In this paper we provide a new mathematical model for front propagation with a nonlocal growth law in any space dimension. Such a problem arises in composite fabrication using the vapor infiltration process and in other physical problems involving transport and reaction. Our model, based on the level set equation coupled with a boundary value problem of the Laplace equation, is an Eulerian formulation, which allows robust treatment for topological changes such as merging and formation of pores without artificially tracking them. When applied to the fabrication of continuous filament ceramic matrix composites using chemical vapor infiltration, this model accurately predicts not only residual porosity but also the precise locations and shapes of all pores.

The characteristics of a ferroelectric Pb(Zr0.52Ti0.48)O3 (PZT) capacitor on conductive BaRuO3 thin films deposited by pulsed laser deposition (PLD) were investigated. The BaRuO3 layer grown epitaxially on LaAlO3(100) substrates at a substrate temperature of 700 °C was found to have a resistivity around 145 μΩ cm at 300 K. The subsequently deposited PZT film showed a c-axis orientation perpendicular to the substrate, and the remnant polarization, ΔP (= P* – P^), and coercive field, EC, of the capacitor were 24.7 μC/cm2 and 52 kV/cm, respectively. Fatigue characteristics of the PZT on BaRuO3 electrodes are far better than those obtained with polycrystalline PZT with Pt structures and comparable to those on epitaxial Yba2Cu3O7−x electrodes. With the new metallic electrode, the PZT layer exhibits no serious degradation in fatigue endurance up to 1010 cycles.

The internal stress and internal friction of electrodeposited multilayered Cu–Ni(100) thin films were investigated as a function of temperature by a sensitive vibrating membrane technique. Each membrane was in a state of biaxial stress (approaching the yield strength) resulting from contributions of the growth stress in the as-deposited film and from the thermal stress as the membrane was heated. The measured internal friction of these stressed multilayered films was enhanced by over an order of magnitude compared to the predicted value of classic damping related to the modulus defect when the effect of the internal stress was taken into account.

Zirconium aerosol was ignited and burned in atmospheric pressure air in microgravity using a 2.2-s drop tower. Combustion products were collected and analyzed using electron microscopy. The elemental composition analyses indicated that combustion product compositions fell along two linear traces on a ternary Zr–O–N diagram. Currently, the equilibrium Zr–O–N phases are not characterized at temperatures above 2000 °C, typical of zirconium combustion in air, and it is suggested that the phases detected in zirconium combustion products can serve as a guide to further studies of the Zr–O–N system at high temperatures. It is also suggested that experimental metal combustion techniques can be adopted for studying high-temperature metal–gas phase equilibria.

Drop-tube experiments have been performed on YxNd1–xBa2Cu3Oy (0.7 ≤ x ≤ 1.0) to understand the effects of partial substitutions of Nd for Y on the phase relationships in these systems at elevated temperatures. Powders 50–100 μm in diameter were processed in pure O2 at furnace temperatures of 1575–1800 °C, every 25 °C. The resulting samples were examined microstructurally by scanning electron microscopy, energy dispersive spectroscopy, and optical microscopy. Powder x-ray diffraction was performed for phase identification. It was found that Nd substitution alters phase selection by introducing at least one new phase and allowing for solidification of the superconducting composition directly from the melt via undercooling to below the peritectic transformation temperature. A decreasing trend in the overall melting temperature with increasing Nd was also identified.

This paper presents the results of drop-tube experiments performed on YxNd1–xBa2Cu3Oy (0 ≤ x ≤ 0.5) to understand some of the effects of partial substitutions of Nd for Y on the phase relationships in these systems at elevated temperatures. Powders from 50 to 100 μm in diameter were processed in pure O2 at furnace temperatures from 1400 to 1800 °C, every 25 °C. The resulting samples were examined microstructurally using scanning electron microscopy, energy dispersive spectroscopy, and optical microscopy. Powder x-ray diffraction was performed for phase identification. It was verified that Nd substitution alters phase selection by introducing at least one new phase and allowing for solidification of the superconducting composition directly from the melt via undercooling to below the peritectic transformation temperature. In addition, solidification pathways are altered for samples processed at temperatures just below the liquidus temperature. Microstructural and x-ray diffraction evidence was used to map the liquidus with increasing Nd substitution. It was found that a minimum in this liquidus occurs at or near the composition Y0.1Nd0.9Ba2Cu3Ox and at a temperature of 1500 °C (±25 °C).

The nucleation and growth of NdBa2Cu3O7–δ (Nd123)–Nd4Ba2Cu2O10 (Nd422) single-grain composites in a controlled 1% O2 in N2 atmosphere were investigated in detail as a function of solidification temperature and Nd422 phase content using a top-seeded melt growth technique. A schematic process phase diagram in the peritectic solidification region of Nd–Ba–Cu–O (NdBCO) was constructed primarily from constant isothermal growth experiments at various temperatures for several compositions and used to fabricate large single-grain material by both isothermal and continuous slow cooling over a limited temperature range. The nucleation at the seed surface and subsequent growth of uniform grains was observed to depend critically on the controlled rate of grain growth and the temperature range over which solidification occurred.

The creep behavior of single-crystal Zn-doped CdTe was examined in the small strain regime. Specimens from two different sources, with tensile axes [110] and [112], were deformed at 1073 and 1173 K. Strain rates were of order 10−6 to 10−7 s−1. A laser interferometer was constructed to measure the small sample displacement. Cadmium overpressure was used to inhibit sublimation of test specimens at elevated temperatures. Some tests showed a transition from secondary to tertiary creep at low levels of strain. An activation energy for steady-state creep was calculated as QC = 1.46 eV, and the creep exponent was found to be approximately n = 4.2. These results, coupled with reported activation energies for self-diffusion of Cd in Cd(Zn)Te, indicate a dislocation creep mechanism. Etch pit density was measured before and after deformation and approached a common level regardless of initial etch pit density.

A 100-nm CuFeS2 ultrafine powder was prepared through a solvothermal reaction at 200–250 °C. X-ray powder diffraction and transmission electron microscopy results revealed that chalcopyrite-phase CuFeS2 was crystallized with single-crystalline nature and preferential orientation growth. Mössbauer spectrum exhibited a six-peak hyperfine magnetic spectrum and a single nonmagnetic peak. Elemental analysis gave the atomic ratio of Cu:Fe:S of 1:1.02:2.10. The influence factors on the formation of CuFeS2 ultrafine powder are discussed.

The effect of solidification rate on the precipitation and microstructure of directional solidification IN792 + Hf alloy was studied. The solidification sequence and the initial precipitation temperature of different phases were determined by the observation of the quenched microstructure combined with the differential thermal analysis measurement. The script carbide was turned into faceted carbide with the drop of solidification rate. It was concluded by microstructure analysis that the faceted carbide was pushed by the γ solid front before it was captured. The incorporation of γ phase into the faceted carbide was due to the dendrite growth of the carbide toward one point and the mergence of the dendrites. Some long carbide bars were formed along the grain boundaries by continual reaction of eutectic (γ + MC carbide) at a solidification rate of 0.5 μm/s. Two zones, the γ′ forming elements enriched zone and depleted zone, were found in the residual liquid area. Eutectic γ/γ′ nucleated in the γ′ forming elements enriched zone. The η-phase precipitation was controlled by the ratio of (Ti + Hf + Ta + W)/Al in the residual liquid. The growth of eutectic γ/γ′ increased the ratio and induced the η-phase precipitation. A lower solidification rate decreased the ratio by sufficient diffusion and hence efficiently suppressed the η-phase precipitation.

The local order around Fe, Co, and Cu atoms was investigated by extended x-ray absorption fine structure spectroscopy in Fe–Co–Cu nanocrystalline alloys prepared by mechanical alloying. In order to study the time evolution of the alloying process, Fe30Co20Cu50 samples were studied after several processing times. The analysis of the data shows that, in a first step, a binary Co–Cu alloy is formed, but iron remains separate in the form of nanocrystals with a high defect concentration. Afterwards, in a second step, the final ternary Fe–Co–Cu alloy with the face-centered-cubic structure is obtained.

Conventionally, the wetting of metallic substrates by liquid metals involves undermining of the substrate–oxide layer by the liquid. Evidence is presented here for an alternative wetting process involving spreading of liquid copper along the exterior of the oxide layer on Ti–48 at.% Al–2 at.% Cr–2 at.% Nb substrates. A mechanism is presented that involves compositional changes in the liquid, which in turn allow a wetting-promoting reaction between the (initially unreactive) liquid and the exterior layer of the substrate oxide.

We report the soldering behaviors of high-temperature (300 °C) lead-free SnSb alloys on Cu foils and phased-in Cu–Cr thin films. By increasing the Sb content from 5 to 15 wt%, the solder surface became rougher and the wetting angle decreased from 50° to 20° on the Cu foils. Interfacial compounds were found to be Cu6Sn5 and Cu3Sn. The Cu6Sn5 showed a scallop-type morphology, whereas the Cu3Sn had a layer-type morphology. The growth of the latter was found to be diffusion limited. On phased-in Cu–Cr thin films, the solders showed much lower wetting angles than on the Cu foils, but the dewetting phenomenon was observed after 1 min of reflow time in the 85Sn15Sb alloy. In comparison, we found no dewetting of the high-temperature 95Pb5Sn solder.

Effective values of the thermal diffusivity, specific heat, and thermal conductivity of a porous 380-aluminum alloy prepared by melting in a gas-fired furnace, were determined as a function of the volume fraction of porosity. For that, photoacoustic, differential calorimetric, density, and image analyzer measurements were done. Thermal conductivity and specific heat capacity decrease with the increase of porosity, whereas the thermal diffusivity shows less dependence. Among the effective models for analysis of the thermal conductivity of a two-phase system, the Maxwell model best fits the experimental data, implying a homogenous distribution of the pores in the aluminum-alloy matrix.

The validity of controlling interfacial toughness in reaction-formed composites was explored using solid-state reaction processing and microanalysis techniques. A variety of rare-earth oxides was added to a yttrium aluminum garnet (YAG)/alumina powder mixture and then melted in air. Some melts retained the crystallography and microstructure of the pure, binary YAG–alumina eutectic. Using scanning transmission electron microscopy in conjunction with energy dispersive X-ray spectroscopy, rare-earth ions were observed both to segregate to the YAG/alumina interface and to form a third phase. Some evidence of increased crack deflection at these interfaces was observed via indentation fracture.

Composite materials containing amorphous iron embedded in poly(methylacrylate) or poly(methylmethacrylate) and amorphous cobalt embedded in poly(methylacrylate) were formed using a sonochemical method. The physical and thermal properties of the composite materials were probed. A significant difference in the solubility of the iron–poly(methylacrylate) and cobalt–poly(methylacrylate) in various solvents was observed. This difference is accounted for by the stronger interaction existing between the cobalt and the surrounding polymer. For iron–poly(methylacrylate) this interaction is weakened due to the formation of an iron complex.

Phase separation during the synthesis and decomposition of lead magnesium niobate (PMN)–ethylenediaminetetraacetic acid (EDTA) and PMN–citrate gels strongly affects perovskite Pb(Mg1/3Nb2/3)O3 phase formation. The PMN–EDTA gel was synthesized from a solution containing Pb–EDTA, Mg–EDTA, and peroxo–citrato–niobium complexes at pH 8. Pb–EDTA precipitation was avoided by using Pb:EDTA in the mole ratio >1:2.5 and flash pyrolyzing the PMN–EDTA solution at 225 °C. Consequently, the PMN yield increased from 80 to 98 wt%. The sequential decomposition of Pb–EDTA, Mg–EDTA, and peroxo–citrato–Nb in the PMN–EDTA precursor in 1 vol% O2 leads to phase separation of Pb and PbO and thus lowers the PMN yield to 92 wt%. At PO2 > 2.5 vol% the Pb, Mg, and Nb complexes cothermolyze to form ≥97 % perovskite PMN. The presence of a heterometallic citrato–Pb–Mg–Nb complex in PMN–citrate leads to oxygen partial pressure independent codecomposition of the Pb, Mg, and Nb complexes. Accordingly, PMN yields of ≥96 wt% were obtained from the PMN–citrate precursor for oxygen partial pressures between 1 and 5 vol%.

The effect of different cations in the anatase–rutile phase transition temperatures for titania prepared by the sol-gel method was studied. The metal dopants were chosen from different periods and groups of the periodic table to see the role played by the electronic configuration, the oxidizing state, the atomic size, etc. on these temperature modifications. Linear relationships between the anatase–rutile phase transition temperatures and the ionic radii for alkali metal, alkaline earth metal, and group 3 and 13 elements were obtained. For elements of the period 4, there was not such a defined tendency; for most of them the modification of the phase transition temperature was too small. The cations used were Li+, Na+, K+, Mg2+, Ca2+, Sr2+, Ba2+, Al3+, Y3+, La3+, Er3+, Ti4+, Co2+, Ni2+, Cu2+, and Zn2+. In all cases the dopant's concentration was 2 mol% with respect to titanium, and the same anion (nitrate) was used for all salts. A variation of more than 330 °C in the anatase–rutile phase transition temperatures was obtained by using these dopants. The transition temperatures from amorphous to anatase and from anatase to rutile phases were obtained from the x-ray diffractograms.

Nanocrystalline titanium dioxide was prepared via aerosol pyrolysis of titanium alkoxide precursor at 200–580 °C in air and in nitrogen atmospheres. Powders were characterized by x-ray diffraction, thermogravimetric analysis, Brunauer–Emmett–Teller analysis, scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy, x-ray fluorescence, Raman and infrared spectroscopy, and Berner-type low-pressure impactor. The anatase phase transition was initiated at 500 °C in nitrogen and at 580 °C in air. Under other conditions amorphous powders were observed and transformed to nanocrystalline TiO2 via thermal postannealing. In air, smooth and spherical particles with 2–4-μm diameter were formed with an as-expected tendency to convert to rutile in the thermal postannealings. In nitrogen, a fraction of the titanium tetrabutoxide precursor evaporated and formed ultrafine particles via the gas-to-particle conversion. At 500 °C thermally stable anatase phase was formed in nitrogen. A specific surface area as high as 280 m2 g−1 was observed for an as-prepared powder.

SiC/mullite/zirconia composites were fabricated by controlling the oxidation of powder compacts of SiC, alumina, and 3 mol% yttria-stabilized zirconia. The powder compacts were first oxidized in air at 1100 °C for various times to obtain proper amounts of amorphous silica. Subsequent reaction sintering at 1500 °C for 2 h combined the amorphous silica with alumina to form mullite with planned amounts. The incorporation of 3 mol% yttria-stabilized zirconia promoted mullite formation and enhanced the densification of the samples. With ≥10 vol% of 3 mol% yttria-stabilized zirconia in the samples, the temperature of mullite formation was lowered from 1400 to 1300 °C, and mullitization was near completion after sintering at 1500 °C for 2 h. The densification of the samples depended on the contents of SiC and 3 mol% yttria-stabilized zirconia. Samples with 20 vol% SiC and 10–20 vol% 3 mol% yttria-stabilized zirconia could be sintered to reach approximately 97% of theoretical density after sintering at 1500 °C for 2 h.