[1] Epoxy models have been used as analogs for fractured rock surfaces in many laboratory investigations of multiphase flow processes. However, there is no agreement on how well or poorly such an analog replicates the surface chemistry of geologic materials, nor is there a satisfactory analysis of the surface properties of epoxy. This paper addresses the issue of accurately characterizing the surface chemistry of a typical epoxy used in laboratory multiphase flow studies and comparing that surface to a polystyrene surface and a radio frequency glow discharge treated polystyrene surface. Surface properties were determined using direct contact angle measurements of polar and apolar liquids on flat test samples. The epoxy was determined to have surface properties as follows: g = 62.3, g LW = 39, g AB = 23.3, g È = 0, and g É = 23.3 mJ/m 2 , where g is the total surface tension of the solid, g LW is the Lifshitz-van der Waals (LW) surface tension component, g AB is the Lewis acid base (AB) surface tension component, g É is the electron-donor (negative) parameter, and g È is the electron-acceptor (positive) parameter. Values of g É < 27.9 mJ/m 2 indicate a hydrophobic surface, which means that epoxy is not a good analog for most geologic materials. This study also explores the use of radio frequency glow discharge plasma to add hydroxyl functionality to polymer surfaces producing a material with alterable surface properties and the same optical and casting properties as epoxy. Using this method, the degree of alteration of the surface chemistry of polymer fracture models can be controlled, allowing the creation of models with a variety of different wettabilities. The resultant models were found to be durable, long lasting, and a potentially very useful alternative to the more typical epoxy models.
This paper presents the preliminary results of a study investigating the application of laboratory X-ray diffraction (XRD) and field portable X-ray fluorescence (XRF) analysis of soils as screening methods for forensic comparison and generalized provenancing. The study area is the Buffalo-Niagara metropolitan region in New York, a glacially draped area of the northeastern USA. For the initial stages of this study, soils are being collected from publicly accessible areas (parks, playgrounds, etc.) for mineralogical and elemental analysis. Initially, minimal sample preparation is being applied to create specimens. An investigation of the published literature reveals that there are a number of different suggested approaches for forensic application of XRD data, not all of which appear to be appropriate to the task at hand. The data being generated in this study are being used to build a reference set for comparison studies. In addition, two simulated forensic samples were collected to test the usefulness of XRD and XRF screening for determining possible regional source areas. For one sample this method was reasonably successful in identifying the general source area, while the results for the second sample were somewhat less satisfactory. In future additional sample handing and analysis protocols will be added.
J Forensic Sci 2006;51(5):967-73. Sir:The authors of this study performed careful analysis by inductively coupled plasma-optical emission spectroscopy (ICP-OES), followed by variable cluster and principal component statistical analysis on the resulting data to distinguish between mixtures of concrete and cremains. The ICP analysis consisted of dissolution of samples followed by measurement of concentration of a suite of 21 elements, seven of which were subsequently removed from the study for various stated reasons.
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