Activated carbons were used to selectively remove NOx from simulated flue gas at temperatures between 25 and 125 °C. Processing conditions and physical/chemical characteristics of the carbons which affected NOx adsorption, storage, and release were investigated. Oxygen as a coreactant was necessary to maximize the conversion of NO to NO2 and condensation of NO2 within the pores of the carbons. A NO-to-NO2 conversion mechanism is presented and discussed relative to previous research. A process for selectively removing NOx and concentrating it as NO2 in an alternate process stream is outlined. The purified NO2 stream could be used for chemicals manufacturing.

The evolution of microstructure in a cast, extruded, and aged eutectoid Zn-Al-Cu alloy is described based on x-ray diffraction an micrographic observations. Whereas the three phases α′, β′, and η′ were found in the as-cast state, the three phases α, T′, and η′E were observed in this alloy after extrusion at 250 °C. The Al-rich fcc α phase appeared as isolated particles with clear boundaries. The Zn-rich η′E phase decomposed upon aging into α, T′, and η phases. It was found possible to control the phase makeup of the alloy by controlling extrusion temperature. At extrusion temperatures greater than 268 °C, α, E, and η′E were detected, whereas temperatures below this, the phases α, T′, and η′E were found. After prolonged aging, the phase makeup of the alloy was found to be the same regardless of prior treatment routes. Early shrinkage of the extruded alloy occurred after aging at 91 and 150 °C and was related to precipitation of aluminum from the η′E phase during its decomposition to α, T′, and η products.

BaZrO3 films were grown on zirconium metal substrates by immersing thin Zr foils in an alkaline solution under hydrothermal conditions. The films were produced at temperatures ranging from 200 °C to 270 °C in a 0.25 M barium hydroxide solution for 3 to 8 h. The resulting films did not have visible pores or defects, and displayed a grain structure which depended on the treatment conditions, especially temperature. X-ray photoelectron and Auger spectroscopies revealed that (a) after removing the surface layer, films were clean, not displaying OH groups nor carbon contamination; (b) the Ba concentration steadily decreased as the depth increased, and did not behave as in BaTiO3 or SrTiO3 films prepared under similar conditions; and (c) the BaZrO3/Zr interface was very broad. Grazing angle x-ray diffraction analysis showed BaZrO3 (cubic), ZrO2 (hexagonal), and Zr (hexagonal), suggesting a layered structure: BaZrO3/ZrO2/Zr. The relative dielectric constant was ≍70 and was independent of the frequency between 100 Hz and 1 MHz. The dielectric loss factor (tan δ) was between 0.01 and 0.02. Dielectric breakdown occurred between 25 and 40 MVm−1.

A novel and easy route for preparing submicrometer particles of zinc oxide, involving hydrolysis of zinc salt in a polyol medium, is proposed. Zinc acetate dihydrate and diethyleneglycol appear to be the best candidates for obtaining a high yield of particles with well-defined morphological characteristics. Monodisperse spherical particles in the submicrometer range (0.2−0.4 μm) have been obtained for a salt concentration less than 0.1 mol 1−1. The particle size depends mainly on the heating rate. The particles are microporous (surface area: 80 m2 g−1) and are formed by aggregation of small crystallites (10 nm). Calcination at moderate temperature drastically reduces this porosity without significant interparticle sintering. At higher concentration, no aggregation occurs and tiny single crystallite particles are obtained.

Solute-atom segregation is studied by Monte Carlo simulations for three high-angle symmetrical (002) twist boundaries in Au-1 at. % Pt and Pt-1 at. % Au alloys at T = 850 K. It complements our previous study, that focused mainly on low-angle boundaries in the same alloys. Solute enhancement occurs on the Pt-rich side of the phase diagram, while on the Au-rich side net depletion in solute is observed. Following the trend observed for low-angle boundaries, Au as a solute prefers the structural units of the perfect crystal type, while Pt as a solute is depleted at those sites. The solutc concentration at structural units depends on the planar fraction of those units in the boundary.

Spray pyrolysis was used to produce submicron Ag-Pd metal alloy particles for applications in electronic component fabrication. The particles were prepared in nitrogen carrier gas from metal nitrate precursor solutions with various compositions. The Ag-Pd alloy was the predominant phase for reactor temperatures of 700 °C and above for all compositions. The 70-30 Ag-Pd partcles were fully dense at 700 °C, but an increased reaction temperature was necessary to produce dense particles at higher Pd to Ag ratios. The extent of palladium oxidation was suppressed with increased amounts of Ag. Single-crystal particles could be produced at sufficiently high temperatures. These results show that particle phase composition, size, oxidation behavior, and morphology can be controlled by the Ag-Pd ratio in the precursor solution and by the reaction temperature.

Optical properties of semi-insulating polycrystalline silicon (SIPOS) thin films containing 30 at. % oxygen atoms are investigated in the near ultraviolet, visible and infrared region to improve knowledge on the structure and chemical bonding of these mixtures. An effective medium approximation model is used for a microscopic investigation of the oxide species involved as a function of the annealing temperature (600–1200 °C). The results are compared with other optical spectroscopies (infrared and Raman) and with transmission electron microscopy to give a selected picture of the pure and oxide components.

Hollow ceramic microspheres of Al2O3, SiO2, and mullite have been prepared by the combination of an emulsion technique with a water extraction sol-gel method. Concentration of sol, initial droplet size, and water extraction rate of the system are found to be the important process parameters controlling the size and wall thickness of the hollow microspheres, and their influences are shown. A model that correlates the morphology of microspheres to concentration and water extraction rate is proposed and is in good agreement with the experimental observations. The capability and limitation of this process for forming hollow microspheres are demonstrated. It was shown that hollow microspheres with sizes greater than 5 μm could be readily prepared, while a limitation was met for sizes less than 1 μm, in which case solid microspheres were normally formed.

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.

Dielectric properties of polycrystalline BaTiO3 ceramics having grain sizes of 1 to 40 μm have been studied. Fine-grained ceramic BaTiO3 of 1 μm average grain size has 90°domains and has shown higher dielectric constant, lower ferroelectric transition temperature (Tc), and lower transition energy than coarser-grained material. 90°domain switching was preferentially produced in the fine-grained BaTiO3 as a result of abrasion. For the fine-grained BaTiO3, the dielectric constant decreased with one-dimensional pressure, whereas, for the coarse-grained material, the dielectric constant increased before decreasing with the pressure. The one-dimensional pressure resulted in increased Tc of both the fine- and coarse-grained BaTiO3, with the effect being the greatest for the coarse-grained material. The relationship between these results and internal stress, and the effect of external pressure imposed on internally stressed lattice, were discussed.

A high Tc ceramic superconductor has been prepared having a high degree of preferred orientation, this having been generated by means of a large magnetic field during the early stages of processing. The texture of the material has been characterized using XRD textural analysis and the microstructure by high resolution electron microscopy. Pyramidal indentation (Vickers indent), deformation, and cracking have been investigated using high resolution SEM. Semispherical deformation zones were formed under indents, a result of slipping of adjacent ab/ab (basal) plane grain boundaries and some microcrack development, together with lattice deformation on the basal plane. Densification of the green compact was also observed in the deformation zones, where lateral cracking has been seen to take place along the ab/ab plane grain boundaries. Radial cracking has been seen to take place along the low angle grain boundaries of the lattice ab/ab plane when indentations were made on the surface perpendicular to the preferred texture surface of the materials and also at the highly deformed corners of indent diagonals. The stresses generated resulted in the fracture of the flake-shaped grains and initiated small radial cracks. The Vickers microhardness of the textured ceramics was found to decrease with increasing load.

Systematic studies have been carried out about the effects of the thermal treatment parameters on melt-spun materials quenched at different cooling rates and based on the 2:14:1 hard magnetic phase. Samples of nominal compositions Dy3Nd10.2Fe79.6B6Si1.2 and Pr3Nd10.2Fe79.6B6Si1.2 were annealed at temperatures above that of crystallization of the amorphous phases present upon quenching, for times ranging from 1 to 30 min and by using different heating rates up to the annealing temperature. It is concluded that best hysteretic properties can be achieved in samples quenched at intermediate cooling rates by means of short-time thermal treatments performed by using high heating rates up to the treatment temperature. Low heating rates and long time anneals led to the deterioration of the hard magnetic behavior, due to the segregation of soft crystalline phases.

Melt processing of YBa2Cu3Ox (Y-123) with a NdBa2Cu3Ox-123 single-crystal seed has been used to grow large single-grain Y-123 samples. Processing parameters have been varied to observe the resulting differences in the levitation force of the samples. Increased hold time above the peritectic temperature and increased undercooling temperature have been observed to be beneficial in enhancing the levitation force of the samples. The levitation force measurements have been correlated with magnetization measurements on the crushed domains.

The microstructure and the high-temperature deformation behavior of the C15 NbCr2 intermetallics alloyed with V, which consist of both the C15 monophase and the duplex structure with the bcc solid solution, are observed by some microscopic techniques and compression tests. The alloys consisting of the C15 monophase microstructure show moderately higher 0.2% yield stress than the unalloyed NbCr2, and the same BDTT as that in the unalloyed NbCr2, indicating a moderate improvement of the high temperature deformability. This result is attributed to the larger atomic free volumes between the atomic stacking layers along the {111} planes than those of the unalloyed NbCr2. The alloys consisting of the duplex microstructure show lower 0.2% yield stress and considerably decreased BDTT than the unalloyed NbCr2. The considerable deformation improvement in this group of alloys is attributed to the existence of the ductile bcc solid solution.

The formation mechanism and ferroelectric properties of Pb(Li1/4Fe1/4W1/2)O3 prepared by solid-state reaction have been investigated in this study. The formation processes of Pb(Li1/4Fe1/4W1/2)O3 are characterized to be an initial reaction of lead tungstates PbWO4 and Pb2WO5 at a low temperature range, followed by a subsequent reaction to produce Pb(Li1/4Fe1/4W1/2)O3 from above 650 °C. Through a two-stage calcination (700 °C/quenching-regrinding-710 °C/8 h), a nearly single phase of Pb(Li1/4Fe1/4W1/2)O3 is obtained. This compound exhibits a cubic perovskite structure (α = 8.0113 Å) with a partial ordering arrangement of B-site cations. Above 720 °C, becomes Pb(Li1/4Fe1/4W1/2)O3 thermodynamically unstable and gradually decomposes in forming elongated Pb2WO5 grains, thereby resulting in a nonhomogeneous microstructure. As the ac frequency increases, the maximum dielectric permittivity of Pb(Li1/4Fe1/4W1/2)O3 significantly decreases; in addition, the corresponding temperature increases. The strong frequency dependence of dielectric properties, as well as the critical exponent and diffuseness evaluated through a modified permittivity-temperature equation proposed in this study, verify the relaxor characteristics of Pb(Li1/4Fe1/4W1/2)O3

Iron/alumina multilayers have been deposited on sapphire wafers using RF magnetron sputtering. To study the interdiffusion, the multilayers were annealed in a tubular furnace under a 10−7 mbar vacuum, and the samples examined by using a combination of classical diffractometry (θ/2θ) and Grazing Incidence Scattering (GIS) for the phase determination, and Small Angle X-ray Scattering (SAXS) for the superstructure of the multilayers. In all cases, in the as-deposited state the alumina is amorphous and the iron is crystalline in the bcc phase. Thermal anneals at temperatures between 573 and 873 K give evidence for segregation to the interfaces. At higher temperatures, interdiffusion occurs, leading to the formation of different phases. The Fe-Al2O3 interdiffusion coefficient has been evaluated in the temperature range from 873 to 1273 K.

The effect of the nickel (Ni) and aluminum (Al) reactant particle size on the micropyretic synthesis of NiAl is studied in this article. A change in the low melting component (Al particle) size is noted to have a limited influence on the micropyretic synthesis conditions. However, a change in the high melting component (Ni particle) size not only influences the combustion temperature and propagation velocity, but also affects the final porosity and grain size of the synthesized products. The combustion mode is also noted to change from stable to unstable when the Ni particle size is increased. It is noted that a diffusion-type control mechanism is dominant for the rapid reaction sequence in the NiAl system. An atomistic mechanism of the Ni-Al micropyretic reaction is also proposed in this article. Following this model, analytical expressions are developed to relatc the variation of the Ni size to the NiAl formation rate with the imposed processing conditions during the micropyretic synthesis. The mechanism of the final grain formation and the grain size changes with changes in the processing variables is also discussed.

Alumina films were fabricated by the sol-gel route under various preparation conditions. The peptization rate and the structure of colloidal particles depend on these conditions. In particular, the peptization of a dried boehmite precipitate prepared from aluminum alkoxide was achieved within a few seconds without heating. The resulting sol is made of highly dispersed crystallites; this allows the formation of well-textured xerogel films as evidenced by the Weissenberg x-ray method.

Novel thin films of ultrafine titanium dioxide particles dispersed in a matrix of hydroxypropylcellulose (HPC) polymer have been made on quartz and silicon substrates. The titanium dioxide particles were made by the hydrolysis and condensation of titanium tetraethoxide (TEOT) in solutions of HPC in a mixture of ethanol and water. HPC controlled the particle size by adsorbing at the particle surface during the growth process and generating repulsive steric forces. The TiO2/HPC composite films were transparent in the visible region and completely blocked ultraviolet radiation at 300 nm. These films were crack-free and uniform in composition and thickness. Transparent films of amorphous TiO2 were made by burning out the HPC at 500 °C. These films were highly uniform and had no macroscopic cracks. X-ray diffraction revealed a transition to the anatase form upon sintering at 600 °C. A film sintered at 700 °C had a porosity of 38%. The crystalline films remained transparent until they densified at 800 °C.

Silicon nitride is a candidate valve material for internal combustion engines. Its low density and attractive mechanical properties relative to conventional metallic alloys portend significant improvements in valve performance. The production of valves involves a significant amount of machining, especially grinding. Grinding of ceramic materials may result in surface and subsurface damage in the form of fracture or residual stresses which may affect impact behavior and, consequently, the behavior of silicon nitride ceramic materials as valves. The effects of residual stresses due to grinding on the impact wear behavior of one silicon nitride composition ground under various conditions have been investigated.