Drying elevated temperature

For more efficient drying at elevated temperatures, the vacuum apparatus (Fig. 48(A)) is often used. The sample to be dried is placed in an inner tube surrounded by a heating jacket. 

Pure holmium has a metallic to bright silver luster. It is relatively soft and malleable, and is stable in dry air at room temperature, but rapidly oxidizes in moist air and at elevated temperatures. The metal has unusual magnetic properties. Few uses have yet been found for the element. The element, as with other rare earths, seems to have a low acute toxic rating. 

Health and Safety Factors. Although butynediol is stable, violent reactions can take place in the presence of certain contaminants, particularly at elevated temperatures. In the presence of certain heavy metal salts, such as mercuric chloride, dry butynediol can decompose violently. Heating with strongly alkaline materials should be avoided. 

Urea.—Forma.IdehydeResins. Cellular urea—formaldehyde resins can be prepared in the following manner an aqueous solution containing surfactant and catalyst is made into a low density, fine-celled foam by dispersing air into it mechanically. A second aqueous solution consisting of partially cured urea—formaldehyde resin is then mixed into the foam by mechanical agitation. The catalyst in the initial foam causes the dispersed resin to cure in the cellular state. The resultant hardened foam is dried at elevated temperatures. Densities as low as 8 kg/m can be obtained by this method (117). 

Shipping and Storage. MaHc acid is shipped in 50-lb, 100-lb, and 25-kg, multiwall paper bags or 100-lb (45.5 kg) fiber dmms. A technical-grade, 50% solution may be shipped in tank cars or tank tmcks. MaHc acid can be stored in dry form without difficulty, although conditions of high humidity and elevated temperatures should be avoided to prevent caking. 

Polymerization. Thermal polymerization or curing of an ink film at elevated temperatures can foUow many different chemical paths. Condensation and cross-linking reactions may be accompHshed with or without the use of catalysts. However, this method of drying generally has not been widely used for printing inks, except those used for metal and glass decoration, and some clear coatings. 

A wide variety of special malts are produced which impart different flavor characteristics to beers. These malts are made from green (malt that has not been dried) or finished malts by roasting at elevated temperatures or by adjusting temperature profiles during kilning. A partial Hst of specialty malts includes standard malts, ie, standard brewers, lager, ale, Vienna, and wheat caramelized malts, ie, Munich, caramel, and dextrine and roasted products, ie, amber, chocolate, black, and roasted barley. 

Waterborne contact adhesives contain an elastomer in latex form, usually an acryflc or neoprene-based latex, and a heat-reactive, cross-linkable phenohc resin in the form of an aqueous dispersion. The phenoHc resin improves metal adhesion, green strength, and peel strength at elevated temperature. A typical formulation contains three parts latex and one part phenohc dispersion (dry weight bases). Although metal oxides may be added, reaction of the oxide with the phenohc resin does not occur readily. 

In dry air at room temperature this reaction is self-limiting, producing a highly impervious film of oxide ca 5 nm in thickness. The film provides both stabihty at ambient temperature and resistance to corrosion by seawater and other aqueous and chemical solutions. Thicker oxide films are formed at elevated temperatures and other conditions of exposure. Molten aluminum is also protected by an oxide film and oxidation of the Hquid proceeds very slowly in the absence of agitation. 

The amphoteric nature of the oxide is illustrated by its abiUty to form siUcates and aluminates in the dry state at elevated temperatures... 

Pyrrohdines also can be obtained by reaction of 1,4-dihydroxyaLkanes with amines in the presence of dehydrating agents at elevated temperatures or by reaction of primary amines with 1,4-dihaloaLkanes. The dry distillation of 1,4-butanediamine dihydrochloride also generates pyrrohdine. Pyrroles can also be catalyticahy hydrogenated to pyrrohdines. 

Fused basic salts and basic oxides react with vitreous siUca at elevated temperatures. Reaction with alkaline-earth oxides takes place at approximately 900°C. Hahdes tend to dissolve vitreous siUca at high temperatures fluorides are the most reactive (95). Dry halogen gases do not react with vitreous siUca below 300°C. Hydrogen fluoride, however, readily attacks vitreous siUca. 

Stability. Ascorbic acid, a white crystalline compound, is very soluble ia water and has a sharp, acidic taste. In solution, the vitamin oxidizes on exposure to air, light, and elevated temperatures. Solutions of ascorbic acid turn yellowish, followed by development of a tan color. Ascorbic acid is stable to air when dry but gradually darkens on exposure to light. 

Diacetone-L-sorbose (DAS) is oxidized at elevated temperatures in dilute sodium hydroxide in the presence of a catalyst (nickel chloride for bleach or palladium on carbon for air) or by electrolytic methods. After completion of the reaction, the mixture is worked up by acidification to 2,3 4,6-bis-0-isoptopyhdene-2-oxo-L-gulonic acid (2,3 4,6-diacetone-2-keto-L-gulonic acid) (DAG), which is isolated through filtration, washing, and drying. With sodium hypochlorite/nickel chloride, the reported DAG yields ate >90% (65). The oxidation with air has been reported, and a practical process was developed with palladium—carbon or platinum—carbon as catalyst (66,67). The electrolytic oxidation with nickel salts as the catalyst has also... 

After curing, the plates are allowed to finish the drying process in ambient or elevated temperature air. The moisture and metallic lead content of the cured plates should be substantially reduced to less than 2%. 

Synthetic resins, such as phenoHc and cresyUc resins (see Phenolic resins), are the most commonly used friction material binders, and are usually modified with drying oils, elastomer, cardanol [37330-39-5] an epoxy, phosphoms- or boron-based compounds, or even combinations of two. They ate prepared by the addition of the appropriate phenol and formaldehyde [50-00-0] in the presence of an acidic or basic catalyst. Polymerization takes place at elevated temperatures. Other resin systems are based on elastomers (see Elastomers, synthetic), drying oils, or combinations of the above or other polymers. 

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