Desorption of moisture

A linearization of the steady-state concentration gradient could be demonstrated by relating the depth to the weight of the tissue, removed per piece of adhesive tape. However, large errors, especially, within the first tapes, cast doubt over these findings [127, 128], The procedure is time-consuming and artifacts, due to absorption and desorption of moisture, formulation excipients, or sebaceous lipids, are likely. 

The environmental resistance of epoxy composites has come to mean the ability to withstand elevated temperature moisture exposure. Many studies have been completed on these composites 86 89) and the major conclusions were that the epoxy matrix absorbs the major portion of the moisture with the result being a reduction in the epoxy matrix Tg and, therefore, a reduction in the upper operating lim it of the composite. If the absorption and desorption of moisture is done at equilibrium conditions, the plasticization of the matrix is reversible. However, there is usually a significant... 

Another factor that is particularly important in the regeneration of molecular sieve driers is the rate at which the temperature is raised during regeneration. If this is too rapid relative to the rate of moisture removal, one may get rapid desorption of moisture from the initial section of the bed, which is in contact with the hot desorbent gas, followed by condensation of liquid water in the cooler regions some distance from the inlet, with serious consequences for adsorbent life. 

Figure 11 Schematic diagram showing the effect of adsorption/desorption of moisture on a tungsten oxide-tltanla system.

The amount of water adsorbed on a solid decreases as the temperature of the solid increases and generally approaches zero when the solid is heated above 100°C. Adsorption or desorption of moisture usually occurs rapidly, with equilibrium often being reached after 5 or 10 min. The speed of the process is often observable during the weighing of finely divided anhydrous solids, when a continuous increase in mass will occur unless the solid is contained in a tightly stoppered vessel. 

As indicated above, the properties of certain plastics may be temporarily modified by the combination effects of moisture and temperature during the autoclaving cycle. In general, the physical properties of rubber formulations are not affected by the moist heat sterilisation other than the fact that closure systems may absorb moisture (depending on the rubber formulation/ materials employed) during the autoclave cycle. This can be an issue for lyophilised products or aseptically filled dry powders where long drying cycles for the rubber closures are sometimes employed to prevent desorption of moisture from the closure into the product. 

At elevated temperature, graphite can be abrasive rather than lubricating, due to desorption of moisture, unless additives (such as dibasic ammonium phosphate) are incorporated. This abrasiveness appears to be more severe in the case of a silicon nitride counterface. Surface profilometry of the silicon nitride disks in the region of contact showed that the ceramics had been polished and, in some cases, grooves had been worn in the ceramic surfaces. 

Similarity, hair dried with heat exhibit a lower moisture content than hair dried at room temperature [124]. After heat-drying, hair absorbs moisture but does not return to the room temperature dried moisture level until it is either rewet with water or conditioned at a higher relative humidity. Thus, a hysteresis exists between heat-dried hair and room-temperature-dried hair similar to that from absorption versus desorption of moisture. 

The Vtyodak sample was utilized for the oxidation studies. A powdered sample of this coal was placed in the DR cell in the neat form (no supporting matrix medium). The pressure was slowly reduced from atmospheric pressure ( 100 kPa) to 1 Pa followed by a gradual Increase in temperature from 27 C to 191 C in order to follow the desorption of moisture. The sample was then heated to 393 C and oxidized in 2.7 kPa of air for 24 hrs. Spectra were periodically obtained throughout this sequence of events. 

Up to now the interaction in the system LCD, surfactants, water and textiles together with solved and dispersed contaminants has not yet been studied under practical conditions. The influence of surfactants on the equilibrium of water in the system of high pressure without airspace (free water, water in LCD emulsion, water adsorbed on textiles) is not yet known. In order to achieve the removal of polar substances from textiles, in conventional cleaning systems a desorption of moisture from textiles is necessary. If this method is compatible with LCD is not yet known. 

In normal service conditions, exposure to high humidity is intermittent and periods of absorption are followed by periods of desorption of moisture. Whilst only exceptional circumstances will lead to a complete drying out of the joint, it is also true that only continuous immersion in water will lead to complete saturation. Even under conditions of tropical rain-belt climates intact joints will not be saturated throughout. 

Moisture Effects in Tensile Creep— It should be noted that there appears to be much more scatter in the tensile creep than in the flexural creep in Figure 2, but not in Figure 3. The observed variations in tensile creep are associated with absorption and desorption of moisture as the relative humidity in the laboratory experiences seasonal fluctuations. These fluctuations are not observed in the short-time tests because the diffusion kinetics are too slow. The observed fluctuations in compliance correspond to strain fluctuations of 5X10", which is consistent with moisture absorption of 0.22 wt /o, epoxies can be used for vinylesters. 

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