Paul Nigel Dyer

Ion transport membrane technology for oxygen separation and syngas production

Abstract Ion transport membranes (ITMs) are made from ceramic materials that conduct oxygen ions at elevated temperatures. Successful application of ITM technology will allow significant improvement in the performance of several large-scale industrial processes. The ITM Oxygen process, in which ITMs are used to separate high-purity oxygen from air, has the potential for significant advantages when integrated with power generation cycles. The ITM Syngas process, by combining air separation and high-temperature syngas generation processes into a single compact ceramic membrane reactor, has the potential for substantially reducing the capital investment for gas-to-liquid (GTL) plants and for distributed hydrogen. The development efforts are major, long-term and high risk, and place severe demands on the performance and property requirements of the ITM materials. Air Products and Chemicals has joined with the U.S. Department of Energy, Ceramatec and other partners to develop, scale-up and commercialize these technologies. In addition, Air Products and Ceramatec are developing the SEOS™ Oxygen Generator, an electrically-driven, small scale, oxygen generation and removal technology using ITMs, which could have a significant impact in the global market for distributed oxygen and inert gases. This paper describes the stages of development of these three related technologies, their industrial applications, and the technical hurdles that must be overcome before successful commercialization.

Support and cluster effects on synthesis gas conversion with supported ruthenium clusters

Abstract [Ru3(CO)12] and [H4Ru4(CO)12] supported on Al2O3 and MgO exhibited differences in catalytic behavior which can be attributed to the surface organometallic chemistry of the clusters. When supported on Al2O3, [Ru3(CO)12] decomposed to Ru metal on reaction with synthesis gas, and exhibited catalytic behavior that is similar to Ru/Al2O3 prepared by classical methods. On MgO, [Ru3(CO)12] resulted in significant CH3OH production from synthesis gas. After catalysis, the anionic cluster [Ru6C(CO)16]2− was identified on the catalyst, which results from the reaction of [HR3(CO)11]− and [Ru6(CO)18]2−, originally present on the support, with CO + H2. [H4Ru4-(CO)12] supported on Al2O3 and MgO also resulted in significant oxygenate yields from CO + H2. [H3Ru4(CO)12]− was originally present on the surface and reacts with synthesis gas to give [Ru6C(CO)16]2−. The oxygenate selectivity is suggested to be a result of the presence of intact metal clusters on the surface.

Characterization of the transport properties of microporous inorganic membranes

Abstract The development of microporous inorganic membranes for gas separation depends crucially on the accurate characterization of gas transport through such membranes. Particularly in the initial development stages, in which low membrane selectivities are common, measurement of pure gas permeance as a function of mean pressure can provide a useful characterization tool. For example, this method can be used to obtain information regarding pore size reduction in microporous membranes. Unfortunately, due to demanding limits on experimental error and misinterpretation of data, this method has been often applied incorrectly. In this paper, a theoretical basis for describing gas transport through both monolithic and multilayer porous systems is described. Implications of this formalism for practical data acquisition and analysis are discussed. Experimental equipment and methods are described for collecting data satisfying these strict criteria for data precision. The reproducibility of the experimental methods is illustrated by data obtained for a microporous membrane layer deposited on a porous support. Application of the present formalism to the prediction of transport characteristics for different gases, as well as to the detailed modeling of the pore structure of multilayer systems, is also illustrated by permeation data for several supported thin film microporous membranes.

Influence of sol-gel synthesis parameters on the microstructure of particulate silica xerogels

The influence of key sol-gel synthesis parameters on the pore structure of microporous silica xerogels was investigated. The silica xerogels were prepared using an acid-catalyzed aqueous sol-gel process, with tetraethoxysilane (TEOS) as the silicon-containing precursor. At high H2O : TEOS ratios, sols synthesized at pH 2–3 yielded minimum values of mean micropore diameter and micropore volume. Analysis of the resulting Type I nitrogen adsorption isotherms and the equilibrium adsorption of N(C4F9)3 indicated micropore diameters for these xerogels of less than approximately 10 Å.Xerogel micropore volumes corresponding to sols prepared at pH 3 and an H2O : TEOS ratio of r = 83 were consistent with nearly close packing of silica spheres in the xerogel. Xerogel microstructure was only weakly dependent upon H2O : TEOS ratio during sol synthesis for r > 10. Xerogel micropore volume increased rapidly with sol aging time during an initial induction period of particle formation. However, the xerogel microstructure changed only slowly with time after this initial period, suggesting potential processing advantages for the particulate sol-gel route to porous silica materials.Surface adsorption properties of the silica xerogels were investigated at ambient temperature using N2, SF6, and CO2. CO2 adsorbed most strongly, SF6 also showed measurable adsorption, and N2 adsorption was nearly zero. These results were consistent with the surface transport of CO2, and to a lesser extent SF6, observed in gas permeation studies performed through thin membrane films cast from similarly prepared silica sols.

Kinetics of chemical vapor deposition of tungsten carbide

Abstract Hard tungsten carbide based coatings were deposited by chemical vapor deposition (CVD) at low temperatures onto metal substrates by hydrogen reduction of tungsten hexafluoride (WF 6 ) in the presence of dimethyl ether (DME). These coatings contain a mixture of tungsten and tungsten carbide in the form of W 3 C, W 2 C, or a combination of W 3 C and W 2 C depending on reaction conditions. They exhibit layered morphology, which is primarily responsible for their excellent erosion and wear-resistance properties. The deposition of these coatings with layered morphology is believed to involve two simultaneous reactions, leading to the deposition of tungsten and tungsten carbide phases with crystallite size varying between 50 and 150 A. Since the deposition of these coatings in a large-scale commercial reactor requires knowledte about the rate and order of simultaneous reactions, a pilot-scale CVD reactor was designed and operated to investigate reaction kinetics. This paper describes an experimental approach to determine the apparent reaction order and kinetic rate constant for depositing the coating with optimal properties. It also discusses the significance of these kinetic parameters on scaling up reactor design.

New OMCVD precursors for selective copper metallization

A novel OMCVD process for the highly selective deposition of pure, adherent, low resistivity copper films onto conductive substrates is described. Central to this process is a new volatile liquid copper/sup +1/ precursor, Cupra Select, designed to thermally disproportionate at low temperatures to cleanly give copper metal and volatile non-corrosive by-products. Thus, selective depositions onto metallic versus insulating dielectric substrates are achieved between 120 to 420 degrees C with growth rates in excess of 100 nm/min and grain sizes as low as 0.1 microns. In addition, a novel complementary copper etching process is discussed that is chemically compatible with the copper CVD chemistry.<<ETX>>

Organometallic Chemical Vapor Deposition of Copper from a New Organometallic Precursor

Thin copper films have been grown on a variety of substrates using Cu(nona-F) 2 , (bis[4-(2,2,2-trifluoroethyl)imino-1,1,1,5,5,5-hexafluoro-2-pentanonato] copper(II)), a new volatile organometallic copper precursor, and the results are compared with those obtained using copper(II) betadiketonates. Copper films were grown in a cold wall reactor at reduced pressure at temperatures between 270°C and 350°C. For Cu(nona-F) 2 , films which are pure as determined by Auger electron spectroscopy and have a resistivity of 2.1 micro-ohm cm were deposited at temperatures above 270°C, 40°C lower than was possible using Cu(hfac) 2 . At low deposition temperatures, Cu(nona-F) 2 shows some selectivity towards silicon oxide surfaces in preference to metals. The effects of CVD process parameters on the deposition rate and microstructure of the films were studied with a designed experiment and were statistically modeled. Deposition rates up to 70 nm/min were measured. The standard enthalpy of vaporization of Cu(nona-F) 2 was found to be 9.6 kcal/mol.

Tungsten Carbide Erosion Resistant Coating for Aerospace Components

An increasing problem faced by the aerospace industry is the erosive wear of engine components. Various PVD protection coatings have been used previously to combat this wear problem, but with limited success. This paper presents results obtained with a low-temperature CVD, erosion resistant, multilayer tungsten carbide coating system. The coating can be deposited at temperatures below 500°C on ferrous alloys used in the aerospace industry. The low temperature of deposition eliminates the problem of degradation of mechanical properties that occurs with normal high-temperature chemical vapor deposition processes. High-cycle fatigue strength and other mechanical property data are presented for coated stainless steel, as well as results on erosion and impact resistance at 90° impingement.

Consecutive Selective Chemical Vapor Deposition of Copper and Aluminum from Organometallic Precursors

For the next generation of integrated microcircuits, there exists a need in the electronics industry for high conductivity, electromigration resistant metallization that can be deposited selectivity by chemical vapor deposition techniques. This paper describes a new process for depositing copper/aluminum metallization selectively onto diffusion barrier surfaces in two consecutive steps. First copper is selectively deposited by OMCVD ontoa patterned diffusion barrier surface using a Cu(I)(hfac)(olefin) precursor. Selective copper deposition onto tungsten or titanium nitride is achieved at 150°C and 100 mtorr. Aluminum is then selectively deposited onto copper using trimethylaminealane as the OMCVDprecursor. Trimethylaminealane gives good selectivity for aluminum deposition onto coppersurfaces over a temperature range of 100–120°C without the use of a surface activating agent. A small amount of copper diffuses into the as deposited aluminum layer atthe low deposition temperature. Complete diffusion of copper into aluminum is achieved by a rapid thermal anneal at a higher temperature. The selectivity of aluminum deposition onto copper surfaces is far superior to that observed for aluminum deposition onto other metal surfaces.

Plasma assisted chemical vapor deposition on ‘‘three‐dimensional’’ substrates

A novel plasma assisted chemical vapor deposition reactor forms ceramic coatings on ‘‘three‐dimensional’’ surfaces of complicated parts such as cutting tools and bearing surfaces. The reactor chamber features a unique rf‐driven electrode configuration to establish uniform, large volume, low temperature plasmas from which the coatings are deposited. Highly adherent silicon nitride coatings formed from silane/ammonia/argon plasmas have hardness values up to 30 GPa. Variations of methane/silane feed gas ratios produce microcrystalline silicon carbide films with C/Si atomic ratios ranging from 0.4 to 3; the coatings consist of free Si and stoichiometric SiC; SiC, free Si and diamond‐like carbon (DLC); or SiC and DLC, depending on the methane/silane fraction. Hardness varies monotonically between about 10 and 60 GPa as the carbon fraction increases. SiC coatings significantly reduced wear rates in abrasive wear tests; Si–SiC coatings effectively protected molybdenum samples during a 180 h oxidation test in 650...