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Portable sensor for hazardous waste

Description: We are part-way through the second phase of a 4-year program designed to develop a portable monitor for sensitive hazardous waste detection. The ultimate goal of the program is to develop our concept to the prototype instrument level. Our monitor will be a compact, portable instrument that will allow real-time, in situ, monitoring of hazardous wastes. This instrument will be able to provide the means for rapid field screening of hazardous waste sites to map the areas of greatest contamination. Remediation efforts can then focus on these areas. Our analysis approach is to excite atomic and molecular fluorescence by the technique of active nitrogen energy transfer (ANET). The active nitrogen is made in a dielectric-barrier (D-B) discharge in nitrogen at atmospheric pressure. Only a few emission lines or bands are excited for each hazardous species, so spectral resolution requirements are greatly simplified over those of other spectroscopic techniques. The D-B discharge is compact, 1 to 2 cm in diameter and 1 to 10 cm long. Furthermore, the discharge power requirements are quite modest, so that the unit can be powered by batteries. Thus an instrument based on ANET can readily be made portable. Our results indicate that ANET is a very sensitive technique for monitoring heavy metals and chlorinated hydrocarbons. We have demonstrated an overall detection sensitivity for most species that is at or below ppb levels. ANET alone, however, appears to be most successful in treating hazardous species that have been atomized. We are therefore developing a hybrid technique which combines a miniature, solid-state laser for sample collection and vaporization with ANET for subsequent detection. This approach requires no special sample preparation, can operate continuously, and lends itself well to compact packaging.
Date: December 31, 1996
Creator: Piper, L.G.; Hunter, A.J.R.; Fraser, M.E. & Davis, S.J.
Partner: UNT Libraries Government Documents Department

Use of complementary neutron techniques in studying the effect of a solid/liquid interface on bulk solution structures

Description: By appropriate combination of neutron scattering techniques, it is possible to obtain structural information at various distances from a solid/liquid interface and thus probe in some detail how the surface structures evolve into bulk structures. We have used neutron reflectometry (NR) with a newly developed shear cell, near surface small angle neutron scattering (NSSANS) again in combination with the new shear cell, and regular small angle neutron scattering (SANS) with a standard Couette shear cell to probe the structures formed in our aqueous surfactant systems and how they react to a flow field, particularly in the near surface region of a solid/liquid interface. We present data for a 20mM aqueous solutions of 70% cetyltrimethylammonium 3,5-dichlorobenzoate (abbreviated CTA3,5ClBz) and 30% CTAB. This system forms a very viscoelastic solution containing long threadlike micelles. NR only probes to a depth of about 0.5 {mu}m from the surface in these systems and clearly indicates that adsorbed onto the surface is, surfactant layer which is insensitive to shear. The depth probed by the NSSANS is on the order of 20-30 {mu}m and is determined by the transmission of the sample, the angle of incidence, and the wavelength. In this region, the rods align under shear into a remarkably well ordered hexagonal crystal. The SANS from the Couette cell averages over the entire sample, so that the signal is dominated by scattering from the bulk. While the near surface hexagonal structure is clearly visible, these data are not consistent with the crystal structure persisting throughout the bulk, leading to the postulate that the bulk structure is a two dimensional (2D) liquid where the rods align with the flow, but do not order in the other two dimensions.
Date: December 31, 1996
Creator: Butler, P.D.; Hamilton, W.A. & Magid, L.J.
Partner: UNT Libraries Government Documents Department

Field-usable portable analyzer for chlorinated organic compounds

Description: In 1992, a chemical sensor was developed which showed almost perfect selectivity to vapors of chlorinated solvents. When interfaced to an instrument, a chemical analyzer will be produced that has near- absolute selectivity to vapors of volatile chlorinated organic compounds. TRI has just completed the second of a 2-phase program to develop this new instrument system, which is called the RCL MONITOR. In Phase II, this instrument was deployed in 5 EM40 operations. Phase II applications covered clean-up process monitoring, environmental modeling, routine monitoring, health and safety, and technology validation. Vapor levels between 0 and 100 ppM can be determined in 90 s with a lower detection limit of 0.5 ppM using the hand-portable instrument. Based on the favorable performance of the RCL MONITOR, the commercial instrument was released for commercial sales on Sept. 20, 1996.
Date: December 31, 1996
Creator: Buttner, W.J.; Penrose, W.R.; Stetter, J.R. & Williams, R.D.
Partner: UNT Libraries Government Documents Department