Strain engineering for thermal conductivity of single-walled carbon nanotube forests

We perform classical molecular dynamics simulations to investigate the mechanical compression effect on the thermal conductivity of the single-walled carbon nanotube (SWCNT) forest, in which SWCNTs are closely aligned and parallel with each other. We find that the thermal conductivity can be linearly enhanced by increasing compression before the buckling of SWCNT forests, but the thermal conductivity decreases quickly with further increasing compression after the forest is buckled. Our phonon mode analysis reveals that, before buckling, the smoothness of the inter-tube interface is maintained during compression, and the inter-tube van der Waals interaction is strengthened by the compression. Consequently, the twisting-like mode (good heat carrier) is well preserved and its group velocity is increased by increasing compression, resulting in the enhancement of the thermal conductivity. The buckling phenomenon changes the circular cross section of the SWCNT into ellipse, which causes effective roughness at the inter-tube interface for the twisting motion. As a result, in ellipse SWCNTs, the radial breathing mode (poor heat carrier) becomes the most favorable motion instead of the twisting-like mode and the group velocity of the twisting-like mode drops considerably, both of which lead to the quick decrease of the thermal conductivity with further increasing compression after buckling.     

Fabrication and microwave absorption properties of magnetite nanoparticle–carbon nanotube–hollow carbon fiber composites

Absorbents with “tree-like” structures, which were composed of hollow porous carbon fibers (HPCFs) acting as “trunk” structures, carbon nanotubes (CNTs) as “branch” structures and magnetite (Fe₃O₄) nanoparticles playing the role of “fruit” structures were prepared by chemical vapor deposition technique and chemical reaction. Microwave reflection loss, permittivity and permeability of Fe₃O₄–CNTs–HPCFs composites were investigated in the frequency range of 2–18 GHz. It was proven that prepared absorbents possessed the excellent electromagnetic wave absorbing performances. The bandwidth with a reflection loss less than −15 dB covers a wide frequency range from 10.2 to 18 GHz with the thickness of 1.5–3.0 mm, and the minimum reflection loss is −50.9 dB at 14.03 GHz with a 2.5 mm thick sample layer. Microwave absorbing mechanism of the Fe₃O₄–CNTs–HPCFs composites is concluded as dielectric polarization and the synergetic interactions exist between Fe₃O₄ and CNTs–HPCFs.     

Alloying behavior and novel properties of CoCrFeNiMn high-entropy alloy fabricated by mechanical alloying and spark plasma sintering

An equiatomic CoCrFeNiMn high-entropy alloy was synthesized by mechanical alloying (MA) and spark plasma sintering (SPS). During MA, a solid solution with refined microstructure of 10 nm which consists of a FCC phase and a BCC phase was formed. After SPS consolidation, only one FCC phase can be detected in the HEA bulks. The as-sintered bulks exhibit high compressive strength of 1987 MPa. An interesting magnetic transition associated with the structure coarsening and phase transformation was observed during SPS process.     

Effect of structure on the properties of polyurethanes based on aromatic cardanol-based polyols prepared by thiol-ene coupling

Industrial-grade cardanol and 2-mercaptoethanol were reacted to generate hydroxyl-functionalized cardanol by UV, free-radical-initiated thiol-ene coupling between the double bond moieties of the cardanol long carbon side chain and thiol functional groups. The average hydroxyl number of the hydroxyl-functionalized cardanol was controlled by reaction time, with the hydroxyl values of this ranging within 168–201 mg KOH g⁻¹. This cardanol was then used as a polyol to prepare cardanol-based polyurethane with hexamethylene diisocyanate and a NCO/OH ratio of 1. To compare the effect of cardanol-based polyols with the properties of cardanol-based polyurethane, cardanol modified with 10-undecylenate was used as a raw material to prepare cardanol-based polyols, including the long carbon chain of 10-undecylenate. All properties were examined, and data revealed that cardanol-based polyols including this long carbon chain can improve the hydrophobic and mechanic properties of the cardanol-based polyurethane.     

Performance analysis of a combined system for cold and power

This paper presents a theoretical study of a combined thermal system, which combines the Rankine cycle and the ejector refrigeration cycle. This combined cycle produces power and refrigeration simultaneously. The thermal system could use low temperature heat sources. A simulation was carried out to evaluate the cycle performance using several working fluids as R123, R141b, R245fa, R601a and R600a. A one-dimensional mathematical model of the ejector was developed using the equations governing the flow and thermodynamics based on the constant area ejector flow model. The ejector is studied in optimal operating regime. The influence of thermodynamic parameters on system performance is studied. The results show that the condenser temperature, the evaporation temperature, the extraction ratio, the fluid nature and the generating temperature have significant effects on the system performances (the coefficient of performance of the combined cycle and the entrainment ratio of the ejector).     

A simple approach for fabrication of interconnected graphitized macroporous carbon foam with uniform mesopore walls by using hydrothermal method

Three-dimensional (3D) highly interconnected graphitized macroporous carbon foam with uniform mesopore walls has been successfully fabricated by a simple and efficient hydrothermal approach using resorcinol and formaldehyde as carbon precursors. The commercially available cheap polyurethane (PU) foam and Pluronic F127 were used as a sacrificial polymer and mesoporous structure-directing templates, respectively. The graphitic structure of carbon foam was obtained by catalytic graphitization method using iron as catalyst. Three different carbon foams such as graphitized macro-mesoporous carbon (GMMC) foam, amorphous macro-mesoporous carbon (AMMC) foam and graphitized macroporous carbon (GMC) foam were fabricated and their physicochemical and mechanical properties were systematically measured and compared. It was found that GMMC possess well interconnected macroporous structure with uniform mesopores located in the macroporous skeletal walls of continuous framework. Besides, GMMC foam possesses a well-defined graphitic framework with high surface area (445 m²/g), high pore volume (0.35 cm³/g), uniform mesopores (3.87 nm), high open porosity (90%), low density (0.30 g/cm³) with good mechanical strength (1.25 MPa) and high electrical conductivity (11 S/cm) which makes it a promising material for many potential applications.     

Yolk–shell structured iron carbide/N-doped carbon composite as highly efficient and stable oxygen reduction reaction electrocatalyst

We report a simple route to synthesize iron carbide/carbon yolk–shell composite via a facile two-step process including polymerization of pyrrole using Fe₃O₄ as a sacrificial template to form a Fe₃O₄/polypyrrole composite, followed by annealing at high temperature in N₂ atmosphere. The yolk–shell composite, with iron carbide (Fe_2.5C) embedded in nitrogen-doped carbon layers, shows impressively high catalytic activity and stability for oxygen reduction reaction in alkaline solution. Both the pyridinic-N and graphic-N in the shell of Fe₃O₄–PPy-700, together with the Fe_2.5C confined in carbon layers are believed to be the active sites for the ORR.     

Chemically modified organic/inorganic nanoporous composite particles for the adsorption of reactive black 5 from aqueous solution

In the present work, we report a chemically modified polyacrylamide/silica nanoporous composite adsorbent for the removal of reactive black 5 (RB5) azo dye from aqueous solutions. The composite adsorbent was synthesized in a packed bed and modified by ethylenediamine (EDA). The adsorbent was characterized by Fourier transformation infrared (FT-IR), thermogravimetric analysis (TGA), thermoporometry, Brunauer, Emmett and Teller (BET) method and scanning electron microscopy (SEM). Mechanical stability of the adsorbent was examined in a packed bed by following the back-pressure of the column. Pore diameter of the composite adsorbent in dry and wet states was estimated to be about 18.71 nm and 12.61 nm, respectively. Adsorption experiments were performed in batch mode and effect of various operational parameters on the adsorption capability of the adsorbent was studied systematically. The maximum adsorption capacity of the modified composites was found to be 454.5 mg RB5/g of adsorbent. The equilibrium data were analyzed by Langmuir, Freundlich, Sips, BET and Redlich–Peterson isotherm models and found to fit well to the BET isotherm. The data kinetically followed the pseudo-second-order model. High adsorption capacity, fast removal mechanism, and good mechanical stability are three advantages of the presented composite for the removal of RB5.