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					RVS                                           Page 1                                   11/20/2012



                             CBE 444/544 REACTOR DESIGN

                                         Homework#3

Problem 1 TiO2 is a wide band gap semiconductor material used in bulk heterojunction solar
cells. Thin film of TiO2 was deposited on a conducting glass (indium tin oxide, ITO) in a CVD
reactor using titanium isopropoxide (TIP). The overall reaction was as follows-

                        Ti(OC3H7)4           TiO2 + 4C3H6 +2H2O

The reaction mechanism was believed to be-

                        TIP (g) + TIP (g)        AI + P(1)
                        AI +S        AI.S
                        AI.S          TiO2 + P(2)

where AI-active intermediate, P(1) reaction products such as C3H6, H2O, and P(2) other reaction
products. Assume that the gas phase reaction of TIP is in equilibrium and derive rate law for the
deposition of TiO2 on ITO.

Problem 2 A powder is to be completely dissolved in an aqueous solution in a large well mixed
tank. An acid must be added to the solution in order to render the spherical particle soluble. The
particles are sufficiently small that they are unaffected by fluid velocity effects in the tank. For
the case of excess acid, Co= 2M, derive an equation for the diameter of the particle as a function
of time when
     (a) mass transfer limits the dissolution: –WA= kc CAo
     (b) reaction limits dissolution: -rA”=krCAo
What is the time for complete dissolution in each case?
De=10-10 m2/s, k=10-18 s-1
Initial diameter = 10-5 m

				
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