Analytical methods melting analysis

ISO 4621 (1986) also specifies analytical methods. Usually, analysis of chromium and the byproducts is preceded by melting with soda and sodium peroxide. The content of water-soluble or acid-soluble chromium is becoming important from the toxicological and ecological point of view. It is determined according to DIN 53 780 with water, or according to ISO 3856, part 1 with 0.1 mol/L hydrochloric acid. 

The reaction of a-naphthyl isocyanate with alcohols has been reported to be a convenient analytical method for the preparation of solid derivatives [16-18]. In addition, the by-product dinaphthylurea is very insoluble in hot ligroin (b.p. 100°-120°C). The urethanes are readily soluble in hot ligroin, and on cooling the solution they recrystallize to sharp-melting solids. It is recommended that two recrystallizations be performed to obtain substances for analysis. Primary alcohols react well without the need for heating the reaction mixture. Secondary alcohols require additional heat, and the yields of urethane oft are smaller than when primary alcohols are used. Tertiary alcohols other than /-butyl [17] or /-amyl [17] were not able to react under the conditions used. Table V lists some representative alcohols and their a-naphthylurethane derivatives. 

Differential scanning calorimetry (DSC), X-ray diffraction (XRD), and infrared spectroscopy are the common techniques used in the characterization of the structure of the congealed solid. Thermal analytic methods, such as DSC and differential microcalorimetric analysis (DMA), are routinely used to determine the effect of solutes, solvents, and other additives on the thermomechanical properties of polymers such as glass transition temperature (Tg) and melting point. The X-ray diffraction method is used to detect the crystalline structure of solids. The infrared technique is powerful in detecting interactions, such as complexation, reaction, and hydrogen bonding, in both the solid and solution states. 

Thermal analysis involves a set of analytical methods by which a physical property of a sample is measured as a function of temperature (time). The properties that are studied are typically enthalpy (DSC/DTA), dimensions (TMA, dilatometry), visco-elastic properties (DMTA), mass (TG), dielectric properties (DETA) and optical properties (TOA). Reproducible and accurate results are currently available and allow a great number of materials and phenomena involving both physical and chemical aspects to be studied. Thermal transitions of polymers, involving both crystallization/melting and glass formation, are irreversible processes and great care must be taken in the interpretation of the data. 

In plastics analysis, there are a variety of analytical methods for characterization of morphological differences related to degradation of resins from reprocessing. These techniques include FTIR, thermal analysis (TGA, DSC, TMA, DMA), Colorimetric analysis, ESCA or XPS, and GPC. These methods can be laborious and require technical expertise and equipment not always readily available. An imaging method correlated to one of these techniques, especially Melt Flow Index, is extremely useful. Such a method is rapid to obtain by imaging, reduces sample preparation time, and provides a scale of intensities for purposes of correlation. The method is surface sensitive. 

The analytical chemistry of titanium has been reviewed (179—181). Titanium ores can be dissolved by fusion with potassium pyrosulfate, followed by dissolution of the cooled melt in dilute sulfuric acid. For some ores, even if all of the titanium is dissolved, a small amount of residue may still remain. If a hiU analysis is required, the residue may be treated by moistening with sulfuric and hydrofluoric acids and evaporating, to remove siUca, and then fused in a sodium carbonate—borate mixture. Alternatively, fusion in sodium carbonate—borate mixture can be used for ores and a boiling mixture of concentrated sulfuric acid and ammonium sulfate for titanium dioxide pigments. For trace-element deterrninations, the preferred method is dissolution in a mixture of hydrofluoric and hydrochloric acids. 

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