Surface composition, weathered

The third complication in assigning surface composition arises from nonstoichiometric dissolution during approach to equilibrium between the solid and solution. This subject is abundantly reported in the geological literature with regard to weathering (50, 55). It appears reasonably correct to conclude that monovalent cations are quickly replaced by hydrogen ion. Bivalent cations are partially lost, probably by ion exchange with H+, particularly if they do not form part of the structural framework of the solid. 

Another environmental factor of prime importance is weathering, i.e. cyclic exposure to water, atmospheric gases, temperature variations, abrasion. These natural processes produce alteration of the surface composition and introduce point defects which have special adsorptive and energetic properties. 

An investigation of the surface composition and chemical state of three naturally weathered arsenopyrite samples exposed for periods ranging from 14 d to 25 yr showed that the arsenopyrite surface has an effective passivating layer that protects the mineral from further oxidation (Nesbitt and Muir, 1998). The same samples were then reacted with mine-waste waters, which caused extensive leaching of the arsenopyrite surface below the oxidized overlayers. The acidic nature of the solution caused dissolution of the previously accumulated ferric arsenite and arsenate salts. 

McFarlane, M.J. (1983b) A low level laterite profile from Uganda and its relevance to the question of parent material influence on the chemical composition of laterites. In Wilson, R.C.L. (Ed.) Residual Deposits Surface Related Weathering Processes and Materials. Special Publication 11, Geological Society of London, pp. 69-76. 

Beusen, J.-M., and R.Gijbels., s. 1983. Alteration in the surface composition of some silicate minerals after hydroitiernalscral treatment, studied by SIMS. p. 257-275. In S.S. Augustithis (ed.) Leaching arddiffusioaoion in rocks and their weathering products. Theophrastus Pub. S.A., Athens. 

Cellulose is more durable than lignin and becomes the main composition on wood surface after weathering, which contributes to the hydroxyl concentration on the surface. When water contacts the weathered wood, a larger amount of interactions between the hydroxyl groups and water would undoubtedly occur. Therefore, weathering definitely increase the wettability of the wood. 

Stark, N.M., Matuana, L.M., Clemons, C.M. Effect of wocesslng method on surface and weathering charactmistics of wood-flour/HDPE composites. J. AppL Polym. Sci. 93(3), 1021-1030 (2004)... 

Surface analyses, such as with X-ray photoelectron spectroscopy (XPS = ESCA), scanning electron microscopy (SEM), and dispersive X-ray analysis (EDX, WDX) are discussed in Section 17.7 because they are used routinely in characterizing vinyl composites. They are also useful in other connections, such as changes to vinyl surfaces from weathering or exposure to aggressive media. Fourier transform infrared (FTIR) analysis is also discussed in Section 17.7. 

Pigments Aftertreatments. The surfaces of pigment particles can have different properties and composition than the particle centers. This disparity can be caused by the absorption of ions during wet milling, eg, the —OH groups, on the surface. In some cases, surfaces are modified intentionaHy to improve the pigments appHcation properties, interaction with the organic matrix, and weather resistance. 

The final composition of stream water is the product of the weathering reactions and related processes outlined above. However, the chemical processes are influenced and controlled by an intricate combination of environmental factors that are characteristic for each drainage system. Therefore, the composition of the bedrock in an area and the residual material left at the surface as soil and subsoil exert a strong influence on the chemical composition of mnoff from the area. The reactions of water with this material are the ultimate geological control and are the source of soluble weathering products. 

Their contribution to the total dissolved load in rivers can be estimated by considering the mean composition of river water and the relative importance of various rocks to weathering. Estimates (18) indicate that evaporites and carbonates contribute approximately 17% and 38%, respectively, of the total dissolved load in the wodd s rivers. The remaining 45% is the result of the weathering of siUcates, underlining the significant role of these minerals in the overall chemical denudation of the earth s surface. 

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