Thermal Conductivity Of Samples Research Articles

A three-probe method for accurate nanoscale thermal transport measurements

Measurements of transport phenomena are constantly plagued by contact resistance, prohibiting the sample's intrinsic electrical or thermal conductivity from being accurately determined. This predicament is particularly severe in thermal transport measurements due to the inability to meet similar impedance requirements for a four-probe method used in electrical resistance measurements. Here, we invent a three-probe measurement method that makes an accurate determination of thermal conductivity possible for nanomaterials. Incorporating electron beam heating provided by a scanning electron microscope (SEM) on a diffusive thermal conductor not only quantifies the thermal contact resistance, which may introduce an error of more than 270% to a sample's thermal conductivity, but also eliminates several device uncertainties that may contribute an additional 17% error in a measurement. The method also enables local temperature measurements, revealing nanoscale structural variations unfound by SEM. The high accuracy of the technique would make standardization of nanoscale thermal transport measurement possible.

Structure and thermal conductivity of high-pressure-treated silica glass. A molecular dynamics study

High-pressure treatment of oxide glasses can lead to significant alteration of various material properties such as increased density, ductility, and elastic moduli. In this study, a model of melt-quenched bulk silica glass was subject to high-pressure treatments (up to 16 GPa) using molecular dynamics simulations. The thermal conductivity of such prepared glass structures was determined using the equilibrium Green–Kubo method. We observed that, up to the pressure treatments of ∼6 GPa, the structure exhibits moderate density increase and a much steeper increase between 6 and 16 GPa, with associated density increase of fivefold silicon atoms. We also observed a noticeable increase (up to 20%) of the thermal conductivity in samples subjected to high-pressure treatments. The observed increases are somewhat, but not significantly, larger than those predicted by the minimum thermal conductivity model, accounting for density and elastic moduli increase.

Theoretical prediction and experiment study on the thermo-physical properties of ternary carbonate for energy storage

This study calculated the optimal formula (sample A) of ternary carbonate based melting salt using a phase diagram firstly and other four sets of ternary carbonates with different ratios were prepared by changing the content of sodium carbonate and lithium carbonate. The results showed that sample A had better comprehensive thermophysical properties, the melting point, phase change enthalpy, upper limit temperature of thermal stability and stability were the optimal. Whose melting point and phase change enthalpy were 395.57 °C and 322.06 J/g, respectively. The specific heat capacity in the solid phase (330–380 °C) enhanced slightly from 1.38 J/(g·K) to 1.84 J/(g·K) with the increase of temperature, while in the liquid phase, the specific heat capacity was maintained at 1.5 J/(g·K). The ternary carbonate only underwent simple physical mixing without chemical reactions, the decomposition temperature and thermal conductivity of sample A were 885.73 °C and 1.325 W/(m·K), respectively. The ternary carbonates exhibited good thermal stability when continuously heating and heating-cooling cycles.

Measuring Thermal Conductivity of Single Thickness Fibrous Gas Diffusion Layers Using Transient Plane Source Method

In a proton exchange membrane fuel cell (PEMFC), the gas diffusion layer (GDL) is a porous material placed between the flow field plates and the catalyst layer. Its primary responsibility is to distribute reactants evenly across the surface of the catalyst layer while allowing for the removal of excess water and heat produced during operation. The GDL is typically made of a carbon-based material, such as carbon paper or carbon cloth, which is treated with polytetrafluoroethylene (PTFE) to become hydrophobic. This treatment allows it to repel water and facilitate the transport of gases such as hydrogen and oxygen during operation. The thermal conductivity of the GDL plays a crucial role in managing the heat and water of PEMFCs.The Guarded Heat Flow (GHF) technique is a well-established steady-state method for measuring the thermal conductivity of carbon fiber papers. This is achieved by testing two different thicknesses of a material that have an identical structure [1-3]. Using this two-thickness method, as per ASTM standard C177-19e1 [4], enables the bulk thermal conductivity to be deconvoluted from the thermal contact resistance at the interface between the sample and the measurement device's surface (an interfacial phenomenon). However, materials with identical structures for two-thickness measurements are not always available for commercial GDLs. In this study, we compare the transient plane source (TPS) thin film method, which measures the thermal conductivity of single thickness GDL samples, with the two-thickness GHF method for measuring thermal conductivity.In this study, GDL samples with the same bulk structure and manufactured in two thicknesses were used: Sigracet series 24BA and 34BA with original thicknesses of 190 µm and 280 µm, respectively. A custom-built Thickness Under Compression and Resistance Under Compression machine (TUC-RUC) was utilized to measure the thickness of the samples under loads ranging from 0.35 MPa to 2 MPa. The thickness under compression was measured for five samples (25.4 mm diameter) of each type of GDL. The standard deviation for each sample thickness was below 4%. As shown in Fig. 1, the stress-strain response of the GDL samples was measured and analyzed to assess the similarity in their mechanical structures. Consistent with the assumptions that both samples have the same structure, the GDL samples with two different thicknesses displayed identical stress-strain behavior under compression, as shown by the curve-fit for stress-strain behavior in proposed Fig. 1.The thermal conductivity of the samples was measured using both the TPS thin films method, as per ISO 2207-2:2022 [5], and the GHFM. On the TPS, three samples of each type of GDL were measured three times. The measured thermal conductivities increased with compression, ranging from 0.15 to 0.47 W/mK, with a standard deviation of less than 5% for each measurement. The results from the TPS technique for a single thickness of GDL were compared with the two-thickness measurements conducted using the GHFM, as shown in Figure 2. The GHFM tests were conducted on three samples of each type of GDL at five compressive loads, and the standard deviation on the deconvoluted thermal conductivity was less than 7% for each measurement. The values measured by the two techniques were found to be in good agreement, with a relative difference of within 6%. This study demonstrates that the transient plane source (TPS) method, when combined with an accurate thickness measurement technique, is a precise technique for determining the bulk thermal conductivity of commercial GDLs produced in a single thickness.[1] H. Sadeghifar, N. Djilali, and M. Bahrami, “Effect of Polytetrafluoroethylene (PTFE) and micro porous layer (MPL) on thermal conductivity of fuel cell gas diffusion layers: Modeling and experiments,” Journal of Power Sources, vol. 248, pp. 632–641, Feb. 2014, doi: 10.1016/j.jpowsour.2013.09.136.[2] M. Ahadi, M. Andisheh-Tadbir, M. Tam, and M. Bahrami, “An improved transient plane source method for measuring thermal conductivity of thin films: Deconvoluting thermal contact resistance,” International Journal of Heat and Mass Transfer, vol. 96, pp. 371–380, May 2016, doi: 10.1016/j.ijheatmasstransfer.2016.01.037.[3] E. Sadeghi, N. Djilali, and M. Bahrami, “Effective thermal conductivity and thermal contact resistance of gas diffusion layers in proton exchange membrane fuel cells. Part 1: Effect of compressive load,” Journal of Power Sources, vol. 196, no. 1, pp. 246–254, Jan. 2011, doi: 10.1016/j.jpowsour.2010.06.039.[4] “Test Method for Steady-State Heat Flux Measurements and Thermal Transmission Properties by Means of the Guarded-Hot-Plate Apparatus.” ASTM International. Doi: 10.1520/c0177-19e01.[5] “ISO22007-2, Plastics-determination of thermal conductivity and thermal diffusivity-part 2: transient plane heat source (hot disc) method”, 2022. Figure 1

Fabrication of fine-grained and high thermal properties Y2O3 transparent ceramics without sintering aids

Infrared transparent pure Y2O3 nanoceramics were fabricated from citric acid sol-gel combustion synthesized nanopowder and through the combination of hot pressing and hot isostatic pressing. The influence of calcination temperature on the morphology, particle size and agglomeration state of the nanopowders during powder synthesis process was investigated. Powder with a particle size of 15.5 nm and agglomeration factor of 3.3 was obtained with the calcination temperature at 700 °C for 4 h. Green compact with homogenous microstructure and improved sintering activity was consolidated by cold isostatic pressing after dry pressing. Y2O3 transparent ceramic was achieved with hot pre-sintering at 1400 °C without holding plus hot isostatic pressing at 1450 °C for 2 h under 200 MPa pressure. As a result, the ceramic prepared with 1.0 mm thickness got the transmission of 80.4 %–83.9 % at 2.5 μm–6.0 μm wavelength with an average grain size of 413 nm. The sample's thermal conductivity was 12.84 W m−1 K−1 and the phonon energy was 592 cm−1, making it a promising material for IR transparent windows and host material for efficient infrared solid-state laser. The sintering mechanism was proposed and discussed.

Revealing the impact of isolated pores on the properties of foam cement using hollow microspheres

Since foam concrete inevitably leads to foam bursting and merging during the molding process, the relationship between specific pore connectivity and pore diameter distribution on foam concrete properties is still difficult to characterize exactly. This study intentionally introduced hollow microspheres of three sizes (40 µm, 60 µm, and 80 µm) into foam concrete to control the number and diameter of isolated pores. The influence of isolated porosity and pore diameter distribution on the properties of foam concrete were evaluated by dry density, mechanical property and thermal conductivity. Meanwhile, the SEM and X-CT technologies were employed to assess the pore structure of the sample, and the measured thermal conductivity was compared with the theoretical thermal conductivity calculated by the formula based on the isolated porosity. Finally, the correlation between isolated pores and heat transfer paths were analyzed by the calculated tortuosity. The results of the dry density and mechanical tests indicated that the dry density tended to be lower with the increase of isolated pores’ diameter, which 80 µm hollow microspheres resulted in a notable reduction in the dry density within the three size groups, whereas 28 days compressive strength trended oppositely. The 40 µm hollow microsphere specimen with a dry density of 400 kg/m3 exhibited the better mechanical property among three groups, which was 1.82 MPa, due to the uniform distribution within the matrix, preventing fusion between foams. Specifically, the trend of the theoretical value calculated by the formula was consistent with that of the measured value, proving that the decrease in thermal conductivity of sample can be attributed to the increase of isolated porosity. The lowest thermal conductivity and highest tortuosity were achieved by specimens mixed with 80 µm hollow microspheres at the dry density of 300 kg/m3, which were 0.07045 W/(m·K) and 2.015, respectively, demonstrating that specimens mixed with 80 µm hollow microspheres exhibited a more complex heat transfer path than the other two groups.

Development of state of art test setup to measure thermal conductivity of soils infused with treated and un‐treated natural microorganisms

AbstractSoil is a natural heterogeneous material and from its formation process, heat transfer capacity (thermal conductivity) of soil is playing vital role in many engineering applications. The aim of this research study is to enhance thermal conductivity using natural and treated bacteria from soil samples procured from four different regions namely Dholera, Navsari, Sabarmati River, and Madhavpur of Gujarat, India. To fulfill this objective, thermal conductivity test set‐up was indigenously developed based on guarded hot plate method and is calibrated up to 150°C temperature. The colonies of microorganisms available in soil were studied by serial dilution and spread plate technique. Further, influence of microorganisms on soil structure aggregation pre and post treatment was analyzed by microscope. Four types of microorganisms were introduced in the soil and the thermal conductivity of sample is measured for curing period of 7, 14, 21, and 28 days. The results indicate increment in k value for thermal conductivity in clayey soil up to 26.67% and decrement in sandy soil is up to 45.45%, while most optimum results were observed for 7 days curing period. Present research demonstrates use of microbes available in various soils to enhance heat transfer mechanism through proper identification and treatment.

Nonnegligible Temperature Drop Induced by Thermocouple on Samples in Gleeble Tests

High-temperature plastic deformation is one of the main methods for the fabrication of titanium-based alloys. Accurate determination of the mechanical constitutive relation is pivotal for the design, optimization, as well as the prediction of the mechanical behavior of materials. In this study, finite element simulations were carried out to simulate the Gleeble thermal compression experiment of titanium alloy samples, focusing on different thermocouple design parameters, including thermocouple material and wire diameter, etc. The results show that the heat dissipation of the thermocouple distorted the local temperature field of the contact point between the sample and the thermocouple, resulting in a deviation of the measured temperature. Through finite element method (FEM) simulation and analysis of the changes caused by various factors and comparison with the metallographic morphology of titanium alloy samples from relevant heat treatment experiments, it was shown that the material and wire diameter of the thermocouple, the thermal conductivity coefficient of sample, and the testing temperature of the sample all affected the measurement results. The thermal conductivity of sample had the largest influence on the measurement accuracy. Based on the finite element simulation and experimental comparison, the corresponding correction method and correction formula are proposed.

Effect of Anti-Hydrolysis AlN Microspheres on the Electrical Insulation and Thermal Conductivity of PMIA Paper

Poly-(meta-phenylene isophthal-amide) (PMIA) has been considered as an ideal insulating medium due to its excellent thermal stability and insulative strength. However, the poor thermal conductivity limits its application in complex electro-thermal environments. In this paper, AlN microspheres were modified with H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> PO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> and Al(H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> PO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> ) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> to gain resistance of hydrolysis, and then p-AlN/PMIA composite paper was prepared with a synergistic enhancement of the insulation and thermal conductivity. The results showed that, after doping with 10wt% of p-AlN, the paper was endowed with the breakdown strength of 35.0 kV/mm, which was 28.2% higher compared to the pure PMIA paper. While the thermal conductivity of PMIA paper was enhanced by only 22.3%. After doping with 40wt% of p-AlN, the thermal conductivity of sample was further improved to 0.277 W/(m∙K), which was 168.7% higher than that of pure PMIA paper, while the breakdown strength was maintained at 24.4 kV/mm.

Performance Analysis of Loose-Fill Thermal Insulation from Wood Scobs Coated with Liquid Glass, Tung Oil, and Expandable Graphite Mixture.

The current study presents the results of monitoring the behavior of loose-fill thermal insulating material for buildings made of wood scobs (WS), which were coated with one, two, and three component-based coatings from liquid glass (LG), tung oil (TO), and expandable graphite (EG). The thermal conductivity of samples in the dry state and under normal laboratory conditions, short-term water absorption by partial immersion, surface wettability, and water vapor permeability were evaluated, and regression equations describing the variations in numerical values of specified properties under different amounts of each coating component were presented. It was shown that LG and TO act as hydrophobic layers that, in conjunction, reduce water absorption by a maximum of 274%, have a contact angle equal to 86°, and lower thermal conductivity by 55% in the dry state due to the specifics of the layer formed on the surface of WS. The addition of EG to LG coating resulted in insignificantly changed water absorption and thermal conductivity values, indicating the potential of this material to be used to improve the fire resistance of wood-based composites in the future. The results showed that the three-component layer of LG/TO/EG reduces water absorption by a maximum of 72%, increases thermal conductivity in the dry state by a minimum of 0.4%, and increases the contact angle to 81° at 100 wt.% LG. The changes in water vapor permeability of all compositions were determined to be insignificant.

Modulating pore microstructure of silica aerogels dried at ambient pressure by adding N-hexane to the solvent

In this work, a kind of superhydrophobic silica aerogels was prepared at ambient pressure using tetraethoxysilane (TEOS) as precursor. Particularly, N-hexane was added in the solvent to modulation pore microstructure and effect on the insulation properties of samples were analyzed. It is discovered that when the volume ratio of N-hexane to TEOS is 1:2.24 the thermal conductivity of samples can reach the lowest of 0.012 W/m·K. Compared with that of samples no addition of N-hexane, the density is decreased, the theoretical average pore size increases and the total pore volume increases. Due to N-hexane it leads cross-linking between the sol particles stronger and inhomogeneous. Thus gelation process is speeded up resulting in a change in pore structure. Low density can reduce the solid-phase heat transfer, perfect pore microstructure reduces the contribution of gas-phase heat transfer, and only when the two aspects forms a suitable combination it can exhibit optimal thermal insulation performance.

Nano Engineered Paraffin-Based Phase Change Material for Building Thermal Management

Thermal energy storage (TES) and harvesting is an effective technique for optimum building thermal management. Phase-change materials (PCMs) are commonly used for TES applications but are troubled by their degraded thermal conductivity. Recent research progress in latent heat energy storage using PCMs and nano additives provides a viable solution for solar TES. A series of hybrid nano-enhanced phase change materials (HNePCMs) were prepared via two-step synthesis. Hybrid graphene–silver nanofillers were dispersed in commercial paraffin (melting point 25 °C) under different dispersion rates (0.1%, 0.3%, 0.5%). Different characterization techniques, e.g., FESEM, FT-IR, UV-VIS, TGA, XRD, DSC, and Tempos, were used in material characterization. A maximum enhancement of 6.7% in latent heat and 5% in heat storage efficiency was noted for nanocomposites with 0.3 wt% of additives. The nanocomposite with 0.3 Wt% showed great potential in shielding UV rays and showed a reduction of 6.5% in bandgap energy. Furthermore, the thermal conductivity of samples was boosted by a maximum of 90% (from 0.2 W/mK-0.39 W/mK) with 0.3 wt% dispersion of graphene–silver nanofillers. The thermophysical characterization results establish that the synthesized paraffin/graphene–silver hybrid nanocomposites are well suited for building thermal management.

A thermal balance method for measuring thermal conductivity by compensation of electric cooling or heating based on thermoelectric modules

To achieve the accuracy and convenience of thermal conductivity measurement, a thermal balance method for measuring thermal conductivity by compensation of electric cooling or heating based on thermoelectric modules is proposed in this paper. In this method, the thermoelectric module is regarded as the compensation unit to achieve the thermal balance between the compensation and test sides. Using the balance principle, the sample's thermal conductivity to be measured can be obtained by knowing the thermal conductivity of the compensation side. According to theoretical and experimental research, the compensation model is divided into self-supply energy and energy supply modes, and the law of thermal conductivity changes in thermoelectric modules in the two supply modes is summarized. To verify the feasibility of the thermal balance method, the thermal conductivity of alumina ceramics and polymethyl methacrylate (PMMA) materials with large differences in thermal conductivity were measured. The experiment proved that the thermal conductivity of alumina ceramic is 19.23 W/mK, slightly smaller than the standard value. The average thermal conductivity of PMMA is 0.21 W/mK, consistent with standard values. Taking the experiment conditions and error into account, the data are effective, which verified the feasibility of this method.

Evaluating the effective thermal conductivity of cement mortar through x-ray scanning

The effective thermal conductivity of cement mortar as a porous material depends on its solid phase and void phase conductivity. Therefore, a sample's pore distribution can highly impact the value of effective thermal conductivity. For this reason, an x-ray CT scanner was applied to detect air-void content in mortars with different mix proportions. After 28 days of curing, the thermal conductivity of samples (40 × 40 × 80 mm3) was measured by the transient plane source (TPS) apparatus, TPS2500. Then, the samples were scanned by a Zeiss Metrotom 1500 CT scanner to detect the macro pore content. Finally, the VGStudio Max 3.0 software was applied to observe the voids and simulate the effective thermal conductivity. The results showed that the total macro void contents (in this study, voids bigger than 52 μm) were increased up to 15% and 33% for samples with the cement the sand ratio of 1:3 and 1:4 compared to the sample with the c:s ratio of 1:2. However, the results indicated that the void fraction is not uniform. Therefore, effective thermal conductivity can vary in different sample locations. The finding shows that x-ray scanning and image analysis is the proper method to precisely determine the effective thermal conductivity of cement-based materials.

Effective Enhancement of Thermal Conductivity and Electrical Conductivity with Poly(3,4‐ethylenedioxythiophene):Poly(4‐styrenesulfonate) through Solvent Treatment

AbstractThe preparation of poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) film is proposed as a simple and industrialized approach. PEDOT:PSS is diluted with deionized water, tetrahydrofuran, dimethyl formamide, and dimethyl sulfoxide before being dry and suction filtered to create a membrane. After treatment with polar organic solvent, the in‐plane thermal conductivity of sample is increased from 1.386 to 2.375 Wm−1 K−1. The electrical conductivity increases from 1.8 to 592 S cm−1. The structural modifications of PEDOT:PSS considerably increase the heat conductivity, according to UV, X‐ray photoelectron spectroscopy (XPS), X‐ray diffraction (XRD), and atomic force microscopy (AFM) characterization. This modification improves the polymer's thermal conductivity by increasing the contact force between molecules and changing the long chain conformation of polymers.

Effect of Ultra-High Pressure Sintering and Spark Plasma Sintering and Subsequent Heat Treatment on the Properties of Si3N4 Ceramics.

In this study, coarse Beta silicon nitride (β-Si3N4) powder was used as the raw material to fabricate dense Si3N4 ceramics using two different methods of ultra-high pressure sintering and spark plasma sintering at 1550 °C, followed by heat treatment at 1750 °C. The densification, microstructure, mechanical properties, and thermal conductivity of samples were investigated comparatively. The results indicate that spark plasma sintering can fabricate dense Si3N4 ceramics with a relative density of 99.2% in a shorter time and promote α-to-β phase transition. Coarse β-Si3N4 grains were partially fragmented during ultra-high pressure sintering under high pressure of 5 GPa, thereby reducing the number of the nucleus, which is conducive to the growth of elongated grains. The UHP sample with no fine α-Si3N4 powder addition achieved the highest fracture strength (822 MPa) and fracture toughness (6.6 MPa·m1/2). The addition of partial fine α-Si3N4 powder facilitated the densification of the SPS samples and promoted the growth of elongated grains. The β-Si3N4 ceramics SPS sintered with fine α-Si3N4 powder addition obtained the best comprehensive performance, including the highest density of 99.8%, hardness of 1890 HV, fracture strength of 817 MPa, fracture toughness of 6.2 MPa·m1/2, and thermal conductivity of 71 W·m−1·K−1.

Preparation and thermal conductivity of tungsten coated diamond/copper composites

Tungsten was plated on the surface of diamond by using thermal diffusion method. Different process parameters were employed to prepare the composites with tungsten, diamond and copper. The micro morphology of different samples was observed, and the thermal conductivity of samples was measured by laser flash method. The optimal process parameters for preparing diamond/copper composites with high thermal conductivity were investigated. The results indicated that plating tungsten on diamond could modify the interface bonding. When the diamond was plated for 60 min, the coating appeared intact, uniform and flat, and the thermal conductivity of the sample could reach as high as 486 W/(m·K). The integrity and uniformity were more important than thickness for the coating. When the tungsten-plated diamond was further annealed, the metallurgical bonding between the coating and the diamond was enhanced, and the thermal conductivity rose to 559 W/(m·K).

ADN Solid Propellants with High Burning Rates as Booster Material for Hypersonic Applications

AbstractRAM‐ and SCRAM‐Jet engines can not generate static thrust and only work at high speeds. This starting velocity of the motor v0 is usually generated by carrier rockets or boosters, which mostly use solid propellants based on ammonium perchlorate (AP) and hydroxyl‐terminated polybutadiene (HTPB). Modern solid propellants based on ammonium dinitramide (ADN) and Glycidyl Azide Polymer (GAP) have significant advantages in terms of environmental compatibility and thermodynamic performance. In the present work, it is shown that the already high burning rate of ADN solid propellants can be more than doubled by means of metallic fibers, which significantly increases the thrust of such engines. In order to achieve such results, 3 wt% of Al−Mg alloy fibers are added to the propellant. A formulation with 3 mm long fibres shows the highest burning rate with 84.0 mm/s at 26.5 MPa. Small scale motor tests confirm these investigations. The burning mechanism is studied by SEM/EDX investigations and by measuring the thermal conductivity. These show that the fibres remain on the burning surface and thus transfer the heat from the flame to the depth of the propellant. The thermal conductivity of samples with AlMg5 fibers is about 22 % higher than the reference.

Analysis of the Density Variation on Thermal Conductivity Wood Plastic Composite Made from Lamtoro Wood (Leucaena leucocephala) And Polypropylene Waste

The thermal conductivity of Wood Plastic Composite (WPC) made with lamtoro wood and polypropylene (PP) was studied by varying its density. The PP was obtained from 240 ml mineral plastic glasses, and the lamtoro wood particles were shieved in 6 mesh sizes. In this study, we considered the composition ratio between PP and wood particles to be 70:30, and the thermal conductivity was measured using a thermal conductivity apparatus. Based on the data analysis, we found that the density of WPC made with PP and lamtoro wood influenced its thermal conductivity. The results showed that the thermal conductivity of sample A is 0.2 W/mºC, sample B is 0.4 W/mºC, and sample C is 0.5 W/mºC, for the densities of 0.4 g/cm3, 0.5 g/cm3, 0.6 g/cm3, respectively. In conclusion, as the density increases, the thermal conductivity of WPC also increases. Thus, based on it thermal conductivity, the WPC made from PP and lamtoro wood is classified as an isolator.

Production of evaporation suppression floating covers using ultra-lightweight alkali-activated slag concrete

Evaporative losses from reservoirs exacerbate water shortage during dry spells. Notwithstanding the extensive application of self-assembling floating covers for suppressing evaporation, the cover material is often overlooked and limited to available choices such as plastics. The present study is aimed at the production of floating covers using ultra-lightweight alkali-activated slag concrete that offers a range of mechanical and chemical features. Concrete specimens were made with different percentages of ground granulated blast-furnace slag as the binder, sodium metasilicate as the alkaline activator and lightweight perlite aggregates with a density of 100–150 kg/m3. To solve the problem of fracture in the preliminary specimens, slag was partially replaced with 15, 20 and 30% lime. In addition, microsilica (10, 12 and 15%) was introduced to improve the mechanical properties of the samples. In designs without microsilica, 30% replacement of slag with lime resulted in the desirable density, strength and permeability of samples. Results showed that microsilica generally increased the density, resistance and thermal conductivity of samples by 7, 74 and 14%, respectively, while water absorption and permeability decreased by 15% and 14%, respectively. The dry density of samples was obtained between 340 and 516 kg/m3 with a compressive strength of 0.2–0.9 MPa and a conductive heat transfer coefficient of 0.067–0.093 W/mK.