Tham khảo tài liệu 'corrosion of ceramic and composite materials part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 46 Chapter 2 FIGURE Sulfuric acid dew point curves. Reprinted with permission of The Institute of Corrosion United Kingdom. From Ref. . PH2SO4 ATM TABLE Dew Points of Common Constituents of Industrial Flue Gases Species Dew point C SO3 H2O 100-140 HC1 40-50 Copyright 2004 by Marcel Dekker Inc. Fundamentals 47 Ca OH 2 precipitated within the pores of the Ca OH 2 being dissolved. The assumptions of Cussler and Featherstone were that all reactions in the solid were much faster than diffusion so that the reactions reached equilibrium the diffusion coefficients of all species were equal and the porous solid was present in excess. Although these assumptions may yield reasonable first approximations for simple systems they generally do not hold true especially for the more complex type systems often encountered. Another effect of water has been reported in the literature in which the reaction with water resulted in the transformation of a metastable phase to the more stable form. This has been reported by Yoshimura et al. for partially stabilized zirconia PSZ where the reaction with yttria causes the transformation of the metastable tetragonal zirconia to the stable monoclinic form. Similarly the adsorption of water onto the surface of zirconia has been reported by Sato et al. to cause this transformation. Yoshimura et al. concluded that if the reactivity of Y2O3 in YSZ was the same as in Y-PSZ the transformation would not be caused by strain release but by the formation of nucleating defects caused by the chemisorption of water that forms stress concentration sites. One of the more practical problems associated with service life of ceramics is the often observed degradation of mechanical properties attributed to attack by atmospheric water vapor. This is commonly called stress corrosion is time-dependent and is capable of decreasing both Young s modulus and fracture strength . For more information concerning property degradation caused by .
