The effect of shock compression on the solid-state chemical reactivity of titanium and carbon powder mixtures was investigated with the objective of forming net-shaped TiC ceramics with a fine-grain microstructure. The combination of defect states and intimate interparticle contacts introduced during shock compression results in significant enhancement of the otherwise sluggish solid-state diffusion of Ti and C through the TiCx boundary layer. The apparent activation energy for TiCx formation was determined using solid-state reaction kinetics models, and was found to be reduced by four-to-six times that of diffusion of Ti into TiCx and two-to-three times that of diffusion of C in TiCx. As a result, net-shaped sections of shock-densified compacts (˜85% dense) were reaction synthesized via solid-state diffusion, producing microstructures with grain size <6 μm and microhardness of ˜2000 kg/mm2, in contrast to statically pressed powder compacts which reacted by a combustion process resulting in a highly porous product.

The inner surface of a cylindrical titanium alloy target was successfully implanted with nitrogen ion using a new plasma source ion implantation method. By means of x-ray photoelectron spectroscopy and x-ray diffraction, the reactive phases and their chemical state in the implanted layer were investigated. In order to characterize the modification effect and its uniformity, the retained dose and the microhardness at seven different positions along the axis on the inner surface of the cylindrical target were measured, respectively. The experimental results show that a TiN reactive phase was formed in the implanted layer, which contributed to the improvement of inner surface microhardness. The root-mean-square deviations of retained dose and microhardness measured along the axis of the target are less than 9% and 4%, respectively, which are well within an acceptable tolerance range for metallic applications of ion implantation.

An infiltration and growth (IG) process which enables the fabrication of three-dimensional (3D) components of REBa2Cu3O7 (RE = Y, Gd, Sm, Nd, etc.) (RE-123) superconductors with a highly textured microstructure is described. The advantages of the process in comparison with conventional melt processing are discussed. The process has been demonstrated to yield highly favorable microstructures in the case Y-123 processed in air, as well as in the case of Gd-123 processed in reduced oxygen partial pressure.

The microwave sintering process not only densified the ZnO materials in a higher rate, but also resulted in significantly better varistor characteristics. Large nonlinear coefficient and low leakage current density were attained by cooling the samples under a rate of 80 °C/min after sintering, followed by 600 °C postannealing for 60 min under oxygen atmosphere. Inappropriate annealing deteriorated the varistor characteristics that can either be attributed to the insufficient reoxidation along grain boundaries when annealed in N2 (or air) or loss of Zn species in these regions when annealed at 750 °C (900 °C). By contrast, the degradation behavior of these materials can be improved by the annealing process regardless of the annealing atmosphere or temperature.

A theoretical model of the combustion synthesis process has been developed to study the ignition of a self-propagating combustion synthesis process in the Nb–C system. Compared with most of the previously published theoretical work on this subject, this model provides a much more detailed description of the combustion synthesis process from a microscale point of view, due to the fact that it takes into consideration the various microprocesses, such as the melting of reactants, the diffusion and mixing of reactants, and the formation of products. Different ignition modes, including constant-temperature ignition, constant-heat-flux ignition, and variable-temperature ignition, are considered in this work. The key parameters that influence the ignition process are also discussed.

A novel wet process to synthesize metal oxide thin films has been developed. The process is called the Liquid-Phase Deposition (LPD) method. In this method, metal oxide or hydroxide thin films are formed on the substrate through the ligand-exchanging (hydrolysis) equilibrium reaction of metal-fluoro complex species and the F− consumption reaction of a F− scavenger. The LPD method is a unique soft solution process, and is performed by very simple procedures. In this paper, we develop a method of preparing composite oxide thin films, Pt-dispersed titanium oxide, and iron-nickel binary oxide thin films.

The structural changes and magnetoresistance (MR) properties of as-grown and post-annealed La0.7Ca0.3MnO3 films were investigated by transmission electron microscopy (TEM) and x-ray diffraction (XRD). The data for the films were compared to that for bulk La0.7Ca0.3MnO3 post-annealed under the same conditions. The main structure of the as-grown films was face-centered pseudo-cubic with a doubled perovskite unit cell, of size ∼2ap × ∼2ap × 2ap, where ap is the single perovskite parameter. The phase showed a cube-on-cube epitaxy with the underlying LaAlO3 substrate. Upon annealing to a saturation point, a minor primitive pseudo-tetragonal structure evolved, of cell parameters . A total of four possible orientations of the two structures was observed by TEM, comprised of one orientation of the ∼ 2ap × ∼ 2ap × ∼ 2ap cell, i.e., the cube-on-cube epitaxy, giving rise to (00l) peaks in x-ray, and three orientations of the cell, giving rise to a single (00l)/(hk0) peak in x-ray. The bulk La0.7Ca0.3MnO3 sample also contains the × structure. The difference between the bulk and the film and the effects of annealing on films can be ascribed to the influence of strain between the film and substate, induced by lattice mismatch.

Carbon nitride crystals have been synthesized from C3N4H4 in the presence of a nickel-based alloy or cobalt as a catalyst at high pressure of 7 GPa and temperature of about 1400 °C. Scanning electron microscopy showed rod-like, well-faceted crystals with size of several micrometers, and the N content in these carbon nitride crystals was 47–62%. X-ray diffraction indicated the crystals were composed of α–C3N4 and β–C3N4. The experimental lattice constants of α–C3N4 (a = 6.425 Å, c = 4.715 Å ) and β–C3N4 (a = 6.419 Å, c = 2.425 Å ) agree with ab initio calculations very well.

The formation of η-phase by a peritectic reaction in the Cu–Sn metallic system has been cited in the literature while discussing the solidification of the high temperature superconductor Yba2Cu3O7 through the peritectic temperature, from Y2BaCuO5 and liquid phases. Similar schematic phase diagrams and driving forces have been invoked to discuss the reactions in both cases. In this paper, we have studied the microstructural evolution of the η-phase from є + liquid in the Cu–Sn system, by observing quenched microstructures at various stages of processing, when subjected to a thermal schedule similar to the one used for the melt-processing of YBa2Cu3O7. A comprehensive picture of the mechanism by which the η phase nucleates and grows has evolved.

Aluminosilicate sodalite Na8[SiAlO4]6Cl2 single crystals are synthesized by hydrothermal processing at 873–973 K and 100–150 MPa in noble metal capsules to avoid contamination. The starting material is aluminosilicate gel, and spontaneous nucleation followed by its growth takes place. The largest size of the single crystals obtained is 1 mm across. Longer aging and heating result in larger single crystals. It is also found that the aluminum source in the synthesis gel and the element used in the noble metal capsules influence the single crystal growth. Judging from x-ray diffraction (XRD) (powder and single-crystal), optical microscopy, and thermogravimetry and differential thermal analysis (TG-DTA), the sodalite single crystals grown have good quality compared with the conventional powder.

The structure, morphology, and mechanical properties of sol-gel zirconia films have been examined using XRD, AES depth profiling, AFM, and ultramicro indentation. There is a systematic variation in the structure and morphology of the zirconia films with increasing thickness. These changes include increases in the amount of monoclinic phase, substrate oxides, and a decrease in grain size. Ultramicro indentation measurements indicate measured hardness increases with film thickness. The highest hardness value was 6.12 GPa for a 900 nm thick film. However, these values may be influenced by the substrate oxide layer at the film/substrate interface which increases with film thickness. The modulus of the films appears to be thickness independent. As the films are made up of a number of separately fired layers, it appears that the property changes observed are also related to the number of thermal cycles experienced by the sample.

Using the hydrolysis of appropriate alkoxide mixtures in water-in-oil microemulsions, nanocrystalline BaTiO3 has been prepared in the form of nonaggregated, cube-shaped crystals at room temperature without any sintering process as is demonstrated by means of x-ray diffractograms and transmission electron micrographs. By variation of the length of the hydrophilic part of the surfactant molecules, the diameter of the water droplets in the microemulsions could be tuned to values between 8 and 55 nm as determined by dynamic light scattering. The size of the resulting nano-BaTiO3 (6 nm ≤ 〈d〉vol ≤ 17 nm) was evaluated from the line broadening of x-ray reflections and correlates to the droplet size. The particle size distribution is very narrow, and in some cases nearly monodisperse.

Lead zirconate titanate (PZT) powder is prepared by the sol-gel method. The formation of pyrochlore and perovskite phases is investigated by high temperature x-ray diffraction (XRD) and thermal analysis techniques. The pyrochlore phase first appears in x-ray amorphous form, and then gets converted to crystalline state on annealing in air. We show that vacuum annealing of the pyrolyzed amorphous PZT gel suppresses the formation of the crystalline pyrochlore phase. This, in turn, enhances the kinetics of conversion of pyrochlore to perovskite, such that a pyrochlore-free perovskite phase can be obtained by annealing at about 500 °C. On the other hand, if annealing is carried out in air, a crystalline pyrochlore phase is formed, which requires annealing temperatures higher than 600 °C for transformation to the perovskite phase. These observations are explained tentatively in terms of the oxygen stoichiometry of the two phases.

Formation of nanocrystalline Al3Ti, TiAl, Ti3Al, and Ti5Si3 composites by mechanically alloying (MA) in the Ti–Al–Si system and subsequent annealing treatment are investigated. Microstructure development was monitored by x-ray diffraction, differential thermal analysis, and transmission electron microscopy. An amorphous phase could be generated through milling for 100 h. The results of annealing at different temperatures on this amorphous phase show that the formation of titanium aluminides (Al3Ti, TiAl, and Ti3Al, according to the initial relative amount of Ti and Al) and Ti5Si3 (the only silicide produced by the crystallization reaction) take place. Annealing produces nanocrystalline composites of Al3Ti, TiAl, Ti3Al, and Ti5Si3 with a grain size less than 20 nm. With increasing annealing temperature, the crystalline sizes of the phases increased.

The absorption length for photon propagation in highly concentrated colloidal dispersions calculated from temporal intensity profiles of 100 femto-second pulses is much longer than the absorption length obtained from the measurements of static light transmission in the pure continuous phase fluid. The difference between these two values is explained on the basis of small interparticle spacing at high particle concentration and hence shorter paths traveled by photons through the absorbing medium relative to the total diffusive path in the dispersion. The two values are in good agreement when the absorption length is rescaled with the interparticle separation.

Thin films of nanostructured silicon (ns-Si:H) were deposited by plasma-enhanced chemical vapor deposition in the presence of silicon nanoparticles at 100 °C substrate temperature using a silane and hydrogen gas mixture under continuous wave (cw) plasma conditions. The nanostructure of the films has been demonstrated by diverse ways: transmission electron microscopy, Raman spectroscopy, and x-ray diffraction, which have shown the presence of ordered silicon clusters (1–2 nm) embedded in an amorphous silicon matrix. Because of the presence of these ordered domains, the films crystallize faster than standard hydrogenated amorphous silicon samples, as evidenced by electrical measurements during the thermal annealing.

A nonfluorinated β-diketonate precursor, bis(t-butylacetoacetato)Cu(II) or Cu(tbaoac)2, was synthesized by modifying bis(dipivaloylmethanato)Cu(II) or Cu(dpm)2 for chemical vapor deposition (CVD) of copper. The complex was characterized by a variety of techniques, such as melting point determination, mass spectrometry, infraredspectroscopy, elemental analysis, thermogravimetric and differential thermal analysis, and x-ray diffraction. Cu(tbaoac)2 has a higher sublimation rate than Cu(dpm)2 over the temperature range 90–150 °C. Pyrolysis of Cu(tbaoac)2 leads to the formation of copper films at 225 °C, compared to 330 °C for Cu(dpm)2. As-deposited copper films ere highly dense, mirror-bright, adhered strongly to SiO2, and showed a resistivity of less than 2.9 μΩ-cm at a thickness as low as 1300 Å. A possible mechanism for the decomposition of the ligand tbaoac has been proposed.

Surface reoxidized-type barrier layer (BL) capacitors were prepared by hot-pressing BaTiO3/SiC powder mixture in argon atmosphere and subsequently oxidizing the semiconducting BaTiO3-based composites with fine SiC particles. Dielectric properties, such as apparent relative dielectric constant, dielectric loss tangent, and Curie temperature, were investigated as a function of SiC content and oxidation procedures. Incorporating SiC particles into BaTiO3 matrix, a thin surface insulating layer was formed, which becomes thinner by increasing the SiC content. BL capacitors showing a higher capacitance than 3 × 102 nF/cm2 could be successfully fabricated. The results were discussed on the basis of high resolution transmission electron microscope (HRTEM) studies. Thin oxidized layer and the resulting high capacitance were associated with the depression of oxygen diffusion due to the presence of intergranular SiC particles. The thickness of the surface layer and some dielectric properties could be controlled by the SiC content as well as oxidation temperature and time.

A micromechanistic model of the combustion synthesis has been extended to study the detailed mechanism and influential parameters of a combustion synthesis process, as well as the development of ignition criteria in the Nb–C system. The case of constant heat-flux ignition conditions has been used to illustrate the details of the ignition process, in order to elucidate the various physical and chemical processes that take place during the initial stages of the combustion synthesis process; however, the results of this study can be generally extended to the other modes of the ignition process. The results showed that the ignition criteria for the Nb–C system corresponded to the establishment of a proper balance between the rates of enthalpy redistribution within the sample, and to the establishment of a kind of positive feedback loop during the ignition process that is necessary for self-propagation to occur. If the heat supplied from an external source to initiate the combustion synthesis process is less than a certain critical value, the combustion wave stops at a certain short distance from the ignition surface. Otherwise, the reaction proceeds in a self-propagating manner.

The kinetics of phase transitions and phase segregation induced by annealing temperature on the Ti–W–O gas-sensing layer was studied by x-ray diffraction, Raman spectroscopy, and scanning electron microscopy. The main goal was to identify, on the basis of kinetics studies, structurally stable Ti–WO3 thin film phases and compare their response to polluting gases in order to determine possible correlations between structural and electrical properties of the sensing layers.