Coating materials mixed layers

Most often, fragments of paint have a multilayer structure. Each layer (about 10-50 pm thick) is made up of paint material and is a mixture of many chemical compounds. Paint smears, on the other hand, are usually made up of one or two layers of paint material mixed with and sunk into the base (e.g. among fibres of the fabric). The morphology of the paint trace can be observed under an optical microscope. The number of layers visible on a cross-section of paint chip, their colour and thickness are characteristic for the coat of paint from which it originates (Fig. 11.1). The layers are often better visible if the sample is illuminated with polarised light or if fluorescence of sample is excited by illumination with UV light. 

A variety of sorbents have been used as the stationary phase in TLC, including silica gel, cellulose, alumina, polyamides, ion exchangers, chemically modified silica gel, and mixed layers of two or more materials, coated on a suitable support. Currently in the pharmaceutical industry, commercially precoated high-performance TLC (HPTLC) plates with fine particle layers are commonly used for fast, efficient, and reproducible separations. The choices of mobile phase range from single component solvent systems to multiple-component solvent systems with the latter being most common. The majority of TLC applications are normal phase, which is also a complementary feature to HPLC that uses mostly reverse-phase columns. 

AN Explosives Containing Nondetonable Sensitizers. Many substances which are not in themselves expls greatly increase the sensitivity of AN when added to it. To these belong powdered metals (such as flaked Al) and combustible org materials (such as rosin, many metallic resinates, hexamethylenetetramine, many org bases, and paraffin oils and waxes). Usually these AN expls are prepd by coating granules of AN, either alone or mixed with NaCl, with a thin layer of sensitizer. If it is desired to make an expl of exceptional safety, there is employed an amt of sensitizer... 

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