I never write comments on TH-cam, but I just cannot not do it here. I am already in Masters studying Materials Science and never have I ever experienced such a fascination with that subject as during your lectures. None of my Professors ever managed to explain everything in such detail and also so simple. It is true what they say: "Only the one who can explain the most difficult things in a simple, understandable way has achieved the true Mastery". Thank you soooo much, Sir. I am a student from Russia now studying in Germany and I am a big fan. Thank you for your work it trully is lifechanging!
Sir, in a book that I am referring(physical metallurgy principles and practices by V. Raghavan, page 15), delta Hf is defined as reversible work done at constant pressure in bringing an atom from inside the crystal to the surface. But, I did not understand what pressure means for solids and even if we define it for solids , why does it remain constant in the process of removal of vacncy . I would also like to add that I am finding these videos very informative and enjoyable an am extremely thankful for the oppurtunity to watch these videos.
You don't have to think in terms of pressure. Work can be done on atom simply in terms of Forcexdisplacement. But I do not know how to do this for this situation. Thus bond breaking approach appareas more convenient to me. If you can share the book I can have a look.
Thank You for your time sir. Yes, I can share the book pdf. May I please know how I can reach you ? Also Sir , in the experimental method for finding fraction of vacancies , I did not understand how it gives us total vacancy fraction after thermal expansion as we actually compute (delta N)/N . How do we account for previous vacancies that contribute to the vacancy fraction in addition to new ones ? Or do we assume there were no vacancies prior to expansion ?
Sir if solid solutions are filled with point defects, can we calculate their solubility limit by the same idea as we used for equilibrium concentration of vacancies? (just a thought)
I think it should be possible and we should be able to get the equation of the solvus line in the phase diagram. Haven't tried it myself. But seems like an interesting idea.
@@rajeshprasadlectures thank you sir for replying to my query. I want to try it after completing the phase diagram lectures. Could you tell me how else can I reach you?
Sir, how does enthalpy increase when the bond is broken. Enthalpy is the sum of internal energy+ product of pressure and volume. So when the bond is broken, energy stored in the form of bonds is lost and thus the internal energy decreases. But you say that enthalpy increases. Can you please clear my doubt Sir?
Good morning sir! and thank you for your great lessons. About the effect of temperature on the vacancy creation. In case of Zinc oxide nanoparticles, it is known that annealing the ZnO in H2 or N2 at higher temperatures (200-300 degree Celcuis) increases the number of oxygen vacancies, now my question is that: if after annealing I use my sample at room temperature, the vacancies created will be still here ? please help me to understand it!
Sir why are vacancies called as thermodynamically stable defects? Only because of they are stable at higher temperatures?? Are line defects also thermodynamically stable?? If not then why?? Thank you
It is applicable to the following process: Crystal with less number of vacancy --> Crystal with higher number of vacancies. The mass is the same before and after the creation additional vacancies as the total number of atoms do not change. The vacancies are not created by the destruction of atoms but only their displacement from a regular site to some other site like free surfaces, grain boundaries, dislocations etc.
@@Riya_njoying Yes mass conservation is again applicable in the sense that total (mass of solvent atoms + total mass interstitial solute atoms) remains the same before and after the diffusion.
Free energy initially decreases with addition of vacancies. But then it reaches a minimum value and subsequently starts to increase. The minimum correspond to the equilibrium number of vacancies.
If the enthalpy of motion of a vacancy is 100 kJ mol-1 , the time that a vacancy takes to jump to an adjacent site at 25° C is about a) 3×10^17 s b) 10^13 s c) 2×10^26 s d) 3×10^4 s Pls solve
It is the Gibbs free energy G as defined in classical thermodynamics by G=H-TS where H is the enthalpy and S is the entropy and T is the absolute temperature. At constant tempearture and pressure a system attains equilibrium by minimizing its Gibbs free energy.
MgO is NaCl structure with Cl at FCC locations and O in OH voids. There is one cation Mg for every anion O. If you add Al2O3 then you are supplying only two cations (Al) but three anions (O). Thus one cation vacancy will be created for every Al2O3 molecule added.
I never write comments on TH-cam, but I just cannot not do it here. I am already in Masters studying Materials Science and never have I ever experienced such a fascination with that subject as during your lectures. None of my Professors ever managed to explain everything in such detail and also so simple. It is true what they say: "Only the one who can explain the most difficult things in a simple, understandable way has achieved the true Mastery". Thank you soooo much, Sir. I am a student from Russia now studying in Germany and I am a big fan.
Thank you for your work it trully is lifechanging!
Ikr! This is poetry!
Helpful video and great thank u...sir
concept clear ho gya sir
These are excellent lectures, your students are very lucky to have you as is IIT.
Thanks for publishing these videos, they are very interesting and stimulating. (I'm watching from Italy)
Thanks for your comment. I have pleasant memories of my one month stay at Trento in 2014.
Rajesh Prasad
Thank you , sir Even my college teachers are not able teach this concept.
Me too
Great video as usual, thank you.
Greetings from Egypt.
hello, Egypt :)
Sir, in a book that I am referring(physical metallurgy principles and practices by V. Raghavan, page 15), delta Hf is defined as reversible work done at constant pressure in bringing an atom from inside the crystal to the surface. But, I did not understand what pressure means for solids and even if we define it for solids , why does it remain constant in the process of removal of vacncy . I would also like to add that I am finding these videos very informative and enjoyable an am extremely thankful for the oppurtunity to watch these videos.
You don't have to think in terms of pressure. Work can be done on atom simply in terms of Forcexdisplacement. But I do not know how to do this for this situation. Thus bond breaking approach appareas more convenient to me. If you can share the book I can have a look.
Thank You for your time sir. Yes, I can share the book pdf. May I please know how I can reach you ? Also Sir , in the experimental method for finding fraction of vacancies , I did not understand how it gives us total vacancy fraction after thermal expansion as we actually compute (delta N)/N . How do we account for previous vacancies that contribute to the vacancy fraction in addition to new ones ? Or do we assume there were no vacancies prior to expansion ?
@@dhruvpendharkar488 I did not mean that you share the pdf. You can just share the name of the author and book and the page number.
@@introductiontomaterialsscience Physical metallurgy principles and practices by V. Raghavan, page 15
22:48 Sir started drinking water? 😂
It was a really good video
y did we take V instead of v in the diff for delta V?
I think its a typo error, I m not sure
Loved how you squeezed in a life lesson along with material science at 0:26
🙂
Sir if solid solutions are filled with point defects, can we calculate their solubility limit by the same idea as we used for equilibrium concentration of vacancies? (just a thought)
I think it should be possible and we should be able to get the equation of the solvus line in the phase diagram. Haven't tried it myself. But seems like an interesting idea.
@@rajeshprasadlectures thank you sir for replying to my query. I want to try it after completing the phase diagram lectures. Could you tell me how else can I reach you?
thanks a lot
Sir, how does enthalpy increase when the bond is broken. Enthalpy is the sum of internal energy+ product of pressure and volume. So when the bond is broken, energy stored in the form of bonds is lost and thus the internal energy decreases. But you say that enthalpy increases.
Can you please clear my doubt Sir?
I think it will not come in competition exam but i watch because i like the great concepts..
I am wonder how (ln N!=0) ?!!!!!!!!!!!
I get different result from my calculator!
lnN!=0 when N=1.....ln1!=ln1=0
How the 4 microstates corresponds to 1 macrostates
Thank you sir
Sir can we consider point defect as a defect which is in thermodynamic equilibrium?
Yes, that is the basis for the calculation of the equilibrium concentration of vacancies.
Good morning sir! and thank you for your great lessons.
About the effect of temperature on the vacancy creation.
In case of Zinc oxide nanoparticles, it is known that annealing the ZnO in H2 or N2 at higher temperatures (200-300 degree Celcuis) increases the number of oxygen vacancies, now my question is that: if after annealing I use my sample at room temperature, the vacancies created will be still here ?
please help me to understand it!
No, on slow cooling vacancy concentration will come back to its equilibrium value at room temperature.
Sir why are vacancies called as thermodynamically stable defects? Only because of they are stable at higher temperatures?? Are line defects also thermodynamically stable?? If not then why??
Thank you
Is Law of Mass conservation applicable for vacancy ?
It is applicable to the following process:
Crystal with less number of vacancy --> Crystal with higher number of vacancies.
The mass is the same before and after the creation additional vacancies as the total number of atoms do not change. The vacancies are not created by the destruction of atoms but only their displacement from a regular site to some other site like free surfaces, grain boundaries, dislocations etc.
@@introductiontomaterialsscience Thank you for the answer. Will it be applicable for interstitial diffusion ?
@@Riya_njoying Yes mass conservation is again applicable in the sense that total (mass of solvent atoms + total mass interstitial solute atoms) remains the same before and after the diffusion.
If crystal with vacancies have lower free energy than pure crystal, then why in the graph the free energy increased with increase in no.of vacancies?
It is because of enthalpy, you have to provide extra energy to break the bond and create vacancy
Free energy initially decreases with addition of vacancies. But then it reaches a minimum value and subsequently starts to increase. The minimum correspond to the equilibrium number of vacancies.
It means in defect no atom loses it unit cell?
Thank you sir!
If the enthalpy of motion of a vacancy is 100 kJ mol-1 , the time that a vacancy takes to jump to an adjacent site at 25° C is about
a) 3×10^17 s
b) 10^13 s
c) 2×10^26 s
d) 3×10^4 s
Pls solve
you got the answer?
@@monishreddy1797 No.. thats why I asked the question
🇧🇩🇧🇩
Thank you sir. If an external "ion" occupies an interstitial site in crystal, can that cause lattice contraction in the crystal?
I think it is possible.
@@introductiontomaterialsscience thank you sir.
what happens once you pass the 'neq' value?
neq is the equilibrium value, i.e., G is minimum at this point. Thus either for n>neq or n
@@introductiontomaterialsscience Sir it means the Gibbs free energy for any crystal can't be more than zero.
Thank you Sir.
Sir , here what is mean by free energy??
It is the Gibbs free energy G as defined in classical thermodynamics by G=H-TS where H is the enthalpy and S is the entropy and T is the absolute temperature. At constant tempearture and pressure a system attains equilibrium by minimizing its Gibbs free energy.
What point defects are possible for Al2O3 as an impurity in MgO? How many Al3+ ions must be added to form each of these defects?
Sir please help me
MgO is NaCl structure with Cl at FCC locations and O in OH voids. There is one cation Mg for every anion O. If you add Al2O3 then you are supplying only two cations (Al) but three anions (O). Thus one cation vacancy will be created for every Al2O3 molecule added.
@@introductiontomaterialsscience thank you sir... 😊