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CORROSION BASIC 2 (Thermodynamics of aqueous corrosion (Free energy change…

- - - - no reaction on Pt
        
        dissolution of Zn
        
        Zn -> Zn+2 + 2e
        
        H2 evolution on Zn
        
        2H+ + 2e -> H2
    - - current flow
        
        dissolution in Zn
        
        evolution of H2 on Pt
- - - - Salt concentration cell
        
        same metal
        
        different concentration
        of solution
        
        current move from metal in
        concentrate to dilute solution
      - Differential aeration cell
        
        same metal
        
        same concentration of solution
        
        current move from metal in
        dilute to concentrate solution
        
        different type gas
- - - - Essential to develop more:
        
        corrosion-resistant materials
        
        improve the method of protection against corrosion
      - Faraday's Law
        
        electrochemical reaction either
        :check:reduce (oxidation) or
        :check:consume electron (reduction)
        
        Measure of reaction rate:
        
        the rate of electron flow to
        Or from a reaction interface
        
        Electron flow is measured as current, I(A)
        
        Mass of metal corroded, m = Ita/nF
        
        Q = charge(Coulomb)
        
        F = Faraday's number
        
        n = number of electrons transferred
        
        m = mass of metal oxidised(corroded)(weight loss)
        
        a = atomic weight of metal(g/mol)
        
        I = current ( A)
        
        t = time (s)
        
        Corrosion rate,
        
        r(mdd : mg/dm^2/day) = m/tA = ia/nF
        
        r (mpy: mills per year) = 0.129ia/nD
        " D : density of the metal (g/cm^3)
      - Influence for corrosion rate:
        
        Electrode potential at anode
        
        Electrode potential at cathode
        
        Presence of passive layer(intermediary
        resistive material)
        
        Areas of electrode surfaces
        
        Temperature