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Determination of the Thermal Conductivity by Means of TCT – Straightforward through Direct Measurement

Introduction

Thermal conductivity can be determined using various methods. One established and recognized method is LFA (Laser Flash Analysis). This primarily determines the Thermal DiffusivityThermal diffusivity (a with the unit mm2/s) is a material-specific property for characterizing unsteady heat conduction. This value describes how quickly a material reacts to a change in temperature.thermal diffusivity, α; then, along with the data for DensityThe mass density is defined as the ratio between mass and volume. density, ρ, and Specific Heat Capacity (cp)Heat capacity is a material-specific physical quantity, determined by the amount of heat supplied to specimen, divided by the resulting temperature increase. The specific heat capacity is related to a unit mass of the specimen.specific heat capacity, Specific Heat Capacity (cp)Heat capacity is a material-specific physical quantity, determined by the amount of heat supplied to specimen, divided by the resulting temperature increase. The specific heat capacity is related to a unit mass of the specimen.cp, it is possible to calculate the Thermal ConductivityThermal conductivity (λ with the unit W/(m•K)) describes the transport of energy – in the form of heat – through a body of mass as the result of a temperature gradient (see fig. 1). According to the second law of thermodynamics, heat always flows in the direction of the lower temperature.thermal conductivity, λ, using Formula 1.

λ = α ∙cp∙ρ (Formula 1)

A total of three measurements of different properties are therefore required to determine the Thermal ConductivityThermal conductivity (λ with the unit W/(m•K)) describes the transport of energy – in the form of heat – through a body of mass as the result of a temperature gradient (see fig. 1). According to the second law of thermodynamics, heat always flows in the direction of the lower temperature.thermal conductivity using LFA. With the TCT 716 Lambda, though, which works according to the GHFM (Guarded Heat Flow Meter) method, the Thermal ConductivityThermal conductivity (λ with the unit W/(m•K)) describes the transport of energy – in the form of heat – through a body of mass as the result of a temperature gradient (see fig. 1). According to the second law of thermodynamics, heat always flows in the direction of the lower temperature.thermal conductivity can be measured directly. This reduces the measurement effort and makes it easy for the user to generate the required measured value.

PEEK (Polyether Ether Ketone)

PEEK (polyether ether ketone) is a high-melting polymer and a high-performance thermoplastic. Due to its excellent resistance, PEEK is often used where it has to withstand high loads under unfavorable thermal and/ or chemical conditions. Examples of applications can be found in the aerospace, medical technology and chemical industries.

Measurement Conditions

The following measurements were carried out on PEEK. All samples were prepared from a larger rod. 

Measurement Results

Figure 1 shows the results for the Thermal ConductivityThermal conductivity (λ with the unit W/(m•K)) describes the transport of energy – in the form of heat – through a body of mass as the result of a temperature gradient (see fig. 1). According to the second law of thermodynamics, heat always flows in the direction of the lower temperature.thermal conductivity of PEEK measured by TCT as a function of temperature. The blue and green dots or diamonds show the results for two PEEK samples on two different TCT instruments from 25°C to a maximum of 250°C. The thermal conductivity tends to increase with increasing temperature. The TCT measurements show a good reproducibility of max. ± 2%. The TCT instruments were calibrated with fused silica for the measurements.

1) Thermal conductivity of two PEEK samples measured with two different TCT 716 Lambda instruments as a function of temperature.

Figure 2 summarizes the results of the TCT and LFA measurements. The orange and yellow crosses represent the results obtained using LFA. For this purpose, the Specific Heat Capacity (cp)Heat capacity is a material-specific physical quantity, determined by the amount of heat supplied to specimen, divided by the resulting temperature increase. The specific heat capacity is related to a unit mass of the specimen.specific heat capacity was determined via DSC, and the DensityThe mass density is defined as the ratio between mass and volume. density was determined at room temperature. The red dots with error bars represent the mean value of all measurements. The results for all tests are within ± 5%.

2) Comparison of the thermal conductivity results for PEEK obtained with the LFA 467 HyperFlash® and TCT 716 Lambda measuring instruments.

Summary

With the TCT 716 Lambda, determination of the thermal conductivity is easy and the measured value can be determined directly. A comparison with other established methods such as LFA shows both good agreement and reproducibility of the measurement results.