Publications

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While surface cleaning is the most common process step in DOE manufacturing operations, the link between a successful adhesive bond and the surface clean performed before adhesion is not well understood. An innovative approach that combines computer modeling expertise, fracture mechanics understanding, and cleaning experience to address how to achieve a good adhesive bond is discussed here to develop a capability that would result in reduced cleaning development time and testing, improved bonds, improved manufacturability, and even an understanding that leads to improved aging. A simulation modeling technique, polymer reference interaction site model applied near wall (Wall PRISM), provided the capability to include contaminants on the surface. Calculations determined an approximately 8% reduction in the work of adhesion for 1% by weight of ethanol contamination on the structure of a silicone adhesive near a surface. The demonstration of repeatable coatings and quantitative analysis of the surface for deposition of controlled amounts of contamination (hexadecane and mineral oil) was based on three deposition methods. The effect of the cleaning process used on interfacial toughness was determined. The measured interfacial toughness of samples with a Brulin cleaned sandblasted aluminum surface was found to be {approximately} 15% greater than that with a TCE cleaned aluminum surface. The sensitivity of measured fracture toughness to various test conditions determined that both interfacial toughness and interface corner toughness depended strongly on surface roughness. The work of adhesion value for silicone/silicone interface was determined by a contact mechanics technique known as the JKR method. Correlation with fracture data has allowed a better understanding between interfacial fracture parameters and surface energy.

Gas-phase processing plays an important role in the commercial production of a number of ceramic powders. These include titanium dioxide, carbon black, zinc oxide, and silicon dioxide. The total annual output of these materials is on the order of 2 million tons. The physical processes involved in gas-phase synthesis are typical of those involved in solution -phase synthesis: chemical reaction kinetics, mass transfer, nucleation, coagulation, and condensation. This report focuses on the work done under a Laboratory-Directed Research and Development (LDRD) project that explored the use of various high pressure techniques for ceramic powder synthesis. Under this project, two approaches were taken. First, a continuous flow, high pressure water reactor was built and studied for powder synthesis. And second, a supercritical carbon dioxide static reactor, which was used in conjunction with surfactants, was built and used to generate oxide powders.

Supercritical carbon dioxide extraction is being explored as a waste minimization technique for separating oils, greases, and solvents from solid waste. The contaminants are dissolved into the supercritical fluid and precipitated out upon depressurization. The carbon dioxide solvent can then be recycled for continued use. Definitions of the temperature, pressure, flowrate, and potential co-solvents are required to establish the optimum conditions for hazardous contaminant removal. Excellent extractive capability for common manufacturing oils, greases, and solvents has been observed in both supercritical and liquid carbon dioxide.

Under the Department of Energy (DOE)/United States Air Force (USAF) Memorandum of Understanding, a system is being designed that will use high pressure carbon dioxide for the separation of oils, greases, and solvents from non-hazardous solid waste. The contaminants are dissolved into the high pressure carbon dioxide and precipitated out upon depressurization. The carbon dioxide solvent can then be recycled for continued use. Excellent extraction capability for common manufacturing oils, greases, and solvents has been measured. It has been observed that extraction performance follows the dilution model if a constant flow system is used. The solvents tested are extremely soluble and have been extracted to 100% under both liquid and mild supercritical carbon dioxide conditions. These data are being used to design a 200 liter extraction system.

A statistical design of experiments approach has been employed to evaluate the particle removal efficacy of the SC-1/megasonic clean for sub-0.15 {mu}m inorganic particles. The effects of megasonic input power, solution chemistry, bath temperature, and immersion time have been investigated. Immersion time was not observed to be a statistically significant factor. The NH{sub 4}OH/H{sub 2}O{sub 2} ratio was significant, but varying the molar H{sub 2}O{sub 2} concentration had no effect on inorganic particle removal. Substantially diluted chemistries, performed with high megasonic input power and moderate-to-elevated temperatures, was shown to be very effective for small particle removal. Bath composition data show extended lifetimes can be obtained when high purity chemicals are used at moderate (eg., 45{degrees}C) temperature. Transition metal surface concentrations and surface roughness have been measured after dilute SC-1 processing and compared to metallic contamination following traditional SC-1.

Supercritical carbon dioxide is being explored as a waste minimization technique for separating oils, greases and solvents from solid waste. The containments are dissolved into the supercritical fluid and precipitated out upon depressurization. The carbon dioxide solvent can then be recycled for continued use. Definitions of the temperature, pressure, flowrate and potential co-solvents are required to establish the optimum conditions for hazardous contaminant removal. Excellent extractive capability for common manufacturing oils, greases, and solvents has been observed in both supercritical and liquid carbon dioxide. Solubility measurements are being used to better understand the extraction process, and to determine if the minimum solubility required by federal regulations is met.

Large quantities of solid wastes such as rags, kimwipes, swabs, coveralls, gloves, etc., contaminated with oils, greases and hazardous solvents are generated by industry and the government. If the hazardous components (offs, greases and solvents) could be segregated from the much larger bulk of non-hazardous material, then these solid materials could potentially be handled as sanitary waste, at a significant cost savings. AlliedSignal KCP, a typical DOE manufacturing site, spent several hundred thousand dollars in CY92 for disposal of contaminated solid wastes. Similarly, Naval Air Station North Island, San Diego, also spent several hundred thousand dollars in CY91 for disposal of rags. Under the Department of Energy (DOE)/United States Air Force (USAF) Memorandum of Understanding, the objective of this joint AlliedSignal KCP/Sandia National Laboratories project is to demonstrate the feasibility of using supercritical carbon dioxide (SC-CO{sub 2}) to segregate hazardous oils, greases, and organic solvents from non-hazardous solid waste such as rags, wipes, swabs, coveralls, gloves, etc. Supercritical carbon dioxide possesses many of the characteristics desired in an ``environmentally acceptable`` solvent system. It is nontoxic, inexpensive, and recyclable. Carbon dioxide possesses a moderate critical temperature (31{degrees}C) and pressure (1071 psi). At 37{degrees}C and pressures greater than 2000 psi, the density is greater than 0.8 g/cc. Contaminants dissolved in the supercritical CO{sub 2} solvent are separated out by expansion of the fluid to a subcritical pressure where CO{sub 2} is a gas and the dissolved materials precipitate out (usually as a liquid or solid). The gaseous CO{sub 2} can then be recompressed and recycled.