Theoretical study of adsorption and dissociation of NH_3 on the Ir{110}(1×2) surface

The adsorption and dissociation of NH3 on Ir{110}(1×2) have been investigated using the densityfunctional calculations at a coverage of 0.25 ML. The adsorption sites, energy, and geometries were obtained for NH3, NH2, and H adsorptions on the surface. The transition state for NH3 dissociation on Ir{110}(1×2) was also identified. It was found that NH3 is adsorbed preferentially at the ridge atop site, while NH2 and H are adsorbed at the ridge bridge site. The activation barrier of NH3 dissociation is 78.4 kJ/mol, which is very close to the NH3 adsorption energy of 90.0 kJ/mol. This indicates that the desorption and dissociation of NH3 on Ir{110}(1×2) are very competitive, which is consistent with the recent experimental results.     

银在M-掺杂石墨烯上吸附的第一性原理计算

Graphene is an ideal reinforcing phase for a high-performance composite filler, which is of great theoretical and practical significance for improving the wettability and reliability of the filler. However, the poor adsorption characteristics between graphene and the silver base filler significantly affect the application of graphene filler in the brazing field. It is a great challenge to improve the adsorption characteristics between a graphene and silver base filler. To solve this issue, the adsorption characteristic between graphene and silver was studied with first principle calculation. The effects of Ga, Mo, and W on the adsorption properties of graphene were explored. There are three possible adsorbed sites, the hollow site (H), the bridge site (B), and the top site (T). Based on this research, the top site is the most preferentially adsorbed site for Ag atoms, and there is a strong interaction between graphene and Ag atoms. Metal element doping enhances local hybridization between C or metal atoms and Ag. Furthermore, compared with other doped structures (Ga and Mo), W atom doping is the most stable adsorption structure and can also improve effective adsorption characteristic performance between graphene and Ag.     

Influences of microstructure and texture on crack propagation path of X70 acicular ferrite pipeline steel

The aspects of two pipeline steels with different technologies were investigated by using transmission electron microscopy (TEM) and electron back-scattered diffraction (EBSD). The microstructure presents a typical acicular ferrite characteristic with fine particles of martensite/austenite (M/A) constituent, which distributes in grains and at grain boundaries. The bulk textures of the pipeline steel plate are {112}<110> and <111> fibers, respectively, and the {112}<110> component is the favorable texture benefiting for drop weight tear test. Moreover, low angle boundaries and low coincidence site lattice boundaries are inactive and more resistant to fracture than high energy random boundaries.     

High temperature oxidation behavior of aluminide on a Ni-based single crystal superalloy in different surface orientations

An investigation on oxidation behavior of coated Ni-based single crystal superalloy in different surface orientations has been carried out at1100 ℃. It has been found that the {100} surface shows a better oxidation resistance than the {110} one, which is attributed that the {110}surface had a slightly higher oxidation rate when compared to the {100} surface. The experimental results also indicated that the anisotropic oxidation behavior took place even with a very small difference in the oxidation rates that was found between the two surfaces. The differences of the topologically close packed phase amount and its penetration depth between the two surfaces, including the ratio of α-Al2O3 after 500 h oxidation, were responsible for the oxidation anisotropy.     

Periodicity-dependent long range coulomb on-site repulsion in hydrogen adsorbed graphene:A DFT+U study

The long rang Coulomb on-site repulsion between u electrons in hydrogen (H) adsorbed graphene has been studied based on DFT+U calculations.This study demonstrates that the rigidity of n electronic structure of graphene is partially destroyed in the cases of H adsorption due to the introduction of un-paired electron in this system.The softness of n conjugation is largely depending on the concentrations as well as the periodicity of H adsorption.Due to the destruction of the rigidity of n conjugation,the Coulomb on-site repulsion increases.The results show that the Coulomb on-site repulsion between n electrons is very sensitive to the periodicity of H adsorption.A considerable enhancement of Coulomb on-site repulsion occurs for the systems with 3n×3n peroidcity.More importantly,the strength and the patterns of Coulomb on-site repulsion in the graphene plane are significantly size-dependent,which further induces the band gap opening at Fermi level.Especially for 6 x 6 system,the on-site repulsion induces a stabilized non-ferromagnetic state.Our results reveal for the first time that the considerable long rang Coulomb onsite repulsion between n electrons exists which plays an important role in the electronic characteristics of H adsorbed graphene.The finding in this investigation provides new insight into the many-body interaction between localized impurities with delocalized n electrons in graphene related materials.     

Influence of slip system combination models on crystal plasticity finite element simulation of NiTi shape memory alloy undergoing uniaxial compression

The influence of various slip system combination models on crystal plasticity finite element simulation of Ni Ti shape memory alloy subjected to uniaxial compression deformation is investigated according to three combinations of slip systems, including combination of {010}100and {110}111slip modes, combination of {110}100and {110}111slip modes and combination of {110}100, {010}100and {110}111slip modes, which consist of 18, 18 and 24 slip systems, respectively. By means of simulating mechanical response,strain distribution, stress distribution and Schmid factor, it can be found that in terms of simulation accuracy,combination of {110}100and {110}111slip modes is in good agreement with combination of {110}100,{010}100and {110}111slip modes. The contribution of {110}100slip mode to plastic strain is primary in plastic deformation of Ni Ti shape memory alloy, whereas {010}100slip mode, which makes small contribution to plastic deformation, can be regarded as the unfavorable slip mode. In the case of large plastic strain, the {010}100slip mode contributes to the formation of(001) [010] texture component, while {110}100and {110}111slip modes facilitate the formation of γ-fibre(111) texture.     

DFT investigation of NH3 gas interactions on TeO2 nanostructures

The structural, electronic and adsorption properties of NH_3 on pristine, Sn and F substituted TeO_2 nanostructures were investigated using density functional theory with B3LYP/Lan L2 DZ basis set. The electronic properties of pristine, Sn and F incorporated TeO_2 nanostructures were explained with ionization potential, HOMO–LUMO gap and electron af fi nity. The dipole moment and point group of rutile TeO_2 nanostructures were also reported. The structural stability of pristine, Sn and F substituted TeO_2 nanostructures were investigated in terms of formation energy. The adsorption properties of NH3 on TeO_2 were studied and the proper adsorption sites of NH_3 on TeO_2 materials were identi fi ed and discussed with the suitable parameters such as adsorption energy, HOMO–LUMO gap, Mulliken population analysis and average energy gap variation. The results show that the substitution of fl uorine in TeO_2 nanostructure enhances NH3 adsorption properties in mixed gas environment.     

Synergistic effect between ceria and tungsten oxide on WO3–CeO2–TiO2 catalysts for NH3-SCR reaction

WO3–CeO2–TiO2 catalysts for NO (nitrogen monoxide) reduction by ammonia were prepared by a sol–gel method. The catalysts were characterized by BET, XRD, Raman, NH3/NO adsorption and H2-TPR to investigate the relationships among the catalyst composition, structure, redox property, acidity and deNOx activity. WO3–CeO2–TiO2 catalysts show a high activity in a broad temperature range of 200–480 1C. The low-temperature activity of catalysts is sensitive to the catalyst composition especially under low-O2-content atmospheres. It may be related to the synergistic effect between CeOx and WOx in the catalysts. On one hand, the interaction between ceria and tungsten oxide promotes the activation of gaseous oxygen to compensate the lattice oxygen consumed in NH3-SCR (selective catalytic reduction) reaction at low temperatures. Meanwhile, the Br?nsted acid sites mainly arise from tungsten oxides, Lewis acid sites mainly arise from ceria. Both of the Br?nsted and Lewis acid sites facilitate the adsorption of NH3 on catalysts and improve the stability of the adsorbed ammonia species, which are beneficial to the NH3-SCR reaction.     

Thermodynamics and density functional theory study of potassium dichromate interaction with galena

The adsorption heat and reaction rate constant of potassium dichromate on the surface of galena were studied. The results indicate that potassium dichromate tends to adsorption on the galena surface. The reaction order is only 0.08385, suggesting that the concentration of potassium dichromate has little influence on its adsorption on the galena surface. In addition, the simulation of CrO₄2? adsorption on the PbS (100) surface in the absence and presence of O₂ was carried out by density functional theory (DFT). The calculated results show that CrO₄2? species adsorb energetically at the Pb-S bond site, and the presence of O₂ can enhance this adsorption.     

Theoretical study on the mechanism of cycloaddition between dimethyl methylene carbene and acetone

The mechanism of the cycloaddition reaction of singlet dimethyl methylene carbene and acetone has been studied by using second-order Moller-Plesset perturbation and density functional theory. The geometrical parameters, harmonic vibrational frequencies and energy of stationary points on the potential energy surface are calculated by MP2/6-31G and B3LYP/6-31G methods. The results show that path b of the cycloaddition reaction （1） would be the major reactive channel of the cycloaddition reaction between singlet dimethyl methylene carbene and acetone, which proceeds in two steps： i） The two reactants form an energy-rich intermediate （INT1b）, which is an exothermic reaction of 23.3 kJ/mol with no energy barrier. ii） The intermediate INT1b isomerizes to a three.membered ring product （P1） via transition state TS1b with energy barrier of 22.2 kJ/mol. The reaction rate of this reaction and its competitive reactions do greatly differ, with excellent selectivity. In view of dynamics and thermodynamics, this reaction is suitable for occurring at 1 atm and temperature range of 300-800 K, in which the reaction will have not only the larger spontaneous tendency and equilibrium constant but also the faster reaction rate.     

Protein adsorption on materials surfaces with nano-topography

Protein adsorption behavior on the surfaces of biomedical materials is highly related to the biocom- patibility of the materials. In the past, numerous research reports were mainly focused on the effect of chemical components of a material’s surface on protein adsorption. The effect of surface topography on protein adsorption, the topic of this review, has recently received keen interest. The influence of surface nano-topographic factors, including roughness, curvature and geometry, on protein adsorption as well as the protein adsorption behavior, such as the amount of protein adsorbed, the activity and morphology of adsorbed protein, is introduced.     

Boron isotopic fractionation during incorporation of boron into Mg（OH）2

Experiments of boron incorporated into Mg（OH）2 from magnesium-free synthetic seawater were carried out at various pH values, in order to investigate the adsorption species and the variation of isotopic fractionation of boron on Mg（OH）2. The results showed that the incorporation of boron into Mg（OH）2 was very rapid and reached the equilibrium after 4 h. The [B]s and the partition coefficient Kd between Mg（OH）2 and final solution decreased with the increasing pH. The maximum values of [B]s and Kd were much higher than that of boron adsorbed on metal oxide or clay minerals, indicating that the incorporation capability of boron into Mg（OH）2 was very strong. When the adsorption reached the equilibrium, the δ 11Bfsw was lower than δ 11Bisw. The boron isotopic fractionation αs-fsw was between 1.0186 and 1.0220 with an average of 1.0203. All these indicated that 11B incorporated into Mg（OH）2 preferentially due to B（OH）3 incorporation into Mg（OH）2 preferentially. The deposition reaction of B（OH）3 with Mg（OH）2 was the direct reason for B（OH）3 incorporation into Mg（OH）2. During the boron incorporation into Mg（OH）2, the isotopic fractionation characteristic of boron was decided by the simultaneous existence of adsorption of boron on Mg（OH）2 and the deposition reaction of H3BO3 with Mg（OH）2. Different from the fact that only B（OH）4-species incorporated into bio-carbonate, B（OH）3 and B（OH）4 incorporated into Mg（OH）2 simultaneously, and B（OH）3 incorporated into it preferentially. The lower pH is, the more incorporated fraction of B（OH）3 will be. Mg（OH）2 exists widely in madrepore, which influences the quantitative correspondence of the boron isotopic composition δ 11Bcarb of corals on the pH of the seawater badly, and brings serious uncertainty to the δ 11Bcarb as the indicator of the ancient seawater pH.     

Atmospheric heterogeneous reaction of acetone: Adsorption and desorption kinetics and mechanisms on SiO2 particles

Acetone plays an important role in photooxidation processes in the atmosphere. Up to date, little is known regarding the heterogeneous fate of acetone. In this study, the adsorption and desorption processes of acetone on SiO2 particles, which are the major constituent of mineral dust in the atmos-phere, have been investigated for the first time under the simulated atmospheric conditions, using in situ transmission Fourier transform infrared spectroscopy. It is found that acetone molecules are adsorbed on the surfaces of SiO2 particles by van der Waals forces and hydrogen bonding forces in a nonreactive and reversible state. The rates of initial adsorption and initial desorption, initial uptake coefficients and adsorption concentrations at equilibrium have been determined at different relative humidity. The presence of water vapor cannot result in the formation of new substances, but can decrease the adsorption ability by consuming or overlapping the isolated OH groups on the surfaces of SiO2 particles. In the desorption process, a considerable amount of acetone molecules will remain on SiO2 particles in dry air, whereas acetone molecules are almost completely desorbed at a high relative humidity. In order to evaluate the role of heterogeneous reactions of acetone and other carbonyl compounds in the atmosphere, a new model fitting the atmospheric conditions is needed.     

Preparation of composite adsorbent with high performance of heat and mass transfer

To develop a new composite adsorbent with high performance,fir sawdust and CaCl2are selected as raw materials.The mass transfer is enhanced by carbonizing and activating the sawdust and heat transfer is enhanced by adding expanded graphite into the adsorbent.The effect of the preparation temperature and the expanded graphite content on the adsorption performance is investigated.The results show that the new adsorbent exhibits a high adsorption performance due to its high porosity,uniform distribution and high content of CaCl2and high thermal conductivity.Also,the experimental results indicate that the rate of ammonia adsorption on the adsorbent depends on the expanded graphite content and the carbonization and activation temperature.The adsorbent prepared at 500°C and with the expanded graphite content of 30%has the best performance in terms of the adsorption refrigeration,which adsorbs ammonia as high as 0.37 g g 1at 10 min.     

NO adsorption study on the distribution of Ni2 + ions on the various micro-environments of carriers

The decrease of the electron density in the d orbits of Ni2+ ions, resulting from the disturbance of micro-environments in which Ni2+ ions are located, makes the frequency of adsorbed NO shift higher. The shift degree is determined mainly by the property of the microenvi-ronments. When Ni2+ ions are located on SII , SII · (SI ·) sites of Y zeolite or on the surface of γ-alumina, their NO adsorption gives rise to IR bands at 1 905, 1 900 and 1 855-1 875 cm-1, respectively. The distribution of Ni2 + ions on the various micro-environments of USY zeolite, AI2O3 and MS mixed carrier has also been discussed according to the different frequencies of adsorbed NO, as well as the influence of NiO loading.     

Determination of stacking fault energies in a high-Nb TiAl alloy at 298 K and 1273 K

The stacking fault energies of Ti-46Al-8.5Nb-0.2W alloy at 298 K and 1273 K were determined. The principle for the determination of the stacking fault energies is based on the fact that the stacking fault energy and the elastic interaction energy acting on the dissociated partial dislocations are equal. After the compress deformations with the strain of 0.2% at 298 K and 1273 K, and water quench to maintain the dislocation structures deformed at 1273 K, the dissociation distances between two partial dislocations were determined by weak beam transmission electron microscopy (WBTEM) technique. Based on these dissociation distances and the corresponding calculation method, the stacking fault energies were determined to be 77-81 mJ/m2 at 298 K and to be 57-60mJ/m2 at 1273 K respectively.     

Observation of Pt-{100}-p(2×2)-O reconstruction by an environmental TEM

The surface structure of noble metal nanoparticles usually plays a crucial role during the catalytic process in the fields of energy and environment. It has been studied extensively by surface analytic methods, such as scanning tunneling microscopy. However, it is still challenging to secure a direct observation of the structural evolution of surfaces of nanocatalysts in reaction(gas and heating) conditions at the atomic scale. Here we report an in-situ observation of atomic reconstruction on Pt {100} surfaces exposed to oxygen in an environmental transmission electron microscope(TEM). Our high-resolution TEM images revealed that Pt-{100}-p(2×2)-O reconstruction occurs during the reaction between oxygen atoms and{100} facets. A reconstruction model was proposed, and TEM images simulated according to this model with different defocus values match the experimental results well.     

Room-temperature NH3 sensors with high sensitivity and short response/recovery times

Micro-sensors are fabricated by co-electrospin- ning In203 and SnO2 nanofibers on the substrates of SiO2/Si with interdigitated Pt signal electrodes. The total sensor area is 1.36 mmx 0.55 mm and the active area is only 0.63 mmx 0.55 ram. Excellent NH3 sensing properties are obtained based on the sensors at room temperature. The sensitivity is at most 28 when the sensors are exposed to NH3 of 10 ppm. The response time is 8 s or so and the recovery time is nearly 2 s. Not only fine selectivity, but also long- time stability is obtained. The results not only demonstrate the obtained micro-sensors are very promising devices for NH3 detection, but also show a possible route for large-scale NH3 sensor fabrication at the industrial level.     

Density functional theory study on the insertion reaction mechanism of dibromocarbene with formaldehyde

The insertion reaction mechanism of CBr2 with CH3CH2O has been studied by using the B3LYP/6-311G(d) and CCSD(T)/6-311G(d) at single point. The geometries of reactions,transition state and products were completely optimized. All the transition state is verified by the vibrational analysis and the internal re-action coordinate (IRC) calculations. The results show that reaction (1) is the dominant reaction path,which proceeds via two steps: i) two reactants form an intermediate (IM1),which is an exothermal re-action of 8.62 kJ·mol?1 without energy barrier; ii) P1 is obtained via the TS1 and the H-shift,in which the energy barrier is 44.53 kJ·mol?1. The statistical thermodynamics and Eyring transition state theory with Wigner correction are used to study the thermodynamic and kinetic characters of this reaction in temperature range from 100 to 2200 K. The results show that the appropriate reaction temperature ranges from 200 to 1900 K at 1.0 atm,in which the reaction has a bigger spontaneity capability,equi-librium constant (K) and higher rate constant (k).     

Characteristic parameters and operational curves of γ-Al2O3 nanofiltration membranes

The γ-Al2O3 nanofiltration membranes were manufactured by the sol-gel technique. The result of N2 adsorption and desorption test indicates that the characteristic parameters of the membranes: BJH desorption average pore diameter, BJH desorption cumulative volume of pores and BET surface area are about 3.9 nm, 0.33 cm^3/g and 245 m^3/g respectively, and the pore size distribution is very narrow.The operational curves of γ-Al2O3 nanofiltration membranes of the Ca^2 retention rate vs the trans-membrane pressure,feed concentration of solution treated and pH of solution treated were studied for the first time. It is found that the retention rate for Ca2~ increases with the transmembrane pressure increasing and decreases with the feed concentration of CaCl2 solution increasing. The retention of Ca^2 is very rmuch dependent on the pH of the solution. Minima Ca^2 retention rate is found at the isoelectric point (pH=7.5).