Study on the phase change thermal storage performance of palmitic acid/carbon nanotubes composites

After oxidization with the mixed acid of H₂SO₄ and HNO₃, carbon nanotubes (CNTs) were further grafted by γ-(2,3-epoxypropoxy)propyltrimethoxysilane. Then, CNTs, oxidized CNTs and grafted CNTs were respectively dispersed into palmitic acid (PA) matrix to prepare phase change composites at a mass ratio of 1/100. According to the comparative analysis results of the FT-IR spectra, morphology, dispersion and latent heat of the three composites, it is discovered that the composite with grafted CNTs showed the greatest dispersion and tube–matrix adhesion, and thus gained the highest latent heat. It is worth mentioning that the composite with grafted CNTs demonstrated a more favorable latent heat and a 34.1% enhancement of thermal conductivity in comparison with PA. Moreover, the composite with grafted CNTs kept homogeneous after 100 times of melting and freezing, and the retention rate of latent heat can be as high as 98.5%.     

Enhanced thermal resistance of phenolic resin composites at low loading of graphene oxide

By incorporating graphene oxide (GO) into phenolic resin (PR), GO/PR composites were prepared, and the effects of the content and reduction degree of GO on thermal resistance of GO/PR composites were studied. The peak degradation temperature of the PR was increased by about 14 °C with GO which was heat treated. The char yield of GO/PR composite at a GO weight fraction of 0.5% was about 11% greater than that of PR. The interactions such as covalent bonds and π–π stacking between GO and PR were regarded as the main reason for the enhancement. Located at the GO–PR interface, GO effectively anchored and structured PR molecular near the surfaces of GO sheets, and thus facilitated the formation of char. The superiority of GO/PR composites over PR in terms of thermal properties enhancement should also be related to the promoting graphitization by the addition of GO.     

Improved ablation resistance of carbon–phenolic composites by introducing zirconium silicide particles

The effect of ZrSi₂ on the thermal degradation behavior of phenolic and the role of ZrSi₂ on the ablation resistance of carbon–phenolic (C–Ph) composites are investigated by introducing ZrSi₂ particles into phenolic, and then ZrSi₂ particles into C–Ph composites. Thermogravimetry (TG) analysis illustrates that the residue yield of phenolic at high temperatures is increased by the introduction of ZrSi₂ particles. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses reveal that the increased residue yield is attributed to the reactions between ZrSi₂ particles and pyrolysis volatiles. Therefore, partial carbon and oxygen elements in the volatiles remain in the thermal residue in the forms of amorphous carbon, ZrO₂ and SiO₂, respectively. Moreover, the ablation resistance of C–Ph composites is significantly improved by the introduction of ZrSi₂ particles with formation ZrO₂ and SiO₂ during the oxygen–acetylene ablation process. The average linear and mass ablation rates of ZrSi₂ modified carbon–phenolic (Z/C–Ph) composites evidently reduce by comparison with those of C–Ph composites under similar conditions. As depicted in the microstructure, the ablation occurs in volume in C–Ph composites. The oxygen-containing molecules penetrate deeply inside the matrix, thus the ablation by oxidation is accelerated. However, the ablation occurs in surface in Z/C–Ph composites. ZrSi₂ reacts with the oxygen-containing molecules to form SiO₂–ZrO₂ layer and molten SiO₂ cover on the ablated surface, thus the ablation by the oxidation of matrix and fibers in the interior has been inhibited.     

Ablative and mechanical evaluation of CNT/phenolic composites by thermal and microstructural analyses

Highly ablation resistant carbon nanotube (CNT)/phenolic composites were fabricated by the addition of low concentrations of CNTs. Tensile and compressive mechanical properties as well as ablation resistance were significantly improved by the addition of only 0.1 and 0.3 wt% of uniformly dispersed CNTs. An oxygen–kerosene-flame torch and a scanning electron microscope (SEM) were used to evaluate the ablative properties and microstructures. Thermal gravimetric analysis (TGA) revealed that the ablation rate was lower for the 0.3 wt% CNT/phenolic composites than for neat phenolic or the composite with 0.1 wt% CNTs. Ablation mechanisms for all three materials were investigated using TGA in conjunction with microstructural studies using a SEM. The microstructural studies revealed that CNTs acted as an ablation resistant phase at high temperatures, and that the uniformity of the CNT dispersion played an important role in this ablation resistance.     

Improving the thermal and mechanical properties of polysulfone by incorporation of graphene oxide

Nanocomposites of polysulfone (PSF)-graphene oxide (GO) were prepared by classical phase inversion method. The structural and surface features and the mechanical and thermal performances of the prepared materials were investigated in detail. TEM and X-ray diffraction analysis indicated a good compatibility and excellent dispersability with PSF matrix for the low GO content (0.25, 0.5 and 1 wt.%) composites. It was observed that GO dispersion was reasonably homogeneous for the composite with 2 wt.% GO. The mechanical properties of the prepared materials were found to be greatly enhanced by the addition of GO for some compositions. The thermogravimetrical investigation demonstrated considerable improvements in thermal stability for the composite with low GO content. This novel material offers a feasible candidate for practical membrane application.     

Synthesis,characterization and in vitro studies of polysulfone/graphene oxide composite membranes

The aim of the study was the synthesis of polysulfone (PS)/graphene oxide (GO) composite membranes by phase inversion method as well as their structural, morphological, thermal and mechanical investigation. The performance of composite membranes in terms of distilled water and ethanol fluxes was investigated. The biological activity of mouse mesenchymal stem cells in contact with the new materials was measured. The successful incorporation of GO nanosheets within the PS matrix was confirmed by X-ray diffraction and transmission electron microscopy. Tensile tests indicated a key contribution of GO to the improvement of mechanical performances of PS. Ethanol and water fluxes decrease was remarked with GO addition and was assigned to the stabilization of composite membrane structure. Composite membranes cytotoxicity, cell viability and proliferation potential tests indicated excellent biocompatibility, enhancing cell proliferation and grouping for higher amount of GO within PS matrix.     

Dynamic mechanical analysis and thermal properties of LLDPE/EVA/modified silica nanocomposites

The effect of hexamethylene disilazane modified nanosilica on the dynamic mechanical analysis (DMA), crystallization, melting and thermal degradation behavior of linear low density polyethylene/ethylene vinyl acetate copolymer (LLDPE/EVA) blends are explored.Detailed DMA analysis is carried out in order to investigate the reinforcing behavior of nanosilica adopting Kerner–Nielson model. Oxidative degradation and thermal stabilities of samples are also studied by the thermogravimetery analysis. The high content of nanosilica particles results in significant shift of degradation temperature to higher temperatures in the oxygen atmosphere. This behavior might be attributed to the barrier properties of nanoparticles against oxygen and gaseous degradation products. However, incorporation of modified nanosilica into LLDPE/EVA blend is decreased the onset of degradation temperature of the unfilled system. In nitrogen atmosphere, no changes are observed in the thermal degradation range and only a reduction is documented in the onset of degradation temperature. Considering important role of onset of degradation temperature, activation energy of starting of degradation temperature is calculated utilizing Kissinger-Ozawa model in both oxygen and nitrogen atmospheres. Results showed that activation energy of degradation reaction is decreased by ∼ 20 kJ/mol. This decrease is owing to the release of modifiers from the nanoparticles.     

Improved electrical insulating properties of LDPE based nanocomposite: Effect of surface modification of magnesia nanoparticles

Three silane coupling agents with amino, long alkyl chain or vinyl functional groups were used to modify magnesia (MgO) nanoparticles. The modified nanoparticles were then mechanically mixed with low-density polyethylene (LDPE) to fabricate insulating nanocomposites. The average size of the modified MgO aggregates dispersed in LDPE matrix was below 100 nm. The pulsed electroacoustic method indicated that the MgO nanoparticles regardless of surface modification were effective to suppress the packet-like charge injection and accumulation in the LDPE sample, decrease the permittivity and tan δ, and also improved the direct-current breakdown strength of LDPE at different temperatures. The best insulating properties were found in the case of vinyl-silane-modified-MgO/LDPE samples probably owing to the improved interfacial adhesion. A multi-core model was used to discuss the results obtained.     

Fabrication of multi-walled carbon nanotube–carbon fiber hybrid material via electrophoretic deposition followed by pyrolysis process

An integrated multi-walled carbon nanotube (MWCNT)–carbon fiber (CF) hybrid material has been fabricated by electrophoretic deposition of acid-functionalized MWCNTs on CF surface followed by soaking in a 10% solution of petroleum pitch in toluene, followed by pyrolysis in a nitrogen atmosphere. It has been revealed that MWCNTs entirely covered the CF surface. Mechanical properties of composites reinforced by MWCNT–CF hybrids were considerably enhanced (up to 120% in tensile strength and 100% in elastic modulus) compared to composites reinforce by as-received CFs. According to fractography observations, robust interlocking occurred between epoxy matrix and MWCNT–CF hybrids.     

Evaluation of thermal,mechanical, and electrical properties of PVDF/GNP binary and PVDF/PMMA/GNP ternary nanocomposites

Graphene nanoplatelet (GNP) was incorporated into poly(vinylidene fluoride) (PVDF) and PVDF/poly(methyl methacrylate) (PMMA) blend to achieve binary and ternary nanocomposites. GNP was more randomly dispersed in binary composites compared with ternary composites. GNP exhibited higher nucleation efficiency for PVDF crystallization in ternary composites than in binary composites. GNP addition induced PVDF crystals with higher stability; however, PMMA imparted opposite effect. The binary composite exhibited lower thermal expansion value than PVDF; the value further declined (up to 28.5% drop) in the ternary composites. The storage modulus of binary and ternary composites increased to 23.1% and 53.9% (at 25 °C), respectively, compared with PVDF. Electrical percolation threshold between 1 phr and 2 phr GNP loading was identified for the two composite systems; the ternary composites exhibited lower electrical resistivity at identical GNP loadings. Rheological data confirmed that the formation of GNP (pseudo)network structure was assisted in the ternary system.     

High temperature thermal stability of pure copper and copper–carbon nanotube composites consolidated by High Pressure Torsion

The thermal stability of ultrafine-grained (UFG) microstructures in pure copper samples and copper–carbon nanotube (CNT) composites processed by High Pressure Torsion (HPT) was compared. The UFG microstructure in the sample consolidated from pure Cu powder exhibited better stability than that developed in a casted Cu specimen. The addition of CNTs to the Cu powder further increased the stability of the UFG microstructure in the consolidated Cu matrix by hindering recrystallization, however it also yielded a growing porosity and cracking during annealing. It was shown that the former effect was stronger than the latter one, therefore the addition of CNTs to Cu has an overall benefit to the hardness in the temperature range between 300 and 1000 K. A good agreement between the released heat measured during annealing and the calculated stored energy was found for all samples.     

Repair of shear-deficient normal weight concrete beams damaged by thermal shock using advanced composite materials

The use of advanced composite materials such as Fiber Reinforced Polymers (FRPs) in repairing and strengthening reinforced concrete structural elements has been increased in the last two decades. Repairing and strengthening damage structures is a relatively new technique. The aims of this study was to investigate the efficiency and effectiveness of using Carbon Fiber Reinforced Polymer (CFRP) to regain shear capacity of shear-deficient normal weight high strength RC beams after being damaged by thermal shock. Sixteen high strength normal weight RC beams (100 × 150 × 1400 mm) were cast, heated at 500 °C for 2 h and then cooled rapidly by immersion in water, repaired, and then tested under four-point loading until failure. The composite materials used are carbon fiber reinforced polymer plates and sheets. The experimental results indicated that upon heating then cooling rapidly, the reinforced concrete (RC) beams exhibited extensive map cracking without spalling. Load carrying capacity and stiffness of RC beams decreased about 68% and 64%, respectively, as compared with reference beams. Repairing the thermal damaged RC beams allowed recovering the original load carrying without achieving the original stiffness. Repaired beams with CFRP plates with 90° and 45° regained from 90% to 99% of the original load capacity with a corresponding stiffness from 79% to 95%, whereas those repaired with CFRP sheet on the web sides and a combination of CFRP plates and sheet regained from 102% to 107% of the original load capacity with a corresponding stiffness from 81% to 93%, respectively. Finally, finite element analysis model is developed and validated with the experimental results. The finite element analysis showed good agreement as compared with the experimental results in terms of load–deflection and load–CFRP strain curves.     

Architecting graphene nanowalls on diamond powder surface

Graphene nanowalls (GNWs) have been synthesized on diamond particle surface by a simple heat-treatment process in vacuum induction furnace. The thickness of the as-grown GNWs is in the range of 20–40 nm, and most of the nanowalls are smooth and flat. The growth of GNWs is affected by the type of catalyst and treatment temperature, and the mixed catalytic effect of Fe and Ni is better than Fe or Ni respectively. High-density GNWs was grown on the diamond particle entire surface, when the heat treatment process is performed at 1473 K. Al/diamond composites with high thermal conductivity of 423 W/(m K) was obtained, which was achieved by the formation of large number of GNWs on the diamond particle surface. Systematic analyses reveal that the growth models such as classic precipitation upon cooling (PUC) model are not applicable to explain this kind of GNW’s growth mechanism. Hereby, an extended PUC model is proposed to interpret the GNW’s growth process on diamond surface.     

Solvothermal synthesis of carbon nanostructure and its influence on thermal stability of poly styrene

Carbon nanostructures were synthesized via a novel solvothermal reaction between ferrocene and sulfur. Carbon nanostructures were then added to poly styrene (PS) matrix. The thermal stability behavior of PS filled with carbon nanostructures were investigated by thermogravimetric analysis (TGA). Nanostructures were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, energy-dispersive X-ray (EDS) analysis and atomic force microscopy (AFM). The flame retardancy behavior of PS–carbon was studied by UL-94 analysis.     

Ablative properties of carbon black and MWNT/phenolic composites: A comparative study

In this work, we investigated the ablative properties of two carbon nanofiller-based composites. In particular, carbon black (CB) and multi-walled carbon nanotubes (MWNTs) were used to produce highly loaded (50 wt%) phenolic composites. The thermal properties and the ablative response of the composites were studied through the pre and post-burning morphology of the burnt surfaces and an evaluation of the in-depth temperature profiles. When compared to the CB-based counterpart, the MWNT-based composite exhibited a higher thermal diffusivity and an erosion rate that was exactly localized above the flame plume. The CB-based system showed a thin charred region whilst the MWNT-based was characterized by a thick and wide pyrolyzed zone.     

New photosensitive semi aramid/organoclay nanocomposite containing cinnamoyl groups: Synthesis and characterization

New poly(ether–amide)/layered silicate nanocomposites (PEAN) containing dibenzalacetone and cinnamoyl moieties were prepared via solution intercalation technique from poly(ether–amide) 6 and organo-MMT in a solution of N,N-dimethylacetamide (DMAc). New dicarboxylic acid 4 was synthesis from two step reactions. At first 4,4′-bis(1,4-diphenoxybutane) dialdehyde 3 was synthesized from 1,4-dibromobutane and 4-hydroxybenzaldehyde, then solvent free reaction using to synthesis 4,4′-bis(1,4-diphenoxybutane) diacrylic acid from dialdehyde 3 and malonic acid. Poly(ether–amide) (PEA) chains were synthesized from 4,4′-bis(1,4-diphenoxybutane)diacrylic acid 4 and 2,5-bis(4-aminobenzylidene)cyclopentanone 5 via a direct polycondensation reaction. The synthesized PEA was characterized by Fourier transform infrared spectra (FTIR), nuclear magnetic resonance (¹H NMR), gel permeation chromatography (GPC) and UV–Vis spectroscopy. The distribution of organoclay and nanostructure of the nanocomposites were investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses. The thermal properties and flammability of the nanocomposites were investigated by thermogravimetric analysis (TGA), differential scanning calorimetric (DSC) and microscale combustion calorimeter (MCC). In the presence of organoclay shows a good effect on improving the flame retardancy of the PEA, reflecting the decrease in heat release rate (HRR) and the total heat release (THR) of the nanocomposites, while the thermal stability of nanocomposites only changed slightly compared to the neat polymer. With the increase of the loading of organoclay, the nanocomposites showed improved flame retardancy and higher char residues.     

Engineering the coefficient of thermal expansion and thermal conductivity of polymers filled with high aspect ratio silica nanofibers

The thermomechanical properties of epoxy filled with two different types of silica nanofillers: spherical nanoparticles and nanofibers were investigated as a function of silica nanofiller aspect ratio and concentration. Results indicated that at room temperature and at 8.74% silica nanofiber concentration (by volume) the thermal conductivity of epoxy increased twofold and coefficient of thermal expansion (CET) decreased by ∼40%. Silica nanofiber filled epoxy showed 1.4 times greater CET and 1.5 times greater thermal conductivity compared to spherical nanoparticle filled epoxy. The significant changes observed in thermomechanical properties of silica nanofiber filled epoxy were attributed to its high aspect ratio by constraining the polymer matrix as well as reducing the phonon scattering due to the formation of a continuous fiber network within the matrix. In addition to being electrically insulating, the improved properties of silica nanofiber filled epoxy make it an extremely attractive material as underfill and encapsulant in advanced electronic packaging industry.     

Novel processing and characterization of Cu/CNF nanocomposite for high thermal conductivity applications

Enhancing the thermal conductivity and reducing the thermal expansion for electronic packaging applications can be achieved by compositing carbon nanofibers in copper-matrices. Though achieving these optimal thermal properties is theoretically possible, such composites are currently not available due to many unresolved practical problems. Conventional compositing processes are incapable of obtaining the desired fiber distribution while controlling the fiber–matrix interfaces for effective heat and load transfers. In this paper, three different powder metallurgy based processes are presented; two based on conventional techniques and the third a relatively new method. The first method is basically the conventional powder metallurgy process. The second and the third methods are also powder metallurgy processes with different ways of modifying the surface of the fibers using either electroless coating or the novel salt decomposition method. It is shown that the salt decomposition method is capable of achieving the desired high thermal conductivity values while the thermal expansion values remain the same in all the three processes.     

Investigation of thermal conductivity and dielectric properties of LDPE-matrix composites filled with hybrid filler of hollow glass microspheres and nitride particles

The hybrid filler of hollow glass microspheres (HGM) and nitride particles was filled into low-density polyethylene (LDPE) matrix via powder mixing and then hot pressing technology to obtain the composites with higher thermal conductivity as well as lower dielectric constant (D_k) and loss (D_f). The effects of surface modification of nitride particles and HGMs as well as volume ratio between them on the thermal conductivity and dielectric properties at 1 MHz of the composites were first investigated. The results indicate that the surface modification of the filler has a beneficial effect on thermal conductivity and dielectric properties of the composites due to the good interfacial adhesion between the filler and matrix. An optimal volume ratio of nitride particles to HGMs of 1:1 is determined on the basis of overall performance of the composites. The thermal conductivity as well as dielectric properties at 1 MHz and microwave frequency of the composites made from surface-modified fillers with the optimal nitride to HGM volume ratio were investigated as a function of the total volume fraction of hybrid filler. It is found that the thermal conductivity increases with filler volume fraction, and it is mainly related to the type of nitride particle other than HGM. The D_k values at 1 MHz and microwave frequency show an increasing trend with filler volume fraction and depend largely on the types of both nitride particles and HGMs. The D_f values at 1 MHz or quality factor (Q × f) at microwave frequency show an increasing or decreasing trend with filler volume fraction and also depend on the types of both nitride particle and HGM. Finally, optimal type of HGM and nitride particles as well as corresponding thermal conductivity and dielectric properties is obtained. SEM observations show that the hybrid filler particles are agglomerated around the LDPE matrix particles, and within the agglomerates the smaller-sized nitride particles in the hybrid filler can easily form thermally conductive networks to make the composites with high thermal conductivity. At the same time, the increase of the value D_k of the composites is restricted due to the presence of HGMs.     

Preparation of reduced graphene oxide-NiFe2O4 nanocomposites for the electrocatalytic oxidation of hydrazine

A reduced graphene oxide (RGO)-NiFe₂O₄ nanocomposite was synthesized by a simple one step hydrothermal approach and its application in the electrocatalytic oxidation of hydrazine was demonstrated. The as-synthesized nanocomposite was characterized by X-ray diffraction, Fourier transform infrared spectroscopy, UV–visible spectroscopy, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, Thermogravimetric analysis, Field emission-scanning electron microscopy (FE-SEM), and Transmission electron microscopy (TEM). The FE-SEM and TEM image analyses revealed that the NiFe₂O₄ nanoparticles were uniformly distributed on the RGO sheets with a diameter and length of ∼10 and ∼100 nm, respectively. The XPS analysis confirmed the ionic states of Ni and Fe to be Ni³⁺ and Ni²⁺, and Fe²⁺ and Fe³⁺, respectively. Further, the electrochemical activity of the RGO-NiFe₂O₄ nanocomposite was investigated by studying the oxidation of hydrazine. The RGO-NiFe₂O₄ modified glassy carbon electrode (GCE) showed an outstanding electrocatalytic activity towards the oxidation of hydrazine as compared to the NiFe₂O₄ and RGO modified electrodes. The enhanced electrocatalytic activity is due to the synergistic effect between RGO and NiFe₂O₄. Using amperometry, the lowest detection limit of 200 nM was achieved with the RGO-NiFe₂O₄ modified GCE. Therefore, the RGO-NiFe₂O₄ modified GCE can be used for the electrochemical oxidation of hydrazine.