Copper reduction and hydroxyl formation by hydrogen process in alumino-silicate glasses

The process of nanometric copper (Cu⁰) precipitation by hydrogen in alumino-silicate glasses was studied regarding the simultaneous formation of hydroxyl bonding. Firstly, copper-ion-doped alumino-silicate glasses were melt-quenched and then heat-treated in the presence of hydrogen gas, which allowed copper ions to be reduced into nanometric metal particles. Along with the metallic copper formation, there was also formed the hydroxyl groups as a byproduct of the reaction. From spectroscopic studies, it was revealed that the reduction process was kinetically controlled by the hydrogen diffusion into the glasses. After the Cu⁰ precipitation, in particular, at temperatures higher than 700 °C or for reduction times longer than 5 h the copper metal was found to move towards the surface, creating a copper metal rich surface. Moreover, an increase in hydrogen permeation with the treatment time was also observed and this tendency was more intense for the matrix, which allowed higher copper reduction.     

Fabrication and application of highly ordered mesoporous Co3O4, NiO, and their metals

Highly ordered mesoporous Co₃O₄, NiO, and their metals were synthesized by nanocasting method using there corresponding mesoporous SBA-15 silica as a template. The obtained porous metal oxides have high surface areas, large pore volume, and a narrow pore size distribution. The N₂-adsorption data for mesoporous metal oxides have provided the BET area of 257.7 m² g⁻¹ and the total pore volume of 0.46 cm³ g⁻¹. The mesoporous metals were employed as a catalyst in the synthesis of (S)-3-pyrrolidinol from chiral (S)-4-chloro-3-hydroxybutyronitrile, and a high yield to (S)-3-pyrrolidinol-salt was obtained on the mesoporous Co metal catalyst.     

Preparation of nanocomposite PbO·CuO/CNTs via microemulsion process and its catalysis on thermal decomposition of RDX

Mixture of carbon black, copper and lead was used as catalyst of high-content RDX-composite-modified double base propellant. To enhance the catalytic effect and improve the flaring performance, metal oxide deposited on carbon nanotubes (CNTs) are replaced with afore-mentioned catalyst. A new type of nano-combustion catalyst is synthesized with microemulsion process. In present work, ternary diagram was adopted to analyze the essential factors which affect microemulsion, including temperature, surfactant or cosurfactant and concentration of solution in order to find the best technical parameters and thus to control the core formation and growth of oxides on the nano-template. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) are applied to characterize the products. Through observation of microstructures and analysis of crystal structure, it is confirmed that nano-oxides are deposited on the surface of carbon nanotubes. Its particle size is below 50 nm. According to propellant components, a certain amount of combustion catalyst and RDX will be mixed. PbO·CuO/CNTs can catalyze thermal decomposition of RDX by thermal analysis. The results show that the new catalysts obviously accelerate the decomposition of RDX, and the peak temperature of decomposition reduce by 14.1 °C. The catalytic effect of nano-catalyst is better than original catalyst.     

A general and low-cost synthetic route to high-surface area metal oxides through a silica xerogel template

Porous metal oxides with a large surface area are synthesised by means of a procedure based on the templating approach. An inexpensive porous silica xerogel synthesised at moderate temperatures (∼100 °C) in order to preserve the silanol superficial groups was used as template. In a first step, the silica porosity was filled with a concentrated solution containing a metallic salt. Then, the impregnated sample was calcined in air at a temperature of 600 °C. Under these conditions, the metal oxides were synthesised within the confined space provided by the silica pores. Finally, the product was recovered after dissolution of the silica framework in 2 M NaOH solution. The materials obtained by this procedure are made up of aggregates of nanoparticles and/or 3D solid structures containing confined pores. In this work, the synthetic route proposed is illustrated by the preparation of various binary metal oxides (i.e. Fe₂O₃, Cr₂O₃, NiO, CeO₂, Mn₂O₃, Co₂O₃ and Al₂O₃). The BET surface areas measured for these materials are in the range of 100-270 m² g⁻¹. The proposed method is not restricted to the binary metal oxides. It can also be used in the preparation of other inorganic materials such as metal sulphides or mixed metal oxides.     

Surface composition of the steel powders pre-alloyed with manganese

The determination of the surface oxide layer composition is vital to facilitate the adjustment of the sintering conditions for sufficient removal of the surface oxides for providing strong metal bonding between the metal particles during sintering. To systematically investigate the composition, morphology and thickness of the surface oxide the influence of manganese content from 0.3 to 1.8 wt.% on the surface products composition in the case of water atomized steel powder was evaluated. Analysis of the powder surfaces by X-ray photoelectron spectroscopy and high-resolution scanning electron microscopy in combination with X-ray microanalysis showed that powder particles in all cases are covered by heterogeneous oxide layer, composed of particulate features of thermodynamically stable oxides (Cr-Mn-Si) and homogeneous iron surface oxide layer in between. For increasing alloying content the fraction of stable oxide cations in the surface layer increases linearly, whereas the thickness of the iron oxide layer decreases. Moreover, from the investigation of the sintering and degassing behavior by thermal analysis coupled with mass-spectrometry (TG/DTA + MS), three different stages of carbothermal reduction process were observed and their correlation with surface oxides composition was established during sintering in argon.     

Surface XPS characterization of NiTi shape memory alloy after advanced oxidation processes in UV/H2O2 photocatalytic system

Surface structure of NiTi shape memory alloy (SMA) was modified by advanced oxidation processes (AOP) in an ultraviolet (UV)/H₂O₂ photocatalytic system, and then systematically characterized with x-ray photoelectron spectroscopy (XPS). It is found that the AOP in UV/H₂O₂ photocatalytic system leads to formation of titanium oxides film on NiTi substrate. Depth profiles of O, Ni and Ti show such a film possesses a graded interface structure to NiTi substrate and there is no intermediate Ni-rich layer like that produced in conventional high temperature oxidation. Except TiO₂ phase, some titanium suboxides (TiO, Ti₂O₃) may also exist in the titanium oxides film. Oxygen mainly presents in metal oxides and some chemisorbed water and OH⁻ are found in titanium oxides film. Ni nearly reaches zero on the upper surface and relatively depleted in the whole titanium oxides film. The work indicates the AOP in UV/H₂O₂ photocatalytic system is a promising way to favor the widespread application of biomedical NiTi SMA by improving its biocompatibility.     

Toxicity of nano- and micro-sized ZnO particles in human lung epithelial cells

This is the first comprehensive study to evaluate the cytotoxicity, biochemical mechanisms of toxicity, and oxidative DNA damage caused by exposing human bronchoalveolar carcinoma-derived cells (A549) to 70 and 420 nm ZnO particles. Particles of either size significantly reduced cell viability in a dose- and time-dependent manner within a rather narrow dosage range. Particle mass-based dosimetry and particle-specific surface area-based dosimetry yielded two distinct patterns of cytotoxicity in both 70 and 420 nm ZnO particles. Elevated levels of reactive oxygen species (ROS) resulted in intracellular oxidative stress, lipid peroxidation, cell membrane leakage, and oxidative DNA damage. The protective effect of N-acetylcysteine on ZnO-induced cytotoxicity further implicated oxidative stress in the cytotoxicity. Free Zn²⁺ and metal impurities were not major contributors of ROS induction as indicated by limited free Zn²⁺ cytotoxicity, extent of Zn²⁺ dissociation in the cell culture medium, and inductively-coupled plasma-mass spectrometry metal analysis. We conclude that (1) exposure to both sizes of ZnO particles leads to dose- and time-dependent cytotoxicity reflected in oxidative stress, lipid peroxidation, cell membrane damage, and oxidative DNA damage, (2) ZnO particles exhibit a much steeper dose–response pattern unseen in other metal oxides, and (3) neither free Zn²⁺ nor metal impurity in the ZnO particle samples is the cause of cytotoxicity.     

Unusual ferromagnetism in nanoparticles of doped oxides and manganites

The observation of unusually large ferromagnetism in the nanoparticles of doped oxides and enhanced ferromagnetic tendencies in manganite nanoparticles have been in focus recently. For the transition metal doped oxide nanoparticles a phenomenological ‘charge transfer ferromagnetism’ model has been recently proposed by Coey et al. From a microscopic calculation with charge transfer between the defect band and mixed valent dopants, acting as reservoir, we show how the unusually high ferromagnetic response develops. The puzzle of nanosize-induced ferromagnetic tendencies in manganites is also addressed within the same framework where lattice imperfections and uncompensated charges at the surface of the nanoparticle are shown to reorganize the surface electronic structures with enhanced double exchange.     

Investigation of the structure and surface characteristics of Cu-Ni-M(III) mixed oxides (M = Al, Cr and In) prepared from layered double hydroxide precursors

The Cu-Ni-M(III) mixed oxides (M = Al, Cr and In) were prepared by calcination of layered double hydroxide precursors with Cu²⁺/Ni²⁺/M³⁺ ratio of 1/2/1. The materials were characterized by means of powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR), thermogravimetric-differential thermal analysis (TG-DTA), X-ray photoelectron spectroscopy (XPS) and low temperature N₂ adsorption-desorption experiments. The results indicated that calcination of precursors at 500 °C gave rise to mixed metal oxides including simple oxides and composite oxides, and the composition distributions of obtained oxides depended on the nature of trivalent cation in precursors. Under mild experimental conditions (atmospheric pressure and 25 °C), oxidation of aqueous phenol solutions by hydrogen peroxide exhibited that the Cr-containing mixed oxide achieved the highest conversion of phenol owing to the presence of more amount of composite oxide phase containing active copper centers, while the aluminum-containing one could significantly enhance deep oxidation of phenol into smaller molecules owing to the presence of more surface oxygen species.     

Energy expression of the chemical bond between atoms in metal oxides

The chemical bond between atoms in metal oxides is expressed in an energy scale. Total energy is partitioned into the atomic energy densities of constituent elements in the metal oxide, using energy density analysis. The atomization energies, ΔE_M for metal atom and ΔE_O for O atom, are then evaluated by subtracting the atomic energy densities from the energy of the isolated neutral atom, M and O, respectively. In this study, a ΔE_O vs. ΔE_M diagram called atomization energy diagram is first proposed and used for the understanding of the nature of chemical bond in various metal oxides. Both ΔE_M and ΔE_O values reflect the average structure as well as the local structure. For example their values vary depending on the vertex, edge or face sharing of MO₆ octahedron, and also change with the overall density of binary metal oxides. For perovskite-type oxides it is shown that the ΔE_O value tends to increase by the phase transition from cubic to tetragonal phase, regardless of the tilting-type or the 〈1 0 0〉 displacement-type transition. The bond formation in spinel-type oxides is also understood with the aid of the atomization energies. The present approach based on the atomization energy concept will provide us a new clue to the design of metal oxides.     

X-ray and AFM studies of polydisperse TiO2 (anatase) particles

Titanium dioxide (TiO₂) materials of a high chemical purity, as-prepared by the thermal hydrolysis, as well as subsequently modified by adsorption of different metal cations (Fe³⁺, Co²⁺, Cu²⁺), have been investigated by the X-ray diffraction, X-ray fluorescence and AFM microscopy methods. All TiO₂ powders have a fine-dispersated anatase structure and consist of grown together nanocrystallites of ∼8-17 nm. TiO₂ particles, usually ranging from 100 to 600 nm, show the ability to form large agglomerates, up to 2 μm in size. Contrary to the pure anatase, metal-modified TiO₂ particles possess a positive charge on their surface and can be lifted away by the AFM tip from the substrate surface during the scanning. This effect is mostly pronounced for the Fe-modified TiO₂ sample, where particles up to 250 nm are removed. The possible interaction mechanisms between different TiO₂ particles and the silicon tip are discussed. The electrostatic force has been found to play an essential role in the sample-tip interaction processes, and its value depends on the type of metal cation used.     

Microstructural effects on the formation and degradation of zinc phosphate coatings on 2024-Al alloy

The formation of zinc phosphate (ZPO) coatings on 2024-T3 aluminum alloy was studied using scanning electron microscopy (SEM), scanning Auger microscopy (SAM) and X-ray photoelectron spectroscopy (XPS), with an emphasis on microstructural effects involving second-phase particles and the alloy matrix. Surface polishing results in an Al-Cu-Mg particle surface that contains metallic Cu as well as an overlayer of aluminum and magnesium oxide, while larger amounts of aluminum oxide are present on the Al-Cu-Fe-Mn particle and matrix. When dipped in an acidic ZPO coating solution, the oxide covering the Al-Cu-Mg particle is etched most easily, and metallic Cu near the surface makes that region most cathodic, allowing more coating deposition compared with the other regions. The oxides on the Al-Cu-Fe-Mn and matrix regions are similar, thereby confirming that the observed differences in ZPO coating characteristics at these two regions arise from their underlying electrochemical characteristics. Immersion of a coated 2024-Al sample in corrosive NaCl solution for extended periods indicates that the ZPO provides better protection to the second-phase particles than to the matrix.     

Surface modification with EDTA molecule: A feasible method to enhance the adsorption property of ZnO

Surface-functionalized zinc oxide (ZnO) nanoparticles were synthesized with ethylene diamine tetraacetic acid (EDTA) as a modification agent, which were used as adsorbents in the adsorption of Cu²⁺ at certain conditions. The transmission electron microscopy (TEM) results show that the average size of ZnO particles is about 45 nm, and it exhibits hexagonal wurtzite structure. Fourier transform infrared (FTIR) spectra reveal that the EDTA species are chemically bonded on the surface of ZnO. Compared with bare ZnO particles, the functionalized ZnO nanoparticles have a better activity in the Cu²⁺ adsorption. The maximum adsorption capacity of functionalized ZnO nanoparticles is 20.97 mg/g, while it is 17.93 mg/g for the bare ZnO. The adsorption isotherm of bare ZnO particles is in accordance with the Freundlich model, and the chemical adsorption is in a dominant position in the adsorption process of Cu²⁺ on functionalized ZnO particles.     

Studies on the influence of surface pre-treatments on electroless copper coating of boron carbide particles

Boron carbide is one of the hard ceramic particles which find application as structural materials and neutron shielding material due to its high neutron capture cross section. Copper coating on boron carbide particle is essential for the synthesis of metal-ceramic composites with enhanced sinterability and dispersibility. Surface characteristics of the substrate and the coating parameters play a foremost role in the formation of effective electroless coating. The effect of surface pre-treatment conditions and pH on electroless copper coating of boron carbide particles has been studied. Surface pre-treatement of B₄C when compared to acid treated and alkali treated particles were carried out. Uniform copper coating was observed at pH 12 in alkali treated particles when compared to others due to the effective removal of inevitable impurities during the production and processing of commercially available B₄C. A threshold pH 11 was required for initiation of copper coating on boron carbide particles. The growth pattern of the copper coating also varies depending on the surface conditions from acicular to spherical morphology.     

Energetic nano-materials: Opportunities for enhanced performances

This paper deals with the contribution of nano-materials to the contemporary pyrotechnics science. The breakthroughs in this domain are illustrated by several examples of energetic nano-materials recently studied in our laboratory.The solidification of energetic phases in a porous matrix (Cr₂O₃) was used to prepare and to stabilize at nano-scale explosive particles. The thermo-chemical behaviour of RDX nano-particles strongly differs from the one of micron-sized RDX. For instance, the temperature at which the decomposition occurs is significantly lowered and the melting point is removed. The effect of the decomposition of RDX nano-particles on the matrix in which they are trapped was observed for the first time by the atomic force microscopy.The Cr₂O₃/RDX nano-composite materials were mixed with aluminium nano-particles in order to formulate gas-generating nano-thermites (GGNT). The combustion of GGNT involves a synergy mechanism in which the decomposition of RDX nano-particles fragments the Cr₂O₃ matrix and primes the thermite reaction.“Classical” nano-thermites were obtained by mixing nano-particles (diameter <100 nm) of metallic oxides (WO₃) with a reducing metal (Al). These materials were used to demonstrate that nano-particles (i) significantly lower the ignition delay time and (ii) remarkably increase the combustion rate.Finally, pure RDX nano-particles are prepared by a continuous process of crystallization.     

Enhanced photoluminescence properties of Sm ions in Cu and Sn co-doped P2O5:BaO glass

Luminescent glasses activated with Sm³⁺ ions are of current interest given their potential for a wide range of photonic applications. In this work, Sm³⁺-containing P₂O₅:BaO glasses are prepared by a simple melt-quench method, and the influence of CuO and SnO co-doping on Sm³⁺ photoluminescence (PL) is investigated. Optical absorption, solid-state ³¹P nuclear magnetic resonance spectroscopy, and PL spectroscopy are employed in the assessment of material optical and structural properties. The data indicates that monovalent copper ions and twofold-coordinated Sn centers are successfully stabilized in the matrix and both species can enhance the orange–red emission of Sm³⁺ ions. The optical properties of the material after heat treatment have been also assessed. Results indicate the chemical reduction of ionic copper via Sn²⁺ ultimately producing Cu nanoparticles as evidenced by the surface plasmon resonance. As a result, Sm³⁺ PL diminishes consistent with an excitation energy transfer to plasmonic Cu particles, i.e. the “plasmonic diluent” effect prevails.     

Identification of adsorbed species at metal surfaces by electron energy loss spectroscopy (EELS)

Electron energy loss spectroscopy (EELS) is a surface analysis method for measuring vibrational spectra of adsorbed species on metal surfaces. This paper summarizes recent work on the study of bonding of simple adsorbates on metal surfaces, and the identification of new chemical intermediates in reactions between two or more species in the adsorbed monolayer. The spectra of atomic oxygen, di-oxygen, water and ammonia adsorbed on platinum, copper and silver are discussed with emphasis on identification of the adsorbed species and their orientations relative to the surface plane. Surface reactions between atomic oxygen and water, methanol and formic acid yield the new surface intermediates hydroxyl (OH), methoxy (CH₃O) and formate (HCOO), respectively, on copper and silver surfaces. Each species was identified by comparison of surface spectra with known infrared spectra and through the use of deuterium isotopic shifts. The ability to identify and distinguish between chemical species at surfaces with high sensitivity will allow direct correlation of low pressure UHV surface experiments with high pressure surface reactions on catalysts and liquid-solid interfaces.     

Application of small-angle scattering for the identification of small amounts of platinum supported on porous silica

Pt-porous glass catalysts have been studied by small-angle X-ray scattering. The catalysts have been prepared by impregnating two micro- or mesoporous glasses with 0.1 wt% of Pt. Two different pore systems of the catalyst supports have been generated and investigated: on the one hand, the mesoporous structure is formed by finely dispersed colloidal silica inside a macroporous glass. On the other hand, micropores are given by the porous glass itself. The pure supports and the supported catalysts have been investigated via chord length analysis for a selected range order, based on the analysis of the scattering intensity for relatively large scattering vectors (up to the upper limit of SAS). The obtained specific structure parameters of both supported catalysts like dispersion, specific metal surface areas, basic arrangement, size distribution and volume fraction of the metal particles basically differ with both pore systems.     

Mechanisms of oxidation-reduction processes on metal and oxide surfaces under ion bombardment

Surface oxidation occurs if metals are bombarded with low-energy (1–5 keV) ions of a chemically active gas (oxygen) in vacuum. It is ascertained that ion bombardment leads to the generation of lower, intermediate, and higher oxides. The composition and thickness of an oxidized layer depend on the metal reactivity and the dose and energy of oxygen ions. The mechanism underlying the ion-beam oxidation of metal surfaces is proposed. Surface reduction is observed if higher oxides are bombarded with low-energy (1–5 keV) ions of inert gases (argon and helium) in vacuum. It is revealed that ion bombardment not only generates intermediate and higher oxides but sometimes gives rise to surface metallization. The composition and thickness of the reduced layer are determined by the oxide type, the kind of inert gases, and the dose and energy of bombardment. The mechanism describing the ion-beam reduction of higher metal oxide surfaces is proposed.     

Influence of nature of precursors on the formation and structure of Cu-Ni-Cr mixed oxides from layered double hydroxides

Analogous layered double hydroxides (LDHs) with the Cu²⁺/Ni²⁺/Cr³⁺ molar ratio of 1/2/1 on the brucite-like layers and interlayer anions (viz sulfate, nitrate and carbonate, respectively) were synthesized by a coprecipitation method. For the first time, the effects of interlayer anions on the structural properties of as-synthesized LDHs and resulting calcined products at 773 K were investigated by means of powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), simultaneous thermogravimetric and differential thermal analysis (TG-DTA), X-ray photoelectron spectroscopy (XPS) and temperature programmed reduction (TPR). The results indicate that the nature of interlayer anions involved within the hydrotalcite (HT)-like structure has a larger influence on the thermal stability of LDHs precursors. Calcination of well-crystallized LDHs leads to the formation of mixed metal oxides including CuO, NiO and Cu²⁺-, Ni²⁺- and Cr³⁺-containing spinel phases, the composition distributions of which obtained from LDHs precursors depend on the nature of interlayer anions, thus resulting in the difference of the reducibility of reducible metal species in the calcined LDHs. Moreover, the surface basicity of the calcined material, which is related to the different behaviour of LDHs precursors during the thermal decomposition depending on the interlayer anions, increases progressively following the order of calcined LDHs from sulfate to nitrate and carbonate.