A study of the phases obtained in an aluminum manganese (Al86Mn14) alloy prepared under relatively slow solidification rates is presented. The identification of the phases presented in the alloy has been carried put using different techniques. Two of the phases were found to be crystalline in nature (Al, Al6Mn), two were amorphous (Al2O3, AlMn–O), and one of them was quasicrystalline (T phase). In the case of the quasicrystalline T phase an investigation on its structural characteristics was carried out, and a possible model for its structure is suggested, based on high-resolution images under fivefold diffraction conditions.

The crystallography of the phases obtained by heat treating a Ni-34.7 at. % Al alloy with 0.9 at. % Hf and 0.04 at. % B was studied in detail using x-ray diffraction techniques. Particular emphasis was placed on characterizing the Ni5Al3 phase, which is obtained by quenching the B2 NiAl phase and aging the resultant martensite. The structure of the Ni5Al3 phase is confirmed to be orthorhombic with space group D192h (Cmmm) and lattice parameters of a0 = 0.7475 nm, b0 = 0.6727 nm, and c0 = 0.3732 nm. The transformation from B2 NiAl to L10 martensite is shown to involve a Bain distortion of the c/a ratio from 0.707 to 0.853, and the further ordering transformation to Ni5Al3 involves a further increase of this c/a ratio to 0.900.

The Ni–Zr system is examined as a representative system for the formation of an amorphous phase by diffusion and for the crystallization of an amorphous phase by diffusion. High-resolution electron microscopy (HREM) is used to show that the amorphous phase grows by bulk diffusion through the amorphous material rather than by short-circuit diffusion. Also, the HREM shows that the amorphous phase formed by diffusion appears to be the same as the vapor-deposited amorphous phase. A correlation between crystallization temperatures (Tx) and the enthalpy of large-atom hole formation is given. This correlation predicts values of Tx that are lower than those predicted from the small-atom hole-formation model. The difference in hole-formation enthalpies for the large and small atoms is given as a criterion for amorphous-phase formation via diffusion.

Amorphous Zr–Rh and Zr–Pd hydrides are prepared both by hydriding metallic glasses and by hydriding metastable, polycrystalline fcc alloys. The thermal stabilities of the amorphous hydrides produced by these two distinct methods are examined by means of differential scanning calorimetry and are found to be similar. The enthalpy difference between the fcc phase and the amorphous phase of Zr81Rh19 is determined to be 0.6 kcal/mol. The thermal stability of Zr–Rh hydrides as a function of hydrogen concentration is investigated.

A sintered aggregate of hydroxyapatite, Ca10(PO4)(6(OH)2, designed for in vitro simulation of some of the physicochemical processes of dental decay is described and characterized. Diffusivity at 35°C (by tritiated water effusion) was (2.9 + 0.6) ⊠ 10−6 cm2/s. The apparent density (2.50 ± 0.04) g/cm3 gave a porosity of 20.8 ± 1.3 vol % based on the theoretical density of hydroxyapatitc. Estimates of the volume percent porosity from water vapor desorption and tritiated water effusion were 19.2 ± 2.9 and 20.7 ± 1.4, respectively Pore-size distribution measurements using mercury porosimetry showed that most of the porosity (approximately 17% of the sample volume) was concentrated between 30 and 60 nm equivalent pore radius. The material, which has been successfully used to simulate some aspects of the dental decay process, should find further application in this and related fields.

During high-temperature storage, glass corrosion in glass-to-metal feedthroughs can limit the lifetimes of lithium batteries designed to operate at ambient temperatures. Ampule tests have been conducted to simulate glass corrosion for Li/So2, Li/SOCl2, and Li/SOCl2 + BrCl batteries. In all lithium battery systems tested, lithium metal has been identified as the source of glass corrosion. On the basis of thermodynamic and kinetic stability, glass compositions have been developed that minimize the corrosion problem in all lithium battery systems tested.

Preliminary procedures have been developed for the ball milling of pristine and brominated P-100 graphite fibers. Because of the lubricative properties of graphite, large ball loads (50% by volume) are required. Use of 2-propanol as a milling medium enhances the efficiency of the process. The fibers, when allowed to settle from the milling medium, tend to be preferentially aligned with rather few fibers standing up. Milled, brominated P-100 fibers have resistivities that are indistinguishable from their pristine counterparts, apparently because of loss of bromine. This suggests that bromine would not be the intercalate of choice in applications where milled fibers of this type are required. It was found that brominated graphite fibers are stable in a wide variety of organic solvents.

The growth of an oriented anatase grain structure from the post-deposition annealing of amorphous reactive ion-beam-deposited thin films of titanium oxide has been demonstrated. The transformation has been observed directly by electron microscopy and the crystallization of the films occurs only when their thicknesses are greater than about 50 nm. Substrate effects were not found to be significant to the crystallization, which could also be induced by annealing freestanding films. The transformation processes can be described in terms of existing theories of crystal growth where the amorphous film is described as a supercooled liquid.

Ion-beam mixing of Ti layers with sintered α-SiC and hot-pressed Si3N4 was measured for 1 McV Au+ at doses of 1X1016 cm−2 and 5X1016 cm−2. Rutherford backscattering (RBS) and cross-section transmission electron microscopy (XTEM) were used to evaluate the mixing. Mixing was observed in Ti/SiC system; however, there was no mixing in Ti/Si3N4 system. Results are discussed in light of the enthalpy of mixing criterion for metal-insulator systems.

High-resolution transmission electron microscopy (HRTEM) and ellipsometry techniques have been employed to measure thicknesses of silicon oxide, grown at 800°C in dry oxygen, in the thickness range of 2–20 nm. While the oxide growth data measured from TEM obey a nearly linear behavior, those obtained from ellipsometry are seen to vary nonlinearly. The interface structure as function of the increasing oxide thickness was studied using HRTEM. At these oxidation temperatures, the earlier reported variations of roughness at the interface on the oxide thickness for oxides grown at 900°C are not seen. Attempts aimed at correlating the high-resolution transmission electron micrographs with some physical parameters like the refractive index and the dielectric breakdown lead to considerations of the importance of the effect of protrusions of silicon atoms of 1 mm size into SiO2 layers on the interface properties. These findings lead to explanations of some key features concerning the refractive index and density of thin SiO2.

A new technique for successfully fabricating high-quality optical waveguides in LiNbO3 is reported. A high concentration of Ti is implanted with the substrate at liquid nitrogen temperature and an amorphous, Ti-rich, nonequilibrium phase is produced in the implanted, near-surface region. Subsequent thermal annealing in water-saturated oxygen atmosphere at up to 1000°C initiates solid-phase epitaxial regrowth onto the crystalline substrate. A highquality single crystalline layer results that is rich in Ti and has excellent waveguiding properties.

A varistor's life has been defined as the time required to reach a limiting power density at which the power generated exceeds the power dissipated. Based on this concept, a working model for predicting the life of a ZnO varistor has been developed in terms of several critical material and design parameters. The model provides a direction as to whether these parameters should be maximized or minimized in order to enhance a varistor's life. Alternately, given a predetermined amount of the varistor's life, the model predicts a safe operating voltage under a given set of conditions.

The magnetic susceptibility of Te, MnTe2, and three dilute TeMn alloys was measured from room temperature to 800°C. The effective magnetic moment of dilute Mn in liquid Te is 5.0(2) μB and appears to be slightly temperature dependent. The effective moment for Mn in MnTe2 is 6.05 μB, approximately equal to that of a free 5/2 spin. The Weiss temperature of MnTe2 is 610(20) K. These data are used to determine an accurate phase diagram for Terich Mnx Te1−x. The eutectic is found at 0.6(1) at. % Mn with a eutectic temperature within 2°C of the tellurium melting temperature. Because liquid tellurium remains in metastable equilibrium with solid MnTe2 as much as 80°C below the eutectic, a metastable lowtemperature extension of the liquidus is also determined.

The visible-laser sublimation of CdTe, HgCdTe, CdS, and GaAs has been studied. A dynamic light guiding has been identified with an active feedback mechanism and is connected to the observation of 0.4 μm wide single-mode guiding structures during deep etching. The incipient stages of sublimation have been studied by mass spectrometry and are discussed in relation to diffusion mechanisms in the solid state.

Mechanical properties of GaAs crystals grown by the liquid encapsulated Czochralski technique and the boat technique are investigated by means of compression tests. Stressstrain characteristics of a GaAs crystal in the temperature range 400°–500°C are very similar to those of a Si crystal in the temperature range 800°–900°C. This seems to reflect the fact that the dislocation mobility in a GaAs crystal in the former temperature range is comparable to that in a Si crystal in the latter temperature range. Dislocations in GaAs crystals are found to be easily immobilized at an intermediate temperature due to gettering of impurities and/or impurity-point defect complexes. In comparison to a Si crystal, the surface of a GaAs crystal seems to involve irregularities that act easily as effective generation centers for dislocations. Thus the magnitude of the yield stress of an aged GaAs crystal is controlled by the surface condition and is not influenced by the density of dislocations involved in the crystal. The socalled steady state of deformation is realized in a GaAs crystal in the deformation stage after the lower yield point as in Si and Ge crystals. Dislocation distributions in a deformed GaAs crystal observed by transmission electron microscopy is very similar to those in deformed Si and Ge crystals.

The reactions between (100) GaAs and the near-noble metals Ni, Pd, and Pt have been investigated by application of high-resolution transmission electron microscopy (TEM), energy-dispersive analysis of x-rays in the scanning TEM and Rutherford backscattering spectrometry. Emphasis is placed on the evolution of the phase distributions, film compositions, and interface morphologies during annealing at temperatures up to 480°C. The first phase in the Ni/GaAs reaction is shown to have the nominal composition Ni3GaAs. Ternary phases of the type PdxGaAs are also found to be the dominant products of the Pd/GaAs reaction. Conversely, only binary phases result from the Pt/GaAs reaction. These observations are used to construct isothermal sections of the M-Ga-As thin-film phase diagrams. The behavior of a thin (1–2 nm) native oxide-hydrocarbon layer during the Ni/GaAs, Pd/GaAs, and Pt/GaAs reactions is also investigated. Only the Ni/GaAs reaction is noticeably impeded in some regions by this intervening layer. In contrast, the Pd/GaAs and Pt/GaAs reactions tend to mechanically disperse the native oxide layers.

Spark erosion is a method for producing fine powders of metals, alloys, semiconductors, and compounds. The technique involves maintaining repetitive spark discharges among chunks of material immersed in a dielectric liquid. As a result of the spark discharge there is highly localized melting or vaporization of the material. The powders are produced by the freezing of the molten droplets or the condensation and freezing of the vapor in the dielectric liquid. Since the powders are quenched in situ, they may be extremely rapidly cooled. Particles can be produced in sizes ranging from 5 nm to 75 μm. The average powder size and production rate depend on the power parameters, material used, and the dielectric liquid.