Effects of NaSbO3 on phase structure and electrical properties of K0.5Na0.5NbO3–LiTaO3–NaSbO3 piezoelectric ceramics

The (0.96–x)K_0.5Na_0.5NbO₃–0.04LiTaO₃–xNaSbO₃ (abbreviated as KNN–LT–xNS, x = 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08) lead-free piezoelectric ceramics were fabricated by conventional ceramic technique. The crystal structure, dielectric, ferroelectric and piezoelectric properties of the ceramics were investigated. The Curie temperature (T _C) and the polymorphic phase transition temperature (T _O?T) of the ceramics decreased gradually with the increase of NaSbO₃. In addition, a coexistence of orthorhombic and tetragonal phases in the ceramics was identified in the composition range of 0.05 ≤ x ≤ 0.08. The ceramic with a composition of x = 0.06, which was close to the orthorhombic side of the polymorphic phase transition (PPT) region, exhibited excellent electrical properties with piezoelectric coefficient d ₃₃ = 233 pC/N, planar electromechanical coupling coefficient k _p = 0.328, remnant polarization P _r = 14.7 μC/cm², coercive field E _c  = 11.7 kV/cm, relative permittivity $ \varepsilon_{33}^{\text{T}} /\varepsilon_{0} $  = 1,033, and loss tangent tan δ = 0.063. The ceramics had relatively low Q _m value in the range of 10–37.     

Effects of Bi excess on the structure and electrical properties of high-temperature BiFeO3–BaTiO3 piezoelectric ceramics

BiFeO₃–BTiO₃(BF–BT) ceramics as a promising candidate for lead-free high-temperature piezoelectric ceramics were studied with a special emphasis on the compositional dependence of piezoelectric properties. Excess Bi was added to compensate for the evaporation of Bi³⁺ ions during sintering and this addition was found to be effective in improving the piezoelectric properties of BF–BT ceramics. The microstructure, dielectric and piezoelectric properties of excess Bi doped BF–BT ceramics were investigated. Maximum piezoelectric constant d ₃₃ = 142 pC/N and k _p = 0.302 were obtained with 0.04 Bi doping. At the same time, an enhanced Curie temperature T _c, 452 °C, was obtained. The combination of improved piezoelectric properties and increased T _c makes these ceramics suitable for elevated temperature piezoelectric devices.     

The effective thermoelectric properties of core–shell composites

Thermoelectric materials are capable of converting heat directly into electricity and vice versa, and they have been explored for both waste heat recovery and thermal management. In this work, we analyze axially symmetric thermoelectric problems, motivated by energy harvesting using waste heat from an automobile exhaust pipe. Thermoelectric field distributions in both homogeneous shell and core–shell composites are solved, and the effective thermoelectric properties of the core–shell composites are analyzed. Numerical results show that higher thermoelectric conversion efficiency can be achieved in core–shell composites, and the mechanism responsible for the enhanced conversion efficiency is also identified. The analysis thus points to a new direction in developing high-performance thermoelectric materials.     

Effects of alkali treatment and elevated temperature on the mechanical properties of bamboo fibre–polyester composites

Bamboo fibre reinforced composites are not fully utilised due to the limited understanding on their mechanical characteristics. In this paper, the effects of alkali treatment and elevated temperature on the mechanical properties of bamboo fibre reinforced polyester composites were investigated. Laminates were fabricated using untreated and sodium hydroxide (NaOH) treated (4–8% by weight) randomly oriented bamboo fibres and tested at room and elevated temperature (40, 80 and 120 °C). An improvement in the mechanical properties of the composites was achieved with treatment of the bamboo fibres. An NaOH concentration of 6% was found optimum and resulted in the best mechanical properties. The bending, tensile and compressive strength as well as the stiffness of this composite are 7, 10, 81, and 25%, respectively higher than the untreated composites. When tested up to 80 °C, the flexural and tensile strength are enhanced but the bending stiffness and compressive strength decreased as these latter properties are governed by the behaviour of resin. At 40 and 80 °C, the bond between the untreated fibres and polyester is comparable to that of treated fibres and polyester which resulted in almost same mechanical properties. However, a significant decrease in all mechanical properties was observed for composites tested at 120 °C.     

Classical estimates of the effective thermoelastic properties of copper–graphene composites

Significant research effort is concentrated worldwide on development of graphene-based metal-matrix composites with enhanced thermomechanical properties. In this work, we apply two classical micromechanical mean-field theories to estimate the effective thermoelastic properties that can be achieved in practice for a copper–graphene composite. In the modelling, graphene is treated as an anisotropic material, and the effect of its out-of-plane properties, which are less recognized than the in-plane properties, is studied in detail. To address the severe difficulties in processing of graphene-based metal-matrix composites, the copper–graphene composite is here assumed to additionally contain, due to imperfect processing, particles of graphite and voids. It is shown quantitatively that the related imperfections may significantly reduce the expected enhancement of the effective properties. The present predictions are also compared to the experimental data available in the literature.     

Effects of high-temperature annealing on the microstructure and properties of C/SiC–ZrB2 composites

C/SiC–ZrB₂ composites prepared via precursor infiltration and pyrolysis (PIP) were treated at high temperatures ranging from 1200 °C to 1800 °C. The mass loss rate of the composites increased with increasing annealing temperature and the flexural properties of the composites increased initially and then decreased reversely. Out of the four samples, the flexural strength and the modulus of the specimen treated at 1400 °C are maximal at 216.9 MPa and 35.5 GPa, suggesting the optimal annealing temperature for mechanical properties is 1400 °C. The fiber microstructure evolution during high-temperature annealing would not cause the decrease of fiber strength, and moderate annealing temperature enhanced the thermal stress whereas weakened the interface bonding, thus boosting the mechanical properties. However, once the annealing temperature exceeded 1600 °C, element diffusion and carbothermal reduction between ZrO₂ impurity and carbon fibers led to fiber erosion and a strong interface, jeopardizing the mechanical properties of the composites. The mass loss rate and linear recession rate of composites treated at 1800 °C are merely 0.0141 g/s and 0.0161 mm/s, respectively.     

Thermo-electro-mechanical response of 1–3–2 piezoelectric composites: effect of fiber orientations

A micromechanics-based analytical model is developed to evaluate the performance of 1–3–2 piezoelectric composite where both matrix and fiber materials are piezoelectrically active. A parametric study is conducted to investigate the effects of variations in the poling characteristics of the fiber phase on the overall thermo-electro-mechanical behavior of a 1–3–2 piezocomposite. The performance of the 1–3–2 composite as a transducer for underwater and biomedical imaging applications is analyzed. The proposed model is capable of predicting the effective properties of the composite subjected to thermo-electro-mechanical loading conditions. The predicted variations in the effective elastic, piezoelectric and dielectric material constants with fiber volume fraction are nonlinear in nature. It is observed that the influence of thermal effects on effective properties of the composite also induces polarization in the composite. The analytical results show that an appropriate selection of the poling characteristics of the individual fiber and matrix phases could lead to the development of a piezocomposite with significant effective properties.     

Effects of environmental aging on the mechanical properties of bamboo–glass fiber reinforced polymer matrix hybrid composites

Short bamboo fiber reinforced polypropylene composites (BFRP) and short bamboo–glass fiber reinforced polypropylene hybrid composites (BGRP) were fabricated using a compression molding method. Maleic anhydride polypropylene (MAPP) was used as a compatibilizer to improve the adhesion between the reinforcements and the matrix material. By incorporating up to 20% (by mass) glass fiber, the tensile and flexural modulus of BGRP were increased by 12.5 and 10%, respectively; and the tensile and flexural strength were increased by 7 and 25%, respectively, compared to those of BFRP. Sorption behavior and effects of environmental aging on tensile properties of both BFRP and BGRP systems were studied by immersing samples in water for up to 1200 h at 25°C. Compared to BFRP, a 4% drop in saturated moisture level is seen in BGRP. After aging in water for 1200 h, reduction in tensile strength and modulus for BGRP is nearly two times less than that of BFRP. Use of MAPP as coupling agent in the polypropylene matrix results in decreased saturated moisture absorption level and enhanced mechanical properties for both BFRP and BGRP systems. Thus it is shown that the durability of bamboo fiber reinforced polypropylene can be enhanced by hybridization with small amount of glass fibers.     

Effects of V2O5 doping on the structure and properties lead-free KNN–LS–BF piezoelectric ceramics

Lead-free [0.996(0.95Na_0.5K_0.5NbO₃–0.05LiSbO₃)–0.004BiFeO₃]–xmol %V₂O₅ (KNN–LS–BF–xV₂O₅) piezoelectric ceramics have been fabricated by the solid-state reaction process and the effects of V₂O₅ doping on the structure and properties of the ceramics have been studied. The results reveal that the addition of V₂O₅ significantly improves the sinterability of KNN–LS–BF ceramics and the comprehensive properties. X-Ray diffraction (XRD) data shows that a small amount of V₂O₅ do not change the phase structure of KNN–LS–BF with smaller and more uniform grains. Main property parameters of KNN–LS–BF–xV₂O₅ ceramics sintered at a low temperature of 1,060 °C are optimized around x = 0.3 mol % with a high piezoelectric coefficient d ₃₃ of 183pC/N, a planar electromechanical coefficient k _p of 0.25, a high dielectric constant ε _r of 638.83 and a low dielectric loss tanδ of 0.7 % at 1 kHz, as well as a high mechanical quality factor Q _m of 53.87.     

High piezoelectric and dielectric properties of 0–3 PZT/cement composites by temperature treatment

Temperature treatment of 0–3 type PZT/cement composites before polarization yielded high dielectric and piezoelectric properties in materials with 50% PZT inclusions by volume and 50% cement matrix. Specimens were treated at seven temperatures from 23 °C to 150 °C and then applied by a 1.5 kV/mm poling field. The dielectric loss of the composites reduces at higher pretreatment temperatures, shorting the trigger time. Temperature treatment increased the piezoelectric strain factor d₃₃, the relative dielectric constant ε_r and the piezoelectric voltage factor g₃₃ of PZT/cement composites, but did not affect significantly the electromechanical coupling coefficient K_t. Piezoelectric factors reach stable values after 70 days of aging, and samples that were not temperature pretreated reached stable values earlier. Specimens pretreated at 150 °C exhibit d₃₃ = 106.3 pC/N and ε_r = 477 on the 70^th aging day, almost two times greater than the composites without temperature treatment. The resonance frequency of the composites on the 70th day decreases with increasing temperature, with the exception of 150 °C. Temperature pretreatment can also improve the phase angle of the composites. In addition, the effect of curing time for PZT/cement composites is an important factor to dominate the feasibility of polarization.     

Effect of Fe on the sintering and thermal properties of Mo–Cu composites

Effects of Fe on the sintering and thermal properties of Mo–Cu composites have been investigated. Mo–Cu–xFe composites are fabricated by powder metallurgy techniques with addition of various Fe contents ranging from 0.4 wt% to 2.2 wt%. The thermal properties and action mechanism of Fe to Mo–Cu composites are discussed. Results have indicated that the coefficient of thermal expansion (CTE) and thermal conductivity (TC) of Mo–Cu composites are greatly affected by the addition of Fe contents. It has also been observed that the fabricated composite powders with Fe additions exhibit high sinterability. Also, the inclusion of Fe can active the sintering course in shorter times and decline the sintering temperature thus also improving the physical properties of composites. Furthermore, it is also concluded that the utilization of steel kettle and steel balls for milling the Mo–Cu powders is also beneficial to improve the physical and thermal properties of Mo–Cu alloy.     

Effects of the intercalation time on the dielectric properties of Na2xMn1−xPS3

Manganese thiophosphate powders have been intercalated with sodium ions at two different intercalation times (150 min and 180 min) in order to evaluate the influence of this parameter on the dielectric properties of the obtained compounds labeled like Na_2xMn_1?xPS₃. In particular, dielectric permittivity measures have been carried out as a function of temperature (80 K–350 K) and frequency (20 Hz to 1 MHz) and compared with each other and with those of the pure matrix and of the Na_2xMn_1?xPS₃ compound corresponding to a 120 min intercalation time. Both investigated compounds show a dielectric response characterized by a loss peak at low temperatures, by a strong dispersion at low frequency and at not very high temperatures and by a crossover frequency showing an Arrhenius temperature dependence in agreement with what already observed in Na_2xMn_1?xPS₃ (120 min). The results have been also discussed in terms of ac conductivity, Maxwell–Wagner–Sillar (MWS) polarization, electrode polarization and dc conductivity and all the above cited features have been attributed to the Na⁺ ions which are, by their nature, hopping charge carriers that behave like jumping dipoles in their alternate motions and simultaneously show conducting characteristics resulting from their extended hopping over many sites. This attribution allows us to classify the analyzed sodium compounds like hopping charge carrier systems in which a greater Na intercalation time translates into a decrease in the loss peak intensity and an increase in the activation energy associated to the crossover frequency.     

Effects of various strengthening methods on the properties of Cu–Ti–B alloys

A copper alloy of Cu–1.9?wt-%Ti–0.7?wt-%B was fabricated by vacuum induction melting and casting followed by cold working and annealing. Four strengthening methods has been involved during the preparation of the alloy, and the combined action of these methods results in the alloy with the tensile strength of 530?±?24?MPa and the electrical conductivity (EC) of 48.0?±?2.1% International Annealed Copper Standard. The specific contribution (or deterioration) of different strengthening methods to hardness and EC was quantitatively evaluated. With regard to combined properties of Cu–Ti–B alloys, age hardening and forming TiB₂ particles are two effective methods to improve hardness and to maintain EC at a relatively high level simultaneously, but solid solution strengthening and work hardening are two inferior strengthening methods.     

The effect of partially stabilized zirconia on the mechanical properties of the hydroxyapatite–polyethylene composites

The effect of partially stabilized zirconia (PSZ) on the mechanical properties of the hydroxyapatite-high density polyethylene composites was studied by investigating the effect of hydroxyapatite and the simultaneous effect of hydroxyapatite and PSZ volume fractions on fracture strength, modulus of elasticity, and absorbed energy in the composite samples. The results showed a decrease in fracture strength, and absorbed energy with an increase in the volume fraction of hydroxyapatite content in the hydroxyapatite-polyethylene samples. Partial replacement of hydroxyapatite with PSZ particles was beneficial in the improvement of both the fracture strength and failure energy values in the composite samples. A transition from ductile to brittle behavior was observed as the volume fraction of ceramic filler particles increased in the samples.     

Effects of coupling agent on the preparation and dielectric properties of novel polymer–ceramic composites for embedded passive applications

The study was carried out to investigate the effects of silane coupling agent, γ-aminopropyl triethoxy silane (KH-550), on the preparation and dielectric properties of Barium titanate (BaTiO₃)/Bisphenol-A dicyanate (2,2′-bis (4-cyanatophenyl) isopropylidene)(BADCy) composites for embedded passive implications. It was found that KH-550 accelerated the polymerization of BADCy and was beneficial to improve the compatibility between BaTiO₃ particles and BADCy matrix. The dielectric constant (ε) and dielectric loss (tanδ) both increased at first and then decreased with the increase of the KH-550 content. With the increase of the frequency, the variation ranges of the dielectric constant and dielectric loss of these composites were not obvious since the dielectric properties of cyanate ester were stable at various frequencies.     

Effect of post-curing on properties of carbon fibre–epoxy composites

Abstract

The effect of post-curing on the moisture absorption characteristics of Fibredux 914/T300 carbon fibre–epoxy composites, and hence on their thermomechanical behaviour, has been examined. Laminates 1 mm thick were post-cured at 190 or 210°C for 4 or 10 h. The various cross-link densities thus established had almost no effect on the moisture absorption behaviour. Interlaminar shear strength and torsion pendulum tests gave similar results, in that the cross-link density had almost no influence on the dynamic shear modulus or the mechanical dissipation factor. From these findings, environmental degradation of the composite is shown to depend on the content of absorbed water. The behaviour of the composite in hot, humid conditions therefore cannot be improved by post-curing treatment.

MST/400     

Effect of heat treatment on the tribological properties of Al–Cu–Mg/nanoSiC composites

In this study, the effect of heat treatment on the tribological properties of Al–Cu–Mg alloy reinforced with 4 wt.% SiC particles with 650 nm average particle size has been investigated. The age hardening process consists of solution treatment at 540 °C for 6 h, followed by water quenching and ageing at different temperatures of 175, 200 and 225 °C with soaking times of 3, 6 and 9 h. Hardness measurements were applied to monitor the precipitation effect and the aged samples were then subjected to wear tests under dry sliding conditions against steel and alumina counterfaces. The results showed that the reinforced material exhibits an enhanced ageing response compared to the unreinforced material in the same heat treatment conditions. The rate of ageing increases with increasing temperature; however, ageing at 200 and 225 °C for more than 6 h resulted in over-ageing. The best combinations for the enhanced tribological properties for the composite material were selected as 6 h ageing at 225 °C. The precipitation effect for this alloy can be enhanced by the small addition of SiC nanoparticles. Having a small amount of nanoSiC particles with fine precipitates inside the matrix further increases the hardness and wear properties.