Question

With the aid of clear sketches, highlight two major difference between homogeneous and heterogeneous nucleation.

b) The iron–iron carbide eutectoid reaction is and is fundamental to the development of microstructure in steel alloys. On cooling, austenite, with an intermediate carbon content, transforms to a ferrite phase, having a much lower carbon content, and also cementite, with much higher carbon. Figure 4.1 is a temperature-timetransformation (TTT) diagram for the said process at 675℃.

i. Determine how long it takes for austenite to transform to pearlite at 675℃.

ii. How long would it takes austenite to transform to pearlite at 600℃ and 700℃.

iii. What can you deduce from solution in (i) and (ii) abov

Answer 1

Homogeneous vs Heterogeneous Nucleation DEFINITION More Information Online WWW.DIFFERENCEBETWEEN.COM Homogeneous Nucleation Heterogeneous Nucleation Homogeneous Heterogeneous nucleation is the process nucleation is the process of nucleation that takes of nucleation that takes place away from the place at the surface of the surface of the system. system Homogeneous Heterogeneous nucleation does not nucleation involves involve any nucleation nucleation sites: the site. nucleus grows at the nucleation site. NUCLEATION SITES Slow Fast SPEED NATURE OF NUCLEATION Less common The most common form of nucleation FREE ENERGY BARRIER The free energy barrier for the free energy barrier homogeneous nucleation for heterogeneous is high nucleation is low. SURFACE AREA The surface area that contributes to the growth of the nucleus is high The surface area that contributes to the growth of the nucleus is low.

o Nucleation cluster Vapour molecules New droplet ✓ O O O ОО O ОО O (a) Homogeneous nucleation, (b) heterogeneous nucleation.

For second part please provide the figure 4.1 as mentioned in the question. Without figure the problem can't be answered. So I humbly request you to upload the question with figure so that you can be helped with the answer.

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