Synthesis and characterization of chlorapatite–ZnO composite nanopowders

The influence of zinc oxide content on the formation of chlorapatite-based composite nanopowders in the mechanically alloyed CaO–CaCl₂–P₂O₅–ZnO system was studied. To mechanosynthesize composite nanopowders, different amounts of hydrothermally synthesized zinc oxide nanoparticles (0–10 wt%) were mixed with ingredients and then were mechanically activated for 5 h. Results showed that in the absence of zinc oxide, high crystalline chlorapatite nanopowder was obtained after 5 h of milling. In the presence of 4 and 7 wt% zinc oxide, the main product of milling for 5 h was chlorapatite–zinc oxide composite nanopowder. On increasing the zinc oxide content to 10 wt%, composite nanopowder was not formed due to improper stoichiometric ratio of the reactants. The crystallite size, lattice strain, volume fraction of grain boundary, and crystallinity degree of the samples fluctuated significantly during the milling process. In the presence of 7 wt% zinc oxide, the crystallite size and crystallinity degree reached 51±2 nm and 79±2%, respectively. During annealing at 900 °C for 1 h, the crystallization of composite nanopowder occurred and as a result the crystallinity degree rose sharply to 96±3%. In addition, the crystallite size increased to 77±2 nm after annealing at 900 °C. According to SEM and TEM images, the composite nanopowder was composed of both ellipse-like and polygonal particles with a mean size of about 98 nm.     

Electrochemical behaviour of Al, Al–Sn, Al–Zn and Al–Zn–Sn alloys in chloride solutions containing indium ions

The electrochemical behaviour of pure aluminium and three of its alloys were investigated in 0.6m NaCl in the presence and absence of In3+ ions. The study comprised polarization and potentiostatic current–time measurements complemented by SEM–EDAX investigation. In 0.6m NaCl the corrosion resistance of the alloys decreases in the following order: Al < Al–Sn < Al–ZnAl–Zn–Sn. The addition of In3+ ions to the test electrolyte revealed activation of pure Al which increases with increase of In3+ concentration. Similar results were obtained for the binary Al–Zn and the ternary Al–Zn–Sn alloys, while Al–Zn alloy displayed a higher activation effect with In3+. It is also concluded that the existence of Zn either as an alloying element or present as a cation in the electrolyte leads to an enhanced activity of aluminium in presence of In3+ ions. Deactivation is observed in the case of Al–Sn alloy on addition of In3+ because tin retards the diffusion pathway of In to the bulk alloy, in addition to the presence of iron as an impurity in the alloy.     

Surface characterization of Au–ZnO nanowire films

Au–ZnO nanowire films have been synthesized by annealing Zn foils coated with a thin layer of gold. An X-ray diffraction study found that the synthesized ZnO consists mainly of a hexagonal wurtzite structure along with a small amount of AuZn₃ phase. Scanning electron images showed that the ZnO wires extend to several microns in length. X-ray photoelectron spectroscopy studies confirmed the oxidation states of Au and Zn. An asymmetric O 1s peak indicates the presence of oxygen in an oxide layer and O–H groups on the films surfaces. Photoluminescence (PL) spectra showed different visible peaks for pre-annealed films, while for annealed films an UV peak appeared. In addition, the PL analysis showed that the overall intensity of photoluminescence decreased significantly after the films were annealed. Raman spectroscopy results also indicated that the crystalline quality of the films improved with annealing. This could be attributed to a decrease in oxygen vacancies and/or absorption of O–H groups on the surface of ZnO film. The highly hydrophilic surface with a water contact angle of ∼155° was obtained after annealing in air.     

Growth and characterization of Ag–Al2O3 composites thin films for thermoelectric power generation applications

Thin films of Ag–Al₂O₃ composites were successfully grown on Si substrate by thermal evaporation method and their thermoelectric performance was modulated using post growth annealing technique. Pellet of Ag and Al mixture having 1:4 ratio was evaporated on Si substrate using the vacuum tube furnace. As grown sample was cut into pieces and post-growth annealing was performed at different temperatures using muffle furnace. XRD results suggested that as-deposited sample has amorphous nature, but crystallinity of the samples increase as an annealing temperature increase from 600 to 900^oC. This structural behavior of annealed samples was further verified by Raman spectroscopy measurements. We have reported an optimal annealing temperature (800 ⁰C) for the best thermoelectric performance of investigated composites. At this specific annealing temperature, charge carriers are highly mobile which resulted in the enhancement of thermoelectric power generation performance of Ag–Al₂O₃ composite. The value of power factor (1.38x10^?2 W/m-K^?2) reported in the current study is the highest value for Ag–Al₂O₃ composites so for reported in the literature according to the best of our knowledge.     

Synthesis of Fe–Pr co-doped ZnO nanoparticles: Structural,optical and antibacterial properties

In the present work, we studied the role of Fe and Pr addition on the structural, optical and antibacterial properties of spherical ZnO nanoparticles synthesized via sol gel method. The lattice constants values increased, while the average crystallite size decreases as the Pr concentration varies from 0.00 to 0.04. The Fe and Pr cations insertion in the Wurtzite structure were also confirmed by the changes in Zn–O bond length (1.9763 Å to 1.9793 Å for 0.00 ≤ y ≤ 0.04). Raman and FTIR spectroscopies validated the ZnO single-phase formation, and the analysis suggests the existence of oxygen vacancies. The samples showed agglomerated spherical morphology and formation of nanoplate homogeneously organized, while the textural properties were affected by the Fe inclusion. All samples presented band gap values lower than expected for bulk ZnO and the lowest values were obtained for samples containing Fe and Pr. The analysis and deconvolution of photoluminescence spectra confirmed the structural defects formation, caused by the synthesis conditions used and dopants ions inclusion. The antimicrobial activity against Escherichia coli and Staphylococcus aureus using the direct contact method showed superior activity for S. aureus due to the nanoparticles-bacteria interactions. The synergistic effect of dopants may have contributed to the better performance observed against S. aureus, while the Pr concentration directly influenced the inhibitory effect of E. coli. Therefore, the synthesized materials are promising to eliminate pathogenic microorganisms.     

Synergetic effect of combined use of Cu–ZnO–Al2O3 and Pt–Al2O3 for the steam reforming of methanol

Commercial Cu–ZnO–Al₂O₃ catalysts are used widely for steam reforming of methanol. However, the reforming reactions should be modified to avoid fuel cell catalyst poisoning originated from carbon monoxide. The modification was implemented by mixing the Cu–ZnO–Al₂O₃ catalyst with Pt–Al₂O₃ catalyst. The Pt–Al₂O₃ and Cu–ZnO–Al₂O₃ catalyst mixture created a synergetic effect because the methanol decomposition and the water–gas shift reactions occurred simultaneously over nearby Pt–Al₂O₃ and Cu–ZnO–Al₂O₃ catalysts in the mixture. A methanol conversion of 96.4% was obtained and carbon monoxide was not detected from the reforming reaction when the Pt–Al₂O₃ and Cu–ZnO–Al₂O₃ catalyst mixture was used.     

Integrated experimental phase equilibria study and thermodynamic modelling of the binary ZnO–Al2O3, ZnO–SiO2, Al2O3–SiO2 and ternary ZnO–Al2O3–SiO2 systems

Phase equilibria of the ZnO–SiO₂, Al₂O₃–SiO₂ and ZnO–Al₂O₃–SiO₂ systems at liquidus were characterized at 1340–1740 °C in air. The ZnO–Al₂O₃ subsolidus phase equilibria were derived from the experiments with the SiO₂- and CaO + SiO₂-containing slags. High-temperature equilibration on silica or platinum substrates, followed by quenching and direct measurement of Zn, Al, Si and Ca concentrations in the phases with the electron probe X-ray microanalysis (EPMA) was used to accurately characterize the system. Special attention was given to zincite phase that was shown to consist of two separate ranges of compositions: round-shaped low-Al zincite (<2 mol.% AlO_1.5) and platy high-Al zincite (4–11 mol.% AlO_1.5). A technique was developed for more accurate measurement of the ZnO solubility in the low-ZnO phases (corundum, mullite, tridymite and cristobalite) surrounded by the ZnO-containing slag, using l-line for Zn instead of K-line, avoiding the interference of secondary X-ray fluorescence. Solubility of ZnO was found to be below 0.03 mol.% in corundum and cristobalite, and below 0.3 mol.% in mullite. Present experimental data were used to obtain a self-consistent set of parameters of the thermodynamic models for all phases in this system using FactSage computer package. The modified quasichemical model with two sublattices (Zn²⁺, Al³⁺, Si⁴⁺) (O^2?) was used for the liquid slag phase; the compound energy formalism was used for the spinel (Zn²⁺,Al³⁺)[Zn²⁺,Al³⁺,Va]₂O^2-₄ and mullite Al³⁺₂(Al³⁺,Si⁴⁺) (O^2?,Va)₅ phases; the Bragg-Williams formalism was used for the zincite (ZnO, Al₂O₃); other solid phases (tridymite and cristobalite SiO₂, corundum Al₂O₃, and willemite Zn₂SiO₄) were described as stoichiometric. Present study is a part of the research program on the characterization of the multicomponent Pb–Zn–Cu–Fe–Ca–Si–O–S–Al–Mg–Cr–As–Sn–Sb–Bi–Ag–Au–Ni system.     

Growth and optical properties of ZnO–In2O3 heterostructure nanowires

ZnO–In₂O₃ heterostructure nanowires were grown on a Si (111) substrate using the thermal evaporation method. Scanning electron microscopy results showed that the ZnO nanowires had spherical caps. The X-ray diffraction (XRD) pattern and energy-dispersive X-ray (EDX) spectrum indicated that these caps were In₂O₃. An analysis of the early growth process revealed that indium oxide might have played a self-catalytic role. Therefore, it was plausible that the vapor–liquid–solid mechanism (VLS) was responsible for the growth of the ZnO–In₂O₃ heterostructure nanowires. The optical properties of the products were characterized using a photoluminescence (PL) technique. The PL results for the ZnO–In₂O₃ heterostructure nanowires showed a strong peak in the ultraviolet region as a result of the near band emission and a negligible peak for the visible emissions that occurred as a result of the defects. Based on these PL results, it was found that the In₂O₃ nanostructures not only introduced the caps at the tips of the ZnO nanowires but also partially passivated the nanowire surfaces, leading to an improved near band edge emission and the suppression of the defect luminescence.     

Electrochemical synthesis and surface characterization of hexagonal Cu–ZnO nano-funnel tube films

An electrochemical deposition technique was used to synthesis hexagonal nano-funnel tube films on zinc foil, utilizing an electrolyte of ZnCl₂+H₂O₂ under ambient conditions. The structures, morphologies, chemical compositions, and optical properties of the synthesized films were characterized using X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–visible diffuse reflectance spectrometry (UV-vis-DRS), photoluminescence (PL) spectrometry, and energy-dispersive X-ray spectrometry (EDS) techniques. The XRD pattern showed a set of diffraction peaks that were indexed to the ZnO, Zn(OH)₂, and Cu phases. The SEM observations revealed a cauliflower-like morphology consisting of branches in the form of nano-funnel tubes. The TEM results demonstrated that the synthesized film was comprised of several branches. The EDS studies confirmed the presence of only Cu, Zn, and O atoms. The UV-vis-DRS spectrum showed the onset of the band gap absorption peak at ～375 nm. The PL studies evaluated various emission bands that originated from different defect mechanisms. In addition, the hexagonal nano-funnel tube film showed a good superhydrophobicity, with a water contact angle of ～153°.     

Morphology and luminescence properties of ZnO micro/nanostructures synthesized via thermal evaporation of Zn–Mg mixtures

ZnO crystals with various morphologies were synthesized by thermal evaporation of Zn/Mg mixtures under air atmosphere. When Zn powder was used as a source material, ZnO crystals had a tetrapod morphology. Depending on the mass ratio of Mg to Zn in the source material, ZnO crystals were synthesized having wires, tubes and grain-like morphologies. This provides strong evidence that Mg had an important effect on the morphology of the ZnO crystals and that the ratio of Mg to Zn is critical to the changes in morphology of the ZnO crystals. All the ZnO crystals had a wurtzite crystallographic structure. The possible role of Mg in the growth of the tubular-shaped ZnO crystals was discussed. Two emission peaks at around 380 (ultraviolet) and 510 nm (green) were observed in the cathodoluminescence spectra. A high intensity ratio of ultraviolet emission to green emission was observed for the tubular-shaped ZnO crystals, indicating the high crystalline quality of the ZnO crystals.     

Effect of Zr–Al Co-Doping on Structure and Photocatalytic Performance of ZnO Photocatalyst

利用水热处理结合焙烧的方法分别制备了Zr、Al掺杂及Zr–Al共掺的ZnO光催化剂。研究了制备的光催化剂样品的相结构和光谱性能;以紫外光（λ=254nm）为光源,酸性橙Ⅱ为降解对象,进行光催化活性测试;考察了Zr、Al掺杂对ZnO光催化剂反应活性的影响。研究表明,制备的产物均为六方晶系纤锌矿结构的ZnO;Zr、Al掺杂及Zr–Al共掺的ZnO样品的光催化活性相对于纯ZnO均有较大程度的提高,而且Zr–Al共掺的ZnO的光催化性能明显优于单一掺杂的。Zr–Al共掺可以明显改善ZnO表面状态,使ZnO具有更丰富的表面羟基,同时可以抑制光生电子–空穴对的复合,从而有利于光催化活性和稳定性的提高。     

Morphology controlled synthesis of ZnO particles through the oxidation of Al–Zn mixture

ZnO particles with different morphologies were synthesized through a simple oxidation process of Al–Zn mixtures in air. The morphologies significantly depended on the Zn content in Al–Zn mixture and the oxidation time. Rod-based brushes, typical tetrapods, and novel tetrapods with triangular wedges were synthesized with the increase of Zn content in Al–Zn mixture. The morphology was also changed from rod to tetrapod shape with oxidation time. The results indicate that the concentration of Zn and the oxidation time might be responsible for the different morphologies of ZnO particles. XRD spectra showed that the ZnO particles were a hexagonal wurtzite structure.     

Preparation of Mn2+-Cu+ co-doped P2O5–ZnO–Al2O3 glasses and their red fluorescence properties

To make a Mn²⁺-doped red glass phosphor that can be excited with ultraviolet (UV) light of light-emitting diodes (LEDs), 60P₂O₅-35ZnO-5Al₂O₃-8MnO-xCu₂O glasses (x = 0-1.00) were prepared by a melt-quenching method at 1200-1400°C for 30-180 minutes in atmospheric air, and the redox of Mn and Cu as well as fluorescence properties were investigated. The Mn²⁺ ion was not reduced and oxidized in the melting, quenching, and annealing processes. The valence of Cu in the glasses changed in the order of 0, 1+, and 2+ with the increase in the amount of Cu₂O and in the melting temperature and time. In this study, a 60P₂O₅-35ZnO-5Al₂O₃-8MnO-0.10Cu₂O glass melted at 1250°C for 90 minutes, having the highest Cu⁺ concentration, showed the strongest Mn²⁺ red fluorescence under the UV light at 275 nm. This strong Mn²⁺ red fluorescence has been caused by the energy transfer from excited Cu⁺ ions to Mn²⁺ ions.     

Preparation and characterization of the bimetallic Pt–Au/ZnO/Al2O3 catalysts: Influence of Pt–Au molar ratio on the catalytic activity for toluene oxidation

The bimetallic Pt–Au catalysts supported on ZnO/Al₂O₃ with different Pt/Au molar ratios were prepared by impregnation (IMP) method using a mixed solution of Pt and Au precursor. These were characterized by X-ray diffraction (XRD), CO chemisorption, temperature programmed reduction (TPR), and transmission electron microscopy (TEM) equipped energy dispersive spectroscopy (EDS). Catalytic activity for complete oxidation of toluene was measured using a flow reactor under atmospheric pressure. In the results, the aggregation of Au particles depended on the molar ratio in the bimetallic Pt–Au catalyst, and Pt particles was well dispersed homogeneously even by the IMP method. The Pt₇₅Au₂₅ and Pt₆₇Au₃₃ catalysts concurrently coated with Pt and Au precursors by IMP method showed higher activity than monometallic Pt and Au catalyst for toluene oxidation. Also, in order of the catalytic activity for toluene was very good agreement compare with the TPR results. The Au particles might promote the toluene oxidation over the bimetallic catalyst concurrently coated with Pt and Au particles. Therefore, the size of Pt and Au particles and catalytic activity were confirmed to be correlated to molar ratio of Pt and Au loaded.     

The structure and properties of 0.95MgTiO3–0.05CaTiO3 ceramics co-doped with ZnO–ZrO2

The (Mg_0.93Ca_0.05Zn_0.02)(Ti_1?xZr_x)O₃ ceramics were prepared by conventional solid-state route. The dielectric properties and structure of (Mg_0.93Ca_0.05Zn_0.02)(Ti_1?xZr_x)O₃ ceramics were investigated. It has been found that MgTiO₃ and CaTiO₃ are the main phases and a second phase CaZrTi₂O₇ appeared in 95MCT ceramics co-doped with Zn–Zr. With Zn–Zr additive, the sintering temperature of 95MCT ceramics can be reduced to 1300 °C, and adjust the temperature coefficient of dielectric constant. With the increasing of Zr content, dielectric constant ?_r decrease from 22.6 to 19.91 and the temperature coefficient of dielectric constant α_c from 5.93 to 2.52 ppm/°C when x = 0.01, 0.02, 0.03 and 0.04 mol respectively. The 95MCT ceramics with x = 0.02 has a dielectric constant ?_r of 22.02, a dielectric loss of 2.78 × 10^?4 and a temperature coefficient of dielectric constant α_c value of 2.98 ppm/°C.     

Evolution of interfacial structures and mechanical performance of sapphire and Sn–9Zn–2Al joints by ultrasound

A method of ultrasonic-assisted soldering was applied to join sapphire with Sn–9Zn–2Al at 250°C in air. The sapphire samples were hot-dipped in the liquid filler metal under the ultrasonic action before ultrasonic-assisted soldering. The experimental results have shown that the joints dipped for different durations had similar morphologies, while the shear strength was dependent on the dipping duration. The shear strength of the joints increased rapidly from 13 to 22 MPa within the hot-dipping duration of 50 seconds, and increased slowly to 46 MPa at 2000 seconds. The evolution of the interface structure and the fracture mode was analyzed. The interfacial strength was dominated by the deposited Al₂O₃ at the interface in the early stage. After the entire surface of sapphire was covered by deposited Al₂O₃, Zn-rich phases at the interface and the thickening of deposited Al₂O₃ layer enhanced the interfacial strength at the later stage. Our study revealed the evolution of the interface structure and the strengthening mechanism in the joint of sapphire with Sn–Zn–Al alloys.     

Synthesis and characterization of twinned flower–like ZnO structures grown by hydrothermal methods

Twinned flower-like ZnO structures have been synthesized by one-step CTAB assisted hydrothermal methods at a low-temperature as 90 °C. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) results disclosed a twinned flower-like morphology and hexagonal wurtzite structures. The XRD pattern and temperature-dependent PL results show a mixed structure of as-grown samples, which are confirmed by the SEM results. The CL spectrum on a single twinned flower-like ZnO structures showed an excellent optical property. Based on experimental results, self-etching and regrowth are suggested as the mechanism to grow the flower-like structures.     

Microhardness and optical property of chalcogenide glasses and glass-ceramics of the Sn–Sb–Se ternary system

The microhardness of chalcogenide glasses (ChGs) of the Sn–Sb–Se (SSS) ternary system was investigated, and the correlation of microhardness with the mean coordination number of the SSS ChGs was determined. To prepare infrared-transparent SSS glass-ceramics (GCs), two SSS ChGs (A, Sn_6.23Sb_14.11Se_79.66; B, Sn_9.8Sb_17.22Se_72.98; by molar composition) were selected and thermally treated at 433 and 448 K, respectively. The improved microhardness (with values that increased by 11.5% and 7.3% for SSS ChG A and B, respectively) of the resulting SSS GCs is attributed to the formation of Sb₂Se₃ nanocrystals.     

Morphology of aluminium oxide nanostructures after calcination of arc discharge Al–C soot

The morphology of nanostructures that were formed during the calcination of aluminium–carbon composite and synthesized by the method of electric arc spraying was studied. It was shown that based on the aluminium content in the sprayed electrode and the buffer gas pressure, nanostructures of different morphologies are formed: chains of γAl₂O₃ nanoparticles, hollow γAl₂O₃ nanoparticles, γAl₂O₃ nanotubes, and hollow nanoparticles with inner partitions.