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Gradient porous materials, particularly carbon-based materials, hold immense potential in the fields of batteries, energy storage, electrocatalysis, and sensing, among others, by synergistically combining the attributes associated with each pore size within a unified structural framework. In this study, we developed a gradient porous aramid (GP-Aramid) by incorporating cellulose acetate as a porosity promoter in the polymer casting solution in different proportions. These GP-Aramids were subsequently transformed into their pyrolyzed counterparts (GP-Pyramids), retaining their original structures while displaying diverse cellular or dense microstructures inherited from the parent aramid, as confirmed via scanning electron microscopy. X-ray diffraction spectra provided evidence of the conversion of aramids into carbonaceous materials. The materials showed structural defects observed through the intensity ratio of the G and D bands (ID/IG = 1.05) in the Raman spectra, while X-ray photoelectron spectra (XPS) revealed that the carbonization process yielded pyrolyzed carbon materials unusually rich in nitrogen (6%), oxygen (20%), and carbon (72%), which is especially relevant for catalysis applications. The pyrolyzed materials showed bulk resistivities from 5.3 ± 0.3 to 34.2 ± 0.6 depending on the meta- or para-orientation of the aramid and the porous structure. This work contributes to understanding these gradient porous aromatic polyamides' broader significance and potential applications in various fields. [ABSTRACT FROM AUTHOR]

Aramids are man-made high performance fibers admitting useful industrial applications. Aramids can be classified into para-aramids and meta-aramids. Kevlar is a para-aramid and Nomex is a meta-aramid. This work is devoted to compute the empirical formula for the Hosoya polynomial of these aramids. The closed form of a number of distance-related topological indices (TIs) is the famous distance-based Hosoya polynomial. These are Weiner, hyper-Weiner and Tratch–Stankevitch–Zafirov indices. Results exhibit that para-aramid and meta-aramid possess different Hosoya polynomials and corresponding distance-based TIs. Further, distance-related TIs derived from Hosoya polynomial for the para-aramid admit larger values as compared to those of the meta-aramid. [ABSTRACT FROM AUTHOR]

Space missions with humans expose the crews to ionizing radiation, mainly due to the galactic cosmic radiation (GCR). All radiation protection programs in space aim to minimize crews' exposure to radiation. The radiation protection of astronauts can be achieved through the use of shields. The shields could serve as a suit to reduce GCR exposure and, in an emergency, as a radiation shelter to perform necessary interventions outside the space habitat in case of a solar proton event (SPE). A space radiation shielding that is suitable for exploration during space missions requires particular features and a proper knowledge of the radiation type. This study shows the results of numerical simulations performed with the Geant4 toolkit-based code DOSE. Calculations to evaluate the performance of Nomex, an aramidic fiber with high mechanical resistance, in terms of dose reduction to crews, were performed considering the interaction between protons with an energy spectrum ranging from 50 to 1100 MeV and a target slab of 20 g/cm2. This paper shows the properties of secondary products obtained as a result of the interaction between space radiation and a Nomex target and the properties of the secondary particles that come out the shield. The results of this study show that Nomex can be considered a good shield candidate material in terms of dose reductions. We also note that the secondary particles that provide the greatest contribution to the dose are protons, neutrons and, in a very small percentage, α-particles and Li ions. [ABSTRACT FROM AUTHOR]

Honeycomb materials are commonly used as cores for sandwich panels. While empirical evidence exists showing that the transverse shear strength of a honeycomb core is affected by its thickness, the accuracy of empirical guidelines and the reasons for the changes in strength are not well understood. Four-point flexural testing of sandwich beams and a detailed cellular finite element model are used to investigate transverse shear failure of Nomex™ honeycomb core material. Transverse shear strengths at varying core thicknesses were compared to manufacturer specifications and used to determine normalised strength correction factors for thickness. These factors correlated well with trends shown in previous literature, where core shear strength decreases with increasing core thickness. The failure mode investigation showed a transition between modes as core thickness increased. The thinner cores experience shear fracturing of individual cell walls followed by local cell wall buckling, intermediate thickness cores initially failed by cell wall local buckling, then fractured and larger thickness cores appeared to fail by overall cell column buckling. [ABSTRACT FROM AUTHOR]

• The presence of ZGV is predicted and confirmed in the CFRP-Nomex honeycomb structure. • The ZGV formation mechanism in the honeycomb structure is analyzed and elaborated. • A new debonding detection method is proposed using ZGV feature. Carbon fiber reinforced plastic (CFRP) − Nomex adhesive honeycomb structures are widely used in aerospace due to their excellent properties. However, debonding defects pose a significant challenge to structural safety due to their hidden nature and high risk. In this work, to address the debonding detection in the CFRP-Nomex honeycomb structure, a method based on the zero group velocity (ZGV) feature is proposed. By calculating the dispersion curve of the structure, it is found that there is the ZGV on the S 1 branch. Further analysis revealed that this ZGV feature is generated by the repulsion between the S 2 and S 1 branches. The simulation and experimental analysis of the acoustic propagation characteristics in the honeycomb structure confirmed the presence of the ZGV feature with its energy localized near the exciting point. When debonding defects occur in the honeycomb structure, this feature disappears. Therefore, the ZGV feature can be used for the debonding detection of CFRP-Nomex honeycomb structures. Compared with ultrasonic C-scan, the results demonstrate that the proposed method can accurately detect and locate debonding defects with a diameter of 20 mm. Due to its simplicity, the method does not require sophisticated equipment or complex signal processing procedures, making it suitable for in-service inspection. [ABSTRACT FROM AUTHOR]

The effect of varying temperature on the compressive properties of a Nomex honeycomb core reinforced with small diameter composite tubes and rods has been investigated experimentally. Compression tests have been undertaken on a commercially-available Nomex core reinforced with tubes or rods at temperatures between 20 and 140 °C. Tests were also undertaken on unreinforced Nomex cores in order to assess the benefits associated with localized reinforcement of the core. Compression tests on the unreinforced cores have shown that the strength decreased steadily with increasing temperature, passing from 4.8 MPa at room temperature to 3.8 MPa at 140 °C. Similarly, the specific energy absorption (SEA) of the plain core samples decreased slightly from 22.3 to 18.9 kJ/kg over this range of temperatures. Reinforcing the cores with either rods or tubes had a positive effect on the compressive properties of the cores over the range of temperatures considered. For example, the room temperature compression strengths of the rod reinforced cores were 70% higher those of the plain core. Similarly, at 140°C, the rod-reinforced systems were 20% stronger than the plain core. Finally, the energy-absorbing capacity of the tube reinforced cores was higher than that of the rod-reinforced cores. [ABSTRACT FROM AUTHOR]

We adopt here a novel approach to identify the para- and meta- aramid fibers using the available free volume in them. Positron Annihilation Lifetime Spectroscopy (PALS) has been employed to characterize the free volume in these fibers. The free volume content in the para- variety (Kevlar) is less and the free volume distribution is narrow as compared to its meta- counterpart (Nomex). The results are further validated by characterizing the free volume content in Nomex IIIA fibers, which is a blend composed mainly of para- and meta- aramid fibers. The free volume results are in good correlation with the mechanical properties of these fibers obtained by Universal Testing Machine (UTM), structural studies by X-ray diffraction (XRD) and storage modulus using Dynamic Mechanical Thermal Analysis (DMTA). The thermal decomposition temperature (T d ) of the fibers is characterized by thermo gravimetric analysis (TGA). We also show here the first results of an appreciable glass transition temperature (T g ) not only for the Nomex fibers but also for its blend Nomex IIIA using the combined results of Differential Scanning Calorimetry (DSC) and DMTA. [ABSTRACT FROM AUTHOR]

In the present paper, the influence of accelerated thermal aging on thermally upgraded Kraft and Nomex 910 insulated power transformers has been determined. The present experimental study also determines the effectiveness of 2, 6-dibutyl-4-methylphenol oxidative inhibitor on the degradation rate of mineral transformer oil with alternative solid dielectrics. From the accelerated aging studies, it has been revealed that Nomex impregnated oil samples have shown around 15% improved thermal characteristics over thermally upgraded Kraft oil samples. Also these samples have exhibited 20% enhanced oxidation stability even at temperatures more than 200°C. Therefore, Nomex insulating materials have been recommended as solid dielectrics for power transformers in order to achieve better operating characteristics and improved oxidation stability. [ABSTRACT FROM AUTHOR]

In this report, we describe the initial colonization of environmental microorganisms associated with ISS on four different materials (Nomex, cable labeling material, printed circuit board, and aluminum), which are commonly used at the ISS. Material substrates were placed in the Russian segment of the ISS in a Target Book for 135 days. After the incubation, the Target Book was analyzed on Earth by determining colony-forming units and identifying the microorganisms by rRNA gene sequencing. The highest cell concentrations and widest biological diversity were on the polymer materials, such as Nomex and cable labeling material. Additional molecular biological identification revealed the following organisms as typical pioneer microorganisms: Staphylococcus spp., Bacillus spp., Streptococcus spp., Cladosporium spp., Sphingomonas spp., Micrococcus luteus, and Stenotrophomonas maltophilia. [ABSTRACT FROM AUTHOR]

The main benefits of using the sandwich concept in structural components are the high stiffness, good fatigue resistance and low weight ratios. Recent advances in materials and construction techniques have resulted in further improvement and increased uniformity of the sandwich composite properties. In order to use these materials in different applications, the knowledge of simply their static properties alone is not sufficient but additional information on their fatigue properties and durability are required. In this paper, first static and fatigue tests on four points bending of nomex honeycomb composite sandwich panels have been performed. Load/displacement and S-N fatigue curves are presented and analysed. Fatigue failure and damage modes are observed with an optical microscope and are discussed. The second is to address such fatigue behaviour by using a damage model and check it by experimentation. This fatigue damage model is based on stiffness degradation, which is used as a damage indicator. Two non-linear cumulative damage models derived from the chosen stiffness degradation equation are examined with assumption of linear Miner's damage summation. Predicted results are compared with available experimental data. [ABSTRACT FROM AUTHOR]

Abstract: Composite sandwich structures are widely used in the high-performance applications where weight reduction is one of the most attractive design parameters. However, structural sandwich components have low resistance to out-of-plane impact due to the thin outer composite skins and the highly deformable cores. The present paper deals with a finite element study on the impact response of sandwich panels, obtained combining phenolic resin-based glass fiber reinforced plastics as skins and phenolic resin-impregnated aramid paper honeycomb structure (Nomex) as core. The numerical analysis has been performed using the LSDYNA software enabling to account for the main sandwich failure modes occurring during impact. The honeycomb core structure and composite skins have been modeled by means of solid and shell elements respectively. The properties of the finite element model have been calibrated on a series of experimental outcomes in order to achieve numerical parameters for both composite facesheet and orthotropic honeycomb material models. The major concerns are related to damage mechanisms, influence of strain-rate effects and energy absorbing capability. The model is validated using the results from experimental impact tests performed on different initial impact conditions. Good agreement was obtained between numerical and experimental results in terms of impact damage and force–displacement trend. [Copyright &y& Elsevier]

Abstract: Sandwich panels with honeycomb cores are used for aerospace frames where mass efficient structures are needed; however the structural integrity of these panels is reduced by low velocity impacts. Their behaviour on impact is investigated in this paper by means of refined numerical Finite Elements simulations. The sandwich panels considered are made of a Nomex™ honeycomb core and thin Al 2024-T3 aluminium alloy skins. A highly detailed FE model (micro mechanical level) has been built by using data obtained from flatwise compressive tests of honeycomb cores and a calibration of the constitutive law and ductile failure of aluminium skins. Numerical results are compared in terms of damage shapes and failure onset with an experimental campaign, carried out using a free-fall apparatus and a spherical steel impactor. The impact phenomena, including the failure of the skin, have been reproduced by means of numerical models with an elevated grade of similarity to a real impact scenario. Discussion and perspective are reported. [Copyright &y& Elsevier]

In a search for mineral oil substitutes, we focus on silicone and ester oil. These insulating oils are fire-resistant and environmentally friendly. In previous studies, we investigated streaming electrification and dielectric breakdown phenomena in these new oils and found that their performance was similar to or better than that of mineral oil. In the present study, we focus on the thermal degradation of insulating oils. Thermal degradation tests in the presence of a solid insulator and copper carried out for 1000 h at 130 and 180 °C. Color changes, chemical analysis and dielectric breakdown characteristics were also investigated during thermal degradation of the insulating oils. We also investigated the mechanical strength of the solid insulator. The characteristics of aged oils were compared with those of fresh oils. Tested silicone oil presents better performance than esters and mechanical characteristics of paper remain unchanged in all resistance liquids. [ABSTRACT FROM AUTHOR]

Abstract: The fabrication of surface functionalized alumina fabric composite membranes using hydrophilic cysteic acid surface stabilized alumina nanoparticles (alumoxanes) have been investigated. Contact angle measurements for a range of carboxylic acids functionalized onto alumina coated silicon wafers was investigated to determine the functionalization that results in the most hydrophilic surface. Highly porous Nomex® fabric was utilized as a membrane support for an alumoxane nanoparticle derived membrane filter. The flux differentiation of heavy hydrocarbons from water, and the separation of oil/water emulsions were studied. Coating techniques utilizing pH control were investigated. Retention coefficients and flux values indicate that surface chemistry of the fabric may be altered by coating with chemically functionalized alumina nanoparticles to provide selective flow of water versus hydrocarbons. [Copyright &y& Elsevier]

Abstract: Electrochemical characterization has been carried out for electrodes prepared of several activated carbon fiber samples derived from poly (m-phenylene isophthalamide) (Nomex) in an aqueous solution. Depending on the burn-off due to activation the BET surface area of the carbons was in the order of 1300–2800m2 g−1, providing an extensive network of micropores. Their capability as active material for supercapacitors was evaluated by using cyclic voltammetry and impedance spectroscopy. Values for the capacitance of 175Fg−1 in sulfuric acid were obtained. Further on, it was observed that the specific capacitance and the performance of the electrode increase significantly with increasing burn-off degree. We believe that this fact can be attributed to the increase of surface area and porosity with increasing burn-off. [Copyright &y& Elsevier]

Abstract: The effect of using multiple layers of the same fabric i.e. Nomex in the foam/fabric combination has been investigated using cone calorimetry. The fabric layers used reduce the peak heat release rate (PHRR) of the foam considerably. The delayed ignition and reduced PHRR with the increase in fabric layers in the foam/fabric combination is due to the reduced rate of heating. Carbon monoxide increases while carbon dioxide decreases with the increase in fabric layers in the foam/fabric combination. [Copyright &y& Elsevier]