Molten salt electrolysis is a proven technology for the extraction of metals—all the world's primary aluminum is produced in this manner. The unique properties of molten salts also make them excellent media in which to treat a variety of forms of waste. Of special note in this regard is electrolysis in molten oxides, a concept put forward by the author, initially as a “clean technology” for producing primary metal. However, in the context of waste treatment, elcctrolysis in molten oxides is a process offering the prospect of changing the valence of dissolved heavy metals while making pure oxygen gas as the main by-product. Laboratory tests conducted at a temperature of 1550 °C on chromate sludge dissolved in melt composed of Al2O3, SiO2, CaO, and MgO have confirmed electrochemical production of oxygen on a carbon-free anode.

The deposition of thin films and coatings frequently results in the generation of toxic waste, volatile organic compounds, or large amounts of waste water and sludge. Vapor deposition in vacuum offers a more environmentally benign alternative, but is not prevalent outside of the microelectronics industry due to economic reasons. However, vacuum coating could be more widely accepted, and could potentially replace nonvacuum deposition methods, if either the cycle time or costs associated with vacuum coating were reduced. In order to reduce the cycle time for vacuum deposition, a robust system for continuous air-to-vacuum-to-air (AVA) transportation of discreet substrates has been developed and constructed in this study. This technology allows the insertion of discrete components into vacuum at high rates, without the need for venting the deposition chamber. Substrates have been repeatedly transported from atmosphere to 10−5 Torr in under a second. The capability of the AVA technology was studied through the deposition and characterization of CdS and CdTe films and photovoltaic devices. With the AVA technology, the need for venting the vacuum chamber to insert the substrates and subsequent pumping of the system for deposition is eliminated. The AVA technology could be applied to the processing of silicon wafers, compact disks, optical components, solar cells, cutting tools, and fasteners.

The Pb-based solder used in microelectronics industry is becoming an environmental issue. To understand the wetting behavior of solders with and without Pb, we have studied the surface morphology and wetting reaction of eutectic SnBi, eutectic SnPb, and pure Sn on Cu through the measurements of wetting angle change and wetting tip stability by SEM and EDX. The wetting angle remains constant after the initial spread, but the eutectic SnPb/Cu continues to react and forms a reaction band in front of the solder edge as well as intermetallic compounds at the interface. For eutectic SnBi/Cu, there is no reaction at the wetting tip, and the wetting angle does not change much; however, the interfacial reaction between eutectic SnBi and Cu forms intermetallic compounds at the solder joint; the wetting tip is not in a static equilibrium. A rough surface and edge was observed on the eutectic SnBi/Cu joint, but the eutectic SnPb/Cu has a smoother surface and edge.

This paper describes a novel technology for a mercury-free metallic direct filling material, a substitute to dental amalgams. The consolidation relies both on cold-welding that takes place under moderate pressure between suitably surface-treated silver particles and on silver-tin intermetallic compound formation at ambient temperature. A dilute acid is used for removing the silver surface oxide layers, thereby promoting the cold-welding process. The condensability, namely the ability of a loose powder to undergo consolidation within a short time duration, at body temperature and under moderate pressure has been investigated for a variety of mixtures of silver, tin, and prealloyed silver-coated intermetallic powders. The resulting metallic composite material displays transverse rupture strength values higher than those of amalgams and somewhat lower values of compressive strength and Knoop hardness.

Aluminum nitride (AlN) powders were produced in an aerosol flow reactor by direct nitridation of aluminum vapor with ammonia and nitrogen in flowing argon. In the presence of excess NH3, pure AlN powders were obtained from 1400 to 1873 K. These powders had higher specific surface areas than commercially available AlN powders. The effects of reactor temperature and gas flow rate on AlN purity, yield, and grain and crystallite size were investigated. The BET grain diameter of AlN increased as the process temperature increased, indicating sintering controlled particle formation and growth. Both the crystallite size and the BET grain size of pure AlN powders slightly decreased as ammonia flow rate was increased. Increasing temperature and flow rate increased the AlN yield.

Hydroxyapatite whiskers have been prepared by the hydrothermal method. The crystals had diameter, length, and aspect ratio in the range of 1–10 μm, 30–50 μm, and 5–20, respectively. Their Ca/P molar ratio varied from 1.59 to 1.62. The morphology of the crystals can easily be controlled by the concentrations of species in the starting solution, while the Ca/P ratio is almost independent of them. Through the reaction with calcite powder at 600 °C, the Ca/P ratio of the whiskers has been improved even to the stoichiometric value of 1.67. Taking into account morphology and chemical composition of the HAp whiskers, they should not be health hazardous and may find applications as substitutes for asbestos and other fibrous materials which presently have restricted use because of their carcinogenic natures.

Carbon dioxide is an attractive organic solvent in today's chemical process environment, in that it is nonflammable, inexpensive, and exhibits low toxicity. Further, materials solubilized in carbon dioxide are easily and completely recovered/concentrated from solution via a simple pressure quench. Despite these favorable properties, CO2 is nonpolar and therefore is a very poor solvent for materials such as conventional metal chelating agents, thus blocking application of carbon dioxide in metal extraction/recovery. Consequently, we are exploring the molecular design of materials which are highly CO2 phillic, that is, they exhibit solubilities in carbon dioxide which are significantly greater than alkanes with the same number of main-chain atoms. By functionalizing chelating moieties with CO2-phillic oligomers, we have generated materials that both effectively extract metals from solid matrices and that dissolve in carbon dioxide in significant quantities. The application of such chelating agents is not limited to soil cleaning operations. In fact, these chelates make the use of CO2 possible in many applications where precision cleanup/recovery of metal ions are required. For example, CO2 has been promoted as a replacement for CFC's in cleaning processes in the electronics industry. Use of these chelates would allow the removal of metals, along with other impurities in a CO2 cleanup procedure.

The refining of lead blast furnace bullion involves the transfer and handling of hot impure lead bullion. Fugitive emissions of lead-containing fumes create a plant hygiene problem. The cause of the emissions is the high vapor pressure of lead and its compounds when lead blast furnace bullion is transferred in an open ladle at ∼1000 °C from the blast furnace and poured into the drossing kettle, and later during the manual skimming of powdery dross. A laboratory study was conducted on a new concept for lead refining that eliminates contact between hot lead and the cnvironment, and thus abates fugitive lead emissions. The new process takes place in two steps: controlled solidification of bullion as it flows from the blast furnace, followed by remelting in a closed centrifuge to separate lead and dross. Refined lead was produced with <0.05% copper and <0.01% of all other impurities. Suggestions are outlined for implementing the process.

Monoclinic ZrO2 and its supported materials Co/Ni/ZrO2 (Co:Ni = 1:1) for catalytic decomposition of N2O have been studied with GC, FTIR, EDAX, XPS, and the evaluation of catalytic activity of the materials. It is found that monoclinic ZrO2 alone has the catalytic effect for N2O decomposition, although higher activities are found for Co/Ni/ZrO2 systems. XPS study shows that only Co exists in the surface region of ZrO2, which is attributed to the formation of NiO–ZrO2 solid solution resulting from an interdiffusion between Ni2+ and ZrO2 matrix. The gas decomposition on Co/Ni/ZrO2 can be described as first order with respect to partial pressure of N2O. Surface reactions on ZrO2 and Co/Ni/ZrO2 will also be addressed.

Some aspects of the industrial development of copper-on-alumina catalytic materials for the combined removal of SO2 (DeSOx and NOx (DeNOx) from flue gas of power plants are discussed. Applications of these catalytic materials for the recovery of sulfuric acid from diluted aqueous solutions of ammonium sulfate are also outlined. In particular, the following specific topics are analyzed: (i) the relationship between textural and reactivity properties. (ii) the problem of the design of samples with improved DeSOx properties in relation to the stability of the samples over extended operations, and (iii) the optimization of the regeneration characteristics of the samples. Details on the flow sheet of the technology are also given.

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.

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.

The influence of single solute atoms and solute clusters on an extended edge dislocation dipole in Al was studied by atomistic simulation. Single Cu and Ag solute/dislocation interaction energy calculations showed that Cu interacts strongly with an Al extended dislocation and prefers sites in the compressive region, in agreement with elasticity theory predictions. Single Ag atoms, however, are strongly repelled by an Al extended dislocation, in contrast with elasticity theory predictions. Monte Carlo simulations of Al: 1% Cu, Al: 2% Cu, Al: 1% Ag, Al: 0.5% Cu, 0.5% Ag, and Al: 0.75% Cu, 0.25% Ag were carried out in the presence of an extended dislocation dipole at 600 K allowing for solute segregation. Cu atoms in the binary alloys were observed to segregate to the compressive regions of the extended dislocation dipole, forming widespread “atmospheres” over the width of both extended dislocations which did not affect the partial dislocation spacing. Ag in the binary alloy formed small Ag zones which also had little influence on the spacing between the partials. The ternary systems, however, exhibited highly localized solute clusters that had a large impact on the extended dislocation dipole structure, increasing the separation between the partial dislocations. The resulting cluster structures are discussed along with their influence on the apparent stacking fault energy of the alloy systems.

The thermodynamic parameters that drive the atomic migration in B2 alloys are studied using Monte-Carlo simulations. The model is based on a vacancy jump mechanism between nearest neighbor sites, with a constant vacancy concentration. The ordering energy is described through an Ising Hamiltonian with interaction potentials between first and second nearest neighbors. Different migration barriers are introduced fur A and B atoms. The results of the simulations compare very well with those of experiments. The ordering kinetics are well described by exponential-like behaviors with two relaxation times whose temperature dependences are Arrhenius laws yielding effective migration energies. The ordering energy contributes significantly to the total migration energy.

By comparing the ultrasonic cavitation in several kinds of transparent liquid mediums, we have investigated the cavitation effect in liquid. It is considered that the shock wave created by the cavitation in aluminum melt induces a high pressure and an elevated temperature field around the fibers, which can promote the wetting between fiber and aluminum and have aluminum melt infiltrate into the fibers. Moreover, the experiment result shows that the fiber resonance matching with the cavitation is also an important factor for SiC/Al composites preparation. There exists a damage of the ultrasonic vibration on SiC fiber, if the fiber is acted long enough.

Additions of O to 9 mol % Ta2O5 to a lithia-alumina-silica glass-ceramic matrix Nicalon SiC-reinforced composite increased the elastic modulus and ultimate strength of the composite. The additive fostered sphereulitic growth of β-eucriptite solid solution crystals which concentrated Ta2O5 at sphereulite boundaries and adjacent to the fiber-matrix carbon-rich interphases. These regions reacted with the interphases as well as soluble carbon monoxide gas to convert them to TaC. The former reaction was shown to be thermodynamically favorable above 983 °C, while the latter was favorable above 1249 °C. The improvement in mechanical properties was attributed to TaC particulate reinforcement, and suggests a simple glass-ceramic route to the fabrication of particulate-reinforced ceramic matrix composites.

Measurements of fiber strength utilization (FSU) in unidirectional carbon/carbon (C/C) composites as a function of heat-treatment tempcrature (HTT) have been extended beyond the original group of DuPont pitch-based E-series fibers to include additional pitch- and PAN-based fibers. Fibers and composites were characterized by tensile strength, optical microscopy, SEM, fiber preferred orientation, and a single-fiber composite (SFC) fragmentation test to provide a relative measure of fiber-matrix interfacial shear strength (IFSS). Results show that fracture behavior and FSU are dominated by the degree of fiber-matrix bonding, as inferred from microscopic observations and measurements of IFSS. In the very high modulus pitch-based fibers, the behavior of the F,130 is strikingly different from that of the Amoco and Nippon Oil fibers, in that it retains good bond strength and high FSU even with HT to 2400 °C, in contrast to the other very high modulus pitch-based fibers that are already weakly bonded at the lowest HTT of 1100 °C. All PAN-based fibers and lower modulus pitch fibers are characterized by strong bonding, brittle fracture, and low FSU for the 1100 °C HTT. Subsequent heat treatment of these composites to 2150 and 2400 °C, in most cases, results in significant recovery of FSU, suggesting an optimum IFSS for each composite. It is suggested that the difference in bonding between the pitch-based E-series and P-series may be related to the similarity in fine structure between the E-fibers and high-modulus PAN-based fibers.

The surface of commercial pitch and PAN-based carbon fibers has been modified by coating the structures with catalytically formed carbon nanofibers. Reaction conditions have been established that enable one to achieve optimum coverage by the secondary nanostructures without inducing any degradation in the mechanical properties of the parent fibers. Using this approach it is possible to produce a dramatic increase in the surface area of the fibrous structure from a nominal value of about 1.0 m2/g (untreated condition) up to between 250 and 300 m2/g (complete nanofiber coverage). This process results in a significant enhancement in the adhesion properties at the interface between the fiber and matrix components in a composite material. Mechanical tests performed on single uncoated and coated T300 carbon fibers demonstrated that it was possible to obtain an improvement of over 4.75 times in the interfacial shear strength of the fibers following deposition of a critical amount of nanofibers.

Recently it was observed through cross-sectional TEM that the preferred orientation of the TiN thin film was changed from (200) to (111) with thickness. In this study, the process of the change in the preferred orientation was studied near the critical thickness by x-ray diffraction, and the value of the critical thickness could be estimated. The change of the critical thickness was also investigated with the strain energy per unit volume. The strain energy could be changed by controlling the energy of the bombarding particle, i.e., by adjusting the rf power, the working pressure, and the substrate bias in sputtering. The critical thickness was decreased monotonically in all cases as the energy of the bombarding particle or the strain energy per unit volume was increased. These results surely show the dependence of the change of the preferred orientation on the strain energy in the TiN thin films.