Impurities in oxides

The compositions contain no sodium salt for the temperature measurement, because at such a high temperature the Na-D lines caused by impurity in oxidizers appear quite clearly. The position where the temperature was measured, was 10 mm apart from the burning surface along the centre line of the flame.. ... 

The limitations of the EPR technique for characterizing paramagnetic impurities in oxides are well exemplified by the axial iron centre observed in KTaOs [126-128]. This centre is described by 5eff = V2, = 4.33 andgn = 2.02 and the... 

The N, which constitutes 99.6 percent of natural nitrogen, is present as residual nitrogen impurity in oxide fuel of water reactors and fast-breeder reactors, as air dissolved in the coolant of water-cooled reactors, and as residual nitrogen in the graphite of HTGRs. The activation cross section for 2200 m/s neutrons is 1.85 b. 

Tlie zinc reduces the coloured impurities in the aniline and also helps to prevent oxidation of the amine during the reaction. 

Type J thermocouples (Table 11.58) are one of the most common types of industrial thermocouples because of the relatively high Seebeck coefficient and low cost. They are recommended for use in the temperature range from 0 to 760°C (but never above 760°C due to an abrupt magnetic transformation that can cause decalibration even when returned to lower temperatures). Use is permitted in vacuum and in oxidizing, reducing, or inert atmospheres, with the exception of sulfurous atmospheres above 500°C. For extended use above 500°C, heavy-gauge wires are recommended. They are not recommended for subzero temperatures. These thermocouples are subject to poor conformance characteristics because of impurities in the iron. 

The residual current, in turn, has two sources. One source is a faradaic current due to the oxidation or reduction of trace impurities in the sample, i . The other source is the charging current, ich> that is present whenever the working electrode s potential changes. 

Acrolein is produced according to the specifications in Table 3. Acetaldehyde and acetone are the principal carbonyl impurities in freshly distilled acrolein. Acrolein dimer accumulates at 0.50% in 30 days at 25°C. Analysis by two gas chromatographic methods with thermal conductivity detectors can determine all significant impurities in acrolein. The analysis with Porapak Q, 175—300 p.m (50—80 mesh), programmed from 60 to 250°C at 10°C/min, does not separate acetone, propionaldehyde, and propylene oxide from acrolein. These separations are made with 20% Tergitol E-35 on 250—350 p.m (45—60 mesh) Chromosorb W, kept at 40°C until acrolein elutes and then programmed rapidly to 190°C to elute the remaining components. 

Also present are 0.3 wt % mixed metal oxides (R2O2) and 5 ppm of arsenic. Impurities in fluorspar may affect yield, plant operabiUty, or product quaUty. 

Anhydrous FeF is prepared by the action of Hquid or gaseous hydrogen fluoride on anhydrous FeCl (see Iron compounds). FeF is insoluble in alcohol, ether, and ben2ene, and sparingly soluble in anhydrous HF and water. The pH of a saturated solution in water varies between 3.5 and 4.0. Low pH indicates the presence of residual amounts of HF. The light gray color of the material is attributed to iron oxide or free iron impurities in the product. 

Hot Corrosion. Hot corrosion is an accelerated form of oxidation that arises from the presence not only of an oxidizing gas, but also of a molten salt on the component surface. The molten salt interacts with the protective oxide so as to render the oxide nonprotective. Most commonly, hot corrosion is associated with the condensation of a thin molten film of sodium sulfate [7757-82-6], Na2S04, on superaHoys commonly used in components for gas turbines, particularly first-stage turbine blades and vanes. Other examples of hot corrosion have been identified in energy conversion systems, particularly coal gasifiers and direct coal combustors. In these cases the salt originates from alkali impurities in the coal which condense on the internal... 

The term lime also has a broad coimotation and frequently is used in referring to limestone. According to precise definition, lime can only be a burned form quicklime, hydrated lime, or hydraiflic lime. These products are oxides or hydroxides of calcium and magnesium, except hydraiflic types in which the CaO and MgO are chemically combined with impurities. The oxide is converted to a hydroxide by slaking, an exothermic reaction in which the water combines chemically with the lime. These reversible reactions for both high calcium and dolomitic types are Quicklime... 

Amoco Purification Process. The Amoco process is used to purify terephthaHc acid produced by the brornine-promoted air oxidation of Nxylene. The main impurity in the oxidation product is 4-formylbenzoic acid] [619-66-9] and the Amoco process removes this to less than 25 ppm. Metals and colored organic impurities are also almost completely removed by the purification. 

Impurities in isophthahc acid from the oxidation process are analogous to those in terephthahc acid, eg, 3-formylbenzoic acid and y -toluic acid. 

Subsequentiy, the PGM solution is oxidized and acidified to reconvert Ir(III) to Ir(IV). Tri- -octylamine is again used as the extractant, this time to extract iridium. The iridium ia the organic phase is reduced to Ir(III) and recovered. The remaining element is rhodium, which is recovered from impurities in the original solution by conventional precipitation or ion exchange (qv). 

Other by-products include acetone, carbonaceous material, and polymers of propylene. Minor contaminants arise from impurities in the feed. Ethylene and butylenes can form traces of ethyl alcohol and 2-butanol. Small amounts of / -propyl alcohol carried through into the refined isopropyl alcohol can originate from cyclopropane [75-19-4] in the propylene feed. Acetone, an oxidation product, also forms from thermal decomposition of the intermediate sulfate esters, eg. 

Generally, cmde sulfur contains small percentages of carbonaceous matter. The amount of this impurity is usually determined by combustion, which requires an exacting technique. The carbonaceous matter is oxidized to carbon dioxide and water the carbon dioxide is subsequently absorbed (18). Automated, on-stream determination of impurities in molten sulfur has been accompHshed by infrared spectrophotometry (35). 

Analytical Methods. A classical and stiU widely employed analytical method is iodimetric titration. This is suitable for determination of sodium sulfite, for example, in boiler water. Standard potassium iodate—potassium iodide solution is commonly used as the titrant with a starch or starch-substitute indicator. Sodium bisulfite occurring as an impurity in sodium sulfite can be determined by addition of hydrogen peroxide to oxidize the bisulfite to bisulfate, followed by titration with standard sodium hydroxide (279). 

In a patent assigned to Mitsubishi, air oxidation is carried out in the presence of copper salts to avoid the formation of complicating impurities in the oxidation of dihydrovitarnin to vitamin (33). In other work, high yields of vitamin were obtained by performing the oxidation in an alkaU medium (34). High purity vitamin can also be obtained by an oxidation in dimethyl sulfoxide (35). 

It is pmdent to perform zone melting in a dry inert atmosphere. Oxygen causes most organic melts to oxidize slowly. Oxygen and moisture not only oxidize metals and semiconductors, but often enhance sticking to the container. Molten salts attack sUica more rapidly in the presence of moisture. Oxygen and water are considered impurities in some inorganic compounds. 

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