Physical stack sampling

The testing program was initially designed to evaluate the effect of parameters such as moisture content, bed temperature and the physical nature of the feed. Subsequently, experiments were conducted to examine long term effects, by simulating commercial operation under a variable load/demand situation for extended periods of time (2 periods of 670 hours continuous operation). Also included in the program were stack sampling tests, and tar production measurements. 

The graphite lattice may show stacking faults or defects within the sheets, and, possibly, bending of the sheets (Fig. 2.25). Omission of a carbon atom (voids), or inclusions of noncarbon elements or molecules, disrupts the orderly configuration and inhibits crystallization of carbon as graphite. These impurities act as sites of local strain that directly influence crystallite size, distribution, and orientation within a sample, and in turn affect the physical and chemical characteristics of the material, especially its strength. 

Molded articles may be prepared from the prepregs by compression and transfer molding. In general, several sheets of the prepreg are cut and stacked in a mold. For example, a prepreg was cured by heating for 80 s at 150-180°C at 100-200 bar. The cured sample had the physical properties shown in Table 11.4. 

Because of the need for better sensitivity of detection in CE, sample concentration is cracial for the widespread and practical use of this technique. Sample concentration can be accomplished by several physical means outside the capillary, such as by liquid- and solid-phase extraction but more easily in CE by concentration on the capillary directly (stacking). Stacking is a general term referring to the contiguous concentrated zones resembling a stack of coins. ... 

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