bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis of La1-xSrxCoO3-δ by a Polymeric Precursor Route Using Microwave Heating
Authors: Gaki Anna , Karavangelis C. , Kakali Glykeria , Wiglusz R.J. , Strek W.
Published: January 2010

La1-xSrxCoO3-δ (x=0, 0.2, 0.5) powders were prepared by a polymeric precursor route, with the application of microwave heating for the precursor preparation. Single-phase oxide powders are obtained after calcination at 700°C for x=0, 0.2 and 1300 °C for x=0.5. XRD, FTIR and TG-DTG measurements were used to examine the powder precursors as well as the intermediate and final products. SEM images indicated the small grain size of samples with x=0, 0.2. Conductivity and thermal expansion were measured by means of DC method and dilatometry respectively. The end member LaCoO3-δ showed a semiconducting behaviour, while doped samples showed a metallic behaviour at high temperatures. La0.8Sr0.2CoO3-δ showed the highest conductivity of all samples investigated, at temperatures higher than 300 °C.
Wet Chemical Synthesis of La1-xSrxGa0.8Mg0.2O3-δ (x=0.1, 0.2, 0.3) Powders
Authors: Kioupis D. , Gaki Anna , Kakali Glykeria
Published: January 2010

In the present work a modified polymeric precursor route is applied for the preparation of La1-xSrxGa0.8Mg0.2O3-δ (x=0.1, 0.2, 0.3). Citric acid and ethylene glycol are used as chelating and complexing agents respectively and microwave heating is used for the preparation of the precursors. The sintering reactions are recorded using TG/DTG measurements, while XRD, FTIR and SEM are used for the characterization of the intermediate and final products. As it is concluded, pure La0.9Sr0.1Ga0.8Mg0.2O3 can be prepared after sintering at 1300 °C for 6h. As the doping level of Sr increases, the formation of single phase perovskite is hindered. La0.8Sr0.2Ga0.8Mg0.2O3 contains minor amounts of SrLaGa3O7, while single-phase La0.7Sr0.3Ga0.8Mg0.2O3 can not be prepared at all. In all cases, the intermediate products at lower temperatures are mainly SrLaGa3O7, SrLaGaO4, La4Ga2O7 and La carbonates.
Impedance Spectroscopy Evolution upon Sintering of Alumina Bodies Containing Al-Rich Anodizing Sludge
Authors: Ribeiro M.J. , Labrincha J.A.
Published: January 2010

Al-rich sludge produced from industrial anodising and surface treatment processes had been tested in the fabrication of alumina-based materials, by using plastic extrusion as shaping technique. Long rods were produced using a vacuum screw extruder, by a careful control of all relevant processing parameters. Then, thick discs were obtained by cutting dried selected rods, to be tested as probes for sintering-dependent electrical properties. The sintering process was followed by common dilatometric/thermal analyses and results were interrelated with the evolution of electrical conductivity, estimated by impedance spectroscopy technique (IS). Results show that sintering-dependent morphological evolution up to 1300°C strongly affects the electrical behaviour of samples, and as a consequence IS seems to be a useful method to follow the firing process.
Influence of Sn Addition on the Amorphization and Thermal Stability of CuTiZrNi Powders Processed by Mechanical Alloying
Authors: Oleszak Dariusz , Kulik Tadeusz
Published: January 2010

The influence of Sn addition on the amorphization of CuTiZrNi alloys processed by mechanical alloying of a mixture of pure elemental powder was studied. The thermal stability and crystallization behaviour of the amorphous mechanically alloyed powders was determined and compared with rapidly quenched ribbons with the same nominal chemical compositions. X-ray diffraction and differential scanning calorimetry were employed as the experimental techniques for samples characterization. Both applied samples preparation techniques resulted in the formation of fully amorphous Cu47Ti34Zr11Ni8 and Cu37Sn10Ti34Zr11Ni8 alloys. However, significant differences in thermal stability and crystallization behaviour have been found, depending not only on the alloy composition, but on the fabrication method as well. The observed influence of Sn addition was more evident for the ribbons, resulting in the change of the number of crystallization effects, their temperatures and activation energy of crystallization. For mechanically alloyed powders these changes were not so dramatic.
Fe K-Edge XAFS Study of Slate Powders Heat Treated up to 1000°C
Authors: Oliveira Fernando A. Costa , Nitani Hiroaki , Nakagawa T. , Yamamoto T.A. , Shohoji Nobumitsu
Published: January 2010

The use of ultra-bright, highly directional, high and variable energy associated to synchrotron radiation beams at SPring-8 when compared with conventional X-Ray diffraction analysis applied to slate powders heat treated at temperatures in the range of 600°C up to 1000°C is reported. Fe K-edge XAFS measurements of the products formed upon heating slate showed that in the temperature range 600-800°C, conversion of FeO present in the as-received slate powder into a mixed -Fe2O3/-Fe2O3 has occurred providing useful information on the short-range order atomic structure of the slate. Above 800°C, mainly -Fe2O3 was identified to be present in the slate. The change of the Fe valences within the slate network is most likely responsible for the detected colour change with the increasing temperature.
Influence of Yttrium Oxide in the Volatilization of the Silica Contained in Zircon
Authors: Barreiro Pablo , Guitián Francisco
Published: January 2010

Selective volatilization of the silica contained in zircon takes place under high temperatures and low oxygen pressures. The presence of Yttrium oxide has the effect of enhancing this volatilization, increasing the yield in zirconia and, at the same time, stabilizing in tetragonal or cubic form.
Effect of RF Power on the Properties of Magnetron Sputtered ZnO:Al Thin Films Deposited at Room Temperature
Authors: Selmi Mabrouk , Chaabouni F. , Abaab Mohamed , Rezig Bahri
Published: January 2010

RF magnetron sputtering is used to deposit Aluminum-doped zinc oxide (ZnO:Al) films on glass and p-Si substrates. This work is a study of ZnO:Al films grown at different RF powers for photovoltaic cells application, as antireflective (AR) coatings. At room temperature and argon gas pressure of 0.6 Pa, RF power was changed from 200 to 400 W. The structural, electrical and optical properties of ZnO:Al films were investigated. Under theses conditions, we have obtained c axis-oriented wurtzite structure ZnO thin films with high transmission (>85%) and low reflection in visible wavelength range and a band gap of 3.34 eV. The results of this study suggest that the variation of the RF power, used for growth, allows the control of the structural and optical properties of the films. ZnO:Al films can be used in optical applications as thin films antireflective coatings.
Evaluation of the Corrosion Protection of Ultra-Thin Plasma Fluorocarbon Film Deposited on 316L Stainless Steel for Long-Term Stable Stents
Authors: Touzin Maryse , Chevallier P. , Turgeon Stéphane , Horny Paula , Mantovani Diego
Published: January 2010

Commonly made of 316L stainless steel and nitinol, metallic intravascular stents are medical devices used to scaffold a biological lumen, most often diseased arteries. While stenting procedures reduce the risk of restenosis, they do not eliminate it completely. Furthermore, other common complications observed are thrombosis, inflammation and corrosion of the stents. The corrosion of the device is induced by blood flow which provokes a degradation of its mechanical properties and leads to a high risk of release of potentially toxic metallic compounds, such as nickel-based oxides and metal ions. To lower these clinical complication rates and to prevent the corrosion of the metallic stent structure, coated stents have been developed during the last decade. Indeed, the coating is expected to improve the surface biocompatibility and corrosion resistance without compromising the stainless steel mechanical properties required for the stent implantation. The Food and Drug Administration (FDA) has already provided guidance on a series of non-clinical test protocols, methods and reports to evaluate the safety and effectiveness of intravascular stents. Properties such as the stability, durability, and adhesion of a stent coating, prior and after deployment, must be clearly assessed to demonstrate its efficiency. This study wants to evaluate the effectiveness against general and local corrosion of an ultra-thin fluorocarbon film deposited by plasma on pre-treated stainless steel. Cyclic polarization tests were used to measure the coating capacity to protect the substrate from localized corrosion and Tafel plot corrosion measurements were used to evaluate the general corrosion behaviour of uncoated and coated, flat and deformed samples.
Effects of Relative Density and Material Distribution on the Elastic Properties and Yield Strength of Metallic Honeycombs
Authors: Zhu H.X.
Published: January 2010

This paper investigates the combined effects of relative density and material distribution on the elastic constants and the yield strength of metallic honeycombs. Periodic regular hexagonal cell is employed as the structural model. Bending, transverse shearing and axial stretching (or compression) are taken into account in the analysis. Closed-form solutions for the yield strength and for all the five independent elastic constants are obtained for honeycombs with cell walls of uniform thickness. For honeycombs with cell walls of non-uniform thickness, the closed-form solutions would be too lengthy to use in practical applications. We instead provide the numerical results to show the combined effects of relative density and material distribution on the yield strength and on all the five independent elastic constants of metallic honeycombs. The results can serve as a guidance for the optimal design of metallic honeycombs.
Novel MEMS Fabry-Perot Interferometric Pressure Sensors
Authors: Padron Ivan , Fiory Anthony T. , Ravindra Nuggehalli M.
Published: January 2010

A novel design for a Fabry-Perot Interferometric Sensor (FPIS) consisting of a Fabry-Perot cavity formed between two bonded surfaces is discussed. The Fabry-Perot cavity and the optical fiber to which it is coupled are used as the sensing element and interconnect, respectively. The Fabry-Perot cavity is fabricated using the Micro Electro Mechanical Systems (MEMS) technology. The introduction of a center rigid body diaphragm gives this sensor considerable advantage when compared with previous Fabry-Perot cavity based sensors.
Modeling Aspects of the Dynamic Response of Heterogeneous Materials
Authors: Ionita A. , Clements B.E. , Mas E.M.
Published: January 2010

In engineering applications, simulations involving heterogeneous materials where it is necessary to capture the local response coming from the heterogeneities is very difficult. The use of homogenization techniques can reduce the size of the problem but will miss the local effects. Homogenization can also be difficult if the constituents obey different constitutive laws. Additional complications arise if inelastic deformation occurs. In such cases a two-scale approach is preferred and this work addresses these issues in the context of a two-scale Finite Element Method (FEM). Examples of using two-scale FEM approaches are presented.
Shear Strength of Titanium Diboride under Shock Wave and Static Compressions
Authors: Dandekar Dattatraya P.
Published: January 2010

The mechanical behavior of ceramics under high pressures and temperatures is a subject of considerable interest. Since high pressures can be generated under static or dynamic conditions, it is necessary to measure mechanical properties of the materials under both. In the present work, compression and shear strength of titanium diboride measured under plane shock wave compression is revealingly compared with the recent measurement of compression and shear strength of titanium diboride obtained under static high pressures.
Recent Developments on the Microstructural Effects Caused by Small-Charge Explosions in FCC Alloys
Authors: Firrao Donato , Matteis Paolo , Pozzi Chiara
Published: January 2010

Metals exposed to small charge explosions, even in absence of overall deformation, show characteristic and permanent microstructural features, that can be related to blast wave properties, e.g. to the charge mass and the charge-to-target distance. In particular, Face Centered Cubic (FCC) alloys with low stacking fault energy may exhibit mechanical twinning due to the high strain rate caused by an explosion, even if in slower processes they mainly deform by slip. In some forensic science investigations, these crystallographic modifications, and particularly the occurrence of twinning, may be among the few remaining clues of a small charge explosion, and may be useful to hypothesize the nature and location of the charge. A wide experimental campaign was performed to correlate the blast wave properties with the ensuing modifications of FCC metal targets, and to investigate the microscopic deformation mechanisms leading to these modifications. In particular, it was attempted to identify the threshold conditions (charge-to-target distance, charge mass, and hence applied stress) that yield barely detectable microstructural modifications, and to study the transition from slip to twinning. FCC metal alloys, with low (α-brass, stainless steel), intermediate (copper, gold alloy), or high (aluminum alloy) stacking fault energy, were exposed to blast waves (caused by 50 or 100 g plastic explosive charges located at increasing charge-to-target distances) and then analyzed by X-ray diffraction, optical microscopy, scanning electron microscopy, and electron backscattered diffraction imaging. A comprehensive review of the most significant findings of the whole research, together with theoretical considerations on the slip and twinning deformation mechanisms, is here presented.
Development of Compact Blast Containment Vessel for 10 kg Explosive
Authors: Kubota Shiro , Saburi Tei , Katoh Katsumi , Homae Tomotaka , Ogata Yuji , Iida Mitsuaki
Published: January 2010

The development study of blast containment vessels for anti-terrorism has been conducted. The goal of this study is to develop safe disposal vessel for 10 kg of explosives. Considering of the use at the airport or railroad stations, it needs to be more compact compared with the conventional explosion chamber. By introducing both the internal structure and attenuation technology in the vessel, sufficient blast proof ability to contain internal explosion is realized. The blast containment vessel can be used repeatedly by exchanging the internal structure. To realize these concepts, model experiments were carried out using high speed photography, strain and pressure measurements. By introducing these technologies, the vessel for the 1 kg of explosive materials has been made, and the experiments employing 1 kg C4 explosive have been conducted. Finally, the compact blast containment vessel for 10 kg explosives was made, and its blast proof ability was shown by the internal blast test.
Phase Transition Behavior of Solids under Shock Compression
Authors: Mashimo Tsutomu
Published: January 2010

Through the measurement of Hugoniot parameters, we can get useful information about high-pressure phase transitions, equations of state (EOS), etc. of solids, without pressure calibration. And, we can discuss the transition dynamics, because the relaxation times of phase transition and compression process are of the same order. We have performed the Hugoniot-measurement experiments on various kinds of compound materials including oxides, nitrides, borides and chalcogenides by using a high time-resolution streak photographic system combined with the propellant guns. The structure-phase transitions have been observed for several kinds of inorganic materials, TiO2, ZrO2, Gd3Ga5O12, AlN, ZnS, ZnSe, etc. The phase transition pressures under shock and static compressions of metals, ionic materials, semiconductors and some ceramics are consistent with each other. Those are not consistent for strong covalent bonding materials such as C, BN and SiO2. Here, the Hugoniot compression data are reviewed, and the shock-induced phase transitions and the dynamics are discussed, as well as the EOS of the high-pressure phase up to evem 1 TPa.
Instrumentation on Impact Shock Study of Polymers and Possibility of Non-Equilibrium Shock Hugoniot
Authors: Nagayama Kunihito , Mori Yasuhito
Published: January 2010

Polymer materials have widespread applications in various situations for structural materials by themselves as well as by combining with other materials such as carbon fiber. Some of them are also candidates for energetic materials in space applications.[1] Due to their general use, shock response of them has attracted attention for many researchers.[2-4] One of the striking characteristics of the dynamic response of them is that stress and/or particle velocity profile has a relaxation structure of s range.[5, 6]
Advanced Use of a Split Hopkinson Bar Setup for the Extended Characterization of Multiphase Steel Sheets
Authors: Van Slycken Joost , Verleysen Patricia , Degrieck Joris
Published: January 2010

In this paper some highlights are presented of an integrated numerical and experimental approach to obtain an in-depth understanding of the high strain rate behavior of materials. This is illustrated by an investigation of the multiphase TRansformation Induced Plasticity (TRIP) steel. ‘Classic’ high strain rate tensile experiments using a split Hopkinson tensile bar setup are complemented with strain rate jump tests, tensile tests at elevated temperatures and interrupted experiments. High strain rate compression and three-point bending experiments are performed on the steel sheets as well. The results reveal the excellent energy-absorption properties in dynamic circumstances of TRIP steels. Advanced experimental setups using the Hopkinson principle provide indeed tools for validation of the material and structural properties of TRIP steels.
Impact Behavior of Concretes Taking Account of Strain-Rate Effect, Stress-State Effect and Damage Evolution
Authors: Wang Li Li , Shi Shao Qiu , Wang Yong Gang , Wang Yong Zhong
Published: January 2010

At high strain rates, the dynamic response of concrete, a heterogeneous material with damage, was experimentally studied under (1) one-dimensional strain state at high pressures from 1 to 4 GPa by using a one-stage gas gun and (2) one-dimensional-stress state by using the SHPB technique. The main results are given and discussed. The results indicate that the effects of strain rate, stress-state and damage evolution should be considered in studies on the nonlinear impact behavior of concretes. A damage-modified visco-elastic model (ZWT model) is proposed for concrete C30.
Characterization of Hydrogen Sorption Properties and Microstructure of Cast Mg-10wt%Ni Alloys
Authors: Cho Young Hee , Dahle Arne K.
Published: January 2010

New Mg-10wt%Ni hydrogen storage alloys were fabricated by casting which is a very simple and cost effective production process. Alloying elements such as Nb and Ti, which have relatively high melting temperatures and very low solubility in solid Mg, were successfully dissolved into the liquid Mg-Ni alloy. The Mg-Mg2Ni alloys contain a well-refined lamellar eutectic microstructure after solidification with a large interfacial area between the Mg and Mg2Ni phases which provides for good hydrogen sorption properties. This is considered to be due to the high diffusivity of hydrogen along the interphase boundaries. Addition of transition metals such as Nb and Ti results in the formation of intermetallic phases with a size about 10-20μm during solidification. Furthermore, Ti was found to be strongly segregated to the eutectic Mg-Mg2Ni interface. In the presence of Nb and Ti, the hydrogen sorption kinetics of the Mg-Mg2Ni alloy is further improved. This suggests that the transition metals act as active catalysts that eases and accelerates the hydrogen diffusion during hydrogenation and dehydrogenation. In this paper, we present the hydrogen storage properties and their relationship to the microstructure of the cast Mg-10wt%Ni alloys. Detailed microstructural analysis was carried out in order to further understand the hydrogen diffusion and storage mechanisms.
Optimal Precipitation Hardening Conditions in Lead Base Anodes for Copper Electrowinning
Authors: Camurri Carlos , Carrasco Claudia , Pagliero Antonio , Colás Rafael
Published: January 2010

The suitable yield stress of Pb-0.07%Ca-1.3%Sn anodes of 6 mm thickness for copper electrowinning is achieved by means of deformation and precipitation hardening processes, being its useful life dependant of this yield stress. In such sense the objective of the present work is to optimize the precipitation hardening, finding for this purpose the best cooling conditions of the anodes in the molds and of the hot rolling temperature. The results show that increasing cooling rate of ingots from natural cooling the precipitation hardening is enhanced, with increases of 10% and 12.5 % on the yield stress and working life of the anodes respectively, and that a minimum of 45 days of ageing is necessary to reach stable conditions for the precipitation hardening, with precipitates formation as CaSn3. The hot roll temperature as not significant effect on the precipitation hardening of the anodes.
Influence of Processing Parameters on the Manufacturing of Anode-Supported Solid Oxide Fuel Cells by Different Wet Chemical Routes
Authors: Menzler Norbert H. , Schafbauer Wolfgang , Buchkremer Hans Peter
Published: January 2010

Anode-supported solid oxide fuel cells (SOFC) are manufactured at Forschungszentrum Jülich by different wet chemical powder processes and subsequent sintering at high temperatures. Recently, the warm pressing of Coat-Mix powders has been replaced by tape casting as the shaping technology for the NiO/8YSZ-containing substrate in order to decrease the demand for raw materials due to lower substrate thickness and in order to increase reproducibility and fabrication capacities (scalable process). Different processing routes for the substrates require the adjustment of process parameters for further coating with functional layers. Therefore, mainly thermal treatment steps have to be adapted to the properties of the new substrate types in order to obtain high-performance cells with minimum curvature (for stack assembly). In this presentation, the influence of selected process parameters during cell manufacturing will be characterized with respect to the resulting physical parameters such as slurry viscosity, green tape thickness, relative density, substrate strength, electrical conductivity, and shrinkage of the different newly developed substrate types. The influencing factors during manufacturing and the resulting characteristics will be presented and possible applications for the various substrates identified.
Impact of Gas-Phase Reactions on SOFC Systems Operating on Diesel and Biomass-Derived Fuels
Authors: Kang In Yong , Carstensen Hans Heinrich , Dean Anthony M.
Published: January 2010

The use of diesel fuel to power a solid oxide fuel cell (SOFC) presents several challenges. A major issue is deposit formation in either the external reformer, the anode channel, or within the SOFC anode itself. These deposits are generally poly-aromatic hydrocarbons (PAHs) produced either by gas-phase pyrolysis of the fuel or by catalytic reactions. In this report we describe n-hexane and ethylene pyrolysis experiments under conditions relevant to reformer or SOFC operation (τ=~1s, T=550~900°C, P~0.8 atm) to explore the potential for gas-phase reactions to produce deposit precursors. N-hexane is very reactive under these conditions and forms significant amounts of olefins (mainly ethylene) which can lead to deposits. The ethylene experiments also demonstrated that higher molecular weight species (deposit precursors) are rapidly formed. Under autothermal reforming conditions, such pyrolytic reactions are possible upstream of the catalyst bed if the fuel, air, and steam streams are not fully mixed. If part of the fuel does not mix with the oxidizer it will simply pyrolyze. At the same time, the remaining fuel fraction mixes with the entire oxidant inlet and thus creates higher local oxidant to fuel ratios than expected. Reaction of this leaner mixture can lead to temperature overshoots as more CO2 is formed. We have used a validated detailed kinetic model for ethane to explore the impact of incomplete fuel mixing on reforming performance. If only half the fuel mixes with the oxidants, this approach predicts formation of ethylene in the pyrolysis zone and excess CO2 with associated very high temperatures in the oxidation zone. This case could result in both excessive deposit formation as well as potential thermal damage to the downstream catalyst. On the other hand, assuming perfect fuel mixing under exothermic ATR conditions (τ=~1s, Ti=800°C, S/C=1.25, O/C=1.4), the gas phase reactions alone are sufficient to drive the system to equilibrium (no olefins or methane formed) due to the substantial increase in temperature. These results demonstrate the necessity for complete mixing of the fuel stream with the oxidant streams to limit both olefin production (and subsequent deposit formation) as well as the temperature overshoots. The model predictions for ethane as fuel suggest that the temperature should be kept below 500oC and the residence time in the mixing region should be minimized to avoid these undesired gas reactions. Since actual diesel fuel is expected to be even more reactive than ethane, the impact of gas-phase reactions is expected to be even greater than predicted in this study.
Analytical Investigation of Fuel Cells by Using In Situ and Ex Situ  Diagnostic Methods
Authors: Schiller Günter , Gülzow Erich , Schulze Mathias , Wagner Norbert , Friedrich K. Andreas
Published: January 2010

The study of the behaviour of fuel cells by using various in-situ and ex-situ diagnostic methods is a main topic at the German Aerospace Center (DLR). The degradation of cell components of polymer electrolyte fuel cells (PEFC, DMFC) and of solid oxide fuel cells (SOFC) are of special interest. For this purpose physical and electrochemical methods are used individually as well as in combination. In addition to routinely applied electrochemical methods different methods for locally resolved current density measurements by means of segmented cell technology and integrated temperature sensors have been developed. The latest development with segmented bipolar plates based on printed circuit boards (PCB) is used both in single PEFC cells and stacks. Furthermore, a measuring system for segmented SOFC cells has been developed allowing for the spatially resolved characterisation of cells in terms of current density/voltage characteristics, impedance spectroscopy data, operating temperature and gas composition. The paper summarises the capabilities at DLR with respect to the analysis of fuel cells’ behaviour and gives examples of analytical studies to discuss the potentials and limitations of the diagnostic methodology that is applied.
Electronic Stress Tensor Study of Aluminum Nanostructures for Hydrogen Storage
Authors: Szarek Pawel , Watanabe Kouhei , Ichikawa Kazuhide , Tachibana Akitomo
Published: January 2010

We report the new structures of aluminum hydrides derived from the Al4 tetrahedral cages. We perform ab initio quantum chemical calculation for these new aluminum hydrides. Our calculation of binding energies of the new aluminum hydrides reveal that stability of these hydrides increases as more hydrogen atoms are adsorbed, while stability of Al-H bonds decreases. We also calculate electronic stress tensor to evaluate the chemical bonds of these hydrides. As a result, we find that the bonds of the Al4 tetrahedral cage are strengthened as more hydrogen atoms are adsorbed on the aluminum hydrides. Our calculation of the potential energy surfaces and the regional chemical potential show that hydrogen atoms are likely to adsorb on bridge site at first.
Enhanced Hydrogen Storage in MWCNTs Decorated by Electroless Nickel Nanoparticles Deposited in Supercritical CO2 Bath
Authors: Chen Chih Yao , Chang Jeng Kuei , Lin Kuan Yu , Chung Sung Ting , Tsai Wen Ta
Published: January 2010

Nano-sized nickel particles were dispersed on multi-walled carbon nanotubes (MWCNTs) via an improved electroless deposition route using a supercritical CO2 fluid. The microstructure, chemical composition and crystallinity of the Ni-decorated CNTs were examined using a transmission electron microscope (TEM), an X-ray energy dispersive spectrometer (EDS), and an X-ray diffractometer (XRD), respectively. The analytical results indicate that, with assistance of the supercritical fluid, Ni nanoparticles with a diameter of approximately 10 nm can be uniformly dispersed on the surface of CNTs. The hydrogen storage capacity of the Ni-decorated CNTs was evaluated with a high-pressure microbalance at room temperature and under a hydrogen pressure of 6.89 MPa. The measured hydrogen adsorption amount of the Ni/CNTs nanocomposite was 1.06 wt%, which was much higher than 0.33 wt% found for the plain CNTs.
SOFC Stacks for Mobile Applications
Authors: Lang Michael , Auer Corinna , Jentsch Paul , Weckesser Tilman
Published: January 2010

Solid Oxide Fuel Cells (SOFCs) are gaining more and more importance as auxiliary power units (APU), e.g. for passenger cars, trucks and airplanes. In this context, the main challenge is the development of SOFC stacks, which fulfill the strong requirements for mobile applications. These are a low weight, a low volume, and a high power density with reformate gases but also low long term degradation rates. The paper presents results of investigations of SOFC short stacks for mobile applications. Therefore, a light weight stack design was developed in an industrial consortium in cooperation with the German Aerospace Center (DLR) in Stuttgart and the Research Center Jülich (FZJ). The SOFC stacks were operated at different temperatures, varying fuel gas compositions and different fuel gas flow rates. The short stacks were electrochemically characterized mainly by long-term measurements, by current-voltage measurements and by impedance spectroscopy. The fuel utilizations and the power densities were determined. In order to analyze the uniformity inside the stacks, the electrochemical behaviour of the individual cassettes were analyzed and compared to each other. Finally, the degradation rates and the degradation mechanisms were determined from the long-term measurements.
Friction Stir Processing: A Novel Approach for Microstructure Refinement of Magnesium Alloys
Authors: Ma Zong Yi , Xiao B.L. , Yang J. , Feng A.H.
Published: January 2010

In this article, recent investigations on magnesium alloys by friction stir processing (FSP) are addressed. It indicates that remarkable grain refinement and breakup/dissolution of second-phase particles could be achieved simultaneously by FSP. High values of superplastic elongation were achieved in the FSP magnesium alloys at a wide range of strain rates and temperatures. The pinning of heat resistant particles on the grain boundaries in Mg-RE alloys stabilized the fine microstructure, leading to the occurrence of superplasticity at higher temperature and higher strain rate.
Metallographic Study of Lapped FSW between Ductile Cast Iron and Austenite Type Stainless Steel
Authors: Nakamura Mitsuru , Sawada Yuki , Sato Yutaka S.
Published: January 2010

This study was investigated the influence of preheat temperature and welding speed by a view point of microstructure of joining zone used by friction stir welding (FSW) between ductile cast irons and stainless steels. FSW conditions were carried out by change of tool rotation by 200, 400 and 600rpm, preheat temperature by non-preheat, 573 and 773K, and welding speed by 1～10mm/s. As a result, microstructure of FCD450 side became a pearlite structure changed by preheat condition. Also, stir zone (SZ) of FSW were crystallized the chill structure because of cast iron melted partially why SZ temperature exceeded the eutectic temperature. However, higher welding speed could inhibited crystallization and found the possibility of bonding between ductile cast irons and stainless steels.
Limitation of Distortion in Friction Stir Welded (FSW) Panels Using Needle Peening
Authors: Larose Simon , Dubourg Laurent , Perron C. , Jahazi Mohammad , Wanjara Priti
Published: January 2010

Friction stir welding (FSWing) induces residual stresses and distortions in welded structures. Such residual stresses reduce the fatigue life of welded components, while the induced distortions prevent the welding of large or thin components. In the present study, needle peening was used to induce additional residual stresses in 2.3-mm thick (FSWed) aluminum alloy (AA) 2024-T3 sheets. This was done with the objective to counterbalance the welding-induced stresses and thus reduce the overall stresses and distortions. The needle peening process, which stems from shot peening, consists of hammering a surface using cylindrical spherical ended shots sliding back and forth in a treatment head. An instrumented needle peening machine was used to carry out peening on as-received (or bare) and bead-on-plate FSWed AA2024-T3 material. In both cases, the width of the peening area corresponded to that of a typical weld. The influence of the peening process parameters such as needle size, applied power and travel speed on the surface quality and magnitude of the induced distortions were evaluated. The results indicate that, by increasing the needle diameter from 1.2 mm to 2.0 mm, the peening-induced deflection on bare sheet material increased by an average value of 27% while the roughness average, Ra, decreased by an average value of 47%. It was also found that a surface finish qualitatively similar to that of conventional shot peening could be obtained by using appropriate needle peening trajectories. Finally, needle peening with an applied power of 10% was sufficient for eliminating 37% of the welding-induced transverse curvature and 82% of the welding-induced longitudinal curvature.
Structure and Mechanical Properties of Friction Stirred Beads of 6082-T6 Al Alloy and Pure Copper
Authors: Avettand-Fènoël Marie Noëlle , Taillard Roland , Herbelot Christophe , Imad Abdellatif
Published: January 2010

Friction stir welding (FSW) is a quite recent welding method which takes advantage of being performed in the solid state. Compared with the usual welding processes, it therefore presents many benefits such as a lower heat-input, a reduction of residual stresses and an elimination of the solidification defects etc.. Up to now, it has essentially been applied to aluminium alloys and far more recently to a small number of bimaterials.
The present study deals with three kinds of beads between pure copper and a 6082 aluminium alloy. Both materials were butt joined by FSW. The welds differ by the location of the tool which was placed either at the interface between the two metals or on the copper or the 6082 side of this surface. Their structure was characterized at a multi-scale level by using a number of techniques. Tensile and microhardness tests were also performed. The tool place is shown to govern the microstructure and the ensuing mechanical behaviour of the weld. Its influence on the plastic flow with its repercussions on i) welding defects and ii) mechanical properties is going to be demonstrated. Some ways of improvement of the welding process will finally be suggested.
Spot Welding between Aluminum Alloy and Steel by Friction Stirring
Authors: Fukumoto Masahiro , Miyagawa K. , Tsubaki M. , Yasui T.
Published: January 2010

Spot welding between Al alloy and some kinds of steels by friction stirring was conducted. In the process, a rotating tool was plunged into the Al alloy which was overlapped onto the steel plate, and held at the plunge depth for a few seconds with rotating condition. In this welding, friction stirring was adopted only inside of the Al alloy, and welding between Al alloy and steel is performed by an interaction of stirred Al alloy to the fixed steel surface. Mechanical strength of the joints was evaluated by both tensile shear test and cross tensile test. From the observation results on the microstructure of the weld interface, it was found that Fe/Al intermetallic compound with a few m thickness was formed at the interface. It was found that Zinc coated layer intrinsically has a role to protect the steel materials at a static condition, however, in the stirring condition of Al alloy, Zinc layer easily moved toward the outside of stirring zone and resultant fresh surface of the steel enables formation of the higher mechanical strength of the joint.
Study and Researches about the Microhardness’s Variation of a Special S.G. Cast Iron
Authors: Milosan Ioan
Published: January 2010

The paper presents some aspects about the influence of the heat treatment’s parameters over the microhardness’s variation of a Bainitic S.G. Cast Iron at the end of an wear process. It was determinate the variation of the rapport () between the microhardness ( H) and the distance of the wear surface (l).
Friction Stir Spot Welding Phenomena in Al Alloy 6061
Authors: Sato Yutaka S. , Fujimoto Mitsuo , Abe Natsumi , Kokawa Hiroyuki
Published: January 2010

Friction stir spot welding (FSSW), developed based on principle of friction stir welding, has been paid attention as a new solid-state spot welding process. Since FSSW can produce high-quality weld in Al alloys more easily than resistance spot welding, this process has been already used for construction of Al components in the automotive industries. Despite the large industrial interests in FSSW, fundamental knowledge on welding phenomena of this process has not been fully understood. In this study, FSSW phenomena, such as the consolidation mechanism, the microstructural evolution and the material flow, were examined in Al alloy 6061. This study clarified that the elliptical zone found in the vicinity of the pin hole on the cross section was characterized by the initially lapped surface of two sheets. Moreover, the following material flow was proposed; capture of the upper material with the threads on the pin surface, spiral flow along the tool rotation, and then release at the tip of the pin.
Quantifying the Usability of a Robot System for Friction Stir Welding
Authors: Soron Mikael
Published: January 2010

Friction Stir Welding (FSW) has been proven an excellent method for joining of non-ferrous alloys in several industrial areas. The introduction of industrial robots in FSW has extended the possibilities, now also including complex 3-dimesional structures to be joined. There is however issues regarding the robot system’s performance as well as how to really benefit from the extended flexibility features. This paper presents how the FSW robot system ROSIOTM is intended to be used to fully explore its potential usage in production and laboratory applications. This include presenting the system’s performance in a set of case studies, but also defining in which way this system may be a subject for increased productivity in FSW.
Recrystallization Textures in Heavily Cold-Rolled Ni3Al Based Single Crystals
Authors: Demura Masahiko , Xu Ya , Hirano Toshiyuki
Published: January 2010

Texture evolution during recrystallization and grain growth was examined for a Ni3Al/Ni two-phase single crystal (binary Ni-18 at.% Al) 83% cold-rolled, then compared with that for a Ni3Al single-phase single crystal (Ni-24 at.% Al). The cold-rolled single crystal had a sharp {110}<001> (Goss) texture. When it was recrystallized at 873K, the texture changed into a complicated one consisting of several components. Most of them had a special rotation relationship to the original Goss texture, i.e. 40˚ about <111>, which special relationship was similarly observed in the single-phase case. The 40˚<111> texture became shaper with no quantitative change as the grain growth proceeded. This high stability of the recrystallized texture contrasted with the single-phase case in which the authors previously found that the texture returned to the original Goss texture. The difference was discussed based on the orientation analysis by an electron backscattered diffraction method.
Comparison of Different Fluorine Treatments for the Protection of TiAl-Alloys Against High Temperature Oxidation
Authors: Donchev Alexander , Schütze Michael
Published: January 2010

The oxidation resistance of TiAl-alloys can be improved by several orders of magnitude by treating the surface of the materials with small amounts of halogens especially Cl and F. The oxidation mechanism changes due to the so called halogen effect. The formation of a fast growing mixed oxide scale on untreated alloys is suppressed, instead a thin protective alumina scale is formed on samples after optimum treatment. The different methods only influence the surface region of the components so that the bulk properties are not affected. Recent results achieved with complex TiAl-samples showed the potential that the fluorine effect could be used for TiAl-components in several high temperature applications e.g. jet engines. TiAl-specimens were treated with fluorine and chlorine in several ways and their performance during high temperature oxidation tests in air was investigated. Results of isothermal and thermocyclic oxidation tests are presented. The long term stability of the fluorine effect lasted for at least one year under thermocyclic exposure at 900°C in laboratory air. The results are discussed in terms of later use of the fluorine effect for technical applications.
University Impact on Thermomechanical Processing in Corus
Authors: Howe Andrew A.
Published: January 2010

After discussion of general issues regarding University/Industry collaboration, some examples are described of how this impacts upon Corus (now part of Tata Steel), including roll friction, work-roll performance, and phase transformation including its detection on line. The deployment of the academic research invokes varying levels of associated industrial RD&T, whether through parallel projects or follow-up projects. Various modes are employed from PhD/EngD student projects through to collaborative consortia. By whatever model, effective collaboration between universities and industries clearly requires the removal of the boundary between the two.
Hot-Workability of Gamma-Based TiAl Alloys during Severe Deformation
Authors: Froebel Ulrich
Published: January 2010

Forged and extruded TiAl products suffer from structural and chemical inhomogeneities that reduce the reliability of components. In an attempt to improve the homogeneity of the material, the feasibility of cyclic axial deformation and cyclic torsional deformation superimposed with compression, where much higher strains can be imparted into the material than during forging and extrusion, were investigated. Accordingly, during torsion superimposed with compression pronounced shear localization and cracking occurs. These difficulties can largely be overcome by cyclic axial deformation.
Ti-Al-Cr Based Coatings for High Temperature Oxidation Protection of γ-TiAl
Authors: Fröhlich Maik , Braun Reinhold , Leyens Christoph
Published: January 2010

In this study the oxidation resistance of Ti-45Al-8Nb (at.%) alloy coated with quaternary Ti-Al-Cr-X layers (X = Si, Hf, Y, Zr and W) was investigated. The Ti-Al-Cr-Si, Ti-Al-Cr-Hf and Ti-Al-Cr-Y coated specimens were exposed to air at 950°C under cyclic conditions, whereas the samples with Ti-Al-Cr-Zr and Ti-Al-Cr-W coatings were thermally cycled at 1000°C. After the maximum exposure time period of 1000 1h-cycles or failure cross-sections of the samples were examined by means of SEM and EDS to analyse the microstructural evolution. At initial stages of exposure, all intermetallic layers formed a thin alumina layer on top, providing a diffusion barrier to oxygen. But interdiffusion between coating and substrate caused depletion of the Ti(Cr,Al)2 Laves phase in the intermetallic layers, which promoted the formation of alumina, as well as transformation into Ti-rich B2-phase. Coarsening of the latter phase beneath the alumina scale resulted in a higher oxidation resistance compared to that of ternary Ti-Al-Cr coating.
Change in Microstructure by Heat-Treatment and Corresponding Deformation Behavior in Ni3V Single Crystals
Authors: Hagihara Koji , Mori Mayumi , Kishimoto Takuya , Umakoshi Yukichi
Published: January 2010

D022-Ni3V contains three variants whose [001] c-axes are mutually perpendicular. In addition, due to the order-disorder transition the anti-phase domains (APD) are also introduced under some heat-treatment conditions. In this study, the influence of such microstructures; the size of variants and APDs, on the plastic deformation behavior of Ni3V was investigated by using single crystals, in which the microstructure was variously controlled by heat-treatments.
Microstructure and Magnetic Properties of NdFeB Magnets Using Fluorides Nano-Coated Process
Authors: Komuro Matahiro , Satsu Yuichi , Suzuki Hiroyuki
Published: January 2010

Nd2Fe14B magnets could be sintered using terbium fluoride coated Nd2Fe14B powders. Fluorine atoms were segregated at the triple junctions and grain boundary after sintering and aging process. NdOF with fcc structure was grown at the triple junction. Terbium atoms were also distributed near grain boundaries by interdiffusion between the fluoride and Nd2Fe14B. No fluorine atoms were detected in Nd2Fe14B phase. The coercivity for 0.5wt% terbium fluoride coated magnet showed 1.23 MA/m which was 1.2 times higher than that for non-coated magnet with 1.04MA/m. The distribution of terbium and fluorine atoms increases the coercivity without reduction of remanence.
The Influence of Deformation Conditions on Structure of Fe-Al Intermetallic Phase ‒ Based Alloys
Authors: Kuc Dariusz , Niewielski Grzegorz , Gawąd Jerzy
Published: January 2010

The major problem restricting universal employment of intermetallic phase base alloy is their low plasticity which leads to hampering their development as construction materials. The following work concentrates on the analysis of microstructure and plasticity of ordered Fe3Al (D03) and FeAl (B2) during hot plastic deformation process.. The microstructure analyses applying optical electron microscopy and EBSD method have revealed the structure reconstruction processes occurring in Fe3Al and FeAl alloys. It has been shown that different mechanisms of the structural changes ensue from the thermal plastic strain in the investigated alloys, which influences their technological plasticity.
Comparison of Fluorination Treatments to Improve the High Temperature Oxidation Resistance of TiAl Alloys in SO2 Containing Environments
Authors: Masset Patrick J. , Yankov Rossen , Kolitsch Andreas , Schütze Michael
Published: January 2010

Surfaces of titanium aluminides were treated by fluorine either physically using Plasma Immersion Ion Implantation (PI³) or chemically with a F-based polymer. By controlling the fluorination parameters, both treatments improve the oxidation resistance even in the presence of sulfur dioxide (0.1 vol%). No sulfur was detected in the oxide scale although thermodynamic calculations predict the formation of sulfides. The inward diffusion of oxygen and nitrogen in the alloy was found to be reduced in the presence of SO2.
Microstructure and Mechanical Properties of Zr-Co-Ni Intermetallic Compound
Authors: Matsuda Mitsuhiro , Hayashi Katsutoshi , Nishida Minoru
Published: January 2010

The relationship between the microstructure and mechanical properties on the ternary ZrCoNi alloys has been investigated. Zr50Co50-xNix alloys undergo martensitic transformation from the B2 to B33 structure by the substitution of Ni for Co. The tensile ductility at room temperature increases remarkably without the loss of yield strength by substituting Ni. Zr50Co39Ni11 alloy has the extremely high plastic elongation of 21%. There are many {021}B33 deformation twins in the B2 parent phase just near the tensile fractured area. These twins are the strain induced martensitic phase due to the tensile deformation. Consequently, the remarkable improvement of the ductility of ZrCoNi alloys is due to the transformation induced plasticity.