Weathering physical changes

The case of liquids is simpler than weathering in that it is essentially a two agent situation, liquid and temperature. As described in Sections 4.12.3 and 6.6.1, the rate of attack may be governed by the rate of diffusion of the liquid into the material, which may be slow in relation to the time scale of an accelerated test. Also, it is necessary to consider that there may be physical change (swelling) of the polymer as well as chemical degradation. 

In addition to chemical and mineralogical alterations, weathering and soil formation also induce physical changes in the rock. A more or less dense, non-porous, massive rock turns into a porous material containing air and water and thereby becomes suit-... 

From the temporal scale of adverse effects we come to a consideration of recovery. Recovery is the rate and extent of return of a population or community to a condition that existed before the introduction of a stressor. Because ecosystems are dynamic and even under natural conditions are constantly changing in response to changes in the physical environment (weather, natural catastrophes, etc.) or other factors, it is unrealistic to expect that a system will remain static at some level or return to exactly the same state that it was before it was disturbed. Thus the attributes of a recovered system must be carefully defined. Examples might include productivity declines in an eutrophic system, re-establishment of a species at a particular density, species recolonization of a damaged habitat, or the restoration of health of diseased organisms. 

The adverse effects of weather on wood and wood finishes and resultant chemical and physical changes on wood surface will be reviewed and discussed in this work. In addition, recent research findings on surface pretreatment of wood for enhancing durability of applied finishes will be presented. 

FIGURE 27.10 Comparison of n-alkane distribution for the ASMB oil at weathered percentages of 0% and 45%, to illustrate the effects of physical evaporative weathering on the oil chemical composition changes. 

Visual inspections After exposure to outdoor weathering, exposed sample must not show any physical changes (e.g., color bleeding, delamination, crazing, cracking, etc.) when compared with the control sample. 

Sohd ammonium nitrate occurs in five different crystalline forms (19) (Table 6) detectable by time—temperature cooling curves. Because all phase changes involve either shrinkage or expansion of the crystals, there can be a considerable effect on the physical condition of the sohd material. This is particularly tme of the 32.3°C transition point which is so close to normal storage temperature during hot weather. 

Exceptional weathering resistance. Samples exposed in Florida for 10 years showed little change in physical properties. 

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