Fabrication and properties of titanium–hydroxyapatite nanocomposites

Titanium–hydroxyapatite nanocomposites with different HA contents (3, 10, 20 vol%) were produced by the combination of mechanical alloying (MA) and powder metallurgical process. The structure, mechanical and corrosion properties of these materials were investigated. Microhardness test showed that the obtained material exhibits Vickers microhardness as high as 1030 and 1500 HV_0.2, which is more than 4–6 times higher than that of a conventional microcrystalline titanium. Titanium nanocomposite with 10 vol% of HA was more corrosion resistant (i_C = 1.19 × 10⁻⁷ A cm⁻², E_C = −0.41 V vs. SCE) than microcrystalline titanium (i_C = 1.31 × 10⁻⁵ A cm⁻², E_C = −0.36 V vs. SCE). Additionally, the electrochemical treatment in phosphoric acid electrolyte results in porous surface, attractive for tissue fixing and growth. Mechanical alloying and powder metallurgy process for the fabrication of titanium–ceramic nanocomposites with a unique microstructure are developed.     

Mechanical and dielectric properties of epoxy–clay nanocomposites

Epoxy–clay nanocomposites were prepared using two types of surface-treated montmorillonite (Closite 30B and Nanomer I28E). Wide angle X-ray scattering showed that all the nanocomposites had an intercalated structure. Improvements in tensile and fracture properties were found. The pure epoxy polymer was very brittle with a fracture energy, G _c, of 131 J m^?2. The addition of the nanoclays significantly increased the value of G _c, up to 240 J m^?2 for 5 wt% C30B. The toughening mechanisms acting in the nanocomposites were identified using scanning electron microscopy as crack deflection and plastic deformation of the epoxy matrix around the clay platelets following debonding. From electrical testing, the permittivity and loss angle of the nanocomposites decreased, and their breakdown strength increased as desired for insulation applications. The breakdown strength of the pure epoxy was found to be 11.7 kV mm^?1, while for a 2 wt% C30B nanocomposite, it increased to 14.7 kV mm^?1. It was concluded that the restriction of chain mobility inhibited electrical polarisation and thus decreased the permittivity and loss angle. The electrical damage zone was analysed using scanning electron microscopy. It was found that the higher resistance-to-surface degradation by partial discharges and the creation of a tortuous electrical path, which delayed the propagation of the electrical tree, were the main factors which improved the breakdown strengths of the nanocomposites.     

Microstructure,mechanical and wear properties of Cu–ZrO2 nanocomposites

Cu–ZrO₂ nanocomposites were produced by the thermochemical process followed by powder metallurgy technique. Microstructure development during fabrication process was investigated by X-ray diffraction, field emission scanning electron microscope and transmission electron microscope. The results show an improved distribution of zirconium dioxide (ZrO₂) nanoparticles (45?nm) in the copper matrix, which resulted in the improvement of mechanical properties of Cu–ZrO₂ composites. The nanocomposite with 9 wt-% ZrO₂ possesses the highest hardness (136.5 HV) and the superior compressive strength (413.5?MPa), resulting in an overall increase by 52 and 25%, respectively. The wear rate of the nanocomposites increased with increasing applied loads or sliding velocity.     

Synthesis of nickel–rubber nanocomposites and evaluation of their dielectric properties

Nanocomposites based on natural rubber and nano-sized nickel were synthesized by incorporating nickel nanoparticles in a natural rubber matrix for various loadings of the filler. Structural, morphological, magnetic and mechanical properties of the composites were evaluated along with a detailed study of dielectric properties. It was found that nickel particles were uniformly distributed in the matrix without agglomeration resulting in a magnetic nanocomposite. The elastic properties showed an improvement with increase in filler content but breaking stress and breaking strain were found to decrease. Dielectric permittivity was found to decrease with increase in frequency, and found to increase with increase in nickel loading. The decrease in permittivity with temperature is attributed to the high volume expansivity of rubber at elevated temperatures. Dielectric loss of blank rubber as well as the composites was found to increase with temperature.     

Fabrication and mechanical properties of silicon carbide–silicon nitride nanocomposites

A powder mixture of ultrafine –SiC–35 wt% –Si₃N₄ containing 6 wt% Al₂O₃ and 4 wt% Y₂O₃ as sintering additives were liquid–phase sintered at 1800°C for 30 min by hot–pressing. The hot–pressed composites were subsequently annealed at 1920°C under nitrogen–gas–pressure to enhance grain growth. The average grain–size of the sintered bodies were ranged from 96 to 251 nm for SiC and from 202 to 407 nm for Si₃N₄, which were much finer than those of ordinary sintered SiC–Si₃N₄ composites. Both strength and fracture toughness of fine–grained SiC–Si₃N₄ composites increased with increasing grain size. Such results suggested that a small amount of grain growth in the fine–grained region (250 nm for SiC and 400 nm for Si₃N₄) was beneficial for mechanical properties of the composites. The room–temperature flexural strength and fracture toughness of the 8–h annealed composites were 698 MPa and 4.7 MPa · m^1/2, respectively.     

Thermal and mechanical properties of hemp fabric-reinforced nanoclay–cement nanocomposites

The influence of nanoclay on thermal and mechanical properties of hemp fabric-reinforced cement composite is presented in this paper. Results indicate that these properties are improved as a result of nanoclay addition. An optimum replacement of ordinary Portland cement with 1 wt% nanoclay is observed through improved thermal stability, reduced porosity and water absorption as well as increased density, flexural strength, fracture toughness and impact strength of hemp fabric-reinforced nanocomposite. The microstructural analyses indicate that the nanoclay behaves not only as a filler to improve the microstructure but also as an activator to promote the pozzolanic reaction and thus improve the adhesion between hemp fabric and nanomatrix.     

Structure and properties of nylon 6–clay nanocomposites: effect of temperature and reprocessing

Melt-compounding is a technique which has been commonly used for producing polymer–clay nanocomposites with enhanced mechanical, thermal, and physical properties. Twin-screw extruders have been found to effectively exfoliate the clay platelets due to their high shear intensity. However, concerns about polymer and organoclay degradation have been raised in some studies. In this investigation, a composite of nylon 6–Cloisite 30B with fully exfoliated and well-dispersed clay particles was produced using a single-screw extruder and hence with limited polymer degradation. We show that processing temperature plays an important role in enhancing dispersion and that reprocessing at a higher temperature can enhance both dispersion and exfoliation and thus can result in composites with superior properties. We attempt to elucidate how the change in melt viscosity—coupled with the change in processing temperature—affects clay exfoliation and dispersion.     

Torsional,tensile and structural properties of acrylonitrile–butadiene–styrene clay nanocomposites

Torsional and tensile behaviour of acrylonitrile–butadiene–styrene (ABS)-clay nano-composites have been investigated and correlated with morphological and rheological characterisations. Nano-composites of ABS are prepared by melt compounding with different loading levels of nanoclay (Cloisite 30B) in a twin screw extruder and have been characterised in terms of torsional, axial and impact behaviour for their application in external orthotic devices. Tensile stress strain curve of nanocomposites are investigated to quantify resilience, toughness and ductility. Torque values of the nanocomposites are observed under torsion (10°–90°) and compared with that of neat ABS. Performance of ABS under torsional load improved by addition of nanoclay. Both modulus of elasticity and rigidity are found to improve in presence of nanoclay. State of dispersion in nano-composites is investigated using conventional methods such as transmission electron microscopy (TEM), X-ray diffraction (XRD), as well as by parallel plate rheometry. Addition of clay exhibits shear thinning effect and results in increase in storage modulus as well as complex viscosity of the nanocomposites. Zero shear viscosity rises tenfold with 1–2% addition of nanoclay, indicating the formation of structural network. It is found that state of dispersion of nanoclay governs the torsional and mechanical properties in ABS-clay nanocomposites.     

Microstructure and mechanical properties of Si3N4–TiC nanocomposites

Abstract

Si₃N₄–TiC nanocomposites are fabricated by hot press sintering from silicon nitride nanopowders and ultrafine TiC powders. The microstructure and mechanical properties are analysed and discussed. Scanning electron microscopy images show that the microstructure consists of equiaxed grains and grain boundary phase. The TiC added as a dispersed phase reacts with the nitrogen from Si₃N₄ during the liquid phase sintering, with the formation of TiC_0.7 N_0.3 , trace of SiC and N₂. The adding of a proper amount of TiC powders increases the flexural strength and has little influence on fracture toughness. The hardness increases with increasing TiC content.     

Effects of dispersion and interfacial modification on the macroscale properties of TiO2 polymer–matrix nanocomposites

This paper quantifies how the quality of dispersion and the quality of the interfacial interaction between TiO₂ nanoparticles and host polymer independently affect benchmark properties such as glass transition temperature (T_g), elastic modulus and loss modulus. By examining these composites with differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and scanning electron microscopy (SEM), we demonstrate changes in properties depending on the adhesive/wetting or repulsive/dewetting interactions the nanoparticles have with the bulk polymer. We further quantify the dispersion of TiO₂ nanoparticles in polymethylmethacrylate (PMMA) matrices by a digital–optical method and correlate those values to the degree of T_g depression compared to neat PMMA. Samples with the same weight percent of nanoparticles but better dispersion show larger shifts in T_g.     

Optical properties of core–shell structured Ag/SiO2 nanocomposites

Silver nanoclusters coated by SiO₂ were synthesized by a reverse micelle technique to obtain a core–shell microstructure with tunable particle size less than 50 nm. The refractive indices of the Ag/SiO₂ nanocomposites were calculated based on a theoretical model for binary composite materials which illustrated a strong correlation to the size of the metallic core and the dielectric shell. Dynamic light scattering analysis of the Ag/SiO₂ nanocomposites revealed that the refractive index of the nanocomposites was about 2.40, which was well in the range predicted by theoretical modeling. Optical absorption spectra and silver quantum dot size induced color change of the Ag/SiO₂ nanocomposites suspension were also investigated.     

Effects of post-annealing on the microstructure and mechanical properties of friction stir processed Al–Mg–TiO2 nanocomposites

Aluminum matrix nanocomposites were fabricated via friction stir processing of an Al–Mg alloy with pre-inserted TiO₂ nanoparticles at different volume fractions of 3%, 5% and 6%. The nanocomposites were annealed at 300–500 °C for 1–5 h in air to study the effect of annealing on the microstructural changes and mechanical properties. Microstructural studies by scanning and transmission electron microscopy showed that new phases were formed during friction stir processing due to chemical reactions at the interface of TiO₂ with the aluminum matrix alloy. Reactive annealing completed the solid-state reactions, which led to a significant improvement in the ductility of the nanocomposites (more than three times) without deteriorating their tensile strength and hardness. Evaluation of the grain structure revealed that the presence of TiO₂ nanoparticles refined the grains during friction stir processing while the in situ formed nanoparticles hindered the grain growth upon the post-annealing treatment. Abnormal grain growth was observed after a prolonged annealing at 500 °C. The highest strength and ductility were obtained for the nanocomposites annealed at 400 °C for 3 h.     

Fabrication and properties of an anisotropic PZT/polymer 0–3 composite

Anisotropic 0–3 PZT platelet/polymer composites were prepared by a route involving the tape casting and sintering of PZT sheets and the subsequent alignment of platelets in a polymer matrix by either calendering or tape casting; both techniques induced a strong alignment of the platelets. At 60 vol 1/2 loading, measured d ₃₃- and d _h-values of ~ 30 pC N^–1 and ~ 100 pC N^–1, respectively, were obtained; the calculated g _h-value was 83 mV mN^–1. A strong relaxation effect observed is considered most likely to be dependent on the characteristics of the polymer phase.     

Effect of MWCNT alignment on mechanical and self-monitoring properties of extruded PET–MWCNT nanocomposites

Self-monitoring aligned MWCNT loaded PET composites, with different CNT content, were prepared via twin-screw extrusion starting from a PET/MWCNT masterbatch, and fully characterized. All electrically conductive samples showed self-monitoring ability, i.e. a variation in electrical resistance as a function of stress. Moreover, the insertion of MWCNTs resulted in mechanical reinforcement with respect to neat PET. It was found that both self-monitoring behavior and mechanical performance are directly related to MWCNT content and to the direction of applied stress with respect to CNT orientation. In particular, too high MWCNT content decreased sensitivity at low strain, whereas a minimum MWCNT content was required to insure ohmic conductivity.     

Effects of PNN/PZT ratios on phase structure,electric properties and relaxation behavior of PZN–PNN–PZT ceramics

Pb(Zn_1/3Ni_2/3)_c(Ni_1/3Nb_2/3)_a(Zr_xTi_y)_bO₃ (PZN–PNN–PZT, the ratios of PNN/PZT a/b were 0.88, 1 and 1.136) piezoelectric ceramics were prepared by a traditional solid-state reaction method. The effects of PNN/PZT ratio on phase structure, microstructure and electric properties as well as the relaxation behaviors of PZN–PNN–PZT ceramics were investigated. The XRD patterns showed that all ceramics samples had a pure perovskite phase structure. Meanwhile, it was found that the phase structure undergoes a tetragonal, tetragonal-rhombohedral to rhombohedral transition as ratios of PNN/PZT increased. With the increasing of a/b from 0.88 to 1.136, the dielectric constant and diffusive phase coefficient decreases, it was indicated that relaxation behaviors also decreased. When ceramics with a/b was 1.136, the dielectric relaxation γ reached the minimum and electrical properties were poor. The electric properties of ceramics with a/b was 1.00 have an excellent properties, it was indicated that ceramics reached an optimization at the MPB structure.     

Influence of surface modified TiO2 nanoparticles on dielectric properties of PVdF–HFP nanocomposites

Polyvinylidene fluoride-co-hexaflouropropylene (PVdF–HFP)/TiO₂ hybrid nanocomposites membranes for electrical applications have been prepared using a solvent casting technique. The interface between PVdF–HFP and TiO₂ was modified using aminopropyltrimethoxysilane (APS) coupling agent. The silane linkages on the TiO₂ surface have been confirmed using Fourier transform infra red spectroscopy. WAXD and DSC analysis has been employed to estimate the variation in crystallinity within the membrane as a function of the incorporation of both untreated and APS treated TiO₂. The dispersion of both nanoparticles in the PVdF–HFP matrix were characterized by atomic force microscopy and differences were observed in the images of APS treated and untreated. Variation in electrical properties such as conductivity, dielectric constant, dielectric loss and electric modulus of the hybrid composite films were studied employing AC impedance spectroscopy over a range of frequency from 1 kHz to 1 MHz at room temperature. Theoretical models like Maxwell, Faruka, Rayleigh and Lichtenecker were employed to calculate the effective dielectric constant of hybrid nanocomposite membranes and the estimated values were compared with the experimental data. Further, the variation in thermal stability of PVdF–HFP membrane as a function of untreated and silane treated TiO₂ reinforcement has been estimated using thermogravimetric analysis.