Constitutional supercooling arises from which of the following?

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BlackTom AI · Accepted Answer

To understand constitutional supercooling, we first consider what factors can influence the stability of a supercooled melt during solidification. 
Option 1: temperature effects. Temperature alone can affect how close a liquid is to its equilibrium solidification path, but constitutional supercooling is more specifically tied to how composition gradients interact with solidification front dynamics rather than just the ambient or local temperature gradient. This means temperature effects exist, but they do not alone define constitutional supercooling. 
Option 2: pressure effects. Pressure can alter phase equilibria and melting points in some systems, yet constitutional supercooling is traditionally described in terms of solute redistribution in the liquid ahead of the solidification interface and how that changes the local liquidus relative to the solidification front. Thus, pressure effects are not the primary driver of constitutional supercooling. 
Option 3: compositional effects. This is the core concept: as solidification proceeds, solute rejection or partitioning at the interface creates a local change in composition in the liquid ahead of the interface, which lowers or raises the liquidus locally and can lead to constitutional supercooling if the liquid remains undercooled with respect to the new liquidus. The misalignment between the thermal gradient and the composition-driven liquidus is what promotes instability and constitutional supercooling phenomena. 
Option 4: all of the above. Since the phenomenon is fundamentally about composition-driven undercooling, and temperature and pressure can modulate solidification conditions but are not the defining cause, saying all of the above would overstate the role of temperature or pressure as the primary mechanism. A precise view attributes constitutional supercooling chiefly to compositional effects, with temperature and pressure playing secondary or indirect roles. 
In sum, the decisive mechanism behind constitutional supercooling is the development of composition gradients in the liquid ahead of the solidification front, which alters the local liquidus and can drive instability in the moving interface. Therefore, the most accurate choice centers on compositional effects rather than attributing the phenomenon to temperature or pressure alone.

2251-1_20MTEN6070001 Lecture 21 Pre-Class Reading Quiz

Constitutional supercooling arises from which of the following?

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