A novel metal oxide composite catalyst for the complete oxidation of carbon monoxide and hydrocarbons was prepared by combining oxygen ion conducting materials with active transition metals. The oxygen ion conductors used were typical fluorite-type oxides, such as ceria, zirconia, and others. Active base metal catalysts, such as copper, were used as additives to promote the catalytic properties of oxygen ion conductors. The intimate contact of the two kinds of materials gave rise to a highly active oxidation catalyst. On Cu-Ce-O composite catalysts, 95% of carbon monoxide was oxidized by air at ∼100 °C. Complete methane oxidation on the same catalyst took place at ∼550 °C. When the stoichiometric amount of sulfur dioxide was used to oxidize carbon monoxide, 96% of sulfur dioxide was reduced to elemental sulfur at temperatures above 460 °C with 99% of sulfur dioxide conversion. This type of composite catalyst also showed excellent resistance to water poisoning.

An endothermic chemical system composed of pulverized iron-based oxide and carbon powder has been investigated by using the temperature swing method (TSM) at 700 to 800 °C. Ferrite of Mn and Zn, and magnetite were studied. The last material showed the most promising result. In the TSM, magnetite as the working material was reduced to wustite and carbon was concurrently oxidized to CO in a flow of N2 gas at 800 °C (the activation step of the metal oxide). In the reverse process, in a flow of CO2, the wustite was oxidized to magnetite and injected CO2 was reduced to CO at 700 °C (the reduction step of CO2 to CO). Following the reduction step, the chemical composition of the magnetite phase was restored to that existing prior to the activation step. The total amount of oxygen donated to carbon during the activation step was the same as that taken from the magnetite during the reduction step. In this system, the following net reaction can be realized at temperatures of 700 to 800 °C: C + CO2 → 2CO. The process will therefore serve for the utilization of coal and other carbonaceous compounds in much lower temperatures than are employed in the traditional water gas and producer gas reactions.

Oxygen-deficient Zn(II)-bearing ferrites (ZnxFe3-xO4-δ, 0≤×≤l, δ>0) have been synthesized and studied for their reactivity in the decomposition of CO2 to carbon at 300 °C. They were prepared by reducing Zn(II)-bearing ferrites with H2 gas at 300 °C. The oxygen-deficient Zn(II)-bearing ferrites consisted of a single phase of a spinel-type structure which was oxygendeficient compared with their stoichiometric compositions. Their lattice constants were larger than those of the corresponding stoichiometric spinels. Decomposition of CO2 to carbon proceeded accompanied by an oxidation of the oxygen-deficient Zn(II)-bearing ferrite. The amount of carbon deposited on the ferrite decreased when Zn content in Zn(II)-bearing ferrite increased. The decrease in the amount of carbon deposited is due to changes in the electron conductivity according to the Zn content in Zn(II)-bearing ferrite. These changes contribute to their reactivity for decomposition of CO2 to carbon.

The methanation of CO2 has been studied by using reduced Ni(II)-bearing ferrite (NixFe3-xO4-δ; x=0.39, δ=0.1∼0.2) in an H2/CO2 mixed gas flow system. A yield of 31% and a high selectivity of 89% were obtained in the methanation for 6h using the H2-reduced Ni(II)-bearing ferrite. The X-ray diffractometry showed that the reduced Ni(II)-bearing ferrite during the methanation retained the spinel-type structure whose lattice constant increased from 0.8375 to 0.8379 nm. The chemical analysis corroborated an increase in the mole ratio of Fe2+/Fetotal in the Ni(II)-bearing ferrite. These results suggest that oxygen-deficient sites were formed in the spinel structure of the reduced Ni(II)-bearing ferrite. It has been found from the analysis using the Langmuir isotherm for dissociative adsorption that CO2 is adsorbed onto oxygen-deficient sites to be decomposed to an elemental carbon and two oxygen-deficient ions. The methanation of CO2 is considered to proceed owing to the oxygen deficient sites. It is considered that the methanation consists of three elementary reaction steps: 1) Formation of oxygen-deficient sites by H2-reduction, 2) Reduction of CO2 to carbon and Incorporation of two oxygen ions of the CO2 into the oxygen-deficient sites, and 3) Hydrogenation of the deposited carbon to CH4.

Oxygen-deficient magnetite (ODM; Fe3O4-δ, δ>0) synthesized by reduction of magnetite with H2 at 300°C decomposed CO2 to carbon with an efficiency of nearly 100% at 300°C. In this reaction, two oxygen ions of the CO2 were incorporated into the spinel structure of ODM and carbon was deposited on the surface of ODM with zero valence to form visible particles. The particles of carbon separated from ODM were studied by Raman, energy-dispersive X-ray and wave-dispersive X-ray spectroscopies. The carbon which had been deposited on the ODM was found to be a mixture of graphite and amorphous carbon in at least two levels of crystallization. X-ray photoelectron spectroscopy and X-ray diffraction patterns of the carbon-bearing magnetite (CBM) showed no indication of carbide (Fe3C) or metallic iron (α-Fe) phase formation. In the C 1s XPS spectra of the CBM, no peaks were observed which could be assigned to CO2 or CO. X-ray diffractometry, chemical analysis and TG-MS measurement showed that the carbon-bearing Ni(II)-ferrite (CBNF) (Ni(II)/Fetotal = 0.15) synthesized by the carbon deposition reaction from CO2 with the H2-reduced Ni(II)-ferrite was represented by (Ni0.28Fe2.72O4.00)1-δ (Ni2+06.9Fe2+2.31O3.00)δCτ (δ= 0.27, τ= 0.17). The carbon of the CBNF gave the CIOlayer-like oxide containing some Ni2+ ions.

Disposal of 200 million waste tires in the US each year has become a major problem. An environmentally sound innovative technology of recycling rubber in cement matrix was examined. Using silane coupling agent the rubber was bonded to the hydrating cement making a lighter composite, which absorbed more energy than ordinary Portland cement. The bonding information was obtained by peel strength analysis. SEM was used to understand the mode of fracture in pure cement paste, cement bonded rubber composite and rubber filled cement paste. It was found that cracks propagate through the rubber particle in rubber bonded cement composite while in unbonded rubber cement mix, the cracks propagate around the interface. The density and shrinkage measurements are also discussed.

This paper discusses some important issues related to the use of recycled thermoplastics and rubber tire waste in asphalt binders for hot-mix pavements. Both high temperature rheological and low temperature fracture studies are presented on recycled polyethylene, devulcanized and crumb rubber-modified asphalt binders. The results are compared to unmodified and commercially available modified binders. This research is especially timely in light of the U.S. Intermodal Surface Transportation Efficiency Act of 1991, Section 1038 which, starting in 1995, will force state and local governments to use significant amounts of recycled rubber tire or plastic waste in federally funded highway projects.

High temperature rheological measurements of the loss modulus, loss tangent and complex modulus show a significant improvement when only small quantities of crumb rubber, devulcanized crumb rubber or waste polyethylene are added to the asphalt binders.

The low temperature fracture performance of the modified asphalts is greatly influenced by the interfacial strength between the dispersed and continuous phase. The fracture toughness increases dramatically, only when low molecular weight polymers are grafted in-situ onto the rubber and polymer dispersed phases in order to strengthen the interface. This points to a crack-pinning mechanism as being responsible for the dramatic increase in fracture toughness that is observed in this work. Single phase, devulcanized crumb rubber-asphalt systems perform quite poorly at low temperatures.

Conventional paint removal methods include chemical stripping with VOCs, blasting with plastic media, and delamination with high pressure water. These methods have many limitations, in that they are labor intensive, pose human health risks, are relatively expensive and pose significant waste disposal problems. However, polymeric coatings are known to contain structural components, such as ester, amide and urea linkages, that can be degraded biologically. We are working to develop a stable, enzyme-based, non-toxic paint stripping strategy that will be environmentally safe and cost effective.

The specific objectives are to identify and characterize microbial systems capable of degrading polymeric coatings, to develop a quantitative degradation assay and to optimize activity levels for subsequent purification and concentration of the biological products required for rapid degradation of coatings.

A water-dispersed colloid of an ester-based polyurethane polymer has been used in solid growth medium to screen about 100 different bacteria for microbial degradation activity. Those with demonstrable activity have been grown in the presence of epoxypolyamide paint- and polyester polyurethane paint-coated aluminum coupons. We have demonstrated delamination under certain conditions and have developed a spectrophotometric method for quantitating degradation activity as a function of dye release.

Environmental and safety issues are becoming increasingly critical for the selection of materials and their processing techniques. While the choice of “green” materials is important from the perspective of disposal of spent or used products, the choice of environmentally sound processes is important to cut down manufacturing waste and limit the use of toxic solvents and solids. Some examples from the electronics and the aerospace industry are described.

Carbon dioxide is an attractive organic solvent in today's chemical process environment in that it is non-flammable, 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 non-polar, and as such 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-philic, 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-philic oligomers, we have generated materials which both effectively extract metals from solid matrices and which dissolve in carbon dioxide in significant quantities.

The flocculation of polystyrene particles with aluminum sulfate or alum (Al2 (SO4)3) by turbulent shear was studied as a function of the applied shear rates (63–129 s−1) and flocculant concentrations (11 and 32 mg/L) in a stirred tank. Increasing the shear rate increased the floc growth rate but decreased the maximum attainable floc size. Increasing the concentration of alum increased the floc growth rate and the maximum floc size. A steady state between floc growth and breakage was attained after which the floc size distribution no longer changed. The normalized steady state size distributions allowed evaluation of the relative contributions of shear rate and flocculant concentration to the performance of the process.

Processes used in the production of epitaxial III-V semiconducting materials employ a wide variety of materials that are environmentally hazardous. As production volumes increase, the need to manage these materials becomes a serious concern. As the leading supplier of production scale single and multi-wafer MOCVD systems, we have taken the approach of minimizing the generation of waste by designing our reactor for high reactant utilization efficiency, and then trapping the remainder so that the exhaust stream is clean. We have paid particular attention to both operational efficiency and operator safety. The traps may be simply removed and replaced, with cleaning being performed off line. The trapped materials are reduced to an inert state for subsequent commercial disposal; this is particularly important for phosphorus, which can be highly flammable if improperly handled. The reactor chamber deposits occur below the wafer level and typically are cleaned only after several hundred deposition cycles. These factors contribute to a quick cycle time and high uptime, both of which increase throughput. These issues become more important as the reactor size is increased and when multiple shifts are utilized. These points are exemplified by our operational experience with our new Enterprise series, which holds four 100mm wafers (or seventeen 50mm wafers) per run. We will discuss the progressive trapping of solid As and P compounds and those hydride gases which are not completely decomposed in the reaction chamber. The use of computer modeling to scale the process to larger dimensions and to optimize the deposition conditions will also be discussed.

The ability to control and eliminate microcontamination from the manufacturing process is becoming a critical technology issues for such diverse industries as semiconductors, aerospace, and automotive. Current industrial cleaning practices use large amounts of water and chemicals which require disposal. Dry environmentally benign technologies can be alternatives. In this paper, we will look at an alternative technology which consists of deep ultraviolet photons coupled with a flowing inert gas, and compare it to current wet cleaning practices in the semiconductor industry.

The environmentally benign precursors diethylsilane and di-t-butylsilane were used with NH3 to synthesize silicon nitride films by plasma enhanced chemical vapor deposition. The growth kinetics and film properties were examined as a function of deposition temperature, total pressure, and NH3/organosilane ratio. The growth rate was observed to decrease with higher temperature and higher NH3/organosilane ratio while increasing with higher total pressure. Values of index of refraction, film stress, hardness, and Young's modulus were measured as a function of processing variables and related to film density and resulting film composition. Oxidation of the films was noted to occur at high pressures, low temperatures, and low NH3/organosilane ratios. Carbon incorporation was present for all deposits and appeared not to be dependent on processing conditions.

A three member ring compound propylene sulfide, C3H6S is employed as a sulfur source for the Metalorganic Chemical Vapor Deposition (MOCVD) of stoichiometric thin films of iron pyrite (FeS2). Iron pentacarbonyl Fe(CO)5, a liquid, was precursor for iron. Propylene sulfide, (PS) a liquid ( b. p. = 72–75 °C, v. p. ∼ 87 torr @ 20°C ) decomposes cleanly and quantitatively as S2 and C3H6 (propylene) above 250°C. Deposition of thin films of pyrite and their analysis by X-ray diffraction and Mossbauer and X-ray Photoelectron spectroscopy is described. Liquid state, long term stability, clean and low temperature generation of active S2 species in vapor phase and gaseous by product C3H6 which can be burned to CO2 and H2O are the key advantages offered by propylene sulfide as a sulfur source.

Certain perfluorocompounds (PFCs) - including CF4, C2F6, SF6, and NF3 - are widely used in gas phase thin film processing applications such as dry etching and CVD chamber cleaning. Through a combination of long atmospheric lifetimes and high infrared absorption cross sections, many PFCs have high global warming potentials (GWPs). Abatement of PFC emissions from semiconductor applications is consistent with existing and developing international, national, and industrial policies for the control of greenhouse gas emissions. For PFC applications in the semiconductor industry, there exist a number of promising options for emissions control. These options include destruction (comprising combustion, plasma, and chemical-thermal routes), recovery, and process replacement.

Several coordinated hazardous waste minimization projects have been undertaken at our facilities involved in III-V device manufacturing. These include modifications to existing processes to reduce or eliminate emissions of CFCs, 1,1,1-TCA, xylenes, ethylene glycol ethers, 1,2,4-trichlorobenzene (in photoresist stripper), and other compounds. These issues are addressed in turn, noting the unique aspects of GaAs and GaP device manufacture that need to be taken into account. Goals achieved have been complete cessation of CFC and 1,1,1-TCA use and 33% reductions in xylene and 1,2,4-trichlorobenzene usage since 1990, despite significant increases in total production volume during the same time period. Specific strategies are also described for tracking chemical use and sharing best practices for hazardous waste reduction across functional groups.

The semiconductor industry uses PFC gases such as CF4 and C2F6 as etchant and cleaning gases during plasma processes. The gases do not fully react within the reactor chamber. The unused gases enter the atmosphere through the process effluent. These gases have long persistence in the atmosphere and absorb infrared radiation. The PFC gases are, therefore, potential global warming gases. A method is described that will recover and recycle PFC gases.

The US semiconductor industry uses 5–7 thousand pounds of arsine annually. Fifty to eighty percent of the arsine used becomes a waste product, which requires abatement. Traditional methods of abatement are reviewed with an emphasis on dry chemical scrubbing. A variety of dry chemical scrubbing materials were evaluated for arsine capacity, using activated carbon as the baseline for comparison. A proprietary mixed oxide composition, employing copper oxide as the active ingredient was identified as having high capacity and efficiency. Disposal and possible reclamation options are discussed.

The paper discusses the potential of silicon-based integration of disciplines of microelectronics, microoptics, and micromechanics, (MEOM), to achieve sensor-based smart subsystems for pervasive environmental applications. The author proposes a federally-focused initiative to establish an R & D institute to expedite progress and achieve global industrial leadership.