ABSTRACTWe successfully prepared Hydroxyapatite/Zinc oxide (HAp/ZnO) composite particles with hexagonal plate-like shapes. The surface of the ZnO particles was treated with (3-aminopropyl)triethoxysilane (APTES) as a scaffold for the crystallization of HAp from the precursor solution. From the results of XRD measurements and SEM images of composite particles, formation of HAp on the ZnO particles was revealed. In addition, diffraction peaks associated with the (0 0 2) and (0 0 4) planes of HAp were clearly observed. They also revealed that the HAp/ZnO composite particles had a c-face orientation. Furthermore, element mapping analysis by EPMA showed that the elemental distributions of Ca, P and Zn of the composites were almost coincident. These results suggested that the formation of HAp occurred on the ZnO particles. In contrast, the ZnO particles without APTES treatment readily dissolved in the precursor solution and the diffused Zn2+ ions reacted with PO43- ions and Ca2+ ions to form CaZn2(PO4)2. APTES treatment of the ZnO surfaces appeared to prevent the dissolution of ZnO in the solution and induce the adsorption of anions such as phosphate on ZnO.

ABSTRACTMultilayer ceramic capacitors (MLCCs) for electric vehicles require their room temperature capacitance to change ≤ ±15% at −55°C to 200°C. The dielectric constant (ε) of BaTiO3, a dielectric material widely used in MLCCs, drops at >125°C making its application to electric vehicles difficult. Here, we propose KCa2Nb3O10 (KCNO)-layered perovskite as a strong candidate for electric vehicle MLCCs as its ε does not change abruptly with temperature. The effect of sintering temperature on the temperature coefficient of capacitance (TCC) of KCNO is studied. The KCNO powder calcined at 900–1200°C is sintered at 1200°C–1300°C. Microstructure and temperature-dependent ε are determined by the sintering temperature, while the sintered density is related to the difference between the calcining and sintering temperatures. Only the room temperature ε of the samples sintered at 1300°C (except the one calcined at 900°C) varies ≤ ±15% at 25°C–200°C (ε ~250 at room temperature). The sample calcined at 1100°C and sintered at 1300°C has highly elongated grains and the highest activation energy. These factors are responsible for the TCC of the 1300°C sintered KCNO being ≤ ±15% at 25–200°C.

ABSTRACTThe features of ferroelectric materials and their applications are presented. State-of-the-art employment of characterization techniques, and the properties of ferroelectric materials are described. Classification of ferroelectric materials, phase transitions, and diffuse phase transition (DPT) have been discussed. Properties of ferroelectrics, polarization-field hysteresis, dielectric hysteresis, reversal of spontaneous polarization, and dielectric properties have been explained. Besides these, piezoelectric and pyroelectric properties of materials have also been demonstrated. The applications of ferroelectric thin films have been discussed with a specific focus on acousto-optic (AO) properties and their applications.

ABSTRACTBinary sulfides were deposited by sequential thermal evaporation with the stacking order glass/CuS/SnS/ZnS and subsequently subjected to a sulfurization-crystallization process, considering two thermal treatment time intervals, 5 and 20 min. The objective of implementing different annealing durations was to identify the best conditions to form CZTS films in the pure kesterite phase. After being subjected to the annealing, the films show structural characteristics of the kesterite phase. However, XRD data showed that prolonged annealing causes degradation of the kesterite phase, leading to the formation of traces of CuS and Cu5Sn2S7. The films annealed for shorter duration, in this case 5 min, present a denser and more uniform surface morphology, better degree of preferential orientation, small Urbach energy of 0.302 eV, and higher photosensitivity. The band gap of the films was 1.46 eV and 1.53 eV for annealing durations 5 and 20 min, respectively.

ABSTRACTControl of nanomaterial morphology has been investigated to utilize for the desired application. 1D nanomaterials are ideal for various applications because of their excellent carrier transportability and huge specific surface area. Due to their advantages, various methods have been developed to grow in a specific direction. Herein, we introduced a simple synthesis method of freestanding Zinc hydroxidefluoride (ZnOHF) nanobelt as 1D material without seed or substrate using aqueous solutions. The ZnOHF nanobelt was synthesized using zinc fluoride and hexamethylenetetramine (HMT) at 80°C for 3 h. Even though low synthesis temperature, ZnOHF demonstrated good crystallinity and a homogeneous nanobelt structure. The ZnOHF nanobelts were grown over several μm to direction with less than 100 nm width. In addition, the growth direction of the nanobelt was controlled by the concentration of HMT. The width of the nanobelt was broader by a decrease in HMT concentration. It was considered that crystal nucleation and growth of ZnOHF could be influenced by OH− and NH4+ ions generated from HMT decomposition.

ABSTRACTA high purity Al2O3 ceramic (HPAOC) metallizing strategy was developed via gradient coating process of metallizing pastes with different ratios of Mo to manganese glass (MnG) contents, to improve the wettability and reactivity of metallized layer (ML) to the ceramic substrate and the secondary metallizing layer or sealed metals. Self-made HPAOC samples firstly coated by a layer of metallizing paste with a lower proportion of Mo:MnG and superposed a layer of metallizing paste with a higher proportion of Mo:MnG were fired at 1450°C in hydrogen atmosphere. The crystal phase structure, microstructure and element distribution of the metallized samples wer characterized by XRD, SEM and EDS. The results of sealing properties show that the tensile sealing strength of as high as 121MPa and the He leakage rate of as low as 4.2 × 10−11 Pa.m3/s can be obtained of the sealed joints of the as-metallized HPAOC and Kovar.

ABSTRACTA titanium aluminum carbide, Ti2AlC, which is classified among MAX phase ceramics, was studied as a potential candidate for various mechanical components used in high-temperature applications. The impact of its chemical composition on its high-temperature oxidation process was determined. Ti2AlC powders with various Al contents and with or without Nb addition were synthesized via a conventional reaction technique followed by 16 h of annealing in vacuum at 1300°C. The synthesized Ti2AlC powders were consolidated by means of 15 min of pulsed electric current sintering at a die temperature of 1300°C in vacuum under a uniaxial pressure of 30 MPa. In the presence of an aluminum reservoir in the form of TiAl3, Ti2AlC has excellent resistance against high-temperature oxidation. The promising results concerning the addition of Nb to TiAl provided the rationale for a similar modification of Ti2AlC. The results of oxidation tests on Nb-doped Ti2AlC likewise showed excellent oxidation resistance. Alloying with Nb can improve the oxidation resistance of Ti2AlC with low Al content, allowing the formation of a protective Al2O3 scale and inhibiting the growth of TiO2.

ABSTRACTA new technique using impedance spectroscopy was developed to estimate the oxidation kinetics of the pyrolytic carbon interphase layer in SiCf/SiC ceramic matrix composites. The AC impedance Nyquist plot showed two semicircles that were curve-fitted using an equivalent circuit with two constant-phase element components. The analysis results revealed that the capacitance in the low-frequency region decreased with increasing oxidation time, whereas that in the high-frequency region remained relatively constant. This change in the capacitance in the low-frequency region was associated with the thickness of the oxidized SiO2 layer. This study might make a significant contribution to the literature, which has mostly focused on the characterization of ceramic matrix composites through measurements of mechanical properties. The limitations and potential applications of the developed method were also elucidated.

ABSTRACTOwing to its wide bandgap (3.4 eV) and high electron mobility, GaN has attracted significant attention for applications in solar cells, power transistors, and high-electron-mobility transistors. Crystallized GaN thin film can be hardly prepared in thin film form by employing physical vapor deposition processes, such as reactive RF sputtering and pulsed laser deposition, because a high driving energy is required to deposit a thin film due to its high binding energy. Herein, GaN thin films were prepared by CO2 laser-assisted RF sputtering at a relatively low temperature of 200°C. The CO2 laser with a 10,600 nm wavelength shows excellent conversion efficiency from optical energy to thermal energy. At the optimized laser energy density of 0.98 W/mm2, GaN thin film can have a (0002) orientation with a bandgap energy of 3.26 eV. The crystalline, surface morphological, and optical properties of the fabricated GaN thin films were evaluated using X-ray diffraction, FE-SEM, X-ray photoelectron (XPS), and photoluminescence (PL) spectroscopy, and UV-vis spectrometry. The energy bandgap of the fabricated GaN thin film was measured using the Tauc plot and confirmed via PL. The film composition thus obtained was analyzed using XPS.

ABSTRACTDysprosium barium copper oxide – bismuth sodium titanate ((1-x)DyBCO−xBNT) ceramics, where x = 0−0.07 mole fraction, were successfully prepared by a solid-state reaction and sintering method. The DyBa2Cu3O7-δ and (Bi0.5Na0.5)TiO3 powders were separately synthesized by calcining their stoichiometric mixtures at 900°C for 4 h and 800°C for 2 h, respectively. The (1-x)DyBCO−xBNT powders were compacted into pellets and sintered at 930°C for 2 h under normal air atmosphere. Phase identification and morphology of all samples were determined using X-ray diffractometer (XRD). The quantitative phase analysis was analyzed by fitting the XRD pattern using the GSAS-II program. Scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS) was used to study microstructure and chemical composition. In all cases, the result of XRD shows that the DyBa2Cu3O7–δ (Dy-123) was identified as the main crystalline phases, due to the good agreement between the observed and calculated patterns after Rietveld refinement. All BNT-doped DyBCO ceramics showed slightly higher density values than the undoped sample, suggesting that BNT helped improve the densification process. The sign of the Seebeck coefficient (S) was positive for all samples at all measured temperatures, confirming a p-type conduction mechanism. Low BNT doping improved the overall thermoelectric properties of DyBCO ceramics by affecting electrical conductivity (σ), Seebeck coefficient (S), and thermal conductivity (κ). The dimensionless figure of merit (ZT=S2σT/κ) of all samples increased with increasing temperature. The highest ZT value of 5.67 × 10−2 was observed for the 0.97DyBCO−0.03BNT sample at 863 K.

ABSTRACTRefractories subject to loading and unloading repeatedly because of physical effects and thermal stress attack in the service process, which is an important issue shortening the service life of the thermal equipment. Therefore, researches of predicting the service life of refractories under cyclic loading have the guiding significance. The present work investigated the synthesis of ZnAl2O4 and discussed its effects on the alumina castables. The results show that the optimized generation temperature of ZnAl2O4 phase is 1400°C and the hysteresis loop in the curves of cyclic loading reveals a general trend of first sparse and then dense. The cycle times of the specimen with 3 wt.% ZnAl2O4 is 50 times, and the time from starting to loop to fracture is about 4300 s. The fatigue resistance of the specimen with 3 wt.% ZnAl2O4 is superior to ZA-0 and ZA-1.5. The new method of cyclic loading was innovatively adopted in refractories, which provide data and theoretical support for the thermal shock evaluation methods.

ABSTRACTSpherical-like β-phase silicon nitride (β-Si3N4) powder has been synthesized by direct nitridation of silicon saw dust recovered from the photovoltaic industry in ammonia gas (NH3) at 1300°C with calcium fluoride (CaF2) as additive. The X-ray diffraction (XRD) analysis indicates that the formation of β-Si3N4 is enhanced and accelerated in NH3 compared to nitrogen (N2). The scanning electron microscope (SEM) examination shows that, compared with N2, NH3 contributes to the formation of spherical-like particles, and all irregular silicon particles are transformed into spherical-like β-Si3N4 particles in the NH3 atmosphere. These results indicate that the NH3 atmosphere is conducive to the formation of submicron spherical-like β-Si3N4 particles. A complete submicron spherical-like Si3N4 powder with 93.12 wt% β phase has been synthesized by direct nitridation of silicon saw dust assisted with 5 wt% CaF2 additives in NH3. The mechanism for the formation of the spherical-like β-Si3N4 powder has also been discussed.

ABSTRACTInfrared temperature measurement is widely used in the MOCVD process, and improving the surface infrared emissivity of the graphite base is beneficial to improve the temperature measurement accuracy. In this study, SiC coatings were prepared by CVD on graphite substrate using different process parameters including CVD temperature, total pressure, H2/MTS ratio. The infrared emissivity of SiC coatings with different microstructures was investigated. All SiC coatings obtained were β-SiC. The infrared emissivities of the three samples with different surface morphologies are 0.93, 0.95 and 0.97, respectively. As the surface roughness increases, the reflection and scattering of thermally radiated electromagnetic waves increases, resulting in higher infrared emissivity. The loose structure of the grain surface makes the surface electromagnetic wave and light wave resonant coupling, thus increasing the infrared emissivity.

ABSTRACTPorous piezoelectric materials have been widely used in hydrophone applications owing to their excellent hydrostatic charge constant (dh) and voltage constant (gh). However, owing to the difficulty in sample manufacturing, the evaluation of the overall piezoelectric properties for reliable device design using simulations is challenging. Herein, a two-step simulation was performed to accurately determine the overall properties of the porous PZT. First, the piezoelectric charge constant was calculated by displacement calculations using the electrostrictive effect. Second, using the calculated piezoelectric charge constant and impedance spectrum obtained from the experiment, the initial value for optimizing the properties was selected, and the overall properties were obtained using the parametric estimation technique. These parametric estimation simulation procedures were performed with the samples of radial and thickness modes based on the IEEE standards. Finally, the piezoelectric properties obtained were compared and verified with the experimental values. Therefore, the overall piezoelectric properties include mechanical, frequency and dielectric properties according to the porosity were obtained with reliable results.

ABSTRACTGel casting technology and a two-stage sintering process were used to produce yttria-stabilized tetragonal zirconia (YTZP) ceramics with excellent mechanical properties. A carbonic acid-based polyelectrolyte dispersant was used as a dispersant to prepare a well-dispersed nano-sized (94 nm) zirconia slurry with a high solid content (45 vol%) for gel casting. The functional carboxyl groups of the polyelectrolyte dispersant reacted with epoxy monomer (ethylene glycol diglycidyl ether, EGDGE) as it was added to the slurry, resulting in a decrease in gelling incubation time and an increase in viscosity, resulting in gel casting failure. Adding hydroquinone (HQ) to the slurry can cause polymerization to be delayed and the gel-casting working time to be extended. To control grain growth, a two-stage sintering process was used. The temperature for the first stage of sintering was set at 1300°C, then lowered to 1240°C and soaked for 24 h in the second stage to achieve a relative density of greater than 99%. The two-stage sintered sample has a Vickers hardness of 15.2 GPa, fracture toughness of 7.8 MPa.m1/2, and flexural strength of 771 MPa.

ABSTRACTPhotoelectrochemical (PEC) water splitting is one of the most sustainable approaches for converting solar energy into hydrogen fuel. Affordable and robust photoelectrodes are crucial for the commercialization of PEC technologies. Recently, transition metal-based co-catalysts, especially Ni- and Fe-based catalysts, have attracted much interest owing to their exceptional OER characteristics. Given this, we here proposed the decoration of a Fe-Ni-based cocatalyst on the surface of the TiO2 photoanode for PEC water splitting. The TiO2 photoanode was hydrothermally synthesized and then decorated by Fe-Ni hydroxide catalyst using photo-assisted electrodeposition. The optimized TiO2/FeNiOOH photoanode exhibited the maximum photocurrent density value of 1.36 mA cm−2, which is almost twice the value obtained for bare TiO2, at 1.23 V vs RHE under the AM 1.5 G illumination. Due to the enhanced light absorption in the UV region, the optimized photoanode exhibited remarkable IPCE and photoconversion efficiency of 87.8% and 0.93%, respectively. Furthermore, excellent faradaic efficiencies of ∼90% for H2 and ∼70% for O2 generations were obtained. Predominantly, the enhancement in the photocurrent potentials was explained in detail. Our study shows the roles and benefits of using bimetallic catalysts with TiO2 photoanodes for sustainable water-splitting applications.

ABSTRACTCordierite-based ceramic is one of the most interesting engineering materials that has attractive and multidisciplinary assets, such as low thermal expansion coefficient, excellent thermal shock resistance, high refractoriness, good mechanical properties, and so on. In this work, cordierite-based ceramics were prepared mainly from stevensite-rich clay or coal fly ash (CFA) and stevensite-rich clay using a solid-state interaction process. The influence of heating temperature, in the range of 800–1250°C, and starting materials on the microstructure-temperature evolutions and mechanical strength were evaluated using TGA-DTA, XRD, FTIR, SEM, and dilatometric analysis. The results revealed, for both formulations heating in the temperature range 800–1100°C, the transformation of stevensite-rich clay into enstatite and its polymorphisms. Further heating induced the formation of the cordierite phase at 1200°C, for the formulation consisted mainly of stevensite-rich clay and CFA, and at 1250°C for that contained mainly stevensite-rich clay. The addition of CFA to stevensite-rich clay enhanced its reactivity and involved the increase in mechanical strength from 5 MPa to 15 MPa at 1200°C.

ABSTRACTA lepidocrocite-like potassium titanate, (Kx(LixTi1-x)O2; Lss) with a layered structure can provide a reactive interlayer space for soft-chemical reaction such as ion-exchange or intercalation and the hydrated sodium derivative (Lss-Na) was obtained by an ion-exchange reaction. The crystal structures of the hydrated and dehydrated Lss-Na were refined by using synchrotron powder X-ray diffraction data. Two steps of dehydrated processes for the Lss-Na were observed by in-situ synchrotron powder X-ray diffraction. The ion-exchange property for Lss-Na was superior to those for Lss and Lss-H and was corelated with the effective basal space which was expanded by formation of two layers of water molecules.

ABSTRACTFully dense Al2TiO5–Al2O3–TiN (ATN) composites were fabricated by reactive sintering using spark plasma sintering at 1400°C for 5 min under 100 MPa in vacuum. An equimolar ratio of Al2O3:TiO2 was used as the starting powder, while the addition of 0–36 mol% AlN was investigated. The thermodynamic calculation indicates that the initial reaction was that of TiO2 and AlN, forming TiN and Al2O3, and then the remaining TiO2 reacted with Al2O3 to produce Al2TiO5. With the increase in AlN precursor, Al2TiO5 gradually decreased, while Al2O3 and TiN increased. The lattice parameters of Al2TiO5 were enlarged with AlN addition, implying the incorporation of N atoms in the Al2TiO5 unit cell. The addition of AlN effectively produced fully densified bodies with small grain size, and microcrack-free, which therefore enhanced the mechanical properties of ATN composites. At 36 mol% AlN addition, the composite shows Vickers hardness and fracture toughness of 16.26 ± 1.61 GPa and 5.20 ± 0.46 MPa.m1/2, respectively.

ABSTRACTβ-Si3N4 whiskers were synthesized by using a moderately low-temperature heat-treatment process, with the aid of a low weight fraction of multiple aids (Y2O3-MgO). The synthesis conditions and aspect ratio of the whiskers were adjusted by changing the MgO content in the composite additive system, heat treatment temperature and holding time. The phase composition and morphology of the whiskers were analyzed by XRD and SEM, respectively. The phase transformation could be completed at 1700°C by introducing only 0.5 wt% MgO. The heat-treated temperature was successfully further reduced to 1650°C by extending the holding time to 5 h. The introduction of MgO can make the whiskers form rapidly at a lower temperature. By introducing a small amount of MgO and appropriately extending the holding time at a lower treatment temperature has been proved to be an effective method to obtain β-Si3N4 whiskers with higher aspect ratio under mild conditions.