75.Describe techniques to study pitting,crevice corrosion and stress corrosion cracking and evaluate them critically. 79.Temper embrittlement is thought to be associated with the segregation of atomic phosphorous to high angle ferrite grain boundaries,that reflect the position of prior austenite grain boundaries.This occurs at temperatures below 550C. (a)From a thermodynamic (energy)viewpoint what drives the segregation, and how would the equilibrium segregation of P change with a rise in the chemical potential of phosphorous? (b)If a homogeneous sample is quenched from 700C to 480C,what will determine the rate at which the concentration of P at the boundary increases? Be as quantitative as you can,i.e.,an equation would help. (c)Solutes with low solid solubilities in the grains are found to segregate more strongly to the grain boundary than solutes with high solubility. Rationalize this as best you can. 82.Consider vaporization of selenium which forms a gaseous oxide,Se02, when a mixture of oxygen and argon gas flows over the tube,as shown in the figure.Selenium vapor and oxygen can diffuse in each other and react. S。+02→S0 The rate of reaction is given by: Ise To kC2XsXo where r is in moles/unit time/unit volume,and C is the molar density of the mixture. The reaction constant,k,is extremely high at elevated temperature,so that the reaction may be considered instantaneous.Determine expressions for the steady-state Se and 02 gradients in the tube,as well as the rate of Se vaporization. 02+Ar MofE5月
75. Describe techniques to study pitting, crevice corrosion and stress corrosion cracking and evaluate them critically. 79. Temper embrittlement is thought to be associated with the segregation of atomic phosphorous to high angle ferrite grain boundaries, that reflect the position of prior austenite grain boundaries. This occurs at temperatures below 550C. (a) From a thermodynamic (energy) viewpoint what drives the segregation, and how would the equilibrium segregation of P change with a rise in the chemical potential of phosphorous? (b) If a homogeneous sample is quenched from 700C to 480C, what will determine the rate at which the concentration of P at the boundary increases? Be as quantitative as you can, i.e., an equation would help. (c) Solutes with low solid solubilities in the grains are found to segregate more strongly to the grain boundary than solutes with high solubility. Rationalize this as best you can. 82. Consider vaporization of selenium which forms a gaseous oxide, Se02, when a mixture of oxygen and argon gas flows over the tube, as shown in the figure. Selenium vapor and oxygen can diffuse in each other and react. e e 2 2 S O SO + → The rate of reaction is given by: 2 2 2 Se O se O r r kC X X = = where r is in moles/unit time/unit volume, and C is the molar density of the mixture. The reaction constant, k, is extremely high at elevated temperature, so that the reaction may be considered instantaneous. Determine expressions for the steady-state Se and 02 gradients in the tube, as well as the rate of Se vaporization
93. (a)Present graphically solubility product information illustrating the relative strengths of Al and Si as molten steel deoxidizers. (b)With appropriate graphs,show the relative ability of the rare earths to deoxidize and desulfurize molten steel. (c)Explain the difference between dissolved oxygen,combined oxygen,and total oxygen,in the context of steel deoxidation. (d)Very briefly,why is it advantageous to use several deoxidizing agents in combination? 94.A liquid flows upward through a rube,overflows,and then flows downward as a film on the outside. (a)For steady-state laminar flow,develop the pertinent momentum balance that applies to the falling film,neglecting end effects. (b)Develop an expression for the velocity distribution. 97. (a)For small spherical droplets of a pure metal,derive an expression for the variation of equilibrium vapor pressure with radius(r)and surface energy (a).Define all appropriate terms. (b)For a regular binary mixture,AHmixine=a X2 where x,and x2 are the mole fractions of components 1 and 2 and a is a constant for the given binary mixture. (i)Describe the system parameters that determine a. (ii)Derive an expression for the partial molar heat of component 2,H2-H2 (c)Is the regular mixing model of part(b)applicable in the case of H dissolving interstitially in Fe?Explain
93. (a) Present graphically solubility product information illustrating the relative strengths of Al and Si as molten steel deoxidizers. (b) With appropriate graphs, show the relative ability of the rare earths to deoxidize and desulfurize molten steel. (c) Explain the difference between dissolved oxygen, combined oxygen, and total oxygen, in the context of steel deoxidation. (d) Very briefly, why is it advantageous to use several deoxidizing agents in combination? 94. A liquid flows upward through a rube, overflows, and then flows downward as a film on the outside. (a) For steady-state laminar flow, develop the pertinent momentum balance that applies to the falling film, neglecting end effects. (b) Develop an expression for the velocity distribution. 97. (a) For small spherical droplets of a pure metal, derive an expression for the variation of equilibrium vapor pressure with radius (r) and surface energy (a). Define all appropriate terms. (b) For a regular binary mixture, Δ Hmixing = a X1X2 where x, and x2 are the mole fractions of components 1 and 2 and α is a constant for the given binary mixture. (i) Describe the system parameters that determineα . (ii) Derive an expression for the partial molar heat of component 2, H2-H2 0 . (c) Is the regular mixing model of part (b) applicable in the case of _H dissolving interstitially in Fe? Explain
