bluuebunny/crossref_metadata_2025 huggingface dataset:
Microstructural evolution of the BSCCO-2223 during powder-in-tube processing
Authors: Briant C.L. , Hall E.L. , Lay K.W. , Tkaczyk I.E.
Published: September 2007

This paper reports a study of the microstructural changes that occur when BSCCO powder is processed by the powder-in-tube method. In this study the initial powder consisted of the 2212 phase plus second phases containing Ca, Cu, Sr, and Pb. When the material was drawn, there was no alignment of the 2212 phase and the second phase particles remained large and blocky. Rolling induced a small amount of alignment into the 2212 phase so that its c-axis was perpendicular to the rolling direction. Rolling also caused the second phase particles to become flatter. When these rolled samples were annealed at 828 °C, the core sintered into a platelet structure, and there was an increase in the amount of aligned material, particularly after annealing treatments of 16 and 32 h. After 8 h at 828 °C, the 2212 variant of the superconducting phase began to transform to the 2223 variant. Pressing this structure improved the alignment, and annealing after pressing allowed further conversion of the 2212 phase to the 2223 phase and apparently removed the strains produced by the pressing. Repeated pressing improved the alignment and repeated annealing allowed more conversion of 2212 to 2223. Both the improved alignment, produced by pressing, and the transformation of 2212 to 2223, produced by the anneals, caused the superconducting properties of the material to improve.
Substitutions in Hg-cuprate superconductors
Authors: Kirtikar V. , Singh K.K. , Morris D.E.
Published: September 2007

Several substitutions have been attempted in the Hg layer of the Hg 1212 and 1223 cuprate superconductors. A new series of (Hg,Bi)1212 superconducting compounds has been synthesized. The highest Tc of the series (92 K) is found for the composition (Hg0.67Bi0.33)Sr2(Y0.5Ca0.5)Cu2O7−δ, with lattice constants a = 3.811 Å and c = 12.002 Å. X-ray diffraction and SEM with EDX analysis confirm that Hg is indeed incorporated in the structure. High-pressure oxygenation at 250 bar and 400 °C changes the magnetization curve, adding a second transition at ∼42 K; the 92 K transition remains unchanged. High-pressure oxygenation of Pb-substituted composition of the 1223 system, (Hg0.67Pb0.33)Ba2Ca2Cu3O8 also leads to the formation of low temperature phase with Tc = 67 K. The low Tc phase is associated with the incorporation of extra oxygen, possibly in the Hg layer.
Diamond-ceramic composite tool coatings
Authors: Fan W.D. , Chen X. , Jagannadham K. , Narayan J.
Published: September 2007

We have developed multilayer composite diamond coatings with improved adhesion and wear resistance on WC(Co) tool substrates. The coatings consist of a first layer of discontinuous diamond crystallites that are anchored to the WC(Co) substrate by an interposing layer of ceramic films. These films consist of TiC, TiN, SiC, Si3N4 or WC deposited to provide a conformal coverage on the first layer of diamond. A second or final layer of continuous diamond film is deposited to provide the cutting edge of the tool. The diamond film in the composite layers is deposited by hot filament chemical vapor deposition (HFCVD) and the interposing layer is deposited by laser physical vapor deposition (LPVD). The different parameters associated with the deposition of diamond and interposing layers are optimized to improve the adhesion and wear resistance. We have studied the adhesion characteristics by indentation tests in which the critical load for peeling of the diamond films is determined. Adhesion and wear resistance of the films are also tested using an overlap polishing on diamond paste with 5–6 μm particle size. The diamond and interposing layers in the composite are characterized by scanning electron microscopy and Raman spectroscopy. Results of improvement in adhesion and wear resistance are correlated with the quality of the diamond film and the interposing layer. Better accommodation of thermal stresses and strains in the composite layers has been shown to be responsible for improvement in the adhesion and wear resistance of the composite diamond films.
High-resolution electron microscopy of dislocations of MgO
Authors: Ohta J. , Suzuki K. , Suzuki T.
Published: September 2007

Dislocations in MgO introduced by ion irradiation and by plastic deformation are observed by HREM. Depending on the Burgers vector and the dislocation character, various types of lattice images are obtained. Image simulations are performed for the inclination of dislocations, as well as for dissociated dislocations. A comparison of observed and simulated images shows that inclination of nondissociated dislocations makes them appear as if they were dissociated; in reality a/2(110) dislocations in MgO are not dissociated.
Nanocrystalline Ni-Mo alloys and their application in electrocatalysis
Authors: Schulz R. , Huot J.Y. , Trudeau M.L. , Dignard-Bailey L. , Yan Z.H. , Jin S. , Lamarre A. , Ghali E. , Van Neste A.
Published: September 2007

The structural and electrocatalytic properties of metastable Ni-Mo alloys have been investigated for the hydrogen evolution reaction in alkaline solutions. Amorphous and nanocrystalline phases have been prepared by mechanically alloying the elemental components under various milling conditions. Fcc nanocrystals are formed when the Mo concentration is smaller than 30 at. %. The nanocrystalline state becomes unstable with respect to the amorphous phase when the Mo content in the solid solution exceeds 30 at. %. The electroactive phase for the hydrogen evolution reaction in alkaline solutions is the nanocrystalline supersaturated solid solution. The presence of oxygen during the milling process improves the properties of the alloys.
Self-limited growth of InAs at 480 °C
Authors: Jung D. , Bedair S.M.
Published: September 2007

Self-limited growth of InAs at 480 °C is achieved by a rotating substrate method with a specially designed susceptor. The residual precursors and the boundary layer are removed by the mechanical shear-off. Prevention of the precursor carryover and the gas-phase decomposition are thought to result in the self-limited growth of InAs at temperatures as high as 480 °C.
Synthesis of β-SiC powder by use of microwave radiation
Authors: Ramesh P.D. , Vaidhyanathan B. , Ganguli Munia , Rao K.J.
Published: September 2007

Monophasic β-SiC powder has been synthesized in a commercial microwave oven operating at 2450 MHz and power levels up to 980 W. This simple method of solid-state synthesis involves a direct reaction between silicon and charcoal powder at temperatures lower than 1250 K.
Size distribution of huntite-borate crystals grown by spontaneous crystallization from flux
Authors: Chani Valery I. , Inoue Keiji , Shimamura Kiyoshi , Fukuda Tsuguo
Published: September 2007

Rare-earth huntite-borates R(Al, Ga)3(BO3)4, where R = Yb, Er, and/or Nd, were grown by spontaneous crystallization from fluxes based on Bi2O3-B2O3. Crystals were removed from the melts and selected to different size fractions using meshes. It was found that dependence of weight for each size fraction on size in double logarithm coordinates was close to a symmetrical function. The dependence of logarithm of crystal amount on size was almost linear.
Local order in YBa2Cu3−yCoyO6+2x studied by anomalous diffuse x-ray scattering
Authors: Renevier H. , Kan X.B. , Quintana J.P. , Zhang K.J. , Cohen J.B.
Published: September 2007

The local order in a single crystal of YBa2Cu2.53Co0.47O7.13 has been studied with anomalous diffuse x-ray scattering. (For such a Co concentration the compound is nonsuperconducting.) Intensity measurements were carried out at two energies below the Co edge. The difference data could then be expressed in terms of the local structure around a Co atom. The short-range order parameters (α's) indicate that the Co and Cu atoms are nearly randomly distributed on the Cu1 sites. The estimated size of the Co-free “domains” is 5-7 Å. The first neighbor in-plane Co-Co distances are significantly shortened, indicating that the Co atoms are displaced from their average positions. The data also show a significant decrease of the Co-O1 distance, leading to an increase of the Cu2-O1 distance. The lengthening of the Cu2-O1 distance implies a lowering of the Cu2 formal valence. The Co substitution also affects the in-plane Cu2 positions. The present study shows that the Cu-O2 structural coherence is altered on a scale smaller than the superconducting coherence length. As far as the superconductivity is concerned, the Cu2 valence remains one of the most important parameters in determining the superconducting properties of the Co-doped 123 compounds. On the other hand, there is some evidence that in order for superconductivity to occur in this and other doped cuprate compounds, the size of dopant-free regions in the basal plane may have to exceed the superconducting coherence length.
Direct measurement of crack shielding in ceramics by the application of Raman microprobe spectroscopy
Authors: Belnap Daniel J. , Tsai Jing-Fong , Shetty Dinesh K.
Published: September 2007

Raman microprobe spectroscopy was employed to measure stresses in ceria partially stabilized zirconia/alumina (Ce-TZP/Al2O3) composites toughened by transformation zone shielding. The near crack-tip stresses inin situloaded compact specimens were measured by measuring stress-induced shifts in the frequency of a Raman peak corresponding to the tetragonal zirconia phase. The peak shift as a function of the applied stress was separately calibrated using a ball-on-ring flexure test. Both analytical function-fitting methods and numerical methods that determine centroids were evaluated for measuring the shift in the frequency with applied stress. A method based on locating the centroid of the intensity peak with a moving range of frequencies was selected because it gave the best correlation between the frequency shift and the applied stress. The stresses measured within an inner core of the transformation zone (∼30 μm), where the volume fraction of the transformed monoclinic phase was essentially constant, were used to estimate a local crack-tip stress intensity (Kl). The amount of total crack shielding (ΔKs) was then estimated from the applied stress intensity (Ka) and the estimated local crack-tip stress intensity. Comparisons with the predictions of two different theories of zone shielding indicated that transformation toughening models can account for 80 to 89% of the measured crack shielding, depending upon the value of the crack-tip stress intensity assumed in the models.
Surface flaw distributions in brittle materials and Hertzian fracture
Authors: Warren P.D. , Hills D.A. , Roberts S.G.
Published: September 2007

Refined mode I and mode II stress intensity factors for short cracks perpendicular to a free surface driven by a Hertzian indenter have been calculated for the case where the sphere and substrate are made of the same material. Computer simulations of Hertzian indentation tests for a variety of random surface flaw distributions show that the ring crack is expected to form outside the contact radius in all cases and that for spheres of small radii, the fracture load is expected to be proportional to the sphere radius (Auerbach's law). Reconstruction of the surface flaw distribution using the “searched area” concept is described. A useful analytical approximation for the stress intensity factors is also presented.
Thermoelectric generators made of FeSi2 and HMS: Fabrication and measurement
Authors: Groβ Erwin , Riffel Michael , Stöhrer Ulrich
Published: September 2007

Single couple thermoelectric generators consisting of n-type FeSi2 and p-type higher manganese silicide were developed and characterized. The leg and the bridge materials were prepared by a powder metallurgical method. Using the Peltier effect the transport properties were measured over the whole working temperature range. Electrical contacts suitable for the hot side could be obtained by conventional vacuum soldering and those for the cold side by ultrasonic soldering. The measured efficiency was in excellent agreement with the calculated values derived from the leg and contact properties.
Mechanical properties of a 20 vol % SiC whisker-reinforced, yttria-stabilized, tetragonal zirconia composite at elevated temperatures
Authors: Dougherty S.E. , Nieh T.G. , Wadsworth J. , Akimune Y.
Published: September 2007

The high-temperature deformation behavior of a SiC whisker-reinforced, yttria-stabilized, tetragonal zirconia polycrystalline composite containing 20 vol % SiC whiskers (SiC/Y-TZP) has been investigated. Tensile tests were performed in vacuum at temperatures from 1450 °C to 1650 °C and at strain rates from 10−3 to 10−5 s−1. The material exhibits useful high-temperature engineering properties (e.g., ∼100 MPa and 16% elongation at T = 1550 °C and at a strain rate of ∼10−4 s−1). The stress exponent was determined to be n ≍ 2. Scanning electron microscopy was used to characterize the grain size and morphology of the composites, both before and after deformation. The grain size in the composite was initially fine, but coarsened at the test temperatures; both dynamic and static grain growth were observed. The morphology of ceramic reinforcements appears to affect strongly the plastic deformation properties of Y-TZP. A comparison is made between the properties of monolithic Y-TZP, 20 wt. % Al2O3 particulate-reinforced Y-TZP (Al2O3/Y-TZP), and SiC/Y-TZP composites.
Shock compression of graphite materials bearing different microtextures and their relations to diamond transition
Authors: Hirai H. , Ohwada T. , Kondo K.
Published: September 2007

Microtexture dependence of diamond transition in starting graphite materials under shock compression was examined, taking account of two critical points. (i) As the starting materials, several different graphite materials, each of which possesses homogeneous microtexture throughout the material, were used. (ii) In order to distinguish the effect of the microtexture from that of other external conditions, an advanced technique that made the pressure-temperature condition common for the individual materials was developed. Four graphite materials, a glassy carbon, two types of carbon black, and artificial graphite foil, were selected and characterized in detail by x-ray diffractometry, Raman spectroscopy, transmission electron microscopy (TEM), and electron energy-loss spectroscopy (EELS) prior to the shock loading. Shock compressions were performed for the materials, changes in the microtexture and transformed products of the recovered samples were characterized by TEM and EELS, and the effect of the microtexture on the transition to diamond was also discussed.
Addendum
Authors: Byrappa K. , Umesh Dutt B.V. , Clearfield A. , Poojary M. Damodara
Published: September 2007

Addendum: “Crystal growth, morphology, structure, and properties of HNaMP2O7 crystals where M = Co and Ni” [J. Mater. Res. 9, 1519 (1994)]
Phase relationships in the system Si3N4–SiO2–Yb2O3
Authors: Nishimura Toshiyuki , Mitomo Mamoru
Published: September 2007

Phase relationships in the system Si3N4−SiO2−Yb2O3have been investigated at 1750 °C and compared with those in the system Si3N4−SiO2−Y2O3. Two types of ytterbium silicon oxynitride, Yb2Si3O3N4(tetragonal) and Yb4Si2O7N2(monoclinic), were confirmed to exist. The x-ray powder diffraction data of two compounds were indexed based on the space group and unit cells. Melting temperature of Yb4Si2O7N2was determined as 1870 °C. Yb4Si2O7N2is a better intergranular phase of silicon nitride ceramics for its high melting temperature.
Vapor grown carbon fiber reinforced aluminum composites with very high thermal conductivity
Authors: Ting Jyh-Ming , Lake Max L.
Published: September 2007

The first use of continuous vapor grown carbon fiber (VGCF) as reinforcement in aluminum metal matrix composite (Al MMC) is reported. Al MMC represents a new material for thermal management in high-power, high-density electronic devices. Due to the ultrahigh thermal conductivity of VGCF, 1950 W/m-K at room temperature, VGCF-reinforced Al MMC exhibits excellent thermal conductivity that cannot be achieved by using any other carbon fiber as reinforcement. An unprecedented high thermal conductivity of 642 W/m-K for Al MMC was obtained by using 36.5% of VGCF.
The use of shape correction factors for elastic indentation measurements
Authors: Hendrix B.C.
Published: September 2007

Elastic properties of small volumes of materials can be measured from the unloading of small indentations using the so-called nanoindenters The analytic elastic solutions for axisymmetric indenters are currently used to calculate modulus from the unloading curve, sometimes using corrections derived for flat, rigid punches. It is shown that these corrections represent an upper limit for the correction. More realistic corrections are derived for the Vickers, Berkovich, and Knoop indenter shapes, using the assumption of a uniformly loaded area. Results show that the axisymmetric solution overestimates the elastic compliance of the Vickers indenter by a factor of 1.0055, of the Berkovich indenter by a factor of 1.0226, and of the Knoop indenter by a factor of 2.682.
Microstructure and growth mechanisms of YBa2Cu3Ox films prepared by rf thermal plasma evaporation
Authors: Tsujino J. , Tatsumi N. , Shiohara Y.
Published: September 2007

We prepared YBa2Cu3Ox films on (100) MgO and (100) SrTiO3 substrates by rf thermal plasma evaporation, and investigated microstructure and growth mechanisms of these films by observation of the surfaces using an AFM technique. As a result, 2D nucleation and further coalescence between vicinal grains were observed in the initial stage of growth. In the films prepared for a deposition time of 3 min, the different complex growth modes, including spiral growth, “birth and spread” growth, and 2D growth, were observed, which might be due to high growth rate over 55 nm/min of this process.
Preparation of barium titanate ceramics from amorphous fine particles of the Ba–Ti–O system and its dielectric properties
Authors: Wada S. , Suzuki T. , Noma T.
Published: September 2007

Using titanium nitrate solution stabilized by chelation, amorphous fine particles of the Ba-Ti-O system were prepared by the mist decomposition method in air. After calcination of these particles, barium titanate ceramics were prepared using the hot uniaxial pressing method, and various properties were investigated. As a result, the grain sizes could be controlled over the range from 58 nm to 187 nm by the sintering temperatures and/or the calcination temperatures, keeping the density almost constant. Moreover, the dielectric properties of the samples showed that the relative permittivity decreased with decreasing grain size, and Curie temperature also shifted to lower temperatures in the same way. In this study, we first found that Curie temperature existed in the barium titanate ceramics with grain sizes from 58 to 147 nm.
Reactive IrO2 sputtering in reducing/oxidizing atmospheres
Authors: Klein J.D. , Clauson S.L. , Cogan S.F.
Published: September 2007

An Ir metal target was reactively rf sputtered in a planar magnetron source to develop iridium oxide deposition conditions. Gas blends of hydrogen, oxygen, and argon were used to provide competitive control over the reduction/oxidation characteristics of the sputter plasma. Optical emission spectroscopy allowed direct observation of hydrogen, oxygen, and iridium atomic peaks and OH molecular bands. Each of the twelve gas flow conditions could be clearly defined as either reducing or oxidizing by plasma emission spectroscopy. A given plasma reduction/oxidation state can be maintained over a wide range of gas flow conditions by coordinated adjustment of hydrogen and oxygen flows. The electrochemical properties of the iridium oxide films change dramatically in the vicinity of the reduction/oxidation plasma transition.
Accelerated microwave synthesis of magnesium sulfide with the pro-heating medium of graphite
Authors: Xu Yan , Xiao Xiaoyue
Published: September 2007

Two reaction routes have been tried for the synthesis of magncsium sulfide by applying microwave irradiation. In the first trial, finely ground Mg and S were mixed thoroughly and heated in a microwave oven for various lengths of time (5 + 5 + 8 + 10 and 12 + 12 + 35 + 45 min) in a sealed quartz tube. In the second trial, the pro-heating medium (PHM) of graphite was introduced into the mixture of Mg and S and microwaved for only 1 min. Results of x-ray diffraction analyses of the reaction products indicated that MgS polycrystallites (cubic, a0 = 5.201 ± 0.001) had formed in the second trial, and that the MgS yield was greater than 98%. Data of EDAX and EPMA gave a formula of MgS with atomic ratio of Mg:S = 1.0:1.0. In contrast, MgS could not be identified in the reaction mixtures in the first trial. Obviously, graphite, as a PHM, played a key role in the dramatic enhancement of the rate of the reaction between Mg and S powders. Furthermore, the effect of different molar ratios of graphite to Mg on the rate of microwave synthesis was investigated.
Development of a scanning laser crack detection technique for corrosion fatigue testing of fine wire
Authors: Schmidt Paul A. , Earthman James C.
Published: September 2007

A scanning laser crack detection technique has been developed for use in corrosion fatigue testing of fine metallic wires. The technique has been integrated into a computerized data acquisition and control system allowing the unattended operation of extended fatigue tests. The system is capable of detecting cracks with surface lengths as small as 100 μm, with crack opening displacements as low as 1 μm. Detection schemes of light loss and light scattering have been successfully used to monitor crack initiation in air and in 0.9% sodium chloride solution. The present scanning laser system has been used for crack initiation detection in over 50 fatigue experiments and has the potential for use in crack growth monitoring. The method can provide information concerning other surface phenomena in addition to the study of cracks. The technique has potential applications beyond metallic wires, including fibers used in optics and ceramic reinforcement fibers used in structural composites.
A model of diffusion/viscous mass transport in silicates during liquid-phase sintering
Authors: Nowok J.W.
Published: September 2007

The model of capillary transport of liquid metals driven by shear stress resulting from the displacement of menisci [J.W. Nowok, Scripta Metal]. Mater. 29, 931 (1993); Acta Metall. Mater. 42, 4025 (1994)] is applicable to liquid-phase sintering of silicate/aluminosilicate glasses. The movement of a liquid phase between adjacent particles is compared with that in capillaries. It appears that the transport property of intergranular melt may be expressed by the viscosity (η) and volume diffusion (D) parameters if mean displacement of menisci is compared with the mean diffusive jump lengths of atoms/molecules (L). This leads to the following relation: (γ/η)Lα = Dcap, where α and Dcap are a specific permeability and volume diffusion coefficient. The use of this model requires the assumption that the diffusing species are also the viscous flow units, and they can be either atoms or structural units. This assumption seems to be applicable for depolymerized silicate melts if the dominant mass transport is initiated by the diffusion of both nonbridging oxygen and silicon atoms.
Exploration of the deposition of submicrometer particles by spin-coating
Authors: Doornkamp C. , Laszlo C. , Wieldraaijer W. , Kuipers E.W.
Published: September 2007

The deposition of Cu, Zn, Pt, and Co precursor particles from solution onto a flat silicon wafer using a spin coater was studied. Homogeneously distributed monodisperse particles can be obtained. The dependence of particle size and number density on solution concentration and rotation frequency was investigated. Different solvents and support modifications were studied. The particles were analyzed using dark-field microscopy, scanning electron microscopy, and atomic force microscopy.
Effect of process variables on the grain growth and microstructure of ZnO–Bi2O3 varistors and their nanosize ZnO precursors
Authors: Hingorani Sunita , Shah D.O. , Multani M.S.
Published: September 2007

The basic building block of the ZnO varistor is the ZnO grain formed as a result of sintering. Nanosized ZnO particles are prepared by carrying out the reaction in the controlled size nanoreactors—the droplets of microemulsions. Chemical doping of the ZnO nanoparticles provides ZnO-based ceramic varistors displaying superior varistor properties. These varistors show a higher value of the nonlinear coefficient, lower leakage current, and higher critical electric field value as compared to those for conventional samples in their log E versus log J curve. The present work has also been aimed at studying the effect of processing variables such as sintering temperature and duration on the microstructure and grain growth of ZnO nanoparticles and ZnO-Bi2O3 ceramics. The activation energy calculated from this data is found to be 175 kJ/mol for pure ZnO. For Bi2O3-doped ZnO, the activation energy is found to decrease considerably (∼148 kJ/mol). All these advantages are due to greater structural homogeneity, smaller particle size, higher surface area, and higher density of the ZnO nanoparticles which are precursors for ZnO varistors, as compared to coarser particles for making varistors.
Design of highly CO2-soluble chelating agents for carbon dioxide extraction of heavy metals
Authors: Yazdi Ali V. , Beckman Eric J.
Published: September 2007

Carbon dioxide is an attractive organic solvent in today's chemical process environment, in that it is nonflammable, inexpensive, and exhibits low toxicity. Further, materials solubilized in carbon dioxide are easily and completely recovered/concentrated from solution via a simple pressure quench. Despite these favorable properties, CO2 is nonpolar and therefore is a very poor solvent for materials such as conventional metal chelating agents, thus blocking application of carbon dioxide in metal extraction/recovery. Consequently, we are exploring the molecular design of materials which are highly CO2 phillic, that is, they exhibit solubilities in carbon dioxide which are significantly greater than alkanes with the same number of main-chain atoms. By functionalizing chelating moieties with CO2-phillic oligomers, we have generated materials that both effectively extract metals from solid matrices and that dissolve in carbon dioxide in significant quantities. The application of such chelating agents is not limited to soil cleaning operations. In fact, these chelates make the use of CO2 possible in many applications where precision cleanup/recovery of metal ions are required. For example, CO2 has been promoted as a replacement for CFC's in cleaning processes in the electronics industry. Use of these chelates would allow the removal of metals, along with other impurities in a CO2 cleanup procedure.
Monoclinic ZrO2and its supported materials Co/Ni/ZrO2for N2O decomposition
Authors: Zeng H.C. , Lin J. , Teo W.K. , Wu J.C. , Tan K.L.
Published: September 2007

Monoclinic ZrO2and its supported materials Co/Ni/ZrO2(Co:Ni = 1:1) for catalytic decomposition of N2O have been studied with GC, FTIR, EDAX, XPS, and the evaluation of catalytic activity of the materials. It is found that monoclinic ZrO2alone has the catalytic effect for N2O decomposition, although higher activities are found for Co/Ni/ZrO2systems. XPS study shows that only Co exists in the surface region of ZrO2, which is attributed to the formation of NiO–ZrO2solid solution resulting from an interdiffusion between Ni2+and ZrO2matrix. The gas decomposition on Co/Ni/ZrO2can be described as first order with respect to partial pressure of N2O. Surface reactions on ZrO2and Co/Ni/ZrO2will also be addressed.
Cluster/dislocation interactions in dilute aluminum-based solid solutions
Authors: Lane Rohrer C.
Published: September 2007

The influence of single solute atoms and solute clusters on an extended edge dislocation dipole in Al was studied by atomistic simulation. Single Cu and Ag solute/dislocation interaction energy calculations showed that Cu interacts strongly with an Al extended dislocation and prefers sites in the compressive region, in agreement with elasticity theory predictions. Single Ag atoms, however, are strongly repelled by an Al extended dislocation, in contrast with elasticity theory predictions. Monte Carlo simulations of Al: 1% Cu, Al: 2% Cu, Al: 1% Ag, Al: 0.5% Cu, 0.5% Ag, and Al: 0.75% Cu, 0.25% Ag were carried out in the presence of an extended dislocation dipole at 600 K allowing for solute segregation. Cu atoms in the binary alloys were observed to segregate to the compressive regions of the extended dislocation dipole, forming widespread “atmospheres” over the width of both extended dislocations which did not affect the partial dislocation spacing. Ag in the binary alloy formed small Ag zones which also had little influence on the spacing between the partials. The ternary systems, however, exhibited highly localized solute clusters that had a large impact on the extended dislocation dipole structure, increasing the separation between the partial dislocations. The resulting cluster structures are discussed along with their influence on the apparent stacking fault energy of the alloy systems.
Modification of the surface properties of carbon fibers via the catalytic growth of carbon nanofibers
Authors: Down W.B. , Baker R.T.K.
Published: September 2007

The surface of commercial pitch and PAN-based carbon fibers has been modified by coating the structures with catalytically formed carbon nanofibers. Reaction conditions have been established that enable one to achieve optimum coverage by the secondary nanostructures without inducing any degradation in the mechanical properties of the parent fibers. Using this approach it is possible to produce a dramatic increase in the surface area of the fibrous structure from a nominal value of about 1.0 m2/g (untreated condition) up to between 250 and 300 m2/g (complete nanofiber coverage). This process results in a significant enhancement in the adhesion properties at the interface between the fiber and matrix components in a composite material. Mechanical tests performed on single uncoated and coated T300 carbon fibers demonstrated that it was possible to obtain an improvement of over 4.75 times in the interfacial shear strength of the fibers following deposition of a critical amount of nanofibers.
Kinetics of the reactive spreading of molten aluminum on ceramic surfaces
Authors: Weirauch Douglas A. , Balaba Willy M. , Perrotta Anthony J.
Published: September 2007

The spreading kinetics of molten aluminum on ceramic surfaces bearing reactive coatings has been studied through the direct observation of sessile drops, either formed in situ or emplaced at temperature. Analysis of videotapes permitted the assessment of the rate of advance of rapidly spreading droplets. Experimental conditions in this study were chosen to avoid the severe retarding effect of the aluminum oxide film which is typically encountered in aluminum wetting experiments. A variety of reactive coating systems were examined (B, Cu, Ni, Ti, and Ti + B), and the effect of coating amount was assessed. Based upon the experiments of this study, the main effect of the coatings is to drive spreading due to strong exothermic interfacial reactions. The intensity of the interfacial reaction causes the change in free energy per unit area of interface to dominate the rate of movement of the triple line.
Epitaxial growth of PbTiO3 thin films on (001) SrTiO3 from solution precursors
Authors: Seifert Andreas , Lange Fred F. , Speck James S.
Published: September 2007

A mixed alkoxide liquid precursor was used to form epitaxial PbTiO3 thin films by spin-coating on cubic (001) SrTiO3 substrates. The films were heat-treated at temperatures between 380 °C/1 h and 800 °C/1 h. X-ray diffraction, atomic force microscopy, scanning and transmission electron microscopy were used to characterize the microstructure of the films and to evaluate the epitaxial phenomena. At ∼400 °C/1 h, a polycrystalline, metastable Pb-Ti fluorite crystallizes from the pyrolyzed amorphous precursor. At slightly higher temperatures (∼420 °C/1 h), the thermodynamically stable phase with the perovskite structure epitaxially nucleates at the film/substrate interface. A small number of epitaxial grains grow through the film toward the surface and consume the nanocrystalline fluorite grains. Coarsening of the perovskite grains leads to a reduction in mosaic spread during further heating. Pores, which concurrently coarsen with grain growth, produce a pitted surface as they disappear from within the film. At 800 °C/1 ha dense epitaxial PbTiO3 film with a smooth surface is observed. Parameters governing the formation of a- and c-domains are discussed as well as the small tilts of the domain axes away from the substrate normal.
Microstructures of a-axis oriented YBCO films made by hybrid plasma sputtering
Authors: Ito W. , Oishi A. , Mahajan S. , Yoshida Y. , Morishita T.
Published: September 2007

Microstructures of a-axis oriented YBa2Cu3O7−x films made by newly developed de 100 MHz hybrid plasma sputtering were investigated using transmission electron microscopy (TEM). The films deposited on (110) NdGaO3 and (100) SrTiO3 substrates were found to grow in a perfect epitaxial fashion and with clear interface. The plan view of the TEM image showed that both films were comprised of two kinds of grains having the c axis aligning along two perpendicular directions in the plane with equal probability. The structures of the grain boundary, however, were found to be very different for the two films from the plan views. The film on NdGaO3 showed a lot of twist boundaries, while the film on SrTiO3 consisted of many symmetrical tilt boundaries and basal-plane-faced tilt boundaries. The type of grain boundary is determined by the anisotropic growth rates of the film between c direction and a-b direction.
Microstructural study of GaAs epitaxial layers on Ge(100) substrates
Authors: Guelton N. , Saint-Jacques R.G. , Lalande G. , Dodelet J-P.
Published: September 2007

GaAs layers grown by close-spaced vapor transport on (100) Ge substrates have been investigated as a function of the experimental growth conditions. The effects on the microstructure of the surface preparation, substrate misorientation, and annealing were studied using optical microscopy and transmission electron microscopy. Microtwins and threading dislocations are suppressed by oxide desorption before deposition. Single domain GaAs layers have been obtained using a 50 nm thick double domain buffer layer on an annealed Ge substrate misoriented 3°toward [011]. The mismatch strain is mainly accommodated by dissociated 60°dislocations. These misfit dislocations extend along the interface by the glide of the threading dislocations inherited from the substrate, but strong interaction with antiphase boundaries (APB's) prevents them from reaching the interface. These results are discussed and compared with previous reports of GaAs growth on Ge(100).
Formation and microstructural development of TiSi2 in (111)Si by Ti ion implantation and annealing at 950 °C
Authors: Jin S. , Aindow M. , Zhang Z. , Chen L.J.
Published: September 2007

A transmission electron microscopy study of the microstructural development for (111)Si wafers implanted with Ti ions and annealed subsequently at 950 °C is presented. The as-implanted wafers have a Ti-rich amorphous layer at the surface with embedded silicides, which correspond to a crystalline form of TiSi2 that has not been reported previously. Below this lies a Ti-lean crystalline layer with extensive radiation damage. The annealed layers have large incoherent islands of C54 TiSi2, with a layered microstructure in the Si between them consisting of twins, then topotaxial silicides, then dislocation loops. It is proposed that this microstructure arises from silicide growth prior to epitaxial regrowth, whereas for the continuous epitaxial films observed previously at lower annealing temperatures, epitaxial regrowth precedes silicide development.
Mullite formation from nonstoichiometric slow hydrolyzed single phase gels
Authors: Wang Yong , Thomson William J.
Published: September 2007

A comparative dynamic x-ray diffraction (DXRD) and differential thermal analysis (DTA) study was performed in the investigation of mullite and spinel formation from slowly hydrolyzed single phase gels with Al/Si ratios ranging from 1/1 to 14/1. Both metastable tetragonal mullite and spinel were observed to form at temperatures <1000 °C in the gels with Al/Si ratios <8/1 and mullite transformed to the orthorhombic structure at ∼1250 °C. However, at higher Al/Si ratios, spinel was the only crystalline phase detected at <1000 °C and orthorhombic mullite formed directly at temperatures >1250 °C. As the Al/Si ratio increases, both the tetragonal mullite and spinel formation temperatures decrease while the orthorhombic mullite formation temperature increases. Based on the Al/Si composition where the formation extents of tetragonal mullite and spinel were maximum, their compositions are estimated to be 2Al2O3 · SiO2 and 6A12O3 · SiO2, respectively.
Constrained-film sintering of a gold circuit paste
Authors: Choe JoonWon , Calat Jesus Noel , Lu Guo-Quan
Published: September 2007

We studied the constrained-film sintering of a gold circuit paste used in microelectronic packaging applications. Optical techniques were developed to determine the shrinkage profiles of constrained and free films and stresses generated during sintering in the constrained films. Constrained films approximately 60 μm thick were made by multiple screen-printing of the gold paste on rigid alumina substrates, while the free films were obtained by peeling off portions of the gold films from the substrate after binder burnout. Constrained films for stress measurement were made by multiple screen-printing on an oxidized 25 μm thick silicon substrate. Sintering runs were done in a hot stage at temperatures between 650 °C and 900 °C. The densification rates were much lower in the constrained films than those in the free films. The in-plane tensile stresses in the constrained films, determined by wafer curvature measurement, rose rapidly to a maximum level of 510 kPa during the initial stage of sintering and then gradually decreased. The reduction in the sintering potential due to the hydrostatic stress is not large enough to completely account for the retarded densification in constrained films. SEM micrographs of the film microstructures after sintering showed no-significant difference in grain growth kinetics between the constrained and free films. However, the activation energy for densification was found to be very different between the two types of films, 90.1 ± 4.3 kJ/mole for the free film and 188.8 ± 6.7 kJ/mole for the constrained film. We suggest that the retarded densification kinetics in the constrained gold films is due to (i) the reduction in the sintering potential by the hydrostatic stress and (ii) a change in the dominant sintering mechanism from grain-boundary diffusion in the free films to lattice diffusion in the constrained films.
Carbon in diesel participate matter: Structure, microwave absorption, and oxidation
Authors: Babu V. Suresh , Farinash L. , Seehra M.S.
Published: September 2007

The structural, microwave absorption, and oxidation characteristics of diesel particulate matter (DPM) collected from a CAT 3304 diesel engine are reported. The x-ray diffraction of DPM yields the characteristic peaks of pregraphitic carbons (cokes and pitches), and its modeling yields d(002) ≍ 3.429 Å and a crystallite size of about 20 Å. The real and imaginary parts of the dielectric constant ∊ = ∊′ + i∊″ are measured at 8.7 GHz using the cavity perturbation technique. The measured values for the DPM are ∊′ = 8.6 ± 1.7 and ∊″ = 7.4 ± 1.5, compared to ∊′ ≍ 1.0 and ∊″ ≍ 6 × 10−5 for the ceramic trap material used for collecting DPM. The oxidation products of the DPM, analyzed by FTIR spectroscopy, are found to contain CO2 and CO with a peak yield occurring around 500 °C. Since microwave power absorption is proportional to ∊″, these results show that selective microwave heating of the DPM in the ceramic traps should be a very efficient process with CO2 and CO as the main oxidation products.
Optimal thickness for Si interlayer as diffusion barrier at the Si3N4/GaAs interface: A transmission electron microscopy study
Authors: Zheng T. , Gibson J.M. , Mui D.S.L. , Morkoç H.
Published: September 2007

Using transmission electron microscopy, we investigate Si3N4 grown in situ on GaAs metal-insulator-semiconductor (MIS) device structures with a Si interlayer, which has been previously shown to improve the electrical properties of field-effect transistors with Si3N4 gates on GaAs. We find that the primary role of the Si interlayer is to prevent the reaction between the nitride or nitrogen used for growth and GaAs. The interlayer thickness dependence of this microstructure, and its relationship to electrical properties, are discussed. The optimal thickness of the thin pseudomorphic Si interlayer appears to be around 0.4 nm. The growth temperature dependence of the critical thickness for morphological instability is demonstrated.
Deformation and fracture of a directionally solidified NiAl–28Cr–6Mo eutectic alloy
Authors: Chen X.F. , Johnson D.R. , Noebe R.D. , Oliver B.F.
Published: September 2007

A directionally solidified alloy based on the NiAl-(Cr, Mo) eutectic was examined by transmission and scanning electron microscopy to characterize the microstructure and room temperature deformation and fracture behavior. The microstructure consisted of a lamellar morphology with a 〈111〉 growth direction for both the NiAl and (Cr,Mo) phases. The interphase boundary between the eutectic phases was semicoherent and composed of a well-defined dislocation network. In addition, a fine array of coherent NiAl precipitates was dispersed throughout the (Cr, Mo) phase. The eutectic morphology was stable at 1300 K with only coarsening of the NiAl precipitates occurring after heat treatment for 1.8 ks (500 h). Fracture of the aligned eutectic is characterized primarily by a crack bridging/renucleation mechanism and is controlled by the strength of the semicoherent interface between the two phases. However, contributions to the toughness of the eutectic may arise from plastic deformation of the NiAl phase and the geometry associated with the fracture process.
Elastic constants of single crystal γ – TiAl
Authors: He Y. , Schwarz R.B. , Migliori A. , Whang S.H.
Published: September 2007

The six independent second-order elastic stiffness coefficients of a Ti44Al56 single crystal (L10 structure) have been measured at room temperature for the first time using a resonant ultrasonic spectroscopy (RUS) technique. These data were used to calculate the orientation dependence of Young's modulus and the shear modulus. Young's modulus is found to reach a maximum near a [111] direction, close to the normal to the most densely packed planes. The elastic moduli and Poisson's ratio for polycrystalline materials, calculated by the averaging scheme proposed by Hill, are in good agreement with experimental data and theoretical calculations.
Densification kinetics of glass films constrained on rigid substrates
Authors: Bang Jaecheol , Lu Guo-Quan
Published: September 2007

The kinetics of constrained-film sintering were studied in a borosilicate glass (BSG) + silica system because of their applications in microelectronic packaging technologies. Samples with a silica content by 20% by volume were prepared from slurries of powder mixtures in a commercial polyvinyl butyral (PVB) binder solution. Constrained films about 0.2 mm thick were formed by doctor-blade casting the slurries on silicon wafers. Free-standing films about 0.6 mm thick were also produced by casting the slurries on a treated mylar sheet for easy lift-off. Sintering experiments were carried out in a hot stage at temperatures between 715 °C and 775 °C. Shrinkage profiles of the free and constrained (shrinkage in thickness only) films were determined in situ using a custom-designed optical system. The densification rates measured in the constrained films were slower than those in the free films. However, the substrate constraint had no effect on the activation energy of densification which was found equal to 385 ± 10 kJ/mol, the same for both free and constrained films. A relation between the constrained-film and free-film densification profiles was derived using the viscous analogy for the constitutive equations of a porous sintering body.
Extended x-ray absorption fine structure determination of local structure in sol-gel-derived lead titanate, lead zirconate, and lead zirconate titanate
Authors: Sengupta S.S. , Ma L. , Adler D.L. , Payne D.A.
Published: September 2007

We report on extended x-ray absorption fine structure (EXAFS) measurements for partially heat-treated gels in the lead zirconate titanate system (PZT). Self-consistent results obtained from the titanium and zirconium K-edges and the lead LIll-edge were used to determine bonding pathways between cations. For lead titantate (PT) and PZT gels, separate networks of predominantly Ti-O-Ti, Zr-O-Zr, and Pb-O-Pb linkages were observed. For lead zirconate (PZ) gels, both Zr-O-Pb and Zr-O-Zr linkages were observed. The results indicate heterogeneity at the molecular level. These findings are discussed in terms of the evolution of structure for PZT materials prepared by our sol-gel method.
3C–SiC/Si/3C–SiC epitaxial trilayer films deposited on Si(111) substrates by reactive magnetron sputtering
Authors: Wahab Q. , Hultman L. , Ivanov I.P. , Willander M. , Sundgren J-E.
Published: September 2007

A trilayer epitaxial structure of 3C-SiC/Si/3C-SiC was grown on Si(111) substrate by reactive magnetron sputtering. The layered structure consisted of a 300 nm thick Si layer sandwiched between two 250 nm thick 3C-SiC layers. Cross-sectional transmission electron microscopy (XTEM) showed that all layers were epitaxial to each other. The 3C-SiC layers contained stacking faults and double positioning domains with a high density in the second SiC layer. The Si layer showed the lowest density of planar faults, but developed growth facets. Observation was made of stacking faults propagating from 3C-SiC to Si layer as well as stacking faults originating at the termination of 3C-SiC double positioning boundaries into Si. The termination of Si stacking faults during growth of SiC is also reported.
Diffusion in a regular solid solution
Authors: Chu J.L. , Lee Sanboh
Published: September 2007

Diffusion in a regular solid solution was investigated. A thin plate of isotropic solid of constant surface molal fraction was considered. The regular solution is described by the parameter α. When α is positive, the attraction between unlike atoms is greater than the attraction between like atoms, and conversely. The depths of penetration and average molal fraction for a given period increase with increasing α. The separation of two curves for given α increase with increasing surface molal fraction. The diffusion coefficient is positive only if α is greater than −1/X(1 - X).