compared with a laser-induced nanostructured one. The combination of the environmentally friendly sol-gel approach with the ultrafast laser crystallization allows for significant reductions in energy consumption and related emissions during the fabrication of VO2 sensors. By decorating the sensors' surface with Pt nanoparticles (NPs), the sensor response was enhanced exploiting the hydrogen spillover effect. The Pt/VO2 sensors, tested at operating temperatures between 20 and 200 °C and for concentration of H2 from few ppm to 50000 ppm, offered a dual chemoresistive and optical sensing mode. Low operating temperatures of 150 °C were achieved, along with a detection limit as low as 2 ppm and a perfect baseline recovery. Both sensors guaranteed specific selectivity toward H2, without response to NO2 or humidity, and long-term stability over 500 h. The H2 sensing mechanism, for both the monoclinic and rutile VO2 phases, was investigated through in operando X-ray Diffraction and in situ X-ray Photoelectron Spectroscopy tests. The interaction was found to be based on the reversible formation of HxVO2 bronze, along with the reversible variations in the oxidation state of V.

Analysis of the Sr2GdTi2Nb3O15 ceramic: Investigation into its structural properties and complex impedance spectroscopy

In this study, we successfully synthesized tetragonal tungsten bronze with the nominal formula Sr2GdTi2Nb3O15 and systematically examined of its structure, dielectric, and electrical properties. The material was synthesized through the solid-state reaction technique at a temperature of 1350 °C. The formation of the tetragonal tungsten bronze in the P4/mbm space group was verified via Rietveld refinement using X-ray diffraction data. The electrical characteristics of the ceramic were examined using non-destructive complex impedance spectroscopy (CIS) across a range of frequencies (10–106 Hz) at various temperatures. The real component of impedance (Z') displayed a decrease with rising frequency, suggesting a negative temperature coefficient of resistance (NTCR) for this sample. The Cole-Cole plot of the compound exhibits two semicircles, with the compound's resistance gradually decreasing as the temperature increased. Moreover, the activation energy (Ea) was found to be approximately 0.9 eV, which confirms that oxygen vacancies are responsible for the observed relaxation behavior. Complex modulus analysis confirmed the presence of non-Debye relaxations. These results contribute to a thorough comprehension of the structural and electrical characteristics of Sr2GdTi2Nb3O15, opening avenues for potential applications in diverse electronic devices.

Relationship between crystal orientation and energy storage capacity in WO3 photoelectrodes for water splitting

For photoelectrochemical water splitting, tungsten trioxide (WO3) films with a monoclinic structure were synthesized on fluorine-doped tin oxide coated glass substrates with a vacuum evaporation method. To control the WO3 film thickness from 0.42 to 5.6 μm, the crystal orientation was intergraded from the (200) crystal plane to the (002) one. In x-ray diffraction measurements, the intensity ratio of the (002) crystal plane to the (200) one was defined as rp. In the WO3 photoelectrode with higher (002)-preferred orientation, the photocurrent continued to flow even when the incident light against the photoelectrode was completely blocked after the irradiation for 60 s. This suggests that hydrogen continues to be produced owing to the electrons charged by the formation of a hydrogen tungsten bronze (HxWO3) phase. After 72 s, the photocurrent density of the WO3 photoelectrode with rp = 42 became one-tenth of the value before the incident light was blocked. This charge release time was remarkably long compared to those of the WO3 photoelectrodes with (200)-preferred orientation and non-orientation. Therefore, it was considered that the hydrogen ion diffusion through the defects in the WO3 crystals tends to occur in the [002] crystal direction. However, the improvement in the (002)-preferred orientation can facilitate the structural change from the WO3 phase to the HxWO3 one for the entire film.

The effects of Sr-substitution in Ba2SmTi2Nb3O15 ceramics: structural study, optical properties, and complex impedance spectroscopy.

Ceramics of (Ba1-xSrx)2SmTi2Nb3O15, denoted as BSxSTN (x = 0, 0.25 and 0.5), were synthesized by the conventional solid-state reactions route. The impact of Sr-substitution in Ba2SmTi2Nb3O15 ceramics on their structural, optical, and dielectric properties are investigated. The Rietveld method was employed to confirm the formation of tetragonal tungsten bronze with the P4bm space group, using X-ray diffraction data. The substitution of Ba by Sr resulted in a decrease in cell parameters, density, and the average crystallite size as determined by Scherrer's formula ranged from 29.4 to 32 nm. The compounds frequency-dependent dielectric properties were studied using complex impedance spectroscopy over a temperature range of 50 to 420 °C at different frequencies. Dielectric measurements revealed a high dielectric constant, and the compounds exhibited characteristics of diffuse ferroelectric behavior. As the Sr content increased, optical gap energy increases from 3.29 to 3.59 eV, diffusivity increased from 1.19 to 1.52, Curie temperature (Tc) decreased from 269 to 213 °C, and the dielectric loss at room temperature and 1 kHz significantly decreased from 3 × 10-3 to 7 × 10-4. The correlation between (Tc) and the off-center cationic displacement of Ti/Nb in the octahedral Ti/NbO6 was analyzed. Cole-Cole plots for each sample displayed a single semicircular arc, indicating the presence of a single relaxation process.

Transition metal oxide-polymer composite supported PtPd/PNVC-WO3 nano-catalyst: Multifaceted functional behavior boosting the performance of ethanol oxidation kinetics

This investigation involves synthesis of PtPd catalyst nano-particles supported on tungsten oxide (WO3) and poly-N vinyl carbazole (PNVC) composite for validation in ethanol oxidation reaction. The tungsten oxide acquires excellent functional property by hydrogen spill over phenomenon that facilitates hydrogen tungsten bronze formation while conducting polymer enhances the charge transfer ability within the direct ethanol fuel cell framework. The catalyst nano-particles are found to be in the size range 3–5 nm, revealed from structure and morphology studies. Electrochemical characterizations derive output power density of ∼54 mW cm−2 and mass activity ∼1.9 A/mgPt, in terms of specific current density for ethanol oxidation. Ion chromatographic analysis quantifies the reaction intermediates, acetate and carbonate to the extent of 396 and 280 ppm using 1 M ethanol solution. Self designed composite nano-structures of PtPd/PNVC-WO3 with reduced Pt share provide astounding opportunity for the catalytic reaction to gear up to the complete oxidation kinetics.

Chronoamperometry-induced transmittance changes approach to detect aqueous sodium ion solutions using tungsten oxide thin films

A simple, inexpensive method to detect sodium ions from aqueous solutions is reported in this paper. The method of detection based on transmittance changes observed in tungsten oxide films on.Tungsten oxide is deposited on ITO glass substrate by continuous electrodeposition method from Peroxo Tungstic Acid precursor. Chronoamperometry at a cathodic potential of −1V was performed on the sample in different concentrations (10 mM-150 mM) of NaCl solutions prepared in TRIS buffer solvent. UV–VIS-NIR transmittance in NaCl solutions was measured for the sample before and after chronoamperometry, and the corresponding transmittance changes (ΔT) were recorded. Due to the formation of tungsten bronze, the transmittance of the sample decreases during chronoamperometry. It was observed that the transmittance change increases with the NaCl concentration, and in the NIR wavelength range, the transmittance change observed was maximum. The sensor has a linear response in the range of 10 to 150 mM Na+ and excellent selectivity towards N+ as compared to interfering ions K+ and Ca2+. Its straightforward design, higher response, and selectivity make sodium detection in food sectors and health monitoring possible.

Chemical reduction of porous WO3 and TiO2 photoelectrocatalysts by atomic hydrogen

The donor properties of atomic hydrogen were exploited to chemically reduce nanoparticle-based WO3 and TiO2 electrodes giving rise to a n-type doping of the semiconductors. For this purpose, a reactor system allowing for meticulous materials processing under high vacuum conditions and for the controlled electrode transfer into an aqueous electrolyte was designed and hydrogen doping-induced activity-changes in water photooxidation were studied. The chemical reduction of monoclinic WO3 electrodes leads to increased charge carrier separation at the semiconductor/electrolyte interface. Importantly, the beneficial doping effect is quite stable. However, bronze formation has a negative impact on the photoelectrocatalytic activity of WO3 electrodes upon strong sample reduction. For anatase TiO2 nanoparticle films de-doping of the reduced film is fast due to the small particle size. Correspondingly, the beneficial doping effect is transient. The small particle size allows, however, to estimate the number and energetic distribution of trapped electrons in hydrogen doped films.

Features of the Interaction of Scheelite with HCl Solutions at 400 and 500°C, 100 MPa, and Various f(O2) (According to Experimental and Calculated Data)

Experimental studies were carried out on the solubility of scheelite in HCl solutions in the concentration range from 0.01 to 0.316 mol/kg H2O at 400 and 500°C, a pressure of 100 MPa and the fugacity of oxygen (hydrogen) specified by the buffers Cu2O–CuO, Fe3O4–Fe2O3, Ni–NiO, and Co–CoO. It was found that scheelite in HCl solutions at the specified parameters dissolves incongruently. In solutions containing from 0.01 to 0.0316 m HCl, minor amounts of WO3 and/or WO3 – x tungsten oxides are found in the run products, along with scheelite. In solutions containing from 0.1 to 0.316 m HCl, the formation of calcium tungsten bronzes CaxWO3 is observed, the average composition of which corresponds to the formula Ca0.07WO3. Based on the analysis of the experimental data obtained, the free energies of the formation of tungsten oxides WO3, WO2.9, scheelite, and calcium tungsten bronze were calculated. Using mutually agreed thermodynamic data, the solubility of Sch in solutions of HCl and (Na, K)Cl with the participation of aluminosilicates is calculated. It is shown that the scheelite has a wide area of congruent solubility in saline systems.

Experimental study on aluminium bronze coatings fabricated by low pressure cold spraying and subsequent heat treatment

Among bronze alloys, strength and corrosion resistance are the distinguishing features of aluminium bronzes. CuAl alloys coatings are commonly prepared using thermal spraying technologies, but low-pressure cold spray, unpopular for this purpose so far, seems to be a good alternative in terms of manufacturing and facility costs. The research studies the effect of aluminium addition on low-pressure cold spray deposition of mixed CuAl feedstock powders (up to 30 wt% of Al) instead of bronze particles. Additionally, hard alumina particles (of the same weight as CuAl feedstock powders together) were added to lower coating porosity, provide good adhesion, and tailor the mechanical properties of coatings. After the implementation of thermal treatment, fine mixing of feedstock powders within the coating facilitated the formation of copper-rich solid solution and Cu4Al9 intermetallic phase for high amounts of Al (≥25 wt%). The coatings were characterized through light and scanning electron microscopy to examine cross-section morphology; energy-dispersive X-ray spectrometry and X-ray diffraction to investigate elemental and phase composition before and after thermal treatment. Additionally, to quantify the individual phases in sprayed coatings Rietveld refinement was performed. For coatings after thermal treatment were bronze formation was observed, the maximum solubility of aluminium in the copper structure was also determined using Vegard's linear dependence.

FEATURES OF THE INTERACTION OF SHEELITE WITH HCl SOLUTIONS AT 400 AND 500 ° C, 100 MPa AND VARIOUS f(O2) (ACCORDING TO EXPERIMENTAL AND CALCULATED DATA)

Experimental studies were carried out on the solubility of scheelite in HCl solutions in the concentration range from 0.01 to 0.316 mol•kg-1 H2O at 400 and 500°C, a pressure of 100 MPa and the fugacity of oxygen (hydrogen) specified by the buffers Cu2O-CuO, Fe3O4-Fe2O3, Ni-NiO and Co-CoO. It was found that scheelite in HCl solutions at the specified parameters dissolves incongruently. In solutions containing from 0.01 to 0.0316 m HCl, minor amounts of tungsten oxides WO3 and (or) WO3-x are found in the run products, along with scheelite. In solutions containing from 0.1 to 0.316 m HCl, the formation of calcium tungsten bronzes (CTB) CaxWO3 is observed, the average composition of which corresponds to the formula Ca0.07WO3. Based on the analysis of the experimental data obtained, the free energies of the formation of tungsten oxides WO3, WO2.9, scheelite and calcium of tungsten bronze were calculated. Using mutually agreed thermodynamic data, the solubility of Sch in solutions of HCl, (Na,K)Cl with the participation of alumino-silicates is calculated. It is shown that the scheelite has a wide area of congruent solubility in saline systems.

Comparative Study of Cu-6Sn Processed by Casting and Powder Metallurgy with Microwave and Conventional Assisted Sintering

Copper is a widely used material in various industries due to its properties like good corrosion resistance, thermal and electrical conductivity, stability at high temperatures, etc. To increase the mechanical and tribological properties, additional reinforcement should be added to the copper matrix. Adding tin into copper will result in the formation of bronze which is stronger and harder than either of the pure metals. This study deals with the comparative study of mechanical and tribological properties of microwave sintered and conventionally sintered Cu-6Sn. The mechanical properties of Cu-6Sn processed through powder metallurgy are compared with that of Cu-6Sn processed through casting. Hardness and wear resistance was observed to be higher for conventionally sintered specimens. Microwave sintered Cu-6Sn exhibit enhanced mechanical properties compared to Cu-6Sn processed through casting.

The erosion and retention properties of tungsten trioxide films exposed to low energy deuterium ions: Temperature dependence

The erosion behavior and retention properties of tungsten trioxide (WO3) and W films exposed to low energy (∼50 eV) deuterium (D) ions were studied at surface temperature from 403 K to 758 K. The initial thickness of WO3 and W films are approximately 7.0 × 1018 atoms cm−2 and 1.8 × 1018 atoms cm−2, respectively. The erosion rate of oxygen (O) by deuterium is thermally enhanced, and tungsten (W) atoms can be sputtered rapidly in the form of WxOy molecules and/or W atoms at higher temperatures due to the relatively weak binding energy between W and O, resulting on an increase in the W sputtering yield with temperature. Nano-sized pinholes appear on the surface at 403 K, however, pinholes with much smaller sizes and cracks appear on the surface at higher temperatures, and their density increases with increasing temperatures. The synergistic effects of ion irradiation and temperature cause the structure change of tungsten oxide films according to Raman spectra. X-ray photoelectron spectroscopy shows that after irradiation with D ions, metallic W appears on the surface, but the tungsten oxide is still present. Trapped D is almost uniformly distributed in WO3 and its concentration is much higher than that in W at lower irradiation temperature, which is mainly related to D atoms chemically bonded to O atoms with the formation of deuterium tungsten bronze. The thermal desorption peak temperatures of D2 (∼465 K or 500 K) and D2O (∼495 K, 730 K (or 790 K) and 825 K) are related to the heating rate (1 K s−1) and it implies that the deuterium tungsten bronze is decomposed under the low D ion irradiation temperatures.

Interaction of Na with 2D WO3 and MoO3 Layers on Pd(100): From Doping to 2D Bronze Formation

Doping of tungsten trioxide (WO3) and molybdenum trioxide (MoO3) materials with alkali atoms, leading to the formation of the so-called sodium bronzes, is a viable approach to achieve a precise control of their electronic, optical, and magnetic properties via electron band structure engineering. Driven by the ongoing trend for thickness reduction and the resulting new functionalities at the nanoscale, using a combination of state-of-the-art experimental and computational techniques, we investigate here the interaction of two isostructural two-dimensional (2D) WO3 and MoO3 layers, grown epitaxially onto a Pd(100) surface, with Na dopants. We identify two interaction regimes as a function of the Na coverage: a low-coverage regime up to 0.3 ML, which we describe in terms of doping interactions, and a reaction regime, where at higher Na coverages, the 2D WO3/MoO3 lattices become destroyed and several ordered 2D bronze-type phases form upon thermal activation. In the doping regime, Na initially decorates the oxide domain boundaries and later adsorbs in a (2 × 2) superstructure, filling the regular adsorption sites within the oxide domains. Further Na accommodation in the 2D oxide lattice is unfavorable due to the poor lateral electrostatic screening and elastic strain increase. In the reaction regime, the most prominent and energetically stable phase is the hexagonal 2D bronze-like layer, whose atomic details are resolved in a density functional theory (DFT) analysis and compared with the structure of the bulk counterpart.

The role of hydrogen bronzes in the hydrogenation of polyfunctional reagents: cinnamaldehyde, furfural and 5-hydroxymethylfurfural over Pd/HxWO3 and Pd/HxMoO3 catalysts

Differences in the activity of Pd/WO3 and Pd/MoO3 (Pd loading 0.4–4 wt%) catalysts in competitive hydrogenations of the CC and CO groups in polyfunctional reagents have been studied as a function of two effects: (1) the in situ formation of hydrogen bronzes, HxWO3 and HxMoO3, and (2) the electronic interaction between the supports and the metallic Pd. The cinnamaldehyde (CAL), furfural (FU) and 5-hydroxymethylfurfural (HMF) were hydrogenated under mild reaction conditions. The formation of hydrogen bronzes in Pd/WO3 and physical mixture of Pd/WO3 with supporting WO3 oxide upon exposure to H2 was also studied using the gas flow-through microcalorimetry. In both Pd/MoO3 and Pd/WO3 catalysts, the electronic interactions contributed to the promotion of selectivity toward the CO hydrogenation in CAL and FU, yet in Pd/MoO3 this effect was much more pronounced. On the other hand, apart from increasing the overall reaction rate, the formation of hydrogen bronzes remarkably enhances the CC hydrogenation in CAL, as well as the decarbonylation of FU to furan and hydrogenolysis of C–OH in HMF to 5-methylfurfural. The bronze effects are significantly stronger in HxWO3, compared to HxMoO3, which may be related to higher H-species mobility and weaker H-bonding in the W–O–H (54 kJ/mol H2) than in the Mo–O–H (100 kJ/mol H2). This may also explain very high tendency of Pd/WO3 to furan ring hydrogenation in FU and HMF as well as almost selective (>98%) hydrogenation of furfuryl alcohol to tetrahydrofurfuryl alcohol.

Fungible Things: Economies of Desire in the (De)formation of Chinese Bronzes

Fungible Things: Economies of Desire in the (De)formation of Chinese Bronzes

Structural and impedance spectroscopic study of Zn-substituted Ba5CaTi2Nb8O30 tetragonal tungsten bronze ceramics

Zn-doped tungsten bronze compounds derived from Ba5CaTi2Nb8O30, with Ba5CaTi2−xZnxNb8O30 composition (x = 0; 0.04 and 0.08) were synthesized by the conventional solid-state reaction route. Both solubility of Zn in Ba5CaTi2Nb8O30 and tungsten bronze formation with the P4bm space group were verified by the Rietveld method using X-ray diffraction data. The average crystallite size was of the order of 0.08 µm according to Scherrer's formula. SEM micrographs of Ba5CaTi2−xZnxNb8O30 ceramics showed high densification, low porosity, thus a homogeneous grain distribution of different sizes over the entire surface. The average grain size was in the range of 1.3–1.6 µm. The frequency-dependent electrical properties were analyzed by complex impedance spectroscopy. Different types of studies such as the Nyquist plot, real and imaginary part of the impedance, conductivity, modulus formalism, and charge carrier activation energy were used to explain the microstructure-electrical properties relationships.

Cu Plating with Sn and Subsequent Bronze Formation under Mild Conditions

In a well-known bronze plating experiment, a Cu coupon is subjected to Sn plating and heating with a Bunsen burner. Currently, aqueous NaOH or HCl is typically used as the plating solution; however, the use of a strong acid or base provides operational risks, particularly in educational settings (e.g., schools). Herein, we introduce a modified method that uses aqueous NaHSO4 as the plating solution. This method reduces the operational risks and allows for the smooth deposition of silver-white Sn onto the Cu coupon in a higher yield than that obtained by the HCl method, which uses 30 times the concentration of the solute. When the Sn-plated Cu coupon is heated, it changes to bronze plating. This experiment is ideal for high school students, as it allows them to observe metal plating and solid diffusion.

Portable Photoelectrochemical Device Integrated with Self-Powered Electrochromic Tablet for Visual Analysis

A portable photoelectrochemical (PEC) device is developed by intergating a self-powered electrochromic tablet for visual analysis. The tablet consists of an electron-injector (EI) part for photo-to-electric conversion and an electrochromic (EC) part for visualized readout, which are coated with dye-sensitized titanium dioxide film and Ni-doped tungsten trioxide (WO3) film, respectively. Under the illumination of a white LED light, the photoexcited electrons generated from EI part convey to EC part through the conductive inner side of indium tin oxide slide and would cause color change of the Ni-doped WO3 film in the presence of protons. Furthermore, the Ni-doped WO3 film exhibits excellent transmittance modulation of more than 80%, providing an enhanced signal for visual analysis. Using pyrophosphate ion (PPi) as a model analyte, we have successfully constructed a visualized PEC sensing platform based on the formation of blue-colored hydrogen tungsten bronzes via the hydrolysis reaction of PPi. Being equipped with a small light source and a dark box, the PEC tablet as a portable device can perform colorimetric measurement with good reversibility and stability. This smart PEC device provides important reference for future studies on the visual application in practice.

青銅を取り出す : 炭素粉末による酸化銅と酸化スズの還元(化学実験虎の巻)

青銅を取り出す : 炭素粉末による酸化銅と酸化スズの還元(化学実験虎の巻)

Numerical modeling of bronze coating formation using concentration-dependent diffusivity

The engineering of a component’s surface is of remarkable importance; it allows applications that surpass what is achievable by the substrate alone by improving surface properties such as hardness, wear, and corrosion resistance and even aesthetic value. In this work, formation of bronze coatings through the diffusion of electrodeposited tin on copper via heat treatment was studied. Specifically, the single phase α was targeted due to its attractive properties. Determining the correct heat treatment parameters is crucial since only a specific range of composition leads to the formation of the desired microstructure and, consequently, properties. The diffusion behavior of tin-copper for the formation of a single phase α is elucidated and a numerical model is developed to predict the composition profile after heat treatment, which agrees with experimental observations.