Adsorbed states of K on the diamond (100)(2×1) surface

The adsorbed states of K on the C(100)(2×1) surface have been studied by electron energy loss spectroscopy (EELS), work function change (Δφ) measurement and thermal desorption spectroscopy (TDS). In the region where the K coverage is less than one-half of a monolayer (θ_K≤0.5), a loss is observed from ∼1.2 eV (θ_K=0.2) to 1.0 eV (θ_K=0.5); the work function decreases upon K adsorption until reaching a shallow minimum of Δφ=−3.35 eV at θ_K=∼0.5; and a desorption peak (β) is observed from ∼825 K (θ_K=0.05) to 525 K (θ_K=0.5). These results indicate that the K–substrate bond is highly polarized; the 1.2 eV loss is attributed to the electronic transition from the bonding to antibonding states formed at the K–substrate interface. In the region between θ_K=0.5 and 1, two losses are observed at 0.7 and 1.4 eV (θ_K=0.6); there is only a small increase of the work function; and a desorption peak (α) is observed in addition to the β peak. These results indicate that the K regains its electron and becomes, essentially, neutral. The 1.4-eV loss is ascribed to the transition from the 4s to 4p states of K. The origin of the 0.7-eV loss is discussed. The Δφ and TDS results are analyzed by the depolarization model.     

Surface stabilities of 3C–SiC and H2O adsorption on the (110) surface

First-principles calculations and thermodynamics analyses were combined to study the surface stabilities of 3C–SiC and H₂O adsorption on the (110) surface. The stoichiometric (110) surface was predicted to be generally the most stable. Only at the extremely C-poor condition, the nonstoichiometric Si-terminated (100) could become more energetically favored. The adsorption and dissociation of single H₂O molecule on the 3C–SiC (110) were then comparatively investigated. Calculations show that H₂O molecules prefer to partially dissociate into one hydroxyl OH and one H adsorbed at the top-most Si and C sites, respectively, leading to the formation of a hydrogen network on the surface. The calculated equilibrium adsorption diagram further suggested that the 3C–SiC (110) surface can be only either completely clean or fully covered by the partially dissociated species of H₂O, for a wide range of temperature and the partial potential of H₂O.     

Progress in the Study on the Phase Equilibria of the CO2·H2O and CO2-HeO-NaCI Systems

To study the feasibility of CO2 geological sequestration,it is needed to understand the complicated mul- tiple-phase equilibrium and the densities of aqueous solution with CO2 and multi-ions under wide geological condi- tions（273.15—473.15K,0—60MPa）,which are also essential for designing separation equipments in chemical or oil-related industries.For this purpose,studies on the relevant phase equilibria and densities are reviewed and analyzed and the method to improve or modify the existing model is suggested in order to obtain more reliable predictions in a wide temperature and pressure range.Besides,three different models（the electrolyte non random two-liquid（ELECNRTL）,the electrolyte NRTL combining with Helgeson model（ENRTL-HG）,Pitzer activity coefficient model combining with Helgeson model（PITZ-HG））are used to calculate the vapor-liquid phase equilib- rium of CO2-H2O and CO2-H2O-NaCl systems.For CO2-H2O system,the calculation results agree with the experimental data very well at low and medium pressure（0—20MPa）,but there are great discrepancies above 20MPa.For the water content at 473.15K,the calculated results agree with the experimental data quite well.For the CO2-H2O-NaCl system,the PITZ-HG model show better results than ELECNRTL and ENRTL-HG models at the NaCl concentration of 0.52mol·L ^-1 .Bur for the NaCl concentration of 3.997mol·L ^-1 ,using the ELECNRTL and ENRTL-HG models gives better results than using the PITZ-HG model.It is shown that available experimental data and the thermodynamic calculations can satisfy the needs of the calculation of the sequestration capacity in the temperature and pressure range for disposal of CO2 in deep saline aquifers.More experimental data and more accurate thermodynamic calculations are needed in high temperature and pressure ranges（above 398.15K and 31.5MPa）.     

The effect of the nature of the gas phase on the surface properties of liquid tin in contact with the (100) face of solid electrolyte ZrO2Y2O3

Using the method of measuring the electrolytic conductivity G between the electrode being investigated and the auxiliary electrode as a function of the potential φ, a study has been made of the surface properties of liquid tin in contact with solid electrolyte 0.90 ZrO₂0.10 Y₂O₃ in an atmosphere of COCO₂ as well as in helium. The G-φ curves obtained exibit two free surface energy (FSE) maxima in the gas mixture COCO₂ at 900°C and only one FSE maximum in the helium atmosphere. In the COCO₂ atmosphere the transition from the (100) face of the solid electrolyte 0.90 ZrO₂0.10 Y₂O₃ single crystal to the sintered material displaces the potential of the first maximum by 0.07 V towards the negative region, that of the second maximum by 0.06 V. It has been found that the change of the gas phase COCO₂ for the gas phase H₂H₂O (hydrogen with an insignificant admixture of water) affects very largely the magnitude of the potentials that correspond to the FSE maximum. The latter circumstance is a demonstration that the adsorption phenomena play a significant part.     

Formation and Geometry of a High-Coverage Oxygen Adlayer on Ru(001), the p(2 × 2)-3O Phase

A detailed low-energy electron diffraction (LEED)-IV analysis, complemented by scanning tunneling microscopy (STM) observations, was carried out for the apparent (2 × 2) structure of the oxygen-covered Ru(001) surface at a coverage of 0.75 ML. We present STM images of incomplete layers which allow one to define the symmetry of the ordered layer, in particular of the novel high density p(2 × 2)-3O phase. In the LEED-IV analysis we have tested 28 model structures; the results can be used for conclusions about the discrimination of this type of geometry determination. Our quantitative LEED analysis in connection with the STM results corroborates the model proposed before and shows that all of the oxygen atoms sit in the hcp sites with an averaged vertical distance to the outermost Ru layer of d^⊥_Ru–O = 1.22 Å. This value falls into the general trend of increasing d^⊥_Ru–O with oxygen coverage observed for the other ordered structures of adsorbed oxygen on Ru and is also predicted by recent total energy calculations. The O–Ru bonding distance of about 2.0 Å is essentially unchanged compared to the other structures. Considerable lateral and vertical displacements of both the O and the Ru atoms are found, with the O atoms being slightly displaced towards the fcc hollow site located in the center of three oxygen atoms. The two uppermost substrate layers are buckled; in the first layer three out of four Ru atoms of the (2 × 2) unit cell are shifted away laterally from their bulk positions. These shifts, globally as well as locally, can be understood in terms of local electron density changes induced by the adsorbed oxygen atoms.     

Co-methanation of CO and CO2 on the Ni X -Fe1?X /Al2O3 catalysts; effect of Fe contents

The co-methanation of carbon dioxide containing syngas was carried out on Al₂O₃ supported Ni _x Fe_1?x (x is 0.1, 0.3, 0.5, 0.7 and 0.9) catalysts for synthetic natural gas (SNG) production. The catalysts were prepared by wet-impregnation method taking 20 weight percent of the metallic component over the support, and its characteristics were analyzed by BET surface area, XRD and H₂-TPR. The maximum carbon conversion and CH₄ selectivity are achieved on Ni_0.7Fe_0.3/Al₂O₃ catalyst. Further, increase of Fe content led to enhancing the water gas shift reaction and hydrocarbon formation.     

The influence of aliphatic amines on the potential of the structural transition (hex) → (1 × 1) for Au (100) electrode

The impact of the aliphatic amines on the potential (E _T) of the structural transition (hex) → (1 × 1) for Au (100) electrode was investigated. This potential was shifted to more negative values as the concentration of a given amine increased. As E _T depends linearly on the log of the bulk concentration for each amine it was suggested to use this relationship for quantitative determination of the amines. Moreover, it was shown that the presence of amines reduced the stability range of the (hex) structure in the following sequence methylamine < ethylamine < propylamine < butylamine due to their increasing adsorbability. Furthermore, for a given concentration the introduction of each subsequent –CH₂– group into the carbon chain of an amine is accompanied by the reduction of the stability range of ca. 23 mV.     

Effects of the pretreatment of a cemented carbide surface on its properties and on the properties of diamond coatings deposited by oxygen–acetylene flame CVD

The influence of the pretreatment of the WC (6% Co) surface on its properties (i.e. roughness, grain size and chemical composition) and on the properties of flame-deposited coatings have been studied. The surface treatments included the action of an oxidizing oxygen/acetylene flame at 1000 °C, scratching with diamond particles (14–20 μm), mixture with iron (<45 μm) in an ultrasound bath, and seeding with a nm-sized diamond suspension. An acid treatment was included in the pretreatment sequence. It is found that the oxidizing flame and the seeding decrease the surface roughness of the substrate as well as the diamond coatings, at the same time increasing the adhesion of the coating. Ultrasound scratching with the diamond/iron suspension increases the roughness of both the substrate and the diamond coating and decreases the adhesion of the coating. Scratching with diamond particles shows a similar but lesser effect. Except for scratching with diamond, all the surface pretreatment procedures lead to an increase in the density of diamond particles: this increase is greatest for seeding. Our results indicate that good adhesion and a small surface roughness are best obtained by the use of an oxidizing flame followed by acid treatment and seeding with nanoparticles.     

Coke formation on the surface of α-Al2O3 in the catalytic pyrolysis of naphtha

The catalytic pyrolysis of naphtha has been carried out in a quartz reactor loaded with 5 mm α-A1₂0₃ spheres. The yields of ethylene and propylene exhibit about 10% and 5% higher values compared to the thermal pyrolysis in the absence of α-A1₂0₂ spheres at the same reaction conditions. The coke formation on α-A1₂0₃ spheres increased continuously along with the axial length of the reactor as well as with reaction time. Results suggest that the concentration of the coke precursors in the gas phase may increase along with the axial length of the reactor. Coke filled up completely the internal pore of the sphere near the exit of the reactor after reaction for 4 hr. The coke film on the external surface of the sphere grew continuously thicker. The coke formation was influenced strongly by the physical properties of the α-Al₂O₃ spheres. Coke deposition was the least on the α-A1₂0₃ sphere with the lowest surface area and pore volume among the tested α-A1₂0₃ spheres.     

Syngas to ethanol on MoCu(2 1 1) surface: Effect of promoter Mo on C—O bond breaking and C—C bond formation

The mechanism of syngas to ethanol on MoCu(2 1 1) surface has been researched by density functional theory (DFT) calculation, and the effects of Mo as a promoter on C—O bond breaking and C—C bond formation have been discussed. Calculations show that Cu-Mo atoms constitute the active sites on MoCu(2 1 1) surface after Mo atom being served as a promoter of Cu catalyst. Compared with Cu(2 1 1), MoCu(2 1 1) has two improvements. Firstly, CH₃ is the most advantageous monomer on the MoCu(2 1 1) surface, which provides abundant CH₃ intermediate for syngas to ethanol. Secondly, the C—C bond is formed mainly by inserting CHO into the abundant CH₃, and the generated CH₃CHO through multiple steps of hydrogenation to generate C₂H₅OH. The key of the promoter Mo on the MoCu(2 1 1) surface also has been verified by the analysis of its electronic properties. Differential charge density shows that the massive electron transfer from Mo to Cu, projected density of states (pDOS) shows that the electron transfer from Mo to Cu makes the d-band center of MoCu(2 1 1) nearer to the Fermi level, these indicate that the MoCu(2 1 1) catalytic capacity increased. The addition of Mo in the Cu-based catalyst not only can effectively solve the problem of C—O bond breaking, but also promote C—C bond formation. About the influence of Mo content on C—O bond breaking and C—C bond formation, compared with MoCu(2 1 1), the DFT results and the d-band center of Mo₂Cu(2 1 1) show that the increase of Mo content could not promote the synergistic effect of Cu/Mo on the generation of ethanol more effectively.     

Effect of diamond volume fraction on the microstructure and mechanical properties of SPS WC–Co/diamond composites

In this research, the effect of the volume percentage of diamond additive on the sintering behavior, microstructure, and mechanical properties of WC–Co was investigated. WC–Co/diamond composites with different percentages of 0%, 2.5%, 5%, 7.5%, and 10% by volume of diamond were made by spark plasma sintering at 1300°C and 40 MPa for 5 min. A small amount of phase transformation from the diamond phase to the graphite phase was observed. The amount of graphitization was low due to low temperature and short sintering time. The addition of diamond leads to a significant enhancement in both the hardness and fracture toughness of the composites, overcoming the trade-off between hardness and toughness typically observed in WC-based materials. The sample reinforced with 5% by volume of diamond showed simultaneously the highest hardness (22.9 GPa), the highest fracture toughness (22.7 MPa m^1/2), and the highest flexural strength (1896 MPa). The uniform dispersion, good bonding of the superhard diamond phase with the matrix, and the fine microstructure caused the high hardness and toughness of composite. The main effective mechanisms in increasing the fracture toughness of the composite were crack deflection, bridging, and blocking of crack propagation by diamond particles.     

Dispersion of Na2CO3 on γ-Al2O3 and the threshold effect in flue-gas desulfurization

Na₂CO₃ can disperse onto the surface of γ-Al₂O₃ and form a quite complete monolayer. The adsorption capacity of SO₂ on Na₂CO₃/γ-Al₂O₃ increases with Na₂CO₃ loading, and reaches a maximum at the dispersion threshold. When the loading is below the threshold, the adsorption is in company with oxidation of SO₂, and the regeneration recovery percentage of the adsorbent is beyond 60%. However, as the loading is at the threshold or higher, the adsorption is only an acidic–basic interaction and the regeneration recovery percentage is much lower. With due consideration for all concerned, the chosen Na₂CO₃ loading should enable Na₂CO₃ in the sample to cover the greater part, but not the whole surface of γ-Al₂O₃.     

Influence of the carbon surface on cathode deposits in non-aqueous Li–O2 batteries

Cup-stacked carbon nanotubes (CSCNT) with different surface properties were used for the non-aqueous Li–O₂ battery cathodes, and then examined at high magnification to understand how the discharge products were deposited on the cathode. As-prepared CSCNT based cathode had many reactive edges consisting of truncated conical graphene layers. After discharge, discharge products with average particle size 50 nm covered a nanotube, resulting in a layer-like texture. On the other hand, a heat-treated CSCNT based cathode was composed of edges terminated by graphitization of several graphene layers. After discharge, the size of the products was almost the same but the products were agglomerated, forming a bulky morphology. It was, thus, found that the carbon surface structure was closely related with the morphology of the cathode deposits after discharge. First principles calculations also indicated that no terminated edges acted as preferential active sites in adsorbing and storing the reaction species. It was, therefore, concluded that the active edges of the carbon surface were indispensable for controlling the morphology of cathode deposits and improving the battery performance.     

Surface reconstruction in electrochemistry: Au(100-(5 × 20), Au(111)-(1 × 23) and Au(110)-(1 × 2)

Au(100, Au(111) and Au(110) electrodes with reconstructed surfaces of the type (5 × 20), (1 × 23) and (1 × 2), respectively, have been prepared by the so-called flame treatment and their properties investigated in various electrolytes by electrochemical and optical methods. The reconstructed (100) and (111) surfaces are found to be stable only in a potential range where no specific adsorption occurs. The Au(100)-(5 × 20) surface has optical properties which are distinctly different from those of the unreconstructed Au(100)-(1 × 1). This difference was used to monitor by in situ spectroscopy the adsorbate-induced (5 × 20) → (1 × 1) transition, in order to obtain information on the transition kinetics. For a certain fraction of the surface, electrochemically induced reconstruction, (1 × 1) → (5 × 20) and (1 × 1) → (1 × 23), has been observed for Au(100) and Au(111). The potentials of zero charge of the reconstructed surfaces have been determined and are compared with those of the unreconstructed ones.     

New evidence on the factors affecting bridging and semibridging character of carbonyl ligands. The structures of Mn2(CO)7(μ-SCH2CH2S) and its phosphine derivatives Mn2(CO)7-X(PMe2Ph)X(μ-SCH2CH2S), × = 1,2

The new ethanedithiolate—dimanganese carbonyl complex, Mn₂(μ-SCH₂CH₂S)(CO)₇, 1 , was prepared in 28% yield from the reaction of 1,2,5,6-tetrathiacyclooctane with Mn₂(CO)₉(NCMe). Complex 1 was characterized crystal-lographically. It contains two Mn(CO)₃ groups joined by a Mn–Mn bond of 2.6470(6) Å in length, a dihapto-bridging ethanedithiolate ligand, and one strong semibridging CO ligand. The reaction of 1 with PMe₂Ph yielded two derivatives: Mn₂(μ-SCH₂CH₂S)(CO)₆(PMe₂Ph), 2 , and gem-Mn₂(μ-SCH₂CH₂S)(CO)₅(PMe₂Ph)₂, 3a , in 48% and 6% yields, respectively. When heated at 40 °C, compound 3a was transformed into three isomers, iso-gem-Mn₂(μ-SCH₂CH₂S)(CO)₅(PMe₂Ph)₂, 3b , 1,2-Mn₂(μ-SCH₂CH₂S)(CO)₅(PMe₂Ph)₂, 3c , and cis-Mn₂(μ-SCH₂CH₂S)-(CO)₅(PMe₂Ph)₂, 3d . Compounds 3b and 3c were characterized by single-crystal X-ray diffraction analyses. The introduction of phosphine ligand into the complexes strongly affects the semibridging character of the carbonyl ligand.     

Influence of B2O3 on viscosity and structure of the CaO–Al2O3-waste electrolyte (WE) based melt

The fluorides contained waste electrolyte (WE) from the electrolytic aluminum industry can be used as a substitution of fluorite (CaF₂) in the newly designed mold flux. In this study, the influence of B₂O₃ on viscosity and structure of CaO–Al₂O₃-WE based melt was investigated. Results show that the viscosity of mold flux melt decreases with both increasing temperature and B₂O₃ content. The apparent activation energy (E_a) also reduces from 78.96 ± 1.75 to 55.26 ± 2.79 kJ/mol with the addition of B₂O₃ from 0 to 7 wt%. The analyses of fourier transform infrared (FTIR) and Raman spectroscopies suggest that the lower symmetry of the original aluminate and silicate structure due to the insertion of [BO₄]-tetrahedral and [BO₃]-triangular, and the formation of more non-bridging oxygen (O⁻) and 2D structural units in the network with the addition of B₂O₃, deceases the viscosity and E_a of the CaO–Al₂O₃-WE Based Melt.     

Role of porosity on the stiffness and stability of (001) surface of the nanogranular C–S–H gel

We present here a nanoscale modeling of the bulk and surface states of the nanogranular Calcium Silicate Hydrate (C–S–H) gel. Regarding the mechanical properties as well as porosity, we identify two main phases: a ductile one, for a porosity from 12.4% to 27% and a brittle phase for a porosity lower than 12.4% or higher than 27%. Particularly, our calculations show that 20% of gel porosity gives a better structural stability to C–S–H and a higher stiffness. Besides, we have explored the (001) surface of C–S–H gel at the nanoscale level and have proved that more water on the surface will stabilize thermodynamically the nanostructure. This means that adsorbed H₂O molecules lead to the coexistence of Si–OH and Ca–OH groups on the surface. The calcium-terminated plane is a polar and unstable surface, and will either reconstruct to neutralize the dipole moment or adsorb ions to remove it. Our results also show that the (001) surface of low density C–S–H tends to be more stable than the surface of high density phase since the obtained surface energy decreases with increasing gel porosity.     

Phase Equilibria in the Sections of the Ca(NO3)2–CO(NH2)2–H2O System and Deicing Properties of Nitrate–Urea Mixtures

Theoretical Foundations of Chemical Engineering - Phase equilibria in the sections of the Ca(NO3)2–CO(NH2)2–H2O system and the deicing properties of calcium nitrate and carbamide...     

Analysis of passivated diamond surface channel FET in dual-gate configuration — Localizing the surface acceptor

The dual gate configuration allows to cascade a Surface Channel MESFET structure with a second MOSFET structure employing the device passivation (ALD-Al₂O₃) as MOS dielectric. Using the MOS gate as potential probe under drain bias stress, it is possible to identify lateral charge injection from the MESFET gate into the MOSFET gate dielectric. If it can be assumed, that the injected charge neutralizes the acceptor of the surface channel, determining the charge centroid allows to identify the surface acceptor location. In the stress experiment performed, 56% of the channel sheet charge could be neutralized with a charge centroid located within the passivation layer.