Weathering surface chemical changes

Surface chemical changes occur very rapidly when wood is exposed to the natural weathering process. Studies on the effect of short periods of weathering before finishing (9, 10) showed that adhesion of both an acrylic latex and an alkyd-oil primer to wood was significantly reduced after the wood substrate had weathered for 4 or more weeks before painting. Reduced paint adhesion and increased failure of the wood-paint interface will inevitably result in poor long-term paint and finish performance. These studies conclude that wood should be protected with a finish that will prevent... 

Weathering produces physical as well as chemical changes. Miniutti, in a series of papers, examined microscopic changes in cell structure of softwood surfaces during weathering and ultraviolet irradiation (21-25). 

The cracks steadily increase in number and size. The chemical changes add to the roughness and soften the surface of the board (9,25). In addition to the minute checks on the surface, most woods soon develop larger and deeper checks or cracks that are easily visible. As the weathering process continues, boards tend to cup, warp, and pull at their fastenings (50. Woods of moderate-to-low density acquire fewer checks than do woods of high density. 

The processes that cause changes to the rocks and minerals of the soil parent material are collectively known as weathering. In the early stages, physical weathering dominates and results in fragmentation of rock, a decrease in particle size, and increase in surface area, but no chemical change. It is brought about by a number of actions ... 

Have surface sediments experienced chemical weathering and, if so, what chemical changes resulted ... 

White A. F., Blum A. E., Schulz M. S., Bullen T. D., Harden J. W., and Peterson M. L. (1996) Chemical weathering rates of a soil chronosequence on granitic alluvium I. Quantification of mineralogical and surface area changes and calculation of primary silicate reaction rates. Geochim. Cosmochim. Acta 60, 2533-2550. 

A more powerful and flexible method, and one that is widely used in watershed weathering studies, relates changes in the chemistry of input-output waters to reactions between the waters and solid phases in the system. This approach, termed chemical mass balance (method (iii)), is considered the best way of making quantitative estimates of rates of elemental transfers in the Earth s surface environment (Clayton, 1979). In method (iii), the hydrochemical method developed by Garrels and Mackenzie (1967), mineralogy and composition of the primary and secondary phases must be well characterized. The composition and volume of the initial water and the final water must be... 

Soils form on the surface of sediments and usually exhibit zones of weathering that reflect changes in the physical and chemical nature of the deposit. There are many different kinds of soils depending on the type of parent material and the conditions of weathering. Soils also vary with temperature, rainfall, and the type of vegetation present. Most soils, however, share common features related to the process of weathering and the solubility of the material. 

The deterioration of mechanical properties is normally assessed by measurements of fracture resistance by pendulum impact test methods or slow speed flexural strength measurements and by ensuring that the surface of the specimens subjected to tensile stresses corresponds to the face exposed to the UV (or weathering) source. These tests are generally more meaningful than nondestructive tests, such as modulus measurements, since the chemical changes and the creation of fine cracks (often invisible to the naked eye) may involve only a very fine layer on the surface of the exposed samples. 

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