bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetics of Thermal Grain Boundary Grooving for Changing Dihedral Angles
Authors: Zhang W. , Sachenko P. , Schneibel J. H.
Published: March 2008

In his classic paper on thermal grain boundary grooving Mullins [W.W. Mullins, J. Appl. Physics 28, 333 (1957)] assumes that the dihedral angle at the groove root remains constant and predicts that the groove width and depth grow αt0.25. Here, we derive models describing groove growth while the dihedral angle changes. In our grooving experiments with tungsten at 1350 °C in which the dihedral angle decreased, the growth exponent for the groove depth reached values as high as 0.44 while the growth exponent for the width decreased slightly from Mullins' value of 0.25. Hence groove width data alone are not sufficient for verifying Mullins' growth law unless the dihedral angle is constant. The observed changes in the dihedral angle are used as an input for numerical simulations. With the simulations we are able to extract the surface diffusion constants. Atomic force microscope observations of groove widths and depths in tungsten are in excellent agreement with the simulations.
Dielectric Relaxation and Microwave Dielectric Properties of Bi2O3–ZnO–Ta2O5 Ceramics
Authors: Youn Hyuk-Joon , Randall Clive , Chen Ang , Shrout Tom , Lanagan Michael T.
Published: March 2008

The permittivity of two primary phases within the Bi2O3–ZnO–Ta2O5 system was measured from 100 Hz to approximately 8.7 GHz. A cubic pyrochlore (Bi3/2Zn1/2)(Zn1/2Ta3/2)O7 phase (a phase) exhibited a dielectric constant of 71 at low frequency which decreased to 64 at approximately 10 GHz. A lower symmetry zirconolite Bi2(Zn1/3Ta2/3)2O7 phase (β phase) was also measured and had a frequency independent dielectric constant of 60. The temperature dependence of the capacitance (τC), measured from −55 to 120 °C, was 78 ppm/°C for the β phase and nonlinear for the α phase having no unique slope. The primary difference in dielectric properties between these two phases was a low-temperature relaxation of the α phase, which is modeled as a basic Debye-type relaxation.
Electrorheological Properties of Suspensions Based on Polyaniline-montmorillonite Clay Nanocomposite
Authors: Lu Jun , Zhao Xiaopeng
Published: March 2008

It is thought that high-dielectric constant, suitable conductivity, and dielectric loss dominate electrorheological (ER) effects. According to this viewpoint, the polyaniline/montmorillonite nanocomposite (PANI-MMT) particles with high-dielectric constant and suitable conductivity were synthesized by an emulsion intercalation method. The electrorheological properties of the suspensions of PANI-MMT particles in silicone oil have been investigated under direct current electric fields. At room temperature, it was found that the yield stress of PANI-MMT ER fluid was 7.19 kPa in 3 kV/mm, which is much higher than that of pure polyaniline (PANI), that of pure montmorillonite (MMT) as well as that of the mixture of polyaniline with clay (PANI+MMT). In the range of 10–100 °C, the yield stress changed only 6.5% with the variation of temperature. The sedimentation ratio of PANI-MMT ERF was about 98% after 60 days. The structure of PANI-MMT particles was characterized by infrared, x-ray diffraction (XRD), and transmission electron microscopy (TEM) spectrometry, respectively. The XRD spectra show that the inner layer distance of PANI-MMT can be enhanced to 1.52 nm when the PANI was inserted into the interlayer of MMT, whereas it is only 0.96 nm for free MMT. TEM shows that the diameter of PANI-MMT particles is about 100 nm. The dielectric constant of PANI-MMT nanocomposite was increased 5.5 times that of PANI and 2.7 times that of MMT, besides, the conductivity of PANI-MMT particle was increased about 8.5 times that of PANI at 1000 Hz. Meanwhile, the dielectric loss tangent can also be increased about 1.7 times that of PANI. It is apparent that the notable ER effect of PANI-MMT ER fluid was attributed to the prominent dielectric property of the polyaniline-montmorillonite nanocomposite particles.
Preparation and Microstructure Evolution of Both Freestanding and Supported TiO2 Thin Films
Authors: Fan Chen-Lung , Ciardullo Daniel , Paladino Jay , Huebner Wayne
Published: March 2008

Thin films of TiO2 were fabricated by spin-coating silicon wafers and cover glass with a titanium citrate complex precursor. The grain growth and phase development of both freestanding and supported films were studied using a combination of atomic force microscopy, x-ray diffraction, and transmission electron microscopy. Freestanding films prepared at 400 °C possess only the anatase phase, while supported films treated under the same conditions formed a small amount of the rutile phase. After heat treatment at various temperatures, results indicated that porosity was introduced into the films when the grain size grew close to the film thickness. Grain growth studies show that the grain size of the freestanding film underwent a drastic increase during the transformation from anatase to rutile. The grain size of the supported films did not show an abrupt change upon heat treatment. The grain size of the freestanding films treated at 900 °C was approximately three times larger than that of the supported films.
Synthesis and Properties of Lead Zirconate Titanate Thin Films Via Metalorganic Chemical Vapor Deposition
Authors: Pan Chih-Yi , Chen Yin-Lang , Tsai Dah-Shyang
Published: March 2008

Ferroelectric PZT thin films were deposited on Pt and SrRuO3 substrates in a cold-wall reactor, using the Pb(C2H5)4/Zr(OBu)4/Ti(OPri)4/O2 reaction system. In comparison with Pt substrate, the growth rate of lead zirconate titanate (PZT) thin film was higher on SrRuO3. Lead content of the thin film deposited on either substrate at low temperatures (723–863 K) was much more temperature dependent than the other two metal contents. The strong temperature dependence originated from the high activation energy in the initial decomposition of Pb(C2H5)4 vapor, which was 54 kcal/mol. The surface reaction constant of lead precursor had much lower temperature dependence. The activation energy of surface reaction for PbO, estimated from deposition in a mini-chamber, was 6 kcal/mol on Pt and 9 kcal/mol on the SrRuO3 substrate. Therefore, the incorporation path of component oxide PbO, whose apparent activation energy was 31 kcal/mol on Pt and 29 kcal/mol on SrRuO3, essentially involved considerable gas-phase reaction. The PZT (50/50) thin film on SrRuO3 bottom electrode possessed a lower coercive field and a smaller remnant polarization than that on Pt. The PZT capacitor on SrRuO3 was also less vulnerable to polarization fatigue.
Microstructure and Characteristics in the Organic Matrix Layers of Nacre
Authors: Song F. , Zhang X. H. , Bai Y. L.
Published: March 2008

The direct observation of a type of microstructure in the organic matrix layers of nacre was obtained with a transmission electron microscope. The microstructure, which is referred to as mineral bridge in the biomineralization, is nanoscale and randomly distributed in the layers. Statistical analysis gives the distribution laws and characteristics of mineral bridges in the organic matrix layers. The existence of mineral bridges in nacre was confirmed, and it was shown that the microarchitecture of nacre should be described as a “brick–bridge–mortar” arrangement rather than traditional “brick and mortar” one.
Crystallization in SiO2–metal Oxide Alloys
Authors: Maria J-P. , Wickaksana D. , Parrette J. , Kingon A. I.
Published: March 2008

HfO2–SiO2 and La2O3–SiO2 amorphous alloys were prepared, and their crystallization behavior was studied. The results suggest that higher permittivities can be achieved in the La-containing system without devitrification. The crystallization mechanisms between systems are distinctly different, yet observations are consistent with bulk material. Hf-containing materials tend toward phase separation, while La-containing materials tend toward silicate formation. For Hf-containing films, negligible thickness or time dependence was observed. In La-containing films, rapid thermal anneals could improve crystallization resistance, and thickness effects related to interface reactions were observed. These behaviors are discussed in the context of phase diagrams and metastable immiscibility.
Characterization of Reduced-pressure Chemical Vapor Deposition Polycrystalline Silicon Germanium Deposited at Temperatures ≤550 °C
Authors: Sedky Sherif , Witvrouw Ann , Caymax Matty , Saerens Annelies , Houtte Paul Van
Published: March 2008

This paper investigates the possibility of reducing the deposition temperature of polycrystalline silicon germanium to a level compatible with complementary metal-oxide semiconductor (CMOS) post processing. To achieve this goal, the exact wafer temperature during deposition was experimentally determined and it was found to be 30 °C lower than the reactor setting temperature. The deposition temperature was reduced from 625 to 500 °C. The impact of varying the deposition pressure from 10 to 760 torr and the germanium content from 15% to 100% was investigated. X-ray diffraction spectroscopy and transmission electron microscopy showed that the SixGe1−x films deposited at an actual wafer temperature of 520 °C are polycrystalline for germanium contents as low as 15%. Also, it was shown that the deposition conditions can be adjusted to yield a low tensile stress at an actual wafer temperature of 520 °C, which is suitable for integrating surface micromachined micro-electromechanical systems on top of standard CMOS wafers with Al interconnects.
Mechanical Performance of 3Y-TZP/Ni Composites: Tensile, Bending, and Uniaxial Fatigue Tests
Authors: Loópez S. , Bartolomeé J. F. , Moya J. S. , Tanimoto T.
Published: March 2008

Dense 3-mol%-yttria-stabilized tetragonal zirconia polycrystals (3Y-TZP/Ni) homogeneous composites were prepared by a wet-processing route with metal concentration ranging from 0 to 40 vol%. Cyclic fatigue stress/life, tensile and bending strength, and fracture toughness were investigated in 3Y-TZP monolithic samples and 3Y-TZP/Ni composites. It was found that the addition of Ni particles to the 3Y-TZP matrix produced an embrittlement effect in the composites, decreasing the mechanical properties. This fact was attributed to the weak bonding between the Ni and 3Y-TZP particles in samples sintered in a reductive atmosphere. Additionally, the presence of Ni particles decreases the cyclic tensile fatigue of the composites probably by an environmentally assisted slow crack growth.
Rate Dependence of Serrated Flow During Nanoindentation of a Bulk Metallic Glass
Authors: Schuh C. A. , Nieh T. G. , Kawamura Y.
Published: March 2008

Plastic deformation of Pd–40Ni–20P bulk metallic glass (BMG) was investigated by instrumented nanoindentation experiments over a broad range of indentation strain rates. At low rates, the load–displacement curves during indentation exhibited numerous serrations or pop-ins, but these serrations became less prominent as the indentation rate was increased. Using the tip velocity during pop-in as a gauge of serration activity, we found that serrated flow is only significant at indentation strain rates below about 1–10/s. This result suggests a transition in plastic flow behavior at high strain rates, in agreement with prior studies of BMGs under different modes of loading.
Dielectric Ceramics with Tungsten-bronze Structure in the BaO–Nd2O3–TiO2–Nb2O5 System
Authors: Zheng X. H. , Chen X. M.
Published: March 2008

Some tungsten-bronze compounds in the BaO–Nd2O3–TiO2–Nb2O5 system were prepared and characterized. Ba4Nd2Ti4Nb6O30 and Ba5NdTi3Nb7O30 had the filled tetragonal tungsten-bronze structure, and Ba3Nd3Ti5Nb5O30 consisted of the tetragonal tungsten-bronze major phase and a minor amount of secondary phase BaNd2Ti3O10. These compounds had significant relaxor behaviors, and the Curie temperatures (at 1 MHz) were 0 and 55 °C for Ba3Nd3Ti5Nb5O30 and Ba5NdTi3Nb7O30 ceramics, respectively. A high dielectric constant (213) combined with low dielectric loss (0.004 at 1 MHz) was obtained in Ba3Nd3Ti5Nb5O30 ceramics. In addition, the solid-solution range of BapNd6−pTi8−pNb2+pO30 was 3 < p ≤ 6.
Formation and Stability of Quasicrystalline and Hexagonal Approximant Phases in an Al–Mn–Be Alloy
Authors: Song G. S. , Fleury E. , Kim S. H. , Kim W. T. , Kim D. H.
Published: March 2008

Phase formation and thermal stability for an Al–Mn–Be alloy have been investigated by melt-spinning and conventional casting. Significant differences in the phase formation and the thermal stability of the microstructure were found as a result of the different cooling rates. In the melt-spun ribbons, a large volume fraction of a metastable icosahedral phase was found to coexist with an Al solid solution. In the bulk cast ingots, the primary phase formed in the two-phase microstructure was a hexagonal approximant phase of quasicrystals. This phase that solidified in the form of faceted particles embedded in the Al solid matrix proved to be thermodynamically stable during annealing at 540 °C for 100 h. The effect of Be addition on the formation of the stable approximant phase is discussed in terms of the Hume–Rothery mechanism.
Fe2+ Contents and Magnetocrystalline Anisotropy in Iron Defect LiZnTiMn Ferrites
Authors: Iglesias A. , Balmaseda J. , Arias A. González
Published: March 2008

An investigation of the effects of the iron defect k in LiZnTiMn ferrites using Mössbauer spectroscopy and ferromagnetic resonance techniques was carried out in single-phased samples. Results show that the isomer shifts have values corresponding to a compound with either low-spin Fe(II), low-spin Fe(III), or high-spin Fe(III). On the other hand, the Lande factor and the ferromagnetic resonance linewidth disclosed that g is always very close to 2, being equal to 2.02 when k = 0.06. A minimum in ΔH was detected for this value of k. From these results, the possible presence of Fe2+ in the samples could be excluded, and it was concluded that the changes in ΔH are due to the variation of the Fe(III) contents in the tetrahedral and octahedral sites. The existence of the minimum in ΔH is due to a compensation point in the magnetocrystalline anisotropy.
Influence of pH on the Structure of the Aqueous Sonolysis Products of Manganese(III) Acetylacetonate
Authors: Kumar V. Ganesh , Aurbach D. , Gedanken A.
Published: March 2008

An aqueous solution of Mn(III) acetylacetonate and LiOH was sonicated at 90 °C yielding nanoparticles of different manganese oxides. The nature of the product and its morphology are strongly dependent on the pH. In parallel nonsonicated reactions were carried out under identical conditions and vigorous stirring, and the results are compared with the sonochemical reactions.
Surface Effects on Nanoindentation
Authors: Zhang Tong-Yi , Xu Wei-Hua
Published: March 2008

In this paper, we report on a study of the surface effect on nanoindentation and introduce the apparent surface stress that represents the energy dissipated per unit area of a solid surface in a nanoindentation test. The work done by an applied indentation load contains both bulk and surface work. Surface work, which is related to the apparent surface stress and the size and geometry of an indenter tip, is necessary in the deformation of a solid surface. Good agreement is found between theoretical first-order approximations and empirical data on depth-dependent hardness, indicating that the apparent surface stress plays an important role in depth-dependent hardness. In addition, we introduce a critical indentation depth. The surface deformation predominates if the indentation depth is shallower than the critical depth, while the bulk deformation predominates when the indentation depth is deeper than the critical depth.
Effects of IrO2/Pt Hybrid Electrodes on the Crystallization and Ferroelectric Performances of Sol-gel-derived Pb(Zr,Ti)O3 Thin Film Capacitors
Authors: Kim Seung-Hyun , Park Dong-Yeon , Woo Hyun-Jung , Lee Dong-Soo , Ha Jowoong , Hwang Cheol Song
Published: March 2008

The effects of IrO2/Pt layered hybrid bottom and/or top electrode structures on the leakage current density versus voltage (J–V), polarization versus voltage (P–V), ferroelectric imprint, and fatigue properties of chemical-solution-derived Pb(ZrxTi1−x)O3 (PZT, Zr/Ti = 35/65) thin films were investigated. The best P–V and J–V performances were obtained from a capacitor with nonhybrid electrodes (Pt/PZT/Pt capacitor). However, the poor fatigue performance of the capacitor required the adoption of hybrid electrode structures. A thin IrO2 layer, as thin as 6 nm, which was inserted between top Pt electrode and PZT layer was sufficient for improving the fatigue performance without any degradation of the other ferroelectric properties. However, the same layer adopted on the bottom Pt electrode was not effective in improving the fatigue performance with degradation in P–V and J–V properties. This was ascribed to IrO2 layer dissolution into the PZT layer during the crystallization annealing of the PZT thin film. A thicker IrO2 layer resulted in more serious degradation.
Comparative Study of Thickness Dependence of Critical Current Density of Yba2Cu3O7–δ on (100) SrTiO3 and on Rolling-assisted Biaxially Textured Substrates
Authors: Kang B. W. , Goyal A. , Lee D. F. , Mathis J. E. , Specht E. D. , Martin P. M. , Kroeger D. M. , Paranthaman M. , Sathyamurthy S.
Published: March 2008

We investigated the dependence of critical current density (Jc) on thickness of Yba2Cu3O7−δ (YBCO) films grown by pulsed laser deposition on (100) SrTiO3 (STO) and on rolling-assisted biaxially textured substrates (RABiTS). The thickness of YBCO films varied from 0.19 to 3 μm. The highest Jcs of 5.3 and 2.6 MA/cm2 at 77 K, self-field were obtained for 0.19-μm YBCO films on STO and RABiTS, respectively. Jc was found to decrease exponentially with YBCO thickness on both substrates. However, the results suggest different mechanisms are responsible for the Jc reduction in the two cases. On STO, growth of a-axis grains within c-axis films and broadening of the in-plane texture were observed in thick films. On RABiTS, degradation in cube texture as well as development of a porous surface morphology were found to correlate with film thickness.
Stress Relaxation of a Patterned Microstructure on a Diaphragm
Authors: Zheng D. W. , Wang X. H. , Shyu K. , Chen C. , Chang C-T. , Tu K. N. , Mal A. K. , Guo Y. F.
Published: March 2008

Stress relaxation of a patterned thin film on diaphragms of different material and thickness was investigated through experimental study and numerical simulation. The diaphragm deflections, caused by relaxation of the residual stress in a patterned thin film residing on top, were measured using a Twyman–Green laser interferometer. The first diaphragm used was a Si3N4(top)/SiO2/Si composite diaphragm and the second a 0.5-μm-thick Si3N4 membrane. Custom-written simulation software, which uses a novel numerical algorithm named Nonlinear Sequential Analysis (N-LISA), was utilized to calculate the stress distribution in the patterned thin film and the diaphragm substrate. Agreement between the model and the experimental results was satisfactory. Simulation of the system balance between a tensile-stressed circular Ti film and a stress-free Si substrate of different thickness clearly shows a transition in the substrate behavior from a pure plate to a pure membrane. Interestingly, the deflection of the Si substrate caused by the residual stress in the Ti film reaches its maximum at a certain substrate thickness where plate and membrane characteristics coexist. This study addresses some basic mechanics issues involved in modern devices dealing with thin diaphragms.
Role of Cement Type on Carbonation Attack
Authors: Goñi S. , Gaztañaga M. T. , Guerrero A.
Published: March 2008

The carbonation of two hydrated ordinary portland cements of alkali content 1.03% or 0.43% Na2O equivalent and hydrated calcium aluminate cement (0.1% Na2O equivalent) was studied in a semi-dynamic atmosphere of 100% CO2, and 65% relative humidity at 20 ± 1 °C, for a period of 100 days. The changes of the microstructure before and during the carbonation were characterized by x-ray diffraction, mercury intrusion porosimetry, and scanning electron microscopy. The kinetics of the process was evaluated from the total CaCO3 content by means of thermogravimetric analysis. The changes of the mechanical flexural strength were also studied. The pore solution was collected and analyzed before and after different periods of time. The results were compared with those obtained under natural carbonation conditions. The results showed that the alkali content of cement does not influence the kinetics of the process when the carbonation is accelerated. In the case of natural carbonation, an induction period is produced in the ordinary portland cement of low alkali content and calcium aluminate cement. The carbonation rate of calcium aluminate cement is the slowest for accelerated and natural carbonation.
Solid-state 27Al Nuclear Magnetic Resonance Investigation of Plasma-facilitated NOx Reduction Catalysts
Authors: Wang Li-Qiong , Aardahl Christopher L. , Rappé Kenneth G. , Tran Diana N. , Delgado Marisol A. , Habeger Craig F.
Published: March 2008

Aluminum coordination distribution for alumina catalysts supported on mesoporous silica was examined. It was shown that aluminum coordination correlates to activity of the catalysts for plasma-enhanced, selective catalytic reduction of NOx with propene. Catalysts were prepared by incorporating aluminum onto the surface of a mesoporous silica support via three different post-synthesis routes to produce varying aluminum coordination. Aluminum trichloride, sodium aluminate, and aluminum isopropoxide precursors were examined. High-resolution, solid state 27Al nuclear magnetic resonance was used to determine aluminum coordination distributions for the resulting catalysts. Unsaturated aluminum sites (i.e., structural defects) correlated with increased activity at high temperatures while tetrahedrally-coordinated aluminum or BrØnsted acid sites correlated with activity at low temperatures.
Thermal Expansion of Low-pressure Chemical Vapor Deposition Polysilicon Films
Authors: Kahn H. , Ballarini R. , Heuer A. H.
Published: March 2008

Polysilicon films were deposited using low-pressure chemical vapor deposition (LPCVD) onto oxidized silicon substrates, after which substrate curvature as a function of temperature was measured. The curvatures changed with temperature, implying that the thermal expansion of LPCVD polysilicon differs from that of the single crystal silicon substrate. Further, polysilicon films with tensile residual stresses displayed an increased thermal expansion, while polysilicon films with compressive residual stresses displayed a decreased thermal expansion. Following high temperature annealing, the residual stresses of the polysilicon films were reduced to near zero, and the thermal expansion of the polysilicon films matched that of the single crystal substrate. The apparent change in thermal expansion coefficient due to residual stress was much larger than predicted theoretically.
Effect of Interface Conditions on Yield Behavior of Passivated Copper Thin Films
Authors: Vinci Richard P. , Forrest Stefanie A. , Bravman John C.
Published: March 2008

Wafer curvature was used to study the thermal–mechanical behavior of 1-μm Cu thin films capped with a 100-nm-thick Si3N4 layer. These films were grown with either a Ta or a Si3N4 underlayer. Films on Si3N4 that were exposed to oxygen at the film/capping layer interface or at the center of the copper layer exhibited Bauschinger-like yielding at low stress. Stacks deposited under continuous vacuum, with a Ta underlayer, with carbon exposure at the upper surface of the copper film, or with oxygen exposure of only the underlayer did not demonstrate the anomalous yielding. Preferential diffusion of oxygen into copper grain boundaries or interfaces is the likely cause of the early yield behavior. Possible mechanisms include an increase in interface adhesion due to the presence of oxygen in solution and diffusion-induced dislocation glide as an additional driving force for dislocation motion at low applied stress.
Wear behavior of bulk Zr41Ti14Cu12.5Ni10Be22.5 metallic glasses
Authors: Li Gong , Wang Y. Q. , Wang Li Min , Gao Yun Peng , Zhang R. J. , Zhan Zai Ji , Sun Li Ling , Zhang Jun , Wang Wen Kui
Published: March 2008

The wear behavior of bulk Zr41Ti14Cu12.5Ni10Be22.5 metallic glasses has been studiedusing sliding wear tests and scanning electron microscopy in both as-prepared and annealed samples. It was found that the wear resistance of differently processed samples increases in the following order: crystallized state; as-prepared state; relaxed state. The thermal stability of worn samples was also investigated by means of differential scanning calorimetry. Under the experiment conditions, no sliding wear-induced crystallization is observed in either as-prepared or relaxed samples indicating good thermal stability of the bulk metallic glasses.
Large-quantity production of high-yield boron nitride nanotubes
Authors: Chen Y. , Conway M. , Williams J. S. , Zou J.
Published: March 2008

A high quantity and yield (up to 85%) of boron nitride (BN) nanotubes have been produced using a mechanothermal method. Elemental boron powders were first mechanically milled at room temperature in NH3 atmosphere and subsequently heated in N2 gas at 1200 °C for up to 16 h. The BN nanotubes obtained have either multiwalled cylindrical or bamboolike structures, suggesting different growth processes. The high formation yield of BN nanotubes is due to a high density of nanostructured nuclei created by an extensive milling treatment.
X-ray photoelectron spectroscopy characterization and morphology of MgO thin films grown on single-crystalline diamond (100)
Authors: Lee S. M. , Ito T. , Murakami H.
Published: March 2008

The morphology and composition of MgO films grown on single-crystalline diamond (100) have been studied. MgO thin films were deposited in the substrate temperature range from room temperature (RT) to 723 K by means of electron beam evaporation using a MgO powder source. Atomic force microscopy images indicated that the film grown at RT without O2 supply was relatively uniform and flat whereas that deposited in oxygen ambient yielded higher growth rates and rough surface morphologies. X-ray photoelectron spectroscopy analyses demonstrate that the MgO film deposited at RT without O2 has the composition closest to that of the stoichiometric MgO and that a thin contaminant layer composed mainly of magnesium peroxide (before etching) or hydroxide (after etching) was unintentionally formed on the film surface, respectively.These results will be discussed in relation to the interaction among the evaporated species and intentionally supplied oxygen molecules at the growth front as well as the interfacial energy between diamond and MgO.
Creep property measurement of service-exposed SUS 316 austenitic stainless steel by the small-punch creep-testing technique
Authors: Saucedo-Muñoz Maribel L. , Komazaki Shin-Ichi , Takahashi Toru , Hashida Toshiyuki , Shoji Tetsuo
Published: March 2008

The creep properties for SUS 316 HTB austenitic stainless steel were evaluated by using the small-punch creep test at 650 °C for loads of 234, 286, 338, 408, and 478 N and at 700 °C for loads of 199 and 234 N. The creep curves, determined by means of the small-punch creep test, were similar to those obtained from a conventional uniaxial creep test. That is, they exhibited clearly the three creep stages. The width of secondary creep stage and rupture timetrdecreased with the increase in testing load level. The creep rupture strength for the service-exposed material was lower than that of the as-received material at high testing loads. However, the creep resistance behavior was opposite at relatively low load levels. This difference in creep resistance was explained on the basis of the difference in the creep deformation and microstructural evolution during tests. It was also found that the ratio between the load of small-punch creep test and the stress of uniaxial creep test was about 1 for having the same value of creep rupture life.
Mechanical and structural characterization of uniaxially cold-pressed Fe2Mo powders
Authors: Morales R. , Seetharaman S. , Agarwala V.
Published: March 2008

In this work, Fe2Mo intermetallic powder, produced by H2gas reduction of Fe2MoO4was characterized by techniques like x-ray diffraction (XRD) and transmission electron microscopy (TEM). The TEM studies confirmed the presence of nano- and microcrystalline grains of Fe2Mo. The above powders when compressed uniaxially showed a logarithmic relation with “relative density”, δr, of the compacts. The multiple compaction mechanisms were analyzed by Kawakita's and Balshin's models. Vickers hardness number, VHN, was found to increase linearly with δrof the compacts. The hardness of Fe2Mo intermetallic when δr= 1 was estimated as 343 VHN. Using Tabor's analysis, the yield strength of Fe2Mo was found to be about 1100 MPa. This value was further confirmed from the details of relative broadening (112) Bragg peak of Fe2Mo obtained from XRD analyses of Fe2Mo at different compaction pressures.
Bonding of silicon nitride ceramic composites with Y2O3–La2O3–Al2O3–SiO2 mixtures
Authors: Zhou Fei , Chen Zheng
Published: March 2008

Silicon nitride ceramic composites were bonded using mixed Y2O3, La2O3, Al2O3, and SiO2 powers. The effect of bonding conditions on the joint strength was studied. The joint strength under different bonding conditions was measured by four-point bending tests. The interfacial microstructures were observed and analyzed by scanning electron microscopy, electron probe microanalysis (EPMA), and x-ray diffraction (XRD), respectively. The results of EPMA and XRD analyses showed that the liquid/glass solders reacted with silicon nitride at the interface, forming a Si3N4//Si2N2O/Y–La–Si–Al–O–N glass/Y–La–Si–Al–O glass gradient interface. From the results of the four-point bending tests, it is known that with an increase in bonding temperature and hold time, the joint strength first increased, reached a peak, and then decreased. LaYO3 precipitated from the joint glass can improve strength of the joint at both room and high temperatures.
Preparation and isolation of gold nanoparticles coated with a stabilizer and sol-gel compatible agent
Authors: Trbojevich R. , Pellegri N. , Frattini A. , de Sanctis O. , Morais P. J. , Almeida R. M.
Published: March 2008

In this work an attractive technique is presented that brings together the advantage of the micelle reverse technique to control the particle growth and the efficiency of the amine silanes as sol-gel-compatible surface modifiers. The diamino silane is far from being a passive agent in the formation process of the gold particle; it strongly modifies the growth of the gold particle in the reverse micelle. The diamino silane allows the gold particles to keep their individual properties unaltered throughout the process, which ends with their incorporation into a SiO2–TiO2 sol-gel thin film.
Hydrothermal preparation of long nanowires of vanadium oxide
Authors: Pan Dengyu , Shuyuan Zhang , Chen Yiqing , Hou J. G.
Published: March 2008

Long beltlike nanowires were successfully synthesized for a semiconducting oxide of vanadium by a hydrothermal route at 180 °C for 5 h and were characterized by x-ray powder diffraction, energy dispersive -ray spectroscopy, and electron diffraction microscopy. The product is mainly layered V2O5 · 0.3H2O with a small fraction of V2O5 · xH2O (0.3 < x < 1.7) and V2O5 phases. The obtained nanowires, several tens of micrometers long and a few of tens of nanometers wide, are crystallized well, growing along the [010] direction. The effects of preparation conditions on the formation of the nanowires are discussed.
Aqueous processing of SiC green sheets I: Dispersant
Authors: Zhang J. X. , Jianga D. L. , Tana S. H. , Gui L. H. , Ruan M. L.
Published: March 2008

Poly(ethylene imine) (PEI) has been used as a dispersant for tape casting of SiC powders in aqueous media. The stability of SiC suspensions was studied and characterized in terms of zeta potential, sedimentation, adsorption, and rheology measurements. Zeta potential studies showed that the particle surface was negatively charged in the absence of PEI in the pH 2.5–13 ranges. Adsorptions of PEI increased the zeta potential and led to the shift of isoelectric point from pH 2.4 to pH 10.5. Sedimentation study showed that, in the absence of PEI, SiC slurries were stable around pH 6, while, in the presence of PEI, stabilization could be achieved at a condition of saturated adsorption (1.07 mg/m2) and was related to the high-;affinity adsorption in the pH = 10.5–11.5 range. The rheological measurements showed that SiC slurries (50 vol%) were well stability with slight thixotropical behavior. Finally, the best conditions to obtain a homogeneous stable slurry with high powder loading suitable for tap casting were determined.
Microstructure formation and phase selection in the solidification of Al2O3–5 at% SiO2 melts by splat quenching
Authors: Li Mingjun , Nagashio Kosuke , Kuribayashi Kazuhiko
Published: March 2008

An Al2O3–5 at% SiO2 specimen was levitated in an Aero-Acoustic Levitation apparatus and then melted when a continuous-wave CO2 laser beam heating system was incorporated. The sample can be highly undercooled when decreasing the laser power. Rapid solidification by splat quenching can be realized at defined temperatures, using well-polished copper as chilling anvils. Microstructure transition from nonfaceted colony to strong faceted dendrites was observed when the melt was quenched at ΔT = 50 K, indicating that a kinetic contribution for roughening the microstructure may be significant for the morphology transition. The impacting, spreading, and solidifying processes were analyzed on the basis of microstructure observation. The additional undercooling was suggested to vary per an exponential relation with distance when the kinetic effect was taken into account. The nucleation behavior was also discussed according to the proposed additional undercoolings to demonstrate the difference in nucleation population at various regions. When the melt undercooling increases to 190 K, a double-phase structure with small polycrystalline inclusion embedded into amorphous matrix was obtained. The continuous cooling transformation profile was proposed to account for the phase selection upon quenching. The present observation and suggested model for acquiring high additional undercoolings are useful in elucidating the work of others.
Tunability of τf in perovskites and related compounds
Authors: Wise P. L. , Reaney I. M. , Lee W. E. , Iddles D. M. , Cannell D. S. , Price T. J.
Published: March 2008

Tuning the temperature coefficient of resonant frequency (τf) in microwave dielectrics has been attributed to two main mechanisms: (i) dilution of the average ionic polarizability; (ii) the onset of an octahedral tilt transition above room temperature. The contributions of each mechanism have been isolated using ceramics in the Srn+1TinO3n+1, SrxCa1−x)3Ti2O7, and (SrxCa1−x)TiO3 series. In the Srn+1TinO3n+1 series, relative permittivity (εr) and τf are linearly proportional over a broad range of values, 100–37 and 800–140 ppm/°C, n = 4 and 1, respectively. No structural phase transitions occur on cooling from the prototype symmetry, and the mechanism of tuning is attributed solely to dilution of the average ionic polarizability as the SrO:SrTiO3 ratio increases. Exchanging Ca for Sr in the (SrxCa1−x)3Ti2O7 series resulted in an 80% reduction in the magnitude of τf from +320 to +50 ppm/°C but only 21% in permittivity (58 to 46). The effect was nonlinear and attributed primarily to the onset of a phase transition involving rotations of the octahedra on cooling. Superlattice reflections associated with the octahedral tilt transition have been identified.
Thermodynamics of crack healing under electropulsing
Authors: Qin Rongshan , Su Shengxia
Published: March 2008

The effect of electropulsing on the evolution of an elliptical cylinder microcrack was studied from a thermodynamic point of view. An analytical expression for the healing driving force with respect to the passing electric current density, crack geometric shape, Young's modulus, and sample size was derived. The critical current density for crack healing was calculated and agreed with the experimental results very well. The heterogeneous temperature rise due to Joule heat was calculated and proved ideal to the crack healing. Earlier experimental results can be fully understood within the present theoretical frame.
Consolidation of tungsten-coated copper composite powder
Authors: Dorfman L. P. , Houck D. L. , Scheithauer M. J.
Published: March 2008

Powder metallurgy (P/M) methods have expanded in recent years to include net-shape fabrication of W–Cu components. Sintering of W–Cu compacts made from previous powders has led to low density and copper bleedout. This paper presents test results on the consolidation of a new powder containing particles composed of a tungsten-coated copper core. This powder effectively eliminates copper bleedout at sintering thereby making possible the net-shape manufacturing of parts. Sintered articles are characterized by microstructural homogeneity and properties comparable to those of infiltrated W–Cu composites.
An in situ transmission electron microscope investigation into grain growth and ordering of sputter-deposited nanocrystalline Ni3Al thin films
Authors: Ng H. P. , Ngan A. H. W.
Published: March 2008

The grain growth kinetics and ordering behavior of direct-current magnetron sputter-deposited Ni75at.%Al25at.% alloy films were investigated using in situ isothermal annealing in a transmission electron microscope. Both normal and abnormal grain growth modes were observed. The normal grain growth kinetics under isothermal heating from 300 to 700 °C were found to comply with the Burke law d = K/dn−1, where d is grain size and K and n are constants with respect to time. The grain boundary mobility parameter K was found to obey an Arrehnius rate law with an apparent activation energy of 1.6 eV, and n was found to increase gradually from 5.2 at 300 °C to 8.7 at 700 °C. Abnormal grain growth occurred at 500 °C or higher, and grain coalescence was identified as an important operative mechanism. It was also observed that the initially as-deposited state of the films was crystalline with a disordered face-centered-cubic structure, but ordering into the equilibrium L12 intermetallic structure followed from annealing at temperatures above approximately 500 °C.
Nanocrystallization of Cu–(Zr or Hf)–Ti metallic glasses
Authors: Louzguine D. V. , Inoue A.
Published: March 2008

Crystallization of the Cu60Zr30Ti10 and Cu60Hf25Ti15 metallic glasses was studied by x-ray diffractometry, transmission electron microscopy, differential scanning and isothermal calorimetries. Metastable Cu–Zr–Ti and Cu–Hf–Ti cubic phases primarily precipitated in the Cu60Zr30Ti10 and Cu60Hf25Ti15 metallic glasses. The Cu60Zr30Ti10metallic glass crystallizes with low energy barrier for nucleation while crystallization of the Cu60Hf25Ti15 metallic glass takes place by nucleation and diffusion-controlled growth of cubic Cu–Hf–Ti phase particles with constant nucleation rate. The Cu60Hf25Ti15 metallic glass is characterized by a low activation energy for nucleation.
Micromachining of mesoporous oxide films for microelectromechanical system structures
Authors: Paik Jong-Ah , Fan Shih-Kang , Kim Chang-Jin , Wu Ming C. , Dunn Bruce
Published: March 2008

The high porosity and uniform pore size of mesoporous oxide films offer unique opportunities for microelectromechanical system (MEMS) devices that require low density and low thermal conductivity. This paper provides the first report in which mesoporous films were adapted for MEMS applications. Mesoporous SiO2 and Al2O3 films were prepared by spin coating using block copolymers as the structure-directing agents. The resulting films were over 50% porous with uniform pores of 8-nm average diameter and an extremely smooth surface. The photopatterning and etching characteristics of the mesoporous films were investigated and processing protocols were established which enabled the films to serve as the sacrificial layer or the structure layer in MEMS devices. The unique mesoporous morphology leads to novel behavior including extremely high etching rates and the ability to etch underlying layers. Surface micromachining methods were used to fabricate three basic MEMS structures, microbridges, cantilevers, and membranes, from the mesoporous oxides.
Investigation of mechanical alloying of Ti–Al compounds using perturbed γγ-angular correlation spectroscopy, x-ray diffraction, and differential scanning calorimetry
Authors: Lauer St. , Guan Z. , Wolf H. , Wichert Th.
Published: March 2008

Ti0.50Al0.50 and Ti0.75Al0.25 compounds were mechanically alloyed by ball milling of elemental Ti and Al powders. Radioactive 111In atoms incorporated into these compounds were used to investigate the different locally ordered crystalline structures by perturbed γγ-angular correlation spectroscopy (PAC). The formation of the intermetallic compounds γ–TiAl and α2–Ti3Al was observed on an atomic scale and occurred as a consequence of the heat treatment of mechanically alloyed Ti0.50Al0.50 and Ti0.75Al0.25, respectively. Due to the sensitivity of PAC to local order on an atomic scale, information about formation conditions and thermal stability of a new metastable phase with an ordered tetragonal crystal structure is presented for Ti0.50Al0.50 samples. In addition, the formation of the ordered phase Ti2AlN was observed, indicating the incorporation of N during the milling process. The PAC investigations were complemented by x-ray diffraction and differential scanning calorimetry measurements.
Thermal stability, crystallization kinetics, and grain growth in an amorphous Al85Ce5Ni8Co2 alloy
Authors: Révész Á. , Varga L. K. , Suriñach S. , Baró M. D.
Published: March 2008

Thermal stability and crystallization kinetics of the melt-quenched amorphous Al85Ce5Ni8Co2 alloy were investigated by x-ray diffraction and differential scanning calorimetry (DSC). The glass transition was followed by a supercooled liquid region (21 °C) and then by a two-step crystallization process. The final microstructure contained Al3Ce, α–Al, Al3Ni, and Al9Co2 phases. Isothermal annealing of the as-quenched samples in the range of 275–285 °C showed that both crystallization reactions occurred through a nucleation and growth process. Continuous heating DSC measurements following pre-anneals for different times were also carried out to study the crystallization kinetics and the stability of the material. The Avrami analysis of the isothermal DSC-curves revealed that the 3-dimensional nucleation and growth process became more dominant with increasing annealing temperature. The average specific grain boundary energy corresponded to high-angle grain boundaries and indicated independent nucleation events.
Lanthanum zirconate: A single buffer layer processed by solution deposition for coated conductor fabrication
Authors: Sathyamurthy S. , Paranthaman M. , Zhai H-Y. , Christen H. M. , Martin P. P. , Goyal A.
Published: March 2008

A single layer of La2Zr2O7 (LZO), deposited on textured Ni and Ni–1.7% Fe–3% W (Ni–W) tapes by a low-cost sol-gel process, is used as buffer layer for the growth of YBa2Cu3O7−δ (YBCO) coated conductors. It is shown for the first time that such single buffer layers can be used for the deposition of YBCO yielding critical current densities (Jc) that are comparable to those typically obtained using CeO2/YSZ/Y2O2 trilayers on identical substrates, i.e., in excess of 1 MA/cm2 at 77 K and self-field. The properties of the YBCO films and the dependence of Jc on thickness of the LZO layer are investigated.
Carbon nanotubular structures synthesis by means of ultraviolet laser ablation
Authors: Braidy N. , Khakani M. M. El , Botton G. G.
Published: March 2008

We report on the synthesis of carbon nanotubular structures produced for the first time by means of pulsed KrF laser ablation of a graphite pellet at high temperature (1150 °C), under high argon gas pressure (500 torr), and at relatively high ultraviolet (UV) laser intensities (8 × 108 W/cm2). The carbon nanotubular structures were directly observed by transmission electron microscopy and characterized by micro-Raman spectroscopy. Nanohorns (∼2.5 nm diameter and ∼10 nm long), a few single-wall nanotubes (1.2 to 1.5 nm diameter), and other nanotubular structures (such as graphitic nanocages and low-aspect-ratio nanotubules) were clearly observed in the carbon deposit. Raman spectra in the low-frequency range confirmed a population of tubular structures with diameters ranging from 0.7 to 2.0 nm. It is shown that the relatively high UV laser intensity used here favors the growth of various nanotubular structures to the detriment of single-wall nanotubes.
Hydrothermal synthesis of well-dispersed TiO2 nano-crystals
Authors: Yang Juan , Mei Sen , Ferreira José M.F.
Published: March 2008

Well-dispersed anatase and rutile nano-particles were prepared via hydrothermal treatment of tetrabutylammonium hydroxide-peptized and HNO3-peptized sols at 240 °C. A broad particle size distribution of anatase crystals was observed in the nonpeptized TiO2 species hydrothermally treated at 240 °C. X-ray diffraction and transmission electron microscopy, as well as zeta potential measurement, were used to characterize the particles. The formation of the well-dispersed anatase and rutile particles from the peptized samples could be attributed to (i) homogeneous distribution of the component in the peptized sols, and (ii) the high long-range electrostatic forces between particles in the presence of both peptizers, which were not present in the nonpeptized samples. This work provided a new way to prepare nano-crystals of titania.
Synthesis and photophysical properties of barium indium oxides
Authors: Yin J. , Zou Z. , Ye J.
Published: March 2008

Barium indium oxides (BaIn2O4, Ba4In6O13, Ba2In2O5, Ba3In2O6, and Ba5In2O8) were synthesized by the citric process and characterized by powder x-ray diffraction. The optical absorption properties of these compounds were investigated by UV–visible diffuse reflectance spectroscopy. It was found that with the increase of the mole ratio of In2O3 in the formula the optical absorption edges of these oxides shift to the longer wavelength side monotonically. The photocatalytic H2 and O2 evolutions under visible light irradiation (λ > 420 nm) from aqueous CH3OH/H2O and AgNO3/H2O solutions were performed. Among these oxides, BaIn2O4 was the most stable compound, and other compounds were not stable chemically in the case of water and visible light irradiation.
Formation of iodine-doped C60 whiskers by the use of liquid–liquid interfacial precipitation method
Authors: Miyazawa Kun'ichi , Hamamoto Koichi
Published: March 2008

Iodine-doped whiskers of C60 (I–C60 whiskers) with diameters ranging from submicrometers to micrometers and lengths longer than 100 μm were successfully obtained by the use of the liquid–liquid interfacial precipitation method. Transmission electron microscopy observations showed that the I–C60 whiskers were single crystalline and had a growth axis parallel to the close-packed direction of C60 molecules and expanded (002) lattice planes indicative of the intercalation of iodine and oxygen atoms between the (002) planes of a body-centered-tetragonal crystal system. The I–C60 whiskers showed nonlinear I-V curves. The electrical resistivity of the I–C60 whiskers was more than three orders of magnitude lower than that of pristine face-centered-cubic C60 crystals.