Intercomparison of thermal conductivity and thermal diffusivity methods for plastics

An intercomparison of measurements of the thermal conductivity and thermal diffusivity of two poly(methyl methacrylates) is reported. A wide variety of methods were used: temperature wave analysis, laser flash, transient plane source (Hot Disk^®), transient line-source probe, and heat flux meter methods. Very good agreement of thermal conductivity results and, separately, of thermal diffusivity results was obtained. Similarly, good agreement between thermal conductivity and thermal diffusivity results, when converted using specific heat capacity and density values, was also obtained. Typically, the values were within a range of approximately ±10%. Considering the significant differences between the methods and the requirements on specimen dimensions, the level of agreement between results was considered to be good.     

Effect of some metallic additives (Ag, Cd, and Sn) on thermal transport properties of a-Se

In this study, we have studied the effect of elements Ag, Cd, and Sn as chemical modifiers on some thermal transport properties (thermal conductivity, diffusivity, and specific heat per unit volume) of amorphous Se. Concurrent measurements of thermal transport properties such as effective thermal conductivity (??_e), thermal diffusivity (??_e), and specific heat per unit volume (??C _v) are used at room temperature for twin pellets of pure Se- and Se-based binary Se₉₈M₂ (M?=?Ag, Cd, and Sn) alloys using transient plane source technique. We have also determined the thermal inertia I _T using the experimental values of thermal conductivity and specific heat per unit volume for present amorphous alloys. The increasing sequence of measured thermal transport properties is also discussed.     

Development of a thermal conductivity cell with nanolayer coating for thermal conductivity measurement of fluids

Various techniques and methodologies of thermal conductivity measurement have been based on the determination of the rate of directional heat flow through a material having a unit temperature differential between its opposing faces. The constancy of the rate depends on the material density, its thermal resistance and the heat flow path itself. The last of these variables contributes most significantly to the true value of steady-state axial and radial heat dissipation depending on the magnitude of transient thermal diffusivity along these directions. The transient hot-wire technique is broadly used for absolute measurements of the thermal conductivity of fluids. Refinement of this method has resulted in a capability for accurate and simultaneous measurement of both thermal conductivity and thermal diffusivity together with the determination of the specific heat. However, these measurements, especially those for the thermal diffusivity, may be significantly influenced by fluid radiation. Recently developed corrections have been used to examine this assumption and rectify the influence of even weak fluid radiation. A thermal conductivity cell for measurement of the thermal properties of electrically conducting fluids has been developed and discussed.     

The thermal diffusivity and thermal conductivity coefficient of methanol vapour

The thermal diffusivity of methanol vapour is measured by the thermal lens technique giving values of 0.76, 1.02, 1.70 and 1.78 N s⁻¹ at 321, 341, 377 and 405 K respectively. These thermal diffusivities are shown to be pressure-independent, the pressure dependence of the thermal conductivity merely reflecting the pressure-dependent heat capacity caused by the presence of dimers and tetramers.     

Effect of in and Zn additives on some thermal properties of a-Se

In the present work, the effect of In and Zn on some thermo–physical properties (thermal conductivity, diffusivity and specific heat per unit volume) of amorphous Se (a-Se) have been studied. For this, simultaneous measurements of effective thermal conductivity (λ_e) and effective thermal diffusivity (χ_e) are used at room temperature for twin pellets of Se, Se₉₀In₁₀ and Se₉₀Zn₁₀ alloys using transient plane source (TPS) technique. It has been found that In and Zn additives changes significantly the values of thermo-physical properties (thermal conductivity, diffusivity and specific heat per unit volume) of a-Se studied in the present work. The results have been analyzed in terms of average bond strength and effective molecular weight of the binary alloys.     

Simultaneous photoacoustic measurements of specific heat and thermal conductivity critical behaviour at a smectic A-nematic phase transition

Simultaneous measurements of the thermal conductivity and specific heat at the smectic A-nematic phase transition in 4-n-octyl-4'-cyanobiphenyl (8CB) have been carried out with the photoacoustic technique. A critical increase in the thermal conductivity is reported. A critical decrease in the thermal diffusivity data confirms that the transition in 8CB is fluctuation dominated as also shown by the critical behaviour of the specific heat.     

Analysis of thermal parameters and factors acting on thermal conduction of low‐k films

The thermal properties of a silicon oxide‐based low‐k film and a thermally oxidized silicon film were investigated using the 3‐omega and laser thermo‐reflectance (LTR) methods. Thermal conductivity and effusivity were successfully estimated by the 3‐omega and LTR methods, respectively. It was confirmed that the combination of thermal effusivity and conductivity can successfully provide the heat capacity and thermal diffusivity of the films. The thermal parameters thus obtained suggested that the lower thermal conductivity of the examined low‐k film comes mainly from the rather low level of thermal diffusivity. Based on an analysis of the X‐ray diffraction profiles of the films, it was found that the low thermal diffusivity of the low‐k film can be attributed to the discontinuity of the network structure of their clusters. The heat resistance at the interface between the film and Si substrate was also evaluated. We found that the low‐k film exhibited, interestingly, negative interfacial heat resistance, although interfacial heat resistance should have a positive value in general. In order to determine the origin of the negative interfacial heat resistance, the interface state of the films was analyzed in detail on the basis of X‐ray reflectivity (XRR) measurements. The XRR results showed clearly that a thin, high‐density layer was present at the interface of the low‐k films. This high‐density layer presumably promoted heat flow to the substrate, resulting in the apparent negative interfacial heat resistance. Copyright © 2008 John Wiley & Sons, Ltd.     

Simultaneous photoacoustic measurements of specific heat and thermal conductivity critical behaviour at a smectic A–nematic phase transition

Abstract

Simultaneous measurements of the thermal conductivity and specific heat at the smectic A-nematic phase transition in 4-n-octyl-4′-cyanobiphenyl (8CB) have been carried out with the photoacoustic technique. A critical increase in the thermal conductivity is reported. A critical decrease in the thermal diffusivity data confirms that the transition in 8CB is fluctuation dominated as also shown by the critical behaviour of the specific heat.     

Determinants of thermal conductivity and diffusivity in nanostructural semiconductors

The origin of size effects in the thermal conductivity and diffusivity of nanostructural semiconductors was investigated through the establishment of a unified nanothermodynamic model. The contributions of size-dependent heat capacity and cohesive energy as well as the interface scattering effects were considered during the modeling. The results indicate the following: (1) both the thermal conductivity and diffusivity decrease with decreasing nanocrystal sizes (x) of Si and Si/SiGe nanowires, Si thin films and Si/Ge(SiGe) superlattices, and GaAs/AlAs superlattices when x > 20 nm; (2) the heat transport in semiconductor nanocrystals is determined largely by the increase of the surface (interface)/volume ratio; (3) the interface scattering effect predominates in the reduction of thermal conductivity and diffusivity while the intrinsic size effects on average phonon velocity and phonon mean free path are also critical; (4) the quantum size effect plays a crucial role in the enhancement of the thermal conductivity with a decreasing x (<20 nm). These findings provide new insights into the fundamental understanding of high-performance nanostructural semiconductors toward application in optoelectronic and thermoelectric devices.     

Effect of treatment on the thermal conductivity and thermal diffusivity of oil‐palm‐fiber‐reinforced phenolformaldehyde composites

The thermal conductivity and thermal diffusivity of oil‐palm‐fiber‐reinforced untreated (Sample 1) and differently treated composites were measured with the transient plane source technique at room temperature and under normal pressure. All the composites were 40% oil‐palm fiber by weight. The fibers were treated with alkali (Composite 2), silane (Composite 3), and acetic acid (Composite 4) and reinforced in a phenolformaldehyde matrix. The thermal conductivity and thermal diffusivity of the composites increased after treatment to different extents. The thermal conductivity of the treated fibers as well as of the untreated fibers was calculated theoretically. The model results show that the thermal conductivity of the untreated fiber was smaller than the thermal conductivity of the treated fibers. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 916–921, 2000     

Effect of thermal decomposition processes on the thermal properties of carbon fiber reinforced cement composites in high-temperature range

Thermal conductivity, specific heat capacity, thermal diffusivity and linear thermal expansion coefficient of two types of carbon fiber reinforced cement composites are measured in the temperature range up to 800°C. Thermal conductivity and thermal diffusivity are also determined for the specimens exposed to thermal load up to 800°C before the measurement. Differential thermal analysis (DTA), mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD) are utilized for the assessment of thermal decomposition processes taking place in the high temperature range under consideration. The high temperature thermal properties of the studied materials are found to be positively affected by the application of the high alumina cement and in the case of the Portland cement based composite also by using the autoclaving procedure in the production process. Also, the randomly distributed carbon fibers that can reduce the damage of the pore structure by the thermal decomposition processes are identified as a positive factor in this respect. A comparison of thermal conductivity vs. temperature curves obtained for the specimens pre-heated to different temperatures is found to be a useful tool in the identification of major dynamic effects in the specimens due to the thermal decomposition reactions. The results are in a good agreement with the DTA, MIP, SEM and XRD analyses. The character of the thermal conductivity measurements that in fact includes the effects of convection and radiation into the thermal conductivity coefficient can be beneficial for a simple assessment of the influence of the fire on a dividing structure.     

Thermal decomposition,kinetic study and evolved gas analysis of 1,3,5-triazine-2,4,6-triamine

The thermo-physical properties for four rock types (granite, granodiorite, gabbro, and garnet amphibolite) from room temperature to 1,173 K were investigated. Thermal diffusivity and specific heat capacity were measured using the laser-flash technique and heat flux differential scanning calorimetry, respectively. Combined with the density data, rock thermal conductivities were calculated. Rock thermal diffusivity and conductivity decrease as the temperature increases and approach a constant value at high temperatures. At room temperature, the measured thermal conductivity is consistently near or lower than the calculated conductivity using the mineral series model, which suggests that real thermal conduction is more complicated than is depicted in the model. Therefore, in situ measurement remains the best method for accurately obtaining thermal conductivity for rocks.     

Thermal conductivity measurements using the flash method

Thermal diffusivity is the speed with which heat propagates through a material. It has a multitude of direct applications, such as determining heat transfer through brake pads at the moment of contact, etc., but more often it is used to derive thermal conductivity from the fundamental relationship tying it with specific heat capacity and density. Using a new multi-sample configuration system, and testing a reference sample adjacent to the unknown, specific heat capacity can be obtained parallel with thermal diffusivity. Thus, a single test yields thermal diffusivity and thermal conductivity with prior knowledge of density. The method is fast and produces results with high accuracy and very good repeatability. The sample size, 12 to 30 mm diameter and 2 to 5 mm thickness, is easy to handle and is well suited for a broad range of materials, even for composites, often a problem for other methods. Typical data on two polymers, Pyrex glass and Pyroceram 9606 are presented. This revised version was published online in July 2006 with corrections to the Cover Date.     

Online measurement of thermal diffusivity during cure of an epoxy composite

Thermal diffusivity was measured online during cure of an epoxy composite using a method somewhat similar to the Ångström Method. It is shown that a simple experimental setup can be used, thus avoiding expensive instrumentation. The experimental instrumentation is explained in detail. The measurements show an increase of thermal diffusivity during the cure of composite material. Using modulated differential scanning calorimetry (MDSC), heat capacity was measured online during the cure of an epoxy composite. Combining thermal diffusivity measurements with MDSC measurements, the thermal conductivity was found to change during the cure process, similar to the measurements of heat capacity. These changes are referred to vitrification at the end of the cure process.     

Thermal conductivity and thermal diffusivity of poly(acrylic acid) by transient hot wire technique

The paper describes a new transient hot wire instrument which employs 25.4 μm diameter tantalum wire with an insulating tantalum pentoxide coating. This hot-wire cell with a thin insulating layer is suitable for measurement of the thermal conductivity and the thermal diffusivity of electrically conducting and polar liquids. This instrument has been used for experimental measurement of the thermal conductivity and the thermal diffusivity of poly(acrylic acid) solution (50 mass%) in the temperature range of 299 to 368 K at atmospheric pressure. The thermal conductivity data is estimated to be accurate within ±4%. Thermal diffusivity measurements have a much higher uncertainty (±30%) and need further refinement.     

Photoacoustic infrared spectroscopy and thermophysical properties of syncrude cokes

This paper presents and interprets photoacoustic (PA) infrared spectra and four different thermophysical properties (thermal conductivity, thermal diffusivity, volumetric specific heat and thermal effusivity) for four sets of hydrocarbon cokes. A total of 12 samples, with varying histories, were analyzed. These cokes are a by-product of the upgrading of bitumen to Syncrude Sweet Blend (a blend of hydrotreated components), and were obtained from several locations in the thermal cokers operated by Syncrude Canada Ltd. in Fort McMurray, Alberta, Canada. PA infrared spectroscopy provides detailed information on the amount and type of residual aromatic hydrocarbons in cokes; aliphatic hydrocarbons are sometimes detected in smaller quantities. Three of the thermophysical properties (thermal conductivity, diffusivity and effusivity) display systematic differences among the cokes. On the other hand, volumetric specific heat hardly varies, a phenomenon that accounts for the observed proportionality between thermal diffusivity and conductivity. Analogous relationships exist between thermal effusivity and both thermal conductivity and thermal diffusivity for these cokes. The magnitudes of these three thermophysical properties tend to increase as aromatics contents, determined by PA spectroscopy, decrease.This revised version was published online in November 2005 with corrections to the Cover Date.     

Effect of sulphur on both thermal and dielectric properties of pre-compressed FEF black-loaded SBR vulcanizates

The thermal properties (thermal conductivity λ, thermal diffusivity a, and specific heat C_p) as well as the dielectric constant ε′ and dielectric loss ε′ of conductive styrene butadiene rubber loaded with different concentrations of sulphur were measured. It was found that both λ and C_p increase gradually at around 1 phr of sulphur content. Meanwhile, the dielectric constant ε′, showed a pronounced peak at 2 phr of sulphur content. Moreover, the effect of hydrostatic pressure on the dielectric constant ε′ and dielectric loss ε′ was found to rise with pre-compression.     

Study of temperature profile and specific heat capacity in temperature modulated DSC with a low sample heat diffusivity

One important application of temperature modulated DSC (TMDSC) is the measurement of specific heat of materials. When the sample has very good thermal conductivity as in the case of metals, the temperature gradient is not normally an important factor and can be ignored most of the time. However, in the case of materials with poor heat transfer properties, for example, polymers, the thermal conductivity is only in the order of 1/1000 or so of that of metals. This could have a major effect on the test results. In this paper, a round analytical solution is given and a numerical model is used to analyze the effects of thermal diffusivity on temperature distribution inside the test sample and specific heat measurement by TMDSC, PET sample test results are presented to demonstrate the effects of material thermal diffusivity.     

Thermal diffusivity and thermal conductivity studies on the zirconate,cerate and uranate of barium

The thermal diffusivity and thermal conductivity of the zirconate, cerate and uranate of barium were investigated by employing the laser flash technique. The variation in the thermal resistivity as a function of temperature was examined and the heat transport behaviour of these materials is discussed.