bluuebunny/crossref_metadata_2025 huggingface dataset:
Combustion synthesis of aluminum nitride powder using additives
Authors: Lin Chun-Nan , Chung Shyan-Lung
Published: March 2008

Aluminum nitride powder was synthesized by a combustion synthesis method using various additives. Each additive was mixed with Al powder, and the powder mixture was then pressed into a compact. The combustion reaction was ignited by heating the compact under N2 atmosphere of 0.4 MPa. Additives containing halogens were found to have a catalytic effect on the combustion reaction. High product yields were obtained when using additives of NH4X, CO(NH2)2, CH3(CH2)16COOH, and CO2H(CH2)2CO2H. In all these cases, eggshell-like skins were observed to form on the Al particles at the early stage of combustion. The catalytic effect, formation of the eggshell-like skins, and their effects on the combustion process were investigated and discussed.
Piezoresistivity in ruthenium-based metal–insulator– metal structures
Authors: Amin Ahmed
Published: March 2008

The resistance change with applied stress was measured for ruthenium-based metal–insulator–metal thick films under tensile and hydrostatic pressures over the temperature range −25 to +135 °C. The derived longitudinal, transverse, and hydrostatic piezoresistivity coefficients were corrected for elastic effects to yield the corresponding piezoresistivity coefficients and their temperature dependencies. The results clearly demonstrate for the first time a hydrostatic piezoresistivity coefficient that is sevenfold larger than the longitudinal component. Symmetry analysis is used to explain this phenomenon and to deduce additional piezoresistivity matrix elements and their degeneracy. In addition, pressure effects on electrical transport support a tunneling mechanism.
Fabrication of heteropolyoxometalate-based photochromic inorganic–organic nanocomposites
Authors: Zhang Tie Rui , Feng Wei , Bao Chun Yan , Lu Ran , Zhang Xin Tong , Li Tie Ji , Zhao Ying Ying , Yao Jian Nian
Published: March 2008

A series of photochromic sol-gel films are prepared through entrapping tungsten heteropolyoxometallates (PW12O403−, SiW12O404−) and molybdenum heteropolyoxometallate (PMo12O403−) into a kind of inorganic–organic matrix cohydrolyzed from tetraethylorthosilicate and 3-aminopropyltriethoxysilane. The films show reversible photochromicity. Irradiated with ultraviolet light, the transparent films change from colorless to blue. Then, bleaching occurs when the films are in contact with air or O2 in the dark. The Keggin-type polyanions interact with R–NH3+ cations strongly, and thus disperse uniformly in the sol-gel matrix, as proved by Fourier transform infrared spectra and x-ray diffraction. The molybdenum heteropolyoxometallate sol-gel film has higher photochromic efficiency and much slower bleaching than its counterparts of tungsten heteropolyoxometallate. A charge-transfer model which is supported by electron spin resonance and related literature [T. Yamase, Chem. Rev. 98, 307, (1998)] is put forth to explain the above experimental results.
Effect of a magnetic field on phase transformation of steel
Authors: Liu W. , Ou D. R. , Zhou H. H. , Tang G. Y. , Wu F.
Published: March 2008

Electromagnetic theory is used to characterize the magnetization processes in metals and alloys. The analysis shows that the free energy of a phase transformation may be reduced or enhanced by the magnetic field depending on the ratio of the permeability of the old and new phases. This means that the magnetic field can either stimulate or inhibit the nucleation process. The theory is in accord with the experimental results by others and us.
Site preference determination in intermetallic compounds by thermal conductivity measurement
Authors: Terada Yoshihiro , Ohkubo Kenji , Mohri Tetsuo , Suzuki Tomoo
Published: March 2008

A method for the determination of site preference of substitutional elements in intermetallic compounds is proposed. It is demonstrated in Ni3Al–X alloys that the ridge direction in thermal conductivity contours in the ternary γ′ phase agrees with that of the solubility lobe of the γ′ phase in ternary phase diagrams. The ridge direction is a reliable indication of site preference of substitutional elements in intermetallic compounds. The present method is conveniently applied to a normal polycrystalline specimen with small size, and therefore, a versatile class of brittle compounds can be studied.
Hardness–depth profile of a carbon-implanted Ti–6Al–4V alloy and its relation to composition and microstructure
Authors: Kunert M. , Kienzle O. , Baretzky B. , Baker S. P. , Mittemeijer E. J.
Published: March 2008

The variation of mechanical properties (hardness, indentation modulus) within a carbon-implanted region of a Ti–6Al–4V alloy—about 350-nm thick—was, for the first time,relatedwith the microstructure and the chemical composition with a depth accuracy as small as ±20 nm. Microstructure, chemical composition, and mechanical properties of the implanted alloy were determined using transmission electron microscopy, Auger electron spectroscopy, and nanoindentation, respectively. The microstructure within the implanted region contains TiC precipitates, the density of which changes with depth in accordance with the carbon content. The hardness depends on the precipitate density: the maximum hardness occurs at the depth where an almost continuous TiC layer had formed. The depth profiles of hardness and indentation modulus were measured using three different methods: the cross-section method (CSM); the constant-load method (CLM); and the load-variation method (LVM). Only the hardness– depth profile obtained using the CSM, in which the indentations are performed perpendicular to the hardness gradient on a cross section of the specimen, reflects the microstructural variations present in the implanted region.
Transient self-dewetting of steels after pulsed electron beam melting
Authors: Mingolo N. , Roviglione A. N. , Marti´nez O. E.
Published: March 2008

Experimental evidence of transient self-dewetting of metallic surfaces is presented. Steel surfaces are melted by a pulsed electron gun, and the subsequent fast cooling against its substrate gives rise to the formation of characteristic patterns that we attribute to the dewetting of the liquid film. The patterns formed are similar to those obtained by spinodal dewetting, that is, when the dewetting action develops from a nonlinear instability on the liquid surface, and not from holes nucleation. High-purity iron does not show a similar behavior, indicating that the origin of the instability is due to the influence of the sulfur in the temperature dependence of the surface tension of the melt, which gives rise to a Be’nard-Marangoni instability.
Solid-state reaction mechanism for the formation of Ba6−xLn8+2 x/3Ti18O54 (Ln = Nd, Sm) solid solutions
Authors: Belous Anatolii G , Ovchar Oleg V. , Valant Matjaz , Suvorov Danilo
Published: March 2008

A solid-state reaction mechanism for the formation of Ba6−xLn8+2x /3Ti18O54 (Ln = Nd, Sm) solid solutions has been studied using x-ray powder diffraction, thermal analyses, and transmission electron microscopy (TEM). During the interaction of the starting reagents, Ln2Ti2O7, BaTi4O9, and BaTiO3 are formed. In the next sequence, these three phases react together to form a high-x end member of the Ba6−xLn8+2x /3Ti18O54 homogeneity region (Ba3.9Nd9.4Ti18O54 and Ba3.9Sm9.4Ti18O54). Subsequently, the reaction of Ba3.9Nd9.4Ti18O54 and Ba3.9Sm9.4Ti18O54 with the residual BaTiO3 takes place. TEM investigations revealed that compositional inhomogeneities and structural defects existed in the Ba4Sm9.33Ti18O54 sample heated at 1370 °C for 1 h. Sintering times, prolonged to ≥3 h, eliminated the structural defects and increased the homogeneity of the sample.
29Si nuclear-magnetic-resonance and vibrational spectroscopy studies of SiO2–TiO2 powders prepared by the sol-gel process
Authors: Rainho J. P. , Rocha J. , Carlos L. D. , Almeida R. M.
Published: March 2008

The sol-gel synthesis and structural characterization of SiO2–TiO2 powders are reported. Samples with titania concentrations in the range of 0 to 30 mol%, calcined at temperatures between 120 and 1300 °C, were characterized by 29Si magic-angle-spinning nuclear-magnetic-resonance (MAS NMR) and cross polarization MAS NMR, Raman and Fourier transform infrared spectroscopies, and powder x-ray diffraction. Tetrahedrally coordinated Ti (IV) ions were found in the titanosilicate matrix. When the titania content increases beyond approximately 10 mol% and upon calcination at temperatures over approximately 700 °C, the segregation of an amorphous silica-rich phase occurs, together with the precipitation of anatase nanocrystallites with average sizes between 3 and 17 nm, depending on the temperature. An increase in the heat treatment temperature, or the titania content, leads to an increase in the degree of homocondensation (Si–O–Si and Ti–O–Ti bonds) and a simultaneous reduction in the degree of heterocondensation (Si–O–Ti bonds).
Precursor scavenging of the resistive grain-boundary phase in 8 mol% yttria-stabilized zirconia: Effect of trace concentrations of SiO2
Authors: Lee Jong-Heun , Mori Toshiyuki , Li Ji-Guang , Ikegami Takayasu , Drennan John , Kim Doh-Yeon
Published: March 2008

The influence that trace concentrations of SiO2have on improving grain-boundary conduction via precursor scavenging using additional heat treatment at 1200 °C for 40 h before sintering was investigated. At a SiO2-impurity level (SIL) ≤160 ppm by weight, the grain-boundary resistivity (ρgb) decreased to 20% of its value, while no improvement in grain-boundary conduction was found at a SIL ≥ 310 ppm. The correlation between the resistance per unit grain-boundary area, rgb, and average grain size indicated that the inhomogeneous distribution of the siliceous phase in the sample with a SIL ≥ 310 ppm hampered the scavenging reaction.
Synthesis and characterization of partially and fully stabilized zirconia fibers made from an inorganic precursor
Authors: Hartridge A. , Taylor M. D. , Bhattacharya A. K.
Published: March 2008

Continuous high-quality fibers of yttria-doped zirconia with 4 and 8 mol% yttria were blow spun using an inorganic sol precursor. The fibers were heated and analyzed using scanning electron microscopy, x-ray diffraction, differential thermal/thermogravimetric analysis, and surface area/porosity by nitrogen adsorption. The fibers were of a single-phase cubic structure after crystallization at 529 °C and typically 3.3–5.5 or 7.5–11.5 μm in diameter depending on the composition. Samples of fibers were heated to various temperatures and their friability index and creep properties analyzed using the bend stress relaxation technique and compared to other fibers of similar composition prepared by different solution techniques and commercially available fibers.
Controlled preparation and characterization of multilayer sol-gel zirconia dip-coatings
Authors: Caruso Ricardo , Di´az-Parralejo Antonio , Miranda Pedro , Guiberteau Fernando
Published: March 2008

We describe a method for controlled preparation of sol-gel ceramic multilayer coatings obtained by dip-coating. The proposed fabrication routine guarantees obtaining crack-free multilayer coatings with control of the thickness and porosity of individual layers. The procedure is applied to obtain a 10-layer ZrO2–3 mol% Y2O3 coating deposited on AISI 310 stainless steel. The microstructure of this coating was investigated by using x-ray powder diffractometry and atomic force microscopy, and special consideration was given to the mechanical characterization of this thin film using ultramicrohardness indentation tests. Our results suggest that these zirconia coatings have good properties for use as protection barriers. Implications concerning general tailoring design of sol-gel dip-coatings are also considered.
Two-dimensional simulation of mass transport in polymer removal from a powder injection molding compact by thermal debinding
Authors: Shengjie Ying , Lam Y. C. , Yu S. C. M. , Tam K. C.
Published: March 2008

Two-dimensional simulation of thermal debinding in powder injection molding based on mass and heat transfer in deformable porous media is proposed. The primary mechanisms of mass transport, i.e., liquid flow, gas flow, vapor diffusion, and convection, as well as the pyrolysis of polymers, and their interactions, are included in the model. The simulated results revealed that polymer removal process is primarily affected by liquid flow, which is mainly dominated by pressure-forced flow rather than capillary-driven flow. A significant phenomenon, enrichment with liquid polymer in the outer surface regions of the compact, is explained.
Formation of eutectic RuAl/Ru nanocomposite by mechanical alloying and subsequent annealing
Authors: Liu K. W. , Mücklich F. , Birringer R.
Published: March 2008

No abrupt reaction was observed during mechanical alloying (MA) of Ru and Al powder mixtures with an eutectic composition (Ru70Al30). As-milled powders constitute mainly a Ru(Al) solid solution and/or mixture (matrix), and a very small quantity of RuAl. The complete reaction between Ru and Al during MA was speculated to be hampered by excess Ru in Ru70Al30. No exothermic heat release was detected in differential scanning calorimetry for as-milled powders. Precipitation of RuAl from as-milled Ru(Al) matrix was observed after annealing at various temperatures. The phase fraction of Ru and RuAl reaches an approximately equilibrium value after annealing at 1173 K.
Ferroelectric domain structure of epitaxial (Pb,Sr)TiO3 thin films
Authors: Kim Yong Kwan , Lee Kyeong Seok , Baik Sunggi
Published: March 2008

Epitaxial (Pb1−xSrx)TiO3 (PST, x = 4 0.0–0.24) thin films were grown on MgO(001) single-crystal substrates by pulsed laser deposition. General x-ray diffraction techniques including θ–2θ scan and rocking curve were used to determine lattice constants, degree of c-axis orientation, and crystal quality of the tetragonal thin films. The degree of c-axis orientation in the epitaxial PST films increased as Sr concentration (x) increased, which in turn induces the systematic change in the Curie temperature as well as the transformation strain at and below the Curie temperature. An inverse relation between the c-domain abundances and the transformation strains is established.
Thermodynamic analysis of combustion synthesis of Al2O3–TiC–ZrO2 nanoceramics
Authors: Dong Q. , Tang Q. , Li W. C. , Wu D. Y.
Published: March 2008

Combustion synthesis of Al2O3–TiC–ZrO2 nanoceramics by reactions in the TiO2–Al–C–ZrO2 system is a new method with advantages of simplicity and efficiency. In this work, the effect of ZrO2 nanoparticles on the thermodynamics of combustion synthesis of the TiO2–Al–C system is studied to obtain desired phases. The result of thermodynamic analysis shows that the adiabatic temperature Tad of the system stays at about 2327 K (the melting point of Al2O3) with the addition of ZrO2in the range of 0–15 wt% and the fraction of molten Al2O3 varied from 100% to 78%. The possible combustion products are discussed with an approach of an overlapped phase stability diagram of the Al–O–N, Ti–O–N, Zr–O–N, and C–O–N systems at 2300 K. It has been shown that the combustion product is a mixture of Al2O3–TiC–ZrO2, which coincides with the results obtained by x-ray diffraction and transmission electron microscopy.
Quantum atomistic simulations of silicon and germanium
Authors: Herrero Carlos P.
Published: March 2008

Quantum atomistic simulations of crystalline silicon and germanium have been carried out by the path-integral Monte Carlo method. The interatomic interactions were modeled by Stillinger–Weber-type potentials, with parameters adequate to quantum simulations. Quantum zero-point motion together with anharmonicity of the interatomic potential led to a lattice expansion of 7 × 10−3 Å for both Si and Ge. Results for the equation-of-state (volume versus pressure) and for the thermal expansion coefficient agreed well with experimental results for both materials at T > 100 K and for hydrostatic pressures up to 100 kbar.
Annealing effect on in-plane alignment and surface morphology of epitaxial Bi4Ti3O12 thin films prepared by the chemical solution deposition
Authors: Hwang K. , Park Y.
Published: March 2008

Bi4Ti3O12 thin films were grown epitaxially on SrTiO3(100) substrates by chemical solution deposition using metal naphthenates as starting materials. Homogeneous Bi–Ti solution with toluene was spin-coated onto the substrates and pyrolyzed at 500 °C for 10 min in air. Highly c-axis-oriented Bi4Ti3O12 thin films were crystallized by annealing pyrolyzed films at ≥650 °C. The x-ray pole-figure analysis indicated that the Bi4Ti3O12 thin films have an epitaxial relationship with the SrTiO3(100) substrates. The surface morphology of the films annealed at lower temperature, i.e., 650 °C, exhibited flat and smooth surfaces, while films annealed at higher temperatures, i.e., 750 and 800 °C, were characterized by three-dimensional outgrowth.
Measurement of the thermal conductivity of thin layers using a scanning thermal microscope
Authors: Meinders Erwin R.
Published: March 2008

A scanning thermal microscope (SThM) was used to measure the thermal conductivity of thin sputter-deposited films in the thickness range of 10 nm–10 μm. The SThM method is based on a heated tip that is scanned across the surface of a sample. The heat flowing into the sample is correlated to the local thermal conductivity of the sample. Issues like the contact force, the surface roughness of the sample, and tip degradation, which determine to a great extent the contact area between tip and surface, and thus the heat flow to the sample, are addressed in the paper. A calibration curve was measured from known reference materials to quantify the sample heat flow. This calibration was used to determine the effective thermal conductivity of samples. Further, the heat diffusion through a layered sample due to a surface heat source was analyzed with an analytical and numerical model. Measurements were performed with films of aluminum, ZnS–SiO2, and GeSbTe phase change material of variable thickness and sputter-deposited on substrates of glass, silicon, or polycarbonate. It is shown in the paper that the SThM is a suitable tool to visualize relative differences in thermal structure of nanometer resolution. Determination of the thermal conductivity of thin layers is possible for layers in the micrometer range. It is concluded that the SThM is not sensitive enough to measure accurately the thermal conductivity of thin films in the nanometer range. Suggestions for improvement of the SThM method are given.
Metastable solidification of NdFeB alloys by drop-tube processing
Authors: Gao Jianrong , Volkmann Th. , Herlach D. M.
Published: March 2008

Metastable solidification of small droplets of Nd11.8Fe82.3B5.9 and Nd14Fe79B7 alloys was performed in an 8-m drop tube filled with helium. The results showed that the solidification path of the droplets depends on the alloy composition and on the droplet size. For Nd11.8Fe82.3B5.9 alloy, larger droplets are solidified by primary iron formation and subsequent Nd2Fe14B crystallization from the residual liquid phase, whereas smaller ones tend to be frozen by metastable primary Nd2Fe17Bx growth (x = 0–1). A similar transition of the solidification path from primary iron formation to primary Nd2Fe17Bx formation occurred in Nd14Fe79B7 alloy with reducing droplet size. However, metastable primary growth of Nd2Fe14B was also observed within a wide droplet size range prior to the appearance of the metastable Nd2Fe17Bx phase. Nucleation and growth of different phases were considered to produce an explanation of the observed phase selection phenomena in these two alloys.
Photoluminescence behavior of Al3+, Pr3+ doped perovskite La2/3TiO3 and pyrochlore La2Ti2O7
Authors: Park J. K. , Kim C. H. , Choi K. J. , Park H. D. , Choi S. Y.
Published: March 2008

The purpose of this study is to develop an understanding of the photoluminescence properties of Al3+, Pr3+ doped perovskite-type La2/3TiO3 and pyrochlore-type La2Ti2O7 phosphor, which is characterized by the red emission (1D2 →3H4 transition) of the Pr3+ ion. The explanation for the energy transfer and the corresponding critical distance is proposed on the basis of the role of Al3+ ions in the perovskite-type La2/3TiO3:Pr phosphor. To clarify the distinction of photoluminescence properties between the perovskite-type La2/3TiO3 and the pyrochlore-type La2Ti2O7, the trap-involved process and the charge transfer band have been investigated, respectively.
Thermochemistry of rare-earth orthophosphates
Authors: Ushakov S. V. , Helean K. B. , Navrotsky A. , Boatner L. A.
Published: March 2008

The enthalpies of formation for the compounds (RE3+)PO4, (where RE = Sc, Y, La–Nd, Sm–Lu) were determined by oxide-melt solution calorimetry. Calorimetric measurements were performed in a Calvet-type twin microcalorimeter in sodium molybdate (3Na2O · 4MoO3) and lead borate (2PbO · 2B2O3) solvents at 975 K. The experiments were carried out using both powdered single crystals grown by a flux technique and powders synthesized by precipitation. Formation enthalpies were derived from the drop-solution enthalpies for (RE)PO4, RE oxides, and P2O5. Enthalpies of formation for the (RE)PO4 compounds with respect to the oxides at 298 K become more negative with increasing RE3+ ionic radius; i.e., in going from ScPO4 (−209.8 ± 1.0 kJ/mol), to LuPO4 (−263.9 ± 1.9 kJ/mol), to LaPO4 (−321.4 ± 1.6 kJ/mol). From structural considerations, a similar trend is expected for the isostructural RE vanadates and arsenates, as well as for the tetravalent actinide orthosilicates.
Impression creep of a viscous layer
Authors: Chen Hong , Li J. C. M.
Published: March 2008

Impression creep of a flat-ended cylindrical punch pushed into a viscous layer overlaid on a rigid substrate is analyzed. The method developed here permits us to relate the impression velocity to the punching stress in terms of an auxiliary function, which represents the solution of a set of Fredholm integral equations with a continuous symmetrical kernel. By a series of numerical analysis, the influence of the boundary conditions and the effect of the thickness of the layer on the impression velocity are obtained. For infinite thickness (i.e., h/a →∞, where h is the thickness of the layer and a is the radius of the punch), the impression creep is independent of the stick or slip boundary condition at the indenter/layer interface. For finite thickness such as h/a = 20, the boundary conditions have about 5% effect on the impression velocity. For a thin film, the impressing velocity is very sensitive to the boundary conditions. In fact it suggests a possible experimental way to detect debonding at the interface between the thin film and the substrate.
Development of nanocrystalline structure during cryomilling of Inconel 625
Authors: He Jianhong , Lavernia Enrique J.
Published: March 2008

Nanocrystalline Inconel 625 alloy, with a uniform distribution of grains, was synthesized using cryogenic mechanical milling. Microstructures of the powder, cryomilled for different times, were investigated using transmission electron microscopy (TEM), scanning electron microscopy, and x-ray diffraction. The results indicated that both the average powder particle size and average grain size approached constant values as cryomilling time increased to 8 h. The TEM observations indicated that grains in the cryomilled powder were deformed into elongated grains with a high density of deformation faults and then fractured via cyclic impact loading in random directions. The fractured fragments from the elongated coarse grains formed nanoscale grains. The occurrence of the elongated grains, from development to disappearance during intermediate stages of milling, suggested that repeated strain fatigue and fracture, caused by the cyclic impact loading in random directions, and cold welding were responsible for the formation of a nanocrystalline structure. A high density of mechanical nanotwins on {111} planes was observed in as-cryomilled Inconel 625 powders cryomilled, as well as in Inconel 625 powder milled at room temperature, Ni20Cr powder milled at room temperature, and cryomilled pure Al.
Reaction kinetics and anisothermal effects in microwave fields: System Y2O3–Fe3O4
Authors: Peelamedu Ramesh D. , Roy Rustum , Agrawal Dinesh K.
Published: March 2008

Yttrium iron garnet (YIG) powder has been synthesized in just less than 10 min in a multimode microwave oven operating at 2.45 GHz. The simple solid-state synthesis involves an anisothermal reaction between a highly microwave absorbing Fe3O4 and a low microwave absorbing Y2O3 at temperatures of 1300 °C. The rapidity of the YIG formation suggests that the reaction rate is possibly enhanced by several times in a microwave field.
Chemical sensors based on dielectric response of functionalized mesoporous silica films
Authors: Domansky Karel , Liu Jun , Wang Li-Qiong , Engelhard Mark H. , Baskaran Suresh
Published: March 2008

Dielectric response of mesoporous silica films was monitored as a function of several gas-phase chemical species. The effects of humidity, ammonia, and methane on dielectric constant and dissipation factor of films subjected to different chemical treatments are described. Dielectric constant and dissipation factor of partially dehydroxylated films were found to be highly sensitive to both water vapor and ammonia in air. The capacitive devices based on mesoporous silica films show potential for use in chemical sensors.
Shear-activated indentation crack in GaAs single crystal
Authors: Li Z. C. , Liu L. , He L. L. , Xu Y. B. , Wu X.
Published: March 2008

Cracks induced by 0.049N load indentation on the surface of gallium arsenide single crystal were investigated before and after annealing. The results revealed that the crack initiation essentially relates to the shear deformation during indentation. There were dislocation generation, lattice distortion, and the transformation from crystalline to disordered structure, leading to the occurrence of an amorphous band in front of the crack tip. After being annealed at 500 °C for 60 min, the amorphous band disappeared, and instead, recrystallized grains appeared along the crack-propagation direction. It is reasonable to propose that crack propagation is the result of the decohesion of the amorphous band rather than the direct debonding along a certain atomic plane.
New technique for pressureless infiltration of Al alloys into Al2O3 preforms
Authors: Rao B. Srinivasa , Jayaram V.
Published: March 2008

Al alloys were infiltrated into alumina preforms without the aid of pressure in N2 as well as in air at and above 750 °C. It was possible to eliminate termination of infiltration that was seen in open conditions (where N2 was in continuous contact with the melt) by modifying the infiltration geometry. This configuration enables the infiltration to continue for longer periods of time, consequently producing greater thickness of composite. In air, Mg placed at the interface getters the in-coming oxygen until the alloy billet melts and seals off the front from the ingress of the furnace atmosphere thereby eliminating the need for prealloying Al with Mg and N2 atmosphere. In addition, experiments in argon revealed that the infiltration requires some critical amount of N2 in the atmosphere.
Preparation and characterization of nanocrystalline PbSe in poly(acrylic acid-co-styrene)
Authors: Sun Yangyang , Qian Xuefeng , Yin Jie , Huang Junchao , Ma Xiaodong , Zhu Zikang
Published: March 2008

The in situ reduction method was used to prepare nanocrystalline PbSe in a poly(acrylic acid-co-styrene) matrix. Metal precursor-doped polymer film was treated with selenium and reducing reagent (NaBH4) in ethylenediamine, leading to the formation of assemblies of crystalline semiconductive PbSe in polymer. The preparation was done at room temperature and ambient pressure. X-ray diffraction, x-ray photoelectron spectroscopy, infrared, scanning electron microscopy, transmission electron microscopy, and ultraviolet-visible spectra were used to characterize the as-prepared materials. The key factor for successful preparation of this composite was also discussed.
Effects of zinc(II) and iron(III) doping of titania films on their photoreactivity to decompose rhodamine B
Authors: Ma Ying , Zhang Xin-tong , Guan Zi-sheng , Cao Ya-an , Yao Jian-nian
Published: March 2008

The heterogeneous photocatalytic oxidation of rhodamine B in aqueous solution containing pure or zinc (iron)-doped titania films has been studied. N-deethylation of rhodamine B was accelerated by iron(III) and zinc(II) doping as compared with pure titania film. It is shown that improvement of electron transfer from dye molecules to the film may be responsible for the high N-deethylation rate for iron-doped (0.5 mol%) film, while for zinc-doped (20 mol%) film, high surface roughness may be the main reason. In addition, both iron and zinc doping brought a new shallow trap to the intragap meaning that the surface defects had increased after doping; this is a possible reason doped films present relative low photoreactivity to catalyze the direct degradation of dye molecules.
Formation and characterization of high-density silver nanoparticles embedded in silica thin films by “in situ” self-reduction
Authors: Compagnini G. , Fragal´ M. M. , D'Urso L. , Spinella C. , Puglisi O.
Published: March 2008

Silver nanoparticles (10–20 nm) embedded into silica thin films have been obtained through the use of a silver organometallic precursor compound dissolved in Spin-On-Glass and subsequently spinned onto suitable substrates. In this paper we present a study of the shape, size, and distribution of silver particles through the use of microscopes, x-ray diffraction, and optical extinction. It has been observed that the obtained films are stable for annealing up to 500 °C with a progressive degradation above this temperature. Furthermore it is possible to obtain high-density silver particles up to 15% in weight without affecting the cluster size and shape.
Plate domain structure of sintered NdFeB magnets and dependence on compacting mode
Authors: Zhang Zhen Rong , Han Bao Shan , He Ye Qing , Zhou Shou Zeng
Published: March 2008

The alignment degree of sintered Nd–Fe–B magnets and its dependence on applied field and compacting mode were studied by magnetic force microscopy. By analyzing the magnetic force images to illustrate the magnetic-domain structure, an experimental method for quantitatively evaluating the alignment degree of sintered Nd–Fe–B magnets was given. The results show that if the compacting mode is the same, the alignment of magnets will be better as field increases. Under the same field, the alignment degree for rubber isostatic pressing with vibration is better than that for nonmagnetic metal die pressing. However, if the sample is compacted by rubber isostatic pressing without vibration, the alignment degree decreases significantly.
Observations of structural order in ion-implanted amorphous silicon
Authors: Cheng Ju-Yin , Gibson J. M. , Jacobson D. C.
Published: March 2008

Medium-range order in ion-implanted amorphous silicon has been observed using fluctuation electron microscopy. In fluctuation electron microscopy, variance of dark-field image intensity contains the information of high-order atomic correlations, primarily in medium-range order length scale (1–3 nm). Thermal annealing greatly reduces the order and leaves a random network. It appears that the free energy change previously observed on relaxation may therefore be associated with randomization of the network. In this paper, we discuss the origin of the medium-range order during implantation, which can be interpreted as a paracrystalline state, that is, a disordered network enclosing compacts of highly topologically ordered grains on the length scale of 1–3 nm with significant strain fields.
Use of combined elastic modulus in the analysis of depth-sensing indentation data
Authors: Fischer-Cripps A. C.
Published: March 2008

It is shown that the substitution of reduced modulus for specimen modulus in the analysis equations for nanoindentation test data is valid. The methods of analysis use the slope of the unloading force–depth response which is assumed to be elastic. Because of this utilization of the slope or unloading stiffness, it makes no difference whether or not the deflection of the indenter is accommodated explicitly or transferred to that occurring within the specimen by artificially reducing the specimen modulus from its true value to lower value, the reduced modulus.
Effect of mechanical alloying on combustion synthesis of MoSi2
Authors: Park Hyung-Sang , Shin Kwang-Seon , Kim Yong-Seog
Published: March 2008

Characteristics of the combustion synthesis of MoSi2 using elemental Mo and Si powder mixtures prepared by mechanical alloying were investigated. The mechanical alloying resulted in powders of pseudolamellar structure and a partial conversion of the elemental powders to hexagonal MoSi2 phase. Combustion reaction of the mixture was ignited around 670 °C, which is much lower than that with the powder prepared by low-energy ball milling. A mathematical model was developed to demonstrate the possibility of the ignition of the combustion reaction of the lamellar structure via a solid-state diffusional process. On the basis of model, effects of mechanical alloying time on the ignition temperature and combustion temperature are discussed.
In situ analysis of gaseous species for chemical vapor deposition diamond synthesis and the possible reaction model
Authors: Uede Mayu , Takagi Yoshiki
Published: March 2008

For a few years, we had been concentrating on development of completely closed diamond synthesizing system aimed for microgravity experiments. Recently we started the new method with a graphite heater as carbon source. With this method, a completely closed system is successfully performed. In situ gaseous species analysis with gas chromatography and the possible reaction model is discussed.
Nucleation and growth of silicon nitride nanoneedles using microwave plasma heating
Authors: Cui H. , Stoner B. R.
Published: March 2008

We report on needlelike silicon nitride nanowires grown on silicon using ammonia microwave plasma heating. Scanning electron microscope reveals that the nanoneedles are either straight, slightly bent, or kinked with sharp tips. Transmission electron microscope shows that the sizes of the nanowire tips are less than 5 nm and the structures are well crystallized. X-ray diffraction on the surface of the as-deposited structures indicates that both α-silicon nitride and β-silicon nitride exist. Catalyst particle splitting and merging explain observed structure derivation and bending. A vapor–liquid–solid model is employed to explain nucleation and growth mechanism.
Novel synthesis of AlN nanowires with controlled diameters
Authors: Liu Jun , Zhang X. , Zhang Yingjiu , He Rongrui , Zhu Jing
Published: March 2008

A relatively low-cost, high-efficiency method is reported to synthesize AlN nanowires, using carbon nanotubes as templates. The AlN nanowires were fabricated at 1100 °C, for 60 min. The diameters of the product could be roughly controlled by the sizes of carbon nanotubes selected as starting materials. The AlN nanowires obtained were among the thinnest ever known. X-ray diffraction, selected-area diffraction, energy dispersive spectroscopy, and high-resolution transmission electron microscopy, etc. were employed to characterize the products, which were found to be single crystals with some defects. The axes of the nanowires are normal to {1010} crystal planes. A new synthesis mechanism is proposed.
Substrate effects on indentation plastic zone development in thin soft films
Authors: Kramer D. E. , Volinsky A. A. , Moody N. R. , Gerberich W. W.
Published: March 2008

Plastic zone evolution in Al–2 wt% Si metal films on silicon and sapphire substrates was studied using nanoindentation and atomic force microscopy (AFM). AFM was used to measure the extent of plastic pileup, which is a measure of the plastic zone radius in the film. It was found that the plastic zone size develops in a self-similar fashion with increasing indenter penetration when normalized by the contact radius, regardless of film hardness or underlying substrate properties. This behavior was used to develop a hardness model that uses the extent of the plastic zone radius to calculate a core region within the indenter contact that is subject to an elevated contact pressure. AFM measurements also indicated that as film thickness decreases, constraint imposed by the indenter and substrate traps the film thereby reducing the pileup volume.
Novel route for the epitaxial growth of (SrBa)Nb2O6 thick films by the sol-gel method using a self-template layer
Authors: Li A-D. , Mak C. L. , Wong K. H. , Wu D. , Ming Naiben
Published: March 2008

A novel sol-gel processing method has been developed to fabricate epitaxial (SrBa)Nb2O6 (SBN) thin films on MgO substrates. It involves the introduction of a SBN self-template layer on MgO by pulsed laser deposition (PLD). Effects of the SBN self-template layer on the structural and morphological properties of the sol-gel-derived SBN films were investigated. Compared to the sol-gel-derived SBN films without a self-template layer, our new technique produces SBN films of excellent epitaxy and more dense grains with uniform distribution. This can be explained by the self-template-layer-induced homoepitaxial growth. The innovative processing method with combination of PLD and sol-gel is a promising technique in preparing high-quality, thick epitaxial SBN films for electro-optics device applications.
Wetting of mullite by Y2O3–Al2O3–SiO2 and B2O3–SiO2 glasses
Authors: Huang T. S. , Rahaman M. N. , Eldred B. T. , Ownby P. D.
Published: March 2008

The wetting of mullite (3Al2O3 · 2SiO2) by a Y2O3–Al2O3–SiO2 (YAS) glass and by a B2O3–SiO2 (borosilicate) glass was investigated in air as a function of temperature through a sessile drop technique. The wetting behavior was found to be strongly dependent on the glass composition and on the temperature. For the YAS glass, the contact angle showed a rapid decrease from 100° to 20° in the temperature range of 1400 to 1450 °C followed by a more gradual decrease to a value of 10–15° at approximately 1600 °C. In the case of the borosilicate glass, the change in the contact angle with temperature was more uniform, with the value decreasing from 100° to 45° between 1300 and 1600 °C. Microstructural observations of the interfacial region between the solidified sessile drop and the mullite substrate revealed significant corrosion of the interface and penetration into the mullite grain boundaries by the YAS glass. In the case of the borosilicate glass, corrosion was limited and the interface was clearly defined. The consequences of the data for the design of in situ toughened mullite are discussed.
Processing of mesoporous alumina from a powder precursor
Authors: Frazee J. Wayne , Harris Thomas M.
Published: March 2008

Oxides with significant mesopore volume can be produced from gels through ambient pressure drying (APD) if the oxide network within the gel is sufficiently strong. To obtain a strong alumina gel, a commercial alumina powder (100 nm diameter) was combined with different amounts of ethanol, water, and acid. Significant mesoporosity was observed in dried and calcined gels prepared from this precursor and ethanol alone, particularly when “poor wettability” was established in the gel through azeotropic distillation in toluene. When water (or water and nitric acid) was also utilized the pore volume decreased dramatically; this observation may be attributed to the creation of amorphous alumina from the crystalline precursor that is displaced into the interparticle pores, and in which mesopores are poorly preserved during APD.
Investigation of crystal properties of TmP/GaAs and GaAs/TmP/GaAs heterostructures grown by molecular beam epitaxy
Authors: Lin C. H. , Hwu R. J. , Sadwick L. P.
Published: March 2008

Single-crystal thulium phosphide (TmP) was grown heteroepitaxially on (001) GaAs substrates by molecular beam epitaxy with the orientation relationship [100]TmP//[100]GaAs and {001}TmP//{001}GaAs. The crystal properties and the defects in TmP/GaAs, GaAs/TmP/GaAs heterostructure were characterized through x-ray diffraction, atomic force microscopy, and transmission electron microscopy. TmP was found to have a huge difference in thermal expansion coefficient compared GaAs, which produced high tensile residual stress and may result in the formation of defects. The major defects in the top GaAs layer are stacking faults or microtwins, and they directly correlated with the islandlike surface morphology of the GaAs overlayer. The composition profiles of the TmP/GaAs heterostructure were measured by secondary ion mass spectrometry. The reason for surface segregation of Tm and Ga atoms is discussed and is primarily due to their higher diffusion coefficient near the surface as compared to that in the TmP epilayer bulk. The thermally stable characters of the TmP/GaAs heterostructures allow them to be promising candidates in various device applications.
Mechanism of improvement of TiN-coated tool life by nitrogen implantation
Authors: Bull S. J. , Sharkeev Yu. P. , Fortuna S. V. , Shulepov I. A. , Perry A. J.
Published: March 2008

The life of TiN-coated tools can be improved by a post-coating ion implantation treatment, but the mechanism by which this occurs is still not clear. Nitrogen implantation of both physical-vapor-deposited TiN and CVD TiN leads to surface softening as the dose increases, which has been attributed to amorphization. In this study a combination of transmission electron microscopy and atomic force microscopy was used to characterize the microstructure of implanted TiN coatings on cemented carbide for comparison with mechanical property measurements (nanoindentation, residual stress, etc.), made on the same samples. Ion implantation leads to a slight reduction in the grain size of the TiN in the implanted zone, but there is no evidence for amorphization. Surface softening is observed for physical-vapor-deposited TiN, but this is probably due to a combination of changes in surface composition and the presence of a layer of bubbles generated by the very high implantation doses used.
Comparison of different models for melting point change of metallic nanocrystals
Authors: Zhao M. , Zhou X. H. , Jiang Q.
Published: March 2008

Our phenomenological model without adjustable parameters for the size dependence and dimension dependence of melting point depression and enhancement of nanocrystals is introduced. The predictions of our models are consistent with both of experimental results and other thermodynamic models for metallic nanocrystals while the difference between our model and other theoretical considerations in mesoscopic size range is discussed.
Titanium oxide nanotube arrays prepared by anodic oxidation
Authors: Gong Dawei , Grimes Craig A. , Varghese Oomman K. , Hu Wenchong , Singh R. S. , Chen Zhi , Dickey Elizabeth C.
Published: March 2008

Titanium oxide nanotubes were fabricated by anodic oxidation of a pure titanium sheet in an aqueous solution containing 0.5 to 3.5 wt% hydrofluoric acid. These tubes are well aligned and organized into high-density uniform arrays. While the tops of the tubes are open, the bottoms of the tubes are closed, forming a barrier layer structure similar to that of porous alumina. The average tube diameter, ranging in size from 25 to 65 nm, was found to increase with increasing anodizing voltage, while the length of the tube was found independent of anodization time. A possible growth mechanism is presented.
Investigation of the stability of glassy state in the Zr- and Hf-based glassy alloys correlated with their transformation behavior
Authors: Saida Junji , Li Chunfei , Matsushita Mitsuhide , Inoue Akihisa
Published: March 2008

The transformation behavior from glassy state was investigated in Zr- and Hf-based glassy alloys. The primary phases are metastable face-centered-cubic (fcc) Zr2Ni and fcc Hf2Ni phases in the Zr65Al7.5Ni10Cu17.5 and Hf65Al7.5Ni10Cu17.5 glassy alloys, respectively. By substitution of 5 at.% Pd for Cu, the primary phase changes to an icosahedral quasicrystalline phase in both alloys. It is found that the addition of elements, which have a positive or weak chemical affinity with one of the constitutional elements in the Zr–Al–Ni–Cu and Hf–Al–Ni–Cu glassy alloys, is effective for the precipitation of the icosahedral phase. It is suggested that Pd plays a dominant role in an increase in the number of nucleation sites. Since an icosahedron is contained as a structure unit in the icosahedral, fcc Zr2Ni and fcc Hf2Ni phases, it is implied that these phases are correlated with the local icosahedral order. The high-resolution transmission electron microscopy images of the as-spun Zr65Al7.5Ni10Cu7.5Pd10 and Hf65Al7.5Ni10Cu12.5Pd5 alloys reveal a possibility of the existence of the icosahedral ordered regions. It is therefore, concluded that the icosahedral short- or medium-range order exists and it stabilizes the glassy state in the Zr- and Hf-based multicomponent alloys.
Morphological effect on the electrochemical behavior of electric double-layer capacitors
Authors: Endo M. , Kim Y. J. , Maeda T. , Koshiba K. , Katayam K. , Dresselhaus M. S.
Published: March 2008

Activated milled mesophase carbon fibers (AC-mMPCF, MP-series) show a higher specific capacitance in spite of a smaller specific surface area than those of powder-type activated carbons (AC-series). This phenomenon can be interpreted to mean that it is difficult to predict the capacitance of an electric double-layer capacitor (EDLC) knowing just the surface area and the pore size. More information is needed about other inherent characteristics of the samples, for example, the equivalent series resistance (ESR), shape of the pores, etc. We investigate here other characteristics of the samples. Consequently, it was deduced that the MP-series of EDLCs have a slit pore shape, which affects the accessibility of the electrolyte ion onto the electrode surface. Moreover, the MP-series of materials have suitable ESR values, and these material properties themselves should be considered as factors that affects the deterioration of the specific capacitance of EDLCs.
Preparation and phase control of nanocrystalline silver indium sulfides via a hydrothermal route
Authors: Hu J. Q. , Deng B. , Tang K. B. , Wang C. R. , Qian Y. T.
Published: March 2008

A hydrothermal route was proposed to prepare and control nanocrystalline silver indium sulfides (orthorhombic AgInS2, tetragonal AgInS2, and cubic AgIn5S8). The reaction was carried out in an autoclave in the temperature range of 100–280 °C with AgCl, InCl3, and thiourea as reactants. X-ray powder diffraction patterns and transmission electron microscopy images showed that the products were AgInS2 and AgIn5S8 phases and well crystallized with grain diameter in the range of 20–70 nm. X-ray photoelectron spectra of the single AgIn5S8 phase revealed the surface stoichiometry (AgIn5.05S8.11), and its room temperature Raman spectrum showed a strong peak at 130 cm−1 and a weak peak at around 290 cm−1. The influence of reaction temperature on the phases in the final products was investigated. A possible reaction mechanism of the formation of silver indium sulfides was also briefly discussed.