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.     

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.     

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.     

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.     

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.     

Mechanical, thermal and ablative properties of interply continuous/spun hybrid carbon composites

The mechanical and thermal properties of interply hybrid carbon fiber (continuous and spun fabric)/phenolic composite materials have been studied. Hybrid carbon/phenolic composites (hybrid CP) with continuous carbon fabric of high tensile, flexural strength and spun carbon fabric of better interlaminar shear strength and lower thermal conductivity are investigated in terms of mechanical properties as well as thermal properties.Through hybridization, tensile strength and modulus of spun type carbon fabric reinforced phenolic composites (spun CP) increased by approximately 28% and 20%, respectively. Hybrid CP also exhibits better interlaminar shear strength than continuous carbon fabric/phenolic composites (continuous CP).The in-plane thermal conductivity of hybrid CP is 4-8% lower than that of continuous CP. As continuous filament type carbon fiber volume fraction increases, the transversal thermal conductivity of hybrid CP decreases.The erosion rate and insulation index were examined using torch test. Spun CP has a higher insulation index than continuous CP and hybrid CP over the entire temperature range. Hybrid CP with higher content of spun fabric exhibits higher insulation index as well as lower erosion rate.     

Effect of BaO substitution for CaO on the structural and thermal properties of SiO2–B2O3–Al2O3–CaO–Na2O–P2O5 bioactive glass system used for implant coating applications

The present study replaced 3.30 and 9.00 mol.% BaO for CaO in a SiO₂–B₂O₃–Al₂O₃–CaO–Na₂O–P₂O₅ bioactive glass system used for implant coating applications. Variations of the glass structure, thermal properties, cytotoxicity, and radiopacity of glasses were studied. As demonstrated by the results, upon adding barium oxide to the glass structure, the weight density increased significantly, while a slight decrease in oxygen density was determined. Introducing barium oxide into glass composition did not cause any considerable change in the spectra of FTIR and Raman. It was demonstrated that the amount of bridging oxygen in the glass structure remained quite unaffected. The hot stage microscopy evaluations revealed further shrinkage of barium-containing frits due to lower viscosity and hence, higher viscous flow of these glasses. By substituting barium oxide for calcium oxide and increasing its concentration, the glass transition temperature (T_g) and the dilatometric softening temperature (T_d) decreased, while the thermal expansion coefficient increased. Moreover, upon substituting 9 mol.% barium oxide for calcium oxide, a 30 °C reduction in maximum sintering temperature (T_ms) of the glass was obtained, whereas the shrinkage rate was increased 1.7 times. It was indicated that the sintering process of barium-incorporated glasses would easily proceed without any phase crystallization. The barium-incorporated glasses exhibited more radiopacity. Additionally, no cytotoxic effect was caused by the substitution, and the Ba-containing glasses could be used for biomedical applications and implant coating as well.     

Multiferroic properties of (1-x)BCZT-xLCMO laminated composites

The electrical, ferromagnetic and magnetoelectric properties of the (1-x) Ba_0.85Ca_0.15Zr_0.10Ti_0.90O₃-xLa_0.67Ca_0.33MnO₃ [(1-x)BCZT-xLCMO] laminated composites were investigated. The ferroelectric and ferromagnetic characteristics demonstrated that the laminated composites are multiferroic in nature. Our results indicated that the performances of the laminated composites showed strong dependence on the thickness ratio between the ferroelectric BCZT layer and ferromagnetic LCMO layer. Enhanced dielectric properties were obtained for the laminated composites compared with that of the pure BCZT. The piezoelectric coefficient (d₃₃) and coercive electric fields (E_C) of the laminated composites declined with the increasing LCMO nonferroelectric layer, while the saturated magnetization (M_S) increased and the coercive magnetic field (M_C) kept constant. The 0.3BCZT-0.7LCMO composites obtained the largest magnetoelectric coefficient of α_E31 = 1.66 mV/cm·Oe.     

BaTiO3系低温烧成高介X7R电容器瓷料

介绍了BaTiO3 系低温烧成高介X7R瓷料。采用了由BaTiO3 与Nd2O3 合成的主基材料 ,添加Bi2O3 ·2TiO2 陶瓷烧结助熔剂和硼硅铅低熔玻璃 ,可适于在低于1100℃下烧成 ,且介电常数大于3200 ,对影响瓷料的各种因素进行分析研究     

矿化剂浓度对水热合成BaTiO3纳米粉体影响的研究简

以氢氧化钠做矿化剂,利用钛酸丁酯和氢氧化钡,通过水热法合成了纳米钛酸钡粉体。通过XRD、差热分析和高倍显微镜观察等分析表征手段,对矿化剂加入量对水热合成纳米钛酸钡粉体的影响进行了初步研究探讨。     

钛酸铝-莫来石复合材料热稳定性的研究

通过引入氧化铁和两相复合的方法对钛酸铝 -莫来石复合材料的热稳定性进行了研究。结果表明 :当烧成温度在 15 0 0～ 16 0 0℃时 ,烧成温度的升高对复合材料的热稳定性有利。氧化铁可与钛酸铝晶体形成连续固溶体 ,改变钛酸铝的晶格常数 ,降低钛酸铝晶体的畸变程度 ,促进烧结 ,提高热稳定性。仅加入莫来石时 ,其对钛酸铝热分解的抑制效果不佳 ;如果同时引入氧化铁作为添加剂 ,莫来石对钛酸铝的热分解有较好的抑制作用。     

A high-temperature structural and wave-absorbing SiC fiber reinforced Si3N4 matrix composites

The SiC_f/Si₃N₄ composite with low–high–low permittivity sandwich structure was designed for high-temperature electromagnetic (EM) wave absorption and mechanical stability. The SiC_f/Si₃N₄ possessed the remarkable mechanical properties at room temperature (the flexural strength is 357 ± 16 MPa and the fracture toughness is 10.8 ± 1.7 MPa m^1/2) for the strong fiber strength, moderate interface bonding strength and uniform matrix. Furthermore, the retention rate is as high as 80% at 800 °C. The A/B/C nanostructure and the sandwich meta-structure endowed the SiC_f/Si₃N₄ with an excellent EM absorbing property at room temperature. The SiC_f/Si₃N₄ still absorbed 75% of the incident EM waves energy in X and Ku bands when the temperature increases up to 600 °C, which is only 6% lower than that at room temperature, for the partial compensation of the decreased interfacial polarization loss for the increased conductivity loss and dipole polarization loss.