Universal Brønsted-Evans-Polanyi Relations for C–C,C–O,C–N,N–O,N–N,and O–O Dissociation Reactions

Abstract  

It is shown that for all the essential bond forming and bond breaking reactions on metal surfaces, the reactivity of the metal surface correlates linearly with the reaction energy in a single universal relation. Such correlations provide an easy way of establishing trends in reactivity among the different transition metals.     

Electroless deposited Ni–Re–P, Ni–W–P and Ni–Re–W–P alloys

Coatings of electroless Ni–W–P, Ni–Re–P and Ni–W–Re–P alloys were plated in alkaline citrate baths containing amino alcohols, but not free ammonia ions. The reference Ni–P alloy was used as an intermediate layer in the sandwich: Ni–Me–P/Ni–P/substrate. An extremely homogeneous thickness distribution of all alloy components was found by applying scanning Auger electron spectroscopy (SAES(. The inclusion of refractory metals at the expense of nickel and without substantial change in phosphorus content was established. A non-oxidized state of the codeposited Re and W in Ni–W–P, Ni–Re–P and Ni–W–Re–P alloys was determined by means of X-ray photoelectron spectroscopy examination, as well as by SAES profiles, revealing the absence of oxygen throughout the coatings. All alloy films are amorphous and paramagnetic.     

New catalytic functions of Pd–Zn, Pd–Ga, Pd–In, Pt–Zn, Pt–Ga and Pt–In alloys in the conversions of methanol

Pd and Pt supported on ZnO, Ga₂O₃ and In₂O₃ exhibit high catalytic performance for the steam reforming of methanol, CH₃OH+H₂OCO₂+3HH₂, and the dehydrogenation of methanol to HCOOCH₃, 2CH₃OHHCOOCH₃+2HH₂. Combined results with temperature-programmed reduction (TPR) and XRD method revealed that Pd–Zn, Pd–Ga, Pd–In, Pt–Zn, Pt–Ga and Pt–In alloys were produced upon reduction. Over the catalysts having the alloy phase, the reactions proceeded selectively, whereas the catalysts having metallic phase exhibited poor selectivities.     

Densification,microstructure, and mechanical properties of ZrC–SiC ceramics

ZrC–SiC ceramics were fabricated by high-energy ball milling and reactive hot pressing of ZrH₂, carbon black, and varying amounts of SiC. The ceramics were composed of nominally pure ZrC containing 0 to 30 vol% SiC particles. The relative density increased as SiC content increased, from 96.8% for nominally pure ZrC to 99.3% for ZrC-30 vol% SiC. As SiC content increased from 0 to 30 vol%, Young's modulus increased from 404 ± 11 to 420 ± 9 GPa and Vickers hardness increased from 18.5 ± 0.7 to 23.0 ± 0.5 GPa due to a combination of the higher relative density of ceramics with higher SiC content and the higher Young's modulus and hardness of SiC compared to ZrC. Flexure strength was 308 ± 11 MPa for pure ZrC, but increased to 576 ± 49 MPa for a SiC content of 30 vol%. Fracture toughness was 2.3 ± 0.2 MPa·m^1/2 for pure ZrC and increased to about 3.0 ± 0.1 MPa·m^1/2 for compositions containing SiC additions. The combination of high-energy ball milling and reactive hot pressing was able to produce ZrC–SiC ceramics with sub-micron grain sizes and high relative densities with higher strengths than previously reported for similar materials.     

Water-gas shift reaction over Cu–Zn,Cu–Fe,and Cu–Zn–Fe composite-oxide catalysts prepared by urea-nitrate combustion

Water-gas shift reaction was investigated over Cu–Zn, Cu–Fe and Cu–Zn–Fe composite-oxide catalysts at atmospheric pressure from 200 to 375 °C in terms of reducing the CO content with maximal H₂ yield. The Cu_0.15ZnFe₂ spinel catalyst expressed a higher CO conversion level and H₂ yield at a lower temperature compared to the Cu_0.15Zn and Cu_0.15Fe catalysts. Adding H₂O to the feed up to 30% (v/v), but not above, increased the CO reduction level, presumably by increasing the hydroxyl species to react with the adsorbed CO. Increasing the W/F ratio to 0.24 g s cm^?3 increased the CO conversion level to 0.76 at 275 °C with the Cu_0.15ZnFe₂ catalyst, and could be further increased to 0.86 at 350 °C by increasing the Cu molar ratio to 0.30 (Cu_0.30ZnFe₂). Nevertheless, increasing the Cu molar content to 0.50 reduced the CO conversion level. No requirement for adding O₂ when using the Cu_0.30ZnFe₂ catalyst at >260 °C was observed. Increasing the CO content in the reactant decreased its conversion level. The performance of the Cu_0.30ZnFe₂ catalyst was stable over a test period in a CO-rich condition. No undesired product was detected, suggesting a higher selectivity for hydrogen production with a low CO content.     

cBN–TiN,cBN–TiC composites: chemical equilibria,microstructure and hardness mechanical investigations

This paper summarizes theoretical and experimental studies of cBN–TiN and cBN–TiC of cBN:TiN/TiC molar ratio 1:1 and 2:1. Theoretical calculations show that, at temperatures between 1000 and 1400°C, TiN reacts with BN forming one new phase, TiB₂, and that TiC reacts with cBN forming two new phases, TiB₂ and TiC_0.8N_0.2.. Experimental cBN–TiC/TiN composites were prepared by high pressure hot pressing and the samples were subsequently heat treated.After heat treatment, sinters of cBN–TiN/TiC were characterized using transmission electron microscopy and X-ray diffraction. The samples exhibited a dense polycrystalline structure, and a thin layer of fine TiB₂ was visible at the BN–binder interface. It was found that hardness decreased significantly after heat treatment.     

Dielectric,ferroelectric, and piezoelectric properties in potassium sodium niobate ceramics with rhombohedral–orthorhombic and orthorhombic–tetragonal phase boundaries

A new phase boundary with rhombohedral–orthorhombic and orthorhombic–tetragonal phase boundaries is designed in (K_0.48Na_0.52)NbO₃ by adding Bi_0.5(Na_0.7K_0.2Li_0.1)_0.5ZrO₃ (BNKLZ), where Zr⁴⁺ and (BNKL)²⁺ are respectively used to improve the temperature of a rhombohedral phase and to decrease the temperature of an orthorhombic–tetragonal phase coexistence. These ceramics endure several continuous phase transitions with increasing BNKLZ content, i.e., an orthorhombic phase (0≤x<0.03), orthorhombic–tetragonal phases (x=0.03), orthorhombic–tetragonal and rhombohedral–orthorhombic (O–T and R–O) phase existence (0.03<x≤0.05), a rhombohedral phase (0.05<x≤0.07). The ceramics with O–T and R–O have a better piezoelectric behavior as compared with other phases because of more polarization states, enhanced ε_r and P_r, and a dense microstructure. Moreover, piezoelectric properties could be further optimized by modifying their sintering and poling temperatures. As a result, the construction of O–T and R–O phase coexistence benefits the improvement of piezoelectric properties in KNN-based ceramics.     

Investigation of Alumina Wetting by Fe–Ti,Fe–P and Fe–Ti–P Alloys

Abstract

The wetting of alumina substrates by Fe–Ti, Fe–P and Fe–Ti–P alloys has been investigated using sessile drop experiments conducted under an inert gas atmosphere in the temperature range of 1550 to 1620°C. The surface and interfacial structures have been explored by scanning electron microscopy and energy dispersive X-ray spectroscopy. Substantial additions of titanium are known to induce steel melts to wet alumina due to the formation of a Ti-rich reaction product at the alloy/ceramic interface, but the present work has shown that even low Ti concentrations can induce a reactive wetting process leading to an improvement of the wettability of alumina by Fe alloys. The contact angle of molten steel containing phosphorus on alumina decreased with increasing P content. The improvement of the wetting behaviour in this system was attributed solely to the adsorption of P onto the surface of the Fe melt. The addition of P as a ternary alloying element to the system Fe–Ti proved to be beneficial to the wetting behaviour. The measured contact angles were much lower than those in the binary systems Fe–Ti and Fe–P. This effect was related to the fact that P enhances the activity of Ti in the Fe melt. According to experimental observations, it turns out that the wettability of liquid Fe-based alloys, when an Al2O3 surface is present, is not only a property of the metal/oxide couple but is also dependent on the oxygen partial pressure, whereas temperature variations bring about a comparatively small effect. This work is of interest in understanding the phenomena pertaining to inclusion engineering and steel– refractory interactions, such as the clogging of submerged entry nozzles by agglomerated alumina particles during the continuous casting process.     

Silica–Titania mixed Oxides: Si–O–Ti Connectivity, Coordination of Titanium, and Surface Acidic Properties

A series of SiO₂–TiO₂ mixed oxides was prepared by the sol–gel route, and the influence of several important preparation parameters (Ti precursors, content, and calcination temperature) on the Si–O–Ti connectivity, coordination of titanium and surface acidity has been studied using various analytical techniques. The solids obtained were largely amorphous and characterized by Ti enrichment on surfaces with low titanium content; however, the addition of titanium greater than 50 mol% into the SiO₂ matrix led to significant phase separation of crystalline anatase. The Ti atoms are tetrahedrally coordinated with Si/Ti ratios higher than 10 and gradually enter into octahedral positions in the silica matrix with further increase in the titanium content. High-temperature treatment can break Si–O–Ti linkages and eliminate hydroxyl groups, resulting in a decrease in acid site density.     

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.     

High strength,low modulus and biocompatible porous Ti–Mo–Fe alloys

Porous Ti–10Mo–xFe (x = 2–5) alloys were prepared by powder metallurgy using ammonium hydrocarbonate (NH₄HCO₃) as the space-holder. When 7 wt% NH₄HCO₃ is added, the porosity of the Ti–Fe and Ti–Mo–Fe alloys is about 20 %. It was found that Fe has a significant strengthening effect on the Ti-based alloys, while Mo is effective in stabilizing the Ti–10Mo–xFe alloys into β-phase. The inherent better ductility of β-phase than that of the α-phase and the efficient strengthening effect Fe provide a good combination of strength and ductility to the Ti–10Mo–xFe alloys. The compressive yield strength of the porous Ti–10Mo–xFe alloys is from 500 to 800 MPa, much higher than that of the Fe–10Mo alloy (about 260 MPa) and human bone (about 130–180 MPa). Elastic modulus of the alloys is <10 GPa. The alloys also have corrosion resistance similar to that of pure Ti. Cytotoxic tests show that the L929 cell RGR values of the Ti–10Mo–xFe alloys are over 80 % at day 1, day 4 and day 7. The cells grew in good condition on the seventh day. The results indicate that the porous Ti–10Mo–xFe alloys have superior mechanical properties, good corrosion resistance, and excellent biocompatibility, and are promising candidates for bone substitute materials.     

Structural,optical, and electrical properties of conducting p-type transparent Cu–Cr–O thin films

Cu–Cr–O films were prepared by DC magnetron co-sputtering using Cu and Cr targets on quartz substrates. The films were then annealed at temperatures ranging from 400 °C to 900 °C for 2 h under a controlled Ar atmosphere. The as-deposited and 400 °C-annealed films were amorphous, semi-transparent, and insulated. After annealing at 500 °C, the Cu–Cr–O films contained a mixture of monoclinic CuO and spinel CuCr₂O₄ phases. Annealing at 600 °C led to the formation of delafossite CuCrO₂ phases. When the annealing was further increased to temperatures above 700 °C, the films exhibited a pure delafossite CuCrO₂ phase. The crystallinity and grain size also increased with the annealing temperature. The formation of the delafossite CuCrO₂ phase during post-annealing processing was in good agreement with thermodynamics. The optimum conductivity and transparency were achieved for the film annealed at approximately 700 °C with a figure of merit of 1.51×10⁻⁸ Ω⁻¹ (i.e., electrical resistivity of up to 5.13 Ω-cm and visible light transmittance of up to 58.3%). The lower formation temperature and superior properties of CuCrO₂ found in this study indicated the higher potential of this material for practical applications compared to CuAlO₂.     

Synthesis,characterization, and photophysical properties of covalent-linked ferrocene–porphyrin–single-walled carbon nanotube triad hybrid

The ferrocene–porphyrin–single-walled carbon nanotube (Fc–H₂P–SWCNT) triad hybrid was prepared by amidation reaction between carboxylated SWCNT and aminoporphyrin bearing an appended ferrocenyl substituent. The hybrid described here was fully characterized by a combination of analytical techniques such as Fourier transform infrared spectroscopy, Raman, absorption and emission spectroscopy, atomic force and scanning electron microscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy. The steady emission characteristics revealed the existence of the effective photoinduced electron transfer among ferrocene, excited porphyrin moiety and SWCNT, which was further confirmed by the results of time-resolved transient absorption spectra. The final lifetime of charge-separation state was observed to be 62.9 μs in N,N-dimethylformamide, which was significant increased compared to the reference nanohybrid porphyrin–SWCNT and the reported ferrocene–porphyrin–fullerene triad. Therefore, Fc–H₂P–SWCNT triad hybrid constructed by amidation is rationally expected to be an improved photon-to-electron conversion system.     

Preparation, characterization, and antibacterial activity evaluation of collagen–Zn complex

The different kinds of collagen–Zn complexes were prepared by zinc acetate, zinc chloride, zinc nitrate, and zinc sulfate reacted with collagen protein. Their antibacterial activities have been investigated by MIC method. It was found that the antibacterial activity of collagen–ZnSO₄ complex is better than that of others. To obtain a better antibacterial activity, collagen–ZnSO₄ complexes with different zinc amount were prepared using zinc sulfate as starting material. These complexes were characterized by FT-IR, XRD, and atomic absorption spectrometry. The results showed that zinc ion could chelate with N–H, C–O, and C=O group in collagen to form the stable complex. Antibacterial activities of collagen–ZnSO₄ complexes containing different Zn amount were evaluated against Escherichia coli and Staphylococcus aureus. The results suggested that antibacterial activity increases with the increase of zinc amount.     

Characterisation and modelling of CNT–epoxy and CNT–fibre–epoxy composites

Abstract

This research presents an experimental and theoretical investigation on the effects of carbon nanotube (CNT) integration within neat epoxy resin (nanocomposites) and a carbon fabric–epoxy composite (multiscale composites). An approach is presented for the prediction of mechanical properties of multiscale composites. This approach combines woven fibre micromechanics (MESOTEX) with the Mori-Tanaka model which was used for the prediction of mechanical properties of nanocomposites in this research. Nanocomposite and multiscale composite samples were manufactured using cast moulding, resin infusion, and hand lay-up process. The CNT concentrations in the composite samples were from 0 to 5 wt-%. The samples were characterised using tensile, shear and flexural tests. The discrepancy between the theoretical predictions and the experimental observations was hypothesised to be due to dispersion and bonding issues and SEM images are presented in support of the hypothesis.     

Polyaniline–Carbon Nanotube Composites: Preparation Methods,Properties, and Applications

Synthesis of polyaniline and hybrid carbon nanotube reinforced polyaniline nanocomposites by various methods has discussed in this review. Different routes used for functionalization of carbon nanotube have been reported. The electrical, mechanical, and thermal properties of polyaniline/carbon nanotube nanocomposites are also discussed. The dispersion of functionalized carbon nanotube, filler concentration, and their alignment in the interior of polyaniline matrix affect their morphology. Furthermore, article focussed upon the various morphologies of polyaniline and polyaniline/carbon nanotube nanocomposites obtained with different methods along with electrical conductivity. Possible applications of polyaniline/carbon nanotube nanocomposites in the areas of actuators, sensors, electromagnetic interference shielding have also discussed.