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.     

Colloidal Stability and Sintering of Yttria–Silica and Yttria–Silica–Alumina aqueous suspensions

The aim of this work was to produce dense yttrium silicate materials by slip casting, with more than 90% of Y₂SiO₅ phase. The rheological behaviour of concentrated aqueous slips was studied considering the effect of the dispersing additives, solids content and pH. The densification kinetics was examined as a function of temperature and time, and the reactions were analysed in the light of the equilibrium phase diagrams. Deflocculation of the slips was achieved by either an electrostatic mechanism using tetraethylammonium hydroxide, thus requiring a high concentration of base, and by a polyelectrolyte through an electrosteric mechanism, which provided more reliable results. In the binary system Y₂O₃–SiO₂, a very low grade of sintering was obtained at 1600°C. The use of alumina allows sintering through a liquid phase, reaching 90% theoretical density.     

Synthesis and characterizations of BNT–BT and BNT–BT–KNN ceramics for actuator and energy storage applications

Dielectric and ferroelectric properties of 0.93Bi_0.5Na_0.5TiO₃–0.07BaTiO₃ (BNT–BT) and 0.93Bi_0.5Na_0.5TiO₃–0.06BaTiO₃–0.01K_0.5Na_0.5NbO₃ (BNT–BT–KNN) ceramics were studied in detail. An XRD analysis confirmed the single perovskite phase formation in both the samples. Room temperature (RT) dielectric constant (ε_r) ~1020 and 1370, respectively at 1 kHz frequency were obtained in the BNT–BT and BNT–BT–KNN ceramics. Temperature dependent dielectric and the polarization vs. electric field (P–E) studies confirmed the coexistence of ferroelectric (FE) and anti-ferroelectric (AFE) phases in the BNT–BT and BNT–BT–KNN ceramics. Substitution of KNN into the BNT–BT system decreased the remnant polarization, coercive field and the maximum strain percentage. The energy storage density values ~0.485 J/cm³ and 0.598 J/cm³ were obtained in the BNT–BT and BNT–BT–KNN ceramics, respectively. High induced strain% in the BNT–BT ceramics and the high energy storage density in the BNT–BT–KNN ceramics suggested about the usefulness of these systems for the actuator and the energy storage applications, respectively.     

The preparation and properties of zirconia-doped Y–Si–Al–O–N oxynitride glasses and glass-ceramics

Two series (N-9 and N-18 series) of zirconia-doped Y–Si–Al–O–N oxynitride glasses and glass-ceramics were designed. Nominal compositions of the glass samples in equivalent percent (eq%) are xZr: (24–0.25x)Y: (15–0.25x)Al: (61–0.5x)Si: 91O: 9 N and xZr: (24–0.25x)Y: (15–0.25x)Al: (61–0.5x)Si: 82O: 18 N (x=0, 2, 4, 6), respectively. The obtained samples were characterized by differential thermal analysis (DTA), X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Densities, Vickers hardness, fracture toughness, glass transition temperature, and thermal expansion coefficient data were established for each sample. Effect of Zr and N content on glass network structure, thermal and mechanical properties was investigated. It was found that the addition of zirconia is effective in preparing Y–Si–Al–O–N oxynitride glasses with lower glass transition temperature and higher hardness.     

Unique and contrasting mixed-metal lithium–calcium and lithium–barium hexamethyldisilazide complexes

Addition of lithium hexamethyldisilazide to calcium or barium bis(hexamethyldisilazide) in THF resulted in the synthesis of two unique but very different mixed-metal complexes: X-ray crystallography shows these to be, respectively, the heterobimetallic complex [Ca{N(SiMe₃)₂}₃Li(THF)] (1), containing two calcium–lithium bridging amide ligands and the remarkable co-crystalline compound [Ba{N(SiMe₃)₂}₂(THF)₃][Li₂{N(SiMe₃)₂}₂(THF)₂] (2).     

Synthesis and Characterization of Linear and Tri-Block PLLA–PEG–PLLA Blends

This study was conducted to synthesize poly(L-lactide)–poly(ethylene glycol)–poly(L-lactide) triblock copolymer (PEGLA) with different poly(L-lactide) block length, and explore its applicability in a blend with linear poly(L-lactide) (3051D NatureWorks) with the intention of improving heat seal and adhesion properties at extrusion coating on paperboard. Poly(L-lactide)–poly(ethylene glycol)–poly(L-lactide) was obtained by ring opening polymerization of L-lactide using poly(ethylene glycol) (molecular weight 6000 g mol^?1) as an initiator and stannous octoate as catalyst. The structures of the PEGLAs were characterized by proton nuclear magnetic resonance spectroscopy. The melt flow and thermal properties of all PEGLAs and their blends were evaluated using dynamic rheology and differential scanning calorimeter. All blends containing 10 wt% of PEGLAs displayed similar zero shear viscosities to neat poly(L-lactide), while blends containing 30 wt% of PEGLAs showed slightly higher zero shear viscosity. However, all blends displayed higher shear thinning and increased melt elasticity (based on tan δ). No major changes in thermal properties were distinguished from differential scanning calorimetric studies. High molecular weight PEGLAs could be used in extrusion coating with 3051D without problems.     

Synthesis and Structural Analysis of Co–Zn–Cd Ferrite by Williamson–Hall and Size–Strain Plot Methods

The work aimed at studying the structural properties of Cd-doped cobalt zinc ferrite (Co_0.5Zn_0.5Cd_0.2Fe_1.8O₄) prepared by simple, low-cost solid-state reaction method and characterized by XRD techniques. The X-ray analysis confirms the formation of ferrite particles with a cubic spinel structure. Crystallite size D, lattice constant a, micro strain ε, X-ray density Δ_X, dislocation density ρ _D , hopping lengths (L_A and L_B), bond lengths (A–O and B–O), ionic radii (r_A and r_B), texture coefficients [TC(hkl)], and mechanical properties are also reported.     

Microstructure and mechanical properties of TiC–TiN–Zr–WC–Ni–Co cermets

Cermet cutting tools are widely used for semi-finishing and finishing work on steel and cast iron. However, their brittleness is still an unavoidable limitation for their utilizations. Zirconium was added to improve the fracture toughness of Ti(C, N) based cermets. The microstructure and the fracture surfaces of cermets were studied by using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The experimental results reveal that Zr dissolved and formed solid solutions during the sintering process. The amount of grains with typical core/rim structure decreases and that of coreless grains increases with increasing Zr addition. Moreover, the fracture toughness is improved clearly due to the increased amount of the coreless grains, the spinodal decomposition in cermets, as well as the crack deflection and crack branching mechanisms. Additionally, hardness and relative density were also measured, respectively.     

Electrocaloric and pyroelectric properties of PZT and PMN–PNN–PZT thin films

The electrocaloric effects (EC) of PZT and PMN–PNN–PZT films were evaluated. PZT and PMN–PNN–PZT thin films with a thickness of 500 nm were fabricated by state-of-the-art chemical solution deposition from a precursor solution with PZT and (PMN?PNN)/PZT=30/70. The polarization hysteresis loop was found to be slim and nonlinear, with smaller hysteretic behavior compared with PZT. The pyroelectric properties evaluated from polarization change and current measurement show that the properties of PMN–PNN–PZT films are superior to those of non-doped PZT films. The electrocaloric temperature changes ΔT due to applied ΔE were calculated. PZT and PMN–PNN–PZT films exhibited ΔT of 2.1 K and 3.6 K at 237.5 °C under a field of 500 kV/cm, respectively. Thermal-electrical energy converters based on pyroelectric effects were investigated for energy harvesting and possible use in ultralow-power sensor modules. The possibilities of pyroelectric energy harvesting using these PZT films were also investigated.     

Measurement and Correlation of Liquid–Liquid Equilibrium Data for Ethanol–Water–KF and Ethanol–Water–K2CO3 Systems

The liquid–liquid equilibrium data for two ternary systems, ethanol–water–KF and ethanol– water–K2CO3, were determined at 25℃. Experiments show that by adding KF or K2CO3 into the ethanol–water system two phases are formed: an ethanol-rich phase with negligible salt and a water-rich phase with negligible ethanol, thus water can be separated out easily. A mathematical calculation of the liquid–liquid equilibrium data was carried out with the Pitzer theory on water activity in the aqueous phase, and with the Wilson or NRTL or UNIQUAC equations for that in the ethanol phase, which is in good agreement with experimental data.     

Preparation and properties of Ge–Ga–La–S–AgI chalcogenide glass

Chalcogenide glasses of 65GeS₂–(25–x)Ga₂S₃–10AgI–xLa₂S₃ (x=0, 1, 3, and 5 mol%) were fabricated through the traditional melt-quenching method. The effects of addition of La₂S₃ on physical, thermal and optical properties of the glass system were investigated. The results showed that the fabricated glasses possess considerably high glass transition temperature, exhibit improved mechanical property and excellent infrared transmission. A redshift at the visible absorbing cut-off edge is observed with increasing of La₂S₃ content. The direct and indirect optical band gap values are also calculated. Raman spectra analysis indicated that the band at 265 cm⁻¹ decreased in amplitude and a new peak at 230 cm⁻¹ was detected manifesting the formation of La-S bond in the network. In addition, the mid-infrared emission at 3.74 µm of the glasses doped with Tm³⁺ ions was achieved. The results indicated that the glasses are promising materials for mid-infrared applications such as imaging, remote sensing and lasers.     

Structure and enhanced properties of perovskite ferroelectric PNN–PZN–PMN–PZ–PT ceramics by Ni and Mg doping

Perovskite ferroelectric oxide ceramics of 0.1Pb(Ni_1/3Nb_2/3)O₃–0.35Pb(Zn_1/3Nb_2/3)O₃–0.15Pb(Mg_1/3Nb_2/3)O₃–0.1PbZrO₃–0.3PbTiO₃ (0.10PNN–0.35PZN–0.15PMN–0.10PZ–0.30PT) with excess MgO and NiO were investigated in this work. The effects of the excess MgO and NiO doping on the ceramic structure, density, dielectric, ferroelectric and piezoelectric properties were studied. The chemical states of nickel were examined using X-ray photoelectron spectroscopy (XPS). Both XPS experimental results and theoretical analyses on the basis of ionic packing indicated that the excess valence-two ions substituted the A-sites in the ABO₃ perovskite structure. By completely eliminating the pyrochlore phase and enhancing densification with the excess NiO and MgO, improved piezoelectric coefficient d₃₃ up to 459 pC/N, higher ferroelectric remnant polarization and dielectric constant were demonstrated when sintered at temperature as low as 850–950 °C.     

Thermal and combustion behavior of phosphorus–nitrogen and phosphorus–silicon retarded epoxy

A novel trizine ring-based phosphorus–nitrogen flame retardant, 1,3,5-tris(3-(diphenylphosphoryl)propyl)-1,3,5-triazinane-2,4,6-trione (PN), was synthesized by the reaction of diphenylphosphine oxide and triallyl isocyanurate with triethylborane as catalyst. Chemical structure of the target compound was confirmed by Flourier transform infrared spectrum, nuclear magnetic resonances, matrix-assisted laser desorption/ionization time-of-flight mass spectrum measurements. The newly developed PN was used in the flame retardancy of o-cresol novolac epoxy/phenolic novolac hardener system. For comparison, another analogous phosphorus–silicon flame retardant, [(1,1,3,3-tetramethyl-1,3-disiloxanediyl)-di-2,1-ethanediyl]-bis(diphenylphosphine oxide) (PSi), was also applied in the same system. Experimental results revealed that PN showed superior flame retardant efficiency to that of PSi. In addition, the incorporation of flame retardants was in favor of the char formation during the thermal degradation process of epoxy thermosets. With the same flame retardant content, the char residue of epoxy thermosets with PSi was higher than that of epoxy thermosets with PN at 750 °C. Cone calorimeter results indicated that PN contributed to gas phase flame retardancy while PSi was more likely to take part in flame retardancy in the condense phase. X-ray photoelectron spectroscopy data revealed that the binding energies of phosphorus changed in different ways in PN and PSi after combustion. This implied that phosphorus exhibited different combustion behaviors when combined with nitrogen or silicon.     

Electroless deposited Ni–Re–P, Ni–W–P and Ni–Re–W–P alloys

Coatings of electroless Ni–W–P, Ni–Re–P and Ni–W–Re–P alloys were plated in alkaline citrate baths containing amino alcohols, but not free ammonia ions. The reference Ni–P alloy was used as an intermediate layer in the sandwich: Ni–Me–P/Ni–P/substrate. An extremely homogeneous thickness distribution of all alloy components was found by applying scanning Auger electron spectroscopy (SAES(. The inclusion of refractory metals at the expense of nickel and without substantial change in phosphorus content was established. A non-oxidized state of the codeposited Re and W in Ni–W–P, Ni–Re–P and Ni–W–Re–P alloys was determined by means of X-ray photoelectron spectroscopy examination, as well as by SAES profiles, revealing the absence of oxygen throughout the coatings. All alloy films are amorphous and paramagnetic.     

Polymer-Salt Synthesis of Photoactive Bactericide ZnO–Ag and ZnO–SnO2–Ag Nanopowders and a Study of Their Structure and Properties

Glass Physics and Chemistry - This paper describes the low-temperature polymer-salt synthesis of ZnO–Ag nanopowders and presents the results of studying their structure, morphology, and...     

Sol–gel preparation and characterization of nano-crystalline lithium–mica glass–ceramic

The nano-crystalline lithium–mica glass–ceramic with separated crystallite size of 13 nm was prepared using sol–gel technique. In such a process, the structural evolutions and microstructural characteristics of the synthesized samples were investigated through X-ray diffraction, transmission electron microscopy, thermal analysis and Fourier transform infrared spectroscopy. It was found that the crystallite size of the mica obtained from sol–gel method is smaller than the one synthesized via conventional melted method. The XRD results also showed that the crystallization of mica occurred above 675 °C and it could originate from MgF₂ so that the next stage will also be the transformation from mica to norbergite and norbergite to chondrodite. The activation energy of the crystallization and Avrami factor were measured as 376.7 kJ mol^?1 and 2.3, respectively. It is found that the bulk crystallization could be considered as the predominant crystallization mechanism for the glass–ceramic.     

Electrochemistry of molten LiCl–KCl–CrCl3 and LiCl–KCl–CrCl2 mixtures

Chemical reactions during dissolution of CrCl3 or CrCl2 in molten LiCl–KCL eutectic have been demonstrated to occur, but the nature of the reactions is not yet well understood. Reduction of CrCl3 to chromium metal occurs through two well-characterized electrochemical steps, at approximately +0.1 and –0.9 V vs Ag/AgCl. Each step was studied in the 0.025–0.085 molar CrCl3 concentration range, at various temperatures between 375 and 550 °C. The Cr(iii)/Cr(ii) electron transfer step exhibited reversible behaviour under all the experimental conditions studied. In contrast, the Cr(ii)/Cr(0) step could involve Cr(ii) adsorbed species and initial chromium electrocrystallization phenomena, mainly depending on the nature of the substrate.     

Structure and Composition of Au–Cu and Pd–Cu Bimetallic Catalysts Affecting Acetylene Reactivity

Au–Cu and Pd–Cu bimetallic model catalysts were prepared on native SiO₂/Si(100) substrate under ultra high vacuum (UHV) by employing buffer layer assisted growth procedure with amorphous solid water as the buffer material. The effect of the bimetallic nanoclusters (NCs) surface composition and morphology on their chemical reactivity has been studied with acetylene decomposition and conversion to ethylene and benzene as the chemical probe. It was found that among the Au–Cu NCs compositions, Au_0.5Cu₃ NCs revealed outstanding catalytic selectivity towards ethylene formation. These NCs were further characterized by employing TEM, XPS and HAADF-STEM coupled EDX analysis. With CO molecule as a probe, CO temperature programmed desorption has been used to investigate the distribution of gold on the top-most surface of the supported clusters. Surface segregation at high relative elemental fraction of gold leads to a decreased activity of the Au–Cu NCs towards ethylene formation. In contrast to the Au–Cu NCs, the Pd–Cu bimetallic system reveals reduced sensitivity to the relative elemental composition with respect to selectivity of the acetylene transformation toward ethylene formation. On the other hand, remarkable activity towards benzene formation has been observed at elemental composition of Cu₃Pd, at comparable rates to those for ethylene formation on clean Pd NCs.     

Synthesis and properties of electrical conductive and antibacterial siloxane-modified carbon fiber–silver–acrylate nanocomposites

First, silanized carbon fiber (SCF) was synthesized, then silanized carbon fiber–silver (SCF-S) was obtained. Finally, silanized carbon fiber–silver–acrylate (SCF-S-A) electrical conductive and antibacterial composites were prepared. The structures of CF, SCF, SCF-S, and SCF-S-A were characterized by X-ray photoelectron spectroscopy, FTIR, scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and UV spectra. The electrical conductive and antibacterial properties of SCF-S-A nanocomposites were studied. The results showed that electrical conductive and antibacterial activity properties of SCF-S-A nanocomposites were improved. When the content of SCF-S was 50%, the conductivity of SCF-S-A nanocomposites was maximum. The SCF-S-A nanocomposites will have promising application in high-performance electrical conductive and antibacterial materials.