Effect of IrO2 crystallinity on electrocatalytic behavior of IrO2–Ta2O5/MWCNT composite as anodes in chlor-alkali membrane cell

IrO₂–Ta₂O₅ multi-wall carbon nanotube (MWCNT) composite coatings were synthesized on Ti electrodes at different calcination temperatures from 350 to 550 °C used as anodes in membrane cell for brine electrolysis. The physicochemical properties and electrochemical performance of the coatings were investigated by simultaneous differential scanning calorimetry/thermogravimetric analysis (DSC-TGA), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), cyclic voltammetry and electrochemical impedance spectroscopy (EIS) analysis. Results indicate that the degree of IrO₂ crystallinity significantly affects the coating properties. XRD pattern of the coating prepared at 350 °C has shown no reflection peaks indicating that the IrO₂ and Ta₂O₅ were amorphous. The DSC-TGA showed two major exothermic peaks at 475 and 575 °C attributed to the crystallization of IrO₂ and oxidation of Ta₂O₅ from chloride precursor solution, respectively. XPS data reveals the presence of both Ir valance states, which confirms the reversible redox transition of Ir (III)/Ir (IV). The Raman spectra of the coatings demonstrated that the MWCNT gradually loses its tube structure at the calcination temperatures of 450 and 550 °C, and they transform into a graphite-like structure by crystallization of IrO₂. However, in the coating without IrO₂, the modification of the MWCNT structure was not observed at the calcination temperature of 550 °C. The performance of calcined anodes for brine electrolysis was studied using a membrane cell, which showed that the output current density reduces with increasing calcination temperature. The results of the EIS analysis at oxygen evolution potential showed that the charge transfer resistance of IrO₂–Ta₂O₅-MWCNT composite increases from 1.1 to 18.2 (ꭥ.cm²) due to gradual IrO₂ crystallization, which illustrates a sharp reduction in the electrochemical OER activity.     

Synthesis of spherical shape borate-based bioactive glass powders prepared by ultrasonic spray pyrolysis

Spherical shape borate-based bioactive glass powders with fine size were directly prepared by high temperature spray pyrolysis. The powders prepared at temperatures between 1200 and 1400 °C had mixed phase with small amounts of fine crystal and an amorphous rich phase. Glass powders with amorphous phase were prepared at a temperature of 1500 °C. The mean size of the glass powders prepared by spray pyrolysis was 0.76 μm. The glass powders prepared at a temperature of 1200 °C had two distinct exothermic peaks (T_c1 and T_c2) at temperatures of 588 and 695 °C indicating crystallization. The glass transition temperature (T_g) of the powders prepared at a temperature of 1200 °C was 480 °C. Phase-separated crystalline phases with spherical shape were observed from the surface of the pellet sintered at a temperature of 550 °C. Crystallization of the pellet was completely occurred at temperatures of 750 and 800 °C. The pellets sintered at temperatures below 700 °C had single crystalline phase of CaNa₃B₅O₁₀. The pellet sintered at a temperature of 800 °C had two crystalline phases of CaNa₃B₅O₁₀ and CaB₂O₄.     

Alumina-silica composite coatings on graphite by CVD at 550°C

Alumina-silica composite coatings were prepared on the surface of graphite paper by chemical vapor deposition using AlCl₃/SiCl₄/H₂/CO₂ as precursor in the temperature range of 300 to 550°C. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to examine the phase composition and the microstructure of the coating, respectively. The results indicated that a dense, uniform, and adherent alumina-silica composite coating can be prepared on graphite paper substrate by chemical vapor deposition at 550°C. Alumina-silica composite coating is composed of particles or nodules of varying size. Each particle is often composed of a number of finer particles. The phases of the 550°C composite coating include γ-alumina and amorphous silica. The elemental chlorine content in the composite coating decreases with increasing deposition temperature. The surfaces of the alumina-silica composite coatings are affected by deposition temperature. There are some obvious micro-cracks in the 300°C composite coating, which are attributed to a mismatch of the coefficient of thermal expansion between composite coating and graphite paper. The 550°C alumina-silica composite coating can be completely turned into mullite after heat-treatment at 1350°C for 0.5 hr in argon atmosphere.     

Comparatively electrochemical studies at different operational temperatures for the effect of nanoclay platelets on the anticorrosion efficiency of DBSA-doped polyaniline/Na-MMT clay nanocomposite coatings

In this paper, DBSA-doped polyaniline (PANI)/Na⁺-montmorillonite (MMT) clay nanocomposite (PCN) materials have been successfully prepared with dodecylbenzenesulfonic acid (DBSA) as emulsifier and dopant for the emulsion polymerization of aniline. The as-prepared DBSA-doped samples were subsequently characterized by FTIR spectroscopy, WAXRD patterns and TEM. It should be noted that the nanocomposite coating containing 1 wt.% of clay loading was found to exhibit an observable enhanced corrosion protection on cold-rolled steel (CRS) electrode at higher operational temperature of 50 °C, which was even better than that of uncoated and electrode-coated with PANI alone at room temperature of 30 °C based on the electrochemical parameter evaluations (e.g., E_corr, R_p, I_corr, R_corr and impedance). In this work, all electrochemical measurements were performed at a double-wall jacketed cell, covered with a glass plate, through which water was circulated from a thermostat to maintain a constant operational temperature of 30, 40 and 50 ± 0.5 °C. Moreover, a series of electrochemical parameters shown in Tafel, Nyquist and Bode plots were all used to evaluate PCN coatings at three different operational temperatures in 5 wt.% aqueous NaCl electrolyte. Effect of material composition on the molecular weight and optical properties of neat PANI and PCN materials, in the form of solution, were studied by gel permeation chromatography (GPC) and UV-vis spectra, respectively. Finally, electrical conductivity at three different operational temperatures of PANI and PCN powder-pressed pellets doped with different inorganic acids such as HCl, HNO₃ and H₂SO₄ was also investigated through the measurements of standard four-point-probe technique.     

The effect of particle size on the formation and structure of carbide-derived carbon on β-SiC nanoparticles by reaction with chlorine

Carbide-derived carbon (CDC) coatings were produced by reaction with pure chlorine gas on the surface of β-SiC nanoparticles. Various CDC thicknesses were obtained using moderate temperatures (565–635 °C) associated with a short time (30 min) of chlorination under atmospheric pressure. Such conditions enable controlled layer-by-layer silicon extraction from SiC material. Kinetics of CDC formation were assessed using three SiC laser pyrolysis-produced nanopowders of different average size. Under the same conditions, the smallest particle size material is more prone to chlorination and exhibits a thicker carbon coating. Effect of particle size distribution on reactivity with chlorine is also discussed. After achieving carbide to carbon partial conversion, tem observations show good covering and adherent carbon coatings on remaining SiC material, N₂ adsorption analysis show that CDC coating is microporous and has a specific surface area exceeding 1000 m² g⁻¹. Thermogravimetric analysis coupled with mass spectroscopy under He gas flow, is used to determine the thermal stability and the nature of volatile species trapped in the microporosity. Under an O₂ gas flow, the amount of CDC formed is measured by burning it off at temperatures of 400–750 °C, before the onset of oxidation of the remaining SiC.     

Electrochemical and time-of-flight secondary ion mass spectrometry analysis of ultra-thin metal oxide (Al2O3 and Ta2O5) coatings deposited by atomic layer deposition on stainless steel

Ultra-thin (5–50 nm) layers of aluminium and tantalum oxides deposited by atomic layer deposition (ALD) on a stainless steel substrate (316L) for corrosion protection have been investigated by electrochemical methods (linear scan voltammetry, LSV, and electrochemical impedance spectroscopy, EIS) and time-of-flight secondary ion mass spectrometry, ToF-SIMS. The effects of the deposition temperature (250 °C and 160 °C) and coating thickness were addressed. ToF-SIMS elemental depth profiling shows a marked effect of the organic and water precursors used for deposition and of the substrate surface contamination on the level of C and OH trace contamination in the coating, and a beneficial effect of increasing the deposition temperature. The polarization data show a decrease of the current density by up to four orders of magnitude with increasing coating thickness from 5 to 50 nm. The 50 nm films block the pitting corrosion in 0.8 M NaCl. The uncoated surface fraction (quantified from the current density and allowing a ranking of the efficiency of the coating, also confirmed by the capacitance and resistance values extracted from the EIS data) was 0.03% with a 50 nm thick Al₂O₃ film deposited at 250 °C. The correlation between the porosity values of the coatings and the level of C and OH traces observed by ToF-SIMS points to a marked effect of the coating contaminants on the sealing performance of the coatings and on the corrosion resistance of the coated systems.     

Structure and thermo-mechanical properties study of polyurethane-urea/glycidoxypropyltrimethoxysilane hybrid coatings

A series of organic–inorganic hybrid coatings were prepared using polyurethane (PU)-urea and glycidoxypropyltrimethoxysilane (GPTMS) To prepare this first acid terminated saturated polyester, having 230 hydroxyl value and acid value 25 mg/KOH, were reacted with coupling agent GPTMS at different concentrations in the presence of base catalyst and each of them were further reacted with isophorone diisocyanate (IPDI) at NCO/OH ratio of 1.6:1 for 4–5 h at 70–80 °C These prepolymers were casted on tin foil and cured at ambient conditions for 6 h and prepared the hybrid coating free films by amalgamation. These free films were stored in the room temperature for 40 days and used for further characterization. The coating without and with different concentrations of GPTMS were named as base polymer and hybrid coatings, respectively. FTIR spectroscopy was used for the structural analysis of the coatings. Thermogravimetric analysis (TGA) showed that thermal stability of the hybrids was significantly higher than the base polymer. The onset degradation temperature of the base polymer starts at 268.9 °C, while it ranges from 279.1 °C to 290.8 °C for the hybrids based on the concentration of GPTMS used. The glass transition temperature (T_g) and storage modulus as determined from DMTA were higher for hybrid coatings as compared to base polymer. T_g of base polymer was 42.3 °C while it varies between 65.8 °C to 83.5 °C for hybrids.     

Characterization of electrodeposited WO3 films and its application to electrochemical wastewater treatment

WO₃ films have been prepared on to IrO₂-coated Ti substrate by cathodic deposition, and as-deposited and annealed films have been characterized using XRD, TEM, Raman and FT-IR spectroscopy. The as-deposited film consists of nanocrystalline, orthorhombic WO₃·H₂O and this phase transforms to amorphous WO₃ by annealing at 250 °C and to monoclinic WO₃ by annealing at and above 350 °C. The as-deposited and annealed films have been used as anodes for electrochemical decomposition of phenol in aqueous solutions with and without chloride ions. The monoclinic WO₃ anodes prepared by annealing at 350 and 400 °C show relatively high electrochemical activity in the chloride-containing solution. In addition, the anodes possess high chemical and physical stabilities: very low dissolution rate of WO₃ during the electrolysis and good adhesion to the substrate. Thus, WO₃ anodes may be promising materials for anodic oxidation of bio-refractory organics in wastewater, although further improvement of electrochemical activity is needed for more effective decrease in total organic carbons in wastewater.     

Microstructural investigations on mixed RuO2-TiO2 coatings

Mixed oxide coatings consisting of varying proportions of RuO₂ and TiO₂ have been prepared on titanium and silica substrates. Development of the microstructure was examined by X-ray diffraction and also monitored by resistivity measurements. The X-ray results suggest that the mixed oxide coatings prepared at 400° C are best described as a metastable solid solution of the two components. The resistivity-composition relationship however is more indicative of a finely interdispersed mixture of conducting and insulating particles. Coatings fired at higher temperatures (700–800° C) exhibit separate X-ray diffraction peaks corresponding to almost pure RuO₂ and TiO₂ phases with no evidence of significant solid solubility.     

Titanium-doped alumina for catalytic dehydration of methanol to dimethyl ether at relatively low temperatures

Mesoporous Al-Ti oxide composites with molar %Ti of 3, 5, 10, and 20 as well as pure γ-alumina were prepared using a template-free sol-gel method in the absence of a catalyst. The prepared composites were characterized by powder XRD, FTIR spectroscopy and N₂ adsorption for BET surface area and porosity measurements. The composites and the pure alumina possessed relatively high surface areas, 350-410 m²/g, and high porosities after calcination at 500 °C. FTIR spectroscopy was employed to study the products of the catalytic dehydration of methanol to dimethyl ether, DME, over the prepared catalysts at reaction temperatures between 180 and 300 °C. Compared with pure γ-alumina, the Ti-modified alumina with %Ti < 10 showed higher catalytic activity in the methanol dehydration and better selectivity to DME. Composites with %Ti of 3 and 5 showed the highest activity at relatively lower temperatures than the other catalysts where they showed their highest activity at 190 and 200 °C, respectively. The activity of all studied catalysts slightly decreased as the temperature was raised to 300 °C and dropped considerably when the temperature was decreased to 180 °C. However, the activity of Al-Ti-3 dropped only slightly at both temperatures. The selectivity to DME was dependent on the reaction temperature where 100% DME selectivity was obtained at temperatures ?220 °C and as the temperature was raised to 300 °C, some CH₄ and CO₂ formed on the account of DME.     

Unsteady oxidative conversion of methane to C2-hydrocarbons over La2O3 catalyst

Unsteady reaction behaviour with periodic fluctuations in reaction temperature and concentration indicating symmetric oscillations in the oxidative coupling of methane over La₂O₃ (obtained from lanthanum acetate by thermal decomposition in air at 600 °C and subsequently calcined in N₂ at 750 °C) above 550 °C but below 700 °C has been observed.     

Effect of silicon/graphite ratio and temperature on oxidation protective properties of SiC/ZrB2–SiC coatings prepared by pack cementation

To investigate the silicon/graphite ratio and temperature on preparation and properties of ZrB₂–SiC coatings, ZrB₂, silicon, and graphite powders were used as pack powders to prepare ZrB₂–SiC coatings on SiC coated graphite samples at different temperatures by pack cementation method. The composition, microstructure, thermal shock, and oxidation resistance of these coatings were characterized and assessed. High silicon/graphite ratio (in this case, 2) did not guarantee higher coating density, instead could be harmful to coating formation and led to the lump of pack powders, especially at temperatures of 2100 and 2200 °C. But residual silicon in the coating is beneficial for high density and oxidation protection ability. The SiC/ZrB₂–SiC (ZS50-2) coating prepared at 2000 °C showed excellent oxidation protective ability, owing to the residual silicon in the coating and dense coating structure. The weight loss of ZS50-2 after 15 thermal shocks between 1500 °C and room temperature, and oxidation for 19 h at 1500 °C are 6.5% and 2.9%, respectively.     

Low-temperature synthesis of superfine barium strontium titanate powder by the citrate method

Ba_0.6Sr_0.4TiO₃ powder was synthesized by a citrate method. The phase development was examined with respect to calcining temperature and heating rate during the calcining process. The results reveal a crucial role of the heating rate to the formation of a pure perovskite phase at low calcining temperatures. It was found that keeping relatively low heating rates ≤0.7 °C/min during the calcining process after 300 °C was favorable to a sufficient decomposition of (Ba,Sr)₂Ti₂O₅·CO₃ intermediate phase at low temperatures and consequently led to the formation of a pure perovskite phase at 550 °C. Ba_0.6Sr_0.4TiO₃ powder calcined at the temperature under the heating rate of 0.7 °C/min showed a superfine and uniform particle morphology and high sintering reactivity. As a result, the ceramic specimens prepared from the powder attained reasonable relative densities (94–95%) at sintering temperatures of 1250–1270 °C.     

Composite anticorrosion coatings for AZ91D magnesium alloy with molybdate conversion coating and silicon sol–gel coatings

This study evaluated the corrosion resistance of AZ91D magnesium alloy coated by composite coatings which consisted of a molybdate conversion coating and three layers of silicon sol–gel coatings. For molybdate conversion treatment, various conditions including the pH of the molybdate baths, immersion time and bath temperature were investigated using electrochemical measurements. The corrosion resistance of the AZ91D magnesium alloy was improved to some extent by the conversion coating with the optimal conversion parameters (7.3 g/L (NH₄)₆Mo₇O₂₄·6H₂O solution with pH 5 for 30 min at 30 °C).     

Preparation and antibacterial activity of Ag/TiO2-functionalized ceramic tiles

An Ag/TiO₂ coating was deposited onto glazed ceramic tiles by a sol-gel and spraying method at high temperatures. The coating was characterized by X-ray diffraction, scanning electron microscopy, and atomic force microscopy. The results showed that silver was present in rutile-TiO₂, and the temperature did not change the phase composition of the samples. The Ag/TiO₂ coating had a higher roughness than the TiO₂ coating. The tape test (D 3359–08) showed that the coatings prepared at 950 °C and 1000 °C had good adhesion to the ceramic tile substrate. The antibacterial activity of the coating was tested by photocatalytic sterilization experiments. The results showed that the Ag/TiO₂ coating had a higher antibacterial activity than the TiO₂ coating, and the sterilization efficiency of Escherichia coli, Staphylococcus aureus, Shigella, and Salmonella exceeded 99.655% under 2 h of visible light irradiation. This research provides a method to create Ag/TiO₂ coatings with good thermal resistance, adhesion, and antibacterial activity. This improves the low photocatalytic activity caused by the anatase-to-rutile transformation of TiO₂ at high temperatures and the poor adhesion at low temperatures.     

High permeability Ni-Cu-Zn ferrites through additive-free low-temperature sintering of nanocrystalline powders

Nanocrystalline Ni-Cu-Zn ferrite powders Ni_0.20Cu_0.20Zn_0.62Fe_1.98O_3.99 were prepared by thermal decomposition of an oxalate precursor. The particle size is 6 nm and 350 nm, respectively, for powders obtained through calcinations at 350 °C or 750 °C. The shrinkage behavior significantly changes with particle size; the temperature of maximum shrinkage rate is T_MSR = 700 °C for particles of 6 nm size and increases to T_MSR = 880 °C for particles 350 nm in size. Dense samples with a permeability of μ = 780 are obtained by sintering at 900 °C for 2 h. Mixtures of nanocrystalline and sub-micron powders allow tailoring of the shrinkage behavior. A maximum permeability of μ = 840 is obtained after sintering of a 1:1-mixture at 900 °C. This demonstrates the potential of nanocrystalline ferrites for co-firing without additives at 900 °C and integration of ferrite inductors into LTCC modules.     

Morphological, structural, microhardness and electrochemical characterisations of electrodeposited Cr and Ni-W coatings

This study examines the corrosion of electrodeposited Cr and of two electrodeposited Ni-W coatings in 0.1 mol L⁻¹ NaCl solution, as well as the influence of heat treatment on the crystallographic structure and microhardness properties of these coatings. Physical characterisation is carried out using scanning electron microscopy, X-ray diffraction, and energy dispersive X-ray analysis. Electrochemical characterisation is carried out using both the potentiodynamic linear polarization technique and open circuit measurements during long-term immersion tests. The corrosion products on the coating surfaces are characterised by ex situ Raman spectroscopy. As-electrodeposited Ni-W samples do not present defects, and the surface evolves from fine globular grains to rough polycrystalline morphology with decreasing electrodeposition current density. All the studied coatings corrode in the chloride medium and the corrosion is non-uniform for the Ni-W coatings. Raman analyses carried out after the immersion tests reveal Cr₂O₃ and Cr(OH)₂ corrosion products on the Cr coating surface, and Ni(OH)₂, NiO and WO₃ corrosion products on the Ni-W coating surfaces. Ni, Ni₄W and Ni-W phases are formed after heat treatment of the Ni₈₆W₁₄ coating at 600 °C. Although all the annealed Ni-W layers are cracked, their microhardness increases as the annealing temperature increases, suggesting that Ni-W coatings are potential substitutes for chromium in industrial applications in which good microhardness properties and stability at temperatures higher than 100 °C are required.     

(Ba0.5Sr0.5)TiO3 modification on etched aluminum foil for electrolytic capacitor

A new method was proposed to form (Ba_0.5Sr_0.5)TiO₃–Al₂O₃ composite oxide film on etched aluminum foils. The specimens were covered with (Ba_0.5Sr_0.5)TiO₃ (BST) layer by dip-coating in citrate solution and subsequent heat-treatment under 400–650 °C, finally by anodizing in a hot boracic acid and borate solution. The BST powders heated under different temperatures were characterized by X-ray diffraction (XRD) and the specific capacitance of the coated specimens heat-treated under different temperatures and times was measured. It is found that the specific capacitance increases initially with enhancing the temperature and reaches to maximum at 550 °C, but slightly decreases with the heat-treatment time. The capacitance was increased by about 35% after BST coating.     

Synthesis and electrochemical performance of bismuth–vanadium oxyfluoride

Bismuth–vanadium oxyfluoride (Bi₂VO₅F) has been synthesized using a simple, solid-state reaction process at different sintering temperatures. The structure and performance of the samples have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge/discharge experiments. The results show that bismuth–vanadium oxyfluoride belongs to a tetragonal crystal system with space group I4mm. The sample that was synthesized at 550 °C (P550) exhibits relatively good electrochemical properties. Sample P550 shows a high, initial discharge capacity of 222 mAh g⁻¹ at a rate of 100 mA g⁻¹ between 1.4 and 3.5 V. Sample P550 also shows acceptable electrochemical cycling properties. After the first cycle, the discharge specific capacity remains between 106 and 155 mAh g⁻¹, which plateaus between 2.1 and 1.9 V during the first 15 cycles.     

Low-temperature solution combustion synthesis of high performance LiNi0.5Mn1.5O4

High-voltage LiNi_0.5Mn_1.5O₄ spinels were synthesized by a low temperature solution combustion method at 400 °C, 600 °C and 800 °C for 3 h. The phase composition, structural disordering, micro-morphologies and electrochemical properties of the products were investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and constant current charge–discharge test. XRD analysis indicated that single phase LiNi_0.5Mn_1.5O₄ powders with disordered Fd-3m structures were obtained by the method at 400 °C, 600 °C and 800 °C. The crystallinity increased with increasing preparation temperatures. XRD and FTIR data indicated that the degree of structural disordering in the product prepared at 800 °C was the largest and in the product prepared at 600 °C was the least. SEM investigation demonstrated that the particle size and the crystal perfection of the products were increased with increasing temperatures. The particles of the product prepared at 600 °C with ~200 nm in size are well developed and homogeneously distributed. Charge/discharge curves and cycling performance tests at different current density indicated that the product prepared at 600 °C had the largest specific capacity and the best cycling performance, due to its high purity, high crystallinity, small particle size as well as moderate amount of Mn³⁺ ions.