Carbon Allotropes-Based Paints and Their Composite Coatings for Electromagnetic Shielding Applications

Development and Experimental Verification of Inorganic Electromagnetic Pulse Shielding Paint for Building Interiors Using Carbon-Based Materials

The term electromagnetic pulse (EMP) generally refers to high-power electromagnetic waves and can be classified into EMPs caused by nuclear weapons, non-nuclear EMPs, and EMPs caused by natural phenomena. EMPs can cause catastrophic damage to any electronic device consisting of electromagnetic components, including communications devices and transportation. In this study, the shielding effectiveness of paint was evaluated depending on the type and content of carbon material and binder. To analyze the compatibility and dispersibility improvement of the raw materials used in paint manufacturing, experiments were conducted in two stages, using 27 mixtures. The shielding effectiveness was evaluated for the optimal mixture developed through mixture experiments. The results of this study confirmed that the developed EMP shielding paint can improve the shielding effectiveness of concrete by 25-40 dB. Additionally, the adhesion strength and moisture resistance evaluation of the EMP shielding paint were evaluated. The average adhesive strength of the EMP shielding paint was 1.26 MPa. In moisture-resistance testing at a temperature of 50 ± 3 °C and a relative humidity of 95% or higher for more than 120 h, no cracks or peeling were observed on the painted surface.

Playing with Low Amounts of Expanded Graphite for Melt-Processed Polyamide and Copolyester Nanocomposites to Achieve Control of Mechanical, Tribological, Thermal and Dielectric Properties

Polyamide 11 (PA11) and copolyester (TPC-E) were compounded through melt extrusion with low levels (below 10%) of expanded graphite (EG), aiming at the manufacturing of a thermally and electrically conductive composite resistant to friction and with acceptable mechanical properties. Thermal characterisation showed that the EG presence had no influence on the onset degradation temperature or melting temperature. While the specific density of the produced composite materials increased linearly with increasing levels of EG, the tensile modulus and flexural modulus showed a significant increase already at the introduction of 1 wt% EG. However, the elongation at break decreased significantly for higher loadings, which is typical for composite materials. We observed the increase in the dielectric and thermal conductivity, and the dissipated power displayed a much larger increase where high frequencies (e.g., 10 GHz) were taken into account. The tribological results showed significant changes at 4 wt% for the PA11 composite and 6 wt% for the TPC-E composite. Morphological analysis of the wear surfaces indicated that the main wear mechanism changed from abrasive wear to adhesive wear, which contributes to the enhanced wear resistance of the developed materials. Overall, we manufactured new composite materials with enhanced dielectric properties and superior wear resistance while maintaining good processability, specifically upon using 4-6 wt% of EG.

Porous Structure and Fractal Dimensions of Activated Carbon Prepared from Waste Coffee Grounds

The present work reports the results of a systematic study on the evolution of the morphological properties of porous carbons derived from coffee waste using a one-pot potassium-hydroxide-assisted process at temperatures in the range of 400-900 °C. Raw materials and obtained carbons were studied by TG, DTG, SEM and nitrogen adsorption porosimetry. The decomposition temperature ranges for hemicellulose, cellulose and lignin as the main component of the feedstock have been established. It is shown that the proposed method for the thermochemical treatment of coffee waste makes it possible to obtain activated carbon with a controllable pore size distribution and a high specific surface area (up to 1050 m2/g). A comparative study of the evolution of the distribution of pore size, pore area and pore volume has been carried out based on the BJH and NL-DFT (slit-like pores approximation) methods. The fractal dimension of the obtained carbons has been calculated by Frenkel-Halsey-Hill method for single-layer and multilayer adsorptions.

Synthesis and Application of Ion-Exchange Magnetic Microspheres for Deep Removal of Trace Acetic Acid from DMAC Waste Liquid

In order to develop a deep method for removing trace acetic acid from industrial solvents, a type of quaternary ammonium-salt-modified magnetic microspheres was developed as a potential nanoadsorbent for low-concentration acetic-acid-enhanced removal from DMAC aqueous solution. The ion-exchange magnetic microspheres (Fe₃O₄@SiO₂@N(CH₃)₃⁺) have been prepared by a two-step sol-gel method with N-trimethoxysilylpropyl-N, N, N-trimethylammonium chloride as functional monomer, tetraethyl orthosilicate as a cross-linking agent, Fe₃O₄@SiO₂ as a matrix. The nanocomposite is characterized by SEM, FI-IR, XRD, VSM, and XPS. Moreover, the optimization of adsorption experiments shows that the maximum adsorption capacity of nanoadsorbent is 7.25 mg/g at a concentration = 30 mg/L, adsorbent dosage = 10 mg, V = 10 mL, and room temperature. Furthermore, the saturated Fe₃O₄@SiO₂@N(CH₃)₃⁺ achieved an efficient regeneration using a simple desorption method and demonstrated a good regeneration performance after five adsorption/desorption cycles. In addition, Fe₃O₄@SiO₂@N(CH₃)₃⁺ was used to remove acetic acid in DMAC waste liquid; the adsorption effect is consistent with that of a nanoadsorbent of acetic acid in an aqueous solution. These results indicate that Fe₃O₄@SiO₂@N(CH₃)₃⁺ can efficiently treat acetic acid that is difficult to remove from DMAC waste liquid.

Comparative Study of Graphene Nanoplatelets and Multiwall Carbon Nanotubes-Polypropylene Composite Materials for Electromagnetic Shielding

Graphene nanoplatelets (GNPs) and multiwall carbon nanotubes (CNTs)-polypropylene (PP) composite materials for electromagnetic interference (EMI) shielding applications were fabricated as 1 mm thick panels and their properties were studied. Structural and morphologic characterization indicated that the obtained composite materials are not simple physical mixtures of these components but new materials with particular properties, the filler concentration and nature affecting the nanomaterials’ structure and their conductivity. In the case of GNPs, their characteristics have a dramatic effect of their functionality, since they can lead to composites with lower conductivity and less effective EMI shielding. Regarding CNTs-PP composite panels, these were found to exhibit excellent EMI attenuation of more than 40 dB, for 10% CNTs concentration. The development of PP-based composite materials with added value and particular functionality (i.e., electrical conductivity and EMI shielding) is highly significant since PP is one of the most used polymers, the best for injection molding, and virtually infinitely recyclable.

Experimental Study on Electromagnetic Shielding Characteristics of a Fe-Based Amorphous Soft Magnetic Composite

An Fe-based amorphous soft magnetic composite with flexibility and elasticity was fabricated to shield harmful electromagnetic waves in industrial and military defense applications. Through the combination and structural arrangement of the amorphous soft magnetic sheet and the conductive sheet, the inlet (POE) form of electromagnetic waves was artificially diversified, and shielding performance was measured according to the criteria of MIL-STD-188-125-1 in the range from 1 kHz to 10 GHz, in consideration of the electromagnetic pulse (EMP) protection. As a result, the shielding effectiveness of 80 dB was achieved in a triple “sandwiched” structure by alternately stacking an iron-based amorphous soft magnetic material on top of a flexible conductive sheet at a 90-degree angle, rather than in parallel.