Production of nanoTiC–graphite composites using Ti-doped self-sintering carbon mesophase powder

This work reports the synthesis of nanoTiC–graphite composites using mesophase pitch containing titanium as TiC or TiO₂ nanoparticles. NanoTiC–graphite composites have been prepared using Ti-doped self-sintering mesophase powders as starting materials without using any binders or a metal carbide-carbon mixing stage. The effect of manufacture variables on the graphite compacts properties was studied. Graphites were characterised using XRD and Raman spectroscopy, SEM and TEM, as well as by their mechanical, electrical and thermal properties. The presence of TiC promotes graphitisation producing materials with larger crystal sizes. The kind of titanium source and mesophase content of the starting pitch affects to the final properties. Mesophase pitch with higher amount of mesophase content produces graphites with higher degree of graphitisation. The incorporation of TiC nanoparticles to the graphites composites improved thermal conductivity more than four times, and mechanical properties are not significantly modified by the presence of TiC.     

Novel dispersion analysis and selective quantification of particulate components in graphene nanoplatelets–polymer–polymer hybrid composites

Up until now, no standard procedure to analyze and quantify the dispersion of particles in the polymer matrix exists. From the conductive hybrid polymer–polymer–graphene nanoplatelets composites we developed, this article attempts to showcase methodologies to analyze and quantify particle with the use of scanning electron microscopy images and collection of the elemental maps of carbon, oxygen, and nitrogen by energy dispersive spectroscopy (EDS) analysis. Image analysis was performed on the resulting map to extract the area and location data of graphene particles by subtracting elemental maps. Shadowing or charging problem in the images acquired from EDS was overcome by the polished surface and analyzing a sample twice using a novel approach of 180° opposed. Merging the data from the two elemental maps, taken 180° opposed, can be an alternative to the use of polished samples. From these different dispersion analysis approaches, it was possible to quantify different particles and their effects on the properties of the composites.     

Effects of graphite nano-flakes on thermal and microstructural properties of TiB2–SiC composites

In the last decades, the production of ultra-high temperature composites with improved thermo-mechanical properties has attracted much attention. This study focuses on the effect of graphite nano-flakes addition on the microstructure, densification, and thermal characteristics of TiB₂–25 vol% SiC composite. The samples were manufactured through spark plasma sintering process under the sintering conditions of 1800 °C/7 min/40 MPa. Scanning electron microscopy images demonstrated a homogenous dispersion of graphite flakes within the TiB₂–SiC composite causing a betterment in the densification process. The thermal diffusivity of the specimens was gained via the laser flash technique. The addition of graphite nano-flakes as a dopant in TiB₂–SiC did not change the thermal diffusivity. Consequently, the remarkable thermal conductivity of TiB₂–SiC remained intact. It seems that the finer grains and more interfaces obstruct the heat flow in TiB₂–SiC–graphite composites. Adding a small amount of graphite nano-flakes enhances the densification of the mentioned composite by preventing the grain growth.     

Epoxy composites with carbon nanotubes and graphene nanoplatelets – Dispersion and synergy effects

Carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs) at different mix ratios were dispersed by ultrasonication into an epoxy matrix and the effects of CNT:GNP ratios on the mechanical and electrical properties of the hybrid composites were investigated. The combination of CNT and GNP in a ratio 8:2 was observed to synergistically increase flexural properties and to reduce the electrical percolation threshold for the epoxy composites, indicating easier formation of a conductive network due to the improved state of CNT dispersion in the presence of GNPs. The state of dispersion was evaluated at different length scales by using optical microscopy, UV–Vis spectroscopy, rheological measurements, scanning electron microscopy, transmission electron microscopy and sedimentation tests. The Fourier transform infrared spectra for CNT and GNP indicate that the GNPs contain oxygen moieties responsible for better interactions with the epoxy matrix.     

Mechanical and physical behaviors of short pitch-based carbon fiber-reinforced HfB2–SiC matrix composites

Short Pitch-based carbon fiber-reinforced HfB₂ matrix composites containing 20 vol% SiC, with fiber volume fractions in the range of 20–50%, were manufactured by hot-press process. Highly dense composite compacts were obtained at 2100 °C and 20 MPa for 60 min. The flexural strength of the composites was measured at room temperature and 1600 °C. The fracture toughness, thermal and electrical conductivities of the composites were evaluated at room temperature. The effects of fiber volume fractions on these properties were assessed. The flexural strength of the composites depended on the fiber volume fraction. In addition, the flexural strength was significantly greater at 1600 °C than at room temperature. The fracture toughness was improved due to the incorporation of fibers. The thermal and electrical conductivities decreased with the increase of fiber volume fraction, however.     

Effect of incorporation of hafnium diboride nanofibers on thermomechanical properties of carbon fiber–phenolic composites

Carbon fiber/phenolic (C/Ph) composites were modified with different weight ratios of hafnium diboride (HfB₂) nanofibers to apperceive thermomechanical properties of C/Ph–Hf nanocomposites. Mechanical properties, thermal stability, and ablation resistance of C/Ph–Hf nanocomposites were found to be optimum when the weight percentage of HfB₂ was equal to one. Maximum flexural strength and modulus were obtained with 118 MPa and 1.9 GPa for C/Ph–1%Hf nanocomposite, respectively. Increasing the proportion of HfB₂, by delaying the temperature of thermal degradation of nanocomposites, enhanced the thermal stability and residual of C/Ph–Hf relative to C/Ph in both nitrogen and air environments. In the oxyacetylene flame test at 2500°C for 160 s, the optimum mass ablation rate of C/Ph–1%Hf nanocomposites was found to be 0.0150 g/s compared to 0.068 g/s for blank C/Ph, along with reducing the back surface temperature by 51%. The ablation mechanism of C/Ph–Hf nanocomposites after the oxyacetylene torch test was concluded from the derivations obtained from X-ray diffraction, energy dispersion spectroscopy, and microstructure analyses. These clarified that the formation of high-temperature species, such as HfO₂, HfC, and B₄C owing to oxidation of HfB₂ and subsequent reaction products with char, resulted in an increased ablation resistance of the nanocomposites.     

Role of fibre–fibre and fibre–matrix adhesion in stress transfer in composites made from resin-impregnated paper sheets

Paper-reinforced plastics are gaining increased interest as packaging materials, where mechanical properties are of great importance. Strength and stress transfer in paper sheets are controlled by fibre–fibre bonds. In paper-reinforced plastics, where the sheet is impregnated with a polymer resin, other stress-transfer mechanisms may be more important. The influence of fibre–fibre bonds on the strength of paper-reinforced plastics was therefore investigated. Paper sheets with different degrees of fibre–fibre bonding were manufactured and used as reinforcement in a polymeric matrix. Image analysis tools were used to verify that the difference in the degree of fibre–fibre bonding had been preserved in the composite materials. Strength and stiffness of the composites were experimentally determined and showed no correlation to the degree of fibre–fibre bonding, in contrast to the behaviour of unimpregnated paper sheets. The degree of fibre–fibre bonding is therefore believed to have little importance in this type of material, where stress is mainly transferred through the fibre–matrix interface.     

Water resistance and thermal stability of hybrid lignocellulosic filler–PVC composites

In this study, composites based on polyvinyl chloride (PVC), pulp fiber (PF), and wood flour (WF) were made by injection molding. The effects of two variable factors, namely the filler form and filler loading level, on the composite physical properties were examined. The result clearly showed that the major part of water absorption was due to water absorption of PF. It was found that the water absorption in the lignocellulosic material base composites is significantly higher than the neat PVC. Besides, the water absorption increased sharply with increasing cellulosic filler loadings in the composites. In case of hybrid composites, the rate of water uptake correlated with percentage weight of WF, lower WF (higher PF) loadings in composites exhibit higher rate of absorption. The higher onset of degradation temperature indicates the improved thermal stability of the samples. In other words, the result clearly illustrates that the thermal property of the composites increases after using PF and further increases after addition of WF.     

Experimental investigation on the mechanical,structural and thermal properties of Cu–ZrO2 nanocomposites hybridized by graphene nanoplatelets

Hybrid Cu–ZrO₂/GNPs nanocomposites were successfully produced using powder metallurgy technique. The effect of GNPs mass fraction, 0, 0.5, 1 and 1.5%, on the mechanical and electrical properties of the produced hybrid nanocomposite was investigated while maintaining ZrO₂ mass fraction constant at 5%. High-energy ball milling was applied for mixing powders followed by compaction and sintering. The morphological analysis of the produced powder showed acceleration of Cu particles fracture during ball milling with the addition of GNPs up to 0.5% with noticeable reduction of agglomeration size. Moreover, the crystallite size of Cu–5%ZrO₂/0.5%GNPs hybrid nanocomposites revealed smaller crystallite size, 142 nm, compared to 300 nm for Cu–5%ZrO₂ nanocomposite. Additionally, the hybrid nanocomposite with 0.5% GNPs shows homogeneous distribution of both reinforcement phases in the sintered samples. The compressive strength increased with the GNPs content and reached 504.6 MPa at 0.5%, 31% higher than the Cu-5%ZO₂. The thermal conductivity had the maximum value at 0.5 wt%GNPs and reached 345 W/m k. The results provide efficient manufacturing process for high strength and good conductivity hybrid nanocomposites, which is applicable in many structural applications such as heat exchange purposes.     

A novel B–Si–Zr hybridized ceramizable phenolic resin and the thermal insulation properties of its fiber-reinforced composites

A novel B–Si–Zr hybridized ceramicizable resin(BSZ-PR) was fabricated by chemical reaction of boric acid, zirconium hydroxyl-containing polyhedral oligomeric silsesquioxane(Zr-POSS) and phenolic. The incorporation of boric acid and Zr-POSS improved the thermal stability of the resin effectively, and the residual carbon rate increased to 72.63% at 800 °C under nitrogen atmosphere. The flexural strength of carbon fiber/BSZ-PR and high silica fiber/BSZ-PR composites were increased by 25.7% and 175.5%, and linear ablation rates were reduced by 37% and 44.75%, respectively. It was discovered that the ceramic structures such as SiO₂, ZrO₂ and SiC can be formed at high temperatures as well as under extreme ablative conditions from both BSZ-PR and its fiber-reinforced composites, which may be the key to the improved thermal, ablative properties.     

Tailored interphase and thermal interface resistance of self-assembled thermally reduced graphene oxide–polyamide hybrid/epoxy composites with enhanced thermal conductivity

Thermally reduced graphene oxide–polyamide (TrGO-PA) hybrids were fabricated by self-assembly between TrGO nanosheets and PA microparticles, and the dispersibility, interphase extension, and thermal conduction mechanism of TrGO-PA/epoxy (EP) composites were investigated. Most of the oxygen-containing functional groups of TrGO were removed, and a conjugated structure of graphene was recovered. TrGO was distributed evenly on the PA surface via electrostatic adsorption between TrGO and PA, which resulted in the inhibition of TrGO aggregation in the epoxy matrix. Compared with that of TrGO/EP and PA/EP composites, the thermal interface resistance (R_TIM) of TrGO-PA/EP composites was greatly decreased to 38.3 mm² kW⁻¹ and the thermal conductivity was improved to 0.268 W/(m K), which was attributed to the enhanced dispersibility of TrGO-PA and the enlarged interphase in TrGO-PA/EP composites. A schematic model of thermal conduction mechanisms was proposed based on the formation of contiguous thermal transfer pathways by bridged TrGO adsorbed on well-dispersed PA microparticles in TrGO-PA/EP composites. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47826.     

Mechanical and thermal shock properties of size graded MgO–PSZ refractory

The effects of the mixture of coarse powder with fine PSZ powder on the thermal-mechanical properties of 10 Mg–PSZ samples were studied. The size graded specimens were injection-molded using 3.5 m% MgO–ZrO₂ powders. The physical properties of the ZrO₂ samples and five thermal shock parameters were measured and calculated. These properties included density (ρ), porosity (p), the ratio of m/(t+c+m) phase, fracture toughness (K_IC), strength (σ_f), Young's modulus (E), shear modulus (G), Poisson's ratio (ν), and the thermal expansion (α) between ambient temperature to 1100°C. The toughness and thermal shock resistance of the PSZ are controlled by the states of porous microstructure which can be represented by a parameter (nominal largest tolerable length of defects) a_t. The PSZ samples show two types of thermal shock behavior differentiated by comparing the value of a_t to the characteristic length L_f of the defects in the sintered PSZ. The states of the defects, i.e. porosity, are the microstructural evidence to explain the relationship between the thermal shock properties.     

Effect of impregnated phenolic resin on the properties of Si–SiC ceramic matrix composites fabricated by SLS-RMI

Selective laser sintering (SLS) combined with reaction melt infiltration was used to fabricate Si–SiC ceramic matrix composites, and the effects of different concentrations of phenolic resin (PF) on the properties of the SLS green body and carbonized and final Si–SiC samples were investigated. The results showed that the impregnation with PF can increase the bulk density, reduce the porosity of the samples at all stages, and improve the mechanical properties of the reactive bonded samples. The degree of densification and mechanical properties of the sample gradually enhanced with an increase in PF concentration. The main phases of the Si–SiC composites were free Si, α-SiC, β-SiC, plus an extremely small amount of Al–Si alloy, and the SiC and the Si phase contents increased and decreased, respectively, as the concentration of PF increased when measured using Rietveld refinement and image analysis software. The macroscopic properties of the samples improved greatly after precursor infiltration pyrolysis (PIP) treatment with 66.7%vol PF-ethanol solution twice. According to the crystal nucleation-growth theory, it was inferred that the infiltrated PF could provide a certain amount of pyrolytic carbon in the carbonized specimen. During the reaction bonded process, the carbon formed by carbonization pyrolysis first dissolves into the molten Si and reaches saturation. With the further dissolution of carbon, [C] and [Si] in the liquid phase contact each other to form β-SiC nuclei, the nuclei that precipitate at the pore wall position and gradually form a continuous interfacial layer of β-SiC. The β-SiC layer prevents the liquid Si from direct contact with C inside the prefabricated body, therefore, further reactants diffuse through the layer. Finally, the fine crystalline β-SiC grains were fabricated inside the specimen.     

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.     

Thermophysical properties of carbon fiber reinforced multilayered (PyC–SiC)n matrix composites

Three kinds of carbon fiber reinforced multilayered (PyC–SiC)_n matrix (C/(PyC–SiC)_n) composites (n = 1, 2 and 4) were prepared by means of layer-by-layer deposition of PyC and SiC via chemical vapor infiltration. Thermal expansion behaviors in the temperature range of 800–2500 °C and thermal conductivity from room temperature to 1900 °C of C/(PyC–SiC)_n composites with various microstructures were investigated. The results show that with increasing PyC–SiC sequences number (n), the coefficients of thermal expansion of the composites decrease due to the increase of interfacial delamination, providing room for thermal expansion. The thermal diffusivity and thermal conductivity also decrease with the increase of sequences number, which are attributed to the enhancement of phonon-interface scattering resulted from the increasing number of interfaces. Modified parallel and series models considering the interfacial thermal resistance are proposed to elaborate thermal conductivity of the composites, which is in accordance with the experimental results.     

Densified multiwalled carbon nanotubes–titanium nitride composites with enhanced thermal properties

Densified multiwalled carbon nanotube (MWNT)–TiN composites with various MWNTs contents were successfully obtained through a spark plasma sintering (SPS) method. The thermal conductivity k was found to increase with the MWNT amount and temperature. In the presence of 5 wt% MWNTs, there was a 97% enhancement in k at 703 K compared with that of TiN. The high thermal conductivity of MWNTs, a good interfacial combination and a homogeneous dispersion of MWNTs are key issues to enhance the thermal conductivity of MWNT–TiN composites.     

Mechanical, thermal and transport properties of nitrile rubber (NBR)—nanoclay composites

The article describes the properties of nitrile rubber (NBR)—nanoclay composites prepared by a two-step method. viz. preparation of a 3:1 [by weight] masterbatch of NBR and nanoclay followed by compounding on a two roll mill and molding at 150 °C and 20 MPa pressure. The tensile strength, elongation at break, modulus, storage modulus (E’) and loss modulus (E”) increased with the nanofiller content, reached the maximum value at 5 phr and decreased thereafter. The solvent uptake, diffusion, sorption and permeation constants decreased with nanoclay content with the minimum value at 5 phr nanoclay. The mechanism of solvent diffusion through the nanocomposites was found to be Fickian. Thermodynamic constants such as enthalpy and activation energy were also evaluated. The dependence of various properties on nanoclay content was correlated to the morphology of the nanocomposites. supported by morphological analysis.     

Mechanical and thermal properties of silicon carbide ceramics with yttria–scandia–magnesia

Two different SiC ceramics with a new additive composition (1.87 wt% Y₂O₃–Sc₂O₃–MgO) were developed as matrix materials for fully ceramic microencapsulated fuels. The mechanical and thermal properties of the newly developed SiC ceramics with the new additive system were investigated. Powder mixtures prepared from the additives were sintered at 1850 °C under an applied pressure of 30 MPa for 2 h in an argon or nitrogen atmosphere. We observed that both samples could be sintered to ≥99.9% of the theoretical density. The SiC ceramic sintered in argon exhibited higher toughness and thermal conductivity and lower flexural strength than the sample sintered in nitrogen. The flexural strength, fracture toughness, Vickers hardness, and thermal conductivity values of the SiC ceramics sintered in nitrogen were 1077 ± 46 MPa, 4.3 ± 0.3 MPa·m^1/2, 25.4 ± 1.2 GPa, and 99 Wm⁻¹ K⁻¹ at room temperature, respectively.