The kinetics of hydride formation and decomposition described by semiempirical models generally do not involve particle and grain-size dependence. However, ball-milled nanocrystalline powders usually exhibit log-normal grain-size and particle-size distribution. Considering size dependence, a total reacted function for a multiparticle system has been developed. We show that the shape of the measured reaction fraction curves do not determine unambiguously the rate-controlling mechanism of hydrogen sorption, since the kinetics are strongly affected by the microstructure. With the application the convolutional multiple whole profile fitting procedure for nanocrystalline MgH2, the parameters, e.g., the median and variance of the log-normal grain-size distribution have been determined. Taking these values into account, the reaction constants corresponding to different sorption states are considerably modified compared with values obtained from classical single-particle models.

This work studies the chemical and structural changes that occur in sols upon heating to form ceramics. Ferrimagnetic Y3Fe5O12 (YIG) was chosen because the geometric and structural constraint of ferrimagnetic interactions allow for a direct measurement of the degree of well-defined structure present within the sol at various stages of development. Glycolate sols of 8% mol total metal were prepared using Y(NO3)3 and Fe(NO3)3 hydrates in stoichiometric ratios. Terminal straight-chain diols were used, ranging from 1,2-ethanediol to 1,6-hexanediol. The temperatures at which mass change occurred during heating were determined by thermogravimetric analysis. Samples were heated to these temperatures and examined by Fourier transform infrared spectroscopy (FTIR), x-ray diffraction, and magnetometry to determine chemical, structural, and magnetic changes. Ferrimagnetic ordering was present after the first heating step. Defined structure, determined by x-ray, occurred in the penultimate step. Analysis of FTIR spectra, in conjunction with the results of thermogravimetric analysis, revealed a predictable decomposition pathway.

The Cu–Sn binary system is important for various applications, especially for recent developments in the electronics packaging industry. The ϵ-Cu3Sn and η-Cu6Sn5 (η′ phases) phases are frequently encountered in electronics products. However, the two phases have been described as line compounds in previous thermodynamic modeling, and their compositional homogeneities were not considered. In this study, the thermodynamic properties of the Cu–Sn binary system are modeled and the phase diagram is calculated by the CALPHAD method, using experimental information reported in the literature. The ϵ and η (η′) phases are described using compound energy models with two and three sublattices, respectively, so that their compositional homogeneities could be calculated. Good agreement was observed between the calculated result and the existing experimental data.

Novel metal-matrix nanocomposites (MMNCs) of Cu–30Ni–20Cr and Cu–50Ni–20Cr (by wt%), having a nanocrystalline Cu–Ni solid solution matrix with the dispersion of Cr nanoparticles, were fabricated by coelectrodeposition. Both nanocomposites exclusively grew external chromia scale during oxidation at 800 °C in air. The codeposited Cr nanoparticles, together with the numerous grain boundaries in the Cu–Ni matrix, promoted the establishment of a continuous chromia scale during the initial and transient oxidation stage, and then they functioned as “a reservoir” supplying sufficient Cr flux for the exclusive growth of the scale during the steady-state stage. The theoretical treatment using a two-phase alloy oxidation model indicates that high Cr diffusivity correlated with the persistence of an ultrafine-grained structure of the Cu–Ni matrix during oxidation is crucial to the exclusive chromia growth. Ni content increase did not significantly affect the chromia scale formation. This is fundamentally different from the oxidation of conventional Cu–Ni–Cr alloys investigated for comparison.

The importance of the secondary electron emission of the protective layer in the alternating current plasma display panels is widely known. However, the difficulty in measuring the secondary electron emission coefficients (γ) of insulating materials has hampered efforts to obtain accurate estimates of their values. To overcome the difficulty of direct measurement, we devised a calculating γ using the spectra of x-ray photoelectron spectroscopy (XPS) and a well-defined theory. The XPS spectra of the valence and core bands of MgO, Al2O3, and Y2O3 films, which were deposited by e-beam evaporation, were measured. Calculations of the γ values were conducted for the case when gas ions such as He, Ne, Ar, and Xe slowly approach the solid surface.

This study probes the relationship between the morphology of anodic titania (TiO2) layers grown on Ti foil substrates and their subsequent photoelectrochemical response in 0.5 M Na2SO4 supporting electrolyte. The effects of anodization variables (voltage and time) and anodization medium composition [water, glycerol, poly(ethylene glycol), ethylene glycol] along with fluoride ion concentration on the oxide layer of morphology and photoresponse are described. The degree of order of the self organized TiO2 nanotube arrays and the extent to which these arrays organize themselves over the entire substrate surface are key variables dictating the corresponding quality of the resultant photoresponse.

Using a confocal laser scanning microscope the development of stress in a micromechanical contact could be measured for ruby with a resolution of ∼1 μm. Ruby (α-Al2O3: Cr3+) spheres with radii of 75 μm were compressed quasi-statically between two sapphire (α-Al2O3) plates. While applying an increasing uniaxial load, confocal microscopy was used to record the fluorescence spectra at the contact region. The peak positions of the fluorescence spectrum shift to longer wavelengths with increasing stress. By detecting the shift in wavelength the local stress could be measured. We adopted two-photon excitation process (800 nm wavelength) to reduce background fluorescence. Loading–unloading cycles were applied with the maximal loading force increased subsequently for each of the next cycle. Progressive fatigue was observed when the load exceeded 1.1 N. As long as the load did not exceed 4 N stress-versus-load curves were still continuous and could be described by Hertz’s law with a reduced Young’s modulus or increasing damage. Once the load exceeded 4 N, spikelike decreases of the stress were observed. This indicates the formation of microcracks on the 10 μm length scale.

CeO2–ZrO2–γ-Al2O3 mixed oxides with different molar compositions have been synthesized by the sol-gel method using nitrate–alkoxide precursors. Some relationships between the molar composition of the ternary systems and their textural and structural properties are presented. CeO2–ZrO2–γ-Al2O3 mixed oxides have been studied and characterized using x-ray diffraction, transmission electron microscopy, and Raman spectroscopic analyses. By complete porosity analyses of all samples before and after hydrothermal (up to 75% steam) treatment at 500 °C, we have been able to optimize a highly hydrothermally stable CeO2–ZrO2–γ-Al2O3 system with a molar ratio of 10:10:80 mol%. γ-Al2O3 alone and CeO2-doped as well as ZrO2-doped γ-Al2O3 were also investigated by the hydrothermal treatment, and their steam-sensitive properties have been compared with those of the ternary CeO2–ZrO2–γ-Al2O3 system.

The structure of a region of a highly Al-rich mullite (Al4+2xSi2–2xO10–x with x ∼ 0.82; 47Al2O3-6SiO2; Al/Si ∼16) in a chemically vapor-deposited, functionally graded mullite coating was studied by high-resolution transmission electron microscopy. The region consisted of a fully ordered and twinned multidomain structure. Within each domain, well-ordered oxygen vacancies resulted in antiphase boundaries (APBs) characterized by a shift vector of [001]. The APBs were oriented parallel to (601) and (601). Along [001], the structure consisted of alternating layers of (601)- and (601)-domains with a spacing of 17d601, separated by (001) twinning planes. The (001) twinning did not generate any additional spots in the [010] mullite diffraction pattern. The lattice parameters of this ultrahigh Al-rich mullite phase were calculated from selected-area electron-diffraction patterns to be: a = 0.762 nm; b = 0.754 nm; and c = 0.291 nm.

Partial and integral enthalpies of mixing of liquid Ag–Cu–Ni–Sn alloys were determined at 1000 °C by a drop calorimetric technique using a Calvet type microcalorimeter. They were obtained by adding Ni to the ternary Ag–Cu–Sn alloys with different composition. The data were evaluated by means of an extended Redlich–Kister–Muggianu polynomial fit for substitutional solutions. The minimum and maximum in the quaternary system were also calculated. It was found that the maximum integral enthalpy of mixing (13,310 J/mol at 41 at.% Ag) occurs in the binary Ag–Ni system while the minimum integral enthalpy of mixing (−21,390 J/mol at 61 at.% Ni) occurs in the binary Ni–Sn system. Moreover the experimental data were compared to values calculated by different extrapolation models based on binary data.

Sn whiskers can form at room temperature on the agglomerated flakes produced by mechanical alloying (MA) of Ti, Sn, and C powders, whether the flakes are stored in air or water. The Sn whiskers forming in air are tens of micrometers to several centimeters in length and 0.5 to ∼10 μm in diameter. Whereas a large amount of Sn polyhedra forms on the flakes that are stored in water, a small amount of Sn whiskers forms on the polyhedra. The driving force for Sn whisker formation is the compressive stress induced by mechanical alloying (MA) and oxidation. The mechanism about the spontaneous growth of metal whiskers is discussed.

Nanocrystalline alloys often show exceptional thermal stability as a consequence of kinetic and thermodynamic impediments to grain growth. However, evaluating the various contributions to stability requires detailed investigation of the solute distribution, which is challenging within the fine structural-length-scales of nanocrystalline materials. In the present work, we use a variety of techniques to assess changes in the grain size, chemical ordering, grain-boundary segregation, and grain-boundary structure during the heat treatment of Ni–W specimens synthesized over a wide range of grain sizes from 3 to 70 nm. A schematic microstructural evolution map is also developed based on analytical models of the various processes activated during annealing, highlighting the effects of alloying in nanocrystalline materials.

We explored the growth and characteristics of CdTe doped with Sn to heighten our understanding of the role of deep levels on electrical compensation and trapping. We demonstrated, for the first time, the strong dependence of the SnCd charge state on the Fermi-level variation (2–3kT) in high-resistivity CdTe. The concentration of deep traps for electrons was determined by the number of doubly positively charged Sn2+ atoms. Thermoelectric-effect spectroscopy and photovoltage measurements revealed the conversion of the SnCd defect from the electron SnCd2+ trap to the hole SnCd0 trap. The results agree well with the existence of a negative U-center in the SnCd0/2+ defect. We also showed that the neutral Sn defect is responsible for the near midgap C-band → bound hole radiative transitions band with a maximum at 0.76 eV.

We report the layer structure and composition in recently discovered TiN/SiN(001) superlattices deposited by dual-reactive magnetron sputtering on MgO(001) substrates. High-resolution transmission electron microscopy combined with Z-contrast scanning transmission electron microscopy, x-ray reflection, diffraction, and reciprocal-space mapping shows the formation of high-quality superlattices with coherently strained cubic TiN and SiN layers for SiN thickness below 7–10 Å. For increasing SiN layer thicknesses, a transformation from epitaxial to amorphous SiNx (x ⩾ 1) occurs during growth. Elastic recoil detection analysis revealed an increase in nitrogen and argon content in SiNx layers during the phase transformation. The oxygen, carbon, and hydrogen contents in the multilayers were around the detection limit (∼0.1 at.%) with no indication of segregation to the layer interfaces. Nanoindentation experiments confirmed superlattice hardening in the films. The highest hardness of 40.4 ± 0.8 GPa was obtained for 20-Å TiN with 5-Å-thick SiN(001) interlayers, compared to monolithic TiN at 20.2 ± 0.9 GPa.

Simultaneous direct current stressing with thermal aging accelerates the migration of conducting species resulting in significant microstructural coarsening. Because of the synergistic fields influence, such coarsening begins from the anode and propagates toward the cathode. Prolonged current stressing with 104 A/cm2 at 150 °C causes the inter-lamellar eutectic SnPb to become a two-layer structure, with a Pb-rich layer adjacent to the anode and an Sn-rich layer adjacent to the cathode. This mass movement causes hillock/valley formation, and the extents of such surface undulations increase with increases in the time duration of current stressing as well as with the joint thickness. In thinner solder joints these events occur sooner, although the extents of surface undulations depend on the thickness of joints. In addition, Cu present in the substrate and in the intermetallic layer at the cathode migrates to form Cu6Sn5 within the Sn-rich layer, in a region close to the Pb-rich layer.