Daniel E. Dedrick

Verification studies of thermophoretic protection for extreme ultraviolet masksa)

A “thermophoretic pellicle” has been proposed as an alternative to the traditional organic pellicle as a means of protecting extreme ultraviolet (EUV) lithographic photomasks from particle contamination. The thermophoretic pellicle protects a mask from particles by exploiting the thermophoretic force, which is exerted on a particle by a surrounding gas in which a temperature gradient exists. Two critical requirements of the thermophoretic pellicle are: (1) the mask is kept warmer than its surroundings and (2) the surrounding gas pressure is kept sufficiently high to enable thermophoretic protection. Experiments are presented which verify the viability of thermophoretic protection for EUV masks. In these experiments, wafers are exposed to a monodisperse, polystyrene-latex-sphere aerosol under carefully controlled experimental conditions. Robust thermophoretic protection is observed over a wide range of argon gas pressures (50–1600mTorr or 6.66–213Pa), particle sizes (65–300nm), and temperature gradients (2...

Performance of a full-scale hydrogen-storage tank based on complex hydrides.

Designing and building a full scale hydrogen storage system revealed several engineering challenges and also demonstrated the capabilities of complex hydrides. Three kg of hydrogen was stored in a four module system using modified sodium alanate as the storage media. Extensive testing of this system demonstrated the ability to follow aggressive hydrogen demand schedules that simulate actual driving. Extensive use of detailed models greatly improved the design and eventual performance of the storage system; the test data permitted further refinement of the models.

Heat and Mass Transport in Metal Hydride Based Hydrogen Storage Systems

Hydrogen storage technologies based on solid-phase materials involve highly coupled transport processes including heat transfer, mass transfer, and chemical kinetics. A full understanding of these processes and their relative impact on system performance is required to enable the design and optimization of efficient systems. This paper examines the coupled transport processes of titanium doped sodium alanates (NaAlH4 , Na3 AlH6 ) enhanced with excess aluminum and expanded natural graphite. Through validated modeling and simulation, we have illuminated transport bottlenecks that arise due to mass transfer limitations in scaled-up systems. Individual heat transport, mass transport, and chemical kinetic processes were isolated and experimentally characterized to generate a robust set of model parameters for all relevant operational states. The individual transport models were then coupled to simulate absorption processes associated with rapid refueling of scaled-up systems. Using experimental data for the absorption performance of a 1.6 kg sodium alanate system, comparisons were made to computed results to identify dominant transport mechanisms. The results indicated that channeling around the compacted porous solid can contribute significantly to the overall transport of hydrogen into and out of the system. The application of these transport models is generally applicable to a variety of condensed-phase hydrogen sorption materials and facilitates the design of optimally performing systems.Copyright

Desalination Utilizing Clathrate Hydrates (LDRD Final Report)

Advances are reported in several aspects of clathrate hydrate desalination fundamentals necessary to develop an economical means to produce municipal quantities of potable water from seawater or brackish feedstock. These aspects include the following, (1) advances in defining the most promising systems design based on new types of hydrate guest molecules, (2) selection of optimal multi-phase reactors and separation arrangements, and, (3) applicability of an inert heat exchange fluid to moderate hydrate growth, control the morphology of the solid hydrate material formed, and facilitate separation of hydrate solids from concentrated brine. The rate of R141b hydrate formation was determined and found to depend only on the degree of supercooling. The rate of R141b hydrate formation in the presence of a heat exchange fluid depended on the degree of supercooling according to the same rate equation as pure R141b with secondary dependence on salinity. Experiments demonstrated that a perfluorocarbon heat exchange fluid assisted separation of R141b hydrates from brine. Preliminary experiments using the guest species, difluoromethane, showed that hydrate formation rates were substantial at temperatures up to at least 12 C and demonstrated partial separation of water from brine. We present a detailed molecular picture of the structure and dynamics of R141b guest molecules within water cages, obtained from ab initio calculations, molecular dynamics simulations, and Raman spectroscopy. Density functional theory calculations were used to provide an energetic and molecular orbital description of R141b stability in both large and small cages in a structure II hydrate. Additionally, the hydrate of an isomer, 1,2-dichloro-1-fluoroethane, does not form at ambient conditions because of extensive overlap of electron density between guest and host. Classical molecular dynamics simulations and laboratory trials support the results for the isomer hydrate. Molecular dynamics simulations show that R141b hydrate is stable at temperatures up to 265K, while the isomer hydrate is only stable up to 150K. Despite hydrogen bonding between guest and host, R141b molecules rotated freely within the water cage. The Raman spectrum of R141b in both the pure and hydrate phases was also compared with vibrational analysis from both computational methods. In particular, the frequency of the C-Cl stretch mode (585 cm{sup -1}) undergoes a shift to higher frequency in the hydrate phase. Raman spectra also indicate that this peak undergoes splitting and intensity variation as the temperature is decreased from 4 C to -4 C.

Clathrate Hydrates for Production of Potable Water

Clathrate hydrates are crystalline inclusion compounds of water and a guest molecule that can form at temperatures above the freezing point of water. Such inclusion compounds exclude dissolved solutes, e.g., sodium chloride present in the aqueous phase, and thereby provide a basis for desalination. Clathrate hydrate formation experiments were performed using several guest molecules, including R141b (CFClH), a commercial refrigerant, and ethylene. Ethylene, a gaseous hydrate guest, readily formed hydrates with saline water at up to 5°C and 20 atm. of pressure. Hydrates of R141b, in the liquid state, were formed at temperatures from 2°C to 6°C and atmospheric pressure from deionized water and 2% - 7% NaCl solutions. Significant reductions in saline content were obtained with both forming agents in a batch reactor without additional separation equipment. Samples of the R141b hydrates were characterized by cold-stage x-ray diffraction and Raman spectroscopy and determined to be structure II. Proof-of-concept experiments were performed to demonstrate a novel technique of desalination using R141b as the hydrate forming agent and an inert secondary fluid.

Reimagining liquid transportation fuels : sunshine to petrol.

Two of the most daunting problems facing humankind in the twenty-first century are energy security and climate change. This report summarizes work accomplished towards addressing these problems through the execution of a Grand Challenge LDRD project (FY09-11). The vision of Sunshine to Petrol is captured in one deceptively simple chemical equation: Solar Energy + xCO{sub 2} + (x+1)H{sub 2}O {yields} C{sub x}H{sub 2x+2}(liquid fuel) + (1.5x+.5)O{sub 2} Practical implementation of this equation may seem far-fetched, since it effectively describes the use of solar energy to reverse combustion. However, it is also representative of the photosynthetic processes responsible for much of life on earth and, as such, summarizes the biomass approach to fuels production. It is our contention that an alternative approach, one that is not limited by efficiency of photosynthesis and more directly leads to a liquid fuel, is desirable. The development of a process that efficiently, cost effectively, and sustainably reenergizes thermodynamically spent feedstocks to create reactive fuel intermediates would be an unparalleled achievement and is the key challenge that must be surmounted to solve the intertwined problems of accelerating energy demand and climate change. We proposed that the direct thermochemical conversion of CO{sub 2} and H{sub 2}O to CO and H{sub 2}, which are the universal building blocks for synthetic fuels, serve as the basis for this revolutionary process. To realize this concept, we addressed complex chemical, materials science, and engineering problems associated with thermochemical heat engines and the crucial metal-oxide working-materials deployed therein. By projects end, we had demonstrated solar-driven conversion of CO{sub 2} to CO, a key energetic synthetic fuel intermediate, at 1.7% efficiency.

Microcantilever Arrays for Multiplexed Biomolecular Analysis

An accurate, efficient, and quantitative method for detection of multiple biomolecules, such as DNA and proteins, would benefit many bio-medical applications. These applications include diagnostics of complex diseases such as cancer, drug discovery, and development of fundamental scientific knowledge regarding signaling pathways. We have developed a chip-level microcantilever array designed for high-throughput biomolecular analysis. In particular, biological reactions on one surface of a microcantilever beam change its surface tension due to intermolecular energetic and entropic interactions. These interactions generate sufficient torque to deflect the cantilever beam. Integration of microfluid cells on the chip allows for individual functionalization of each cantilever. Each cantilever is designed to respond uniquely to a specific target analyte allowing for simultaneous and quantitative analysis of multiple bio-molecules. Experiments testing the physical response of the microarray describe the repeatability of the cantilevers while providing information regarding the limits on the detection time for reaction-induced deflections to dominate over random drift of the cantilevers. Statistical analysis shows that the cantilevers exhibit thermomechanical sensitivity within ±7% variation. The maximum observed trend of the long-term drift is about 2.1nm/min, which suggests reactions should be completed within 10 minutes, for a reliable bioassay.Copyright

Safety, codes and standards for hydrogen installations. Metrics development and benchmarking

Automakers and fuel providers have made public commitments to commercialize light duty fuel cell electric vehicles and fueling infrastructure in select US regions beginning in 2014. The development, implementation, and advancement of meaningful codes and standards is critical to enable the effective deployment of clean and efficient fuel cell and hydrogen solutions in the energy technology marketplace. Metrics pertaining to the development and implementation of safety knowledge, codes, and standards are important to communicate progress and inform future R&D investments. This document describes the development and benchmarking of metrics specific to the development of hydrogen specific codes relevant for hydrogen refueling stations. These metrics will be most useful as the hydrogen fuel market transitions from pre-commercial to early-commercial phases. The target regions in California will serve as benchmarking case studies to quantify the success of past investments in research and development supporting safety codes and standards R&D.

System level permeability modeling of porous hydrogen storage materials.

A permeability model for hydrogen transport in a porous material is successfully applied to both laboratory-scale and vehicle-scale sodium alanate hydrogen storage systems. The use of a Knudsen number dependent relationship for permeability of the material in conjunction with a constant area fraction channeling model is shown to accurately predict hydrogen flow through the reactors. Generally applicable model parameters were obtained by numerically fitting experimental measurements from reactors of different sizes and aspect ratios. The degree of channeling was experimentally determined from the measurements and found to be 2.08% of total cross-sectional area. Use of this constant area channeling model and the Knudsen dependent Young & Todd permeability model allows for accurate prediction of the hydrogen uptake performance of full-scale sodium alanate and similar metal hydride systems.

Durability study of a vehicle-scale hydrogen storage system.

Sandia National Laboratories has developed a vehicle-scale demonstration hydrogen storage system as part of a Work for Others project funded by General Motors. This Demonstration System was developed based on the properties and characteristics of sodium alanates which are complex metal hydrides. The technology resulting from this program was developed to enable heat and mass management during refueling and hydrogen delivery to an automotive system. During this program the Demonstration System was subjected to repeated hydriding and dehydriding cycles to enable comparison of the vehicle-scale system performance to small-scale sample data. This paper describes the experimental results of life-cycle studies of the Demonstration System. Two of the four hydrogen storage modules of the Demonstration System were used for this study. A well-controlled and repeatable sorption cycle was defined for the repeated cycling, which began after the system had already been cycled forty-one times. After the first nine repeated cycles, a significant hydrogen storage capacity loss was observed. It was suspected that the sodium alanates had been affected either morphologically or by contamination. The mechanisms leading to this initial degradation were investigated and results indicated that water and/or air contamination of the hydrogen supply may have lead to oxidation of the hydride and possibly kinetic deactivation. Subsequent cycles showed continued capacity loss indicating that the mechanism of degradation was gradual and transport or kinetically limited. A materials analysis was then conducted using established methods including treatment with carbon dioxide to react with sodium oxides that may have formed. The module tubes were sectioned to examine chemical composition and morphology as a function of axial position. The results will be discussed.