How does the thermal conductivity of alloys vary with temperature and on what factors does the conductivity of a conductance depend?
Hi,
The following link might be helpful.
Regards,
Simon
https://www.doitpoms.ac.uk/tlplib/thermal_electrical/printall.php
The thermal conductivity, k~dCvl; d – alloy density; C – heat capacity of heat carriers; v – average speed of heat carriers; l is the free path of heat carriers. The dependence of the alloy density and the average speed of heat carriers on temperature is weak.
In alloys, heat is carried mainly by electrons.
At low temperatures – Cе ~ Т and lе ~ const.;
at high temperatures – Cе ~ Т and lе ~ 1/Т.
Therefore, kе(Т) of alloys goes from kе(Т) ~ Т at low temperatures to kе(Т) ~ const. at high temperatures without a maximum at intermediate temperatures.
Thermal Conductivity of Alloys: Temperature Dependence and Factors
The thermal conductivity of alloys, like most materials, generally decreases with increasing temperature. This is because heat transfer primarily occurs through vibrations of atoms and electrons within the material. As temperature rises, these vibrations become more intense, scattering the heat-carrying particles and hindering their efficient movement.
However, the specific relationship between temperature and thermal conductivity can be complex in alloys due to several factors:
- Alloy composition: Different elements have varying thermal conductivities. Adding elements with lower intrinsic conductivity can significantly reduce the overall conductivity of the alloy compared to its pure constituents.
- Microstructure: The arrangement and size of different phases within the alloy can impact heat conduction. For example, dispersed intermetallic compounds can act as scattering centers, further reducing conductivity.
- Processing methods: Manufacturing processes like heat treatment or cold working can alter the microstructure, influencing thermal conductivity.
Here's a breakdown of the factors affecting the thermal conductivity of any material, including alloys:
- Material type: Metals generally have higher thermal conductivity than ceramics or polymers due to their free electrons facilitating heat transfer.
- Crystal structure: Crystalline materials with well-ordered atomic arrangements typically conduct heat better than amorphous materials with disordered structures.
- Presence of impurities and defects: Impurities and defects like vacancies or dislocations can disrupt heat flow, reducing conductivity.
It's important to note that the specific impact of each factor can vary depending on the specific alloy and its intended application. Consulting material property databases or specific technical references for the chosen alloy is crucial for obtaining accurate thermal conductivity values at different temperatures.
Thermal conductivity of the gases and liquids increases with the increase in temperature. Thermal conductivity of the metal decreases with the increase in temperature. In alloys the change in electrical conductivity is usually smaller and thus thermal conductivity increases with temperature, often proportionally to temperature. The coefficient of thermal conductivity depended upon Temperature. It also depends upon the Physical properties of the material such as the nature of the material. Water content also affects the coefficient of thermal conductivity. The pressure of material changes the coefficient of thermal conductivity. In the case of pure metals and alloys, the thermal conductivity predominantly depends on the electronic effect. As temperature increases, both the number of free electrons and lattice vibrations increase. Thus the thermal conductivity of the metal is expected to increase. Thermal conductivity is not only affected by changes in thickness and orientation; temperature also has an effect on the overall magnitude. Because of the material temperature increase, the internal particle velocity increases and so does thermal conductivity. The effect of pressure on thermal conductivity, , is much greater than the effect of temperature. In fact, conductivity decreases with temperature at low pressures and increases with temperature at high pressures, the pressure of reversal being about 0.3 GPa. In pure metals the electrical conductivity decreases with increasing temperature and thus the product of the two, the thermal conductivity, stays approximately constant. However, as temperatures approach absolute zero, the thermal conductivity decreases sharply. Therefore alloy is a metal with addition of some alloy elements such as iron, chromium and aluminum. The addition of alloy elements to pure metals caused additional scattering of the conducting electrons and thus the thermal conductivity is decreased during alloying.
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