Sir i am a Msc student in Tu Delft (Netherlands) and your videos help me a lot for many different courses. Thank you verymuch i love the way you make concepts easy to understand
sir, such an amazing lecture; I really impressed by your way of presentation. It was too difficult to understand when I was doing Ph.D. Now it is given a great impact to enhance my skill in the research field. Thank you very much for your great lecture.
amazing ! i think a school student would understand such lecture.. i lost my time yesterday trying to understand these concepts during my PhD study this video illustrates everything and answers all of my questions. ThankYou!
Why does a ball of critical radius form in first place since its delta Gf is positive? Why is critical radius not when delta Gf = 0 but when it is maximum?
You have asked a very serious and interesting question. In fact, in this regigon thermodynamics breaks down!! The formation of nuclei can only be explained by statistical fluctuations of atoms which is beyond thermodynamics :-( We are essentially cheating by applying thermodynamics such small systems.
Sir..earlier in the lecture you said if del(G) is negative then the reaction is feasible/spontaneous...but at 19:38 we are seeing if del(G) is increasing or decreasing..that is we are seeing if del(del(G)) is positive or negative..why are we considering that..also at r* del(G) is positive..so reaction should not be spontaneous..shouldn't we be considering the point where del(G) becomes zero..that is the x-intercept of curve..please correct me if iam wrong
This is what is termed as heterogeneous nucleation. If the ferrite nucleus forms inside the austenite grain (homogeneous nucleation) then only new ferrite/austenite interfaces form. This happens also in heterogeneous nucleation of ferrite on austenite/austenite grain boundaries. But in this case original austenite/austenite grain boundaries disappear. This leads to a release in energy making the heterogeneous nucleation favourable.
how can liquid exist below its freezing temperature i mean by that time everything would have been converted solid itself right how will nucleation occur below Tm as what i understood was freezing will occur till complete liquid changes to solid and until then T will remain constant at Tm
What you are stating is the condition of equilibrium solidification where the entire solidification can happen at the melting point. But this requires an extremely slow cooling. If you cool rapidly it is possible to retain liquid, for some time, in metastable state below the meting point before it starts freezing.
Sir, in the previous lecture you said undercooling is Tm - T and in this lecture you wrote undercooling is T - Tm. Is it wrong or both these have same undercooling values ?
sir at 19.26 , why it is not thermodynamically favourible situation ?? and as r less than r* you said thermodynamically growth is not possible and i would like to know the reason from that point of view
Well, the situation of r=r* is critical, that's why it is called the critical radius. If a few atoms join the particle with r=r* it will grow. If few atoms leave it then it will dissolve. So it is in unstable equilibrium.
A million appreciation from South Korea. You have saved my day ! So catchy and enjoyable explanations !
박설bina amazing
Being from South Korea you needed to learn from an Indian teacher ?
I'm surprised
Jinjao
@@zaidpansare4210 😑😑😑
@@zaidpansare4210 bruh😑😑
Sir , ur way of teaching is superb. U have made this subject so interesting.
This was beautiful. Wish we were taught like this the first time round.
Sir i am a Msc student in Tu Delft (Netherlands) and your videos help me a lot for many different courses. Thank you verymuch i love the way you make concepts easy to understand
sir, such an amazing lecture; I really impressed by your way of presentation. It was too difficult to understand when I was doing Ph.D. Now it is given a great impact to enhance my skill in the research field. Thank you very much for your great lecture.
Sir what is the scope of phd in materials in india?
A huge thanks and gratitude!
Thank you Prof. Rajesh Prasad, highly appreciate, your lecture help me understanding nucleation thermodynamically.
Soft words filled with knowledge.
dear Sir.thanks.
splendid lecture sir
Your teaching reminds me of my private college days . It sucks . Thanks Prof .🙏
U are the best teacher ever for material science
Sir, I have one quick question. Why is γ(gamma) always positive? Is it because we use/need energy to create that solid-liquid interface?
thanks sir! for providing such a great lecture
Impressive presentation. Thank you Sir
Respected sir, how does viscosity affect the nucleation rate in pure metal?
Sir, How this is possible for a cylindrical nuclei? It involves critical height and critical radius.
Sir what is the significance of r* ? Does r* say anything about phase transformation time or grain size
Thank you so much sir. clear and detail lecturing.
Love from
Dpt of MSE,Ruet..😷
Very fruitful lecture sir.
Can I get summer internship in IIT Delhi as I'm from NIT Rourkela.
The lower the temperature of solidification the smaller the critical r.
Can anyone tell me it mean we have to give energy to make critical size radius and what type of energy is given
Just Amazing.
Best lecture I have seen so far
Thank you for this explanation.
amazing ! i think a school student would understand such lecture..
i lost my time yesterday trying to understand these concepts during my PhD study
this video illustrates everything and answers all of my questions.
ThankYou!
are you from Turkey ?
Why does a ball of critical radius form in first place since its delta Gf is positive?
Why is critical radius not when delta Gf = 0 but when it is maximum?
You have asked a very serious and interesting question. In fact, in this regigon thermodynamics breaks down!! The formation of nuclei can only be explained by statistical fluctuations of atoms which is beyond thermodynamics :-( We are essentially cheating by applying thermodynamics such small systems.
@@introductiontomaterialsscience Does the result by applying thermodynamics satisfy the result of statistical fluctuations of atom?
super ❤️️
absolutely sensational
AMAZING AMAZING AMAZING...
During the calculation of critical radius, is the temperature supposed to be all converted to kelvins?
Yes, like in any thermodynamic calculations.
sir if radius is just above r* still the term is positive then how does the nucleation start
same doubt
Sir..earlier in the lecture you said if del(G) is negative then the reaction is feasible/spontaneous...but at 19:38 we are seeing if del(G) is increasing or decreasing..that is we are seeing if del(del(G)) is positive or negative..why are we considering that..also at r* del(G) is positive..so reaction should not be spontaneous..shouldn't we be considering the point where del(G) becomes zero..that is the x-intercept of curve..please correct me if iam wrong
Please see my reply to Naga Sai who has also asked the same question.
@@introductiontomaterialsscience thank you sir
why a proeutectoid phase (ferrite or cementite) forms along austenite
grain boundaries
This is what is termed as heterogeneous nucleation. If the ferrite nucleus forms inside the austenite grain (homogeneous nucleation) then only new ferrite/austenite interfaces form. This happens also in heterogeneous nucleation of ferrite on austenite/austenite grain boundaries. But in this case original austenite/austenite grain boundaries disappear. This leads to a release in energy making the heterogeneous nucleation favourable.
👌👌👌👌👌
love from India
Good Evening Sir ,
Sir at 29:39 you told Driving force is inversely proportional to Radius, but will the negative sign will not influence the result
The negative sign in the expression of radius makes it positive because the denominator (Gs-GL) is negative.
how can liquid exist below its freezing temperature i mean by that time everything would have been converted solid itself right how will nucleation occur below Tm as what i understood was freezing will occur till complete liquid changes to solid and until then T will remain constant at Tm
What you are stating is the condition of equilibrium solidification where the entire solidification can happen at the melting point. But this requires an extremely slow cooling. If you cool rapidly it is possible to retain liquid, for some time, in metastable state below the meting point before it starts freezing.
Sir we are converting liquid to solid, so solid is product and in free energy expression, should it be GL - Gs?
We define DG=G_final-G_initial. Thus for L->S it is Gs-GL.
@@introductiontomaterialsscience thanks
Sir, in the previous lecture you said undercooling is Tm - T and in this lecture you wrote undercooling is T - Tm. Is it wrong or both these have same undercooling values ?
Tm-T is correct check It in textbook
yeah, he made a silly mistake in this video. It was correct in the previous one.
He rarely makes mistakes
It's for signing purpose T - Tm
@@ayush7805 he didn't made silly mistake
Make sure uh r perfect 😂😂😂😂
Life saver
sir at 19.26 , why it is not thermodynamically favourible situation ?? and as r less than r* you said thermodynamically growth is not possible and i would like to know the reason from that point of view
Because if you allow a particle with r
Sir in previous lecture you told dT= (Tm- T ). But in this lecture at last you write dT = (T-Tm) why ??
Sorry for the confusion. You can define it in either way. But one has to take care of the sign. So below the melting point, T
@@rajeshprasadlectures thank you so much sir 🙏
Sir, what is mean by undercooling?
I mean what is mean undercooled liquid?
@@rajulinga6298 If a liquid remains as liquid below its equilibrium freezing point it is called an undercooled liquid.
Sir does nucleation will take place if r=r*??
Well, the situation of r=r* is critical, that's why it is called the critical radius. If a few atoms join the particle with r=r* it will grow. If few atoms leave it then it will dissolve. So it is in unstable equilibrium.
@@rajeshprasad101 Thank u so much sir..
@@priyanshusinha1209 I just edited metastable to unstable in my answer.
Thankyou so much sir
sir how to start nucleation????
when temperature is less than Tm certain number of atoms assemble together to form solid mass of radius = critical radius, nucleus form.
thnx sir
If u know telugu , then like ❤️ you made the material science subject easy
watch at 1.25x
5:33 😮
3:13
sir,what is r* here?
How to find it?
r* is the critical radius of the spherical surface which is needed for nucleation
@@pathlavathganesh5055 r*= -2γ/[Gs-Gl] he has derived this expression.
Sir please explain in hindi for..... Weak student
U are the best teacher ever for material science