Sample preparation, diamond anvil cell

A new technique for the identification of components of polymer laminates is the diamond anvil cell technique supplied by Perkin Elmer [29]. A laminate is separated by cutting a small portion of the sample with a razor blade. The layers are then separated by sectioning each piece with the blade. All sample preparation is performed under a stereo microscope. The separated layers are then individually placed in the diamond cell and a spectrum is obtained. This work was performed using a Perkin Elmer model 1650 instrument (a DTGS detector) at 8 cm resolution and 16 scans. Figure 3.7 shows spectra identifying the components of a three-layer polymer laminate. 

Fibrous materials may be analyzed by a number of different methods, including the standard method for sample preparation—compressed halide pellets. In this latter case, normally the fiber structure is destroyed during sample preparation. Alternatively, one can consider using diffuse reflectance, photoacoustic, or infrared microscopy. With due consideration to the preparation procedures, the fibers may be retained in their original form with these methods. In some cases, such as with IR microscopy, it is possible to study the orientation characterisitics of the fiber material and to correlate this information to certain mechanical properties of the fiber. The use of IR polarizers is imphed with this type of measurement. Diamond compression cells work well for single-filament fibers by both transmission (diamond anvil cell) and ATR. 

FTIR has been used extensively for identification of coatings. Important methods for the study of paint material are KBr pellets prepared from scratched off paint material, ATR measurement of coated surfaces and measurements on cross sections of a coating with FTIR microspectroscopy. FTIR is an excellent way of obtaining information quickly about the basic chemical class of a binding material. Samples are placed in a diamond anvil cell and compressed to a thin film a beam condenser focuses the IR beam to an area of 1.0 mm [99]. Qther methods for determining the binder structure of cross-linked systems comprise PyGC. 

The utility of the diamond anvil cell is great, but it comes with a price the device costs several thousand dollars. This is no surprise since diamonds are expensive. Add to this the cost of an infrared microscope, which is typically tens of thousands of dollars, and you end up with a hefty price tag. Another disadvantage of the diamond anvil cell is that diamond absorbs in the mid-infrared between 2200 and 2200 cm". It will typically mask the peaks of samples that absorb in this region such as materials containing C C and C N bonds. If your sample has important peaks in this wave-number range, it may be necessary to analyze the sample using some other sample preparation technique. 

Diamond Anvil Cell A device used to prepare samples for transmission sampling by infrared microscopy. The cell consists of two diamonds with flat faces. The sample is placed on one diamond face, and the second diamond face is brought into contact with the sample to flatten it. The entire assembly is then placed in the infrared beam of an infrared microscope. 

Diamond cell experiments were performed between -40° and 60°C, and at pressures up to 900 MPa. To prepare samples, synthetic methane hydrate [11, 12] was loaded in the sample chamber of the cell. After the sample chamber is sealed, the total mass of the sample remains constant. The bulk density (and sample pressure) is then adjusted by changing the volume of the sample chamber, which is achieved by adjusting the distance between the two diamond-anvil faces. Once the volume of the sample chamber is fixed, the sample remains under isochoric conditions [6]. Thermal expansion of various parts of the cell, within the small temperature range of this study, has a negligible effect on the sample volume under these experimental conditions. Occasionally, samples were prepared by sealing AI4C3 and distilled water in the sample chamber, and CH4 was generated at temperatures above 200 °C by the reaction... 

In a diamond cell, the sample volume is sacrificed for the sake uf higher pressures, and hence, all operations connected with (he cell have lo be performed under a microscope. In preparing the DAC for an experiment, the first step is to indent Ihe metal gasket (hardened stainless steel strip nr Inconel strip) with the anvil diamonds to the correct thickness (5(1 to UK) micrometers) and then drill a IOO- to 200-micrumeter hole as close lo the center of the indentation as possible. The gasket is seated on the face of one of the diamonds in the same orientation as it had when the indentation was made. The sample material and a small chip of ruby for pressure calibration are (lien placed in the hole. Finally, to maintain hydrostatic pressure the hole is tilled with a tiny drop of fluid from a syringe and then (he hole is quickly sealed by (he diamond fucus before Ihe fluid evaporates. 

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