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3.3 Thermal Characterization
Thermal characterization studies the changes of the properties of materials with
temperature. The changes include both the physical and chemical changes which
take place over a wide range of temperature. Generally, materials particularly nanomaterials are designed to be used under various service conditions such as arctic
cold to tropical heat, in corrosive environments, variable humidity, and under load
(stress), which require different operating temperatures. Therefore, it is important
to characterize these nanomaterials and their behavior over a range of temperatures
to determine their suitability for specific purposes and to determine the appropriate
operating temperature range. The obtained results can then be used to forecast the safe
operating conditions and the expected lifetime for the products. This section presents
four major techniques for thermal characterization of nanomaterials including the
thermal conductivity, thermal gravimetric analysis, differential scanning calorimetry,
and differential thermal analysis.
3.3.1 Thermal Conductivity and Expansion
Thermal conductivity is a temperature-dependent property which measures the
capacity of a material to conduct heat while thermal expansion denotes ability of
materials to change shape upon heating. Therefore, assessing material response
to temperature change is important especially in thermal devices and electronics
where heat conduction, removal, and expansion are important (Asafa et al. 2020a,
b; Durowoju et al. 2019). In electronics, materials with high thermal conductivity
and low coefficient of thermal expansion are needed as heat sinks to dissipate heat
with minimal thermal expansion (Schubert et al. 2007). Generally, the rate of heat
transfer is lower for materials of low thermal conductivity than those of high thermal
conductivity (Huang 2017).
Thermal conductivity of materials can be measured using different approaches
with each method depending on the thermal properties and the medium temperature.
In general, there are two basic techniques of measurement. First is the steady-state
technique where measurement is performed when material that is analyzed is in
complete equilibrium. In as much as there is no temperature change during the
measurement at the various points as the sample is tested, the heat flow through
the section of the sample is the same. Furthermore, the thermal conductivity of the
sample can be estimated from the temperature gradient and heat flux. Second is the
dynamic measurement where the temperature change rate overtime is measured to
obtain the thermal diffusivity (Liu and Chen 2014). Thermal conductivity is derived
based on the specific heat capacity of the material. There are four main types of
instruments available to measure thermal conductivity: guarded hot plate based on
Lee Disk setup, hot wire, modified hot wire, and laser flash diffusivity. They differ in
technique, sample size, testing time, capability, and methodologies of measurement.
Coefficient of thermal expansion (CTE) can be calculated from the linear shrinkage
T. B. Asafa et al.
3.3 Thermal Characterization
Thermal characterization studies the changes of the properties of materials with
temperature. The changes include both the physical and chemical changes which
take place over a wide range of temperature. Generally, materials particularly nanomaterials are designed to be used under various service conditions such as arctic
cold to tropical heat, in corrosive environments, variable humidity, and under load
(stress), which require different operating temperatures. Therefore, it is important
to characterize these nanomaterials and their behavior over a range of temperatures
to determine their suitability for specific purposes and to determine the appropriate
operating temperature range. The obtained results can then be used to forecast the safe
operating conditions and the expected lifetime for the products. This section presents
four major techniques for thermal characterization of nanomaterials including the
thermal conductivity, thermal gravimetric analysis, differential scanning calorimetry,
and differential thermal analysis.
3.3.1 Thermal Conductivity and Expansion
Thermal conductivity is a temperature-dependent property which measures the
capacity of a material to conduct heat while thermal expansion denotes ability of
materials to change shape upon heating. Therefore, assessing material response
to temperature change is important especially in thermal devices and electronics
where heat conduction, removal, and expansion are important (Asafa et al. 2020a,
b; Durowoju et al. 2019). In electronics, materials with high thermal conductivity
and low coefficient of thermal expansion are needed as heat sinks to dissipate heat
with minimal thermal expansion (Schubert et al. 2007). Generally, the rate of heat
transfer is lower for materials of low thermal conductivity than those of high thermal
conductivity (Huang 2017).
Thermal conductivity of materials can be measured using different approaches
with each method depending on the thermal properties and the medium temperature.
In general, there are two basic techniques of measurement. First is the steady-state
technique where measurement is performed when material that is analyzed is in
complete equilibrium. In as much as there is no temperature change during the
measurement at the various points as the sample is tested, the heat flow through
the section of the sample is the same. Furthermore, the thermal conductivity of the
sample can be estimated from the temperature gradient and heat flux. Second is the
dynamic measurement where the temperature change rate overtime is measured to
obtain the thermal diffusivity (Liu and Chen 2014). Thermal conductivity is derived
based on the specific heat capacity of the material. There are four main types of
instruments available to measure thermal conductivity: guarded hot plate based on
Lee Disk setup, hot wire, modified hot wire, and laser flash diffusivity. They differ in
technique, sample size, testing time, capability, and methodologies of measurement.
Coefficient of thermal expansion (CTE) can be calculated from the linear shrinkage