Thermal Conductivity Coefficient Research Articles

Ultrahigh room and high − temperature mechanical properties of SiCf/SiC composites prepared by hybrid CVI and PIP methods: Effects of PIP temperature

Unidirectional (UD) SiCf/SiC composites were prepared using chemical vapor infiltration (CVI)-polymer infiltration and pyrolysis (PIP) hybrid procedure at different PIP temperatures of 1100 °C (1100PIP), 1300 °C (1300PIP), and 1500 °C (1500PIP). The effect of PIP temperature on the microstructure of each component was studied. Results showed that SiC fiber strength and interfacial shear strength (IFSS) were the main factors affecting the mechanical properties of the composite. At 1100 °C, the fiber was thermally stable and IFSS was high, due to which 1100PIP achieved ultrahigh mechanical performance with tensile strength of 901.0 ± 87.7 MPa, flexural strength of 2186.5 ± 192.5 MPa, and toughness of 80.6 ± 12.0 MPa·m1/2. At 1300 °C, IFSS decreased slightly, due to the crystallization of BN interphase. Hence, the mechanical performance of 1300PIP decreased slightly to 789.8 ± 42.9 MPa, 1935.9 ± 163.2 MPa, and 58.2 ± 4.0 MPa·m1/2, respectively. At 1500 °C, severe fiber ceramization and decrease in IFSS caused severe decline in mechanical performance to about half of that of 1100PIP. The crack could be deflected not only at the fiber/BN (F/B) interface, but also at the CVI SiC/PIP SiC (C/P) interface, due to the existence of free carbon layers at the C/P interface, which played an important role in improving the strength and toughness of the composite. 1300PIP also showed excellent strength at high − temperature. At 1350 °C and 1500 °C, its flexural strengths were as high as 1529.0 ± 73.0 MPa and 1223.1 ± 81.1 MPa, respectively. The thermal conductivity and thermal expansion coefficient were also tested. Their values were mainly affected by the grain size and thermal stabilities of the SiC fiber and PIP matrix.

Photothermal measurement of material properties for translucent thermal barrier coatings

In this study, a photothermal nondestructive method was proposed to measure the material parameters of semi-transparent or translucent thermal barrier coatings (TBCs). We derived a theoretical model for the photothermal signal from a two-layer semi-infinite material system with a translucent first layer after a pulse laser excitation. Its solution was verified by numerical solution. A data regression algorithm based on a least-squares fitting was used for the determination of the material parameters in the translucent first layer material. To verify this new method, an experimental system was set up with a pulse laser for thermal excitation and an infrared camera for image acquisition of the thermal emission transient from several translucent EBPVD TBC samples. The predicted coating thickness is consistent with the measured value by an optical microscope. The predicted thermal conductivity and optical attenuation coefficients in the absorption and emission band are found to be in good agreement with reference values.

Influence of specularity factor on heat transport in nanoribbons of different sizes

In this paper, the phonon heat transfer in two-dimensional conductors with different types of phonon reflection from the boundaries is examined. Heat conductors with arbitrary ratios of width W to length L are studied assuming that the mean free path between phonon-phonon collisions is infinite. The integral equations for the angular distribution functions of the incident and reflected phonons at a specific point on the conductor boundary were proposed. To solve these integral equations a new iterative method is proposed. The proposed iterative approach formally corresponds to taking into account subsequent collisions of phonons with the edges of the conductor. It ensures the convergence of the desired solution for any W/L ratio and for any value of the specularity coefficient p. Interpolation formulae are found to describe with sufficient accuracy the solution of the system of integral equations in the entire region of the specularity coefficient p from 0 to 1, and the W/L ratios ranging from 10 to 0.01. These formulae allow the construction of the isolines of the thermal conductance coefficient values, from which it is possible to determine the necessary values of W/L and parameter p to get the desired value of the thermal conductance.

Use of macromolecules lignosulfonate and graphene oxide to prepare non-autoclaved aerated concrete

The development of new structural materials with thermal insulation properties is urgently need in the construction of smart buildings. Besides, there is a need to develop environmentally friendly and sustainable concrete mix designs. Lignosulfonate (LS) macromolecule and graphene oxide (GO) were used to prepare non-autoclaved aerated concrete (NAC). The addition of a complex GO/LS additive of the composition (0.16/0.0002 wt%) increased the compressive strength by 54 %, and bending strength by 45 % at the age of 28 days' strength gain. The addition of an effective complex GO/LS additive to NAC made it possible to achieve a reduction in water absorption by up to 63 % and thermal conductivity by up to 29 % in comparison. The thermal conductivity coefficient of such NAC specimens was 0.092 W/m·K with water absorption of 9 %. The options for the interactions of the GO/LS modifier with calcium hydroaluminates using the type of ion exchange were proposed. Thus, the introduction of GO/LS nano modifier contributed to high-quality filling of free areas of the cement mixture with mineral formations, which helpd to increase the strength of the aerated concrete and its durability.

Mathematical model for constructing a matrix of coefficients thermal conductivity under low-temperature influence on the multilayer epidermis of biological tissue

Objective. The purpose of the study is to develop a mathematical model for constructing a matrix of thermal conductivity coefficients under low-temperature exposure to the multilayer epidermis of biological tissue. Method. The research is based on methods of thermo dynamic analysis, full-scale and computational modeling of processes under low-temperature influence. Result. A mathematical model of the matrix of thermal conductivity coefficients under low-temperature effects on biological tissue has been developed. Heat transfer in a multilayer medium under low-temperature influence on biological tissue is presented as a process with a discrete step in time and coordinate. Thermal properties are evenly distributed throughout the volume of layers of biological tissue. For exposure to cold, layers of the epidermis of biological tissue were used, divided into uniform identical cells, where the cell area of the biological tissue was taken to be equal to one. Conclusion. The results obtained in this work can be useful to specialists who deal with modeling problems with free boundaries.

Thermophysical properties, and figures-of-merit analyses of nanodiamond/CuO ionanofluids: Experimental and artificial neural network predictions

The nanodiamond/copper oxide (ND/CuO) nanoparticles were dispersed into 1-ethyl-3-methylimidazolium chloride [EMiM]Cl to create ionanofluids. The experiments were performed to analyse the thermophysical properties under particle volume loadings from 0.2 % to 1.0 %, and temperature ranging from 30 to 60 °C. Theoretical approach was made to understand the Figures-of-Merit (FoM) of the prepared ionanofluids, while they flow in a tube, and helical coil through the evaluated thermophysical properties. The lower thermal conductivity augment of 14.27 % was noticed at 0.2% vol. and larger thermal conductivity enhancement of 35.20 % was noticed at 1.0% vol. and at a temperature of 60 °C, against the base fluid. Moreover, the viscosity of 1.0% vol. of ionanofluid was enhanced by 61.66 % at a temperature of 30 °C, over the base fluid. The other properties like density was increased with an increase of volume loadings, and specific heat was decreased with an increase of volume loadings. The FoM results indicated that, all the prepared volume concentrations of ionanofluids flow in a tube was benefited fluid when the fluid operating temperature was exceeds to 35 °C, on the other side, the prepared ionanofluids flow in a helical coil was benefited fluid when its operating temperature was above 30 °C for 0.8 %, and 1.0% vol. loadings. The estimated thermophysical properties were also used as input and output data for an artificial neural network of Levenberg-Marquardt (LM) algorithm. It is noticed from the LM algorithm results, the predicted data is well agreed with an experimental data. For all the data, the correlation coefficient (R2) of thermal conductivity is 0.99283, viscosity is 0.9971, density is 0.99887, and specific heat is 0.99817, was observed, respectively.

Preparation and Electrothermal Transport Behavior of Sn8[(Ga2Te3)34(SnTe)66]92 Bulk Glass.

High-conductivity tellurium-based glasses were anticipated to be the attractive candidates in chalcogenide glass systems on account of their distinctive characteristics and extensive application prospects. In this paper, the high-density (>96%) Sn8[(Ga2Te3)34(SnTe)66]92 bulk glass with the density of 5.5917 g/cm3 was successfully prepared by spark plasma sintering (SPS) technology at 460 K, using a 5 min dwell time and 450 MPa pressure. The room-temperature thermal conductivity of Sn8 bulk materials significantly decreased from 1.476 W m-1∙K-1 in the crystalline sample to 0.179 W m-1∙K-1 in the glass, and the Seebeck coefficient obviously increased from 35 μV∙K-1 in to 286 μV∙K-1, indicating that the glass transition of tellurium-based semiconductors could optimize the thermal conductivity and Seebeck coefficient of the materials. Compared to the conventional tellurium-based glassy systems, the fabricated Sn8 bulk glass presented a high room-temperature conductivity (σ = 6.2 S∙m-1) and a large glass transition temperature (Tg = 488 K), which was expected to be a promising thermoelectric material.

Recent Advances in High-Entropy Ceramics: Synthesis Methods, Properties, and Emerging Applications

High-entropy ceramics (HECs) represent an emerging class of materials composed of at least five different cations or anions in near-equiatomic proportions, garnering significant attention due to their extraordinary functional and structural properties. While multi-component ceramics have played a crucial role for many years, the concept of high-entropy materials was first introduced eighteen years ago with the synthesis of high-entropy alloys, and the first high-entropy nitride films were reported in 2014. These newly developed materials exhibit superior properties over traditional ceramics, such as enhanced thermal stability, hardness, and chemical resistance, making them suitable for a wide range of applications. High-entropy carbides, borides, oxides, oxi-carbides, oxi-borides, and other systems fall within the HEC category, typically occupying unique positions within phase diagrams that lead to novel properties. HECs are particularly well suited for high-temperature coatings, for tribological applications where low thermal conductivity and similar heat coefficients are critical, as well as for energy storage and dielectric uses. Computational tools like CALPHAD streamline the element selection process for designing HECs, while innovative, energy-efficient synthesis methods are being explored for producing dense specimens. This paper provides an in-depth analysis of the current state of the compositional design, the fabrication techniques, and the diverse applications of HECs, emphasizing their transformative potential in various industrial domains.

Measurement of thermophysical parameters of artificial skin

Computer methods for process research and methods for processing the measurement results of the parameters of these processes are widely used in biology and medicine. Therefore, the problem of automation of biophysical measurements and computer processing of the results of such experiments is relevant. In the treatment of wounds and burns with a large surface area of tissue damage, medicine has to resort to artificial skin. A procedure for studying thermal processes in artificial skin and measuring its thermophysical parameters was developed. The measurement process was described. The thermophysical parameters of the artificial skin samples used in medicine for the treatment of wounds and burns were determined. The samples of the artificial skin used were made in Ukraine. Each sample was made from six layers of skin. To control the temperature distribution in the sample between the skin adjacent layers and on the surface of the sample, thermocouples were placed. The surface of the sample was heated with an incandescent lamp. The thermocouple signals were sent to an analog-to-digital converter (ADC), amplified, and digitally transmitted to a computer. Processing was carried out using the ADC software and the MATHCAD program. A mathematical model was obtained. For this purpose, a differential equation describing thermal processes in the sample was solved. The found temperature distribution function and its changes over time are in a good agreement with experimental data. The analysis of the function allows finding the thermal conductivity coefficient of artificial skin, its volume heat capacity, thermal diffusivity coefficient, and heat exchange coefficient with the external environment. The proposed method of measuring and processing experimental data makes it possible to detect main thermophysical parameters of artificial skin. Based on these results, a theoretical model was obtained that well describes the course of thermal processes in artificial skin, which makes it possible to predict the course of these processes. Such method is based on heating the skin with optical radiation. The thermal conductivity and thermal diffusivity of artificial skin are significantly less than such parameters of human skin, which should be considered when using it.

Analysis of Thermal Properties of Materials Used to Insulate External Walls.

This article emphasizes the significance of understanding the actual thermal properties of thermal insulation materials, which are crucial for avoiding errors in building design and estimating heat losses within the energy balance. The aim of this study was to analyse the thermal parameters of selected thermal insulation materials, particularly in the context of their stability after a period of storage under specific conditions. The materials chosen for this study include commonly used construction insulations such as polystyrene and mineral wool, as well as modern options like rigid foam composites. Experimental studies were conducted, including the determination of the thermal conductivity coefficient λ, as well as numerical analyses and analytical calculations of heat flow through a double-layer external wall with a window. The numerical analyses were performed using the TRISCO software version 12.0w, based on the finite element method (FEM). A macrostructural analysis of the investigated materials was also performed. The findings indicated that improper storage conditions adversely affect the thermal properties of insulation materials. Specifically, storing materials outdoors led to a deterioration in insulating properties, with an average reduction of about 4% for the standard materials and as much as 19% for the tested composite material. Insufficient understanding of the true thermal properties of insulation materials can result in incorrect insulation layer thickness, degrading the fundamental thermal parameters of external walls. This, in turn, increases heat loss through major building surfaces, raises heating costs, and indirectly contributes to greenhouse gas emissions.

Assessment of Physico-Chemical Behavior and Sorptivity-Diatomaceous Earth as Support for Paraffinic Phase-Change Materials.

Diatomite's most common application is its use as a sorbent for petroleum substances. Since paraffin is a petroleum derivative, this paper investigates the sorption capacity of diatomite to absorb it. In this paper, the physical and chemical properties were studied for 4 different fractions of diatomite (0-0.063 mm; 0-2 mm; 0.5-3 mm; and 2-5 mm) in the crude and calcined states, and the sorption capacity of diatomite earth for absorbing paraffinic phase-change substances was determined. The physical and chemical studies of the material included conducting an oxide chemical composition analysis using XRF, examining the composition of the mineral phases using X-ray diffraction, and determining the particle size, porosity, and thermal conductivity of the diatomite. Morphology images were also taken for all 8 diatomite variants using scanning electron microscopy. Each fraction was subjected to static calcination at 850 °C for 24 h. The results showed that the calcination of the diatomite increased the porosity of the material and reduced the thermal conductivity coefficient, and most importantly, the sorption capacity to absorb paraffins. The highest sorption capacity was characterized by calcined diatomite powder, that is, diatomite with the smallest particle size. Absorption of paraffinic substances by diatomite exceeding 200 wt.% is possible. Thus, diatomite is one of the feasible candidates for an economical and lightweight building material for making PCM composites for thermal energy storage in buildings.

The Influence of Diatomite on the Sound Absorption Ability of Composites.

Diatomites are well-known mineral materials formed thousands of years ago from the skeletons of diatoms. They are found in many places around the world and have a wide range of applications. This article presents innovative research related to the possibility of using diatomite as a filler in composites to improve their sound absorption properties. The results of the study of the effect of diatomite processing (calcination) and its degree of fineness on the sound absorption coefficient of thermoplastic composites are presented. Three fractions of diatomite (0 ÷ 0.063 mm; 0.5 ÷ 3 mm; 2 ÷ 5 mm) and its variable mass proportion (0, 25, and 50 wt.%) were used. The composites were made with flax fibers as a reinforcement, polylactide as a matrix, and diatomite as an additional filler. This paper also presents the results of oxide chemical composition, diatomite mineral phase composition, morphology, and thermal conductivity coefficient of all diatomite fractions studied. In addition, the average particle size for diatomite powder was also determined. The most important of the studies was the determination of the acoustic properties of the aforementioned composites. As a result of the tests, it was found that the smallest fraction of diatomite particles and a variant without thermal treatment give the best effect in terms of sound absorption.

Experimental investigation of zinc ferrite/insulation oil nanofluid natural convection heat transfer, AC dielectric breakdown voltage, and thermophysical properties

Improving the thermal and dielectric properties of insulation oil (INO) with nanoadditives is an important challenge, and achieving dispersion stability in these nanofluids is quite challenging, necessitating further investigation. The main goal of this study is the synthesis and use of the hydrophobicity of zinc ferrite (ZnFe2O4) nanoparticles, which can improve both the thermal and dielectric properties of the INO. This oil is made from distillate (petroleum), including severely hydrotreated light naphthenic oil (75–85%) and severely hydrotreated light paraffinic oil (15–25%). A comprehensive investigation was carried out, involving the creation of nanofluids with ZnFe2O4 nanoparticles at various concentrations, and employing various characterization methods such as X-ray diffraction (XRD), Fourier-transform infrared (FTIR), scanning electron microscopy, energy dispersive X-ray (EDX), zeta potential analysis, and dynamic light scattering (DLS). The KD2 Pro thermal analyzer was used to investigate the thermal characteristics, including the thermal conductivity coefficient (TCC) and volumetric heat capacity (VHC). Under free convection conditions, the free convection heat transfer coefficient (FCHTC) and Nusselt numbers (Nu) were evaluated, revealing enhancements ranging from 14.15 to 11.7%. Furthermore, the most significant improvement observed in the AC Breakdown voltage (BDV) for nanofluids containing 0.1 wt% of ZnFe2O4 amounted to 17.3%. The most significant finding of this study is the improvement in the heat transfer performance, AC BDV, and stability of the nanofluids.

Self-similar flow behind a shock wave in a gas under the effect of viscosity, heat conduction, and variable ambient density

Self-similar solutions have been investigated to describe the propagation of planar shock waves in a non-ideal gas generated by a piston under viscous stress and heat flux. The equation of state for non-ideal gas incorporates the correction in pressure and volume of the gas. The piston position and ambient density vary exponentially with time. Newton’s law of viscosity is used for the viscous stress and Fourier’s law of heat conduction is taken for heat flux. The viscosity coefficient is taken as constant whereas the thermal conductivity coefficient varies with temperature and density following the power law. The shock jump conditions have been derived for the viscous non-ideal gas using integral form of conservation laws. The shock Reynolds number Re s has been introduced to study the effect of viscosity on shock propagation in non-ideal gas. It is found that similarity solution exists only in an ideal gas under the condition that the ambient density exponent is equal to twice the shock position exponent. This study shows that shock Reynolds number Re s and heat conduction parameter Γ c can be used to control the variation of the flow variables and piston position significantly. The shock strength decreases with increase in the value of shock Reynolds number Re s but is independent of the heat conduction parameter Γ c . The pressure, density, and adiabatic compressibility have significant deviations from high to low viscous flow of ideal gas but the velocity and heat flux undergo negligible change. The results do not support the claim of negligible effect of viscosity in earlier studies and establish the impact of viscosity and heat flux on shock propagation in an ideal gas.

The effect of oxygen vacancies on the optical and thermophysical properties of (1-x)Si3N4 – xAl2O3 ceramics

Interest in composite ceramics based on silicon nitride (Si3N4) and aluminum oxide (Al2O3) is due to the possibility of using them as semiconductor applications associated with their operation under conditions of external influences, including heating. The paper presents the results of assessing the influence of variations in the phase composition of (1-x)Si3N4 – xAl2O3 ceramics on alterations in optical and thermophysical parameters, as well as their relationships. Analysis of the optical characteristics of the ceramics under study showed that changes in the phase composition associated with the dominance of the Al2O3 phase in the composition of the ceramics lead to a change in covalent bonds and an increase in the number of ionic bonds, which also affects the change in the semiconductor nature of the ceramics, and therefore, a change in the thermophysical properties. According to the assessment of changes in the thermal conductivity coefficient of the studied ceramics, with the dominance of the Al2O3 phase in the composition, the observed growth in the concentration of structural defects, as well as oxygen vacancies, results in the thermal conductivity coefficient decrease, as well as an elevation in the thermal expansion of ceramics during thermal heating. It has been determined that the presence of a combination of Al2(SiO4)O and Si3N4 phases in the ceramic composition leads to an increase in the thermal conductivity coefficient, as well as maintaining its stability over a wide temperature range.

Natural Deep Eutectic Solvent-Assisted Construction of Silk Nanofibrils/Boron Nitride Nanosheets Membranes with Enhanced Heat-Dissipating Efficiency.

Natural polymer-derived nanofibrils have gained significant interest in diverse fields. However, production of bio-nanofibrils with the hierarchical structures such as fibrillar structures and crystalline features remains a great challenge. Herein, an all-natural strategy for simple, green, and scalable top-down exfoliation silk nanofibrils (SNFs) in novel renewable deep eutectic solvent (DES) composed by amino acids and D-sorbitol is innovatively developed. The DES-exfoliated SNFs with a controllable fibrillar structures and intact crystalline features, novelty preserving the hierarchical structure of natural silk fibers. Owing to the amphiphilic nature, the DES-exfoliated SNFs show excellent capacity of assisting the exfoliation of several 2D-layered materials, i.e., h-BN, MoS2, and WS2. More importantly, the SNFs-assisted dispersion of BNNSs with a concentration of 59.3% can be employed to construct SNFs/BNNSs nanocomposite membranes with excellent mechanical properties (tensile strength of 416.7MPa, tensile modulus of 3.86GPa and toughness of 1295.4 KJ·m-3) and thermal conductivity (in-plane thermal conductivity coefficient of 3.84 W·m-1·K-1), enabling it to possess superior cooling efficiency compared with the commercial silicone pad.

Construction of mathematical models of thermal conductivity for modern electronic devices with elements of a layered structure

This paper considers a heat conduction process for isotropic layered media with internal thermal heating. As a result of the heterogeneity of environments, significant temperature gradients arise as a result of the thermal load. In order to establish the temperature regimes for the effective operation of electronic devices, linear and non-linear mathematical models for determining the temperature field have been constructed, which would make it possible to further analyze the temperature regimes in these heat-active environments. The coefficient of thermal conductivity for the above structures was represented as a whole using asymmetric unit functions. As a result, the conditions of ideal thermal contact were automatically fulfilled on the surfaces of the conjugation of the layers. This leads to solving one heat conduction equation with discontinuous and singular coefficients and boundary conditions at the boundary surfaces of the medium. For linearization of nonlinear boundary value problems, linearizing functions were introduced. Analytical solutions to both linear and nonlinear boundary value problems were derived in a closed form. For heat-sensitive environments, as an example, the linear dependence of the coefficient of thermal conductivity of structural materials on temperature, which is often observed when solving many practical problems, was chosen. As a result, analytical relations for determining the temperature distribution in these environments were obtained. Based on this, a numerical experiment was performed, and it was geometrically represented depending on the spatial coordinates. This proves that the constructed linear and nonlinear mathematical models testify to their adequacy to the real physical process. They make it possible to analyze heat-active media regarding their thermal resistance. As a result, it becomes possible to increase it and protect it from overheating, which can cause the destruction of not only individual nodes and their elements but also the entire structure

Effect of welding parameters on microstructure and mechanical properties of dissimilar AISI 304/ductile cast iron fusion welded joints

Problems associated with dissimilar fusion welding are mainly originated from the differences in melting points, coefficients of thermal conductivity and thermal expansion, …etc., and carbon content when welding dissimilar ferrous materials. In this study, the problems associated with dissimilar fusion welding of stainless steel AISI304 with ductile cast iron DCI grade A536 were investigated. Using shielded metal arc welding (SMAW) process, various welding parameters were studied to investigate the successful/accepted dissimilar welded joint(s). Welding electrodes and welding techniques were the main studied parameters. Microstructural and mechanical investigations were carried out for welded joints under different welding parameters. Tensile, impact and hardness tests coupled with optical and scanning electron microscopic examinations with EDX analysis were made for metallurgical and mechanical evaluations of welded joints. This extensive study could solve the problem of dissimilar welding between ductile cast iron and 304 stainless steel. The main results showed that joints welded by ENiCrFe-3 electrode in root pass and ENiFe-CI in filling passes were the successful dissimilar welded joints with 422 MPa tensile strength which represents 104% of annealed DCI base metal and without any changes in toughness properties, where toughness at HAZ of DCI was 18 J. High Ni content in weld metal increased the strength, ductility and reduced the weld metal dilution.

The influence of stochastic interface defects on the effective thermal conductivity of fiber-reinforced composites

In this paper, a novel microscopic modeling strategy is proposed to investigate the effective thermal conductivity of composites with consideration of stochastic interface defects. To this end, the subdomain boundary element method combined with asymptotic homogenization is proposed to effectively solve the thermal conduction problem. In order to accurately capture the heat flux on the boundary and the internal region in the representative volume element (RVE), a parameterized sub-cell is constructed to discretize the RVE. On this basis, the influence of stochastic interface defects on the thermal conductivity of composites is investigated by utilizing the Monte Carlo method. Specifically, the effect of the location, length, thickness, and area of the interface defects on the thermal conductivity is investigated. A proportional decrease in the transverse thermal conductivity coefficient is found for interface defect areas ranging from 1% to 10%.

Effect of Microwave Radiation on the Properties of Hydrogel, Cork, Perlite, and Ceramsite.

The present work analyzes the effect of releasing physically bound water from hydrogel, cork, perlite, and ceramsite on materials exposed to microwave radiation and subsequently investigates possible changes in the physical properties of these materials (water absorption and thermal conductivity coefficient). The release of physically bound water from individual materials has potential practical applications in materials engineering, for example, in the internal curing of concrete, where individual aggregates could, under the influence of microwave radiation, release water into the structure of the concrete and thus further cure it. Experimental analysis was carried out with samples of the above-mentioned materials, which were first weighed and then immersed in water for 24 h. Then, they were weighed again and exposed to microwave radiation. After exposure, the samples were weighed again, left immersed in water for 24 h, and weighed again. The focus of the study was on the ability of the aggregates to release water due to microwave radiation and on the changes in the properties (water absorption, thermal conductivity coefficient) of these materials when exposed to microwave radiation. The samples were further monitored by digital microscopy for possible changes in the surface layer of the materials. The hydrogels show the highest water absorption (1000%) and the fastest water release (45 min to complete desiccation). After the release of water due to microwave radiation, their ability to absorb water is maintained. Of interest, however, is that in the case of almost complete removal of water from the soaked hydrogel, the original powdered state of the hydrogel is not obtained, but the outcome has rather a solid structure. In the case of cork, the water absorption depends on the fraction of the material.