Icosahedral samples of nominal composition Al63.5Cu24Fe12.5, which normally grow a rhombohedral approximant crystal, were submitted to heat treatments of various durations. The atmosphere in contact with the surface of the specimens was either dry air or secondary vacuum in order to test whether the formation of the icosahedral phase is sensitive or not to the nature of the atmosphere. Materials annealed in air showed a very thin surface layer of oxide which contained hydrogen. Beneath this oxide layer, small quantities of oxygen and hydrogen were also detected within the underlying lattice. This contamination was sufficient to shift the composition of the samples out of the stability domain of the icosahedral phase and has induced formation of a significant amount of the cubic phase. In contrast, the rhombohedral compound no longer appeared. This behavior goes along with the great sensitivity of the icosahedral phase stability to a sharply denfined electron to atom ratio.

The structural, microwave absorption, and oxidation characteristics of diesel particulate matter (DPM) collected from a CAT 3304 diesel engine are reported. The x-ray diffraction of DPM yields the characteristic peaks of pregraphitic carbons (cokes and pitches), and its modeling yields d(002) ≍ 3.429 Å and a crystallite size of about 20 Å. The real and imaginary parts of the dielectric constant ∊ = ∊′ + i∊″ are measured at 8.7 GHz using the cavity perturbation technique. The measured values for the DPM are ∊′ = 8.6 ± 1.7 and ∊″ = 7.4 ± 1.5, compared to ∊′ ≍ 1.0 and ∊″ ≍ 6 × 10−5 for the ceramic trap material used for collecting DPM. The oxidation products of the DPM, analyzed by FTIR spectroscopy, are found to contain CO2 and CO with a peak yield occurring around 500 °C. Since microwave power absorption is proportional to ∊″, these results show that selective microwave heating of the DPM in the ceramic traps should be a very efficient process with CO2 and CO as the main oxidation products.

La:Mn = 1:1 mixtures of lanthanum oxide and manganese carbonate were heat-treated under various oxygen partial pressures at 1400 °C or 1300 °C. The Mn valence of the samples was measured by a chemical analysis, and the crystal structures were refined by the powder x-ray diffraction and the Rietveld analysis. A novel orthorhombic perovskite phase, belonging to the space group Pbnm and containing - Mn2+ ions, was formed by heat-treatment under low oxygen partial pressures. The structure was very close to a cubic symmetry. It is supposed that the micro Jahn-Teller effects of Mn2+ ions were nearly canceled by one another.

Thin films of carbon nitride have been prepared using triode ion plating. It has been observed that the compound formation occurs at ambient substrate temperature itself. Though the films are completely amorphous at temperatures below 900 °C. they are hard and transparent down to a wavelength of 200 nm. It has also been observed that the film transmission can be modulated using nitrogen ion flux and partial pressure. The IR transmission spectra clearly show the C-N stretch band around 2200 cm−1. Onset of crystallization, as evidenced from electron diffraction, occurs around 900 °C substrate temperature.

Thin films of Y-stabilized ZrO2 (YSZ) were deposited by RF diode sputtering on R-plane sapphire as a buffer layer for the deposition of YBa2Cu3O3 (YBCO). By increasing the partial pressure of oxygen in the sputter gas mixture from 20% to 50%, it was found that the substrate temperature required to obtain (100) oriented YSZ deposition could be lowered to 630 °C from 800 °C. This change is attributed to heating or mixing effects at the film surface, due to an increase in negative ion bombardment, which supplements the effects of external heating. Increases in the partial pressure of oxygen beyond 50% were found to be counterproductive. YBCO films, deposited on the YSZ buffer layers via magnetron sputtering, showed c-axis orientation and transition temperatures of 82 K. Orientation of both the YSZ and YBCO films was confirmed by x-ray diffraction and SEM characterization.

X-ray photoelectron spectroscopic measurements of oxidation of the AglnTe2 surface at different temperatures are reported. The results are analyzed quantitatively. The oxidized surface was shown to have TeO2, Te, and In2O3. The presence of In2O is also identified. The experimental results are explained on the basis of the heat of formation.

Epitaxial β-SiC thin films were grown on modified Si(100) substrates from methyltrichlorosilane (CH3SiCl3 or MTS) in a hot wall reactor by using low pressure chemical vapor deposition (LPCVD). At 1150 °C, the growth rate of the β-SiC films was 120 Å/min. Epitaxial β-SiC(100) thin films were deposited after the deposition time of 12.5 min. However, the crystallinity of the deposited films was influenced by the deposition time. For example, the occurrence of rotational β-SiC(100) crystals and polycrystalline β-SiC with a highly preferred orientation of (100) planes was obtained for the deposition time of 50 min. XRD and TEM showed the appearance of polycrystalline β-SiC films with a preferred orientation of β-SiC(111) after further increasing the deposition times (time ≥ 75 min). At 1100 °C, polycrystalline β-SiC films with poor surface morphology were observed even though the film had a preferred orientation of β-SiC(100) for short deposition time (e.g., 12.5 min). Polycrystalline β-SiC(111) film was obtained for the deposition time of 200 min at this temperature.

The gas phase densities of CH3 and CH and the hydrogen dissociation fraction are measured in a hot filament diamond deposition system for each of several different hydrocarbon input gases. The crystal growth rate and the appearance of the diamond grown from the different input gases are also examined. A comparison of the measurements indicates that the nature of the input hydrocarbon is relatively unimportant because fast gas phase reactions completely scramble the identities of the input carbon atoms. The addition of oxygen greatly alters the gas phase densities and other experimental factors such as the filament surface condition. Small concentrations of atomic impurities in the gas phase are also detected using high sensitivity absorption spectroscopy.

The gas-condensation technique is used to produce the nanocrystalline (NC) WO3−x, Pt/WO3−x, and Pd/WO3−x powders under different atmosphere and pressure. HRTEM images show that a coherently bonded interface exists between Pt or Pd and WO3−x. The nanocrystal WO3−x, Pt/WO3−x, and Pd/WO3−x grow into a needle shape with a plate inside when these as-evaporated powders are compacted and sintered at 900 °C for 2 h. The plate grows preferentially in {220} plane along the 〈0011〉 direction. However, the mean particle size of nanophase Pt and Pd increases only from <10 nm to 30 nm and 50 nm, respectively. The results of CO oxidation show that nanophase Pt/WO3−x powders have better catalytic effects on converting CO to CO2 than nanophase WO3−x and Pd/WO3−x powders.

A new carbon crystal named carbolite has been synthesized by quenching high temperature carbon gas on a room temperature substrate. The crystal has a density as small as 1.46 g/cm3 and is transparent for visible light. The crystal structure is hexagonal, and the dimensions of the unit cell are 1.193 nm in the α-direction and 1.062 nm in the c-direction. Along the c-axis, a parallel array of carbon chains is proposed. The array is made up of a triangular lattice in which the interchain distance is 0.344 nm and the mean interatomic distance within a carbon chain is 0.133 nm. The former value is close to the van der Waals distance between the honeycomb planes of graphite, and the latter value is close to the C-C bond length in the honeycomb plane. Intercalations of potassium, sodium, and iodine atoms are performed.

Using transmission electron microscopy, we investigate Si3N4 grown in situ on GaAs metal-insulator-semiconductor (MIS) device structures with a Si interlayer, which has been previously shown to improve the electrical properties of field-effect transistors with Si3N4 gates on GaAs. We find that the primary role of the Si interlayer is to prevent the reaction between the nitride or nitrogen used for growth and GaAs. The interlayer thickness dependence of this microstructure, and its relationship to electrical properties, are discussed. The optimal thickness of the thin pseudomorphic Si interlayer appears to be around 0.4 nm. The growth temperature dependence of the critical thickness for morphological instability is demonstrated.

The solid state reaction between Co and Si has been studied in bulk diffusion couples between 850 and 1100 °C. At the scale of the observations made, the three phases Co2Si, CoSi, and CoSi2 are found to grow simultaneously, according to diffusion controlled kinetics. The results are analyzed in term of the Nernst-Einstein equation that directly relates diffusion fluxes to the free energy changes driving the formation. The growth rates obtained for CoSi2 at high temperatures, in the present bulk samples, are compared with those determined by others in thin films, at much lower temperatures. The comparison requires that attention should be paid to two factors. The first one is that the laws of growth are slightly different for a phase growing simultaneously with two other ones (bulk) and one phase growing alone (thin films). The second factor is the grain size of the various samples, which varies with the temperature of reaction. Once this is done, excellent agreement is obtained between the two sets of measurements. Moreover it is shown that knowing the grain size, it is possible to calculate quite accurately the growth rate from the respective isotope diffusion coefficients both for lattice and grain boundaries of Co and Si in CoSi2.

We present a detailed investigation on the decagonal quasicrystal (D-phase) formed from an Al-Pd-Mn icosahedral quasicrystal (I-phase) through a solid-state phase transformation, including its formation, compositional and crystallographical relationships with the matrix I-phase, growth mode, and structural characteristics. The as-melt-spun Al70Pd20Mn10 alloy contains only I-phase. By annealing at 800 °C, the D-phase is found to grow cpitaxially from the I-phase to establish a D/I two-phase equilibrium with distinctly different composition between them. The D-phase exhibits a stepped growth interface, which consists of a facet plane, formed by sharing the tenfold plane with a fivefold plane of the matrix I-phase, and some ledges across it. The growth of the D-phase into the I-phase proceeds through lateral movement of the ledges along the tenfold plane. High-resolution electron microscopy reveals that the structure of the D-phase is constructed by an aperiodic arrangement of decagonal atom clusters with definite linkages and long-range quasiperiodic correlation.

Undoped and Cr doped rodlike Al-Al3Ni eutectics have been studied as initial alloys of Raney nickel catalysts. The aim was to localize the dopant at different stages of the catalyst life: in the initial alloy, after Al leaching out, and after hydrogenation reaction. We have followed this dopant by STEM analysis and high resolution Auger spectroscopy. The outcome is that during Al leaching out, the dopant is also extracted from its initial phase and then forms a deposit on the Ni crystallites of the catalyst. Moreover, during the hydrogenation, the quantity of Cr remains roughly constant.

A directionally solidified alloy based on the NiAl-(Cr, Mo) eutectic was examined by transmission and scanning electron microscopy to characterize the microstructure and room temperature deformation and fracture behavior. The microstructure consisted of a lamellar morphology with a 〈111〉 growth direction for both the NiAl and (Cr,Mo) phases. The interphase boundary between the eutectic phases was semicoherent and composed of a well-defined dislocation network. In addition, a fine array of coherent NiAl precipitates was dispersed throughout the (Cr, Mo) phase. The eutectic morphology was stable at 1300 K with only coarsening of the NiAl precipitates occurring after heat treatment for 1.8 ks (500 h). Fracture of the aligned eutectic is characterized primarily by a crack bridging/renucleation mechanism and is controlled by the strength of the semicoherent interface between the two phases. However, contributions to the toughness of the eutectic may arise from plastic deformation of the NiAl phase and the geometry associated with the fracture process.

The creep properties of lots of NiAl eryomilled with and without Y2O3 have been determined in compression and tension. Although identical cryomilling procedures were used, differences in composition were found between the lot ground with 0.5 vol % yttria and the lot ground without Y2O3. Compression testing between 1000 and 1300 K yielded similar crecp strengths for both materials, while tensile creep rupture testing indicated that the yttria-containing alloy was slightly stronger than the Y2O3-free version. Both compression and tensile testing showed two deformation regimes; whereas the stress state did not affect the high stress exponent (n ≍ 10) mechanism, the low stress exponent regime n was ∼6 in tension and ∼2 in compression. The strengths in tension were somewhat less than those measured in compression, but the estimated activation energies (Q) of ∼600 kJ/mol for tensile testing were closer to the previously measured values (∼700 kJ/mol) for NiAl-AlN and very different from the Q's of 400 and 200 kJ/mol for compression tests in the high and low stress exponent regimes, respectively. A Larson-Miller comparison indicated that cyromilling can produce an alloy with long-term, high-temperature strength at least equal to conventional superalloys.

The six independent second-order elastic stiffness coefficients of a Ti44Al56 single crystal (L10 structure) have been measured at room temperature for the first time using a resonant ultrasonic spectroscopy (RUS) technique. These data were used to calculate the orientation dependence of Young's modulus and the shear modulus. Young's modulus is found to reach a maximum near a [111] direction, close to the normal to the most densely packed planes. The elastic moduli and Poisson's ratio for polycrystalline materials, calculated by the averaging scheme proposed by Hill, are in good agreement with experimental data and theoretical calculations.

Intercalation of AlCl3 into stage 2 FeCl3-graphite intercalation compound (GIC) using an ordinary two-bulb method has been studied by x-ray diffraction. Stages 2, 3, and 4 ternary AlCl3-FeCl3-GlC's are obtained when the temperatures of the stage 2 FeCl3-GIC were set at T (GIC) = 503, 523, and 553 K, respectively, for the AlCl3 intercalate material at T (AlCl3) = 473 K, that is, the vapor pressure of (AlCl3)2 (g) of the main vapor species to be held at p {(AlCl3)2} = 2.4 × 105 Pa. However, for the temperature of the stage 2 FeCl3-GIC at T (GIC) = 573 K, the (AlCl3)2 (g) vapor is found to promote the decomposition of the stage 2 FeCl3-GIC, resulting in the formation of graphite. The decomposition of the stage 2 FeCl3-GIC is considered to take place because the complex AlFeCl6 (g) in the gas phase, which is formed from both (AlCl3)2 (g) and FeCl3 existing at the edge of the FeCl3-GIC, is thermodynamically more stable than the FeCl3 and AlCl3 intercalates in their GIC at p {(AlCl3)2} = 2.4 × 105 Pa and T (GIC) = 573 K.

Analytical models are presented for the elastoplastic deformation of multilayered materials subjected to fluctuating temperatures. The layered structure comprises an elastic-perfectly plastic ductile material sandwiched between two elastic brittle materials. With creep, heat transfer, and edge effects excluded, closed-form solutions for different characteristic temperatures for thermal cycling are presented as a function of the layer geometries and the thermomechanical properties of the constituent phases. The evolution of curvature, the generation of thermal residual stresses within each layer, and the onset and spread of plasticity in the ductile layer are also examined. It is theoretically shown that reversals of curvature in the layered solid can occur during monotonic changes in temperature, even when the thermomechanical properties of the layer do not vary significantly with temperature. The predictions of the analytical model are seen to compare favorably with experimental observations of curvatures during thermal cycling in the limiting case of bilayer composite with Al–Al2O3 layers and Al–Si layers and in a Si–Al–SiO2 trilayer system. Case studies of the effects of the relative variations in the geometry, elastic properties, and plastic response of the constituent phases on the overall deformation are examined for two practically significant layered systems: a Si–Al–SiO2 layered solid with extensive applications in the electronics industry and a Cr2O3-coated steel with an interlayer of a Ni–Al alloy which is used in structural applications.

The microstructure of Al/α-Al2O3 composites made by infiltrating molten Al into dense mullite preforms has been characterized using transmission electron microscopy. The growth of the Al/Al2O3 composites was found to proceed through three stages. Initially, Al infiltrates into a dense mullite preform through grain boundary diffusion, and reacts with mullite at grain boundaries to form a partial reaction zone. Then, a complete reaction takes place in the reaction region between the partial reaction zone and the full reaction zone to convert the dense mullite preform to a composite of α-Al2O3 (matrix) and an Al-Si phase (thin channels). Finally, the reduced Si from the reaction diffuses out of the Al/Al2O3 composite through the metal channels, whereas Al from the molten Al pool is continuously drawn to the reaction region until the mullite preform is consumed or the sample is removed from the molten Al pool. Based on the observed microstructure, infiltration mechanisms have been discussed, and a growth model of the composites is proposed in which the process involves repeated nucleation of Al2O3 grains and grain growth.