1、2OMeOPPlnRTG volume of oxide produced by oxidationP.B.ratiovolume of metal consumed by oxidation 2+-2-2Oxidation partial reaction:MM+2e1Reduction partial reaction:O+2eO2M a r k e r s buriedM+OxideOxide driftOxidee-MetalMetalZone of Metal ConsumptionGasZone of Oxide Zone of Oxide FormationFormation(a
2、)When cations diffuse,the initially formed oxide drifts toward the metal.Metal ConsumptionGasO2-OxideOxide driftOxidee-MetalMetalM a r k e r s remain on surfaceO x i d e O x i d e FormationFormation(b)When anions diffuse,the oxide drifts in the opposite direction.TimeLogarithmicLinearParabolicWeight
3、 gained per unit areaThe parabolic(抛物线抛物线)rate law assumes that the diffusion of metal cations or oxygen anions is the rate controlling step and is derived from Ficks first law of diffusion.The concentrations of diffusing species at the oxide-metal and oxide-gas interfaces are assumed to be constant
4、.The diffusivity of the oxide layer is also assumed to be invariant.This assumption implies that the oxide layer has to be uniform,continuous and of the single phase type.lcontrol the amount of residual hydrogen lControl the amount of hydrogen pickup in processingldevelop alloys with improved resist
5、ance to hydrogen embrittlementldevelop low or no embrittlement plating or coating processeslrestricting the amount of in-situ(in position)hydrogen introduced during the service life of a partlAt elevated temperatures lThe primary effect of hydrogen decarburization,removal of carbon from an alloy.C(F
6、e)+2H2=CH4lresults in a reduction of tensile strength and an increase in ductility and creep rate.llong-term exposure to hydrogen at elevated temperatures steels tend to lose their strength.lHydrogen sulfide may act as an oxidizing agent in the formation of sulfide scales on metal substances at high temperatures.lnickel and nickel-rich alloys are usually rapidly attacked in the present of hydrogen sulfide and other sulfur-bearing gases.lIron-base are often used;chromium additions are in general beneficial.
