Reactions of benzophenone imine complex [Tp(NH═CPh2)(PPh3)Ru–Cl] with alkyne and dimerization of terminal alkynes in the presence of Et3N

Treatment of benzophenone imine complex [Tp(PPh₃)(NH═CPh₂)Ru–Cl] (1) {Tp═HB(pz)₃, pz = pyrazolyl} with 4-Ethynyltoluene in the presence of H₂O in distilled ethanol afforded the chelate alkenyl ketone complex [Tp(PPh₃)RuCCH₂(p-MeC₆H₄)═CHC(O)(p-MeC₆H₄)] (2). On the other hand, reaction of 1 with HC≡C(O)OR₁ in R₂OH produced the chelate vinyl ether complexes [Tp(PPh₃)Ru–C(OR₂)═CHC(O)OR₁] (3a, R₁ = Me, R₂ = Me; 3b, R₁ = Et, R₂ = Me; 3c, R₁ = Et, R₂ = Et; 3d, R₁ = Me, R₂ = Et), respectively. Preliminary results on the catalytic activity of 1 are also presented. Intriguingly, complex 1 is found to catalyze the dimerization of terminal alkynes HC≡CR (R = p-MeC₆H₄, C(O)OCH₃) in the presence of Et₃N to give eynes. The structures of 3c and 3d have been determined by X-ray diffraction analysis.     

Preparation and characterization of MnOOH and β-MnO2 whiskers

MnOOH and β-MnO₂ whiskers are obtained for the first time in our work. MnOOH whiskers are chemically synthesized in the presence of cationic surfactant cetyltrimethylammonium bromide (CTAB). The product is obtained under extremely low surfactant concentrations under basic conditions, using MnSO₄·H₂O as the manganese source and ethylamine as the alkali source. After the subsequent heat treatment of MnOOH at 300 °C for 1 h, β-MnO₂ whiskers retaining the similar morphologies are obtained. Powder X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and thermogravimetry analysis (TGA) are used to characterize the products.     

Grain-boundary segregation and precipitates in La2O3 and Pr2O3 doped SnO2·CoO-based varistors

Structural heterogeneities in SnO₂·CoO-based varistors were analyzed by transmission electron microscopy. In SnO₂·CoO-based system doped with La₂O₃ and Pr₂O₃ two kinds of precipitate phases at grain boundary region were found. Using energy dispersive spectrometry they were found to be Co₂SnO₄ and Pr₂Sn₂O₇, presenting a defined crystalline structure. It was also identified that such precipitate phases are mainly located in triple-junctions of the microstructure. HRTEM analysis revealed the existence of other two types of junctions, one as being homo-junctions of SnO₂ grains and other due to twin grain boundaries inside the SnO₂·CoO grain. The role of these types of junction in the overall nonlinear electrical features is also discussed.     

Nuclear γ-resonance spectra and local surrounding of 121Sb and 129I atoms in CuI-PbI2-As2Se3 and CuI-SbI3-PbI2-As2Se3 films

The local surrounding of copper, antimony, and iodine atoms in multicomponent chalcogenide films CuI-PbI₂-As₂Se₃ and CuI-SbI₃-PbI₂-As₂Se₃ deposited from solutions of chalcogenide glass in n-butylamine has been studied by the Mössbauer spectroscopy method on ¹²¹Sb and ¹²⁹I isotopes. It was established that antimony atoms are in the Sb (III) state, where each antimony atom is surrounded by three selenium atoms. Copper atoms are in the Cu (I) state and are surrounded by iodine atoms. The local surrounding of copper, antimony, and iodine atoms in chemically deposited chalcogenide films is analogous to the local surrounding of atoms in the initial chalcogenide glass.     

Imaging and chemical probing on the atomic scale: reconstruction and dynamics of the systems O2/Rh and NO2–H2/Pt

This paper presents two case studies of adsorbate-induced surface reconstruction, on the one hand, and dynamical reaction imaging along with local chemical probing, on the other hand. The first one deals with the oxygen-induced reshaping of 3D Rh crystals. Field ion microscopy (FIM) was applied to image in real-space the change from a nearly hemispherical shape in the absence of oxygen toward a polyhedral one in the presence of oxygen. Shape transformation occurs at temperatures of 380–550 K and is associated with the appearance of facets with {111} and {001} orientation. The only high-index planes present in the polyhedral form are of {137} symmetry. (1×2) and (1×3) missing-row reconstructions appear in the {113} and {011} planes. The polyhedral form has also been imaged under in situ conditions of the oxygen–hydrogen reaction on Rh at 505 K. The second case study deals with kinetic non-linearities occurring in the NO₂ reaction with hydrogen on the surface of a 3D Pt crystal reconstructed to a top- and edge-truncated pyramid. The reaction was found to ignite in the {012} corner planes of the crystal. One-dimensional wavefronts were subsequently observed to move along the 211 zone lines. These studies were performed by video-FIM and could be correlated with a local chemical analysis by time-of-flight mass spectrometry of ionised species. The mass spectrum provided information on water product (H₂O⁺ and H₃O⁺) and NO intermediate formation. Strong fluctuations in the NO ₂ ⁺ current indicated the occurrence of NO₂ surface diffusion. These species are most likely responsible for the field ion image formation.     

Hydration kinetics and microstructure development of normal and NaAlO2-activated Al-doped β-C2S pastes

Sodium aluminate (NaAlO₂) can be used to accelerate hydration of Portland cements. Here, we compare the use of NaAlO₂ solutions with deionized water on the hydration of Al-doped β-C₂S. The microstructure development of hydration product C-S-H obtained from hydrated Al-doped β-C₂S was investigated. NaAlO₂ significantly improved the hydration kinetics of Al-doped β-C₂S due to the enhancement in the precipitation of calcium hydroxide and stimulation of C-(A)-S-H nucleation and increased the early-age mechanical strength of Al-doped β-C₂S pastes. NaAlO₂ promoted the incorporation of Al in the C-(A)-S-H structure and accelerated the formation of C-(A)-S-H phases containing tetra-, penta- and hexa-coordinated Al in its composition. The alkali cations modified the electrostatic equilibrium of the C-(A)-S-H, thus promoting the development of the nano-mechanical properties.     

Electrodeposition of PbO2 and Bi–PbO2 on Ebonex

Electrodeposition of PbO2 and Bi–PbO2 on Ebonex was carried out under various conditions, and the surfaces and coating/substrate interfaces examined by SEM, XPS and SIMS. Excellent adhesion to Ebonex was obtained with both crystalline and amorphous surfaces. Low plating temperatures resulted in dark grey, bright PbO2 and black, mirror-like Bi–PbO2 surfaces. Extrapolation of electrode lifetime test data indicated corrosion rates of 716 m yr–1 for PbO2 and 158 m yr–1 for Bi–PbO2.     

Physical Properties and Hydration Resistance of CeO2—and CeO2／Fe2O3—Bearing Dolomite Refractory Products

Dolomite refractory products with excellent hydration resistance have been produced by using CeO2-and CeO2/Fe2O3-bearing dolomite clinkers,Their physical properties as well as hydration resistance have been investigated,The addition of CeO2 has little harmful effect on the high temperature properties of dolomite refractory products such as hot MOR and slag resistance,And the shelf lives of the dolomite refractory products containing CeO2 and CeO2/Fe2O3 additions at the same condition are two times that of the common dolomite refractory produt.The dolomite refractory product containing CeO2/Fe2O3 combination possesses the best hydration resistance,but gives poor slag resistance.     

Structural parameters and oxygen ion conductivity of Y2O3–ZrO2 and MgO–ZrO2 at high temperature

The oxygen ion conductivity of zirconia-based solid electrolytes doped with 8 mol% Y₂O₃–ZrO₂ (YSZ) and 9 mol% MgO–ZrO₂ (Mg-PSZ) at high temperature was investigated in terms of their thermal behavior and structural changes. At room temperature, YSZ showed a single phase with a fluorite cubic structure, whereas Mg-PSZ had a mixture of cubic, tetragonal and some monoclinic phases. YSZ exhibited higher ionic conductivity than Mg-PSZ at temperatures from 600 °C to 1250 °C because of the existence of the single cubic structure and low activation energy. A considerable increase in the conductivity with increasing temperature was observed in Mg-PSZ, which showed higher ionic conductivity than YSZ within the higher temperature range of 1300–1500 °C. A monoclinic-to-tetragonal phase transformation was found in Mg-PSZ and the lattice parameter of the cubic phase increased at 1200 °C. The phase transformation and the large lattice free volume contributed to the significant enhancement of the ionic conductivity of Mg-PSZ at high temperatures.     

Synthesis and Metal‐ion Binding Properties of New N2S4O2‐ and N2S5O2‐Donor Macrocycles

Abstract

Synthetic procedures for new mixed‐donor macrocycle compounds were reported. The macrocyclic compounds were used in solvent extraction metal picrates such as Ag⁺, Hg²⁺, Cd²⁺, Zn²⁺, Cu²⁺, Ni²⁺, Mn²⁺, Pb²⁺, and Co²⁺. The metal picrate extractions were investigated at 25±0.1°C with the aid of UV‐visible spectrometry. It was found that 6,7,9,10,12,13,23,24‐octahydro‐19H,26Hdibenzo[h,t](1,4,7,13,16,22,10,19) dioxatetrathiadiazasiclotetracosine‐20,27(21H,28H)‐dione showed selectivity towards Ag⁺, Hg²⁺, and Cd²⁺ among the other metals. The extraction constants (Log K_ex) and complex compositions were determined for the Ag⁺ and Hg²⁺ complexes for this compound and 9,10,12,13,23,24,26,27,29,30‐decahydro‐5H,15H‐dibenzo‐[h,w][1,4,7,13,16,19,25‐,10,22] dioxapentathiadiazacycloheptacosine‐6,16(7H,17H)‐dione.     

The CO2–CeO2 interaction and its role in the CeO2 reactivity

The interaction between CO₂ and CeO₂ and its role in the surface reactivity of alumina-supported cerium oxide has been studied by programmed thermodesorption (TPD) of CO₂ and FTIR spectroscopy. The performance of Ce/Al₂O₃ systems was then analyzed for the propane oxidation in presence of CO₂. The results have shown that the catalytic activity decreased when carbonate species are formed at the surface of CeO₂. This behavior was attributed to the presence of CO₂ from three different sources: contamination before use, during the handling of the samples, contamination proceeding from the reactants and from CO₂ produced by the reaction itself. This revised version was published online in July 2006 with corrections to the Cover Date.     

Composite materials with ZrO2–TiO2 matrix and ZrO2 containing ceramic fibres

Abstract

The aim of the work reported in the present paper was to obtain composites consisting of a ZrO₂–TiO₂ matrix reinforced with ceramic fibres containing 12 wt-% ZrO₂, which are resistant to temperatures higher than1500°C. The resulting ceramic matrix consisted of 95 wt-% ZrO₂, partially stabilised with CaO, and 5 wt-% rutile TiO₂. A ceramic fibre content of 0·82 vol.-% was used and for the matrix, several grades of ZrO₂ partially stabilised with CaO were explored, prepared by dry and wet grinding for various grinding periods. Composites were prepared by uniaxial die pressing at 350 MPa and sintered at two temperatures: 1360°C for 1 h and 1500°C for 3 h. The resulting composites showed the following range of properties: total drying and firing shrinkage 0·4–3·3%; apparent density 3·51–3·96 g cm^-3; porosity 25–34%; water absorption 6–10%; bend strength 12–43 MPa. The optimum ZrO₂ grades were determined based on physical and mechanical properties, and on structural determinations carried out by thermodifferential and thermogravimetric analyses, X-ray diffraction (XRD), and scanning electron microscopy (SEM). SEM evaluation illustrated the increase in average size of crystallites typical of ZrTiO₄ solid solution as a function of temperature, from 2 μm at 1360 up to 14 μm at 1600°C, and of their tendency to sinter.     

Sintered ZrO2–TiO2 ceramic composite and its mechanical appraisal

This work mainly considered the effect of different TiO₂ additions and of sintering temperatures on the structural change, densification and mechanical properties of ZrO₂–TiO₂ ceramic composites obtained by cold compaction and subsequent sintering. The results demonstrated that the structural transformation happens from pristine monoclinic zirconia into tetragonal zirconia, amount of cubic phase in as-obtained ZrO₂–TiO₂ specimens could be distinguished as well. The increasing concentration of TiO₂ addition facilitated lower the sintering temperature and densification of ZrO₂ matrix. The grain growth and bulk density of ZrO₂–TiO₂ ceramic composites varied with the sintering temperatures and dopant concentrations. Full evaluation of the role of TiO₂ addition and sintering temperature on the mechanical properties of ZrO₂–TiO₂ samples was carried out in terms of Vickers hardness, flexural strength and fracture toughness. In particular, the ZrO₂ matrix with a value of 5 wt % TiO₂ generated the desired flexural strength and fracture toughness at the sintering temperature of 1400 °C.     

Stability and excitation of potassium promoter in iron catalysts – the role of KFeO2 and KAlO2 phases

The kinetics of the NO SCR with propane has been studied on a low‐exchanged Cu‐ZSM‐5 catalyst. The study of the kinetics of individual reaction stages (2‐nitrosopropane isomerization to acetone oxime and reaction of adsorbed acetone oxime with gaseous NO) has shown that the NO reaction with acetone oxime is the rate‐determining stage in the whole chain of transformations leading to the formation of molecular nitrogen in the low‐temperature region below 300 °C. The kinetic analysis of the reaction has revealed that at the temperatures above 300 °C propane plays a more important role. This revised version was published online in July 2006 with corrections to the Cover Date.     

Studies on electroless Ni-P-Cr_2O_3 and Ni-P-SiO_2 composite coatings

本文对化学镀镍及化学镀镍磷基质中SiO2与Cr2O3的共沉积进行了研究。微粒在不断生长的膜层中共沉积引起了新的化学复合镀层的出现,这些复合镀层许多都具有优异的耐磨及耐蚀性能。通过选取镀层合金/复合微粒/金属基体的组分可改进镀层,获得所需的性能,以满足特别的需求。在对这些复合镀层的应用需求正在迫近与增长的同时,其市场正在迅速扩张。本文开发出了一种合适的复合化学镀镍液,并通过维氏硬度法对化学复合镀镍层进行了表征。采用动电位极化及交流阻抗法测定了镀层的Taber耐磨性能及耐蚀性能。采用SEM及XRD对复合镀层的表面形貌进行了分析。     

Synthesis and characterization of corrosion-resistant and biocompatible Al2O3–TiB2 nanocomposite films on pure titanium

Alumina is widely used as a coating on a metal implant due to its favorable mechanical and biological properties. In this research, in order to improve mechanical and biological properties of alumina, a composition of nanoparticles of alumina (instead of microparticles) and titanium diboride micro powder is introduced. The atmospheric plasma spray (APS) technique was applied to deposit Al₂O₃–TiB₂ on the pure titanium substrate. The properties of Al₂O₃–TiB₂ nanocomposite coatings with various weight percent of TiB₂ (20, 30 and 40 wt%) were experimentally studied. The characteristics of nanocomposite films of TiB₂ (20, 30 and 40 wt%) were analyzed using Field Emission Scanning Electron Microscopy (FE-SEM), energy dispersive electron spectroscopy (EDX) and X-Ray Diffraction (XRD) tests. The XRD spectra exhibited that in addition to alumina and titanium diboride, the films contained titania. Thickness and morphology of the films were calculated from FE-SEM images and the thickness of the optimized coating (Al₂O₃-30 wt% TiB₂) was about 30–45 μm. Also, the roughness, corrosion resistance, hardness and cytotoxicity (MTT) tests were studied. The highest of hardness and roughness of the samples were obtained from Al₂O₃-30 wt% TiB₂. According to the obtained results from the polarization test, Al₂O₃-30 wt% TiB₂ coating had the highest corrosion resistance (222558.9962 Ω cm²). Therefore, the toxicity of Al₂O₃-30 wt% TiB₂ was investigated as the optimized coating and the results confirmed its non-toxicity and biocompatibility.     

Influence of sol–gel derived ZrO2 and ZrC additions on microstructure and properties of ZrB2 composites

ZrB₂ powder was coated with 5% ZrOC sol–gel precursor and sintered by SPS. Relative densities >98% were achieved at 1800 °C with minimal grain growth and an intergranular phase of ZrC. Carbon content in the precursor determined the type of reinforcing phase and porosity of the sintered composites. XRD, SEM and EDS studies indicated that carbon deficiency resulted in ZrO₂ retention, improving ZrB₂ densification with oxide particle reinforcement. Excess carbon resulted in ZrC formation as the reinforcing phase, but could yield porosity and residual carbon at grain boundaries. These two types of ZrB₂ composites displayed different densification and microstructural evolution that explain their contrasting properties. In the extreme oxidative environment of oxyacetylene ablation, the composites with ZrC-C maintained superior leading edge geometry; whereas for mechanical strength, a bias towards the residual ZrO₂ content was beneficial. This highlighted the sensitivity of processing carbon-precursors in the initial sol–gel process and the carbon content in ZrB₂-based composite systems.     

Microwave hybrid sintering of Al2O3 and Al2O3–ZrO2 composites,and effects of ZrO2 crystal structure on mechanical properties,thermal properties,and sintering kinetics

Structural ceramics such as Al₂O₃ and Al₂O₃–ZrO₂ composites are widely used in harsh environment applications. The conventional sintering process for fabrication of these ceramics is time-consuming method that requires large amount of energy. Microwave sintering is a novel way to resolve this problem. However, to date, very limited research has been carried out to study the effects of different ZrO₂ crystal structures on Al₂O₃–ZrO₂ composites, especially on the sintering kinetics, when fabricated by microwave sintering.The microwave hybrid sintering of Al₂O₃ and Al₂O₃–ZrO₂ composites was performed in this study. Tetragonal zirconia and cubic zirconia were used as two different reinforcements for an α–alumina matrix, and the mechanical and thermal properties were studied. It was found that Al₂O₃ experienced a remarkable increase in fracture toughness of up to 42% when t-ZrO₂ was added. Al₂O₃–c-ZrO₂ also showed increased fracture toughness. The sintering kinetics were also thoroughly investigated, and the average activation energy values for the intermediate stage of sintering were estimated to be 246 ± 11 kJ/mol for pure Al₂O₃, 319 ± 71 kJ/mol for Al₂O₃–c-ZrO₂, and 342 ± 77 kJ/mol for Al₂O₃–t-ZrO₂. These values indicated that the activation energy was increased by the addition of either type of ZrO₂, with the highest value shown by Al₂O₃–t-ZrO₂.     

Synthesis and properties of hyperbranched polyimides from A2+ B′B2 monomers and A2+ B′B2 + B2 monomers with various comonomer ratios

A series of hyperbranched polyimides were successfully synthesized by A₂ + B??B₂ approach based on 2,4,6-triaminopyrimidine(TAP) and biphenyl dianhydride(BPDA) . The resulting polyimides were characterized by FTIR, SEC/MALLS, NMP, DSC, TGA. The results showed that BPDA-TAP hyperbranched polyimides had poor thermal stability. In accord with this fact, difunctional B₂ comonoer (4,4??-oxydianiline(ODA))was added into the polymer structure to improve heat resisting property of HBPIs by incorporation. This approach could be described as A₂+ B??B₂ + B₂ or more simply A₂ + B₃ + B₂ copolymerization. Both for the BPDA-TAP-ODA and BPDA-TAP hyperbranched polyimides, the amine-terminated polyimides showed higher glass transition temperature and 10?% weight loss compared with the corresponding anhydride-terminated ones, which can be attributed to the different terminal functional groups and the anhydride residues.