Thermal conductivity and diffusivity of carbon-reinforced polyetherketoneketone composites

Heat transfer properties play an important role in processing of polyetherketoneketone (PEKK)/carbon fiber (CF) composites. Accordingly, thermal conductivity and diffusivity of PEKK, PEKK/glassy carbon (GC), and PEKK/CF composites have been studied. Observed increase in conductivity and diffusivity with carbon filler addition was analyzed using the Maxwell–Eucken model. PEKK/GC composites with low carbon fraction indicated good fitting experimental points of the model, indicating good dispersion of particles. For PEKK/CF composites, the thermal conductivity and diffusivity increase is a reflection of a decrease in porosity. Results as observed from the model points to a homogenous dispersion within the PEKK/CF composites as well. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47975.     

Thermal diffusivity of three-dimensional needled C/SiC-TaC composites

Three-dimensional needled carbon fiber reinforced SiC-TaC composites were prepared by combination of slurry infiltration and reactive melt infiltration. The thermal diffusivity of the composites with different TaC contents was characterized in the temperature range from room temperature to 1400 °C. The results revealed that the temperature dependent thermal diffusivity behavior was independent on TaC content, while the thermal diffusivity values of the composites were influenced by their microstructures. A model based on lattice vibration and microstructure was used to discuss the thermal diffusivity behavior of the C/SiC-TaC composites.     

Thermal diffusivity of fiber-reinforced composites using the laser flash technique

The applicability of the flash technique for measuring thermal diffusivity of fiber-reinforced composites has been examined. While the usefulness of this technique has been demonstrated previously for randomly dispersed composites and for layered structures, problems arise from preferential heat paths in fibrous-reinforced composites. For these materials the concept of diffusivity must be expanded to include dependencies upon sample thickness to unit cell ratios and transient times in addition to the usual constituent property ratios and temperature dependencies of properties. Nevertheless, the flash technique has been shown to be a powerful tool for examining heat flow in these materials. It is possible to obtain diffusivity data which are equivalent to steady-state properties. In addition, it is possible to determine in situ properties for the fiber and matrix and to examine defect structures.     

Thermal diffusivity of rubber compounds

Abstract

During the vulcanisation process, rubber compounds are heated to temperatures of ～200°C and then cooled. An increase in temperature occurs in rubber tyres during use as a result of heat produced by repeated deformation. This temperature increase can be so high that it can cause tyre destruction. From this point of view, knowledge of thermal diffusivity data of rubber compounds and reinforced rubber is very important. Despite thermal diffusivity being a crucial value, which determines the rate of heating or cooling of solid bodies, only limited data of this kind are available in the literature for elastomers. A new method, developed especially for determining the thermal diffusivity of thick fibre composite materials and reinforced rubber, has been used to measure the thermal diffusivity of rubber compounds. Both the content and the type of rubber and carbon black determine the thermal diffusivity. The content of other components, however, has a very limited influence on this parameter.     

Thermal diffusivity of 3D C/SiC composites from room temperature to 1400 °C

A 3D C/SiC composite and a bulk CVD SiC material were prepared. The effects of the CVD SiC coating and the heat treatment on the longitudinal and transverse thermal diffusivity of the C/SiC composites were investigated. The thermal diffusivity of the C/SiC composites could be well fitted by a multinomial function from room temperature to 1400 °C which includes a power term, an exponential term and a constant term. The exponential term affected the thermal diffusivity and led to its increase above 1200 °C with activation energy of 77 kcal/mol. The microstructure change in the composites was the reason that the thermal diffusivity was increased above 1200 °C. The longitudinal thermal diffusivity of the composite was twice or more than the transverse one and increased more rapidly by the exponential term. The former was decreased by the CVD SiC coating, but the latter was increased by it. The heat treatment could increase the thermal diffusivity and make the exponential term disappeared in the functions. The functional curve before the treatment intersected that after the treatment at the treatment temperature.     

Thermal diffusivity and conductivity of crystalline polymers

The thermal diffusivity and conductivity of the isotropic and drawn samples of five semicrystalline polymers—nylon 6, poly(ethylene terephthalate), poly(butylene terephthalate), polybutene-1, and poly(4-methylpentene-1)—were measured by the flash method over the temperature range 100–350 K. The temperature dependence of the thermal diffusivity was found to follow a simple phenomenological pattern, while a more detailed understanding of the temperature dependence and the effect of orientation on thermal conductivity was obtained by using the modified Maxwell model.     

Thermal diffusivity of polyolefins by temperature wave analysis

The thermal diffusivities of 25 kinds of polyolefin films, including high‐density polyethylene, low‐density polyethylene, linear low‐density polyethylene, polypropylene, 4‐methylpentene, and ethylene–octene copolymer, were determined by temperature wave analysis in a continuous temperature scan. The thermal diffusivity decreased with increasing temperature, and the temperature dependence was steeper in the solid state than in the melt state. A supercooling phenomenon was observed in the crystallization process during cooling. The thermal diffusivity of polyethylene in the solid state was in a good correlation with the density at room temperature, and a higher temperature coefficient was observed in high‐density polyethylene with a higher thermal diffusivity. The influence of the catalyst system on the thermal diffusivity was also observed in the ethylene–octene copolymer. The thermal diffusivity was sensitive to the precise change in the microstructure of the crystalline polyolefin, which was influenced not only by the chemical structure but also by the thermal history. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1104–1110, 2006     

Thermal diffusivity of polymers by the flash method

We have adopted the flash method to the measurement of thermal diffusivity α of polymers in the temperature range 100–400K. The pulsed radiant energy from a flash tube is applied to the ‘front’ side of a suspended sample disc, and α is deduced from the exponential decay time constant of the subsequent transient temperature difference between the ‘front’ and the ‘back’ side, while correction against radiation loss is made by measuring the much longer decay time of the back-side temperature. Calibration runs on polycarbonate (PC) samples of several thicknesses show that the method is quick, precise and fairly accurate, and the results obtained are in reasonable agreement with previous determinations. We have also carried out measurements on polyoxymethylene (POM), poly (vinylidene fluoride) (PVF₂) and poly (ethylene terephthalate) (PET) and computed their thermal conductivities. Results on POM and PVF₂, which are semicrystalline, are analysed in the framework of several two-phase models, and the effect of crystallization (produced by annealing) on the glass transition behaviour of PET has also been studied.     

Thermal diffusivity in diamond,SiCxNy and BCxNy

Thermal diffusivity (α) of free standing diamond, amorphous silicon carbon nitride (a-SiC_xN_y) and boron carbon nitride (a-BC_xN_y) thin films on crystalline silicon, has been studied using the travelling wave technique. Thermal diffusivity in all of them was found to depend on the microstructure. For a-SiC_xN_y and a-BC_xN_y thin films two distinct regimes of high and low carbon contents were observed in which the microstructure changed considerably and that has a profound effect on the thermal diffusivity. The defective C(sp)N phase plays a key role in determining the film properties.     

Magnetic properties of nanocarbon

Our experimental results provide the evidence that ferromagnetic properties of polymerized fullerenes are of non-trivial origin. Comparison of magnetic measurements, impurity analysis and Raman spectroscopy proves that in certain cases the sample structure affects the magnetic ordering. We provide the explanation of the results obtained of fullerenes within the model of charged fullerenes, where the charge comes from various defects and impurities. It is important that the impurities do not have to be magnetic: even carbon impurity in the all-carbon fullerene network can act as a magnetic trigger.     

Thermal diffusivity characterization of europium zirconate,cerate and hafnate

The following paper presents study on synthesis and thermal diffusivity of europium zirconate, cerate and hafnate as a new types of materials with pyrochlore or fluorite type of lattice, dedicated to replacement of conventional 8YSZ (yttria stabilized zirconia) in TBC (thermal barrier coatings) systems for aircraft gas turbines.All materials were synthesized via solid-state reaction (SSR) preceded preparation of powder mixtures (mechanical milling in ethanol). The feedstock powders were characterized by analysis of crystallite size, particle size distribution and phase composition. On the base of DSC measurements, the parameters of high temperature sintering were selected (1350?°C/2?h/15?MPa). Structural characterization of obtained materials inclusive analysis of morphology, chemical and phase composition of sinters was performed. Thermal diffusivity was measured in temperature range 25÷1400?°C by laser flash analysis (LFA). The obtained materials with pyrochlore and fluorite type of lattice exhibit lower thermal diffusivity compared to that of yttria-stabilized zirconia at high temperatures. In particular, the most promising material in view of insulating properties is Eu₂Ce₂O₇, which exhibit much lower thermal diffusivity than Eu₂Zr₂O₇ and Eu₂Hf₂O₇, especially at temperature higher than 1000?°C. However, in temperature range 25–700?°C, europium hafnate and zirconate exhibit lower thermal diffusivity compared to that of europium cerate and 8YSZ.     

Thermal analysis of elastomer composites

Thermal analysis of polychloroprene elastomer composites was carried out. Addition of reinforcing fillers such as precipitated silica (Vulcasil‐S), carbon black (FEF N‐550), and short silk fiber led to significant changes in the degradation pattern, depending on their reinforcement and adhesion ability with the elastomer matrix. Attempts were made to correlate the variations of thermal properties with the surface chemistry and the reinforcement characteristics of these fillers. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 646–651, 2001     

Thermal diffusivity measurement of papers by an ac Joule heating method

The thermal diffusivity (α) of paper, a porous and thin material, was determined by an ac Joule heating method developed in our laboratory. With this technique the thermal diffusivity of paper was obtained directly with high reproducibility without the need for special preparations, such as the black coating, required in conventional methods. The thermal diffusivity (α) of paper was obtained as a function of temperature and the apparent density (ρ). The apparent thermal conductivity (λ) of paper was calculated from α, ρ, and the heat capacity at constant pressure (C_p): α decreased with increasing apparent density, but λ did not show a density dependence. © 1998 SCI.     

Solubility and diffusivity of CO2 in polypropylene/micro-calcium carbonate composites

This work is aimed at studying the effects of the fillers and interface bonding condition between the fillers and polymer matrix on the solubility and diffusivity of CO₂ in polypropylene (PP)/Micro-calcium carbonate (MicroCaCO₃) composites. The solubility of CO₂ in PP and its composites containing 5% and 10% MicroCaCO₃ was determined precisely by using magnetic suspension balance (MSB) combined with experimental swelling correction at 200 and 220 °C and CO₂ pressures up to 22 MPa. It was found that the solubility of CO₂ in the PP/MicroCaCO₃ composites without the interface compatibilizer increased with increasing the filler content, while the CO₂ solubility remained almost unchanged in PP composites with compatibilizer. The Henry's law and a modified Henry's law were used to well correlate the solubility of CO₂ in the PP composites with and without the interface compatibilizer, respectively. The diffusion coefficient of CO₂ in the PP composites was found to decrease with increasing the filler content. The mutual diffusion coefficients of CO₂ in the PP composites can be correlated within an average relative deviation of 10% by the free volume model proposed by Kulkarni and Stern with a parameter accounting for the barrier effect of the filler.     

Thermal diffusivity of graphite paper and its joint with alumina substrate

Though graphite paper exhibits unique thermal conduction characteristics, a backing layer is needed to provide its structural rigidity. In the present study, the graphite paper is bonded to alumina substrate using an active brazing technique. The thermal diffusivity of graphite paper and of alumina/braze/graphite joint is measured. The thermal diffusivity of the alumina/braze/graphite joint is slightly higher than that of alumina substrate alone, and much higher than that of the graphite paper perpendicular to the planar direction. The high thermal diffusivity of joint can be related to the structure distortion of graphite paper.     

Thermal diffusivity of heteroepitaxial diamond films: Experimental setup and measurements

The thermal diffusivity of heteroepitaxial CVD diamond films grown on iridium buffer layers has been measured using a combined laser flash and converging thermal wave setup. Absolute values and anisotropy for a fiber-textured reference sample were in the range of former reports in the literature. The in-plane thermal conductivity for three heteroepitaxial samples grown on Ir/YSZ/Si(001) as deduced from the diffusivity measurements was around 20 W/cm K, similar to high purity large grain polycrystalline films. Laser flash measurements of the perpendicular diffusivity suggest that the defect rich first microns of the heteroepitaxial films represent a thermal series resistance which limits the perpendicular heat transport especially for thin films. For the parallel component of the diffusivity the contribution of this shunt resistance is negligible. The absolute values for the parallel component in the heteroepitaxial films with in-plane angular spread of the crystal lattice below 0.5° were discussed in the framework of the model proposed by Klemens for phonon scattering by grain boundaries. The present data indicate that the remaining defects in heteroepitaxial diamond films with low mosaic spread are significantly less detrimental for the heat transport than large angle grain boundaries. In addition we speculate that the exclusive deposition on the {100} growth sector may also reduce the influence of nitrogen in the gas phase on the heat transport properties.