1) LaNi 5 metal alloys are well known for their ability to reversibly store and

Question

1) LaNi5 metal alloys are well known for their ability to reversibly store and desorb hydrogen at

               temperatures just below atmospheric pressure and at room temperature.

A) (2 pts.) The hydrogen is an example of what kind of defect/dislocation: _________________________-

B) (6 pts.) Use greater than, less than, or equal signs to indicate whether LaNi5 metal or LaNi5Hx metal is

                              going to be superior for each of the following properties (Note the last one is different.):

Yield stress                                       LaNi5     LaNi5Hx

Modulus of elasticity                      LaNi5     LaNi5Hx

Brittleness                                         LaNi5     LaNi5Hx

Ultimate compressive strength      LaNi5     LaNi5Hx

Electrical conductivity                    LaNi5     LaNi5Hx

Brittleness                                        LaNi5     LaNi5Hx

C) (5 pts.) Assume the diffusivity of hydrogen atoms, DH, through LaNi5Hx obeys the relationship below,

that the LaNi5Hx has a crystal diameter of 10-6 m, absorbs hydrogen at 333 K,

and has an activation energy for diffusion of 10000 J/mole. First, estimate the

diffusivity of hydrogen in m2/sec at 333 K.

                              DH = 1 x 10-14 * exp (-Ediff/(8.314*T)), where DH 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 hydrogen to diffuse the length of the diameter of

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

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

part D before finishing this one. Your answer will be > 1 minute.

D) (3 pts.) When Dr. Brenner worked in industry, the civilian application for LaNi5Hx was as a hydrogen storage medium for a hydrogen-driven bus. The biggest problem to overcome was the time necessary to fill the tank. In terms of particle or crystal diameters or other microstructural characteristics, explain how one might modify the LaNi5Hx hydride materials to shorten the time necessary to fill the tank with hydrogen. Hint: There may be an alternate pathway for diffusion.

Explanation / Answer

A). The hydrogen is an example of Ripple-like facile dislocations.

B).  

Yield stress             -                          LaNi5       < LaNi5Hx

Modulus of elasticity      -                LaNi5    > LaNi5Hx

Brittleness                  -                      LaNi5       >    LaNi5Hx

Ultimate compressive strength   -    LaNi5    <    LaNi5Hx

Electrical conductivity             -          LaNi5      <    LaNi5Hx

Brittleness                  -                    LaNi5      >    LaNi5Hx

C). Temperature = 333 K

Activation energy for diffusion, Ediff = 10000 J/mole

Diffusivity is given as,

DH = 1 x 10-14 * exp (-Ediff/(8.314*T))

= 1 x 10-14 * exp ( - 10000 / (8.314*333))

= 1 x 10-14 * exp ( - 10000 / 2768.562)

= 1 x 10-14 * exp (- 3.612)

= 1 x 10-14 * 0.0269

= 2.69 x 10-16 m2/sec

Related Questions

Navigate

• Browse (All)
• Browse 1
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.