Catalytic oxidation of VOCs on Au/Ce-Ti-O

Ce_xTi_1−xO₂ oxides have been synthesised by sol–gel method with x varying from 0 to 0.3 and characterised by XRD and TPR. The structure of oxides changes with the Ce/Ti molar ratio. The presence of ceria in Ce-Ti oxides inhibits the phase transition from anatase to rutile. When x = 0.3 (Ce_0.3Ti_0.7O₂ sample), the solid presents an amorphous state. The TPR results indicate that the presence of Ti enhances the reducibility of cerium oxide species. Catalytic oxidation of propene is investigated on Ce-Ti oxides and the better conversion is obtained with Ce_0.3Ti_0.7O₂ but the CO₂ selectivity reaches 63% at 400 °C. Gold is then deposited on theses oxides to improve the catalytic activity. On the basis of characterisation data (H₂ TPR), it has been suggested that gold influences the reduction of the Ce-Ti oxide support and the catalytic activity to the propene oxidation. Thus, Au/Ce-Ti-O system catalysts are promising catalysts for propene oxidation.     

Novel synthesis of cerium hexaboride by hexamine route

An endeavor has been made to prepare cerium hexaboride using a mixture of cerium nitrate, boron trioxide, and hexamine as a fuel burning at a relatively low temperature (500°C). The product was characterized by X-ray diffraction (XRD), FT-IR, TGA/DTA, SEM, and TEM. The upshot of the exploration exemplifies that CeB6 with a crystallite size of about 50 nm can be beneficially prepared. Some impurities are also perceived with the pure compound, which embodies the presence of lower valence cerium borides.      

Alumina supported Mo–V–Te–O catalysts for the ammoxidation of propane to acrylonitrile

The effect of Te addition over Mo–V–O catalysts supported on alumina is discussed for the ammoxidation of propane to acrylonitrile. Catalyst composition and atmosphere of activation are evaluated. Catalysts are characterized before and after catalytic reaction by XPS, XRD and in situ Raman spectroscopies. The absence of Te in catalysts formulation and the presence of a high amount of vanadium induce the presence of V⁵⁺ species and the formation of V₂O₅ oxide; associated with a decrease in acrylonitrile selectivity. The presence of Mo-based polyacids structures decreases the selectivity to acrylonitrile. V⁵⁺ sites are responsible of propane activation and of the subsequent -H abstraction to form the intermediate propylene. Then, a Mo–V rutile-like structure in which vanadium species are reduced as V⁴⁺, is responsible for nitrogen insertion and acrylonitrile formation. The formation of such structure is favoured when Te is added to catalysts and is promoted during propane ammoxidation.     

Near infrared emitting Cr3+ doped Zn3Ga2Ge2O10 long persistent phosphor for night vision surveillance and anti-counterfeit applications

The Cr³⁺ doped Zn₃Ga₂Ge₂O₁₀ long persistent phosphor materials were synthesized by solid state reaction method. The crystal structure of the synthesized phosphors are cubic with space group Fd3m. The band gap of the undoped host is about 4.48 eV. The materials show three photoluminescence excitation bands peaked at 260 nm, 412 nm and 580 nm. Due to the broad excitation band, the phosphors can be excited by UV light or visible light or sunlight. The phosphors shows a photoluminescence emission band peaked at 698 nm when excited by UV light. The afterglow emission shows a broad emission band with maximum at 700 nm. The detection of NIR light from the sample was observed by Night Vision Monocular for 24 h after switch off the excitation source. A mechanism is introduced to describe afterglow phenomenon and trap depth was calculated from thermoluminescence curve. As the material emit NIR persistent light, it was used as a secret light source for night vision devices. The developed material was used for tagging, tracking and locating purposes in defence application. The acrylic based paint was prepared to develop long persistent near infrared (NIR) paint, which can be coated on combat vehicle, ship, weapon, helmet, cloth, tent, rock for defence application. The NIR security ink was prepared and demonstrated to prevent counterfeit. Encryption and decryption method of confidential information was presented by using NIR security ink.     

Microstructural analyses of artificial ageing in 5 commercially and non-commercially available Zirconia dental implants

ObjectivesThe presentin vitro study evaluated the effect of LTD (Low Temperature Degradation) on microstructural properties, phase transformation and micro-crack formation of 5 commercially and non-commercially available Zirconia dental implant systems.MethodsAccelerated ageing at 134 °C and 2 bar pressure for 30 h was completed. Focused Ion Beam-Scanning Electron Microscopy (FIB/SEM), X-ray diffraction (XRD) and cathodoluminescence quantified phase transformation and micro-crack formation.ResultsTransformation of the tetragonal grains towards the monoclinic symmetry was observed in all systems. The highest depth was measured in non-commercial TAV dental with the largest grain size (8.7 μm). A micro-cracked layer was associated with the transformation zone. The ageing-related micro-crack formation was parallel to the surface for all groups and was deepest for the non-commercial TAV dental with the largest grain size (7.4 μm).ConclusionLTD following in vitro ageing using an autoclave was minimal for all implant systems investigated.     

Sol gel derived MnTi doped Co2 W-type hexagonal ferrites: Structural,physical, spectral and magnetic evaluations

W-type BaSr Co₂ hexaferrites doped with Mn and Ti of the following composition Ba_0.5Sr_0.5Co₂Mn_xTi_xFe_16-2xO₂₇ (x = 0.00, 0.50, 1.00, 1.50, 2.00, 2.50) were synthesized by sol-gel auto ignition method. The structure, phase, spectral bands, microstructure, and magnetic behaviors of the MnTi doped BaSr Co₂ W-type ferrites were determined using XRD, FTIR, FESEM, and VSM respectively. Structural and physical parameters such as lattice parameters ‘a’ and ‘c’, crystallite size, cell volume, micro strain, porosity, bulk and X-ray density of the MnTi doped BaSr Co₂ W-type hexaferrites were evaluated. The detailed and refined structural properties were determined using the Rietveld refinement of the MnTi doped BaSr Co₂ W-type hexagonal ferrites. MAUD software was used for the refinement of the MnTi doped BaSr Co₂ W-type hexagonal ferrites patterns. Rb, Rwp and Rexp values were found in the range of 10–19 for MnTi doped BaSr Co₂ W-type hexagonal ferrites. The force constants at respective sites were also investigated through FTIR studies. FESEM images showed the hexagonal shape of the MnTi doped hexaferrites. Magnetic properties were estimated from the hysteresis loops recorded by VSM. The magnetic properties were decreased with the MnTi doping. However, anisotropic field was also found to be decreased with MnTi doping. This might be due to the ionic radii and nonmagnetic substitution of Ti in BaSr Co₂ W-type hexagonal ferrites. The low coercivity values of these ferrites suggest the use of MnTi doped BaSr Co₂ W-type ferrites for microwave absorption, memory devices and magnetic radar absorbing materials (MRAMs) in high frequency regime.     

Ti-6Al-7Nb合金随温度的组织与性能演变

为揭示Ti-6Al-7Nb合金随热处理温度的不同,显微组织、力学性能及相组成的变化规律,研究了合金在650℃-1030℃热处理空冷条件下的组织演变,进行室温力学性能测试与XRD分析。结果表明：650℃属于时效温度,热加工得到的原β转变组织中析出细小的α相,合金的强度和弹性模量有所提高。700℃-850℃之间进行热处理,可以获得良好的综合性能,满足相关标准要求。合金弹性模量处于94-100 GPa。950℃-1030℃温度范围内,随着温度的升高,由于二次针状α相的析出,或者生成α"相,呈现强度上升,塑性下降的趋势。650℃、850℃两个温度热处理后,Ti-6Al-7Nb合金的XRD图谱未出现β相的衍射峰,均为α相的衍射峰。1030℃热处理后,α"相具有较强的(002)、(101)衍射峰,其它晶面的衍射峰能量很弱。合金弹性模量达最大值108GPa。通过金相观察,推算Ti-6Al-7Nb合金α+β→β转变的开始温度处于900℃-920℃,终了温度处于1010℃-1030℃。     

Comprehensive study on corrosion protection properties of Al2O3, Cr2O3 and Al2O3–Cr2O3 ceramic coatings deposited by plasma spraying on carbon steel

In this study, individual Al₂O₃ and Cr₂O₃ coatings and Cr₂O₃-25, 50, 75 wt% Al₂O₃ composite coatings were applied on carbon steel by atmospheric plasma spraying method. Corrosion experiments were performed on as-sprayed and epoxy resin sealed coatings including potentiodynamic polarization, electrochemical impedance spectroscopy and long-term immersion in 3.5 wt% NaCl solution. Phase composition and microstructure of the coatings were investigated by x-ray diffraction, optical microscopy and scanning electron microscopy, before and after the corrosion experiment. The results showed that the Cr₂O₃ coating exhibited the best corrosion resistance, due to the densest microstructure and highest adhesion strength. The Cr₂O₃-25 wt% Al₂O₃ coating had the highest interconnected porosities and thus had the least corrosion resistance compared to other coatings. In general, the as-sprayed coatings induced a maximum increase of 3.93 times the polarization resistance (R_p) in the polarization experiment and a 3.5 times increase in the charge transfer resistance (R_ct) in the EIS experiment, which was not significant. Stresses caused by increased volume of corrosion products in the coating-substrate interface resulted in the spallation of Cr₂O₃-25, 50 wt% Al₂O₃ coatings from the substrate over long-term of immersion. The adhesion strength of the coatings was a determining criterion for the long-term durability of the coatings. The sealing treatment resulted in a significant increase in R_p and R_ct.