Catalytic effect of water,water dimer,water trimer,HCOOH, H2SO4, CH3CH2COOH and HN(NO2)2 on the isomerisation of HN(NO2)2 to O2NNN(O)OH: a mechanism study

In this article, the isomerisation mechanisms of HN(NO₂)₂ to O₂NNN(O)OH without and with catalyst X (X = H₂O, (H₂O)₂, (H₂O)₃, HCOOH, H₂SO₄, CH₃CH₂COOH and HN(NO₂)₂) have been investigated theoretically at the CBS-QB3 level of theory. Our results show that the catalyst X (X = H₂O, (H₂O)₂, (H₂O)₃, HCOOH, H₂SO₄ and CH₃CH₂COOH) shows different positive catalytic effects on reducing the apparent activation energy of the isomerisation reaction processes. Such different catalytic effects are mainly related to the number of hydrogen bonds and the size of the ring structure in X (X = H₂O, (H₂O)₂ and (H₂O)₃)-assisted transition states, as well as different values of pK_a for H₂SO₄, HCOOH and CH₃CH₂COOH. Very interesting is also the fact that H₂SO₄-assisted reaction is the most favourable for the hydrogen transfer from HN(NO₂)₂ to O₂NNN(O)OH, due to the smallest pK_a (?3.0) value of H₂SO₄ than H₂O, HCOOH, H₂SO₄ and CH₃CH₂COOH, and also because of the largest ∠X???H???Y (the angle between the hydrogen bond donor and acceptor) involved in H₂SO₄-assisted transition state. Compared to the self-catalysis of the isomerisation mechanisms of HN(NO₂)₂ to O₂NNN(O)OH, the apparent activation energy of H₂SO₄-assisted channel also reduces by 9.6 kcal?mol^?1, indicating that H₂SO₄ can affect the isomerisation of HN(NO₂)₂ to O₂NNN(O)OH, most obvious among all the catalysts H₂O, (H₂O)₂, (H₂O)₃, HCOOH, H₂SO₄, CH₃CH₂COOH and HN(NO₂)₂.     

Effects of coating parameters on the morphology of SiO2-coated TiO2 and the pigmentary properties

SiO₂-coated TiO₂ powders were prepared by the chemical deposition method starting from rutile TiO₂ and Na₂SiO₃. The SiO₂-coated TiO₂ powders were characterized by X-ray photoelectron spectroscopy, Zeta-potential analysis, Fourier transform infrared spectroscopy, and transmission electron microscopy. The evolution of island-like and uniform coating layers was found to depend upon the ratio of Na₂SiO₃ to TiO₂, reaction temperature, and pH. The whiteness and brightness of the SiO₂-coated TiO₂ powders increased in response to an increase in the SiO₂ loading, but there was a maximum value among the light scattering indexes. The SiO₂-coated TiO₂ powders possessed more negative Zeta potentials than the naked TiO₂. The dispersibility of the SiO₂-coated TiO₂ powders with the continuous and uniform SiO₂ coating layers was higher than that of the naked TiO₂ and the SiO₂-coated TiO₂ powders with the island-like SiO₂ coating layers.     

Surface modification of Mg2B2O5 whisker and its effect on the mechanical properties and thermostability of polycarbonate/Mg2B2O5w composites

The Mg₂B₂O₅ whiskers (Mg₂B₂O₅w) were modified by boric acid ester (BE) coupling agent and used to prepare polycarbonate (PC) composites. Surface wettability test and evaluation of dispersibility of BE-modified Mg₂B₂O₅w (BE-Mg₂B₂O₅w) in n-heptane were carried out by water contact angle measurement and polarizing microscopy, respectively. The surface chemical characteristics of BE-Mg₂B₂O₅w and estimation of the amount of tightly bonded organic modifier were examined by Fourier transform infrared spectrometry (FT-IR) and thermogravimetric analysis (TGA), respectively. The influence of BE-Mg₂B₂O₅w on the mechanical property, morphology and thermostability of PC composites was investigated by using universal testing machine, scanning electron microscopy (SEM), dynamic mechanical analysis (DMA) and TGA, respectively. It was found that BE was successfully grafted to the surface of Mg₂B₂O₅w, and the hydrophobic BE-Mg₂B₂O₅w leads to high ratio of adhesion work to interfacial tension between PC and BE-Mg₂B₂O₅w, and its better dispersibility in n-heptane. Furthermore, the incorporation of BE-Mg₂B₂O₅w into PC matrix resulted in higher tensile properties of PC/BE-Mg₂B₂O₅w than that of PC/Mg₂B₂O₅w composites and lower maximum weight loss rate than that of PC. The storage modulus of the PC/Mg₂B₂O₅w composites increased obviously as a function of whisker content, especially for the composites with BE-Mg₂B₂O₅w, but the T_g value changed little.     

IR-Spectra of M2UO2F4.H2O Complexes

This work is devoted to the study of and Rb₂UO₂F₄.H₂O and Cs₂UO₂F₄. H₂O IR-spectra with the aim of obtaining a set of vibration frequencies characterising M₂U0₂F₄.H₂O complexe elucidating the role and nature of water bonds in the structures of the above-mentioned compounds; and receiving preliminary information on the structure of M₂UO₂F₄.H₂O. The investigated compounds were synthesized in accord with our previous paper¹. M₂UO₂D₂O and M₂UO₂F₄.HDO were obtained by recrystallizing M₂UO₂F₄.H₂O from D₂O and HDO respectively     

Photocatalytic activity of Nb2O5/SrNb2O6 heterojunction on the degradation of methyl orange

The pure SrNb₂O₆ powders were prepared at 1400 °C by a conventional solid-state method and characterized by X-ray powder diffraction and UV-vis diffuse reflection spectrum. The powders of Nb₂O₅ and SrNb₂O₆ were ball-milled together and annealed to form the Nb₂O₅/SrNb₂O₆ composite. Photocatalytic activities of the composites were investigated on the degradation of methyl orange. The results show that the proportion of Nb₂O₅ to SrNb₂O₆ and the annealing temperature greatly influence the photocatalytic activities of the composites. The best photocatalytic activity occurs when the weight proportion of Nb₂O₅ to SrNb₂O₆ is 30% and the annealing temperature is 600 °C. The tremendously enhanced photocatalytic activity of the Nb₂O₅/SrNb₂O₆ composite compared to Nb₂O₅ or SrNb₂O₆ is ascribed to the heterojunction effect taking place at the interface between particles of Nb₂O₅ and SrNb₂O₆. The powders also show a higher photocatalytic activity than commercial anatase TiO₂.     

Synchrotron X-ray diffraction and absorption studies of CeM2X2 (M=Cu, Ni and X=Si, Ge) at high pressure

The equations of state of CeCu₂Si₂ and CeCu₂Ge₂ to about 60 GPa, as well as that of CeNi₂Ge₂ to 22 GPa and the valence state of Ce in CeCu₂Ge₂ to 20 GPa have been studied at room temperature in a diamond-anvil cell using synchrotron radiation sources. In each compound, the ambient-pressure phase (tetragonal ThCr₂Si₂-type structure) persisted to the highest pressure studied. The unit cell volumes of CeNi₂Ge₂ at ∼5 GPa and CeCu₂Ge₂ at ∼7 GPa, respectively, approached that of CeCu₂Si₂ taken at ambient pressure. From the equation-of-state data, the bulk modulus was derived to be 112.0±5.1 GPa for CeCu₂Si₂, 125.6±4.3 GPa for CeCu₂Ge₂, and 178.4±14.3 GPa for CeNi₂Ge₂. The valence state of Ce in CeCu₂Ge₂ remained trivalent throughout the pressure range investigated.     

BaB2O4低温相单晶体的生长及其相关体系相图的研究

本文用差热分析和X射线衍射等方法研究了BaO-Na₂O-B₂O₃三元系的两个截面:BaB₂O₄-Na₂B₂O₄和BaB₂O₄-Na₂O赝二元系的相平衡关系。BaB₂O₄-Na₂B₂O₄属共晶体系,其共晶温度为826±3℃。在BaB₂O₄-Na₂O体系中发现一个新化合物BaB₂O₄·Na₂O,该化合物在846±3℃同成分熔化。BaB₂O₄·Na₂O对BaB₂O₄和Na₂O均为共晶体系,其共晶温度分别为755±3℃和573±3℃。并根据所得的结果,分别以15mol％Na₂O和13mol％Na₂B₂O₄为助熔剂,用提拉法培养出2×4×6mm³和2×4×8mm³的低温相BaB₂O₄单晶体。 关键词：     

Production of highly concentrated 13C by continuous two-stage IRMPD. CBr2F2/HI,CCl2F2/HI,and CBrClF2/HI mixtures

Difluoromethane CH₂F₂ containing 90–98% ¹³C was obtained in the selective IRMPD of mixtures of CBr₂F₂/HI, CCl₂F₂/HI, and CBrClF₂/HI. In CBr₂F₂/HI mixtures, the intermediate product CHBrF₂ resulting from the reaction between the initial decomposition fragment CBrF₂ and HI underwent secondary selective IRMPD to form highly ¹³C-enriched CH₂F₂ in continuous laser irradiation. The intermediate product in the mixtures of CCl₂F₂/HI and CBrClF₂/HI was found to be CHClF₂, but no significant secondary photodecomposition in CBrClF₂/HI mixtures occurred owing to the low absorption cross section of CHClF₂ at the adopted laser frequencies and fluences. The observed decomposition probabilities and selectivities under different conditions with respect to laser frequency, fluence, and partial pressures of halogenated difluoromethanes and HI suggest that CBr₂F₂ is one of the better candidates for practical ¹³C separation by IRMPD.     

Infrared and Raman spectra and vibrational assignments of diiodomethane and its deuterated analogs

The infrared (from 4000 to 100 cm^?1) and Raman spectra of CH₂I₂ and CD₂I₂ have been recorded in the liquid and gaseous phases. Assignments have been made for all observed bands and, in the case of CH₂I₂, compared with those previously reported. Some bands appearing in the CD₂I₂ spectrum have been attributed to the presence of CHDI₂. The wavenumbers of the fundamental bands of CHDI₂ have been calculated from those of CH₂I₂ and CD₂I₂ using Brodersen and Langseth's rule, and compared with those observed in the CD₂I₂ spectrum.     

Chemical reactions following the IRMPD of C2F3Cl

C₂F₃Cl is photolyzed with a TEA-CO₂ laser at 1050.44 cm^–1 with focussed fluences up to 280 J/cm². The stable products in the IRMPD of C₂F₃Cl are determined for up to 10 Torr of C₂F₃Cl being photolyzed both neat and with added O₂. C₂F₄ and trans-C₂F₂Cl₂ are found to occur in the greatest yield though C₃F₅Cl, C₃F₄Cl₂, C₄F₇Cl, and C₂F₃Cl₃ also appear to be primary products. When O₂ is present F₂CO, FClCO, and CF₂ClCOF are the exclusive products. The formation of these products are for the most part consistent with a carbene formation dissociation mechanism for C₂F₃Cl IRMPD. C₂F₃Cl₃ may best be explained by another mechanism competitive with carbene formation. Many products attributed to secondary photolysis mechanisms are observed for long photolysis times.This work was performed at Department of Chemistry and chemical Engineering, Michigan Technological University, Houghton, MI 49931, USA     

Structure of Artificial Grain Boundaries in Sapphire Bicrystals with Intermediate Layers

The structure of the artificial grain boundaries in Al₂O₃ bicrystals withY₃Al₅O₁₂ and Y-stabilizedZrO₂ (Y-ZrO₂) intermediate layers was studiedwith high resolution electron microscopy, electron diffraction and energydispersive X-ray analysis. TheY₃Al₅O₁₂ intermediate layer wasfound to be polycrystalline with three different orientation relationshipsbetween the ₂O₃ and theY₃Al₅O₁₂. The structure of theY₃Al₅O₁₂/₂O₃ interfaces is described.Also₂O₃ bicrystals with an Y-ZrO₂/₂O₃/Y-ZrO₂/₂O₃/Y-ZrO₂intermediate layer, prepared at two different temperatures, werestudied.Recry stallization of the intermediate layers occurred during thesolid phase intergrowth of the ₂O₃ bicrystalsparts and only an Y-ZrO₂ layer was found as intermediatelayer. The misorientation between the consecutive Y-ZrO₂grains was less than 1.5°. Misfit dislocations and atomic height stepsdecorate the Y-ZrO₂/₂O₃interface.     

Raman characterizations and structural properties of the binary TeO2?WO3, TeO2?CdF2 and ternary TeO2?CdF2?WO3 glasses

The Raman spectroscopy technique was used to characterize the microstructure and the crystallization properties of the as‐cast and heat‐treated binary TeO₂ WO₃, TeO₂ CdF₂ and ternary TeO₂ CdF₂ WO₃ glasses and glass ceramics. The results were compared with those obtained by using the X‐ray diffraction technique. The effect of the WO₃ and CdF₂ contents on the TeO₂ glass network and the intensity ratios of the deconvoluted Raman peaks were determined. The shifts in the Raman band wavenumbers and the intensity values for each band were investigated. The Raman results indicated that the glasses were mainly formed by the [TeO₄] and [TeO₃] units. The [TeO₄] units convert to [TeO₃] units with the addition of WO₃ and CdF₂ into tellurite glasses. All the crystalline phases such as α‐TeO₂, δ‐TeO₂ and γ‐TeO₂ existing in the TeO₂ WO₃, TeO₂ CdF₂ and TeO₂‐ WO₃ CdF₂ glasses were determined. The transformation of the metastable γ‐TeO₂ phase into stable α‐TeO₂ was observed for the (1 − x)TeO₂ xWO₃ (where x = 0.15, 0.20, 0.25), 0.90Te₂ 0.10CdF₂, the 0.85TeO₂ 0.10CdF₂ 0.05WO₃ and 0.80TeO₂ 0.10CdF₂ 0.10WO₃ glasses, and the transformation of the metastable δ‐TeO₂ phase into the stable α‐TeO₂ was also observed for the TeO₂ CdF₂ WO₃ glass system. In addition, an unidentified phase formation, labeled ε, was determined. Copyright © 2009 John Wiley & Sons, Ltd.     

Effect of some additions on the sinterability and magnetic properties of barium hexaferrite

The effect of additions on the densification of previously prepared stoichiometric barium hexaferrite, during the initial and intermediate stages of sintering, as well as on the coercivity and remanence were studied. The effect of non-stoichiometry, SiO₂, Al₂O₃, Cr₂O₃, TiO₂, SnO₂, MnO₂, MgO, NiO and Bi₂O₃ is included.While SiO₂ and Bi₂O₃ form liquid phases that increase the density, Al₂O₃, Cr₂O₃ and MnO₂ form a limited solid solution and are generally beneficial when added in the proper amounts. At 1300 SiO₂ up to 0.55% and Al₂O₃ up to 1% gave better magnetic properties. On the other hand addition of TiO₂, MgO, NiO or SnO₂ has a deleterious effect.     

Electromotive force of a COCO2 sensor in COCO2H2H2O atmospheres and simultaneous determination of partial pressures of CO and CO2

The electromotive force (EMF) of the COCO₂ sensor using Na₂CO₃ and NASICON (Na₃Zr₂Si₂PO₁₂) as solid electrolytes has been examined in COCO₂Ar atmospheres. The EMF is related to the partial pressures of CO and CO₂ and proportional to log(P²_CO2P⁻¹_CO). The simultaneous use of the oxygen sensor of stabilized zirconia gives the EMF proportional to log(P_CO2P⁻¹_CO). The EMF's of two sensors permit to determine individually partial pressures of CO and CO₂. The existence of H₂ with high concentration does not affect the EMF's. This fact proves the applicability of the two-sensor system to the monitoring and the controlling of reducing atmospheres in industrial processes.     

The system Na2CO3–CaCO3–MgCO3 at 6 GPa and 900–1250°C and its relation to the partial melting of carbonated mantle

In order to constrain the Na₂CO₃–CaCO₃–MgCO₃ T–X diagram at 6?GPa in addition to the binary and pseudo-binary systems we conducted experiments along the Na₂CO₃–Ca_0.5Mg_0.5CO₃ join. At 900–1000°C, melting does not occur and isothermal sections are presented by one-, two- and three-phase regions containing Ca-bearing magnesite, aragonite, Na₂CO₃ (Na₂) and Na₂(Ca_1–0.9Mg_0-0.1)_3-4(CO₃)_4-5 (Na₂Ca_3-4), Na₄(Ca_1–0.6Mg_0–0.4)(CO₃)₃ (Na₄Ca), Na₂(Ca_0-0.08Mg_1–0.92)(CO₃)₂ (Na₂Mg) phases with intermediate compositions. The minimum melting point locates between 1000°C and 1100°C. This point would resemble that of three eutectics: Mgs–Na₂Ca₃–Na₂Mg, Na₂Mg–Na₂Ca₃–Na₄Ca or Na₂Mg–Na₄Ca–Na₂, in the compositional interval of [45Na₂CO₃·55(Ca_0.6Mg_0.4)CO₃]–[60Na₂CO₃·40Ca_0.6Mg_0.4CO₃]. The liquidus projection has seven primary solidification phase regions for Mgs, Dol, Arg, Na₂Ca₃, Na₄Ca, Na₂ and Na₂Mg. The results suggest that extraction of Na and Ca from silicate to carbonate components has to decrease minimum melting temperature of carbonated mantle rocks to 1000–1100°C at 6?GPa and yields Na-rich dolomitic melt with a Na# (Na₂O/(Na₂O?+?CaO?+?MgO))?≥?28?mol%.     

Studies on partially oxidised one-dimensional bis(oxalato)platinate salts containing divalent cations

The preparation and electrical conduction properties of the isostructural one-dimensional conductors Ni_0.84[Pt(C₂O₄)₂]·6H₂O(Ni-OP) and Mn_0.81[Pt(C₂O₄)₂]·6H₂O(Mn-OP) are described. Ni-OP exhibits a similar tem dependence of conductivity to the isostructural compounds Co_0.83[Pt(C₂O₄)₂]·6H₂O(Co-OP) and Zn_0.81[Pt(C₂O₄)₂]·6H₂O whereas the behaviour of Mn-OP is rather like that of K₂[Pt(CN)₄]Br_0.3·3H₂O. These differences are discussed in terms of the variation from compound to compound of the critical temperature for the formation of the “non-Peierls” superstructure (T_c) and the temperature at which the CDW/PD on adjacent conducting chains undergo three-dimensional ordering (T_3D). The variation of thermopower with temperature for Co-OP and Mg_0.82[Pt(C₂O₄)₂]·6H₂O is reported and related to the conduction properties and phase changes which have been observed for these compounds. For the isostructural series M_0.8[Pt(C₂O₄)₂]·6H₂O (M = Mg, Mn, Co, Ni or Zn) the variation of (T_3D) from compound to compound is related to differences in the polarizing power of the cations.     

Facile synthesis of flower-like α-Fe2O3/ZnFe2O4 architectures with self-assembled core-shell nanorods for superior TEA detection

Uniform flower-like α-Fe₂O₃ architectures with self-assembled core-shell nanorods are constructed and successfully prepared via the facile process. The concentration of Fe salt plays a great significance for morphological evolution from nanorods to self-assembled microflowers. Flower-like α-Fe₂O₃/ZnFe₂O₄ consisting of α-Fe₂O₃ core and ZnFe₂O₄ shell nanorods are derived from FeOOH/ZIF-8 precursors. The detailed studies reveal that the tunable growth of ZIF-8 nanoparticles on three-dimensional FeOOH microflowers at room temperature and the availble calcination regulation are responsible for the formation of core-shell Fe₂O₃/ZnFe₂O₄ composites. The highest response value of flower-like α-Fe₂O₃/ZnFe₂O₄ architectures to 100 ppm triethylamine (TEA) has been improved to 141 at 280 °C, which is calculated to be 6.2 times compared with flower-like α-Fe₂O₃ architectures (22.7). The enhanced gas-sensing mechanism of α-Fe₂O₃/ZnFe₂O₄ composites can be attributed to the typical microflowers structures, the large specific surface area, the effective heterojunctions between α-Fe₂O₃ core and ZnFe₂O₄ shell, and the improved electron transfer process.     

Physical and electrical properties of band-engineered SiO2/(TiO2) x (SiO2)1−x stacks for nonvolatile memory applications

In our study, the physical properties of (TiO₂) _x (SiO₂)_1?x , including band-gap, band-offset, and thermal stability and the electrical properties of band-engineered SiO₂/(TiO₂) _x (SiO₂)_1?x tunnel barrier stacks, including the tunneling current and charge-trapping characteristics for applications to nonvolatile memory devices were investigated. It was observed that the band-gap and band-offset of (TiO₂) _x (SiO₂)_1?x can be controlled by adjustment in the composition of the (TiO₂) _x (SiO₂)_1?x films. Ti-silicate film with TiO₂:SiO₂ cycle ratio of 1:5 was maintained in an amorphous phase, even after annealing at 950 °C. The tunneling current of the band-engineered SiO₂/(TiO₂) _x (SiO₂)_1?x stacked tunnel barrier was larger than that of a single SiO₂ barrier under a higher external bias, while the tunneling current of a SiO₂/(TiO₂) _x (SiO₂)_1?x stacked tunnel barrier under a lower external bias was smaller. Charge-trapping tests showed that the voltage shift for SiO₂/(TiO₂) _x (SiO₂)_1?x is slightly larger than that for single SiO₂.     

Reaction mechanism of elemental mercury oxidation to HgSO4 during SO2/SO3 conversion over V2O5/TiO2 catalyst

Experiments and density functional theory calculations were conducted to uncover the reaction chemistry of Hg⁰ oxidation during SO₂/SO₃ conversion over V₂O₅/TiO₂ catalyst. The results show that SO₂ promotes Hg⁰ oxidation over V₂O₅/TiO₂ catalyst with the assistance of oxygen. The promotional effect is dependent on the reaction temperature, and is associated with the bimolecular reaction between Hg⁰ and SO₃ over V₂O₅/TiO₂ catalyst. SO₂ can be oxidized to SO₃ which has high oxidation ability for Hg⁰ oxidation. SO₂/SO₃ conversion proceeds through a three-step reaction process in the sequence of SO₂ adsorption → SO₂ oxidation → SO₃ desorption. SO₂ oxidation presents an activation energy barrier of 223.84 kJ/mol. HgSO₄ species is formed from the bimolecular reaction between Hg⁰ and SO₃ over V₂O₅/TiO₂ catalyst. Hg⁰ oxidation by SO₃ over V₂O₅/TiO₂ catalyst occurs through three reaction pathways, which are energetically favorable for HgSO₄ formation. SO₂* → SO₃* is identified as the rate-determining step of HgSO₄ formation. During Hg⁰ oxidation by SO₃ over V₂O₅/TiO₂ catalyst, HgSO₄ desorption is a highly endothermic reaction process and requires a higher external energy. The proposed skeletal reaction network can be used to well understand the reaction mechanism of Hg⁰ oxidation during SO₂/SO₃ conversion over V₂O₅/TiO₂ catalyst.     

Ohmic-rectification conversion that is tuned using H2O2 for enhanced rectification and optoelectronic performance in MoS2/ZnO nanorod devices

The characteristics of a p–n junction that consists of MoS₂ thin films and ZnO nanorods grown on heavily-doped n-type Si substrate are reported. The current–voltage characteristics for MoS₂/ZnO nanorod devices exhibit ohmic conduction. The measured current is limited by thermionic emission in MoS₂/ZnO nanorod devices that are treated with H₂O₂. H₂O₂ treatment results in the modification of the MoS₂–ZnO interface, so the rectification performance for MoS₂/ZnO nanorod devices is improved. H₂O₂ treatment also increases the responsivity of MoS₂/ZnO nanorod devices to solar irradiation. This phenomenon is caused by induced ohmic-rectification conversion due to H₂O₂ treatment.