Transition-state selectivity of H-ZSM—5 in isomerization of n-butenes

The isomerization of n-butenes took place over H-ZSM—5 and H-Y zeolite catalysts. The rates of the reaction and the activation energies were measured. It was found that H-ZSM—5 acted as a solid Brönsted acid which appeared to suppress the cis-trans isomerization. It is strongly suggested that this suppression is due to a kind of molecular shape-selectivity, transition-state selectivity.     

Hybrid pore formation by directed insertion of α-haemolysin into solid-state nanopores

Most experiments on nanopores have concentrated on the pore-forming protein α-haemolysin (αHL) and on artificial pores in solid-state membranes. While biological pores offer an atomically precise structure and the potential for genetic engineering, solid-state nanopores offer durability, size and shape control, and are also better suited for integration into wafer-scale devices. However, each system has significant limitations: αHL is difficult to integrate because it relies on delicate lipid bilayers for mechanical support, and the fabrication of solid-state nanopores with precise dimensions remains challenging. Here we show that these limitations may be overcome by inserting a single αHL pore into a solid-state nanopore. A double-stranded DNA attached to the protein pore is threaded into a solid-state nanopore by electrophoretic translocation. Protein insertion is observed in 30-40% of our attempts, and translocation of single-stranded DNA demonstrates that the hybrid nanopore remains functional. The hybrid structure offers a platform to create wafer-scale device arrays for genomic analysis, including sequencing.     

Fabrication of laminated metal–intermetallic composites by interlayer in-situ reaction

A simple and cost-effective method, interlayer in-situ reaction process, has been developed to produce laminated metal-intermetallic materials. Layered NiAl₃ and Ni₂Al₃/Ni composites have been fabricated successfully by using the process. It is shown that volume friction of the intermetallic layers can be well controlled by the thickness of the metals. It is difficult to produce high strength composites if the original metals are directly exposed at high temperature. This is rectified by a pre-treating processing in which a prefect interface is formed to prevent the metals from oxidation at high temperature. The pre-treated composites have an improvement in tensile strength and thermal stability. SEM observations show that the composites exhibit a mixing fracture mode suggesting that the composites would have high toughness.     

Optical emission from metal targets bombarded by 5–20 keV argon ions

The spectral composition of optical emission from high-purity iron (99.99% Fe), zirconium (99.98% Zr), and tungsten (99.96% W) targets bombarded by 5–20 keV Ar⁺ ions has been studied. The ion-bombardment-induced emission spectra of all metals exhibit two broad bands in the visible and IR spectral range. The first band is assigned to the emission from thermal spikes representing nanosized regions heated to 5000–6000 K, which are formed at the target surface in the course of evolution of high-density atomic collision cascades. The presence of an IR emission band is explained by the integral heating of targets to 500–800 K in the course of ion irradiation. This interpretation is confirmed by agreement between the experimentally measured and calculated temperatures in the region of thermalized collision cascades and the relative intensities of emission bands.     

Role of metal ions of Langmuir–Blodgett film in hydrophobic to hydrophilic transition of HF-treated Si surface

Hydrophobic to hydrophilic transition of HF-treated Si surface strongly depends upon the metal ions, which are present in the headgroups of the deposited Langmuir–Blodgett (LB) film. Structure of LB films studied by X-ray reflectivity technique and chemical analysis of LB film–substrate interfaces studied by X-ray photoelectron spectroscopy combinedly suggest that the partial transition or partial oxidation of the HF-treated Si surface takes place under the subphase water but further transition or oxidation is possible only in the presence of metal ions. Electrovalent and covalent natures of the metal ions tune this transition or oxidation. Ni ions, for which bonding with headgroups are electrovalent in nature, are favorable for such transition/oxidation and as a result, complete transition/oxidation takes place when nickel arachidate LB film is deposited. On the other hand, Cd ions, for which bonding with headgroups show covalent nature, is not favorable for such transition and can not oxidize the underlying H-passivated Si substrate totally when cadmium arachidate LB film is deposited on such HF-treated Si surface. This ion-specific hydrophobic to hydrophilic transition is visualized by X-ray reflectivity, contact angle and X-ray photoelectron spectroscopy measurements.     

Room-temperature ferromagnetic and photoluminescence properties of indium–tin-oxide nanoparticles synthesized by solid-state reaction

In the present study, indium–tin-oxide (ITO) nanoparticles were synthesized using solid-state reaction and studied for their structural, vibrational and magnetic properties. The ITO nanoparticles were prepared under reduced pressure, which can increase the oxygen vacancies in the samples. The X-ray diffraction studies confirmed singe-phase cubic bixbyite structure of ITO with average crystallite size of 47 nm. The lattice vibrational studies (FT-IR and Raman spectroscopy) at room temperature indicated that Sn ions were occupied in In₂O₃ lattice and gives corresponding active vibrational modes in the respective spectra. The magnetic studies at room temperature reveal the ferromagnetic nature of ITO and the strength of magnetization is superior to those of In₂O₃ and SnO₂. However, the magnetic studies at 100 K revealed reduced ferromagnetism, which could be attributed to reduced itinerary electrons at low temperature. Blue and blue–green emissions were found from the ITO nanoparticles, which could be due to vacancies or surface defects present in the system.     

Arrhenius plot for a reaction catalyzed by a single molecule of β-galactosidase

The activity of a single enzyme molecule of Escherichia coli β-galactosidase was measured using a capillary electrophoresis continuous flow assay. As the enzyme molecule traversed the capillary the incubation temperature was increased from 27 to 37 °C, providing a continuous record of the change in rate with temperature. This data was used to develop a single enzyme molecule Arrhenius plot, from which the activation energy of the reaction was determined to be 31 kJ mol(-1).     

Characterization of a solid solution of Cu in Al—Cu—SiCp metal matrix composites processed by spray atomization and co-deposition

The effect of silicon carbide particulate (SiCp) reinforcement on the formation of a solid solution of copper (Cu) in Al–Cu alloys during spray atomization and co-deposition is investigated. The extent of Cu solid solubility in sample compositions of Al–1.3, 5.9 and 18.3 wt% Cu and Al–1.5, 5.9 and 19.4 wt% Cu+6 vol% SiCp was characterized using X-ray diffraction scanning electron microscopy, (SEM) microanalysis and high resolution electron microscope techniques. The copper content retained in the -Al solid solution in Al-alloys both with and without SiCp additions was determined by initially deriving the lattice parameter (a) values of the samples by X-ray diffraction and the copper content in the solid solution was determined using a plot of a versus copper content previously, reported in the literature. Results of SEM microanalyses performed on the above alloys in regions of -Al solid solution showed a good agreement on the amount of Cu retained in solid solution with values determined by X-ray diffraction especially for alloys containing small amounts of Cu. High resolution electron microscopy images of the matrix and the matrix/SiCp interface were employed in order to determine values of the interplanar spacing (d) for the -Al solid solution and to correlate these values using the plot of lattice parameter as a function of copper content retained in solid solution. The results were in good agreement with those determined by the scanning electron microscopy microanalyses.     

Electronic structures of transition metal dioxides studied by the spin-polarized self-consistent-charge extended Hückel tight-binding method

Band theory based on the spin-polarized self-consistent-charge extended Hückel tight-binding (SP-SCC-XHTB) method, which includes all the relativistic effects and the spin-polarized self-consistent-field (SP-SCF) atomic-structure calculation based on the Hartree-Fock-Slater method, has been applied to the electronic-structure calculations of tetragonal rutile-type MO₂s, such as nonmagnetic (n) TiO₂, VO₂, NbO₂, TaO₂, CrO₂, MnO₂, ferromagnetic (f) CrO₂ and antiferromagnetic (af) MnO₂. It is shown that the calculations are consistent with the experimental observations for all systems except the case of MnO₂. It is demonstrated that the semiconductive nature of MnO₂ can be explained by adding an assumption that three electrons in the Mn t_2g orbital are localized in the crystal into the SP-SCC-XHTB band-structure calculation.     

Comparative X-ray diffraction and Mössbauer spectroscopy studies of BiFeO3 ceramics prepared by conventional solid-state reaction and mechanical activation

The aim of this work was to prepare BiFeO₃ by modified solid-state sintering and mechanical activation processes and to investigate the structure and hyperfine interactions of the material. X-ray diffraction and Mössbauer spectroscopy were applied as complementary methods. In the case of sintering, BiFeO₃ phase was obtained from the mixture of precursors with 3 and 5 % excess of Bi₂O₃ during heating at 1023 K. Small amounts of impurities such as Bi₂Fe₄O₉ and sillenite were recognized. In the case of mechanical activation, the milling of stoichiometric amounts of Bi₂O₃ and Fe₂O₃ followed by isothermal annealing at 973 K resulted in formation of the mixture of BiFeO₃, Bi₂Fe₄O₉, sillenite and hematite. After separate milling of individual Bi₂O₃ and Fe₂O₃ powders, mixing, further milling and thermal processing, the amount of desired BiFeO₃ pure phase was significantly increased (from 70 to 90 %, as roughly estimated). From Mössbauer spectra, the hyperfine interaction parameters of the desired BiFeO₃ compound, paramagnetic impurities of Bi₂Fe₄O₉ and sillenite were determined. The main conclusion is that the lowest amount of impurities was obtained for BiFeO₃ with 3 % excess of Bi₂O₃, which was sintered at 1023 K. However, in the case of mechanical activation, the pure phase formed at a temperature by 50 K lower as compared to solid-state sintering temperature. X-ray diffraction and Mössbauer spectroscopy revealed that for both sintered and mechanically activated BiFeO₃ compounds, thermal treatment at elevated temperature led to a partial eliminating of the paramagnetic impurities.     

Sol-gel transition of a mixture of gelatin and κ-carrageenan

Abstract

The characteristics of sol-gel transition of a mixture made by mixing two kinds of gelling agents of different nature, i.e. gelatin and carrageenan were examined. The sample solutions consisted of 3.00 wt % gelatin solution, 1.00 wt % κ-carrageenan solution and 4.00 wt% mixed solution which was prepared by mixing the said gelatin and carrageenan solutions in the ratio 3:1. In the experiment, the optical rotation and the dynamic viscoelasticity were measured under the same temperature change program. As the sample solutions were cooled, the carrageenan solution started to show a change in the specific rotation in the first place, followed by the mixed solution and finally the gelatin solution. The gelatin and the mixed solutions had the same increasing tendency in the specific rotation, whereas the carrageenan solution changed a little. When the mixed solution was chilled to set, it turned into a highly elastic gel. In the mixed solution, the gelation of carrageenan was found to precede that of gelatin.     

Temperature dependence of spectral positions and widths of 5DJ → 7FJ fluorescence lines originating from Sm2+ ions in SrFCl crystals

The temperature dependence of the spectral positions and widths of the photoluminescence lines corresponding to the ⁵D₀ → ⁷F₀, ⁵D₀ → ⁷F₁ and ⁵D₁ → ⁷F₀ electronic transitions in Sm²⁺-doped SrFCl crystal was measured between 87 and 625 K at ambient pressure. The temperature dependence of the homogeneous line width Γ_h(T) for all these transitions in the whole temperature range used can be described by the two-phonon Raman scattering of acoustic phonons with the Debye temperature T_D ≈ 230 K. Comparison of the temperature- and pressure-induced shifts revealed why all the emission lines studied show the blue temperature shifts. It is so because a greater part of the line shift is caused by the thermal expansion of the host crystal and not by enhancement of the electron–phonon coupling with increasing temperature.     

Interaction of Ag ions with a vanadium pentoxide hydrate—Formation of silver vanadate at low temperature

Reactions between V₂O₅·nH₂O sol and Ag⁺ solution were investigated and new conventional reaction processes to produce silver vanadate bronzes were found. Reactions were surveyed as a function of the concentration ratios of Ag and V, and the reaction regions were divided into 4 parts dependent upon the reaction products. System 1: ion-exchanged sediment to produce -Ag_0.35V₂O₅; System 2: needle-like -AgVO₃ and hydrate to produce Ag_{2 – x}V₄O₁₁ upon heating; System 3: new fine needle-like particle and small proportions of various dendrite crystallites; System 4: hydrate to produce -AgVO₃ upon heating. The new needle-like particle of system 3 was analyzed by use of electron diffraction and XRD and found to be monoclinic, a = 32.96 Å, b = 2.60 Å, c = 3.62 Å, and = 91.88°. The material is named -AgVO_3· -Ag_0.35V₂O₅ and Ag_{2 – x}V₄O₁₁ were reversibly crystallized after melt. -AgVO₃ was crystallized when the melt was cooled slowly, while -AgVO₃ was crystallized when quenched rapidly.     

Hump on upper shelf of ductile—brittle transition temperature curve of a plain carbon steel

The ductile—brittle transition temperature (DBTT) in a plain carbon steel has been studied in a series of Charpy V notch samples. Both non-standard and standard samples were used in the as drawn, normalised and annealed conditions. In all cases, a hump was recorded on the upper shelf of the DBTT. Examination of fractures in the SEM in the vicinity of the hump showed typical microvoid coalescence. Low temperature fractures showed classical cleavage fractures with river markings. In the normalised and annealed conditions, both yield stress σ_y and impact transition temperature T_c varied inversely with square root of the ferrite grain size, in agreement with previous workers. However, the points for ‘as drawn’ samples lay off the linear plot. The reasons for this are discussed. The hump on the upper shelf of the DBTT is thought to be associated with dynamic strain aging.     

Ultrafast room-temperature synthesis of hierarchically porous metal–organic frameworks by a versatile cooperative template strategy

Hierarchically porous MOFs (HP-MOFs) are commonly prepared by means of hydrothermal synthesis. Nonetheless, its relatively long crystallization time and harsh synthesis conditions have strongly obstructed the enhancement of HP-MOFs space–time yields (STYs) and the decrease in energy consumption. Herein, a simple and versatile method for preparing various HP-MOFs at room temperature was demonstrated, which had introduced surfactant as the template, whereas zinc oxide (ZnO) has been used as an accelerant. The resulting HP-MOFs showed multimodal hierarchical porous structures and excellent thermal stability. More importantly, the synthesis time was reduced dramatically to 11 min, with a maximal HP-MOFs STY of as high as 2575 kg m^?3 d^?1. Furthermore, the rapid formation process of HP-MOFs was examined through quantum chemistry calculation, and a feasible synthesis mechanism was also proposed. Notably, our synthesis strategy had shown a versatility, since other surfactants could also be used as the templates for the rapid room-temperature fabrication of diverse stable HP-MOFs. Importantly, the porosity of the HP-MOFs could be readily tuned through controlling the type of template. Moreover, gas adsorption measurement of HP-MOFs revealed high CH₄ uptake capacity at 298 K due to the increase in surface area and pore volume. Our findings suggest that such method is applicable for the rapid synthesis of a wide variety of HP-MOFs on an industrial scale.     

Synchrotron X-ray computed microtomography investigation of a mortar affected by alkali–silica reaction: a quantitative characterization of its microstructural features

Alkali–silica reaction (ASR) is one of the most important weathering processes in cement-based materials. The damages caused by ASR have been qualitatively investigated with a number of different techniques. In this study, we present a procedure to obtain quantitative morphological parameters of the ASR reaction effects using synchrotron X-ray microtomography data. We found three different kinds of voids due to the effect of three different mechanisms: (i) cracks from ASR expansion, (ii) irregular-shaped voids due to the aggregate particles dissolution, and (iii) bubbles due to the cement paste preparation. We were able to separate them using morphological parameters (such as surface/volume ratio and aspect-ratio) calculated for each object, thus obtaining, e.g., volume fractions for each kind of voids. From the orientation data, we also studied if any shape preferred orientation was present in the sample, concerning the fractures network, and we found no appreciable preferred orientation. The new analysis procedure we applied in this study proved to be an effective approach for the quantitative characterization of the effects (cracks and porosity development by aggregate weathering) of the ASR reaction in mortars.     

Synthesis and regulation of α-LiZnPO4·H2O via a solid-state reaction at low-heating temperatures

A simple and novel route for the synthesis of a lithium zinc phosphate hydrate, α-LiZnPO₄·H₂O, was studied, and the target product was obtained with LiH₂PO₄·H₂O and ZnCO₃ as raw materials and polyethylene glycol-400 (PEG-400) as a surfactant via a one step solid-state reaction at room temperature (25 °C). The product was characterized with X-ray powder diffraction (XRD), thermogravimetric analysis and the 1st derivativative of thermogravimetric analysis (TG/DTG) and Fourier transform infrared spectroscopy (FTIR). The comparison experimental results suggested that aging temperature controlled the products of the synthesis, that is, the α-LiZnPO₄·H₂O was formed when the reaction mixture was aged at room temperature, and the α-LiZnPO₄ was obtained when the reaction mixture was aged at 80 °C.