Weathering factors

It is primarily for testing materials to be used in products subject to indoor exposure and to sunlight. Exposure in the Fadeometer cannot be related directly to exposure in direct sunlight, partially because other weather factors are always present outdoors. 

This form of approach is probably the only way to deal with multiple agents, for example where contaminants are added to the normal weathering factors of light, heat and water, and it can be extended to include synergistic effects. However, this quickly becomes very complicated and attempts at such analysis are not common. 

In point of fact, when considering the weathering performance of plastic materials, there exists even more interplay between weathering factors than the factors noted above, such as the ambient temperature, temperature of the actual specimens under exposure and the humidity during exposure of the materials. If the... 

There are several accelerated tests which differ in the selection of light source and cyclic exposure to varying degrees of humidity. Some accelerated tests include salt spray, heat, cold, and other weather factors. 

Pesticides and their metabolic products move through treated plants, soil, water, and air primarily by such interrelated weathering factors as rain, wind, and sunlight. An example of this interrelationship of climatic factors and the mode of pesticide movement transfer, transformation, volatilization, and eventual breakdown in our environment is illustrated by Figure 5. 

Weathering Factors. Moisture. One of the principal causes of weathering is frequent exposure of the wood surface to rapid changes in moisture content (J). Rain or dew falling upon unprotected wood is quickly absorbed by capillary action on the surface layer of... 

For instance, a simple unit placed outdoors in a stationary or mobile setting is going to be affected by the weather. Factors such as temperature changes and the rate at which the temperature changes occur can have a marked effect on materials. Some plastics, for example, do well in cold weather and others do not. 

Weather factors are of importance in site selection, site construction and site operation. Preliminary advice on the climatological picture will often point out potential atmospheric pollution hazards and help in making a decision on selecting one particular site out of several. 

Will the seal or gasket be exposed to chemicals, ozone, weather factors, etc. ... 

After the first period s high temperatures and low precipitation, temperatures began to moderate, and rainfall increased over subsequent periods. These weather factors appear to have combined to result in the increased moisture content values following the first period for the first-thinning stand and after the second period for the other two stand types. 

Weathering Factors. The deleterious effect of wood weathering has been ascribed to a complex set of reactions induced by a number of factors (2). The weathering factors responsible for changes in the wood surface are as follows moisture (dew, rain, snow, and humidity), solar radiation (ultra-... 

Fig. 4-2. Agent vaporization increases in proportion to energy sources such as heat from explosive charges or from ambient heat (as measured by air or surface temperatures). Vapor persistence is then determined by weather factors such as wind and humidity. Hydrolysis rates are affected by factors such as temperature and solubility. Agents show characteristic hydrolysis rates in water, and water vapor, as described by humidity, may cause significant hydrolysis of vaporized agent. The vesicant Lewisite, for example, shows relatively rapid hydrolysis in water vapor, while the nerve agent VX is more resistant to hydrolysis.

Weather Factors include rain, wind velocity, wind direction, as well as temperature. For most estimates, assumptions are made that the weather is sunny and the wind is <5 mph. 

Under long-term outdoor exposure, involving frost action and car-bonation, latex-modified mortar shows increased resistance to weathering in comparison with conventional mortar and concrete. The weatherability of the latex-modified mortars is shown in Fig. 4.69The exposure test was done at the Building Research Institute Outdoor Exposure Site in Ibaraki Prefecture, Japan. Except for PVAC-modified mortars, the flexural and compressive strengths of most latex-modified mortars under outdoor exposure conditions tend to become nearly constant at one year or more, and a weatherability factor is greater or similar to that of unmodified mortar. 

Exposure to the outdoor environment affects not only the polymeric material itself but also other components within the matrix, such as dyes, pigments, processing additives, and stabilizers. Complex interactions of the combination of weather factors with the polymer and its components result in irreversible changes in the chemical structures and physical properties in a direction that generally changes both the appearance and mechanical properties and reduces the useful life of the material. Most organic polymeric materials require the use of one or more types of stabilizers for protection against the effects of the environment in order... 

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