(Knowledge for Diffusion,Phase diagram,Phase transformation,Corrosion,Oxidation is required)• Define...

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(Knowledge for Diffusion,Phase diagram,Phase transformation,Corrosion,Oxidation is required)• Define steady state diffusion and non-steady state diffusion, respectively, using words, equations or diagrams.• For steady state diffusion, Fick's first law applies, i.e. J --DdCd x Explain the variables and terms in this equation. Why is there a minus sign? What affects D?• For non-steady state diffusion, Fick's second law should be used. One of the analytical solutions corresponding to the following conditions — Att=0,C=CoatOx_03- fort>O,C=Csatx=OandC=C.atx=coiscx -co-1 erd x CS -co "12-Jb7) Plot the composition profiles at t = 0 and t = 11> 0, and annotate the graph.
	
Document Preview: Question 1 (Diffusion)Question 2 (Phase Diagram)Question 3 (Phase Diagram)Question 4 (Phase Transformation)Question 5 (Phase Transformation)Question 6 (Corrosion)Question 7 (Oxidation)

Robert · Accepted Answer

Question 1 (Diffusion)
Solution  
Steady state diffusion: 
In steady state diffusion flux does not depends upon time, and fick’s law holds good for steady state diffusion 
Diffusion flux along the x – direction in steady state diffusion is, 
J = – D dC/dx 
Where dC/dx is  the gradient of the concentration C, and D is the diffusion constant.
Non Steady state diffusion: 
In non steady state diffusion condition diffusion flux depends upon time which means that a type of atoms accumulates 
in a region or that it is depleted from a region. 
For a non steady state diffusion fick’s second law can be written as,,
Fick’s First law for steady state diffusion: 
From the first law diffusion flux along x direction is given by , 
J = – D dC/dx 
Where 
J is the diffusion flux  
dC/dx is the rate of change of concentration 
D is called the diffusion coefficient or diffusivity having units m2/s 
And –ve sign shows that concentration of diffusing species decreases with position. 
D is affected by the concentration of diffusing species and surrounding medium of the system.
Plot of the composition profile for Non Steady state diffusion.
In the above graph it is clearly visible that at  
t = 0 Concentration approaches   
Whereas,  
At t =    
Concentration approaches to a constant value C0
Question 2 (Phase Diagram)
Solution 
Equilibrium in Phase Diagrams: 
Equilibrium diagram defines the region of stability of the phases that can exist in an alloy system under constants 
conditions of pressures. Equilibrium diagrams are presented in the form of a graph plotted temperature versus 
composition of an alloy system. 
When an alloy is cooled very slowly it undergoes a phase change from liquid to solid form. It can be clearly seen from the 
graph that in every phase change temperature drops to a new value. And cooling allows the material to stabilize.  
In the graph shown below red region indicates when system is in liquid state, green region indicates when system cools 
down to solid state. Where the curved region shows the phase change equilibrium between the two states of the 
system.
Phase Diagram for an isomorphous system:
Phase diagram for a eutectic system:
 Data that can be obtained and calculated from phase diagram.

(Knowledge for Diffusion,Phase diagram,Phase transformation,Corrosion,Oxidation is required) • Define steady state diffusion and non-steady state diffusion, respectively, using words, equations or...

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