bluuebunny/crossref_metadata_2025 huggingface dataset:
Frequency Dependence of Electrical Conductivity and Loss Tangent in Studies on Water-Solution of Irradiated Bones
Authors: Pankowski Edward , Kubisz Leszek
Published: March 2009

Bovine bone which has been irradiated with the dose bigger than 10 kGy dissolves in water after having been powdered. Bone has been irradiated with the doses of 10, 25, 50, 100, 500, 750 and finally 1000 kGy. The electrical conductivity of solution was measured at the frequency range of 0.1-1 MHz. For the dose range of 10-100 kGy the electrical conductivity and the loss tangent, in the limits of the measurement errors, were dose independent. For the doses higher than
100 kGy both electrical conductivity and loss tangent revealed higher values then for the dose range of 10-100 kGy. Moreover, the relaxation time of the dissolved molecules was assessed as longer than 10-5s.
Magnetic and Mechanical Properties of Magnetic Glass-Coated Microwires with Different Glass Coating
Authors: Zhukova V. , Zhukov A. , Larin V. , Torcunov A. , González J. , de Arellano-López António Ramirez , Quispe Cancapa J.J. , Pinto-Gómez A.R.
Published: March 2009

Glass coated microwires with two metallic nucleus compositions Co57Fe 6.1Ni10B15.9Si11 and Fe36,4Co41,7B11,8Si10,1 with 3 different glass coating compositions (Pyrex – 74.5% SiO2, 15% - B2O3, 3%- Na2O, 2%- Al2O3 1.5% -K2O; Nonex – 73% SiO2, 16.5% - B2O3, 6% - PbO 3 %-Na2O, 1.5% -K2O;
and F1 – 70.2% SiO2, 27% - B2O3, 0.8 %-Na2O, 2%- LiO2 1% -K2O;) with very similar geometry (metallic nucleus diameter 7 µm, total diameter 19 µm) have been successfully fabricated and studied. Ferich microwires in as-prepared state show rectangular hysteresis loops, which is connected with the strong internal stresses induced by the fabrication process. Co-rich compositions show inclined hysteresis loop with smaller value of coercive field. The coercivity, Hc, of Co-rich microwires is the highest and of Ferich samples is the lowest in the case of Pyrex coated microwires. The Nonex coated microwires are in the intermediate position while the F1 coated Co-rich microwires have the lowest Hc while the Fe-rich samples have the highest Hc. The mechanical tests show that the best tensile strain yield is observed in samples coated by Nonex glass followed by Pyrex and F1. In this way the variation of the glass coating material allows to tailor both magnetic and mechanical properties of glass coated tiny microwires.
Viscoelastic Properties of Ceria Gel
Authors: Phonthammachai Nopphawan , Rumruangwong Morakot , Jitkanka Sirirat , Gulari Erdogan , Jamieson Alexander M. , Wongkasemjit Sujitra
Published: March 2009

The viscoelastic behavior of different ceria gelling systems prepared through sol-gel transition were investigated by the rheological measurement. The gelation time was observed by the frequency independence of tand, and increased with increasing acid:alkoxide molar ratio. At the gel point, both storage and loss moduli (G’µ wn, G” µ wn)exhibited a power law dependence of applied frequency with n’ = n” = n. The viscoelastic exponents and gel strength parameter were dependent on the composition of system. The increase in HCl:alkoxide molar ratio increased the n value while decreased the S parameter.
Optical Activity of Deuterated Analog of L-Arginine Phosphate Single Crystals
Authors: Herreros-Cedrés J. , Hernández-Rodríguez C. , Guerrero-Lemus R.
Published: March 2009

The complete optical gyration tensor of monoclinic pure L-arginine phosphate
monohydrate (LAP) and deuterated LAP (d-LAP) crystals has been determined. Variation of the optical activity in the presence of birefringence of d-LAP crystal with pure LAP is found from the high-accuracy universal polarimeter (HAUP) method at a wavelength of 632.8 nm. The gyration tensor components in terms of rotatory power were found to be r11 = -6.6(3) º/mm, r22 = 19(2)
º/mm; r33 = 49.7(7) º/mm; and r13 = -43.7(8) º/mm for the LAP, and r11 = -1.2(1) º/mm, r22 = 5.0(4) º/mm; r33 = 41.4(3) º/mm; and r13 = -38.0(4) º/mm for d-LAP at room temperature.
Analysis of Dielectric Relaxation Parameters in the Range of Glass Transition
Authors: Neagu Eugen R. , Marat-Mendes José N. , Neagu Radu
Published: March 2009

The apparent activation energy W, the temperature Ta at which the molecular movement is assumed frozen (the relaxation time is infinitely large) and the preexponential factor t0 were determined for Nylon 11 using the data obtained by fractional polarization thermally stimulated discharge current technique. The aim was to investigate the temperature dependence of the relaxation time in the range of the glass transition temperature. An experimental thermogram can be analyzed equally well using the Vogel-Fulcher-Tammann-Hess relationship or the Arrhenius equation. Experimental results and simulations, for nearby peaks, demonstrate that the relaxation time at peak temperature changes from about 100 to 500 s revealing a very narrow distribution in relaxation times. On contrary, W and especially t0 varies in large limits and the values for t0 are in many situations physically meaningless. It was found that the temperature at which the molecular movement can be assumed frozen for electric effects is about 150 K below the glass transition temperature in Nylon 11. A small change in W (in the limit ± kTm which represents the minimum uncertainty interval in W) induces a change in t0 of about two decades, indicating (i) that any analysis assuming t0 constant should be avoided and (ii) the selectivity limit of the method.
Production of Ge Heterofullerenes by Arc-Discharge Technique
Authors: Yilmaz M. , Uluğ B.
Published: March 2009

Germanium containing heterofullerenes are produced by arc-discharge technique under ~100 torr He atmosphere and were extracted from the soot using CS2. Production and extraction procedures are detailed. FTIR spectrum of extract was presented. The mass distribution of the extract analyzed by FAB mass spectrum showed the stability of heterofullerene structures.
Preparation of Nanocrystalline Copper and Copper Silicon Sulphide by Mechanochemical Route
Authors: Baláz Peter , Boldižárová E. , Godočíková E.
Published: March 2009

The composition and properties of powders prepared by high-energy milling of copper sulphides with silicon have been studied by methods of X-ray diffractometry and surface area measurement. The combination of several methods was utilized to develop a coherent picture of the process. The overall process of mechano-chemical transformations in copper sulphide-silicon system proceeds via complicated mechanism with several overlapping steps. Phase transformations in copper sulphide phases, the formation of elemetal nanocopper with X-ray determined particle size of 23 nm and creation of ternary sulphide Cu8SiS6 with anomalous surface area values are the main products of the mechanochemical reaction.
Temperature of Formation Studies for LiMn1.5Ni0.5O4 Using X-Ray Diffraction
Authors: Mat A. , Yahya M.Z.A. , Sulaiman Mohd Ali , Puteh R. , Arof A.K.
Published: March 2009

The objective of this paper is to show that annealing lithiated transition metal oxide
(LTMO) precursors obtained by the sol-gel method at insufficiently high temperatures may not produce the intended pure cathode active materials required in lithium batteries. In this work, LiMn1.5Ni0.5O4 which is a potential cathode active material in the 5 V-class is prepared by the solgel method. The precursor material was obtained when the solid gel was dried and heated at different temperatures in the range between 200 °C and 900 °C for 4 hours. It was observed that on
heating the precursor material at least at 500 °C for 4 hours the material produced was LiMn1.5Ni0.5O4 in the present form as proven by the x-ray diffractogram (XRD). On heating at temperatures below this, the formation of LiMn1.5Ni0.5O4 was uncomplete and at temperatures above 500 °C the intensity of the peak at 2q = 18° decreases. The noise level also increased at temperatures above 500 °C.
Ab-Initio Study of Mechanical Properties of Transition-Metal Aluminides: A Case Study for Al3(V,Ti)
Authors: Jahnátek M. , Krajčí M. , Hafner J.
Published: March 2009

On the basis of ab-initio density-functional calculations we have analyzed the character of interatomic bonding in the intermetallic compounds Al3(V,Ti) with the D022 and L12 structures. In all structures we found an enhanced charge density along the Al-(V,Ti) bonds, a characteristic feature of covalent bonding. The bond strength is quantitatively examined by tensile deformations.
The ideal strength of Al3V and Al3Ti under uniaxial tensile deformation was found to be significantly higher than that of both fcc Al and bcc V. We investigated also the changes of the interatomic bonding in Al3V during tensile deformations. We found that the covalent interplanar Al- V bonds disappear before reaching the maximal stress. The weakening of the bonding between the atomic planes during the deformation is accompanied by a strengthening of in-plane bonding and an enhanced covalent character of the intraplanar bonds. Interplanar bonding becomes more metallic under tensile deformation.
Locally Initiated Elastic Waves in 2D Metals
Authors: Poletaev Gennady M. , Aksenov M.S. , Starostenkov Mikhail D. , Patzeva J.V.
Published: March 2009

Locally initiated elastic waves in two-dimensional metals were studied by the method of molecular dynamics. Local initiation of the elastic waves was produced by the impulse, which was given to one or several atoms. The mechanism, the velocity of elastic waves and their spread were studied by the visualization of atomic displacements, registration of the value of these displacements. Whirl mechanisms of the distribution of cross waves were considered in the paper.
Disorientations and Their Role on the Work-Hardening in Stage IV
Authors: Pantleon Wolfgang
Published: March 2009

The eect of deformation-induced disorientations on work-hardening of metals
is modelled by dislocation dynamics. By incorporating excess dislocations related to disori- entations, Kocks' dislocation model describing stage III hardening is extended to stage IV. Disorientations evolving from purely statistical reasons still lead to stage III behavior and a saturation of the ow stress, but deterministic contributions to the development of disorienta- tions, as dierences in activated slip systems across boundaries, cause a linear increase of the flow stress at large strains. Such a constant work-hardening rate is characteristic for stage IV.
Stability and Motion of Low Angle Dislocation Boundaries in Precipitation Hardened Crystals
Authors: Holec David , Dlouhý Antonín
Published: March 2009

The present study investigates stability and motion of low angle dislocation boundaries in an array of precipitates. The model considers discrete dislocations and precipitates that are treated as impenetrable particles. Peach-Koehler forces, which originate due to the combined effect of dislocation-dislocation interactions and the applied stress, act the individual dislocations on. Both, the dislocation glide and the dislocation climb at elevated temperatures are taken into account. Results of the numerical study suggest that a critical applied shear stress (CASS) always exists
which separates stable and unstable low angle boundary configurations. Varying particle size, interparticle spacing and density of dislocations in the boundary cause changes of the CASS that are systematically investigated. It is shown that the CASSs can considerably differ from the standard Orowan stress controlling the equilibrium of an isolated dislocation in a given microstructure. This result underlines the importance of long-range dislocation interactions that influence the high
temperature strength of the precipitation-hardened alloys.
Annealing Behaviour of Fe-C-N Nanopowder: Formation of Iron/Graphite Core-Shell Structured Nanoparticles
Authors: David B. , Pizúrová N. , Schneeweiss O. , Bezdička Petr , Filip J. , Alexandrescu R. , Morjan I. , Crunteanu A. , Voicu I.
Published: March 2009

We are reporting the core-shell structured iron/graphite nanoparticles formed by
annealing of a nanopowder. The original Fe-C-N based nanopowder has been synthesized by the laser pyrolysis of gas phase reactants. TEM, XRD, Raman spectroscopy, Mössbauer spectroscopy and magnetic measurements were used for its characterization. Nanopowder was heated up to 800°C at ~ 1 Pa vacuum. Presence of iron nanoparticles with the mean diameter of 40 nm in the annealed state of the nanopowder was confirmed from the width of α-Fe X-ray diffraction lines and their core-shell structure was observed under TEM.
Study of Carbon Films on Silicon Substrates
Authors: Jašek O. , Eliáš M. , Frgala Z. , Matějková Jiřina , Rek Antonín , Kadlečíková M.
Published: March 2009

Carbon based films on silicon substrates have been studied by high resolution FE SEM equipped by an EDS analyzer. The first type are carbon nanotube (CNT) [1] films prepared on Si/SiO2 substrates with Ni or Fe layers by radiofrequency plasma chemical vapor deposition. Dependence of nanotube films properties on Ni and Fe thickness and deposition conditions have been studied. The second type of films discussed are microcrystalline and nanocrystalline diamond films grown on pre-treated Si substrates by microwave plasma chemical vapor deposition (MPCVD). The pre-treatment was varied and its effect on diamond films was studied.
Application of Silicon for a Protection of Titanium against High-Temperature Oxidation
Authors: Vojtech Dalibor , Kubatík Tomáš , Čížová Hana
Published: March 2009

The paper describes a positive influence of silicon on the high-temperature oxidation
resistance of titanium. Since silicon additions can be realized both by bulk and by surface alloying, the surface siliconizing techniques, as well as structure of the Si-rich layers, are illustrated. Furthermore, the high-temperature cyclic oxidation resistance of the surface siliconized titanium and of the TiSi2 alloy are compared to that of pure Ti and TiAl6V4 alloy, and the oxidation mechanism is discussed.
Microstructure and Creep Properties of AISI 316LN Steels with Niobium Additions
Authors: Vodárek Vlastimil , Rožnovská Gabriela , Sobotka Jaromír
Published: March 2009

The long-term creep rupture tests have been carried out on three casts of a type AISI 316LN steel at 600 and 650°C. Two of the casts investigated contained additions of 0.1 and 0.3 wt.% of niobium. The growing niobium content strongly reduced the minimum creep rate and prolonged the time to the onset of the tertiary stage of creep and also shortened this stage. The enhanced creep resistance of niobium containing steels is not accompanied by the longer creep life that might have been expected. At both temperatures of creep exposure the niobium-bearing casts displayed an inferior creep ductility. Microstructural investigations revealed that niobium provoked significant grain size refinement and the formation of Z-phase. Particles of this phase were considerably dimensionally stable. Furthermore, niobium accelerated the formation and coarsening of s-phase, h-Laves and M6(C,N). The coarse intergranular particles facilitated the formation of cavities which resulted in intergranular failure mode.
New Description of Steady-State Creep Rate, Yield Stress, Stress Relaxation and Their Interrelation
Authors: Kohout Jan
Published: March 2009

The steady-state creep rate increases with temperature according to the Arrhenius
equation and its increase with applied stress is mostly described by the power law. Combining both these laws, equation ) exp( RT Qa n − µ s e& is obtained, where apparent activation energy a Q and stress sensitivity parameter n are considered to be constants. But most measurements show some dependence of activation energy on applied stress and of stress sensitivity parameter on temperature. An equation respecting these facts is derived in the paper and verified using some published results of creep tests. Based on this derived equation, the dependence of yield stress on temperature and strain rate and an equation describing the relaxation curves are deduced.
Computational Modelling of Spherical Cavity Behaviour in Rubber-Like Solids
Authors: Skacel Pavel , Bursa Jiri
Published: March 2009

A characteristic rubber failure process, termed cavitation, has been observed and analysed by several authors. This paper deals with the stress concentration effect of a hypothetical void (cavity) that is assumed to be present in rubber-like solids. Commercial software based on finite element method and up-to-date Arruda-Boyce material model is used here for rubber material behaviour modelling. A detailed study of the effects of particular material parameters on the cavity behaviour under far-field hydrostatic tension condition is presented. The results are compared to
those, which can be obtained for the case of simple neo-hookean material model of rubber. In opposite to standard crystalline materials there is no general failure criterion applicable for elastomeric materials. This analysis is motivated by the endeavour to determine a general criterion describing the failure of elastomers as a consequence of static loading.
Modelling of the Charpy Impact Test in the DBTT Range
Authors: Haušild Petr , Berdin Clotilde , Rossoll Andreas
Published: March 2009

The finite element method was used in order to compute the energy balance and the
stress-strain distribution in the Charpy V-notch specimen. Inertial effects were taken into account by a fully dynamic computation. It was shown that inertial oscillations are damped by viscoplasticity ahead the notch and vanish rapidly. 3D modelling is needed since large scale yielding and ductile crack growth occur. The ductile crack front is curved, which is important to account for in order to correctly describe the stress distribution in the specimen. Ductile crack growth in Charpy specimen was predicted by the GTN (Gurson-Tvergaard-Needleman) model. The GTN model allows a good failure prediction with strain rate and temperature independent damage parameters.
A Fracture Mechanics Investigation on Crack Growth in Massive Forming
Authors: Trattnig Gernot , Sommitsch Christof , Pippan Reinhard
Published: March 2009

To understand the crack growth in massive forming and to consequentially avoid crack growth in workpieces, it is necessary to investigate its dependence on the crack depth and thus on the state of hydrostatic stress. Prior work shows that the crack opening displacement (COD) for shallow cracked tension specimens with low stress triaxiality is twice as high as for deep cracked specimens with high stress triaxiality. This work examines the crack growth in compression specimens with pre-cracked cylindrical upsetting samples. The compression samples were cut in the stress symmetry plane in order to observe crack initiation and crack growth by a single specimen technique. In this way it is possible to observe blunting, crack initiation and crack growth inside the upsetting specimens. The resulting COD does not differ significantly from the values achieved in tension samples with short surface
cracks.
Effect of Interfaces on Fiber Fracture in Mg and MgLi Matrix Composites
Authors: Kúdela S. , Wendrock H. , Ptáček L. , Menzel S. , Wetzig K.
Published: March 2009

Fibers fracture in tensile strained Mg and MgLi matrix composites strengthened with
~10% vol. short δ-Al2O3 fibers (Saffil) is investigated by „in-situ“ scanning electron microscopy and ex-situ“ determination of the length of fibers chemically recovered from tensile failed composites. Little interfacial reaction in Mg matrix composite results in poor interfacial bond so that composite failure proceeds via fiber pull-out with negligible fiber fragmentation. On the other hand, extensive
fiber/matrix reaction in MgLi matrix composites promotes formation of strong interfaces which are linked with multiple fiber cross-breakage during tensile straining. These results are consistent with experimental tensile strengths of related composites.
Mechanical Properties of AS21 Magnesium Alloy Based Composites
Authors: Trojanová Zuzanka , Száraz Zoltán
Published: March 2009

The high temperature behaviour of composites with the AS21 magnesium alloy matrix, reinforced by short Saffil fibres was investigated in the temperature interval from room temperature to 300 °C. The yield stress and the maximum stress decrease with increasing temperature. Two types of specimens were investigated – one with fibres plane oriented parallel to the stress axis and the other with perpendicular fibres plane orientation. Light and scanning electron microscopy were
used for study of the microstructure of composites. Possible hardening and softening mechanisms are discussed. The shear stress at fibre/matrix interface was of greatest importance in this regard, though the contribution resulting from the dislocation density increase was also significant.
Nanoscale Measurement of Stress and Strain by Quantitative High-Resolution Electron Microscopy
Authors: Hÿtch Martin J. , Putaux Jean-Luc , Pénisson Jean-Michel
Published: March 2009

The geometric phase technique (GPA) for measuring the distortion of crystalline lattices from high-resolution electron microscopy (HRTEM) images will be described. The method is based on the calculation of the “local” Fourier components of the HRTEM image by filtering in Fourier space. The method will be illustrated with a study of an edge dislocation in silicon where displacements have been measured to an accuracy of 3 pm at nanometre resolution as compared
with anisotropic elastic theory calculations. The different components of the strain tensor will be mapped out in the vicinity of the dislocation core and compared with theory. The accuracy is of the order of 0.5% for strain and 0.1° for rigid-body rotations. Using bulk elastic constants for silicon, the stress field is determined to 0.5 GPa at nanometre spatial resolution. Accuracy and the spatial resolution of the technique will be discussed.
Anisotropic Behaviour of Grain Boundaries
Authors: Paidar Vaclav , Lejček Pavel
Published: March 2009

Grain boundaries are decisive for many properties of materials. Due to short-range stress field their influence is primarily based on their atomic structure. Special character of grain boundary properties related to their structure, follows from the nature of atomic arrangements in the boundary cores, from the interfacial dislocation content and from the boundary mobility. All those aspects of boundary behaviour are strongly influenced by the boundary chemistry including various
segregation phenomena. Approaches to the boundary classification and the interpretation of recent experimental results are discussed in the context of the complex relationship between microstructure and material properties. Such findings are essential for Grain Boundary Engineering proposed to improve the performance of polycrystalline materials.
Plasticity of Copper with Small Grain Size
Authors: Champion Yannick , Langlois Cyril , Guérin Sandrine , Lartigue-Korinek Sylvie , Langlois P. , Hÿtch Martin J.
Published: March 2009

Based on the Taylor theory, a critical length scale is defined as the minimum dislocations cell size obtained at the maximum work-hardening for metals and alloys. When grain size is smaller than this length scale, corresponding also to a critical dislocation mean free path, new behaviours occur; such as ductility and strength, near perfect elasto-plasticity, high strain-rate sensitivity. Bulk samples are fabricated from Cu nanopowders (particle size 50 nm) by powder metallurgy
techniques. The final grain size is comprised between the critical mean free path, evaluated at 130 nm and the size where transition to the so-called nano regime occurs (when unit dislocation no longer exists below 30 nm for Cu). Tensile tests are carried and microstructural analysis are performed before and after deformation.
Cause and Effect of Factors Affecting the ΔKth of Small Crack
Authors: Kondo Yoshiyuki
Published: March 2009

The threshold stress intensity factor (ΔKth) of small crack is affected by various factors, especially by material hardness, stress ratio and crack size. Test results showed that harder material had higher ΔKth and smaller crack had lower ΔKth. The crack closure measurement on a very small crack was done to make clear the root cause of those effects. Most of those effects could be explained by the peculiar behavior of crack closure for crack deeper than 100µm. However, everything could not be understood only by the crack closure behaviour. In addition to the difference in crack closure, (ΔKeff)th itself was also dependent on crack size when the crack depth was shallower than 100µm. Another remarkable phenomenon was experienced in this study. Unusual decrease in ΔKth was found in some case. The large decrease of ΔKth occurred under the conjunction of three factors, that is,
extremely high stress ratio (R) higher than 0.8, small crack and hard material. This kind of large reduction in ΔKth in high R region is of much importance in turbo machinery that operates under high mean stress with small vibratory stress.
Modeling of Photon Recycling in GaN-Devices
Authors: Velmre Enn , Udal Andres , Klopov Mihhail
Published: March 2009

The strength of recombination radiation reabsorption in GaN is discussed. For material comparisons a distance-dependent radiative recombination transfer function F(u) is introduced. In spite of high absorption rates of GaN, calculations predict ca. one order of magnitude higher photon recycling efficiency in GaN than in GaAs. Simulations of 2H-GaN p −i −n structures predict appearance of S-shaped forward I/V characteristics due to the generation of extra carriers in the base
center. The study of GaN bipolar transistors shows that the radiative recombination will reduce the carrier lifetimes in the base and thereby restrict essentially the achievable current gains.
Heteroepitaxy of GaN on Silicon: In Situ Measurements
Authors: Krost A. , Dadgar Armin , Schulze F. , Clos R. , Haberland K. , Zettler T.
Published: March 2009

Due to the lack of GaN wafers, so far, group-III nitrides are mostly grown on sapphire or SiC substrates. Silicon offers an attractive alternative because of its low cost, large wafer area, and physical benefits such as the possibility of chemical etching, lower hardness, good thermal conductivity, and electrical conducting or isolating for light emitting devices or transistor structures, respectively. However, for a long time, a technological breakthrough of GaN-on-silicon has been
thought to be impossible because of the cracking problem originating in the huge difference of the thermal expansion coefficients between GaN and silicon which leads to tensile strain and cracking of the layers when cooling down. However, in recent years, several approaches to prevent cracking and wafer bowing have been successfully applied. Nowadays, device-relevant thicknesses of crackfree
group-III-nitrides can be grown on silicon. To reach this goal the most important issues were the identification of the physical origin of strains and its engineering by means of in situ monitoring during metalorganic vapor phase epitaxy.
High Temperature Contacts to GaN and SiC Based on TiBx Nanostructure Layers
Authors: Boltovets Mykola S. , Ivanov V.N. , Avksentyev A.Yu. , Belyaev A.E. , Borisenko A.G. , Fedorovitsh O.A. , Konakova Raisa V. , Kudryk Ya.Ya. , Lytvyn Petr M. , Milenin Victor V. , Sachenko A.V. , Sveschnikov Yu.N.
Published: March 2009

In this communication we present the results of study of new contact systems to GaN epitaxial layers grown on sapphire and n-type 6H-SiC monocrystals. The TiBx nanostructure phase has been used during manufacturing Ti – Al – TiBx – Au and TiBx contact systems. The n-GaN epitaxial layers of 1 µm thickness were grown on [0001] sapphire substrate by vapor-phase epitaxy. The n-type 6H-SiC monocrystals were grown by Lely method with the donor concentration of
2x1018 cm3. The layers of Ti, Al, TiBx and Au were deposited by magnetron sputtering followed by high-temperature annealing.
3d-Transition Metals in Cubic and Hexagonal Silicon Carbide
Authors: Machado W.V.M. , Justo João F. , Assali Lucy V.C.
Published: March 2009

The electronic and structural properties of isolated 3d-transition metal impurities
in 3C, 4H, and 2H silicon carbide have been investigated bytotal energy ab initio methods. The stability, spin states and transition energies of substitutional (Si sub-lattice) Cr, Mn, and Fe impurities in several charge states were computed. Our results are discussed in the context of available experimental data.
An In-Situ Post Growth Annealing Process for the Improvement of 4H-SiC/SiO2 MOS Interface Prepared by CVD Using TEOS, and its Characteristic Study
Authors: Ramanujam Kumaresan , Furuichi Hidetsugu , Taguchi Koshi , Yukumoto Satoshi , Nishino Shigehiro
Published: March 2009

Investigations were carried out to achieve high performance Silicon Carbide
Metal-Oxide-Semiconductor device structures. 4H-SiC/SiO2 interface was prepared by growing amorphous SiO2 layers by an alternate low temperature atmospheric CVD technique using TEOS as source material and the interface properties were compared with the one prepared by conventional
thermal oxidation technique. The low temperature CVD technique offered the improvement of the interface properties with reduced Dit in comparison with thermally oxidized interface. As a new attempt, an in situ post growth annealing technique in N2 atmosphere was carried out to reduce the Dit further. Both the CVD technique and the in situ annealing processes that were used in the present
study have been identified to be potential approaches to improve the interface quality.
Step Structures Produced by Hydrogen Etching of Initially Step-Free (0001) 4H-SiC Mesas
Authors: Powell J. Anthony , Neudeck Philip G. , Trunek Andrew J. , Abel Phillip B.
Published: March 2009

This paper presents new observations resulting from in-situ high temperature hydrogen etching of 4H-SiC mesas that were step-free prior to initiation of etching. In particular, it was found that well-ordered pyramidal-shaped step train structures could be produced on mesa top surfaces via stepflow etching proceeding inward from the sides of mesas. In many cases, the height of steps etched inward from {112 0} mesa sides is 0.5 nm (2 Si-C bilayers), while the height of steps etched inward from {11 00} sides of the same mesa is 1.0 nm (4 Si-C bilayers, the repeat distance of the 4H-SiC polytype). We propose that stepflow etching starting from the mesa sidewall and involving step-to-step repulsive forces produces the observed step train structures.
Reduction of Fluoride Species and Surface Roughness by H2 Gas Addition in SiC Dry Etching
Authors: Mikami Hideno , Horie Yasutaka , Hatayama Tomoaki , Yano Hiroshi , Uraoka Yukiharu , Fuyuki Takashi
Published: March 2009

We study for the effects of additional gas such as oxygen (O2) and hydrogen (H2) into SF6. When H2 gas was added to SF6, surface fluoride atomic concentration and surface roughness were lower than the other additional gases. Surface fluoride atomic concentration under this experiment
was reduced from 28 at % to 6 at % by the H2 addition. In post-processing, the fluoride atomic concentration was succeeded in a large reduction by processing H2, O2 plasma and high temperature hydrogen annealing. In hydrogen annealing, surface fluoride atomic concentration could be suppressed to less than 3 at %. This is new result succeeded in reduction of surface fluoride species greatly by hydrogen processing.
Trench Formation on Ion Implanted SiC Surfaces after Thermal Oxidation
Authors: Bahng Wook , Song Geun Ho , Kim Nam Kyun , Kim Sang Cheol , Kim Hyoung Wook , Seo K.S. , Kim Eun Dong
Published: March 2009

The effects of the damage induced during ion implantation on the surface roughening and oxide growth rate were investigated. Using several scheme of doses and acceleration energies, it is found that the amount of the dose predominantly produce damage rather than the acceleration energy,
especially near the surface region. It was also found that the damage affects not only the oxide growth rate but also the surface roughening during high temperature annealing. The edge of highly implanted area may have higher doping concentration due to the vicinal side wall effect of the thick oxide mask for ion implantation. It was confirmed by the trench formation after thermal oxide remove.
SiC Power Device Packaging Technologies for 300 to 350°C Applications
Authors: Johnson R.Wayne , Williams John R.
Published: March 2009

The challenges of packaging SiC power devices for high temperatures include high
operating temperature, wide thermal cycle range, high currents and high voltages. This paper describes ongoing research to develop suitable materials and processes for packaging SiC power devices. Ohmic and Schottky contacts must be protected from oxidation at elevated temperatures. TaSi2:N2 is an effective oxidation barrier, protecting the contacts when exposed to 350 oC in air. For
package substrates, silicon nitride ceramics with a thick brazed copper foil are used. A nickel/thick gold or nickel/thick silver surface finish is plated onto the copper foil; depending on the die attach brazing process. With the nickel/thick gold finish, gold-tin eutectic has demonstrated no degradation in die shear strength after 2000 hours at 350 oC or after 500 hours at 400 oC. Work is currently underway with nickel/thick silver and gold-silicon eutectic die attach. No degradation in
shear strength has been observed with this system after 100 hours at 400 oC. Gold wire (250 µm) bonding has been demonstrated on both substrate and SiC metallizations. An initial decrease in strength is observed due to annealing of the gold wire, but shear and pull strengths remain high. Polyimide has been used to increase the dc breakdown strength of a test pattern by a factor of ~3x at
300 oC compared to no passivation. The breakdown strength increased with storage in air at 300 oC through 1000 hours.
Numerical Simulation and Optimization for 900V 4H-SiC DiMOSFET Fabrication
Authors: Kim Sang Cheol , Bahng Wook , Kim Nam Kyun , Kim Eun Dong , Ayalew T. , Grasser Tibor , Selberherr Siegfried
Published: March 2009

We report the simulation results of 25µm half cell pitch vertical type 4H-SiC DiMOSFET using the general-purpose device simulator MINIMOS-NT. The best trade-off between breakdown voltage and on-resistance in terms of BFOM is around 19MW/cm2 with a p-well spacing 5µm. The specific on -resistance, RON, sp, simulated with VGS=10V and VDS=1V at room temperature, is around
22.76mWcm2. An 900V breakdown voltage is simulated with ion-implanted edge termination.
Broadband RF SiC MESFET Power Amplifiers
Authors: Jonsson Rolf , Rudner Staffan
Published: March 2009

We have designed and characterized preliminary versions of two wideband SiC-based RF power amplifiers using SiC MESFETs from Chalmers University and Lateral Epitaxy SiC MESFETs fabricated at AMDS AB. When optimized transistors are available they will be used in the design of amplifiers for a 100 – 500 MHz multifunction EW system.
Comparison of High-Voltage 4H-SiC Insulated-Gate Bipolar Transistor (IGBT) and MOS-Gated Bipolar Transistor (MGT)
Authors: Zhu Lin , Balachandran S. , Chow T. Paul
Published: March 2009

In this paper, the performance of high-voltage (10kV) 4H-SiC n- and p-channel IGBTs and n-channel MOS-Gated Bipolar Transistor (MGT) are investigated and compared using 2- dimensional numerical simulations. We have found that the MGT in SiC is not suitable for applications at high blocking voltages and the p-channel IGBT is a better choice because of a much higher conductivity modulation in the drift region.
Temperature Impact on High-Current 1.2kV SiC Schottky Rectifiers
Authors: Jordá Xavier , Tournier Dominique , Rebollo Jose , Millan José , Godignon Philippe
Published: March 2009

SiC 600 V Schottky barrier diodes (SBD) are already available in the market and 1.2 kV have been announced. As the highest market for power devices is foreseen for blocking voltages in the range of 600 up to 1700V, we have developed 1.2kV SBDs. In this paper we report the latest results obtained on those diodes, underlining their high temperature working operation capability (up to 200°C). Forward characteristics, reverse leakage current and switching recovery time
dependence on temperature have been analysed. The good thermal behaviour of the 1.2 kV SiC SBDs is compared with that of ultra-fast PN-Si diodes (RHRP8120) of the same breakdown voltage.
Design, Fabrication and Characterization of 1.5 mΩcm2, 800 V 4H-SiC n-Type Schottky Barrier Diodes
Authors: Furno M. , Bonani F. , Ghione G. , Ferrero Sergio , Porro Samuele , Mandracci P. , Scaltrito Luciano , Richieri G. , Perrone Denis , Merlin Luigi
Published: March 2009

We present a theoretical and experimental study on the design, fabrication and
characterization of Schottky Barrier Diodes (SBD) on commercial 4H-SiC epitaxial layers. Numerical simulations were performed with a commercial tool on different edge termination structures, with the aim of optimizing the device behavior. For each termination design, SBD were fabricated and characterized by means of electrical measurements vs. temperature. Simulations provided also useful data for the assessment of the device process technology.
New High-Voltage Unipolar Mode p+ Si/n– 4H-SiC Heterojunction Diode
Authors: Hayashi Tetsuya , Tanaka Hideaki , Shimoida Yoshio , Tanimoto Satoshi , Hoshi Masakatsu
Published: March 2009

We demonstrate a new high-voltage p+ Si/n- 4H-SiC heterojunction diode (HJD) by numerical simulation and experimental results. This HJD is expected to display good reverse recovery because of unipolar action similar to that of a SiC Schottky barrier diode (SBD) when forward biased. The blocking voltage of the HJD is almost equal to the ideal level in the drift region of n- 4H-SiC. In addition, the HJD has the potential for a lower reverse leakage current compared with the SBD. A HJD was fabricated with p+-type polycrystalline silicon on an n--type epitaxial layer of 4H-SiC. Measured reverse blocking voltage was 1600 V with low leakage current. Switching characteristics of the fabricated HJD showed nearly zero reverse recovery with an inductive load circuit.
Steady-State and Transient Characteristics of High-Voltage 4H-SiC Junction Diodes
Authors: Ivanov Pavel A. , Levinshtein Michael E. , Mnatsakanov Tigran T. , Palmour John W. , Singh Ranbir , Irvine Kenneth G. , Das Mrinal K.
Published: March 2009

Forward current-voltage characteristics, reverse current recovery and post-injection voltage decay are measured for high voltage 4H-SiC p+non+-diodes. The effects of both minority carrier lifetime in diode no-base and injection coefficient of p+-emitter are investigated with respect to device performance at high injection levels.
Increased High Temperature Oxidation Resistance of Ni20Cr20Fe5Nb1Y2O3 Alloy with Nano-Sized Grains
Authors: Kim Il Ho , Kwun S.I.
Published: March 2009

The oxidation and tensile properties of a Ni20Cr20Fe5Nb alloy and a Ni20Cr20Fe
5Nb1Y2O3 alloy with nano-sized grains were compared with those of the comercial IN718 alloy. The oxidation resistance of the Ni20Cr20Fe5Nb1Y2O3 alloy was superior to that of the Ni20Cr20Fe5Nb and IN 718 alloys. This superior oxidation resistance was the result of both the formation of dense oxides on the surface of the alloy and the interruption of Cr migration in the alloy by the addition of
Y2O3. Moreover, the tensile property of the Ni20Cr20Fe5Nb1Y2O3 alloy at room temperature and 400oC was higher than that of the Ni20Cr20Fe5Nb and IN718 alloys by more than 300MPa (30%). This result can be attributed to the dispersion strengthening of Y2O3. The relatively low tensile strength at 600°C and 800°C of the alloys fabricated by mechanical alloying was attributed to grain
refinement showing intergranular fracture at high temperatures.
Hardness and Wear Resistance of Reaction Bonded SiC-B4C Composite
Authors: Lee Kee Sung , Han In Sub , Chung Yong Hee , Woo Sang Kuk , Lee Soo Wohn
Published: March 2009

Hardness and wear resistant characteristics of reaction-bonded silicon carbides with boron carbide additions are evaluated relative to those of reaction bonded silicon carbide (RBSC). The reaction-bonded SiC-B4C composites exhibit a distinctive improvement of hardness and wear resistance, indicative of high resistance against wear environment. Removal rates for the wear tests
are decisively reduced by the addition of boron carbide in the composites. Controlling the amount of carbon content in the starting composition more enhances the hardness of the reaction-bonded composites. Implications concerning the partial decomposition of B4C during reaction process are considered.
Fabrication and Thermoelectric Properties of N-Type Bi2Te3 Based Compounds by Spark Plasma Sintering
Authors: Lee D.M. , Lim Cheol Ho , Cho Dong Choul , Shin Seung Y. , Cho Won Seung
Published: March 2009

N-type Bi2Te3 based thermoelectric compound was prepared by spark plasma sintering with a temperature range of 340~460°C and powder size of ~75㎛, 76~150㎛, 151~250㎛. Thermoelectric properties of the compound were measured as a function of the sintering temperature and powder size. With increasing sintering temperature, the electrical resistivity and thermal conductivity of the compound greatly changed because of the increase in relative density. The Seebeck coefficient and electrical resistivity were varied largely with increasing powder size. Therefore, the compound sintered at 460°C, with the powder of ~75㎛, showed a figure of merit of 2.44 x 10-3/K. Also, the bending strength was 75MPa.
Nutrients Recovery by Struvite Formation from Wastewater in a Fluidized Bed Reactor
Authors: Lee Chan Won , Kwon H.B , Kim Young Jin , Jeon Hong Pyo
Published: March 2009

Nutrient removal and recovery from wastewater is being challenged to avoid
eutrophication problems, and the discharge standards have also been tightened by water regulations. Therefore, this study was undertaken to recover the nutrients from both synthetic wastewater and swine wastewater in a fluidized bed reactor (FBR). The operational parameters were changed to find out the optimum conditions for struvite formation. The most suitable pH was identified around pH 9. When the molar ratio of magnesium as Mg: P was 2:1 in the FBR, the removal efficiency of NH4-N and PO4-P was 79 and 90 %, respectively. The seed material was effective to form struvite in the condition of 30 g dosage. Struvite crystallization in reaction was completed in 20 minutes. The growth of struvite crystals was confirmed by the analysis of XRD, FT-IR and TG-DTA. In addition, the struvite was successfully recovered when the optimum conditions were applied to the swine wastewater.
Effect of Initial Grain Size on Deformation Behavior and Dynamic Recrystallization of Magnesium Alloy AZ31
Authors: Yang Xu Yue , Sanada Masayoshi , Miura Hiromi , Sakai Taku
Published: March 2009

Hot deformation and associated structural changes were studied in compression of a
magnesium alloy AZ31 with initial grain sizes (D0) of 22 µm and 90 µm at a temperature of 573K. D0 influences significantly the flow curve and the kinetics of grain refinement during hot deformation. For D0 = 22 µm, grain fragmentation takes place due to frequent formation of kink bands initially at corrugated grain boundaries and then in grain interiors in low strain, followed by full development of new fine grains in high strain. For D0 = 90 µm, in contrast, twinning takes place in coarser original grains, and then kink bands and new fine grains are formed mainly in finer ones at low strains. Then new grains are formed in necklace along the boundaries of coarse original grains, followed by their development into the grain interiors. Grain refinement in the Mg alloy can be concluded to result from a series of deformation-induced continuous reactions, they are essentially similar to continuous dynamic recrystallization (cDRX).
Formability and Process Conditions of Magnesium Alloy Sheets
Authors: Zhang Shi Hong , Xu Yong Chao , Palumbo G. , Pinto S. , Tricarico Luigi , Wang Z.T. , Zhang Q.L.
Published: March 2009

Comparing the formability with each other, extrusion and various rolling experiments
were carried out to make fine-grained AZ31 Mg sheets, and uni-axial tensile tests were carried out at different strain rates and temperatures to investigate the effect of different variables. A warm deep drawing tool setup with heating elements, which were distributed under the die surface and inside the blank holder, was designed and manufactured, and deep drawing was performed. Extruded Mg alloy AZ31 sheets exhibit the best deep drawing ability when working in the temperature range
250-350°C. Extruded and rolled sheets of 0.8 mm thick were also deep drawn in the lower temperature range 105-170°C，showing good formability and reaching a Limit Drawing Ratio up to 2.6 at 170°C for rolled sheets. At last, a sheet cup 0.4 mm thick was deep drawn successfully at 170 °C.
High Strength Mg-Zn-Y-Ce-Zr Alloy Bars Prepared by RS and Extrusion Technology
Authors: Guo Xuefeng , Kinstler Jacob , Glazman Lilia , Shechtman Dan
Published: March 2009

Based on the commercial alloy ZK60 which contains 6%Zn, high strength Mg-6.0%Zn-1.0%Y-0.6%Ce-0.6%Zr magnesium alloy bars of 10 to 50 mm in diameters were
prepared by rapid solidification (RS) and extrusion processes （RSE）. For those RSE solid bars, the ultimate tensile strengths steadily maintain on a level of 490 to 520 MPa, the elongations are between 6 to 10%. The HV50 hardness is between 85 and 90. In order to reveal materials microstructures both RS ribbons and RSE solid bars, the Mg-6.0%Zn-1.0%Y-0.6%Ce-0.6%Zr alloy was analyzed with an optical microscopy (OM), a scanning electron microscopy (SEM) equipped with an energy-dispersive X-ray spectrometer (EDS) and an X-ray diffraction apparatus. It was found that the microstructure of the RS ribbon consists of super saturated (Mg) solid solution; thermally stable Mg3Y2Zn3 (W) and
Mg7Ce2 intermetallic compound particles which uniformly dispersed interior grains and W and Mg7Ce2 compound networks at grain boundaries. After extrusion, the microstructure of RSE Mg-6.0%Zn-1.0%Y-0.6%Ce-0.6%Zr solid bar consists of the same phases as the RS ribbons. The networks existing at RS ribbon’s grain boundaries were break up into submicron particles and dispersed uniformly on the matrix formed after extrusion.
Corrosion and Protection of Magnesium Alloys: An Overview of Research Undertaken by CAST
Authors: Song Guang Ling
Published: March 2009

There is growing interest in magnesium alloys as structural materials for the
automotive, aerospace and electronic industries. However, the corrosion performance of most magnesium alloys is not good enough for the increasingly diverse practical applications. The Cooperative Research Centre for Cast Metals Manufacturing (CAST) is an Australian research organisation established to cope with the problems associated with development and application of light metals. Corrosion and prevention of magnesium and its alloys has been an important part
of CAST’s research program since 1995. The research effort in this area is focused on solving corrosion problems relative to the application of magnesium alloys in the automotive industries. Nevertheless, encompassed by the requirements of the applied research, some fundamental studies have also been conducted. This paper presents a brief summary of some of the research achievements in this area recently made by CAST. They include studies of corrosion behaviour, alloying effects, corrosion inhibition and surface treatment of magnesium alloys.
Phosphate Conversion Coating on Diecast AZ91D and Its Corrosion Resistance
Authors: Zhou Wan Qiu , Shan Da Yong , Han En-Hou , Ke Wei
Published: March 2009

A phosphate conversion coating was deposited on diecast AZ91D magnesium alloys, the film was a complex phosphate containing Mg and Al,which showed amorphous structure. Corrosion resistance of conversion coating in 3.5%NaCl was investigated by polarization curve. It was showed that the anodic branch of polarization curve for the phosphate conversion coating presented typical passivation characteristic. Immersion test results showed that the corrosion rate of phosphate conversion coating was less than that of chromate Dow7 film.