ARTICLE This journal isViscoelastic properties of cellulose solutions with 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) and dimthylsulfoxide (DMSO) as solvents were studied by rheological experiments. From the results of rheological behaviors, the non-monotonous decrease of viscosity with DMSO content was observed. When the content of DMSO in [BMIM]Cl/DMSO is lower than 5 wt% in [BMIM]Cl/DMSO, the viscosity and gelation temperature (T gel ) decreased with the increase of DMSO. However, the values of viscosity and T gel showed nonlinear change with the further increase of DMSO. It could be understood that DMSO acted as the diluent when the content of DMSO is below 5 wt%. The local micro-aggregation or micro-phase separation of cellulose could be happened when the content of DMSO further increased due to the weak action between cellulose and DMSO.B Headings should always be subordinate to A headingse.g. Synthetic procedures, Materialsand methods, Crystallography. C headings should always be subordinate to B headings e.g. General procedure for synthesis of compound X. The main paragraph text follows directly on here.
With the development of modern industrial technology, tungsten products prepared from traditional tungsten powder cannot meet the demands of industry. However, the properties of tungsten products produced from ultra-fine tungsten powder have been greatly improved:they have high strength, high toughness, and low metal plasticity-brittle transition temperature. Hence, it is necessary to carry out theoretical research of the micro-adsorption dynamics during hydrogen reduction of W20O58, which is beneficial to synthetizing ultra-fine tungsten powder. In this article, to comprehend the crystal characteristics of W20O58 (010) surface and provide the theoretical reaction law for hydrogen reduction on W20O58 (010) surface, the absorption mechanism of H2 molecule on W20O58 (010) surface is studied by the first-principles calculation based on density functional theory in a plane wave pseudo-potential framework. The results show that the indirect band gap of W20O58 is 0.8 eV, indicating that it has metallic characteristic. The W20O58 (010) surface has different terminations, i.e., WO-terminated (010) surface and O-terminated (010) surface. After the geometrical optimization of the two surfaces, the W–O bond length and bond angle of W–O–W are both changed. In addition, six absorption configurations of H2 on W20O58 (010) surface, including WO-L-O1c, WO-V-O1c, WO-L-O2c, WO-V-O2c, O-L-O1c and O-V-O1c, are chosen to be investigated. The calculation results show that the WO-L-O1c, WO-V-O1c and WO-L-O2c absorption system are unstable, while the WO-V-O2c, O-L-O1c and O-V-O1c absorption configuration are stable. When H2 molecule is dissociated into two H atoms, the absorption energies of the three stable configurations are-1.164 eV,-1.021 eV and-3.11 eV, respectively. It is obvious that the O-V-O1c absorption configuration is the most stable one. The analysis of density of states reveals that the 1s state of H atom interacts with the 2p and 2s states of O atom. The outermost O1c atom of O-terminated (010) surface contains an unsaturated bond, which results in the formation of bonding between two H atoms and O1c atom. As a result, an H2O molecule is formed and an oxygen vacancy on the surface is generated after absorption reaction. By combining experimental observations with simulation calculations, the mechanism of hydrogen reduction of W20O58 can be revealed from a microscopic view.
With the development of modern industrial technology, tungsten products prepared from normal tungsten powder cannot meet the demands of industry. The tungsten product produced from ultra-fine tungsten powder exhibits high strength, high toughness, and low metal plasticity-brittleness transition temperature, which greatly improves the performance of materials. Hence, it is necessary to carry out theoretical research on the micro adsorption dynamics during hydrogen reduction of tungsten trioxide to prepare ultra fine tungsten powder. In order to understand crystal characteristics of WO3 and WO3(001) surface characteristics, and to provide beneficial theoretical support for reaction law of hydrogen reduction on the WO3(001) surface, the mechanisms of H atom adsorption on cubic WO3 and WO3(001) surface are studied by the first-principles calculation based on the density functional theory (DFT) plane wave pseudo-potential method. The results show that theoretically calculated band gap of the cubic crystalline WO3 is 0.587 eV. There are two kinds of WO3(001) surfaces, WO-terminated (001) surface and O-terminated (001) surface. The W-O bond length and the bond angle of W-O-W structure change after the geometric optimization of the surface, and thus the surface relaxation is realized. The WO-terminated (001) surface shows n-type semiconductor characteristics while the O-terminated (001) surface shows p-type semiconductor characteristics. Four adsorption configurations of H atoms on the WO-terminated (001) surface and the O-terminated (001) surface, including H-O2c-H, H-O2 cH-O2c, H-O1c-H, and H-O1cH-O1c, are calculated. Among them, the adsorption energy of the H-O1c-H configuration is the smallest (-3.684 eV) with the shortest bond length of H-O bond (0.0968 nm), and hydrogen atoms lose the most of electrons (0.55e), which indicates that the H-O1c-H adsorption configuration is the most stable one. The band gap of the H-O1c-H configuration increases from 0.624 eV to 1.004 eV after adsorption, while the bandwidth of valence band is almost unchanged. The results about the density of states (DOS) reveal that 1s state of the H atom interacts with 2p and 2s states of the O atom. Strong isolated electron peaks are formed to be at about -8 and -20 eV. The outermost O1c atoms of O-terminated (001) surface contain an unsaturated bond, facilitating the bonding between two H atoms and one O1c atom. Thus, two H atoms and one O1c atom form chemical bonds respectively, and an H2O molecule is generated, leaving an oxygen vacancy on the surface after adsorption reaction. By combining experimental observations with simulation results, the mechanism of hydrogen reducing tungsten trioxide can be elaborated profoundly from a micro view.
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