Hot pressed hydroxyapatite–carbon fibre composites

Composite samples were obtained from hydroxyapatite powder and carbon fibres by hot pressing at 1100°C and 25 MPa for 15 min in argon atmosphere. Two types of cut carbon fibres produced in a carbonisation process of polyacrylonitrile (PAN) precursor were used both in non-coated or coated form. The coatings of calcium phosphate were applied by sol–gel technique. The highly sintered composite with the best strength properties was obtained from coated carbon fibres with basic character of the surface. The existence of hydroxyl groups on fibre surface makes possible formation of bonds with the calcium phosphate layer formed as a result of polycondensation following the sol–gel procedure.     

Cyclic ablation behavior of C/C–ZrC–SiC composites under oxyacetylene torch

Cyclic ablation behavior of C/C–ZrC–SiC composites prepared by precursor infiltration and pyrolysis process was studied using oxyacetylene torch. After repeated 30 s ablation for four times, the composites exhibited better ablation properties than those under single ablation for 120 s because of the lower surface temperature, and their linear and mass ablation rates were −3×10^–4 mm/s and −2.29×10^–3 g/s, respectively. A continuous ZrO₂–SiO₂ layer formed on the surface of center ablation region and acted as an effective barrier to the transfer of heat and oxidative gases into the inner material. Thermal stress induced by repeated impact of oxyacetylene led to some cracks on the ZrO₂–SiO₂ layer; however its destructive power was weaker than that of higher temperature. Stick like silica as grown silica nanowires were generated in the transition ablation region due to the evaporation of silicon oxide at appropriate temperature.     

Morphology and microstructure of SiC/SiC composites ablated by oxyacetylene torch at 1800°C

An oxyacetylene torch tested the ablation of SiC/SiC composites at 1800℃. According to the distribution of ablation product silica, the morphology could be divided into three regions. The fibers in the oval central region were ablated and broken, and the fracture surface is the conical tip. The silica liquid film in the transition region plays a role in resisting the ablation of the material. However, the generation of airflow channels destroys the liquid film's continuity and reduces the material's ablation resistance. Bean sprouts-like nano-sized silica was grown on the surface of the dome-top SiC matrix in the marginal region.     

Ablation behavior and mechanism of C/C–ZrC–SiC composites under an oxyacetylene torch at 3000 °C

C/C–ZrC–SiC composites with continuous ZrC–SiC ceramic matrix were prepared by a multistep technique of precursor infiltration and pyrolysis process. Ablation properties of the composites were tested under an oxyacetylene flame at 3000 °C for 120 s. The results show that the linear ablation rate of the composites was about an order lower than that of pure C/C and C/C–SiC composites as comparisons, and the mass of the C/C–ZrC–SiC composites increased after ablation. Three concentric ring regions with different coatings appeared on the surface of the ablated C/C–ZrC–SiC composites: (i) brim ablation region covered by a coating with layered structure including SiO₂ outer layer and ZrO₂–SiO₂ inner layer; (ii) transition ablation region, and (iii) center ablation region with molten ZrO₂ coating. Presence of these coatings which acted as an effective oxygen and heat barrier is the reason for the great ablation resistance of the composites.     

Chemically modified fibrin–gelatin composites: Preparation and characterization

The crude fibrin which is hitherto discarded as waste in slaughterhouses was recovered and purified. Using this fibrin, fibrin–gelatin composites were prepared and crosslinked with either basic chromium sulfate or glutaraldehyde. These composites were also graft-copolymerized with polyhydroxyethyl methacrylate using hydrogen peroxide–ferrous ammonium sulfate initiation technique. The graft copolymers were characterized for their moisture content, water absorption capacity, tensile strength, infrared spectroscopy, scanning electron microscopy, and thermogravimetric profile. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1109–1115, 1998     

Preparation and characterisation of diopside-based glass–ceramic foams

Foaming and crystallisation behaviours of compacted glass powders based on a diopside glass–ceramic composition were investigated using the sintering route. The foaming agent was 2 wt.% SiC particles. The effect of PbO on the foaming ability of glasses was investigated. The results showed that the addition of PbO not only improved the foaming ability, by improving the wettability of the glass–SiC particles but also increased the crystallisation temperature and widened the temperature interval between the dilatometric softening point and the onset of crystallisation. The glass–SiC wetting angle was decreased from 85° for the lead-free glass, to 55° for the glass that contains 15 wt.% PbO.     

Characterisation and modelling of CNT–epoxy and CNT–fibre–epoxy composites

Abstract

This research presents an experimental and theoretical investigation on the effects of carbon nanotube (CNT) integration within neat epoxy resin (nanocomposites) and a carbon fabric–epoxy composite (multiscale composites). An approach is presented for the prediction of mechanical properties of multiscale composites. This approach combines woven fibre micromechanics (MESOTEX) with the Mori-Tanaka model which was used for the prediction of mechanical properties of nanocomposites in this research. Nanocomposite and multiscale composite samples were manufactured using cast moulding, resin infusion, and hand lay-up process. The CNT concentrations in the composite samples were from 0 to 5 wt-%. The samples were characterised using tensile, shear and flexural tests. The discrepancy between the theoretical predictions and the experimental observations was hypothesised to be due to dispersion and bonding issues and SEM images are presented in support of the hypothesis.     

Mechanical and thermal properties of hybrid carbon fibre–phenolic matrix composites containing graphene nanoplatelets and graphite powder

Carbon fibre–phenolic matrix (CF–P) composites containing graphene nanoplatelets (GNPs) were manufactured for improved mechanical and thermal properties. For comparison, micrometer-size pyrolytic graphite powder (GP) was also incorporated in CF–P composites. The loading of carbon fibres was kept constant at 60?wt-% while the quantity of GNPs was varied from 0.1?wt-% to 0.3?wt-% and GP from 1.0?wt-% to 3.0?wt-%. Only GNPs were functionalised by ultraviolet-ozone treatment to improve their dispersion in the matrix while all the composites were manufactured by hand layup method and characterised by scanning electron microscopy, impact, flexural, thermogravimetry and ablation tests. The composite containing 0.3?wt-% GNPs showed considerable improvement in ablation, flexural and impact testing as compared to CF-P composites containing GP. Finally, the ablation mechanisms of post-ablated composites were discussed in the light of available data in the literature.     

Polyaniline/polyacrylate core–shell composites: Preparation,morphology and anticorrosive properties

Polyaniline/partially phosphorylated poly(vinyl alcohol)/polyacrylate nanoparticles ((PAn/P-PVA)_x/PAc_y) were synthesized by encapsulation of varying amounts of PAn/P-PVA nanoparticles (x = 0.3, 0.5 or 0.7 g) with PAc (y = 4, 6 or 8 g acrylate monomers) via emulsifier-free emulsion polymerization. A monomer conversion level of 93.9% was achieved for the synthesis of the (PAn/P-PVA)_0.5/PAc₄ nanoparticles. X-ray diffraction analysis revealed that PAc was intercalated between the PAn/P-PVA layers, whilst transmission electron microscopy analysis of the different nanoparticles revealed they were spherical PAn/P-PVA agglomerates coated with PAc. Thermogravimetric analysis revealed that the thermal stability of the (PAn/P-PVA)/PAc nanoparticles decreased with increasing amounts of PAc. Cyclic voltammetry based analysis of the different (PAn/P-PVA)/PAc nanoparticles coated onto carbon fiber electrodes revealed that the PAn/P-PVA nanoparticles were encapsulated sufficiently by the non-conductive PAc and that the peak current decreased with increasing amounts of acrylate. With respect to the corrosion resistance in 1.0 M sulfuric acid, steel coated with the (PAn/P-PVA)_0.7/PAc₈ nanocomposite showed the best corrosion resistance (11.4%), but for the nanocomposites at each PAn/P-PVA loading level, the anticorrosive properties increased with increasing PAc levels, presumably due to the increasing tortuosity of the diffusion pathway through the coating for any corrosion agents.     

Further studies on the use of Raman spectroscopy and X-ray diffraction for the characterisation of TiC-containing carbon–carbon composites

Raman spectroscopy and X-ray diffraction are used to study the crystalline structure of carbon–carbon and TiC-containing composites. The advantages and drawbacks of these techniques for the characterisation of carbon–carbon composites are analysed in the light of the distribution and arrangement of their components and the microstructural orientation of the supporting matrix. Analyses performed on longitudinal and transverse sections of the composites confirm that the measurements are affected by the orientation of the crystals. The overall crystalline parameters calculated by X-ray diffraction were unequivocally resolved for each single component by means of Raman spectroscopy. A significantly higher degree of order was observed in the TiC-containing matrix as a result of the catalytic graphitisation of the carbon achieved by the addition of titanium. In addition, Raman spectroscopy corroborated that the incorporation of TiC into the carbon matrix does not disrupt the orientation of the graphene planes of the matrix parallel to the fibre axis, a necessary characteristic for achieving an optimum heat transfer through the material.     

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.     

Preparation and characterisation of titania-supported vanadium–phosphorus oxide catalysts

A series of vanadium–phosphorus oxides (mainly with V P ) supported on pigmentary anatase (10 m² g^-1) has been prepared using aqueous NH₄VO₃ and (NH₄)H₂PO₄ solutions, with loadings up to 11.3 wt%, equivalent to about 12.7 monolayers. Characterisation by X-ray diffraction, laser Raman spectroscopy, X-ray photoelectron spectroscopy and temperature-programmed reduction suggests that the main phase present at loadings below about 10 wt% is an amorphous V–P oxide which exists chiefly as blocks of disordered material. The presence of small amounts of crystalline -VOPO₄ and of V₂O₅ is indicated at the highest loadings, especially when and V P ratios are used. The two materials having the lowest loadings are active for methanol oxidation at 473–533 K, and show high selectivity to formaldehyde. This revised version was published online in June 2006 with corrections to the Cover Date.     

Mullite/ β-spodumene composites: Preparation and characterization

Mullite/ β-spodumene composites were fabricated by the addition of 5 up to 20 mass% β -spodumene powder to mullite matrix. Both mullite and β-spodumene were prepared by sol-gel technique. The batches were uniaxially pressed into discs and rectangular bars, then pressureless sintered at 1400 °C up to 1700 °C for 1 h. Mechanical and thermal properties, as well as microstructure and phase composition were carried out on the sintered composites. The results show that although the increase in the soft β-spodumene reduces the hardness and the thermal expansion of the composites, they lower the firing temperature and enhance the flexural strength. The study indicates that β-spodumene content has a noticeable effect on the composites thermal expansion coefficient. It also shows that it is possible to tailor mullite/ β-spodumene composite with adjusted thermal expansion coefficient by changing the mullite to β-spodumene ratio.     

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.     

Microstructure and ablation behavior of carbon/carbon composites infiltrated with Zr–Ti

Carbon/carbon(C/C) composites infiltrated with Zr–Ti were prepared by chemical vapor infiltration and reactive melt infiltration. Their microstructure and ablation behavior at different temperatures and time were investigated. The results show that C/C composites infiltrated with Zr–Ti have good interface cohesion between carbon fibers, pyrocarbon and carbide. Compared with C/C composites and C/C–ZrC composites, the synthesized sample with Zr_0.83Ti_0.17C_0.92 and Ti_0.82Zr_0.18C_0.92 exhibits better ablation resistance at 2500 °C due to the newly formed protective layer composed of ZrTiO₂ pinned by ZrO₂ grains after ablation. The ablation resistance of the sample with Zr_0.57Ti_0.43C_1.01 increased gradually with the decrease of temperature from 3000 °C to 2000 °C, whereas the ablation resistance of the sample with Zr_0.83Ti_0.17C_0.92 and Ti_0.82Zr_0.18C_0.92 first increased obviously and then decreased slightly. In addition, the work indicates that surplus particles or liquid phases of oxides cannot protect the matrix, and that the liquid oxides may even cause severe ablation. Furthermore, a protective layer of oxides tends to be formed with the increase of ablation time.     

Preparation and electrochemical properties of SiO2–non-graphitizable carbon composites as negative electrode materials for Li-ion batteries

SiO₂–non-graphitizable carbon composites were prepared by pyrolysis of a mixture of ethyl cellulose and nano-sized SiO₂. The composite electrode showed high reversibility in insertion and/or extraction reactions of Li ions at potentials below 1 V with little hysteresis after the 2nd cycle, whereas a large irreversible capacity was observed in the 1st cycle. This reversible capacity increased with increasing SiO₂ content above 5 wt%. Li ion transfer at the interface between a composite electrode and an electrolyte was studied by ac impedance spectroscopy. In the Nyquist plots, a semi-circle that was assigned to charge-transfer resistance (R _ct) because of Li ion transfer across the interface between the composite electrode and electrolyte appeared at potentials below 1 V. The values of R _ct decreased with increasing SiO₂ content. These results indicate that both a decrease in R _ct and an increase in reversible capacity can be achieved by use of SiO₂–non-graphitizable carbon composite electrodes; this would lead to Li-ion batteries with higher power and energy density.     

Preparation and structural characterisation of a novel ferrocene–amino acid conjugate

A new type of ferrocene–amino acid conjugate, 2-[(methoxycarbonyl)methyl]-2-aza[3]ferrocenophane (1), was obtained in a rather low yield via condensation reaction of 1,1′-bis(hydroxymethyl)ferrocene and glycine methyl ester in the presence of [RuCl₂(PPh₃)₃] as a catalyst. The compound was characterised by combustion analysis and by spectroscopic method, and its solid-state structure was established by single-crystal X-ray diffraction analysis. Compound 1 is reluctant towards alkylation with MeI but readily forms a stable picrate salt. Cyclic voltammetry experiments on 1 (in CH₃CN at Pt electrode) revealed the compound to undergo a one-electron reversible oxidation attributable to ferrocene/ferrocenium couple (E^o′ = ?5 mV vs. ferrocene itself), which shifts towards more positive potentials upon protonation with HCl.     

Preparation of interpenetrating ceramic–metal composites

Ceramic reinforced metals are attractive because of their enhanced elastic modulus, high strength, tribological properties and low thermal expansion. Most work in this sector has focused on particle- or fiber-reinforced composites where the ceramic phase is not continuous. This work presents aluminium–alumina composites where both phases are interpenetrating throughout the microstructure. Ceramic preforms were produced with sacrificial pore forming agents leading to porosities between 50% and 67%. Pore wall microstructure was varied by changing the sintering temperature. Permeability and strength was measured for the porous preforms and infiltration results were compared with theoretical predictions based on capillary law and Darcian flow. A direct squeeze-casting process was used to infiltrate the preforms with aluminium resulting in an interpenetrating microstructure on both macropore and micropore scale.     

Preparation of interpenetrating alumina–copper composites

To prepare interpenetrating alumina–copper composites, alumina foams were activated with titanium coating by chemical vapor deposition and then were infiltrated with molten copper by expendable casting process. The microstructure and phase composition of the composites were analyzed, and bending strength, electrical conductivity, friction and wear properties were tested. The results showed that the bonding between ceramic and metal was fine in the composites while no reactions took place between them because of the undissolved titanium coating. With increase of ceramic fraction, the electrical conductivity of the composite decreased, whereas the bending strength increased. The composite failure occurred by ductile fracture of the metal followed by fracture of the ceramic. The wear rate of the composites decreased with increase of ceramic fraction. And the wear of the composites was featured with ceramic struts peeling compared with ploughing and adhering wear for pure copper.