Humidity, Water

Composite materials must survive in the environment to which they are subjected at least as well as the conventional materials they replace. Some of the harmful environments encountered include exposure to humidity, water immersion, salt spray, jet fuel, hydraulic fluid, stack gas (includes sulfur dioxide), fire, lightning, and gunfire as well as the combined effects of the space environment. 

The soil atmosphere also contains water vapor and, in most cases, is at 100% relative humidity. Water vapor evaporating from the soil surface is one mechanism by which water and dissolved components can move upward in a soil profile. 

Accelerated weathering is based on using an artificial light source in a cabinet in which the humidity, water spray and temperature can also be controlled. The core feature of an... 

Hanel, G., and B. Zankl, Aerosol Size and Relative Humidity Water Uptake by Mixtures of Salts, Tellus, 31, 478-486 (1979). 

The origin of this absorption may be water molecules with one OH group bonded to the membrane and the second OH group non-H-bonded or water molecules with H-bonds to weak acceptors of the membranes. In both cases the water transport through these membranes may be related to weak H-bonds water-membrane. In addition the spectroscopic observations show in celluloseacetate — or polyimide — membranes are less water molecules of the type of liquid water. In agreement with this observation we have found in model glass membranes with low salt rejection (about 70%) at high relative humidity water spectra not far from the spectra of liquid water. As result of these first experiments we may discuss two possible mechanism of membranes for desalination processes ... 

Under ambient conditions, the atmosphere contains water and organic contamination. Depending on the relative humidity, water can condense around the contact site and result in capillary forces (Fig. 3b). The meniscus curvature varies with the relative vapour pressure and the tip shape [77,78]. For a small spherical tip, the capillary contribution to the adhesion force can be calculated as... 

The vapor pressure of water absorbed on silica gel can be expressed as a function of the vapor pressure of pure water for various gel loadings in spacecraft humidity-water-recovering systems. For the water loading of 0.1 lb water/lb dry silica gel, the following data were obtained ... 

Reduction in the water holding capacity of the corneum can also make the corneocyte proteins brittle and vulnerable to cracking. Keratins in the corneum have a glass transition temperature just below the body temperature28 and this is sensitive to humidity levels. Glass transition temperature is the point below which the material is brittle. As the humidity/water content of the SC decreases, glass transition temperature increases to values above the body temperature thus making the corneocytes brittle at body temperature. 

A gravimetric method is often used for the measurement of water vapor permeability. The water vapor transmission rate (WVTR) according to this method is the amount of water vapor in g that permeates in 24 hours under standard test conditions (temperature, air relative humidity, water vapor sorbant) through aim2 sample surface area. The method measure a flux and not a permeability coefficient. 

Rel. Humid. Water vapour source 94 % Hum. indicator (Veisala)... 

Reduced Smoke. Propellants without metals or primary smoke, but containing oxidizers such as AP which gives HC1 gas as a principal combustion product, are called reduced smoke propellants. If HC1 is exhausted in atmospheres of high or moderate humidity, water droplets will coalesce about the HC1 molecules, resulting in a visible exhaust trail of what is called secondary smoke. In atmospheres of low humidity, the exhaust plume of reduced smoke propellants is not visible. 

Environment effects have been described by Law (1987) in studies of a dual-layer photoreceptor with a squaraine-pigment-based generation layer. Seasonal fluctuations in dark decay and charge acceptance were observed and related to humidity. Water adsorption on the pigment particles was suggested as the underlying cause. 

Key variables temperature, pressure, relative humidity, water vapor mixing ratio, wind speed, wind direction, cloud fraction, stability, PBL height, photolysis rates, and the emission rates of met-dependent primary species (e.g., dust, sea-salt, biogenic aerosol, marine phytoplankton-produced... 

The finish is resistant to humidity, water and steam and also to dry cleaning. It does not, however, resist washing in househod washing machines. 

Fig. 1 schematically describes the important steps in the uptake of water vapor by crystalline water-soluble solids. At low relative humidities, water is adsorbed to... 

At relatively low humidities, water molecules coordinated around adsorbed cations such as Ca and Mg may yield incomplete molecular layers of water (Hendricks et al., 1940 Mering, 1946). 

Chemicals Used in Processing. Water is perhaps the most important chemical used in the textile manufacturing process. It is supplied primarily as high atmospheric humidity, often sprayed into the air to supplement the natural humidity. Water serves to plasticize the hydrophilic fibers and to minimize static electrical effects with the hydrophobic. Humidifying the air has made the expansion of the textile industry in the South possible, and now air conditioning has entirely removed geographical limitations on textile processing. 

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