Chemical impurities

Figure Cl.5.9. Vibrationally resolved dispersed fluorescence spectra of two different single molecules of terrylene in polyetliylene. The excitation wavelengtli for each molecule is indicated and tlie spectra are plotted as the difference between excitation and emitted wavenumber. Each molecule s spectmm was recorded on a CCD detector at two different settings of tire spectrograph grating to examine two different regions of tlie emission spectmm. Type 1 and type 2 spectra were tentatively attributed to terrylene molecules in very different local environments, although tlie possibility tliat type 2 spectra arise from a chemical impurity could not be mled out. Furtlier details are given in Tchenio [105-1071.

Hydraulic hydrated lime is a chemically impure form of lime with hydraiflic properties of varying extent. It contains appreciable amounts of sflica, alumina, and usually some iron, chemically combined with much of the lime. Hydraiflic hydrated lime is employed solely for stmctural purposes. 

For caustic crevice environment, a plant-specific chemical impurity molar ratio <0.5 is defined, eg, Na Cl molar ratio <0.5. ... 

Chemical Analysis. Chemical impurities commonly analyzed include Na20, Fe202, and Si02. The hydroxide is first dissolved in boiling concentrated HQ. Atomic absorption methods have replaced older colorimetric procedures. 

Bulk production of United States Pharmacopeia (USP) and reagent grades is based on the reaction of sodium carbonate or hydroxide with an acidic iodide solution, typically hydriodic acid or a metal iodide. After removal of chemical impurities, the solution is filtered and concentrated. Evaporation gives the anhydrous Nal. Controlled cool-down produces either the dihydrate or the pentahydrate [81626-33-7]. 

The dramatic improvements in the physical and chemical properties of tantalum powder produced by the sodium reduction process are evident in the lessening of chemical impurities (see Table 5). The much-improved chemistry reflects the many modifications to the process put in place after 1990. 

Flaws in the anodic oxide film are usually the primary source of electronic conduction. These flaws are either stmctural or chemical in nature. The stmctural flaws include thermal crystalline oxide, nitrides, carbides, inclusion of foreign phases, and oxide recrystaUi2ed by an appHed electric field. The roughness of the tantalum surface affects the electronic conduction and should be classified as a stmctural flaw (58) the correlation between electronic conduction and roughness, however, was not observed (59). Chemical impurities arise from metals alloyed with the tantalum, inclusions in the oxide of material from the formation electrolyte, and impurities on the surface of the tantalum substrate that are incorporated in the oxide during formation. 

Photoluminescence is a well-established and widely practiced tool for materials analysis. In the context of surface and microanalysis, PL is applied mostly qualitatively or semiquantitatively to exploit the correlation between the structure and composition of a material system and its electronic states and their lifetimes, and to identify the presence and type of trace chemicals, impurities, and defects. 

Process validation should be extended to those steps determined to be critical to the quality and purity of the enantiopure drug. Establishing impurity profiles is an important aspect of process validation. One should consider chemical purity, enantiomeric excess by quantitative assays for impurity profiles, physical characteristics such as particle size, polymorphic forms, moisture and solvent content, and homogeneity. In principle, the SMB process validation should provide conclusive evidence that the levels of contaminants (chemical impurities, enantioenrichment of unwanted enantiomer) is reduced as processing proceeds during the purification process. 

COD Chemical oxygen demand as above, but related to chemical impurities. 

In dry air, a film of zinc oxide is initially formed by the influence of the atmospheric oxygen, but this is soon converted to zinc hydroxide, basic zinc carbonate and other basic salts by water, carbon dioxide and chemical impurities present in the atmosphere. 

In addition to revealing constants, Bjerrum curves are a valuable diagnostic tool that can indicate the presence of chemical impurities and electrode performance problems [165]. Difference curve analysis often provides the needed seed values for refinement of equilibrium constants by mass-balance-based nonlinear least squares [118]. 

Used oil is any oil that has been refined from crude oil or any synthetic oil that has been used and, as a result of such use, is contaminated by physical or chemical impurities. In other words, used oil must meet each of the following three criteria origin, use, and contamination. First, the used oil... 

The composition of the particles is related to that of the source rocks. Quartz sand [composed of silica (silicon dioxide)], which makes up the most common variety of silica sand, is derived from quartz rocks. Pure quartz is usually almost free of impurities and therefore almost colorless (white). The coloration of some silica sand is due to chemical impurities within the structure of the quartz. The common buff, brown, or gray, for example, is caused by small amounts of metallic oxides iron oxide makes the sand buff or brown, whereas manganese dioxide makes it gray. Other minerals that often also occur as sand are calcite, feldspar and obsidian Calcite (composed of calcium carbonate), is generally derived from weathered limestone or broken shells or coral feldspar is an igneous rock of complex composition, and obsidian is a natural glass derived from the lava erupting from volcanoes see Chapter 2. 

Keywords Additives, Chemicals, Impurities, Life cycle assessment (LCA), Paper, Printing industry, Recycling... 

During the last decade large progresses have been performed in the so much difficult art of zeolites synthesis. As a consequence, the amounts of structural defects and chemical impurities have been reduced in zeolite samples (crystallites of larger sizes and well-defined morphology have been synthesized ). At the same time, the zeolite sorption capacities increase. Such an observation is well illustrated by the sorption... 

Effect of Residual Stress, Chemical Impurities and Degradation... 

The achievement of the corresponding monocrystals of sufficient optical and crystalline quality is made possible only after very thorough purification. Chemical impurities are known to disturb the crystal lattice through the occurence of twins, veils dislocations, rounding-off of faces ultimately quenching further growth. Any crystalline defect dramatically increases the residual absorption coefficient and lowers the optical damage threshold. 

There has been an increasing global trend in the wire and cable industry to restrict and remove the presence of lead in materials used for insulation and jacketing applications. The various standards that apply to lead in electrical applications are discussed. One of the issues is how to define the low levels of lead. Many minerals contain trace levels of lead as a chemical impurity. These minerals are used in rubber and plastics and thus the final composition is likely to contain trace amounts of lead. With modem analytical techniques, lead can be found at levels lower than five parts per million. Therefore, to satisfy increasing demands on wire and cable materials, a new series of thermoplastic vulcanisates (TPV) has been introduced that contains no added lead chemicals. These TPV materials have recently been granted a UL listing for flexible cord applications. The properties of these materials are presented and highlighted. 6 refs. 

At point 1, the only form that is supersaturated is Form I, and because supersaturation is a pre-requisite to crystallization it is the only form that could precipitate as a solid phase. If the metastable zone is crossed for Form I before the solubility curve is reached for Form II then Form I will crystallize first and continue to grow unhindered. Unfortunately the width of the metastable zone cannot be predicted theoretically at the present time and is sensitive to physical and chemical impurities and the surface quality of the crystallization vessel. This leads to uncertainty in process scale up. 

Bottle polymer should have a minimum of contaminants, the determination of which is carried out by the same methods as mentioned above for fiber polymers. It should be noted that the quality of the TPA as a starting material has a significant influence on that of the polymer. The color is affected by the content of chemical impurities in the raw material, such as heavy metals, carboxyben-zaldehyde and toluenic acid. 

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