Microstructure and properties of silicon carbide whisker reinforced zirconium diboride ultra-high temperature ceramics

Hot-pressed zirconium diboride (ZrB₂) matrix composites containing 0–30 vol% silicon carbide (SiC) whiskers have been investigated to determine the effect of composition (i.e. amount of SiC whiskers) on the microstructure, mechanical properties and thermal properties. With increasing SiC whisker volume contents, the flexural strength and fracture toughness of the composites were improved compared to those of monolithic ZrB₂. Flexural strength increased from 629 MPa for pure ZrB₂ to 767 MPa for ZrB₂–30 vol%SiCw. Likewise, fracture toughness ranged from 5.4 to 7.1 MPa m^1/2 over the same composition range. Specific heat capacity increased with SiC whisker addition, while thermal diffusivity and thermal conductivity decreased slightly with the increase of SiC whisker content.     

Fe-N/C catalysts for oxygen reduction based on silicon carbide derived carbon

Two different Fe-N/C(SiC) catalysts (Fe + Bipyr/C(SiC) and Fe + Phen/C(SiC)) for oxygen reduction based on silicon carbide derived carbon were synthesized and investigated in 0.1 M KOH aqueous solution by rotating disc electrode method. It was found that the electrocatalytic activity and stability are significantly influenced by the change of the nitrogen ligand in the catalyst. Comparable current density values obtained for 20%Pt-Vulcan electrode could be achieved for Fe + Bipyr/C(SiC) and Fe + Phen/C(SiC) catalysts in alkaline media. The durability tests (~ 150 h) showed that the decrease of the activity for Fe + Bipyr/C(SiC) and Fe + Phen/C(SiC) is only 0.5 mV h^− 1 and 0.17 mV h^− 1, respectively. The Fe + Bipyr/C(SiC) catalyst demonstrated higher activity in the RDE measurements, but during the long-term test the Fe + Phen/C(SiC) catalyst prove to be more stable than Fe + Bipyr/C(SiC).     

Mechanical Analysis of Bio Nanocomposite Prepared from Luffa cylindrica

Luffa cylindrica (LC), a tropical vegetal product, consists of highly vascular system. It has been modified by calcium phosphate and calcium carbonate separately to produce composites of Ca-salts. The modified form of LC has been reinforced with novolac resin at 30 °C to provide cross linked polymer composites. The composites have been further sonicated at 40 °C for 1 h to produce bio nano composites. The final yield is more than 80% of the raw materials used. The physical and chemical analysis of the composites have been done. Incorporation of resin in to the inner fiber surface of LC which is rich in cellulose is confirmed from ultra-violet spectroscopy (UV), and Fourier transform infrared (FTIR) analysis. Thermal studies of the composites done in an inert atmosphere reveals that the composites decompose within a temperature range of 250 - 550 °C. The tensile parameters such as maximum stress, Young's modulus and yield strength were measured. The compressive and flexural strength of the LC fiber- reinforced composites were also studied by varying the weight of fiber in the resin.     

Preparation and properties of new flame retardant unsaturated polyester nanocomposites based on layered double hydroxides

The preparation of new layered double hydroxides/unsaturated polyester (LDH/UP) nanocomposites was performed and the effect of LDH on the resin properties was studied. Two different organo-LDHs have been prepared, adipate-LDH (A-LDH) and 2-methyl-2-propene-1-sulfonate-LDH (S-LDH); in order to evaluate the influence of these nanofillers, samples with two different concentrations were dispersed in the matrix. The physical, thermal, mechanical and fire reaction properties of nanocomposites were studied. Intercalated layered structures were observed for the different organo-LDH loadings (1 and 5 wt%). Mechanical properties studied under flexural tests show that incorporation of organo-LDH in the resin reduces the flexural strength of polyester resin while the flexural modulus is unchanged for the S-LDH/UP composites and increased with 1 wt% of A-LDH. Adding 1 wt% of A-LDH to the resin produces an important reduction on the flexural strength, but an increase of the flexural modulus. The study of fire reaction properties, using cone calorimeter, suggested a significant reduction in the UP flammability, by 46 and 32%, by incorporating 1 wt% of A-LDH and 5 wt% S-LDH, respectively. Mass loss curves show enhanced char formation with the different loads tested while the amount of evolved smoke remains quite unchanged.     

Modelling physical properties of highly crystallized polyester reinforced with multiwalled carbon nanotubes

The effects of carbon nanotubes dispersion into thermoplastic polymers are complex and strongly dependent upon their aggregation state. A poly(ethylene terephthalate) (PET) matrix has been reinforced through addition of multiwalled carbon nanotubes (MWCNTs). Such an addition has generated an increase in flexural modulus and a decrease in flexural strength at room temperature, and an increase in both properties above the glass transition temperature (at 100 °C). These different behaviours, dictated by temperature, have been investigated through two different micromechanical models that have permitted to put forward hypothesis on failure mechanisms and to shed light on the role played by crystalline phase. The results of thermal analyses have shown that the heat capacity of PET nanocomposites varies according to the MWCNTs content as the flexural modulus. Such a similarity has suggested to modify the Halpin-Tsai equations (H-T), typically used to predict elastic properties of short fibres reinforced composites, in order to determine the relationships occurring between PET specific heat and aspect ratio of dispersed MWCNT. The analyses performed by means of either classical H-T (elastic modulus) or modified H-T (heat capacity) equations, provided very similar estimation of the MWCNT aspect ratios. In addition, a simple elaboration of the modified H-T equations permitted the calculation of rigid amorphous fraction (RAF) into PET. The obtained values were slightly higher than those evaluated by means of a procedure based on the loss tangent peak variation measured through dynamic mechanical experiments. The detected strength decrease at 25 °C have been attributed to crack propagation through a percolative path between crystalline coating layer of MWCNTs and PET (favoured by matrix brittleness), while at 100 °C the crack propagation is hampered by rubbery behaviour of the matrix.     

Electronic structure,Compton profiles and optical properties of TaC and TaN

Isotropic Compton profiles of TaC and TaN have been measured for the first time, at an intermediate resolution, using 662 keV γ-radiation. Energy bands, density of states and Fermi surface topology of TaC and TaN have been computed using linear combination of atomic orbitals with density functional theory and full potential linearised augmented plane wave method. Both band structure calculations predict the metallic character of TaC and TaN. The electron momentum densities calculated using various approaches of density functional theory are compared with the present measurements. On the basis of Mulliken’s population, it is also seen that TaC has more covalent bonding than TaN. The optical properties computed using full potential linearised augmented plane wave method are explained in terms of intraband transitions.     

One-step synthesis of hollow structured Si/C composites based on expandable microspheres as anodes for lithium ion batteries

Si/C composites of carbon hollow structures loaded with Si nanoparticles (NPs) (Si/C-HSs) were prepared by one-step pyrolysis of a mixture of Si NPs and expandable microspheres (EMs). For the Si/C-HSs, hollow carbon shells with rough surfaces were formed by directly carbonizing the polymer shells of EMs, and the Si NPs fell into the void space or were loaded on the rough surfaces of the carbon shells. The EM-based carbon shells accommodated the volume expansion of the Si NPs and improved the electrical conductivity of the composites. As a result, the Si/C-HSs exhibited a high capacity (initial reversible capacity: 854.4 mAh g^− 1 at 300 mA g^− 1), stable cycling performance (capacity retention: 80% after 50 cycles), and excellent rate capability.     

Evaluation of Mechanical Properties of Epoxy/Nanoclay/Multi-Walled Carbon Nanotube Nanocomposites using Taguchi Method

This paper reports the improvement of the mechanical properties of epoxy/nanoclay/multi-walled carbon nanotube (MWNT) nanocomposites prepared by the solution casting method for a range of pre-cure temperatures (room temperature, 50, and 70 °C), cure temperature (120, 130, and 140 °C), nanoclay content (0.5, 1.0, 1.5 wt%) and content of MWNT (0.2, 0.6, 1.0 wt%) for three levels. The influence of these parameters on the mechanical properties of epoxy/nanoclay/MWNT has been investigated using Taguchi's experimental design. The output measured responses are the tensile properties (tensile modulus, tensile strength and strain at break), impact strength and fracture toughness. From the Analysis of Mean (ANOM) and Analysis of Variance (ANOVA), MWNT content, pre-cure temperature and cure temperature had the most significant effects for the impact strength with contribution percentages of 38%, 28% and 23% respectively. However, for the fracture toughness and strain at break, the enhancements of properties come from the nanoclay content (59%), MWNT content (18%) and pre-cure temperature (23%). While the improvement in tensile strength was influenced by nanoclay and MWNT content, the cure temperature has a stronger effect on the tensile modulus. In this respect, Taguchi method points to the Taguchi method, in this way, points to the dominant parameters and gives the optimum parameter settings for each mechanical property. Confirmation experiments were performed with the optimum parameter settings and the mechanical properties were measured compared with the predicted results.     

Spherical Sn–Ni–C alloy anode material with submicro/micro complex particle structure for lithium secondary batteries

Submicro/micro-scaled spherical Sn–Ni–C alloy powders synthesized from oxides of Sn and Ni via carbothermal reduction at 900 °C were examined for use as anode materials in Li-ion battery. The synthesized spherical Sn–Ni–C particles show a loose micro-sized structure and a multi-phase composition. The reaction product carbon oxide gases yielded in the carbothermal reduction process should be responsible to the loose structure characteristics of Sn–Ni–C particles. The prepared Sn–Ni–C alloy composite electrode exhibits a stable reversible capacity of 310 mA h g⁻¹ at constant current density of 100 mA g⁻¹, and can be retained at 290 mA h g⁻¹ after 25 cycles. The space existing in loose particle can accommodate the large volume changes during charge/discharge cycling. The ductile component Ni plays as a buffer to relieve the mechanical stress induced by the large volume changes upon cycling. The remained carbon can prevent the aggregation between small alloy particles. All these factors contribute greatly to the excellent cycling stability of Sn–Ni–C alloy electrode. This carbothermal reduction method is simple, cheap and mass-productive, thus suitable to large scale production of alloy anode powders used for lithium ion batteries.     

Highly active PtRuFe/C catalyst for methanol electro-oxidation

High methanol electro-oxidation activity was obtained on novel PtRuFe/C (2:1:1 at.%) catalyst. Mass and specific activities were 5.67 A  g⁻¹ catal. and 177 mA m⁻² for the PtRuFe/C catalyst while those of the commercial PtRu/C catalyst were 2.28 A g⁻¹ catal. and 87.7 mA m⁻², respectively. CO stripping results showed that on-set voltage for CO electro-oxidation was lowered by incorporation of Fe. XRD and XPS results revealed that Fe₂O₃ was formed instead of Fe(0), which resulted in large electron deficiency in Pt and easy CO electro-oxidation. The electron deficiency of Pt was proved by XPS results of Pt4f peaks, which moved to higher binding energies in PtRuFe/C than PtRu/C.     

The Effect of Acrylic Acid on Tensile and Morphology Properties of Wollastonite Filled High Density Polyethylene/Natural Rubber Composites

Inorganic filler manufactured for incorporation into thermoplastic elastomers usually are surface treated with organic reagents in order to improve the interfacial adhesion between filler and the matrix. In the present paper, the effects of acrylic acid (AA) on tensile and morphology properties of wollastonite (WS) filled high density polyethylene (HDPE)/Natural Rubber (NR) composites were studied. The untreated and treated HDPE/NR/WS composites were melt-blending at 180 °C with rotor speed of 50 rpm for 10 minutes. The composites were tensile-tested according to ASTM D638 and the etched surfaces were observed using scanning electron microscope (SEM). Tensile strength and elongation at break of the compositesdecreased upon the addition of wollastonite, but Young's modulus improves. The results of this study showed that the treated composites are found to have better tensile properties than the untreated composites. The morphology of treated composite showed better interfacial interaction between HDPE/NR and wollastonite.     

Low-temperature performance of LiFePO4/C cathode in a quaternary carbonate-based electrolyte

The low-temperature performance of LiFePO₄/C cathode in a quaternary carbonate-based electrolyte (1.0 M LiPF₆/EC+DMC+DEC+EMC (1:1:1:3, v/v)) was studied. The discharge capacities of the LiFePO₄/C cathode were about 134.5 mAh/g (20 °C), 114 mAh/g (0 °C), 90 mAh/g (−20 °C) and 69 mAh/g (−40 °C) using a 1C charge–discharge rate. Cyclic voltammetry measurements show obviously sluggish of the lithium insertion–extraction process of the LiFePO₄/C cathode as the operation temperature falls below −20 °C. Electrochemical impedance analyses demonstrate that the sluggish of charge-transfer reaction on the electrolyte/LiFePO₄/C interface and the decrease of lithium diffusion capability in the bulk LiFePO₄ was the main performance limiting factors at low-temperature.     

Surface modified Pt/C as a methanol tolerant oxygen reduction catalyst for direct methanol fuel cells

A new procedure has been successfully developed by which PtN_x/C is synthesized to enhance methanol tolerance while maintaining a high catalytic activity for the oxygen-reduction reaction (ORR). The nitrogen-modified Pt surface, which is prepared using a chelating agent followed by heat treatment, exhibits considerable selectivity toward the ORR in the presence of methanol. The high methanol tolerance could be attributed to the suppression of methanol adsorption resulting from the modification of the Pt surface with nitrogen. A direct methanol fuel-cell (DMFC) test showed that a power density of up to 120 m W cm⁻² was generated when PtN_x/C was used as the cathode catalyst (1 mg cm⁻²) in 6 M methanol and oxygen at 70 °C.     

Improved anode performance of thermally treated SiO/C composite with an organic solution mixture

A pristine composite anode material comprising of silicon monoxide and graphite was prepared through ball milling process and made in the form of a slurry using a simple solution mixture consisting of propylene carbonate (PC) and acetone (AC) and then heat treated. Cycle life study of the pristine composite and heat treated organic slurry composite showed the charge capacity values as 318 and 500 mAh g⁻¹, respectively at 100th cycle. Analysis of change of delithiation capacity with cycling and delithiation current between 0.3 and 0.6 V from cyclic voltammogram (CV) along with scanning electron microscope (SEM) and X-ray diffraction (XRD) of the electrodes/composites leads to conclude thermal processing of the organic slurry treated pristine composite converts dispersed active materials of the pristine composite into a compact structure trapped/wrapped with carbon particles (Cx, x varies from 1 to 3) providing apparently a resistor like behaviour and makes the anode deliver a stable reversible capacity with cycling.     

Transparent and ductile poly(lactic acid)/poly(butyl acrylate) (PBA) blends: Structure and properties

Poly(butyl acrylate) was prepared by the free radical polymerization of butyl acrylate as an initiator in the presence of 2,2′-Azoisobu-tyronitrile (AIBN) and the average molecular weight, polydispersity and thermal stability were evaluated. PLA and PBA were melt blended using a Haake Rheometer, and the light transmission, thermal properties, dynamic rheological properties, mechanical properties, phase morphology of blends and toughening mechanism were investigated. Dynamic rheology, SEM and DSC results show that the PLA is partial miscible with PBA. The PBA component improved the crystallization ability of PLA and the crystallinity of PLA increased with content of PBA (<15 wt.%). With the increase of PBA, the tensile strength and modulus of the blend decreased slightly while the elongation at break and toughness were dramatically increased. With the addition of PBA, the failure mode changes from brittle fracture of neat PLA to ductile fracture of the blend. Rheological results revealed the complex viscosity and melt elasticity of the blends decreased with increasing content of PBA and phase segregation occurred at loading above 11 wt.% PBA. UV–vis light transmittance showed that PLA/PBA blends with a high transparency, and the transmittance decreased with the amount of PBA.     

Application of Design of Experiment (DoE) for Parameters Optimization in Compression Moulding for Flax Reinforced Biocomposites

Lately, widespread research on polymer composites that consist of natural fiber as reinforcement have been widely discussed. In this work, an attempt on optimizing the hot press forming process parameters using Response Surface Methodology (RSM) have been made to improve the mechanical properties of the woven flax/PLA composites. Three independent process variables, including moulding temperature, time and pressure were studied. Through the Box Behnken approach, a set of experiment runs based on various combination of compression moulding via Minitab 16 were established. As a results the optimum value for the variables of compression moulding technique parameters were 200 °C, 3 min and 30 bar in order to yield 48.902 kJ/m^-2ofimpact strength.     

Optimization of structured cellular foam-based catalysts for low-temperature carbon dioxide methanation in a platelet milli-reactor

Here, we present a preliminary study to choose a catalyst with enough catalytic activity at temperatures below 250 °C, in order to study heat transfer in a platelet milli-reactor (PMR) with an infrared camera and a commercial window inserted on the top of our reactor that only withstands a maximal temperature of 250 °C. The higher methane productivity of foam catalysts compared to powder catalysts was revealed. Foam catalysts, all impregnated with the same amount of active phase (Ni + Ru) and with different coatings, were compared to SiC only impregnated with Ni + Ru. The different coatings studied were: carbon nanofibers (CNF), ceria–zirconia (CZ) and the combination of both. Both CNF and CZ washcoats were able to increase the low specific surface area of the SiC foam. Moreover, the presence of ceria–zirconia was proven to be essential for ensuring high methane productivities. The catalyst combining both CNF and CZ showed the best results.     

Product characterization of waste printed circuit board by pyrolysis

This paper is part of a project which studies pyrolysis as an alternative for recycling printed circuit board (PCB); the sample (2.0 cm × 2.0 cm) was pyrolyzed under nitrogen atmosphere, at 300, 400, 500, 600 and 700 °C in a tubular type oven, maintaining 30 min, and during the pyrolysis process the organic part is decomposed to pyro-oils and pyro-gases, which can be used as fuels or chemical material resources: the solid residues of about 75–80 wt.%, liquid yields of ∼9.0 wt.% and gas yields of 12–14 wt.%. No significant influence of temperature was observed over 500 °C, however, there was certainly influence under 500 °C in both volatile substance. The pyro-oils have fairly high gross calorific values (∼30 kJ/kg), mainly with aromatic and with oxygenated compounds. The pyro-gas is very rich in CO, CO₂, H₂, CH₄ and in small part of O₂; after being purged it can be combusted for the pyrolysis self-sustain. The tensile strength decreases about 35% at 773 K, while the impact and tear strength increases above 773 K, and then decreases along with the temperature increase. The strength changes can offer guidance for used as a replacement for virgin fibres in SMC manufacture. The residues are better laminated can be easily liberated for metals recovery.     

Electrochemical performance of a novel CoTETA/C catalyst for the oxygen reduction reaction

In this communication, we report a novel CoTETA/C catalyst for the oxygen reduction reaction (ORR) which was prepared from a carbon-supported cobalt triethylenetetramine chelate, followed by heat treatment in an inert atmosphere. Electrochemical performances were measured using rotating disk electrode (RDE) technique and a PEM fuel cell test station. For a H₂–O₂ fuel cell system, the maximum output power density reached 162 mW cm^?2 at 25 °C with non-humidified reaction gases. We found a nanometallic face-centered cubic (fcc) α-Co phase embedded in the graphitic carbon after pyrolysis, based on X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) measurements. These results indicated that CoTETA/C is a promising catalyst for the ORR.     

Electrochemical performance of nanocomposite LiMnPO4/C cathode materials for lithium batteries

A LiMnPO₄/C composite cathode was prepared by a combination of spray pyrolysis and wet ball milling. The cathode showed stable performance at various cutoff voltages up to 4.9 V. The cutoff voltage increase up to 4.9 V allowed the achievement of a high discharge capacity in galvanostatic charge–discharge tests. The discharge capacities of 153 mAh g^?1 at 0.05 C and 149 mAh g^?1 at 0.1 C were achieved at room temperature; the trickle-mode discharge capacities at room temperature were 132, 120 and 91 mAh g^?1 at 0.1, 1 and 5 C discharge rates, respectively. The cell exhibited a good rate capability in the galvanostatic cycling up to 5 C discharge rates at both ambient temperature and 50 °C.