Stress measurement in alumina scales on high temperature alloys using X-ray stress evaluation and laser Raman spectroscopy

The effect of silicon and titanium on the spallation resistance of alumina scales grown on NiCrAlY-type alloys has been investigated using model alloys with different additions of Si or Ti. For this purpose cyclic oxidation experiments have been carried out at temperatures between 950 and 1100° C. After various times stresses in selected Si-doped samples have been determined by X-ray stress evaluation (XSE) at ambient temperature. The compressive stresses in the scales have been found to increase with an increasing oxidation time tending to become constant for long times. The development of stress is affected by the presence of Si. Laser Raman spectroscopy (LRS) has been calibrated for strain measurement using XSE results. Then LRS has been applied for strain measurement at higher temperatures.     

Stress measurement in alumina scales on high temperature alloys using X-ray stress evaluation and laser Raman spectroscopy

The effect of silicon and titanium on the spallation resistance of alumina scales grown on NiCrAlY-type alloys has been investigated using model alloys with different additions of Si or Ti. For this purpose cyclic oxidation experiments have been carried out at temperatures between 950 and 1100 degrees C. After various times stresses in selected Si-doped samples have been determined by X-ray stress evaluation (XSE) at ambient temperature. The compressive stresses in the scales have been found to increase with an increasing oxidation time tending to become constant for long times. The development of stress is affected by the presence of Si. Laser Raman spectroscopy (LRS) has been calibrated for strain measurement using XSE results. Then LRS has been applied for strain measurement at higher temperatures.     

Identification of selective oxidation of TiC/SiC composite with X-ray diffraction and Raman spectroscopy

Open cell 3D titanium carbide/silicon carbide (TiC/SiC) composite was oxidised to titanium oxide/silicon carbide (TiO₂/SiC) following different temperature profiles in a thermal gravimetric analysis (TGA) instrument in continuous air-flow and static air (oven) environments. The TiC oxidation to anatase, starting at temperatures over 450°C, was confirmed by Raman spectroscopy and X-Ray diffraction (XRD). By increasing the temperature, the mass fraction of anatase diminished, while the mass fraction of rutile increased. SiC oxidation started at 650°C when a mixture of TiO₂/SiO₂/SiC could be observed by Raman, XRD and HRTEM.     

SiO-Au法制备硅纳米线

在低真空的CVD系统中直接热蒸发SiO粉末并以金为催化剂在硅衬底上制备出大量长达几十微米的硅纳米线(SiNWs), 通过X 射线衍射谱(XRD)、场发射扫描电子显微镜(FESEM)、透射电子显微镜(TEM)、选区电子衍射仪(SAED)和Raman光谱等技术对硅纳米线进行形貌及结构分析. 实验结果表明, 在不同生长温度下制备得到的硅纳米线质量不同, 其中在700 ℃温区生长的硅线质量最好; 与晶体硅Raman的一级散射特征峰(TO)520.3 cm−1相比, 纳米硅线的Raman特征峰(TO)红移至514.8 cm−1.     

NIR- and VIS-raman spectroscopy of CVD diamond films

Raman spectroscopy is a widely used method for the analysis of CVD diamond layers, because it enables to distinguish between different carbon phases, such as diamond, graphite, amorphous carbon and nanocrystalline carbon, which are all commonly present in CVD diamond films. A comparison of visible Raman spectroscopy and near-infrared Raman spectroscopy applied to CVD diamond layers on various substrates (Si, SiAlON, Au, Pd, Mo, W and cemented carbides) has been carried out with the result that visible Raman spectroscopy can be preferably used for characterizing the diamond quality, but for the detection of non-diamond carbon phases NIR-Raman spectroscopy exhibits certain advantages. The NIR-Raman spectra of diamond on silicon substrates are interfered by thermal activation of the Si.Dedicated to Professor Dr. Dr. h.c. mult. J.F.K. Huber on the occasion of his 70th birthday     

ZnO thin films prepared on titanium substrate by PLD technique at different substrate temperatures

ZnO thin films were grown by pulsed laser deposition on titanium substrates at different substrate temperatures ranging from 300 to 700 °C. X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS),photoluminescence, and Raman spectroscopy are employed to investigate the change of properties. XRD, XPS, and Raman data showed that the films consisted of TiO₂ at high substrate temperature, which will deteriorate the crystallization quality of ZnO films. The optimum temperature for the growth of ZnO films on the Ti substrate is about 500 °C in this paper. The ZnO films grown on titanium substrate can be used in direct current, microwave, and medical applications. Copyright © 2014 John Wiley & Sons, Ltd.     

石墨烯对镍钛形状记忆合金耐腐蚀性能的影响

利用化学气相沉积法在镍钛形状记忆合金表面原位生长出石墨烯,拟提高镍钛形状记忆合金的抗腐蚀性能。通过X射线光电子能谱、拉曼光谱与扫描电镜等手段对其表征,分析石墨烯修饰后的合金表面结构和形貌。在人工唾液环境中探究了石墨烯对镍钛形状记忆合金的腐蚀速率、细胞毒性和金属释放的影响。结果表明,石墨烯在金属基体和腐蚀介质之间可以起到物理屏蔽作用,可明显地降低金属基体发生腐蚀的速率,对镍钛合金具有较强的保护能力。     

Titanium arsenide films from the atmospheric pressure chemical vapour deposition of tetrakisdimethylamidotitanium and tert-butylarsine

Thin films of titanium arsenide have been deposited from the atmospheric pressure chemical vapour deposition (APCVD) of [Ti(NMe(2))(4)] and (t)BuAsH(2) at substrate temperatures between 350-550 °C. Highly reflective, silver coloured films were obtained which showed borderline metallic-semiconductor resistivities. The titanium arsenide films were analyzed by scanning electron microscopy (SEM), Raman spectroscopy, wavelength dispersive analysis of X-rays (WDX), powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The films showed variable titanium to arsenic ratios but at substrate temperatures of 500 and 550 °C films with a 1 : 1 ratio of Ti : As, consistent with the composition TiAs, were deposited. Powder XRD showed that all of the films were crystalline and consistent with the formation of TiAs. Both nitrogen and carbon contamination of the films were negligible.     

Structural studies of gel phases—IV. An infrared reflectance and Fourier transform Raman study of silica and silica/titania gel glasses

Infrared reflectance and Fourier transform Raman spectroscopy have been used to study silica and silica/titania monoliths produced by the sol—gel route which had been subjected to a series of heat treatments. With increasing thermal treatment temperature, the gel—glass matrix is strengthed by bond shortening and a reduction in mean SiOSi bond angle and angular distribution for this feature. Results obtained at a range of temperatures were in good agreement to those obtained for vitreous silica. The incorporation of low levels (3% by weight) of titanium led to more disordered glasses which contain titanium in tetrahedral sites only. Evidence was obtained for the formation of SiOTi bonds, principally during the latter stages of densification at temperatures between 615 and 1000°C.     

Production and characterization of nitrided CVD-SiC films

Silicon Carbide (SiC) and SiC with free silicon [SiC(Si)] thin films were prepared by chemical vapor deposition (CVD) using a CH₃SiCl₃-H₂-Ar gas mixture at a temperature of 1223 K. Afterwards these layers were gas nitrided in an ammonia-hydrogen-argon mixture at 1273 K. The solid product is an extremely thin film of silicon nitride on SiC or SiC(Si)-basic layers. These ultra thin silicon nitride films were investigated by glow discharge optical spectroscopy (GDOS) and x-ray photoelectron spectroscopy (XPS). The thickness of the layers was determined to a maximum value of 30 nm.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

Flame emission studies of several metal chlorides with vapor-phase sampling

A method is described for the production of spectra of aluminum chloride, iron(III) chloride, silicon tetrachloride and titanium tetrachloride vapors by flame emission spectrometry. The aluminum and iron(III) chloride vapors were prepared by heating solid samples in reaction flasks; silicon and titanium tetrachlorides have sufficient vapor pressures at ambient temperatures to produce vapor-phase samples. Techniques have been developed to introduce the sample into the flame as a vapor, and to accommodate a large concentration of sample while requiring minimum preparation. Spectra were obtained individually and as a mixture over 240–600 nm. The analytical wavelength was chosen for each element, and 10-s integrations were made by utilizing a microcomputer to slew rapidly to the line of interest, hold for 10 s on the emission line, move off wavelength, hold for a 10-s background measurement and slew rapidly to the next line of interest. The microcomputer was also used to digitize and display the number of photons counted.     

Characterization of vanadium and titanium oxide supported SBA-15

Supported vanadium and titanium oxide catalysts were prepared by adsorption and subsequent calcination of the vanadyl and titanyl acetylacetonate complexes, respectively, on mesoporous SBA-15 by the molecular designed dispersion (MDD) method. Liquid and gas phase depositions at different temperatures were carried out with vanadyl acetylacetonate, and the different results together with those of titanyl acetylacetonate in the liquid phase deposition were discussed. The bonding mechanism, the influence of the metal interaction with the support material, and differences due to the way of deposition and the temperature were investigated by TGA, chemical analysis, FTIR, and Raman spectroscopy. Elevated dissolving temperatures in the liquid phase led to higher final loadings on the SBA-15 without the formation of clusters, even at high loadings. The decomposition of the anchored vanadium and titanium complexes, their thermal stability, and the conversion to the covalently bound VO(x) and TiO(x) species on SBA-15 were studied and investigated by in situ transmission IR spectroscopy. In general, the titanium complex is more reactive than the vanadium complex toward the surface of SBA-15 and has a higher thermal stability. The MDD method of the VO(acac)2 and TiO(acac)2 enables to create a dispersed surface of supported VO(x) and TiO(x), respectively. The structure configurations of VO(x) and TiO(x) oxide catalysts obtained at different metal loadings were studied by Raman spectroscopy. Pore size distributions, XRD, and N2 sorption confirmed the structural stability of these materials after grafting. VO(x)/SBA-15 and TiO(x)/SBA-15 samples, with different metal loadings, were also catalytically tested for the selective catalytic reduction (SCR) of NO with ammonia.     

Dépôt de revêtements peu rugueux de diamant sur un alliage de titane

Deposition of smooth diamond coatings on titanium alloy. A new process has been perfected to deposit smooth diamond coatings, at 600 °C, on titanium alloys. Scanning electron microscopy, X-ray diffraction, visible and UV Raman spectroscopy show that these coatings are smooth and mainly composed of crystalline diamond with a fine-grained morphology. The results are compared here to those obtained with classical rough polycrystalline coatings. Optical emission spectroscopy reveals important differences between the plasma species produced for the deposition of these smooth coatings and the plasma species produced for the deposition of both polycrystalline diamond and nanocrystalline films. © 2000 Académie des sciences / Éditions scientifiques et médicales Elsevier SASdiamond / coating / titanium alloy / plasma / roughness / Raman spectroscopy / emission spectroscopy     

Structural and Optical Properties of Sol-Gel Derived Aluminosilicate Planar Waveguides Doped with Er3+ Ions

Er3+ doped-aluminosilicate thin films were prepared on silica and silica/Si substrates by the sol-gel process and dip-coating. The sol-gel aluminosilicate planar waveguides were prepared from silicon and aluminium alkoxides. Their structural characterization has been carried out by Raman spectroscopy, Atomic Force and Scanning Electron Microscopies. The results indicated that these films present an amorphous structure until an annealing temperature of 900°C, while at temperatures higher than 1000°C, crystallization occurs. An estimate of microcrystallite sizes using Raman spectroscopy is given, which agrees with data from scanning electron microscopy. The optical properties have been investigated by Fluorescence spectroscopy in the visible region.     

Thermal stability and reactivity of metal halide filled single-walled carbon nanotubes

Thermal stability and reactivity to oxidation of several nanocomposite systems obtained by encapsulation of metal halides in single-walled carbon nanotubes are studied. Thermogravimetric analysis coupled with Raman spectroscopy allows insight into the various contributing factors, such as charge transfer, strain, and defect formation, and establishing a hierarchy of reactivity for the systems studied (AgX@SWCNTs, with X = Br, I; SWCNTs = arc discharge and HiPCO). The activation energy for oxidation decreases considerably after filling, indicating that filled nanotubes are more amenable to controlled modifications based on chemical reactivity than the originating empty nanotubes. The complete removal of the carbon shell at high temperatures does not preserve the nanowire morphology of the encapsulated halides; these are freed on surfaces in the form of nanoparticles arranged in 1D patterns. Metallic nanoparticles were obtained after hydrogen reduction of the halides, and growth of silicon nanowires in the footprint of the originating nanocomposites was demonstrated from such Co seeds. MX@SWCNTs (M = Ag, Co) can thus be used as environmentally stable nanoscale containers that allow the deliverance of catalytic nanoparticles in a prepatterned and aligned way.     

Temperature-dependent Raman scattering of silicon nanowires

Silicon nanowires with narrowly distributed diameters of 20-30 nm have been fabricated by chemical vapor deposition on an anodized aluminum oxide (AAO) substrate. The first-order and second-order Raman scatterings of the silicon nanowires have been studied in a temperature range from 123 to 633 K. Both of the first-order and second-order Raman peaks were found to shift and broaden with increasing temperature. The experimental results were analyzed by combining the phonon confinement effect, anharmonic phonon processes and lattice stress effect. It was found that the intensities of the first-order and second-order Raman bands have different dependences on temperature. The value of relative intensities I(2TA)int/I(2TO)int for silicon nanowires was found to be larger than that of bulk silicon, and increase with rising measurement temperature. We ascribe this phenomenon to the participation of phonons with a large wave vector value of Raman scattering caused by both the phonon confinement effect and the temperature effect.     

Analysis of corrosion layers on protective coatings and high temperature materials in simulated service environments of modern power plants using SNMS,SIMS, SEM,TEM, RBS and X-ray diffraction studies

In three different examples, the effects of the oxidation behaviour as well as the microstructural stability of high temperature materials and protective coatings was determined by combining the results of kinetic studies with extensive analytical investigations using, among other techniques, SNMS, SIMS, SEM, TEM, Rutherford back scattering (RBS) as well as X-ray diffraction. 1). The effect of water vapour on the oxidation behaviour of 9% Cr steels in simulated combustion gases has been determined. The effects of O2 and H2O content on the oxidation behaviour of 9% Cr steel in the temperature range 600-800 degrees C showed that in dry oxygen a protective scale was formed with an oxidation rate controlled by diffusion in the protective scale. In the presence of water vapour, after an incubation period, the scales became non-protective as a result of a change in the oxidation limiting process. The destruction of the protective scale by water vapour does not only depend on H2O content but also on the H2O/O2-ratio. 2). The increase of component surface temperature in modern gas turbines leads to an enhanced oxidation attack of the blade coating. Improvements in corrosion resistance and longer lifetime thermal barrier coatings in gas turbines have been achieved by improvement of the high temperature properties of MCrAlY coatings by additions of minor alloying elements such as yttrium, silicon and titanium. 3). The use of oxide dispersion strengthened (ODS) alloys provides excellent creep resistance up to much higher temperatures than can be achieved with conventional wrought or cast alloys in combination with suitable high temperature oxidation/corrosion resistance. Investigation of the growth mechanisms of protective chromia and alumina scales were examined by a two-stage oxidation method with 18O tracer. The distribution of the oxygen isotopes in the oxide scale was determined by SIMS and SNMS. The results show the positive influence of a Y2O3 dispersion on the oxidation resistance of the ODS alloys and its effect on growth mechanisms.     

DMTA study of a nickel-titanium wire

The nickel-titanium alloys are usually known as Shape Memory alloys because of their ability to return to some previously defined shape or size when subjected to the appropriate thermal procedure. Mechanical properties of a nickel titanium wire were investigated by DMTA using cylindrical tension mode. The Young"s modulus, the maximum strain and residual deformation have been calculated. Recovery of previously deformed samples was observed in constant stress temperature ramp tests. Relaxation stress behaviour at temperatures above the austenitic transformation has been studied. The strain and frequency ranges of linear response have been determined by dynamic experiments. Strain amplitude of 0.1% and frequency of 1 Hz have been chosen for the temperature ramp dynamic experiments. A big change between 65 and 95°C is observed in the storage modulus. The values of E' at temperatures below and above the transition are essentially constant. Finally, the effects of the frequency at different temperatures have been examined. This revised version was published online in July 2006 with corrections to the Cover Date.     

Ammonia oxidation on electrodeposited Pt–Ir alloys

Ammonia electro-oxidation on Pt–Ir alloys has been studied applying cyclic voltammetry and differential electrochemical mass spectrometry (DEMS), and the results were compared with pure Pt. Bimetallic alloys were prepared by electrodeposition and characterized using X-ray diffractometry (XRD) and Auger spectroscopy, before and after oxidation of ammonia. Pt/Ir atomic composition was 70:30 obtained from 1:1 solutions. Substitution alloys were established where Ir atoms replace Pt positions in the face-centered cubic structure. Preferential crystal orientations were detected in the electrodeposits with the development of a crystallographic texture. DEMS showed that N₂ is the main product during ammonia oxidation for both Pt and Pt–Ir, but the formation of nitrogen oxides is observed for E > 0.8 V_RHE. The yield of N₂ is higher for the alloy, which also displays lower poisoning of the surface when increasing ammonia concentration. These results confirm Pt–Ir alloys as alternatives to Pt electrodes concerning ammonia oxidation. Finally, it was observed that XRD patterns, as well as texture coefficient values, change after using the electrodeposits for ammonia oxidation, with the less compact planes the more affected ones. Dedicated to Prof. Dr. Teresa Iwasita on the occasion of her 65th birthday in recognition of her numerous contributions to interfacial electrochemistry.     

Effect of contact surfaces on the thermal and photooxidation of dehydrated castor oil

The effect of stainless steel, glass, zirconium and titanium enamel surfaces on the thermal and photooxidative toughening mechanism of dehydrated castor oil films deposited on these surfaces was investigated using different analytical and spectroscopic methods. The conjugated and non-conjugated double bonds were identified and quantified using both Raman spectroscopy and 1D and 2D NMR spectroscopy. The disappearance of the double bonds in thermally oxidised oil-on-surface films was shown to be concomitant with the formation of hydroperoxides (determined by iodometric titration). The type of the surface had a major effect on the rate of thermal oxidation of the oil, but all of the surfaces examined had resulted in a significantly higher rate of oxidation compared to that of the neat oil. The highest effect was exhibited by the stainless steel surface followed by zirconium enamel, titanium enamel and glass. The rate of thermal oxidation of the oil-on-steel surface (at 100 °C, based on peroxide values) was more than five times faster than that of oil-on-glass and more than 21 times faster than the neat oil when compared under similar thermal oxidative conditions. The rate of photooxidation at 60 °C of oil-on-steel films was found to be about one and half times faster than their rate of thermal oxidation at the same temperature. Results from absorbance reflectance infrared microscopy with line scans taken across the depth of thermally oxidised oil-on-steel films suggest that the thermal oxidative toughening mechanism of the oil occurs by two different reaction pathways with the film outermost layers, i.e. furthest away from the steel surface, oxidising through a traditional free radical oxidation process involving the formation of various oxygenated products formed from the decomposition of allylic hydroperoxides, whereas, in the deeper layers closer to the steel surface, crosslinking reactions predominate.