Chemical Engineering Question

1) (40 pts. total) Using the Hf-V phase diagram on page 6, if you start with 100 kg of a Hf-V mixture at

2000^oC and 30 wt. % V and cool down very slowly to points A (2000^oC), B (1495^oC,

just above the line), C (1190^oC, just above the line), and D (1000^oC), sketch the microstructure

associated with each letter, determine what phases are present at each letter, determine the

compositions for each phase, and determine the weight in each phase.

 

Point A)  Microstructural drawing    Phase(s) present

 

Weight % of Vanadium in each phase

 

 

 

Weight of each phase

 

 

 

 

 

 

 

 

 

 

 

Point B)  Microstructural drawing    Phase(s) present

 

Weight % of Vanadium in each phase

 

 

 

Weight of each phase

 

 

 

 

 

 

 

 

 

 

 

Point C)  Microstructural drawing    Phase(s) present

 

Weight % of Vanadium in each phase

 

 

 

Weight of each phase

 

Point D)  Microstructural drawing    Phase(s) present

 

Weight % of Vanadium in each phase

 

 

 

Weight of each phase

 

 

 

 

 

 

 

2) Molybdenum carbides are efficient catalysts for taking the nitrogen out of molecules in crude oil as ammonia.  Prior to use as a catalyst, the molybdenum carbide should be reduced using hydrogen.

 

1. A) (2 pts.) List two interstitial elements in the molybdenum carbide catalyst.

 

1. B) (4 pts.) What positions in a Mo carbide catalyst are likely places for reaction to take place? What effect does planar density have on the catalytic reactivity of a material? Where might the molecules stick?

 

 

 

 

 

 

 

1. C) (9 pts.) Assume the diffusivity of carbon atoms through Mo carbide obeys the following relationship,

that the Mo carbon has a crystal diameter of 3 nm and is an active catalyst at 600 K,

and that the activation energy for diffusion is 38000 J/mole.  First, estimate the

diffusivity of carbon in m²/sec.

 

D = 1.4 x 10^-8 * exp (-E_diff/(8.314*T)), where D for carbon is in m²/sec and T is in K.

 

 

 

Then, using the dimensionless group relationship you learned with regard to diffusion, estimate

the amount of time that it would take the carbon to diffuse the length of the diameter of

the crystal, assuming that if the dimensionless group is approximately one, then the

carbon atom had sufficient time to diffuse across the entire diameter of the crystal.

 

 

 

 

 

 

 

 

1. D) (7 pts.) When the interstitial elements interact with Mo carbide, what effect will they have on the melting point, electrical conductivity, ductility, and other mechanical properties (ultimate compressive strength, modulus of elasticity, and yield stress)? Speculate as to what might happen to the particle size of the Mo carbide catalyst particles over time based on one of the boldfaced properties.

 

 

 

 

 

 

 

 

 

 

 

 

1. E) (8 pts.) Sketch stress-strain curves for Mo carbide and Mo metal on the same plot. On EACH curve,

label the following:  ultimate compressive strength  (UCS), yield stress (YS), modulus of

elasticity (E), and rupture stress (RS).  Points will be assigned for getting trends correct.

 

 

 

 

 

 

 

 

 

 

 

1. F) (4 pts.) Properties of materials are also, of course, dependent on how you process them. Use greater

than, less than, or equal signs to indicate whether a material cooled from the liquid

state will have superior properties if cooled quickly or cooled very slowly.

 

Ductility                                                 Cooled quickly     Cooled very slowly

Corrosion resistance                            Cooled quickly     Cooled very slowly

Ultimate compressive strength          Cooled quickly     Cooled very slowly

Melting point                                        Cooled quickly     Cooled very slowly

 

 

3)  (26 pts.) Given the time-temperature transformation diagram on page 6, what would be the phases

present for a 4340 steel with no alloying elements?  Use the bottom of this page

to show any work, including any phase diagram-related calculations (worth 5 pts.).

Presume that the M(90%) line is actually M(100%).

 

1. A) quenched in cold water to 650^oC in 0.1 second, then held at 650^oC for 1000 seconds, then

quenched to room temperature

 

 

 

 

 

1. B) quenched in cold water to 600^oC in 0.1 second, then held at 600^oC for 5 seconds, then

quenched to 350^oC, held at 350^oC for 60 seconds, and finally quenched to room temperature

 

 

 

 

 

1. C) cooled in air at 2^oC/minute to 650^oC, then quenched to room temperature

 

 

 

 

1. D) quenched in cold water directly to room temperature in 0.1 second

 

 

1. E) quenched in cold water directly to room temperature in 0.1 second, then heated to 425^oC and

held there for 1000 seconds, and finally quenched to room temperature

 

 

 

1. F) quenched in cold water to 550^oC in 0.1 second, then held at 550^oC for 5 seconds, then

quenched to room temperature

 

 

 

1. G) quenched in cold water to 380^oC in 0.1 second, then held at 380^oC for 100 seconds, then

quenched to room temperature

 

 

 

 

 

 

Necessary Steel Phase Diagram Calculations (continued on p. 6 if necessary):

 

 

 

 

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