Insoluble plutonium- and americium-bearing colloidal particles formed during simulated weathering of a high-level nuclear waste glass. Nearly 100 percent of the total plutonium and americium in test ground water was concentrated in these submicrometer particles. These results indicate that models of actinide mobility and repository integrity, which assume complete solubility of actinides in ground water, underestimate the potential for radionuclide release into the environment. A colloid-trapping mechanism may be necessary for a waste repository to meet long-term performance specifications.
A wide variety of complex devices are being developed for implantation into the human body; these include artificial joints containing metal and polymeric parts, electronic components for pacemakers, and small stents for treatment of cardiovascular conditions, to cite just a few examples. This variety is reflected in the array of client inquiries typically handled by an industrial consulting laboratory where there is no such thing as a routine sample.Client concerns may include contamination of devices during manufacturing or packaging, reaction of components with fluids or tissues in the body, determination of wear or failure mechanisms, and validation of results obtained from simulated aging tests. To address these concerns, the consulting laboratory must be able to meet challenges such as representatively sampling limited amounts of material for multiple analyses, isolating small contaminant particles from tissue or other unwanted bulk, and preparing thin sections for TEM analysis. In the real world, these challenges are met with varying degrees of success, as is illustrated in the following examples.Several projects at McCrone Associates have involved isolation and identification of small particles that contaminate implant devices as a result of manufacturing and polishing processes, or through contact with packaging materials. A great deal of work has also centered on characterization of particles found in tissue samples removed from implant patients [1]. Figure 1 shows a TEM image of chromium-rich particles in such a sample. Specialized preparation techniques using optical microscopy have been developed to locate metal particles and low contrast particles such as polyethylene, and digest the tissue while leaving the particles in place, allowing them to be mounted for characterization using SEM, TEM and other techniques [2].Preparation of thin sections for TEM examination presents special challenges. Figures 2a and 2b show thin sections of a porous metal/oxide implant device prepared using ultramicrotomy. The device is formed by sintering metal grains, and subsequently growing an oxide layer on the grain surfaces, forming a porous network. Preparation of thin sections for high resolution imaging of the metal/oxide interface proved difficult due to the hardness of the metal and the porosity of the structure, which tended to break apart when it was thinned to electron transparency. Various preparation approaches used to date have met with limited success.Recent work has included characterization of 316L stainless steel before and after chemical modification to enhance radiopacity. The client requested that several samples of both materials be examined to determine the extent of formation of secondary phases that might affect the performance properties of the modified metal. TEM imaging, and EDS mapping and spot analysis were used to provide a statistical comparison of the materials.
In the field of document examination, several approaches can be taken to probe the authenticity of a piece of ancient writing. Scholars have the task of analyzing, and possibly translating, the language and content of a document, and assessing the character and quality of the script. Materials characterization plays another role. Both the document substrate and the ink can be examined to determine whether the materials and methods of creation are consistent with those known to be used during the historical period to which the document is attributed.
Extended abstract of a paper presented at Microscopy and Microanalysis 2006 in Chicago, Illinois, USA, July 30 – August 3, 2006
It is sometimes necessary to obtain cross-sections of pharmaceutical patches for purposes of quality control, analysis of individual layers and contaminants within layers, or for forensic identification. A reliable method has been developed for preparing cross-sections of patches from samples as small as 1mm 2 , which can then be analyzed by any suitable means, and compared to known reference samples.The method involves immersing the sample briefly in liquid nitrogen, and cross-sections are cut by hand while the sample is still partially frozen. The process utilizes a series of specially modified glass slides that allow for ease of handling of small samples.Step-by-step instructions will be provided in the form of text and diagrams. Photomicrographs of cross-sections of various pharmaceutical patches will be displayed, along with infrared spectra of individual layers of some of the patches.The advantage of this method is that the resulting specimens maintain their original cross-sectional dimensions, with little to no dragging or deformation. The cross-sections are comparable to specimens produced by cryo-microtomy, and are much thinner than those prepared by hand at room temperature. Typical cross-sections obtained by this method are on the order of 30 to 60 µm in thickness. The cross-sections can be used to examine the thickness of the individual layers, size distribution of particles within the layers, presence/absence of voids, separation of the layers, and contamination within or between layers.A cross-section of a Nitro-Dur® nitroglycerin patch is shown in Figure 1, and illustrates the quality of the cross-sections that can be obtained with this method. Note the parallel layers and smooth surfaces of the sample, which would be impossible to achieve with a room-temperature preparation. The cross-section was then pressed with a cover slip to flatten it and cause the layers to spread out to at least twice their original size, providing thin specimens of each layer with areas that were large enough to obtain micro-FTIR spectra of good quality. Figure 2 is a cross-section of an OrthoEvra® birth control patch, showing the structural details that can be seen in the cross-sections. Notice the fibers within the adhesive layer, and the small isotropic particles that can be clearly seen. The layer of plastic wrap that was used to stabilize the sample during the cross-sectioning process remains attached to the cross-section.The hand-sectioning method is a reliable, quick, and relatively simple way to prepare cross-sections of good quality from pharmaceutical patches. With practice, multiple sections can be obtained from a patch in less than 30 minutes. This method will be especially useful for laboratories that do not have access to a cryo-microtome.
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