Answered

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Fast cooling rates tends to promote transformations that result in relatively course structures (e.g. for a reaction resulting in multiple product phases, the secondary phase particles are (i) fewer in count (ii) larger in size and (iii) relatively spherical). True or False
For most materials, the formation of a glass from a liquid typically requires extremely slow cooling rates, thereby taking on the order of years or even centuries to produce. True or False
For a system below its melting point, a glass (or non-crystalline / amorphous) configuration is the most energetically stable state that is possible, since it offers the lowest Gibbs free energy for all possible solid configurations. True or False
When measured experimentally, most materials tend to exhibit the same exact temperature value for both melting and freezing (crystallization). True or False
Gray iron is a microstructure that tends to result when a cast iron of appropriate composition is cooled fairly quickly. True or False
Coarsening refers to the scenario where, upon heating and/or annealing for sufficient time, the scale of a microstructure tends to reduce (e.g. grains become smaller, secondary phase particles separate into smaller particles and become more finely dispersed, often reverting to high aspect ratio or high surface-area-to-volume ratio configurations. True or False

Sagot :

Answer:

1) correct answer is ii  larger size

2) false, 3) false, 4) true, 5) true, 6) true

Explanation:

In this exercise, the answer is asked if the statement is true.

1) in the rapid cooling speed, there is no thermodynamic equilibrium, so the secondary phases do not have time to transform into the main one, therefore many phases appear in the products,

the correct answer is ii

2) False. The transformation of a material to the glass state requires a fixed temperature and rapid changes to reach this temperature,

3) False. The most stable state is the crystalline state, the glass states are metastable, their Gibbs energy is not the lowest possible and they must transition to the crystalline state over time, it can be years or centuries.

4) True. The melting and freezing temperatures change for each material, within the same material it always has the same value, since it corresponds to a change in the state of the system.

5) true. Cast iron is called gray because of the impurities inside that have not had time to move due to rapid cooling.

6) True. The microstructure is reduced in the process of cooling and heating

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