Thermal Properties Of Materials Research Articles

Effective thermal diffusivity and conductivity of a fluid-saturated solid foam

The thermal properties of composite materials, such as fluid-saturated solid foams, can be estimated in two ways: using equivalent models based on both the thermal properties of the liquid and solid phases or by direct measurements, which, however, are not always straightforward. In this paper, we provide a new experimental device based on the four-layer (4L) method to measure the effective thermal diffusivity of a solid foam filled with different fluids (glycerol and water). The specific heat of the solid part is measured using differential scanning calorimetry, and the volumetric heat capacity of the composite system is estimated using an additive law. The effective thermal conductivity deduced from experiments is then compared with the maximum and minimum values obtained from the parallel and series equivalent models. The proposed 4L method is first validated by measuring the thermal diffusivity of pure water and then used afterward to measure the effective thermal diffusivity of the fluid-saturated foam. Experimental results converge with those obtained from equivalent models in the case where the different components of the system have similar thermal conductivities (e.g., glycerol-saturated foam). On the other hand, when the liquid and solid phases have very different thermal properties (e.g., water-saturated foam), the experimental results differ from what equivalent models predict. This highlights the need to make appropriate experimental measurements to estimate the overall thermal properties of these latter multicomponent systems or to consider more realistic equivalent models.

Prospective of functionalized graphene as shape memory and self-healing polymer: A review

Polymer matrix composites despite having potential as high-performance smart materials face challenges in various sectors including infrastructure, biomedical and automotive due to their lower strength and stiffness. The incorporation of graphene into the polymer matrix has shown significant improvement in mechanical, thermal and other material properties. Furthermore, due to certain shortcomings of graphene such as agglomeration and poor transfer of properties, functionalization of graphene has revolutionised the research field. It also exhibits futuristic applications as filler in stimuli-responsive smart materials. The prospective of functionalized graphene's potentiality as shape memory and self-healing polymers and their realistic applications in various areas have been discussed.

Thermal contact conductance between additively manufactured carbon fiber reinforced thermoplastic composite: An experimental study

As the additive manufacturing provides an advanced method for fabricating polymeric composite components in thermal engineering applications, the thermal contact conductance (TCC) between the contact composites can become an important problem. In order to understand the interfacial heat transfer mechanism between thermoplastic composites, TCC between additively manufactured carbon fiber reinforced polyamide 12 (CF/PA12) composites was experimentally studied with steady-state measurements in this work. By considering the material surface microstructure, thermal and mechanical properties, the effects of interface temperature, contact pressure, surface morphology, carbon fiber (CF) content and orientation in composites on TCC were analyzed. The results show that the TCC is dependent on the actual contact area and the thermal conduction path inside the material. In general, high surface roughness decreases the TCC because of the reduction of contact area; while it is the opposite of temperature and pressure. The CF distribution affects the internal thermal conduction path and surface roughness, leading to the variations in TCC.

Thermal contact resistance measurement between two intersecting PAN type carbon fibers using the T-type 3ω method

The prediction of the effective thermal conductivity of composites filled with carbon fibers requires the knowledge of the microstructure, the relative amount and thermal properties of filler and matrix materials, the orientation of non-isometric filler phases and the thermal contact resistances between fibers and matrix and also between fibers. However, information at small scale are often missing especially thermal contact resistances. The present work describes the measurement of the thermal contact resistance (TCR) between two crossed carbon fibers which is performed by an adaptation of the T-type 3ω method for thermal conductivity measurement of wires. The first carbon fiber is connected to two copper blocks supplied by a modulated electrical current providing a volumetric heating. The second fiber fixed on a U-shape holder is delicately implemented over the first one. After performing a secondary vacuum, the 3ω voltage V3ω of the first fiber is recorded as function of the frequency of the modulated current. Knowing the applied force, the contact area between the two carbon fibers is calculated from bending and deformations then a 3D numerical model describing heat transfer in two crossed carbon fibers is used to estimate the TCR at their intersection. In addition, a detailed sensitivity analysis of the unknown parameter TCR is performed allowing to find optimal operating conditions especially the frequency range. Measurements are performed with PAN type carbon fibers (FT300B) picked up from the same bundle. Different TCR estimations were performed by fitting numerical and computed V3ω voltage as function of frequency. Finally, values of TCR between crossed carbon fibers were found equal (10.4 ± 10.1) 105 kW−1 which provides an order of magnitude for such phenomenon.

Thermo-smart composite materials: Exploring the potential of graphene-doped porous silica foams

In this work we investigate an example of combining the thermal insulation properties of porous oxide material with the exceptional thermal conductivity properties of graphene flakes. Blocks were prepared using the original sol–gel method, with fumed silica and water glass as the main components, to form a porous glass foam matrix by heat treatment at 450 °C. The microstructure of the samples was determined by scanning electron microscopy, Raman spectroscopy and X-ray diffraction. The thermal and mechanical properties of the samples were also analysed and discussed with respect to their potential applications as novel thermo-smart composite materials.

Screening outstanding mechanical properties and low lattice thermal conductivity using global attention graph neural network

Mechanical and thermal properties of materials are extremely important for various engineering and scientific fields such as energy conversion and energy storage. However, the characterization of these properties via high throughput screening at the quantum level, although highly accurate, is inefficient and very time- and resource-consuming. In contrast, prediction at the classical level is highly efficient but less accurate. We deploy scalable global attention graph neural network for accurate prediction of mechanical properties which bridge the gap between the accuracy at the quantum level and efficiency at the classical level. Using 10,158 elastic constants as training data, we trained the models on 5 mechanical properties, namely bulk modulus, shear modulus, Young's modulus, Poisson's ratio, and hardness. With the trained model, we predicted 775,947 data in search of materials with ultrahigh hardness. We further verify the recommended ultrahigh hardness materials by high precision first principles calculations, and we finally identify 20 structures with extreme hardness close to diamond, the hardest material in nature. Among those, two super hard materials are completely new and have not been reported in literature so far. We further recommend potential materials from bulk modulus prediction to search low lattice thermal conductivity, and we verify the thermal conductivity of 338 structures with first principles. Our results demonstrate that one can find materials with extreme mechanical properties recommended by graph neural network and low thermal conductivity material from bulk modulus prediction with minimal first principles calculations of the structures (only 0.04%) in the large-scale materials pool.

Thermal performance of concrete masonry units containing insulation and phase change material

The stationary thermal performance requirements of building energy codes are mainly met by compounding insulation materials in building envelope or adding air interlayers. However, with the transformation of building envelope to lightweight and hollow, its thermal capacity value decreases significantly, which causes the indoor thermal environment to fluctuate with the outdoor space. The introduction of phase change materials is a potential solution to improve the transient performance. However, since the thermal properties of phase change materials vary with several environmental factors, it is a complex problem to rationalize the use of phase change materials, including their location in enclosures, the selection of types, quantities, and how to couple with insulation materials, so that the enclosures can achieve high stationary and transient performance simultaneously. In this study, a thermal environment simulator was built for the investigation of a series of triple concrete masonry unit blocks (bricks) equipped with insulation materials or/and phase change materials using dynamic testing method. The experiments were conducted under three typical boundary conditions reflecting different orientations of walls. A complete specification of the thermal performance of the walls with different configurations is summarized. It is found that the performance of insulation materials is stable, while the performance of phase change materials is influenced by the type and quantity of materials, indoor and outdoor temperatures, and the location in envelope. Phase change materials can show much higher thermal performance than insulation materials if under appropriate conditions. A series of construction optimization cases that can significantly improve the thermal performance of envelope are summarized, and general construction principles for envelopes with high thermal performance are given. From the influence laws of thermal performance to the improvement measures and the general rules of envelope configuration, this study provides the theoretical basis, optimization cases, and guidance rules for thermal applications of insulation-phase change building envelopes.

Thermal and mechanical properties of polymeric materials for automotive applications using molecular dynamics simulation

In the development of next-generation eco-friendly vehicles, it is crucial to measure the properties of polymeric materials under standardized conditions due to potential deterioration caused by factors such as temperature, humidity, and the driving environment. In this study, we used molecular dynamics simulation to analyze the thermal and mechanical properties of three polymers (PC, PMMA, and PBT) that are commonly used in automobile headlights. The densities of the polymers were measured and found to be similar to experimental values, with PBT showing a slightly larger deviation due to its relatively high crystallinity compared to the other two polymers. The glass transition temperatures of the polymers were measured using the same cooling rate, and the results followed the order of PC, PMMA, and PBT. Similarly, Young's moduli of the polymers were measured using the same strain rate, with the results following the order of PMMA, PC, and PBT. This approach enables the comparison of polymer properties under standardized conditions, ensuring accurate and reliable comparisons. Moreover, our research has the potential to make a significant contribution to the development of a molecular dynamics (MD) simulation protocol for the efficient generation of polymeric material properties. Such a protocol would greatly support experimental measurements in the automobile industry.

Buoyancy-driven melting and solidification heat transfer in finned latent heat storage units

The thermal expansion and contraction property of phase change materials (PCMs) is a significant factor in affecting the buoyancy-driven melting/solidification heat transfer performance in latent heat storage (LHS) units. To reveal the intrinsic mechanisms, a mathematical model of buoyancy-driven melting/solidification processes in finned LHS units is constructed. The phase-change behaviors, thermal transport properties of different PCMs, and roles of heat transfer fluid (HTF) direction and fin layout in melting/solidification performance are explored. The results indicated that when compared to conduction-dominated cases, the buoyancy-driven melting duration of gallium and n-octadecane increases by 1.8% and decreases by 32.6%, respectively, while the corresponding solidification times decrease by 8.4% and increase by 15.2%, respectively. The downward HTF enhances the melting rate of gallium with thermal-contraction properties and the solidification rate of n-octadecane with thermal-expansion properties. Conversely, the upward HTF enhances the melting rate of n-octadecane with thermal-expansion properties and the solidification rate of gallium with thermal-contraction properties. For finned LHS units with upward HTF, the ladder-type and reverse ladder-type fins facilitate the melting performance of n-octadecane and gallium, respectively. Moreover, the ladder fins with non-uniform layouts weaken the solidification performance of PCMs with different thermal characteristics.

Development of Stereocomplex Polylactide Nanocomposites as an Advanced Class of Biomaterials-A Review.

This review paper analyzes the development of advanced class polylactide (PLA) materials through a combination of stereocomplexation and nanocomposites approaches. The similarities in these approaches provide the opportunity to generate an advanced stereocomplex PLA nanocomposite (stereo-nano PLA) material with various beneficial properties. As a potential "green" polymer with tunable characteristics (e.g., modifiable molecular structure and organic-inorganic miscibility), stereo-nano PLA could be used for various advanced applications. The molecular structure modification of PLA homopolymers and nanoparticles in stereo-nano PLA materials enables us to encounter stereocomplexation and nanocomposites constraints. The hydrogen bonding of D- and L-lactide fragments aids in the formation of stereococomplex crystallites, while the hetero-nucleation capabilities of nanofillers result in a synergism that improves the physical, thermal, and mechanical properties of materials, including stereocomplex memory (melt stability) and nanoparticle dispersion. The special properties of selected nanoparticles also allow the production of stereo-nano PLA materials with distinctive characteristics, such as electrical conductivity, anti-inflammatory, and anti-bacterial properties. The D- and L-lactide chains in PLA copolymers provide self-assembly capabilities to form stable nanocarrier micelles for encapsulating nanoparticles. This development of advanced stereo-nano PLA with biodegradability, biocompatibility, and tunability properties shows potential for use in wider and advanced applications as a high-performance material, in engineering field, electronic, medical device, biomedical, diagnosis, and therapeutic applications.

Density functional theory (DFT) calculations of structural, elastic, and thermal properties of Zn3P2 compound

In this paper, theoretical investigations of structural, elastic and thermal properties of Zn3P2 material were done using Quantum ESPRESSO code based on density functional theory. The generalized gradient approximation (GGA) exchange correlation-functional helped to model the atomic interaction. First, the structural optimization procedure was carried out, and hence, the optimized structural parameters were utilized to obtain six independent elastic constants [Formula: see text], and [Formula: see text] for the Zn3P2 tetragonal structure. Accordingly, these elastic constants were used to determine the elastic moduli such as the Bulk modulus, Young’s modulus, and shear modulus, as well as other mechanical parameters such as Pugh’s ratio, Poisson’s ratio, anisotropic ratio, sound velocities and Debye temperature. Calculations of thermodynamic properties such as vibrational energies, vibrational free energies, and fixed volume heat capacities, were performed within the implementation of the Thermo_pw code. Elastic calculations confirmed that this compound is characterized by mechanical stability at zero pressure and 0K temperature, ionic bonding, a high degree of anisotropy, and typical ductility. An observable increase in Debye vibrational energies, entropies and constant volume heat capacities of this compound with increasing temperature was detected throughout the thermodynamic calculations, unlike vibrational free energy which revealed a pronounced decrease as temperature increased.

Controllable preparation and thermal properties of SiC spherical high temperature shape-stable composite phase change materials based on gel-casting

The development of high-temperature composite phase change materials (CPCMs) suitable for mass-production and high-performance is still a very urgent problem in the efficient utilization of renewable energy. In this study, a SiC spherical high-temperature CPCMs based on aqueous gel-casting suitable for batch molding using commercially available silicone molds is proposed. The porosity of the porous SiC framework can be adjusted by changing the content of starch granules in the slurry. The sample containing 20 wt% starch has relatively high open porosity and thermal conductivity, which is considered to be close to the optimal formulation of CPCMs. This formula possesses a high thermal conductivity of 10.2 W·m−1·k−1 benefiting from the continuous thermal transport channels consisting of the uniformly distributed large spherical pores and interconnected small pores. Meanwhile, the thermal storage density of the CPCMs reaches 395.21 J·g−1 in the temperature range of 550 ℃ and 750 ℃ since up to 89.06% of the pores are filled with molten salts. At the same time, the CPCMs exhibit excellent cycle stability in 100 thermal cycles. In particular, these CPCMs can be easily integrated into thermal energy storage (TES) system. Based on the rapid heat storage simulation of the C-D model, the packed-bed latent thermal energy storage system containing spherical CPCMs will have a more uniform temperature distribution and a 26.7% reduction in charging time compared with the traditional packed-bed system. This work provides a new reference for the design of spherical CPCMs in TES systems.

Thermal properties of SiC-bonded diamond materials produced by liquid silicon infiltration

Silicon carbide bonded diamond composites are a class of materials with great potential for a wide range of demanding applications in industry. They can be produced by pressureless infiltration of diamond preforms with liquid silicon. In addition to their high hardness and very high wear resistance, the materials have a high thermal conductivity of up to 636 W/m⋅K, which is about 50 % higher than the value of silver. The analysis of materials with different diamond contents and grain sizes shows that the thermal conductivity increases with increasing grain size of the diamonds as well as with the volume content. Based on the experimental data, an interface conductance can be estimated for the SiC diamond interface. This value is similar to the values determined for diamond/Si interfaces. An increasing graphitization of the interface leads to a strong reduction of the thermal conductivity of the composites.

Thermal properties of the core of magnetar

During very early age of neutron stars, the core cools down faster compared to the crust creating a large thermal gradient in the interior of the star. During 10−100 years, a cooling wave propagates from the core to the crust causing the interior of the star to thermalize. During this duration thermal properties of the core material is of great importance to understand the dynamics of the interior of the star. The heat capacity and thermal conductivity of the core depends on the behaviour of matter inside the core. We investigate these two properties in case of magnetars. Due to presence of large magnetic field, the proton superconductivity is quenched partially inside the magnetars depending upon the comparative values of upper critical field and the strength of the magnetic field present. This produces non-uniformity in the behaviour of matter throughout the star. Moreover, such non-uniformity arises from the variation of nature of the pairing and values of the pairing gap energy. We find that the heat capacity is substantially reduced due to the presence of superfluidity. On the other hand, the thermal conductivity of neutron is enhanced due to proton superconductivity and gets reduced due to neutron superfluidity. Hence, the variation of the thermal properties due to superfluidity in presence of magnetic field is different at different radius inside the star. However, in all the cases the maximum variation is of the order one. This affects the thermal relaxation time of the star and eventually its the thermal evolution.

Mechanical recycling of expanded polystyrene and tire rubber waste as compatibilized and toughened blends

AbstractPackaging represents a significant source of all polymer waste produced in the world. Thus, improving recycling methods is essential to achieve an environmentally sustainable condition since the volume of produced polymer and of related waste has grown. Expanded polystyrene (EPS) foam is a thermoplastic with important performance of properties such as thermal isolation and absorption of mechanical energy that allow large application in packaging and other segments. However, the EPS recycling is a challenger due to its low density and poor properties. The rubber incorporation to the recycled EPS is an alternative for the toughening of the polymer matrix as well as improving its mechanical properties. In present study, EPS waste from electric and electronic products packaging was treated by three distinct methods for polymer densification and after it was thermo‐mechanically processed by extrusion with variable content of ground tire rubber (GTR) and compatibilizer agent styrene‐butadiene‐styrene (SBS) copolymer to produce compatibilized and toughened PS/rubber blends. Mechanical, thermal and rheological properties of materials were evaluated by different analyses. The incorporation of rubber to the recycled EPS has significantly improved the mechanical properties of the material and the presence of the SBS agent was effective to compatibilize the PS/rubber blends. Therefore, the preparation of compatibilized PS/rubber blends showed to be a way to the mechanical recycling of EPS and rubber tires waste.

Halloysite clay nanotube composites as coating materials with enhanced properties

Energy efficiency and thermal control are of critical importance as the world moves from traditional fossil fuel energy sources and looks to limit resource and environmental impacts. This paper describes the development of a novel thermal insulative coating material prepared by blending natural clay nanotubes (halloysite nanotubes - HNT) with latex primers. This represents a “green” approach to an insulative paint, focused on naturally occurring HNTs as the primary additive and useful in multiple applications, including new or existing construction. The HNTs were mixed with 0.5–4% weight ratios using several blending approaches. Investigation of the study included changes in viscosity, adhesion, and thermal properties of the primers resulting from the addition of the HNTs. Results indicated that viscosity and shear stress increased gradually. Impact on the adhesion properties was also found depending on the host surface material. The addition of the HNTs altered the thermal conductivity properties of the primer materials. SEM images showed good dispersion of HNTs in the primer irrespective of mixing technique. A comparison was made between the properties of the latex primers after the HNTs were mixed. The outcome of the study has the potential to modify the thermal conductivity properties of commonly used coating materials and, thus, limit energy loss through walls and ceilings.

Gamma Rays as Modifiers of the Compressive and Flexural Properties of Polyester Polymer Concrete

To improve the mechanical and thermal properties of materials, alternative posttreatments have been proposed. One of these posttreatments is based on the use of ionizing radiation. This work studied the effects of gamma rays on the mechanical and thermal properties of polymer concrete (PC) produced with 80% silica sand and 20% polyester resin. High gamma irradiation doses (100–500 kGy) were used. Mechanical properties (compressive and flexural strength), and thermal properties (thermal conductivity, specific heat, and thermal diffusivity) were analyzed. The results show that the highest values of compressive and flexural strength and elasticity modulus occur when polymer concrete is irradiated at 400 kGy. The compressive strength of the reference concrete was 51 MPa; this resistance increased to 62 MPa (23% higher) when polymer concrete was irradiated at 400 kGy. The modulus of elasticity increased 12%, from 2.17 to 2.44 GPa, whereas the flexural strength increased from 16.2 to 17.7 MPa (9%). Changes in the thermal properties (mainly the specific heat) were obtained at 100 and 200 kGy doses. The results were related to the surface modifications produced in the irradiated polyester resin (analyzed by scanning electron microscopy) and its chemical structure (studied by Fourier-transform infrared and Raman spectroscopies).

Optical, and electrical conductivity properties of ZnO and TiO2 nanoparticles scattered in PEO-PVA for electrical devices

Polyvinyl alcohol (PVA)/Polyethylene oxide (PEO) has been blended and doped with zinc oxide and titanium oxide nanoparticles. Different concentration of the prepared ZnO and TiO2 NPs make a change in PVA/PEO- ZnO/TiO2 NPs nanocomposites films improve the characterization of PVA/PEO. XRD scans show two broad peaks at about 18.8° and 21.95° for PVA/PEO blend. XRD scans show of PVA/PEO- ZnO/TiO2 NPs nanocomposites films obtain the hexagonal structure of ZnO and the anatase phase of TiO2 NPs. The addition of dopants in the PVA/PEO blend results in a reduce in degree of crystallinity compared to the pure blend. This is evident from the decrease in the crystallinity index (Xc value) from 37.25 to 22.31. This reduction in crystallinity can have implications for the material's opticla, thermal, and electrical properties, and should be considered when evaluating its suitability for specific applications. FT-IR results show changes in intensity of bands that could be assigned to the strong interaction between PVA/PEO and ZnO/TiO2 nanoparticles. The Egopt values reduced by raising laser ablation time due to unstructured defects that enhanced the density of localized states in the band gap, dropping from 4.72 eV to 3.0 eV for direct transitions and from 3.05 eV to 2.35 eV for indirect transitions. It undergoes complete decomposition at a higher temperature, resulting in a mass percentage of 45 ± 0.3 wt%. In comparison, the pure polymer blend sample has a lower mass percentage of 33 ± 0.03 wt% during the same temperature range. The fabricated system of PVA/PEO- ZnO/TiO2 NPs nanocomposites films showing improved in AC conductivity and dielectric characteristics and could be suggested in electrical applications.

Solid state sensible heat storage technology for industrial applications – A review

Cost effective methods of storing heat can be an enabling technology to promote utilization of solar thermal and heat recovery systems for industrial applications. The technology can reduce the use of conventional heat sources like coal and gas by offering a competent option of producing industrial process heat. Solid state sensible thermal energy storage (TES) systems have emerged as a viable method of heat storage especially with the prospect of using natural stones as heat storage media which are cheap, locally available, and harmless to the environmental. This study reviews research work on solid state sensible heat storage systems focusing on the solid materials being used for heat storage applications. Also, the review covers numerical and experimental investigations that have been done to evaluate different design parameters and thermal performance of solid-state TES systems. In addition, the environmental impact of adopting this heat storage technology is also discussed. The study has revealed that, there are areas that still need further research, and these include, experimental characterization of thermal properties of natural solid materials with potential for heat storage purposes, investigations on improving thermal performance as well as durability of solid-state sensible TES systems.

Thermal fatigue testing with repeatable temperature cycles on thermomechanical simulator

This paper presents two thermal fatigue tests developed to simulate the typical thermal fatigue behavior of hot-work tools and rolls. The tests are carried out on a Gleeble 1500D thermomechanical simulator with computer-controlled heating and cooling of the test specimens. In the first test, internal cooling of the specimens is performed, and in the second test, external cooling is performed. This allows constant test conditions and the collection of reliable experimental data on the thermal fatigue behavior. The internally cooled test rig is used for testing the thermal fatigue properties of bulk materials. Indefinite chill double-poured cast iron is used to present the basic capabilities of the test. At the material, the cracks take flattened graphite–cementite pathways. The external cooling test rig, on the other hand, is designed for comparative testing of four surfaces simultaneously. Thus, the capabilities of the second test are presented in the comparative testing of three different laser-welded functionally graded material surface layers and the basic H13 tool steel, simultaneously. The highest thermal fatigue resistance is shown by the weld with the lowest silicon (Si) content. Quantitative evaluation of thermal fatigue resistance as well as following of degradation processes in both tests is enabled.