Chemical equilibria thermodynamics passivation

Transport across biological membranes is classified according to the thermodynamics of the process. Passive transport is a thermodynamically downhill process the species move toward the equilibrium. The driving force for the passive transport is the potential difference between the two sides of the membrane. Active transport is a thermodynamically uphill process, it is coupled to a chemical reaction and is driven by it. The following transport mechanisms have been recognized ... 

Popular approaches to molecular self-assembly, which can give structures in the nanometer to millimeter range, are based on SAMs and LBL deposition of electrolytes. Self-assembly leads to equilibrium structures that are close to the thermodynamic minimum and result from multiple weak, reversible interactious betweeu subuuits which include hydrogen bonds, ionic bonds, and van der Waals forces. As information is already coded in the building blocks, this is a means to avoid defect formation in aggregate formation. SAMs are molecular assemblies of long chain alkanes that chemisorb on the patterned and unpat-temed surfaces of appropriate solid materials. The structures of SAMs, effectively 2D-crystals with controllable chemical functionality, make them a means to modify substrates to direct protein adsorption and cell attachment, surface passivation, ultrathin resists and masks and sensor development. 

Here is a solvated ion, e is an electrom, and n represents the ion state of charge. The electrons, liberated by the oxidation, must flow through the material M to be consumed in an appropriate cathodic reaction. Beyond a solubility limit, precipitates of hydroxide or hydrated oxide are formed, and this surface film can provide a barrier to further dissolution. In fact, there are two film formation mechanisms the dissolution-precipitation mechattism addressed before and also the solid-state oxidation proeess M + H2O MO + 2H+ + 2e. Some films are termed passive, for stainless steels or aluminum alloys, for instance. These films can play an important role in environment-sensitive erack mitiation and fracture. Under thermodynamic equilibrium conditions, the film stability may be inferred from E =y(pH) diagrams, where E is the electrical potential related to the chemical free energy G by G = -nEF, and F is Faraday s ntrmber. At eqirilibrium, one can define the electrode potential (related to AG) and the eurrent density 1(1 ... 

The aqueous corrosion and passivation of metal surfaces involve electrochemical processes at the electrode-electrolyte interface. Like for all chemical reactions, the two aspects of equilibrium and kinetics have to be treated. Thermodynamic data give an important first insight into layer formation. They have been used to compose potential-plT diagrams for all elements and thus for all metals [26,27]. In Chapter 1 of this book on the fundamentals of corrosion, passivity of iron has been mentioned and the calculation of some of the lines based on thermodynamic data has been described. Here a more detailed description of foe potential-pH diagrams of iron and copper are presented. 

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