Fracture behaviour of alumina-YAG particulate composites

Particulate composites of the Al₂O₃–YAG system were produced by precipitation of the yttrium oxide precursor in the aluminium oxide suspension. The solid state reaction took place during thermal treatment of the resulting powder and led to the creation of the YAG phase. This method allowed fine and homogenously distributed YAG inclusions within the alumina matrix to be obtained. The performed investigations involved determining of the critical stress intensity factor (K_IC), Vickers hardness and bending strength of the materials. The composites showed higher hardness (HV) than α-Al₂O₃. The presence of YAG inclusion in the amount higher than 7.5 vol.% improved also fracture toughness when compared to polycrystalline alumina. In the case of the material with the best mechanical properties measurements of subcritical cracking were conducted and the threshold value of K_IC (K_I0) was determined.     

Enhanced dielectric permittivity of BaTiO3/epoxy resin composites by particle alignment

Barium titanate (BaTiO₃)/epoxy resin composites with a novel structure, in which the BaTiO₃ particles were directionally aligned in the epoxy resin matrix, were fabricated using the ice-templating method. The effects of the filler particle alignment and the filler fraction on the dielectric permittivity as well as the dielectric loss of the composites were studied. The results show that the aligning filler particles can significantly improve the dielectric permittivity while maintaining the dielectric loss compared with the traditional composite structure (homogeneously distributed). Due to the feasibility of the enhancement of the dielectric properties of the composites, the particle alignment that is achieved via the ice-templating method can be used in the field of high energy density capacitors.     

Structural,ferroelectric, magnetic and magnetoelectric properties of (1-x) Ba0.85Ca0.15Zr0.1Ti0.9O3 -x La0.67Sr0.33MnO3 lead-free magnetoelectric composites

The influence of an additional La_0.67Sr_0.33MnO₃ (LSMO) magnetic phase on the structural, ferromagnetic, ferroelectric, and magnetoelectric properties of Ba_0.85Ca_0.15Zr_0.1Ti_0.9O₃ (BCZT) ferroelectric phase was studied for composites of (1-x)BCZT -xLSMO (x = 0, 25, 50, 75 and 100%). The ferroelectric BCZT sample showed a perovskite single phase formation with a tetragonal crystal structure of the P4mm space group, and the magnetic phase of LSMO presented a rhombohedral crystal structure of R3c space group as shown by XRD. The composite sample with 25% LSMO exhibited large ferroelectric and piezoelectric properties with remnant, saturation polarization, and coercive electric field P_r ~7.74 μC/cm², P_s ~11.69 μC/cm² and E_C ~12.22 kV/cm with a piezoelectric coefficient d₃₃ ~ 231 pC/N. The magnetic characterization for the composites showed that the sample containing 75% of LSMO revealed the highest remnant, saturation magnetization, and coercive field of M_r ~1.358 emu/g, M_s ~19.17 emu/g, and H_C ~33.19 Oe, respectively. Moreover, it revealed the largest magnetoelectric coupling coefficient α_ME ~2.51 mV/cm.Oe with high coupling quality at a lower applied magnetic field. The results highlight the value of these composites as lead-free room temperature magnetoelectric sensors and actuators.     

Investigation on the structural,multiferroic and magnetoelectric properties of BaTi1-xNixO3 ceramics

In this paper, we report the influence of Ni doping on the structural, electrical, magnetic and magnetoelectric properties of BaTiO₃ (BTO) ceramics. X-ray diffraction (XRD) analysis indicates a phase transition from tetragonal to hexagonal at x?=?2.5?mol%. Further, XRD data has been refined using Rietveld method to extract the phase formation, lattice parameters, and the phase fraction of BaTi_1-xNi_xO₃ $\left(\mathrm{BTNO}\right)(0\le x\le 10\mathrm{mol}\%)$ ceramics. The ferroelectric polarization decreases with Ni doping concentration. The relative permittivity of BTNO compositions decreases while the corresponding dielectric loss increases with Ni doping concentration. Room temperature magnetic hysteresis (M-H) loop of all BTNO samples exhibit ferromagnetic nature with a saturated loop except for x?=?2.5?mol% Ni doping concentration. At x?=?2.5?mol% Ni doping concentration, a small amount of diamagnetism is observed at higher fields along with ferromagnetism. The origin of ferromagnetism is due to the F- center exchange interaction via oxygen vacancies. The highest remnant magnetization (M_r) is 11.76 memu/g for x?=?10?mol%. The Magnetodielectric coefficient (MD) and magnetoelectric coefficient (ME) gradually increases with increasing Ni doping concentration, and are 1.72% and 4.51 $\mathrm{mV}{\mathrm{cm}}^{?1}{\mathrm{Oe}}^{?1}$ respectively for x?=?10?mol%.     

Stoichiometry control and structure evolution in hydrothermally derived (Ba,Sr)TiO3 films

(Ba,Sr)TiO₃ films were synthesized on the titanium metal substrates in solution of Ba(OH)₂ and Sr(OH)₂ by hydrothermal method. Crystallinity and microstructure of the films changed with time, concentration and temperature. Effects of the mole ratio of barium and strontium in solution on the composition of film have been studied. The barium contents in the BST films are fairly lower than those in the original solutions. This indicates that strontium is more readily incorporated into the BST films, relative to barium. The results of narrow-scan of XPS spectrum confirm that the valences of Ba, Sr, Ti and O elements of hydrothermally prepared BST films are +2, +2, +4, and −2, respectively. SEM photographs show that the BST films are dense and well-compact. AFM analyses show that the average surface roughness of the films is 40–50 nm. It is concluded that BST films of different mole ratio of barium and strontium with thickness of up to 2 μm have been prepared successively by the environmentally benign hydrothermal method.     

Economics of rare earth elements in ceramic capacitors

Ceramic capacitors are an indispensable component in electronic circuits, since they are used in various applications such as timing, filtering, and decoupling. These capacitors are doped with REEs that improve their operating life and electrical properties. In this paper, the economics of rare earth elements (REEs) are reviewed in light of their importance in ceramic capacitors. The developing rare earth element supply and demand crisis that can negatively impact the ceramic capacitor industry and, hence, the global economy, is explained. The cause of this crisis and the response of the world are also discussed.     

Optical properties of multi-stacked BaTiO3/SrTiO3 thin films synthesized via chemical method

In this work, the BaTiO₃ and SrTiO₃ thin films as well as BaTiO₃/SrTiO₃ lamellar composites are synthesized via sol-gel spin-coating method. The formation of corresponding phases from their sols is investigated by virtue of X-ray diffraction on their powders, which confirms the formation of tetragonal structure for BaTiO₃, but cubic structure for SrTiO₃. The field emission scanning electron microscopy images show that crack-free films with different morphologies are formed in each sample. Likewise, by changing periodicity of the samples, the morphology of the composite samples is changed. As the number of layers increases from 1 to 20, the band gap reduces from 4.38 eV to 4.10 eV for BaTiO₃ samples and from 4.13 eV to 3.80 eV for SrTiO₃ samples confirmed by UV–Vis spectra. The band gap of periodicity = 1 sample is higher than that of BaTiO₃, while band gaps of periodicity = 2 and 5 composites mount between those of BaTiO₃ and SrTiO₃. In addition, the refractive indices of multi-stacked composites are about 0.2 lesser than refractive indices of BaTiO₃ sample in high wavelengths. The periodicity dependence of optical frequency dielectric constant, dielectric loss, impedance, Urbach tail, extinction coefficient, and electric modulus of multi-stacked composites are also studied.     

Investigation of long-term thermal aging-induced damage in oxide/oxide ceramic matrix composites

Long-term thermal aging is a typical factor affecting the thermo-mechanical fatigue life for hot-end components in the gas turbine. The present work focuses on the development of thermal aging-induced damage in 2-D woven oxide/oxide ceramic matrix composites from micro-mechanism and macroscopic mechanical performance. The porosity evolution and mechanical performance after long-term thermal aging were characterized through mercury intrusion measurements and uniaxial compressive tests, respectively. The results show that the decrease of micro-porosity directly reflects the irreversible evolution of material microstructure in the thermal aging process, and the decrease of compressive strength after aging is the macroscopic reflection of the microstructure variation. The porosity increment of matrix was thus used to characterize the thermal aging-induced damage, establishing a unique analysis model between the increment of micro-porosity under thermal aging and the corresponding degradation of material compressive strength. The experimental results are in good agreement with the established model.     

Effect of Barium Titanate on the Thermal,Morphology, Surface,and Mechanical Properties of the Thermoplastic Polyurethane/Barium Titanate Composites

The aim of this study was to improve thermal stability, mechanical, and surface properties of thermoplastic polyurethane (TPU) with the addition of BaTiO₃. The TPU/BaTiO₃ composites having various ratios of TPU and BaTiO₃ were prepared. The chemical structure of the prepared composites was investigated by FTIR. Thermal stability of the samples were evaluated by thermogravimetric analysis and differential scanning calorimetry. Mechanical properties of the samples were characterized with stress–strain test. Hydrophobicity of the samples was determined by the contact angle measurements. Moreover, the surface morphology of the samples was investigated by a scanning electron microscopy.     

3D microstructure-based modelling of the deformation behaviour of ceramic matrix composites

In this paper the experimental and numerical investigations of microstructure modelling of multilayer actuator are considered. BaTiO₃ powder is manufactured using the solid-state technique. The main parameter influencing the possibility of application of BaTiO₃ ceramics on actuators is the grain size of the sintered materials. Three kinds of pellets with different average grain sizes were considered. The adhesive joints of a BaTiO₃ and Ag-based conducting electric current epoxy adhesive were used to fabricate the model of actuator. A 3D microstructure model of BaTiO₃ and composites were generated using Digimat-FE software. The Mori–Tanaka and double inclusion homogenization models for representative volume elements of multilayer actuator were carried out using Digimat-MF software, in order to obtain the failure characteristics of the composite material. To investigate the failure of the ceramic matrix composite the Hashin-Rotem criterion was used.     

Modelling of multilayer actuator layers by homogenisation technique using Digimat software

This paper is concerned with the microstructure of adhesive joints composed of BaTiO₃ ceramic material and two kinds of adhesives, with a special emphasis on the numerical modelling of grain size, shape and material porosity. BaTiO₃ powder for use in stacked-disk multilayer actuator production is manufactured using the solid-state technique. The properties of BaTiO₃ material at each stage of its fabrication that influence its application for the stacked-disk multilayer actuator are presented and discussed. The parameters characterising the properties of the fabricated pellets are also described. Implicit time-discretisation and consistent tangent operators are employed. A 3D microstructure model of BaTiO₃ using Digimat-FE software is generated. Then, effective elastic constants of BaTiO₃ and epoxy adhesive composites are calculated by numerical simulation. The Mori-Tanaka homogenisation scheme for representative volume elements of BaTiO₃ and epoxy adhesives composites is carried out using Digimat-MF software in order to obtain failure characteristics of the composite material.     

Fabrication of bulk piezoelectric and dielectric BaTiO3 ceramics using paste extrusion 3D printing technique

A simple and facile method was developed to fabricate functional bulk barium titanate (BaTiO₃, BT) ceramics using the paste extrusion 3D printing technique. The BT ceramic is a lead-free ferroelectric material widely used for various applications in sensors, energy storage, and harvesting. There are several traditional methods (eg, tape casting) to process bulk BT ceramics but they have disadvantages such as difficult handing without shape deformation, demolding, complex geometric shapes, expansive molds, etc. In this research, we utilized the paste extrusion 3D printing technique to overcome the traditional issues and developed printable ceramic suspensions containing BT ceramic powder, polyvinylidene fluoride (PVDF), N,N-dimethylformamide (DMF) through simple mixing method and chemical formulation. This PVDF solution erformed multiple roles of binder, plasticizer, and dispersant for excellent manufacturability while providing high volume percent and density of the final bulk ceramic. Based on empirical data, it was found that the maximum binder ratio with good viscosity and retention for desired geometry is 1:8.8, while the maximum BT content is 35.45 vol% (77.01 wt%) in order to achieve maximum density of 3.93 g/cm³ (65.3%) for 3D printed BT ceramic. Among different sintering temperatures, it was observed that the sintered BT ceramic at 1400°C had highest grain growth and tetragonality which affected high performing piezoelectric and dielectric properties, 200 pC/N and 4730 at 10³ Hz respectively. This paste extrusion 3D printing technique and simple synthesis method for ceramic suspensions are expected to enable rapid massive production, customization, design flexibility of the bulk piezoelectric and dielectric devices for next generation technology.     

Novel polymer composites of RuO2@nBaTiO3/PVDF with a high dielectric constant

The dielectric properties of a novel polymer dielectric material were investigated. The conductive phase of RuO₂ was synthesized for deposition on the surface of a nanosized BaTiO₃ (nBT). The RuO₂@nBT hybrid particles were incorporated into a poly (vinylidene fluoride) (PVDF) as a three-phase composite (RuO₂@nBT/PVDF). The obtained dielectric constant (ε′) was significantly high (3837.16) for the composite with a volume fraction of $f_{Ru{O}_2@nBT}$ = 0.50. The large interfacial polarization between the RuO₂?nBT and RuO₂?PVDF interfaces considerably increased the value of ε′. Therefore, interfacial polarization is a critical factor in improving the dielectric properties. The dielectric behavior of the RuO₂@nBT/PVDF composites can be described using the effective medium percolation theory model, which indicates the significant contributions of the conductive RuO₂ phase and high-permittivity nBT phase.     

Microstructure effects on BaTiO3/BaTi0.8Zr0.2O3 composites properties

The dielectric, pyroelectric and ferroelectric properties of bilayered BaTiO₃/BaTi_0.8Zr_0.2O₃ ceramics are described and correlated with their microstructure. Different sintering times are employed to change the microstructure and promote interdiffusion between the layers. The effects of constrained sintering on both compositions are analyzed and their properties are compared to that of single phase BaTiO₃ and BaTi_0.8Zr_0.2O₃ ceramics. The results show that, at sintering times until 2 h, the bilayer properties are predominantly affected by the presence of residual stresses. Only after 4 h sintering, the properties are predominantly affected by interdiffusion between the layers.     

Fire reactions of ceramic and polymer moulding composites

Abstract

Abstract

Low cost ceramic dough moulding compounds/composites (CDMC) are composed of inorganic metal silicates and chopped fibre reinforcements. This paper investigates the fire reactions of these materials under severe thermal and heat conditions. This research is targeted to potential applications in the replacement of glass fibre reinforced polymeric insulation materials such as phenolic composites as engine heat shields which experience high temperature and heat transmission. The materials developed can provide good properties, including heat insulation with high thermal stability for engine drafts, where traditional glass/phenolic composites were used and gave a very short life cycle. This work compares the thermal properties of the glass fibre reinforced phenolic composites and metal silicate composites produced under the same processing conditions. The results show that CDMC possesses significantly better thermal stability and heat resistance in comparison with phenolic moulding composite (phenolic dough moulding composites). The indication was that under the testing condition of heat flux of 75?kW?m^?2 intended for materials used for applications in marine, transport and possibly nuclear waste immobilisation, the integration of the CDMC was kept intact and survived as a high temperature insulation material.     

Electrical characterization of BaTiO3 and Ba0.77Ca0.23TiO3 ceramics synthesized by the proteic sol–gel method

In this work, we introduce a simple, low-cost, and ecofriendly method for producing barium titanate (BaTiO₃–BT) and barium calcium titanate (Ba_0.77Ca_0.23TiO₃–BCT) powders. The synthesis was performed by using a proteic sol–gel route which use coconut water in the polymerization step of the metallic precursor. We investigated the effects of the processing parameters with the density, microstructure, and (di)electric properties as sample quality indicators. The sintered ceramics exhibit single crystalline phase, relative density of 95%, a homogeneous microstructure, and an average grain size of 4?µm. The respective dielectric constants of 1200 (BT) and 700 (BCT), measured at room temperature, and the activation energy values for the conductive process are according to those reported in the literature for conventionally prepared ceramics.     

LCD-SLA 3D printing of BaTiO3 piezoelectric ceramics

Stereolithography-based 3D printing is a promising method to produce complex shapes from piezoceramic materials. In this study, LCD-SLA 3D printing was used to create lead-free piezoceramics based on barium titanate (BaTiO₃, BT). Three types of BT powders (micron, submicron and nanoscale) were tested in LCD-SLA 3D printing, and a technique for the preparation of a ceramic slurry suitable for LCD-SLA printing has been developed. Using TGA-DSC analysis, the thermal debinding parameters to obtain crack-free samples were determined, followed by further sintering and the study of the piezoelectric properties (ε_r = 1965, d₃₃ = 200 pC/N, tan = 1,7 %). The results of the study demonstrate high potential for the production of complex piezoceramic elements that can be used in aviation, in particular, aviation radio equipment; in the marine industry for transceiver modules of hydroacoustic antennas; and in the nuclear industry for pressure control sensors in the steam–water path.     

Improved thermal conductivity of graphite though infiltration with SiC and Si3N4 inclusions

High thermal conductivity, wear resistant graphite is desirable for a range of applications, for example as an electrode to minimize energy consumption in aluminium smelting. This paper demonstrates that by infiltrating the porosity by reactive infiltration with SiC at levels ranging from 4 to 12 vol.% or Si₃N₄ ranging from 7 to 19 vol.% the thermal conductivity can be raised progressively from ～41 W/m K to ～53 and 64 W/m K respectively. A simple analytical model predicts thermal conductivity rises with increasing reinforcement fraction only 7–9 % higher than that observed. This suggests that heat transfer between the graphite and the reinforcing particles is good making these materials good options where improved thermal conductivity and wear resistance over graphite is required.     

Preparation of polyimide-epoxy composites

The formation of a three dimensional network of crosslinked epoxy leads all unmodified epoxies to have inherent brittleness and relatively low degradation temperatures. Polyimides, on the other hand, are widely used for applications that require high degrees of flexibility and thermal resistance. Here, we have focused on the preparation of epoxy systems cured with polyamic acids instead of traditional amino-group-containing hardening agents. The cure behavior and potential reaction mechanisms of EPON 828 resin and polyamic acid mixtures were evaluated by DSC and TGA. Thermal analysis showed a complex reaction sequence taking place in the mixture and also determined the extent of reaction of the polyamic acid with itself and the competitive reaction of the polyamic acid with the epoxy. The compositions of the mixtures were varied to see the dependence of the cure behavior on component concentrations. Solutions of the two components did not phase separate and also phase separation was not apparent either optically or microscopically in the cured samples. This phase behavior was attributed to a unique in situ reaction. A novel solvent system for the polyamic acid precursor was also used.     

Ultrahigh electric breakdown strength,excellent dielectric energy storage density,and improved electrocaloric effect in Pb-free (1-x)Ba(Zr0.15Ti0.85)O3-xNaNbO3 ceramics

In this study, NaNbO₃ (NN) was introduced into Ba(Zr_0.15Ti_0.85)O₃ (BZT) to form a solid solution with relaxor ferroelectric characteristics. The dielectric breakdown strength (BDS) of the specimen with 6 mol.% NN reached 680 kV/cm, the corresponding recoverable energy storage density (W_rec) was 5.15 J/cm³, and the energy storage efficiency (η) was 77%. The dissolution of Na ⁺ ions at the A position and Nb⁵⁺ ions at the B position of the perovskite structure reduced the concentration of oxygen vacancies in the lattice and compensated for defects. The doped ceramics exhibited lower dielectric loss and better thermal stability: the W_rec value was 2 ± 1% J/cm³ at 30–120 °C. In particular, in the 0.02NN ceramics, a ΔT of 1.81 K was achieved at 130 kV/cm, and the operating temperature zone expanded with the increase in doping concentration. The introduction of NN resulted in BZT ceramics that possess excellent energy storage performance and electrocaloric effect properties.