The progressive miniaturization of electronic devices necessitates effective protection against electromagnetic interference and overheating. This study aims to explore the potential of polymer ...nanocomposites as multifunctional materials to address these challenges in applications related to airborne and space technology. Our investigation focuses on the hypothesis that the incorporation of graphene nanoplatelets (GNPs) into a fluoropolymer matrix (fluorinated ethylene propylene—FEP) will yield a composite material capable of simultaneously providing electromagnetic interference (EMI) shielding and enhanced thermal properties. This research presents initial studies as the foundational step toward designing multifunctional materials for specialized airborne and space technologies applications. The samples, comprising FEP and GNP, were fabricated using a simple powdered masterbatch hot pressing technique, ensuring optimal filler dispersion within the matrix. The dispersion quality was evaluated using Raman mapping and sheet/volume resistivity analyses. Subsequently, adding 25 wt% GNP results in outstanding EMI shielding effectiveness: SE
TOT
~ 50 dB at 5 GHz for only 1-mm-thick sample and almost 3000% enhancement of thermal conductivity (exceeding 4 Wm
−1
K
−1
), similarly nearly 2000% enhancement of thermal diffusivity (2 mm
2
s
−1
) and an electrical conductivity of over 7 S cm
−1
were observed. These results stand out for their remarkable values, especially considering the use of straightforward production methods without further structural improvements or metallic additives.
A three-dimensional (3D) sintering method of bulk magnetron targets has been developed recently. However, the use of bulk target had the following limitations: constrained geometry, limited ...chemical-phase composition, small size and cost-effectiveness. Thus a novel approach of surface sintering (2D) was arranged by a method of electromagnetic discharge evolution without applying any mechanical press. In the proposed method, the internal energy of pulsed plasma flux (~102.3 J) was dissipated at a tungsten (W) powder interface, therefore providing a form of sintered body with a density of 9.24–14.21 g/cm3 in the crystal structure of (α)-W. The morphology view indicates that, for the most part of sinters, only a subsurface (< 100 nm) was well-consolidated, which was in accordance with an almost fourfold increase in thermal diffusivity there, as showed the results of laser flash analysis. Subsequently, the decrease in mean porosity distribution (Vv) from 42.4% to 27.1% in consolidated surface was confirmed by using the microcomputed tomography (μCT) reconstruction. The (2D) sintered target was then used in the synthesis of pure metallic films by gas injection magnetron sputtering. As a result, a conductive (β)-W phase was recognized (103–405 μΩ cm), giving a promising hope for spintronic device applications.
Display omitted
•Surface sintering of W powder was arranged under the “pressureless glow discharge”.•A novel vapor source was encouraged due to the mass transport between W particles.•In-situ sliding front of sinter gave a lossless material input in W cathode design.•As consolidated tungsten favored a metastable (β)-W nucleation in deposited film.•Free-impurities W film proven to be promising for conductive spintronic application.
Despite the fact that thermal conductivity is a crucial parameter for SiAlON ceramics with respect to their suitability in various applications, including high-temperature structural components, wear ...parts, and cutting tools, studies on SiAlON ceramics reported thus far mainly focus on the improvement of their mechanical properties. In view of the lack of sufficient studies on the thermal conductivity of SiAlON ceramics, this study investigates the improvement in the thermal diffusivity behaviour of SiAlON ceramics by the addition of highly conductive SiC particles. As solid-solution SiAlON ceramics exhibit complex crystal structures typically composed of defects, the phonon scattering increases, subsequently decreasing diffusivity. In particular, the improvement in the thermal diffusivity of both α- and β-SiAlONs was investigated by the addition of 0.25wt% SiC. In addition, the effect of the SiC particle size on the thermal diffusivity of β-SiAlON was examined. Using inverse diffusivity data, intrinsic and extrinsic scattering parameters were determined, and compared to intrinsic scattering, extrinsic scattering was a dominant factor. Furthermore, transmission electron microscopy (TEM) images of SiCp-reinforced α and -β-SiAlON ceramics were recorded to examine the SiC particle distribution.
Display omitted
•Efficient exfoliation of hexagonal boron nitride by supercritical fluid processing.•The exfoliation benefited from the solvation power of supercritical ethanol and water.•Boron ...nitride nanosheets produced are of larger aspect ratios and less defects.•The nanosheets exhibited good compatibility with poly(vinyl alcohol) polymer.•The obtained nanocomposite films are flexible and of superior thermal diffusivity.
In the present study, a supercritical fluid (SCF) mixture was used for the rapid and efficient exfoliation of hexagonal boron nitride (h-BN), yielding high-quality boron nitride nanosheets (BNNs) of larger aspect ratios and less defects. The essence of this exfoliation strategy lies in the advantageous properties of SCFs, including especially the ultrahigh diffusivity and near-zero surface tension, as well as the special solvation power of water and ethanol under SCF conditions. These fluid medium conditions are ideally suited for the diffusion of solvent molecules into the interlayer spacing, coupled with their enhanced interactions with the B and N sites, to facilitate more efficient interlayer expansion and separation. The BNNs thus produced exhibited good compatibility with the selected polymer matrices, with the resulting polymeric nanocomposite films mechanically flexible and of superior thermal transport performance in terms of the observed thermal diffusivities higher than those based on BNNs from other exfoliation methods.
We are reporting the results of our exploration of the thermal lens method to determine the thermal diffusivity of Ppy and Ppy/Ag nanocomposites synthesised by simple, cost effective in situ chemical ...oxidative polymerisation. EDAX spectrum confirms the presence of silver in the samples. Raman analysis shows that the increase in the concentration of silver in composite results in an increase in the conjugation length of the samples. We have adopted the dual-beam pump-probe technique to determine the thermal diffusivity of polypyrrole and polypyrrole silver nanocomposite with varying silver concentrations. We report suppression of thermal diffusivity of polypyrrole with the addition of a small concentration of silver and an enhanced thermal diffusivity with an increase in the concentration of silver with ethanol as the base fluid. Increased thermal diffusivity of the samples makes them suitable for use as coolants.
Display omitted
In this work, iron oxide thin films were grown on glass slides and AISI 304 austenitic steel substrates using carbon steel as the cathodic cage in the plasma deposition process. For the deposition on ...steel 304, the temperature, time and concentration of oxygen (O) and argon (Ar) gases were kept constant, with the only variable being the concentration of hydrogen (H). However, the deposition on glass substrate was performed at temperature and concentration of O, Ar, and H gases with varying the deposition time. Structural, morphological, electrochemical, and thermal-optical properties of the films were investigated. Raman analysis showed an iron oxide layer composed of a hematite crystalline structure (α-Fe2O3). The images obtained using a field emission scanning electron microscope showed the formation of thin films well-shaped, with thickness ranging from 1.90 to 2.56 µm. The thermal-optical parameters showed that the thermal diffusivity of films grown on the glass slide varied with deposition time. Electrochemical experiments such as open circuit potential, electrochemical impedance spectroscopy, and polarization curves were performed, revealing that the iron oxide film formed with the gas flow rate of 4H2/4O2/4Ar improved the pitting corrosion resistance in the presence of corrosive saline solution. The electrochemical measurements highlighted that the steel treated in the above condition (gas flow rate of 4H2/4O2/4Ar) had a pitting potential (Epit = +0.842 V vs. Ag/AgCl, KCl sat.) of ∼x223C 400 mV, higher than the untreated steel.
The structure and thermal diffusivity of SiC - NbC ceramic materials are investigated. It is shown that with a change in the composition in sintered ceramics, the lattice parameter changes, and also ...in the near-contact region there is a mutual diffusion of silicon and niobium. This indicates the formation of solid solutions. As the niobium carbide content and temperature increase, the thermal diffusivity of SiC - NbC ceramic materials decreases.
•Geopolymer concretes have no signs of spalling when exposed to a hydrocarbon fire.•Residual strength of 60% was maintained after fire exposure.•Geopolymers have excellent fire resistance due to low ...thermal incompatibility.
This study presents an investigation of the effect of hydrocarbon fire exposure on the residual compressive strength properties of geopolymer concrete panels and cylinders. Gladstone flyash was utilized as the binder whilst the alkaline solution/fly-ash ratio and sodium silicate to sodium hydroxide (Na2SiO3/NaOH) ratio was 0.4 and 2.5 respectively. The compressive strength at the test date was 64MPa. Two different cylindrical specimens’ sizes (150 and 100mm diameter×300 and 200mm high) were exposed on all sides to the hydrocarbon fire scenario for 120min whilst panels of 1075×1075×200mm were exposed on one side for the same time duration. Results showed that no significant spalling occurred in any of the specimens and the mass loss during heating was between 2.70 and 4.65% respectively which was attributed due to moisture loss. Low differential gradients and thermal incompatibility between the geopolymer paste and aggregates provides geopolymer concrete with superior spalling resistance than Ordinary Portland cement concrete. Residual compressive strength testing showed that the panels maintained approximately 60% of their initial compressive strength indicating that geopolymer concrete specimens can maintain sufficient load bearing capacity in the event of fire exposure. The residual strength profiles indicated that specimen size effect was also exhibited with the remaining strength of the cylinders being approximately 10 and 20% for the 100mm and 150mm dimeter specimens respectively. The dull red color exhibited in all specimens after fire testing indicated the presence of high iron content in the geopolymer matrix. Insitu temperature analysis showed that the geopolymer concrete had excellent heat resistance capabilities with temperatures at a depth of 100mm from the exposed surface ranging between 39°C and 45°C after 30min of fire exposure even though the temperature at exposed surface exceeds 1000°C. This is reinforced by the fact that the geopolymer has a high heat storage capacity as indicated by the geopolymers lower thermal diffusivity than OPC concrete.
PDF
