Transport of reactants during scale formation on copper in SO2+O2 atmosphere at 973 and 1073 K

The reaction between copper and a mixture of SO₂+O₂ was studied at 973 and 1073 K. The experimental methods included optical microscopy, X-ray diffraction, scanning electron microscopy (SEM), energy-dispersive X-ray analysis, and radiotracer. It is concluded that the inward transport of oxidants through the scale as well as oxygen and sulfur dioxide liberation in the reactions taking place at phase boundaries suggest that secondary processes occur inside the oxide-sulphate layer. Therefore, Cu₂O and CuOCuSO₄ appear inside this layer. In the metal-consumption zone, a Cu₂O layer forms, which contains small amounts of a sulfide phase near the metal-scale interface.     

Effect of misch-metal substitution on structure and hydrogen desorption characteristics of Ti<Subscript>0.16</Subscript>Zr<Subscript>0.05</Subscript>Cr<Subscript>0.22</Subscript>V<Subscript>0.57</Subscript> alloy

Misch-metal (Mm) substituted (Ti_0.16Zr_0.05Cr_0.22V_0.57)_1−xMm_x (x = 0.0, 0.03, 0.05, 0.10) alloys were synthesized by arc-melting. Phase analysis and microstructural studies were carried out using powder X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. The proportion of phases was estimated by Reitveld analysis of the powder X-ray diffraction data. The addition of Mm results in a decrease in the hydrogen storage capacity as well as a change in structure. The DTA analysis shows two endothermic peaks from ZrCr₂H₄ and BCC hydride.     

Microwave ECR plasma CVD of cubic Y2O3 coatings and their characterization

Yttrium oxide (Y₂O₃) thin films are deposited by microwave electron cyclotron resonance (ECR) plasma assisted metal organic chemical vapour deposition (MOCVD) process at a substrate temperature of 350 °C using indigenously developed metal organic precursors (2,2,6,6-tetra methyl-3,5-heptane dionate) yttrium, commonly known as Y(thd)₃ synthesized by ultrasound method. The deposited coatings are characterized by X-ray photoelectron spectroscopy, glancing angle X-ray diffraction, scanning electron microscopy, EDS and infrared spectroscopy. The characterization results indicate that it is possible to deposit non-porous coatings with excellent uniformity of a single phase cubic Y₂O₃ on various substrates by this process at reasonably low substrate temperature that is desirable in various manufacturing processes.     

Crystal structure and its stability in CeCuAl3 single crystal

We present the crystal structure investigation of CeCuAl₃ compound. Our X-ray diffraction study confirms unambiguously BaNiSn₃-type structure as the crystal structure of CeCuAl₃ in whole temperature range. Moreover, phase transition around 300 °C was found by our high-temperature powder X-ray diffraction measurement. This transition preserves BaNiSn₃-type structure, only structural parameters change during the transition. The study is provided on single crystalline and polycrystalline samples as well as on La counterpart to compare mainly high-temperature behavior of these compounds.     

Crystal structure of novel hydrides in a Mg–Ni–H system prepared under an ultra high pressure

The crystal structure of novel hydrides in the Mg–Ni–H system has been studied using a powder X-ray diffraction and transmission electron microscopy. A cubic-anvil-type apparatus was utilized to prepare samples. The new hydride with a chemical composition of around MgH₂–60 at% Ni was synthesized at 1073 K for 2 h under a pressure as high as 5 GPa. From TGA analysis, the new hydride was found to be Mg₂Ni₃H_3.4. Orthorhombic and monoclinic crystal systems with a primitive cell were proposed as possible symmetries of the new hydride. X-ray and electron diffraction patterns of the new hydride were indexed in an orthorhombic structure with a=0.8859(4), b=1.3740(5), c=0.4694(2) nm. Moreover, decomposition of the hydride into Mg₂Ni was observed by the transmission electron microscopy.     

Thermoelastic martensitic transformations,mechanical properties,and shape-memory effects in rapidly quenched Ni<Subscript>45</Subscript>Ti<Subscript>32</Subscript>Hf<Subscript>18</Subscript>Cu<Subscript>5</Subscript> alloy in the ultrafine-grained state

Methods of transmission and scanning electron microscopy and chemical microanalysis, electron diffraction, and X-ray diffraction were used to study the structure and the chemical and phase composition of ribbons of the four-component quasi-binary alloy Ni₄₅Ti₃₂Hf₁₈Cu₅. The influence of the synthesis regimes and subsequent heat treatment of the alloy on the formation of the amorphized state and ultrafine-grained structure has been determined. The critical temperatures of the devitrification and of the _B2 ? _B19' thermoelastic martensitic transformation have been established based on the data of the temperature dependences of the electrical resistivity. The lattice parameters of the _B2 and _B19' phases and the (Ti,Hf)₂Ni phase have been determined by X-ray diffraction. The mechanical properties of the alloy were determined in tensile tests, and the shape-memory effects in the ribbons of the alloy were measured using bending tests.     

Characterization of Microstructure and Mechanical Properties of Mg–8Li–3Al–1Y Alloy Subjected to Different Rolling Processes

The mechanical properties and microstructure evolution of Mg–8Li–3Al–1Y alloy undergoing different rolling processes were systematically investigated. X-ray diffraction, optical microscope, scanning electron microscopy, transmission electron microscopy as well as electron backscattered diffraction were used for tracking the microstructure evolution. Tensile testing was employed to characterize the mechanical properties. After hot rolling, the MgLi₂Al precipitated in β-Li matrix due to the transformation reaction: β-Li?→?β-Li?+?MgLi₂Al?+?α-Mg. As for the alloy subjected to annealed hot rolling, β-Li phase was clearly recrystallized while recrystallization rarely occurred in α-Mg phase. With regard to the microstructure undergoing cold rolling, plenty of dislocations and dislocation walls were easily observed. In addition, the microstructure of alloys subjected to annealed cold rolling revealed the formation of new fresh α-Mg grains in β-Li phase due to the precipitation reaction. The mechanical properties and fracture modes of Mg–8Li–3Al–1Y alloys can be effectively tuned by different rolling processes.     

Solvothermal synthesis of monodisperse ultrasmall cubic-structure Ba2YbF7 nanocrystals with intense upconversion

A series of monodisperse ultrasmall Ba₂YbF₇ nanocrystals with intense upconversion emission were synthesized via a facile solvothermal method by using oleic acid as capping ligands. X-ray diffraction (XRD) and transmission electron microscopy (TEM) assays revealed that the as-synthesized Ba₂YbF₇ nanocrystals are of cubic structure, rather than the reported tetragonal structure. The cell parameter of the particles is 5.918 Å. The Er³⁺ or Tm³⁺ doped Ba₂YbF₇ nanocrystals with the size of sub-10 nm can give an intense upconversion emission under the 980 nm laser excitation and the upconversion processes were discussed. The Ba₂YbF₇ nanocrystals show a potential application as a bioimaging agent.     

Activation of thermal processes in mixtures of some vanadium compounds with LiOH as a result of plastic deformation under high pressure

V₂O₅, V₂O₃, HVO₃, and mixtures of these compounds with 15% LiOH were subjected to plastic deformation at a pressure of 2 GPa and room temperature on high-pressure testing machines of the type of Bridgman anvils. The investigation of the samples was performed using differential scanning calorimetry, thermogravimetry, and X-ray diffraction analysis. The presence of LiOH in the mixtures decreased the thermal stability of vanadium compounds. During plastic deformation the LiV₃O₈ phase was formed in mixtures, the amount of which increased with heating the samples to 200°C. It is assumed that the ions that form by treatment under pressure can affect the structure formation processes in mix samples.     

Ni–Si<Subscript>3</Subscript>N<Subscript>4</Subscript>: Electrodeposition,properties and corrosion behavior

Ni–Si₃N₄ composite coatings were developed by electrodeposition from a nickel sulfate bath solution on a mild steel substrate. The corrosion behavior of the obtained coatings was analyzed by electrochemical methods. The amount of Si₃N₄ particles in the deposit was identified and estimated by the energy dispersive X-ray diffraction spectrometry. The structure and surface morphology of the coatings were characterized by the X-ray diffraction and scanning electron microscopy. In this work a comparative corrosion behavior and surface morphology of the composites generated in both the absence and the presence of sodium dodecyl sulfate with Si₃N₄ was accessed.     

大尺寸Zr基块体金属玻璃环形件铸造过程的数值模拟及实验验证

以29320调心滚子轴承外圈为研究对象,对Zr41Ti14Cu12.5Ni10Be22.5非晶合金的铸造成形进行实验研究.通过对充型和凝固过程的数值模拟,得到合金熔体在充型过程中的速度场和温度场,以及凝固过程中的温度场和温度梯度场.结果表明,当浇铸温度为1200℃时,能以大于临界冷速率的冷却速率获得外形完整的铸件.采用...     

Long term corrosion of X70 steel and iron in humid supercritical CO2 with SO2 and O2 impurities

Abstract

The corrosion of X70 steel and iron in supercritical CO₂/SO₂/O₂/H₂O environment were investigated after a 454 h exposure. Optical microscopy was applied to observe the morphology of etch pits and synthesise the three-dimensional morphology. X-ray diffraction and X-ray photoelectron spectroscopy were employed to detect the composition of product scales. Experimental results verified that the localised corrosion occurred on the X70 steel sample under corrosion product deposits. Ferrous sulphate, sulphur and iron sulphide were detected as the corrosion products.     

Hot Corrosion Behavior of a Ni3Al-Based IC21 Alloy in a Molten Salt Environment

Ni₃Al-based alloys have become important candidates for hot components in turbine engines, owing to their low densities and outstanding mechanical properties in service environments. The hot corrosion behavior of a Ni₃Al-based IC21 alloy in a molten salt environment of 75 wt% Na₂SO₄ and 25 wt% NaCl at 900 °C was studied, via oxidation kinetics analyses, scanning electron microscope observations and energy dispersive as well as diffraction analyses by X-ray. A multilayer corrosion oxide scale and dendritic morphology internal corrosion zone formed after hot corrosion, and inter-phase selective corrosion phenomena were also observed. Salt fluxing and oxidation-sulfidation processes were inferred to be the essential hot corrosion mechanisms of the alloy. Moreover, additions of Cr and Y proved to be beneficial to the hot corrosion resistance of the IC21 alloy, while the Mo content should be strictly controlled.     

Mechanisms of localized corrosion of carbon steel associated with magnetite/mackinawite layers in a cement grout

Carbon steel electrodes covered with a specific low-pH cement grout (pH ~10.7 at 20°C), designed for nuclear waste management applications, were immersed for 30 days in a 0.01-M NaCl + 0.01-M NaHCO₃ solution (pH 7 measured at 20°C), in aerated conditions, at 80°C. The corrosion processes were studied by voltammetry and linear polarization resistance measurements while the corrosion product layers were analyzed by µ-Raman spectroscopy and X-ray diffraction. Most of the electrodes (75%) suffered from localized corrosion, a phenomenon associated with the formation of a heterogeneous Fe₃O₄/FeS layer. It is proposed that the mechanisms of the particular corrosion process observed here are associated with galvanic effects, the large magnetite-covered zone acting as cathode and the locally mackinawite-covered zones being anodic regions.     

均匀自支撑的二氧化钒纳米线的水热合成及相变特性研究

二氧化钒(VO₂)在接近室温时发生由半导体态向金属态的Mott相变,在智能窗和红外自适应伪装技术领域具有一定的应用前景。本文采用一种新颖的水热法制备均匀自支撑的VO₂纳米线。合成的纳米线的直径为150±30 nm,长度达到几十微米。通过X射线衍射、X射线光电子能谱、高分辨透射电镜和选取电子衍射等手段验证了高纯单斜相VO₂纳米线的成功制备。而且,VO₂纳米线的可逆相变性能采用差示量热扫描、变温XRD和变温Raman光谱进行了探究。结果表明：VO₂纳米线升温相变点为65.2 °C,磁滞回线宽度窄至6.5 °C,具有良好的可逆相变性。这些为VO₂纳米线的金属-半导体相变研究提供基础。     

Uptake of iron,oxygen and nitrogen in molybdenum during ball milling

Molybdenum powder was ball milled in a steel vessel with hardened steel balls under Ar, O₂ and N₂ atmosphere, respectively. The milling products were examined by chemical analysis, X-ray diffraction and neutron diffraction. During milling under Ar or O₂ the iron as well as the oxygen content of the samples increases dependent on the number of interruptions of the milling process. The presence of dissolved oxygen seems to facilitate the solubility of iron in the molybdenum powder. Milling in a nitrogen gas atmosphere results in the formation of a nanocrystalline cubic γ-Mo₂N phase and a Mo-rich amorphous-like grain boundary phase. The microstructural imperfection was characterised by X-ray diffraction-line profile analysis. A method was proposed for the evaluation of the crystallite size and the microstrain in nanocrystalline materials, as well as the amount and structure of disordered grain boundaries from the reduced pair correlation function.     

Role of C: Zr stoichiometry in the formation of a nanocrystalline structure and magnetic properties in Fe87-x Zr13Cx films

X-ray diffraction analysis was used to study the structure of as-sputtered and annealed Fe-13 at. % Zr-C films, which were produced by reactive magnetron sputtering and characterized by stoichiometric and nonstoichiometric (with respect to ZrC) at. % C to at. % Zr ratios. A special packet of programs was used to resolve wide reflections observed in X-ray diffraction patterns of the films. The as-sputtered films of all compositions were found to be amorphous in terms of X-ray diffraction. The thermal stability of the amorphous phase increases as the C: Zr ratio in the films departs from the stoichiometric ratio (1: 1) characteristic of the monocarbide ZrC. Annealing leads to the formation of a mixed (amorphous + nanocrystalline) structure. Depending on the carbon content and annealing temperature, the phase composition of the films is represented by different combinations of phases, such as bcc α-Fe (the basis phase), fcc ZrC, monoclinic Fe₂C, monoclinic Fe_2.5C, orthorhombic Fe₃C, and Fe₂₃Zr₆. After annealing at 550°C, the best magnetic properties are characteristic of the films having the stoichiometric composition with respect to ZrC (at. % C: at. % Zr ～ 1).     

Corrosion behaviour and characterisation of Ni–Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> composites prepared by pulse electrodeposition

The Ni–Nb₂O₅ composites were prepared by pulse electrodeposition method. Operating variables were optimized for getting a good deposit. The quantity of Nb₂O₅ particles in the coating was analyzed by an energy-dispersive X-ray diffraction spectrometer. X-ray diffraction and scanning electron microscopy were used to analyze the structure and surface morphology of the coatings. Texture coefficient and hardness of the deposits were determined and discussed. The corrosion behavior of the coatings was analyzed by traditional weight loss and electrochemical methods. Comparisons of the corrosion behaviour of coatings obtained by direct current (DC) and pulse current (PC) were investigated.     

Microstructural and mechanical study of nanocrystalline (Ti0.8W0.2)C synthesized by high-energy ball milling

The microstructural characteristics of nanocrystalline (Ti_0.8W_0.2)C elaborated by mechanical alloying process were investigated by using both X-ray diffraction and electron microscopy. The diffraction crystallite size (DCS) and the microstrain of (Ti_0.8W_0.2)C ball milled powders have been determined according to the Rietveld refinement method. The results obtained showed that the (Ti_0.8W_0.2)C diffraction crystallite size decreases and its microstrain increases as the milling duration increases. A transition from grain-size hardening to grain-size softening was observed at DCS = 8 nm. It is demonstrated that, as the grain size decreases, the plastic deformation mechanism undergoes a transition from an intragranular deformation by dislocation sliding to an intergranular deformation by grain boundary sliding, as a result of increasing volume fraction (39%) of the grain boundary (GB) zone.     

Characterisation of R.F. magnetron sputtered Cr-N,Cr-Zr-N and Zr-N coatings

Binary Cr-N, Zr-N and Cr-Zr-N films were synthesised using a R.F. reactive magnetron sputtering technique by co-sputtering Cr and Zr. The crystalline structure, morphology, mechanical and tribological properties of the films as a function of Zr content were characterised by X-ray diffraction, microanalysis X (WDS, EDS), X-ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy, nanoindentation, scratch adhesion and pin-on-disc sliding wear tests. The residual stress was calculated with the Stoney formula. The Cr-Zr-N films exhibit a two-phase microstructure, containing a cubic (CrN, ZrN) with hexagonal (Cr₂N, Zr₂N) phases, as shown by X-ray diffraction. As the Zr content increased, a columnar and compact structure is developed with a low surface roughness. The results reveal that the mechanical and tribological properties of the films were found to depend on the Zr content and the hardness (maximum 26.3?GPa) is greatly improved in comparison with CrN and ZrN films, especially at 31?at.-% Zr. In the scratch test, the hardest film (Cr_0.18Zr_0.31N_0.47) exhibited an adhesive failure at Lc_2?=?34.3?N.