The phase stability of Ni–Al clusters of nanometer size was studied by using the embedded atom model and Monte Carlo simulation techniques. For temperatures of 500 and 1000 K and for a range of compositions below 70 at.% Al, the equilibrium structures of the system were determined and compared with the bulk results. We found that the bulk NiAl (B2) and Ni3Al (L12) phases were stable phases in the nanoparticle system; however, for deviations from ideal composition, the analysis revealed that, because of the surface effect, the composition of the clusters was not uniform. There was a core region in which the structure was ordered, B2 or L12, with a composition very close to the ideal, and a chemically disordered mantle region that allocated the deviations from ideal stoichiometries; in this way, a larger phase field appeared, indicating trends similar to those found in experiments on nanocrystalline Ni–Al powder [S.K. Pabi and B.S. Murty, Mater. Sci. Eng. A214, 146 (1996)]. For concentrations between 37 and 51 at.% Al, an intermediate phase, similar to the tetragonal L10 martensite, appeared.

A nanocrystalline magnetic particle/oligomer hybrid was successfully synthesized by polymerization of iron(III) 3-allylacetylacetonate (IAA) followed by in situ hydrolysis. An iron oxide particle/oligomer hybrid was synthesized by hydrolysis of the IAA oligomer under alkaline and reducing conditions by the addition of hydrazine or methylhydrazine. Crystalline particles of approximately 10 nm were found to be dispersed in the oligomeric matrix. The nanocrystalline particles were identified to be iron oxide spinel by x-ray diffraction analysis and electron diffraction. The nanometer-sized ferrimagnetic iron oxide particle/oligomer hybrid showed a typical superparamagnetic behavior.

The magnetic properties of carbon-coated Co and Ni nanoparticles aligned in chains were determined using transmission electron holography. The measurements of the phase change of the electron wave due to the magnetization of the sample were performed. The ratio of remnant magnetization to bulk saturation magnetization Mr/Ms of Co decreased from 53% to 16% and of Ni decreased from 70% to 30% as the particle diameter increased from 25 to 90 nm. It was evident that the inhomogenous magnetic configurations could diminish the stray field of the particles. After being exposed to a 2-Tesla external magnetic field, the Mr/Ms of Co increased by 45% from the original values with the same dependency on the particle size. The Mr/Ms of Ni particles, on the other hand, increased only 10%. The increased magnetization could be attributed to the merging of small domains into larger ones after the exposure to the external magnetic field. The validity of the interpretation of the holograms was established by simulation.

This article discusses the mechanical properties of vapor-grown carbon fiber (VGCF)/nylon and VGCF/polypropylene composites. Fibers in the as-produced condition yielded composites with marginally improved mechanical properties. Microscopic examination of these composites clearly showed regions of uninfiltrated fibers, which could account for the unsatisfactory mechanical properties. The infiltration of the fibers by both polymers was improved by carefully ball milling the raw fiber so as to reduce the diameter of the fiber clumps to less than 300 μm. Properties of composites made with ball-milled material were improved in every respect. VGCF reinforcement in nylon slightly improved the tensile strength and doubled the modulus, while VGCF in polypropylene doubled the tensile strength and quadrupled the modulus compared to unreinforced material. Moreover, the composites were sufficiently improved that differences in fiber surface preparation became important. For example, air-etched fibers and fibers covered with low concentrations of aromatics produced polypropylene composites with significantly better mechanical properties than did fibers whose surfaces were heavily coated with aromatics. Both the tensile strength and the modulus of the composites fabricated with clean fibers exceeded theoretical values for composites made with fibers randomly oriented in three dimensions, indicating that the injection-molding process oriented the fibers to some extent.

Scanning acoustic microscopy (SAM) was used to obtain the critical fragmentation length of a 7-μm-diameter carbon fiber embedded in an optically transparent epoxy matrix and was subjected to a standard fiber fragmentation test. The SAM-assessed critical fragmentation length of 356 ± 59.5 μm compared favorably with the value 341 ± 52.3 μm obtained independently from commonly used photoelastic techniques. Additionally, the SAM images allowed an assessment of regions of fiber-matrix debond, including the measurement of an average debond of 61.0 ± 11.8 μm along the fiber from the fragment ends, which could not be obtained with photoelastic methods. The application of SAM to the assessment of optically opaque composite materials is explained in this paper.

Interfacial phenomena and microstructure in Ag–Si multilayers with a modulation period of 7.64 nm during annealing from 323 to 573 K were investigated by in situ x-ray diffraction and high-resolution transmission electron microscopy. Uphill and downhill diffusion were observed on annealing. The temperature dependence of the effective diffusion coefficient from 373 K (as to downhill diffusion regime) to 523 K was De = 2.02 × 10−20 exp(−0.24 eV/kBT) m2/s. Diffusion of silicon atoms along silver grain boundaries was proposed as the main diffusion mechanism. After annealing, continuous silver sublayers changed to nanometer-sized silver particles (about 4.5 nm) coated completely by amorphous silicon.

The degree of mixing is a critical factor in controlling the magnetic properties and mechanical properties of polymer-bonded magnets. Pretreatment of the NdFeB fillers with a silane coupling agent improved the degree of mixing of the fillers in the polymer matrix. The observed improvement in the degree of mixing of the silanetreated fillers was ascribed to good wetting as evidenced by viscosity reduction of the coupled polymer-bonded magnets. However, traditional materials characterization methods could not be used to quantitatively determine the degree of mixing of the polymer-bonded magnets. This paper describes use of thermogravimetric analysis to quantify the degree of mixing of polymer-bonded magnets. The intensity of segregation of the fillers was calculated from the measured weight change of the magnetic filler in the samples. The results of this work showed that the thermogravimetric analysis method was useful in determining the degree of mixing of NdFeB fillers in polymer-bonded magnets.

Thermal curing of the (4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedionato)silver(I)-containing poly(amic acid) formed from 3,3′,4,4′-benzophenone tetracarboxylic acid dianhydride (BTDA) and 4,4′-oxydianiline (4,4′-ODA) in dimethylacetamide gives both polyimide films via cyclodehydration and reduction of silver(I) to the native metal. Silver(0) migrates to the surface resulting in surface metallized composite films, which can have excellent reflectivity, but do not exhibit surface electrical conductivity. The films retain mechanical and thermal properties similar to those of the parent polyimide. X-ray diffraction shows crystalline face-centered-cubic silver in the films after thermal curing. Microscopy data show that the surface particle sizes are in the range of approximately 50–100 nm. Significant silver remains in the bulk of the polyimide film with varying particles sizes generally less than approximately 15 nm. The interior of the metallized films is not electrically conducting. Films were characterized by x-ray diffraction, differential scanning calorimetry, thermal gravimetric analysis, x-ray photoelectron spectroscopy, transmission electron microscopy, scanning electron microscopy, and mechanical measurements.

Epitaxial (Ba0.5Sr0.5) TiO3 thin films of two different thickness (∼25 and ∼134 nm) on MgO(001) prepared by a pulsed laser deposition method were studied by synchrotron x-ray scattering measurements. The film grew initially with a cube-on-cube relationship, maintaining it during further growth. As the film grew, the surface of the film became significantly rougher, but the interface between the film and the substrate did not. In the early stage of growth, the film was highly strained in a tetragonal structure (c/a = 1.04) with the longer axis parallel to the surface normal direction. As the growth proceeded further, it relaxed to a cubic structure with the lattice parameter near the bulk value, and the mosaic distribution improved significantly in both in- and out-of-plane directions. The thinner film (∼25 nm) showed only one domain limited mainly by the film thickness, but the thicker film (∼134 nm) exhibited three domains along the surface normal direction.

Extremely fine, tubular graphite nanofibers of varying geometries and degrees of crystallinity were produced by the decomposition of CO and hydrogen over various compositions of nickel–iron particles supported on silica. High-resolution transmission electron microscopy coupled with temperature programmed oxidation studies revealed that, as the iron content of the catalyst was increased, the bimetallic particles precipitated a chainlike graphitic fibrous structure in a stepwise mechanism. The high-iron-content system Fe–Ni (8:2) yielded a small amount of these chainlike graphite fibers that were extremely resilient to oxidation, suggesting a highly crystalline structure. When the catalyst particles consisted of a nickel–iron mixture, Fe–Ni (5:5), there was a decrease in the degree of crystallinity of the fibers (78% graphite) and a corresponding increase in the amount of amorphous carbon precipitated (22% amorphous) within the structure. The high-nickel catalyst Fe–Ni (2:8) generated the largest amount of the tubular nanofiber product. It was significant that there was an increase in the amorphous carbon content (58%) precipitated as opposed to graphitic carbon (42%) in the structures. In some cases, amorphous carbon was deposited inside the graphite core of the nanofibers. The influence of the catalyst composition and nature of the metal-support interaction are key factors in the continuing development of graphite nanofibers possessing desired structures for potential uses in a variety of applications.

The effects of borosilicate glass (BSG) on the kinetics and mechanism of anataseto- rutile phase transformation have been investigated. The displacive anatase-to-rutile phase transformation kinetics of TiO2 were greatly enhanced in the presence of BSG. The transformation kinetics followed the Avrami equation, and the results showed an apparent activation energy of 260–370 kJ/mol, which was close to the bond strength of Ti–O, suggesting a reaction-controlling mechanism. The values of the Avrami exponent were in the range of 1.4–2.3, which could be interpreted as two-dimensional reaction-controlled growth at zero nucleation rate. The rutile particles obtained by the phase transformation were always much larger than the starting anatase powders, which was explained by a mechanism of phase-transformation–induced particle coalescence.

The products obtained from MnO2–V2O5 mixtures at the ambient oxygen pressure and temperatures up to 900 °C were studied by means of thermal analysis and x-ray diffraction methods. The following phases were found to exist in equilibrium, depending on the composition: (I) Mn2O3–Mn2V2O7, (II) Mn2V2O7–MnV2O6, and (III) V2O5–solid solution of VO2 in MnV2O6. A phase diagram was obtained for the composition region III. The data are instructive for syntheses of manganese vanadates by thermal methods.

Ba(Ti1−xSnx)O3 (0 ≤ x ≤ 0.3) thin films were deposited on a platinized silicon substrate by a solution deposition process with methoxyethanol, water, and propylene glycol as solvents. Dielectric properties and current–voltage characteristics of the thin films were investigated in conjunction with phase evolution and microstructures by varying heating temperatures and Sn contents (x). Thin films annealed above 700 °C showed a pure perovskite phase with nanoscaled grains (20–30 nm). The dielectric constant of the thin films depended on the Sn content and showed a maximum value of 330 at x = 0.15. The leakage current behavior of an optimum composition corresponding to x = 0.15 was examined by correlating with charge transport mechanisms. Schottky emission was found to be predominant at voltages less than 6.8 V, and Fowler–Nordheim tunneling appeared to be responsible above 6.8 V. The Schottky barrier of the Ba(Ti0.85Sn0.15)O3–Pt interface was determined to be 1.49 eV.

Lanthanum-modified lead zirconate titanate ferroelectric ceramics (Pb0.96La0.04)(Zr0.40Ti0.60)0.99O3 were synthesized by the conventional powder processing technique. X-ray diffraction experiments revealed that the samples belong to the tetragonal phase with a = b = 0.4055 nm, c = 0.4109 nm, and c/a = 1.013. After being poled, the samples were indented with a 5-kg Vickers indenter, and lateral electric fields of 0.4 Ec, 0.5 Ec, and 0.6 Ec (Ec = 1100 V/mm) were applied, respectively. Field-emission scanning electron microscopy showed that 90° domain switching appeared near the tip of the indentation crack under a lateral electric field of 0.6 Ec. A mechanism of 90° domain switching near the crack tip under an electric field is discussed.

Epitaxial, continuous, approximately 40-nm-thick films of SrZrO3 on SrTiO3 substrates prepared by a chemical solution deposition method including a postdeposition heat treatment at 900–1000 °C were subjected to further heat treatments at higher temperatures (approximately 1200–1300 °C) to investigate their high temperature stability. Experimental investigations included scanning electron microscopy, atomic force microscopy, and conventional transmission electron microscopy. The investigations have demonstrated a morphological instability of the films. Concentration profiles of the cations determined by energy dispersive x-ray spectroscopy, as well as investigations by x-ray diffraction, revealed that the film islands consisted of a solid solution. As shown by high-resolution electron microscopy, the reaction between film and substrate also led to an increase in the separation distance of the misfit dislocations that were introduced during the lower temperature heat treatment to relax the lattice mismatch strain. The morphological and structural changes of the films are reported and discussed in this paper.

Dense, uniform, and adherent chemically vapor-deposited mullite coatings were deposited on SiC substrates using the AlCl3–SiCl4–H2–CO2 system. Typical coating morphology consisted of a thin interfacial layer of γ–Al2O3 nanocrystallites embedded within a vitreous SiO2-based matrix. When a critical Al/Si ratio of 3.2 ± 0.29 was reached within this nanocrystalline layer, mullite crystals nucleated and grew as columnar grains. The thickness of the nanocrystalline layer decreased as the input AlCl3/SiCl4 ratio was increased. In all cases, the Al/Si composition in the coating increased from the coating/substrate interface to the coating surface. Critical factors leading to the nucleation and growth of mullite crystals are discussed in this article.

Silicon nitride was fabricated by adding Y2O3 and Nd2O3 as sintering additives, sintering for 8 h at 1900 °C, and heat treating for 4 h at 2200 °C to enhance grain growth. The microstructure was investigated by scanning electron microscopy, high-resolution electron microscopy, energy dispersive x-ray spectroscopy (EDS), and electron microdiffraction. This material had a duplex microstructure composed of many fine grains and a few coarse grains. In β–Si3N4 grains, second-phase particles with the composition of liquid phase, Y–Nd–Si–O or Y–Nd–Si–O–N, in the size of 10–30 nm were observed. EDS spectra and microdiffraction patterns revealed that those were amorphous or crystalline particles of Y–Nd–apatite, (Y,Nd)10Si6O24N2. These particles were presumably formed during cooling by the precipitation of Y–Nd–Si–O–N, which was trapped in the β–Si3N4 grains as solid solution or trapped liquid. The results suggest that attention should be paid to the trace amounts of trapped elements in β–Si3N4 grains in trying to improve the thermal conductivity of sintered silicon nitride.

A proper powder preparation technique was used to develop elongated β–Si3N4 particles as seeds from raw materials. The phase transformation and development of microstructure in Si3N4 ceramics containing β–Si3N4 seeds were investigated. The specimens of seeded silicon nitride had higher phase transformation rates than the specimens without seed. A core/shell structure was observed by transmission electron microscopy in seeded specimens owing to the difference in aluminum concentration in Si3N4 grains. The misfit between the core and the shell was accommodated by interfacial dislocation that has a rotation character. The growth mode was epitaxial, although there was some compositional difference between the core and the shell. A relatively larger grain size and wider grain size distribution in seeded Si3N4 specimens was due to the amount of β-phase seeds that could act as the nuclei, and the final modification of the microstructure was due to the coalescence process. The crack wake process characterized the mechanism of toughening.

A significant difference of strength was noted in alumina ceramics made through the powder compaction process with spray dryers of two sizes. The origin of the change was examined by new characterization methods involving optical microscopy. The granules were found to have irregular shape. Defects in compacts were formed from these dimples and also from the nonuniform packing of powder particles at the granule boundaries. These defects are responsible for major defects in sintered bodies. The change of strength in the ceramics can be explained by the change of granule size with the spray dryer. The size of granules was found to directly affect the size of defects in the green and sintered bodies. The size of granules, defects in granules, green bodies, and sintered bodies were approximately 20–30% smaller for granules made with the small spray drier. There was a direct correlation between the size of defect and the strength of ceramics.

A hydroxyapatite [HAp; Ca10(PO4)6(OH)2] coating layer was formed on a Ti-based alloy by the electron-beam deposition method. When pure HAp was used as a target for the deposition, an amorphous layer was formed on the metal substrate. By heat treatment in a vacuum at 630 °C, the layer was crystallized into tricalcium phosphate [Ca3(PO4)2]. The crystallization improved the dissolution rate of the layer remarkably; however, at the same time, it deteriorated the bond strength with the substrate. When extra CaO (up to 25 wt%) was added to the target and processed under the same conditions, a layer compositionally close to crystalline HAp was deposited. Before the heat treatment, even though the layer was in amorphous state, the dissolution rate in the physiological solution was extremely low. Furthermore, the bond strength increased remarkably compared to the layer formed by the pure HAp target. Compositional and structural resemblance of the layer with the crystalline HAp was attributed to these improvements in properties.