A commercially available aromatic polyimide film Kapton H 25-μm thick was heat-treated at temperatures between 490 and 540 °C in a nitrogen flow. Magnetization was measured as a function of magnetic field at 5 and 300 K and function of temperature in a field of 1 T. Diamagnetic and paramagnetic components were observed for all heat-treated films. Ferromagnetism was discovered even at 300 K in the films heat-treated at 490–520 °C. The saturation magnetization, coercive force, and residual magnetization for the 520 °C treated film were 0.059 J T−1 kg−1, 0.004 T, and 9 × 10−4 J T−1 kg−1, respectively, at 300 K. The ferromagnetism has been maintained 5 months after. Original Kapton H and the heated films were found to contain no metallic elements. The ferromagnetism should be caused by a long-range magnetic spin ordering of unpaired electrons located on slightly decomposed imide molecules with defects or on intermediates with free radicals formed by thermal decomposition. The ordering is probably established three dimensionally throughout the heat-treated films with a structural regularity similar to that of the original Kapton H.

Dislocations around precipitates in undoped AlGaN were investigated by transmission electron microscopy. The dislocation images were taken under different diffraction conditions. The dislocations are classified into two types, a pure edge dislocation loop and a close-;coiled helical dislocation. Both types of dislocations were found to depend on the shape and size of the precipitate sources. It is suggested that the pure edge dislocation loop results from homogeneous shear stress and the close-;coiled helical dislocation is caused by spherically symmetrical stress concentration at round ends of the precipitates and chemical force due to defect concentration change.

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.

Well-dispersed SiC slurries in the presence of binder and plasticizer were prepared and investigated in this series of work. In this part, poly(vinyl alcohol) (PVA) 1788 was investigated as a potential binder for aqueous tape casting process. The minimum amount of binder was determined through a primary calculation. Effects of the binder on SiC slurries properties were analyzed in term of zeta potential measurement and rheological test. Coupled with PEI as dispersant and glycerol as plasticizer, they lead to homogeneous systems which seem compatible. The suspensions (formulated with 47.9 wt% SiC powder, 1 wt% dispersant, 3.5 wt% binder, and 3.5 wt% plasticizer) exhibited a shear-thinning behavior with a very limited time-dependent character. After tape casting and drying process, the properties of green tapes were evaluated in term of solid content and gap height. The optimal solid content of SiC was found to be near 22.25 vol%, and the gap height, near 200 μm. The microstructure of green tape was characterized by TEM. Results showed that preparation of homogeneous green tapes with relative densities at about 51 vol% was feasible.

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.

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.

A2B2O7 pyrochlore oxides are being considered as potential host materials for the immobilization of fission products. It is therefore important to establish the relative ability of these compounds to accommodate fission product ions. We address this issue by using computer simulations to predict the structures and relative equilibrium energies associated with solution of Sr2+ over an extensive compositional range. Results indicate that strontium is accommodated via substitution for A host cations with oxygen vacancy compensation. This results in a nonstoichiometric composition. Optimum compositions and defect clusters structures are identified by constructing contour energy maps.

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.

Sm2+ ion-doped Al2O3–SiO2 glasses were prepared using sol-gel and melt-quenching methods; the redox equilibrium and spectral hole burning were investigated. The Sm3+ ions were reduced into Sm2+ by heating in H2 gas or x-ray irradiation. The redox between the Sm3+ and Sm2+ obeyed first-order kinetics, the rate of which was larger for the sol-gel glasses. The Sm3+ ions were also reduced by x-ray irradiation and the activation energy for redox equilibrium was half of that for the glasses treated in H2 gas. Two different mechanisms were proposed for the redox reaction of the samarium ions. In the x-ray irradiated glasses, the Sm3+ ions were reduced into Sm2+ by electron transfer from the oxygen defect center, whereas the H2-gas reaction removed the oxygen ions to reduce the Sm3+ ions. The spectral hole burning of the x-ray-irradiated glasses could be burned by the reverse reaction of the reduction of the Sm3+ ions; that is, the electron transfer from the excited Sm2+ into the surrounding oxygen. A short distance between the Sm2+ and oxygen defect centers allowed fast hole burning. On the other hand, the hole burning in the H2-treated glasses was performed by electron transfer between Sm2+ and another trapping center such as Sm3+.

We have developed a real-time phase-shifting interferometer capable of imaging interfacial morphology with a depth resolution of approximately 25 Å, with a lateral resolution of approximately 0.5 μm across a field of view of 2 × 2mm2, and with time resolution of 0.1 s. The method is applied in situ to the (101) face of potassium dihydrogen phosphate crystals growing from an aqueous solution. We image the formation and evolution of solution-flow-induced step bunches and determine their characteristic wavelength to be λc = 45 μm. This wavelength is within the range predicted by a stability theory on the basis of the balance between the diffusion interaction between steps and capillarity. The value of λc suggests that step–step interactions are the likely major factor for instability.

Advanced analytical transmission electron microscopy has been used to investigate microstructural evolution during pyrolysis in triol-based sol-gel thin films. At pyrolysis temperatures up to 300 °C, the films remained amorphous; however, nanometer-sized precipitates were observed in films heat-treated up to 400 °C for 10 min. Analytical transmission electron microscopy indicated that the precipitates were Pb-rich, as well as deficient in O, Ti, and Zr. Films pyrolyzed up to 500 °C for 10 min were composed of a nanocrystalline pyrochlore phase; however, pores could be observed, situated in the same position as the nanometer-sized precipitates at 400 °C. Face-centered cubic Pb-rich crystallites were also present on the surface of pyrolyzed films but absent in the fully crystallized films annealed at 650 °C. A tentative mechanism is proposed to explain these observations.

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.

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.

Planar thin films of dye-doped silica were prepared by sol-gel synthesis. The optical properties of the films were characterized by transmittance measurements in the visible-infrared range and by photoluminescence. Micropatterns whose feature size was on the order of 2.4 μm, were imprinted on the film surface by a simple soft lithography approach. An optical microscope interfaced to a charge-coupled device camera was used to image the imprinted patterns and to analyze the patterned films photoluminescence. A sensitive spectral narrowing of the emission, which occurred only in micropatterned films, was attributed to the lateral confinement of the luminescence due to the micrometer-scale modulation of refractive index produced by the embossing procedure.

Pulsed laser ablation deposition was used to fabricate Ni films. The structure of the as-deposited films is hexagonal (a = 0.267 nm and c = 0.435 nm), and its resistivity is nearly one order of magnitude larger than the resistivity of bulk Ni. No spontaneous magnetization was observed in the as-deposited samples. Annealing above 200 °C induced an irreversible structural transformation from the metastable hexagonal phase to the stable face-centered-cubic (fcc) one. Parallel to this transformation, the magnetic moment of the annealed Ni samples increased, and their resistivity decreased. On annealing at 440 °C, the structural transformation from the hexagonal-close-packed to the fcc phase was completed, and the magnetic moment, Curie temperature, and electrical resistivity of the fcc Ni films were found similar to the ones observed in bulk Ni. A direct correlation between the volume fraction of the fcc Ni phase in our films and their magnetic moment was established.

High current electropulsing was applied to a low-carbon steel in the solid state. The relationship between grain size and experimental conditions was revealed. It was found that the ultrafine-grained (UFG) microstructure could be formed when electric current density, heating rate, and cooling rate all were high. The UFG samples prepared by applying electropulsing were free of porosity and contamination, and had no large microstrain. Also, their tensile strength was dramatically enhanced over that of their coarse-grained counterparts, without a decrease in ductility. The mechanism for grain refinement and formation of the UFG microstructure was discussed. It is proposed that the effect of a decrease in thermodynamic barrier and enhancement of nucleation rate in a current-carrying system cannot be neglected.

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.

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.

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 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.