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Chapter 19: Problem 16

Briefly explain why the thermal conductivities are higher for crystalline than noncrystalline ceramics.

Short Answer

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Question: Explain the difference in thermal conductivities between crystalline and noncrystalline ceramics. Answer: The difference in thermal conductivities between crystalline and noncrystalline ceramics can be attributed to their distinct atomic structures and the behavior of their atomic vibrations. Crystalline ceramics have a highly ordered atomic structure, which facilitates efficient phonon propagation and has fewer defects, resulting in higher thermal conductivities. In contrast, noncrystalline ceramics have a more random atomic arrangement that hinders heat transfer and possesses more defects, leading to lower thermal conductivities.

Step by step solution

01

Understanding Thermal Conductivity

Thermal conductivity is a material property that describes the ability of a substance to conduct heat. It depends on factors such as the structure of the material, the presence of defects, and the nature of atomic vibrations.
02

Crystalline vs. Noncrystalline Ceramics: Structural Differences

Crystalline ceramics have a well-ordered and long-range atomic structure, whereas noncrystalline ceramics, also called amorphous ceramics or glasses, have a more random and short-range atomic structure. The arrangement of atoms in crystalline ceramics facilitates the transfer of heat, while the disordered structure of noncrystalline ceramics hinders it.
03

Atomic Vibrations and Phonons

Atoms in materials are in constant vibrational motion. In crystalline materials, these vibrations are more ordered and can be described as a collective motion of atoms called phonons. Phonons are the primary carriers of heat in crystalline materials, and the more ordered vibrations in crystalline ceramics allow phonons to travel long distances without interruption, resulting in high thermal conductivity.
04

Defects and Scattering of Phonons

The presence of defects in a material can hinder the propagation of phonons and reduce the material's thermal conductivity. Crystalline ceramics have fewer defects compared to noncrystalline ceramics due to their ordered structure. Fewer defects mean fewer obstacles for phonons to encounter, allowing them to travel longer distances and contribute to increased thermal conductivity in crystalline ceramics.
05

Conclusion: Why Crystalline Ceramics have Higher Thermal Conductivities

Crystalline ceramics have higher thermal conductivities compared to noncrystalline ceramics because of their highly ordered atomic structure, which allows for more efficient phonon propagation and fewer obstacles in the form of structural defects. The more random atomic arrangement in noncrystalline ceramics hinders the transfer of heat, resulting in lower thermal conductivities.

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Most popular questions from this chapter

(a) Briefly explain why \(C_{v}\) rises with increasing temperature at temperatures near \(0 \mathrm{~K}\). (b) Briefly explain why \(C_{v}\) becomes virtually independent of temperature at temperatures far removed from \(0 \mathrm{~K}\).

For some ceramic materials, why does the thermal conductivity first decrease and then increase with rising temperature?

(a) Briefly explain why thermal stresses may be introduced into a structure by rapid heating or cooling. (b) For cooling, what is the nature of the surface stresses? (c) For heating, what is the nature of the surface stresses?

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For aluminum, the heat capacity at constant volume \(C_{v}\) at \(30 \mathrm{~K}\) is \(0.81 \mathrm{~J} / \mathrm{mol} \cdot \mathrm{K}\), and the Debye temperature is \(375 \mathrm{~K}\). Estimate the specific heat (a) at \(50 \mathrm{~K}\) and (b) at \(425 \mathrm{~K}\).
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