Absorption of moisture

Pigment used for dry blending is dried overnight at 150°C in a vacuum oven to remove absorbed gases and moisture. It is screened through a 149-p.m (100-mesh) screen directly onto the cubes, which are roUed or tumbled for at least 15 min. The pigmented resin is stored in an airtight container to prevent absorption of moisture. 

Metal Pan Assemblies. These units consist of tiles and panels formed from perforated aluminum or steel with pads of fiber glass or mineral wool inserted into the pans to provide the sound absorption. They are used primarily for ceilings in a similar manner to acoustical tiles and panels. The pads are sometimes sealed in plastic film to prevent absorption of moisture, dirt, and odors. The perforated metal is relatively sound transparent and functions as the finished ceiling and the support for the sound-absorbing material. The perforated metal by itself has no acoustical value. 

Although the above experiments involved exposure to the environment of unbonded surfaees, the same proeess oeeurs for buried interfaces within an adhesive bond. This was first demonstrated by using electrochemical impedance spectroscopy (EIS) on an adhesive-covered FPL aluminum adherend immersed in hot water for several months [46]. EIS, which is commonly used to study paint degradation and substrate corrosion [47,48], showed absorption of moisture by the epoxy adhesive and subsequent hydration of the underlying aluminum oxide after 100 days (Fig. 10). After 175 days, aluminum hydroxide had erupted through the adhesive. 

This action is reversible, so that to maintain the ester value it is obvious that the removal of water is advantageous. As a matter of fact, if transpiration is increased, or the absorption of moisture by the roots is diminished, the esterification is more rapid. 

The electrical resistance of a coating on a pipeline will depend upon the effectiveness of its initial application to the metal and on its condition at the time of testing absorption of moisture may decrease the resistance by as little as 10% during a 2y-year period. The leakage resistance of a given section of pipeline can be determined by the following procedure ... 

An absorbent may also be necessary when the formulation contains a hygroscopic ingredient, especially when absorption of moisture produces a cohesive powder that will not feed properly to the tablet press. In such instances, silicon dioxide has been found to be of particular value. 

An unopened bottle of anhydrous aluminium chloride erupted when the rubber bung with which it was sealed was removed. The accumulation of pressure was attributed to absorption of moisture by the anhydrous chloride before packing (but see comment following text of masthead reference 2). The presence of an adsorbed layer of moisture in the bottle used for packing may have contributed. Reaction with water is violently exothermic [1], The unsuspected presence of 100 kg of the chloride in a vessel led to bursting of a glass vent when the vessel was being flushed with water [2],... 

Addition of water to an intimate mixture of zinc powder and the salts causes spontaneous ignition [1], and a mixture of ammonium nitrate and ammonium chloride (9 1) sprinkled with zinc dust ignites vigorously when moistened [2], Premature spontaneous ignition of the mixture was attributed to absorption of moisture by the hygroscopic salt mixture [3],... 

The absorption of moisture critically affects other important resin properties, particularly those associated with low-dielectric and thermomechanical applications. Results of a 96-h boiling water immersion test are presented in Table 2.2. The moisture absorbed decreased substantially with fluoromethylene chain length from n = 3 to n = 6, followed by only modest decreases for n = 8 and 10. This latter behavior was somewhat unexpected and may be the effect of decreased cross-link density counteracting the increased fluorine content. These 100°C measurements are just above the glass transition and the situation may be different at room temperature. These measurements are in progress. 

Phosphorus(V) oxide is very hygroscopic and the bottle must be closed except when an addition is made. The reactor is cooled with ice water so that the reaction temperature is maintained at 5-10°. Methanol (125 mL)is added drop-wise to the stirred solution to precipitate the crude ammonium tetrametaphos-phate, which is collected by suction filtration, washed with methanol, and dried in vacuum over anhydrous CaS04. The product weighs 33 g and contains about 65% of its phosphorus as tetrametaphosphate. The remainder is a mixture of ortho-, trimeta- and short-chain phosphates. Any lumps are crushed and the crude ammonium tetrametaphosphate is spread in a no. 1 porcelain evaporating dish and heated for 2 hours at 240° in a slow stream,of anhydrous ammonia (about 100 mL/min or 3-5 g/hr). Care is taken to avoid absorption of moisture before or during heating, as this adversely affects the formation of the product. 

The exposure of explosive materials and related parts should be so controlled as to minimize the absorption of moisture from the atmosphere or other sources during handling and batching operations... 

Table A2 (see the appendices) lists briefly the purification methods applicable to many of the solvents listed. It is, however, often advisable to guard solvents, once their bottles have been opened, from the absorption of moisture from the atmosphere, and in the case of basic solvents, also from the absorption of carbon dioxide. If purification is deemed to be necessary and no method is specified in table A2, then usually a method noted for a chemically similar solvent can be employed.

Accdg to Demougin (Ref 2, p 134) the best antiflash ("antilueurs ), arranged in approx order of decreasing effectiveness, are KC1 (preferably paraffined to avoid the absorption of moisture), technical KH hydrate,... 

Ignitable Waste A liquid with a flash point less than 60°C (140°F), a waste which is an oxidizer, or ignitable compressed gas or non-liquid which is liable to cause fires through friction, absorption of moisture, spontaneous chemical changes or when ignited bums so vigorously and persistently as to create a hazard. 

Not every drug product is susceptible to degradation by all of these factors not all drug products are fight sensitive. Not all tablets are subject to loss of quality caused by absorption of moisture. Sensitivity to oxygen is most commonly found with liquid-based dosage forms. Laboratory studies can be used to determine which of these factors actually have an influence on a particular drug product. 

Refs l)Colver(l918),639 2)C.E.Munroe, ChemMetEngrg 26, 541(1922) 3)J-L-Sherick, ArOrdn 24, 329 395(1924) 4)G.W.Jones, ArOrdn 5, 599(1924) 5)D-B.Gawchrop, ArOrdn 6, 47(1925) 6)Cook(l958),29-31 Absorption of Moisture by Explosives, Propellants and Pyrotechnic Compositions. See Hygroscopicity Action of Light on Explosives, etc. See Light, Action on Explosives, etc Aptitude a I inflammation, Es ai. Same as Capability to Inflame Test... 

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