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.
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 ?
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.
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.
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
