High permittivity and excellent high-temperature energy storage properties of X9R BaTiO3–(Bi0.5Na0.5)TiO3 ceramics

We fabricated x(Bi_0.5Na_0.5)TiO₃–(1−x)[BaTiO₃–(Bi_0.5Na_0.5)TiO₃–Nb] (BNT-doped BTBNT-Nb) dielectric materials with high permittivity and excellent high-temperature energy storage properties. The initial powder of Nb-modified BTBNT was first calcined and then modified with different stoichiometric ratios of (Bi_0.5Na_0.5)TiO₃ (BNT). Variable-temperature X-ray diffraction (XRD) results showed that the ceramics with a small amount of BNT doping consisted of coexisting tetragonal and pseudocubic phases, which transformed into the pseudocubic phase as the test temperature increased. The results of transmission electron microscopy (TEM) showed that the ceramic grain was the core-shell structure. The permittivity of the 5 mol% BNT-doped BTBNT-Nb ceramic reached up to 2343, meeting the X9R specification. The discharge energy densities of all samples were 1.70-1.91 J/cm³ at room temperature. The discharge energy densities of all samples fluctuated by only ±5% over the wide temperature range from 25°C to 175°C and ±8% from 25°C to 200°C. The discharge energy density of the 50 mol% BNT-doped BTBNT-Nb ceramic was 2.01 J/cm³ at 210 kV/cm and 175°C. The maximum energy efficiencies of all ceramics were up to ~91% at high temperatures and were much better than those at room temperature. The stable dielectric properties within a wide temperature window and excellent high-temperature energy storage properties of this BNT-doped BTBNT-Nb system make it promising to provide candidate materials for multilayer ceramic capacitor applications.     

High and temperature-stable dielectric constants in PNb9O25 ceramic

PNb₉O₂₅ ceramic was prepared using a sparking plasma sintering (SPS) method. Microstructure, dielectric and electrical properties of the ceramic were investigated. Dense ceramic was obtained, and the ceramic exhibited a high dielectric constant (>1000) and a low dielectric loss (∼2%) in the investigated frequency range of 100 Hz-100 kHz at room temperature. Dielectric relaxations with strong frequency dispersion occurred at temperatures higher than 250°C, which were due to oxygen vacancies. A highly stable capacitance (< 10% deviation) over a wide temperature range of –30°C to –200°C was obtained. The ceramic also showed a relatively high electrical conductivity (>4 × 10⁻⁸ S/cm) with an activation energy of approximately 0.9 eV in the temperature range of >200°C.     

Temperature‐stable dielectric and energy storage properties of La(Ti0.5Mg0.5)O3‐doped (Bi0.5Na0.5)TiO3‐(Sr0.7Bi0.2)TiO3 lead‐free ceramics

A new type of (0.7?x)Bi_0.5Na_0.5TiO₃‐0.3Sr_0.7Bi_0.2TiO₃‐xLaTi_0.5Mg_0.5O₃ (LTM1000x, x = 0.0, 0.005, 0.01, 0.03, 0.05 wt%) lead‐free energy storage ceramic material was prepared by a combining ternary perovskite compounds, and the phase transition, dielectric, and energy storage characteristics were analyzed. It was found that the ceramic materials can achieve a stable dielectric property with a large dielectric constant in a wide temperature range with proper doping. The dielectric constant was stable at 2170 ± 15% in the temperature range of 35‐363°C at LTM05. In addition, the storage energy density was greatly improved to 1.32 J/cm³ with a high‐energy storage efficiency of 75% at the composition. More importantly, the energy storage density exhibited good temperature stability in the measurement range, which was maintained within 5% in the temperature range of 30‐110°C. Particularly, LTM05 show excellent fatigue resistance within 10⁶ fatigue cycles. The results show that the ceramic material is a promising material for temperature‐stable energy storage.     

Electrical Conductivity of Mullite Ceramics

The electrical conductivity of a lab‐produced homogeneous mullite ceramic sintered at 1625°C for 10 h with low porosity was measured by impedance spectroscopy in the 0.01 Hz to 1MHz frequency range at temperatures between 300°C and 1400°C in air. The electrical conductivity of the mullite ceramic is low at 300°C (≈0.5 × 10^?9 Scm^?1), typical for a ceramic insulator. Up to ≈ 800°C, the conductivity only slightly increases (≈0.5 × 10^?6 Scm^?1 at 800°C) corresponding to a relatively low activation energy (0.68eV) of the process. Above ≈ 800°C, the temperature‐dependent increase in the electrical conductivity is higher (≈10^?5 Scm^?1 at 1400°C), which goes along with a higher activation energy (1.14 eV). The electrical conductivity of the mullite ceramic and its temperature‐dependence are compared with prior studies. The conductivity of polycrystalline mullite is found to lie in‐between those of the strong insulator α‐alumina and the excellent ion conductor Y‐doped zirconia. The electrical conductivity of the mullite ceramic in the low‐temperature field (< ≈800°C) is approximately one order of magnitude higher than that of the mullite single crystals. This difference is essentially attributed to electronic grain‐boundary conductivity in the polycrystalline ceramic material. The electronic grain‐boundary conductivity may be triggered by defects at grain boundaries. At high temperatures, above ≈ 800°C, and up to 1400°C gradually increasing ionic oxygen conductivity dominates.     

Energy storage performance of 0.55Bi0.5Na0.5TiO3-0.45SrTiO3 ceramics doped with lanthanide elements (Ln = La,Nd, Dy,Sm) using a viscous polymer processing route

Lead-free bismuth sodium titanate-strontium titanate (NBT-ST) dielectric ceramic materials have been extensively investigated energy storage materials because of their relaxor characteristics. In this study, four different lanthanide elements were introduced into the ferroelectric NBT-ST ceramic to improve their relaxor properties. The introduction of the lanthanide resulted in an increase in disorder at location A within the perovskite lattice and improved relaxor characteristics, leading to a stored energy density of more than 3.5 J/cm³. In particular, an ultrahigh recoverable stored energy density of 4.94 J/cm³ and efficiency of 88.45% were achieved at 440 kV/cm when the NBT-ST ceramic was modified with neodymium. The modified ceramic also exhibited good thermal stability in the range of 30–120 °C, as well as a fast discharge time of ～153 ns, indicating that Nd-incorporated NBT-ST is a promising candidate for electrical energy storage ceramic.     

Temperature-dependent electrical transport behavior and structural evolution in hollandite-type titanium-based oxide

Electrical transport behavior and structural characteristics directly determine the use of functional ceramic materials in electronic information storage, catalytic conversion, and energy field applications. However, these properties are poorly understood because most of the relevant experiments were performed in a rather narrow temperature range. Herein, we used hollandite-type K_xTi₈O₁₆ as an example to systematically study the temperature-dependent structure and electrical transport properties in a wide temperature range from 25 to 900°C. The electrical transport involves both potassium ionic conduction and electronic conduction. With increasing temperature, the ionic conductivity increases below 800°C and decreases above 800°C. The electronic conductivity displays two maxima at 0.15 S/cm at 400°C and 5.2 × 10⁻⁴ S/cm at 800°C. These interesting variations in the conductivities are related to the presence of Ti³⁺ and the structural transformation from hollandite to a mixture of rutile and jeppeite. The findings reported herein support the potential application of titanium-based hollandites and provide an understanding of the electrical transport properties of functional ceramic materials.     

碳化硅质高温陶瓷膜的低温烧成

本文以碳化硅骨料、章村土系结合剂和核桃壳粉为原料,通过等静压成型工艺和 低温烧结制备了碳化硅质高温陶瓷膜材料。研究了成型压力对坯体强度以及成型压力和烧成温 度对膜材料强度、孔径、气孔率和透气阻力的影响。结果发现,当成型压力为 70 MPa、烧成温 度为 1250~1270?C 时,制品综合性能较优。     

Hexagonal SrFe12O19 ferrite with high saturation magnetization

Hexagonal M-type ferrites with a nominal composition SrFe₁₂O₁₉ (SrM) were prepared via a ceramic route using acicular goethite (α-FeOOH) nanopowders obtained at different hydrothermal temperature as one of the starting materials, and their structural and magnetic properties were investigated. The best hydrothermal temperature of α-FeOOH used was found to be 1ower than 180?°C, and the best sintering temperature of SrM should be 1200?°C. The highest saturation magnetization of SrM reaches 76.7?emu/g, a very high value rarely found in the SrM ferrites without any substitution or dopant.     

In-Situ Measurement of Emissivities of Ceramic—Polymer Composite Materials

Emissivities of high-dielectric ceramic composites used in microelectronic packaging were measured by a modified hot-filament ASTM method and infrared thermometry; total hemispherical emissivities were measured using the hot-filament method, and effective band emissivities were measured using infrared thermometry. Two ceramics—5μm alumina and 2–3μm aluminum nitride—were chosen as the base of the substrate. They were blended with poly(vinyl butyral) (PVB) with proper amounts of solvents and cast on a 304-stainless-steel strip used as the heating filament. Emissivity measurements in the temperature range of 380–1000 K were performed using three different sets of experiments. In the first set of experiments, the emissivities of unfired polymer composites were measured in the temperature range of 380–450 K, a temperature at which thermal degradation starts to occur. In the second set, the specimens were heated overnight in a furnace at 673 K for binder burnout, and measurements were conducted on fired composites in the temperature range of 380–1000 K. In the last set, the emissivity of the specimens were measured in situ in the temperature range of 380–1000 K by condensing the degradation products using a liquid-nitrogen cryogenic jacket on-line before the pump line to avoid contamination of the turbomolecular pump. The system pressure was controlled below 5 × 10⁻⁵ torr (}6.7 × 10⁻³ Pa) in all experiments to constrain nonradiative types of heat transfer inside the bell jar.     

Preparation and performance study of cordierite/mullite composite ceramics for solar thermal energy storage

The employment of solar energy in recent years has reached a remarkable edge. It has become even more popular as the cost of fossil fuel continues to rise. Energy storage system improves an adjustability and marketability of solar thermal and allowing it to produce electricity in demand. This study attempted to prepare cordierite/mullite composite ceramics used as solar thermal storage material from calcined bauxite, talcum, soda feldspar, potassium feldspar, quartz, and mullite. The thermal physical performances were evaluated and characterized by XRD, SEM, EPMA, and EDS. It was found that the optimum sintering temperature was 1280°C for preparing, and the corresponding water adsorption was 11.25%, apparent porosity was 23.59%, bulk density was 2.10 mg·cm^?3, bending strength was 88.52 MPa. The residual bending strength of specimen sintered at 1280°C after thermal shock of 30 times decreased to be 57 MPa that was 36% lower than that before. The thermal conductivity of samples sintered at 1280°C was tested to be 2.20 W·(m·K)^?1 (26°C), and after wrapped a PCM (phase change materials) of K₂SO₄, the thermal storage density was 933 kJ·kg^?1 with the temperature difference (ΔT) ranged in 0‐800°C. The prepared cordierite/mullite composite ceramic was proved to be a promising material for solar thermal energy storage.     

Novel SiC/C composite targets for the production of radioisotopes for nuclear applications

A partially porous SiC ceramic, reinforced with 30 vol% short carbon fibers, was hot pressed and characterized as potential ISOL target for nuclear applications. Powder milling and hot pressing were effective for the realization of a ceramic with about 40% interconnected porosity in the 0.6–0.8 µm size range. A fiber-free porous SiC material was also synthesized for the sake of comparison. Compression strength of the fiber-rich SiC passed from about 200 MPa at room temperature to about 120 MPa upon testing at 1200 °C. The thermal conductivity was higher than the fiber-free SiC and other state-of-art ISOL target materials and was 48 W/m·K at 600 °C and decreased to 17 W/m·K at 1400 °C, owing to the porosity. Remarkably, this fiber-rich ceramic in form of thin disk, possessed suitable thermo-mechanical behavior to successfully withstand a 350 °C thermal gradient without failure.     

Temperature dependence of field‐responsive mechanisms in lead zirconate titanate

An electric field loading stage was designed for use in a laboratory diffractometer that enables in situ investigations of the temperature dependence in the field response mechanisms of ferroelectric materials. The stage was demonstrated by measuring PbZr_1?xTi_xO₃ (PZT) based materials—a commercially available PZT and a 1% Nb‐doped PbZr_0.56Ti_0.44O₃ (PZT 56/44)—over a temperature range of 25°C to 250°C. The degree of non‐180° domain alignment (η₀₀₂) of the PZT as a function of temperature was quantified. η₀₀₂ of the commercially available PZT increases exponentially with temperature, and was analyzed as a thermally activated process as described by the Arrhenius law. The activation energy for thermally activated domain wall depinning process in PZT was found to be 0.47 eV. Additionally, a field‐induced rhombohedral to tetragonal phase transition was observed 5°C below the rhombohedral‐tetragonal transition in PZT 56/44 ceramic. The field‐induced tetragonal phase fraction was increased 41.8% after electrical cycling. A large amount of domain switching (η₀₀₂=0.45 at 1.75 kV/mm) was observed in the induced tetragonal phase.     

Preparation and characterization of ceramic nanofiltration membrane prepared from hazardous industrial waste

Kiln rollers, which are widely used in ceramic tiles production, are usually subjected to surface grinding to remove the contaminations. The resulted fine powder is considered useless waste and a hazardous source of environmental pollution particularly as it contains health-threatening fine free silica. In the present paper, the grind waste from kiln rollers was reused as raw material in the fabrication of nanofiltration ceramic membrane. The samples of produced ceramic membranes were formed into disks by adding 15% (by weight) organic binder solution with 2% concentration, then pressed at 35 MPa, dried and fired at temperatures range from 1100°C to 1300°C for 1 hour soaking time. It was found that the best firing temperature to produce nanofiltration ceramic membrane is 1250°C, where the ceramic membrane provides high removal of turbidity and high monovalent, divalent, and trivalent salts separation percentage.     

High-temperature electro-ceramics and their application to SiC power modules

This paper presents the research achievement in Japan to develop highly-refractive electro-ceramics for application to silicon carbide (SiC) power modules such as heat-resistive passive components (snubber capacitors and resistors), metalised substrates, ceramic circuit boards, and high-temperature packaging technologies. To enable the operation of SiC devices at high temperatures, the ability to withstand 250 °C and temperature cycle between ?40 and 250 °C must be ensured for all the ceramic components and packaging technologies. For the passive components, the following properties were achieved, which would enable the operation of SiC devices at high switching speeds and high temperatures: low-resistance resistors which exhibit a resistance variation of less than 2% over a temperature range of ?40 to 250 ℃ and with almost no variation at frequencies of less than 10 MHz; multi-layered ceramic capacitors (MLCCs) with a capacitance variation of less than ± 10% within the above-mentioned temperature range and with high self-resonant frequencies of about 10 MHz. In addition, Cu-metalised ceramic substrates using high thermal conductive Si₃N₄ (180 W /(m·K)) and ceramic circuit boards produced using a co-firing process were developed. It was shown that prototype SiC power modules (2-in-1 structure) fabricated using the developed ceramic components could be operated at 225 °C, while exhibiting a high switching speed, 10–20 times faster than that of conventional Si IGBT (150 °C operation).     

Enhanced microwave-assisted sintering of X7R ceramic dielectrics for use in multilayer capacitors

A hybrid furnace, allowing the simultaneous application of microwave (2.45 GHz) and radiant energy, has been used to investigate the sintering of a commercial X7R powder commonly used in multilayer capacitors. Samples were processed at temperatures in the range 1060–1120 °C. Enhanced sintering has been observed in the form of accelerated densification when a microwave field is applied. At 1090 °C for example, 99.4% dense material was obtained by microwave-assisted heating but only 96.9% density was reached by conventional heating. The relative permittivity of the microwave sintered material was ～2200, typically 10%, higher than for conventionally sintering. The Curie temperature was lower by 5 °C in the microwave heated samples.     

Light‐weight thermal insulating fly ash cenosphere ceramics

Light weight fly ash cenosphere (FAC) ceramic composites were developed by simple slip casting method. Thermal properties, Bulk density, Microstructure, flexural strength, and phase analysis of the FAC ceramic composites were measured. The results proved that the FAC have ability to lower bulk density and thermal conductivity effectively. The lowest thermal conductivity achieved for FAC ceramic composites (0.27 W/m.K) was further reduced 0.21 W/m.K by adding combustible additives ie activated charcoal and corn starch. The flexural strength, bulk density and thermal conductivity of FAC ceramic composites reduced consistently with an increase in FAC content. The maximum flexural strength of 13.45 MPa was achieved with 50% FAC and the minimum flexural strength of 4.07 MPa was obtained with 80% FAC. The open porosity increased from 35.51% to 43.76% and 38.19% with an addition of 15% activated charcoal and corn starch, respectively, when compared to no additives. The bulk density of 699, 619, and 675 kg/m³ was achieved with 80% FAC, 80% FAC with the addition of 15% activated charcoal and corn starch, respectively. The 80% FAC ceramic composite shows low thermal expansion coefficient 6.54 × 10^?6/°C at the temperature of 50°C then it varies between 3.7 and 5 × 10^?6/°C in the temperature range above 100°C. These results prove that the developed light weight FAC ceramic are excellent low‐cost thermal insulating materials.     

Integrated utilization of high alumina fly ash for synthesis of foam glass ceramic

Due to the numerous increase of the building energy consumption and huge volume of industrial wastes produced in China, the development of thermal insulation materials is quite needed. Herein, foam glass ceramic, a kind of thermal insulation materials, was fabricated by using solid wastes high alumina fly ash and waste glass as the main raw materials. First, in this study the proportion scheme of this research was designed by using Factsage 7.1 and the foaming agent was CaSO₄. Secondly, the decomposition of calcium sulfate and the influence of process parameters, namely the sintering temperature and the foaming agent additive amount, on the microstructure and mechanical properties of foam glass ceramic were investigated. The experimental results showed that when the proposed foam glass ceramic was sintered at between 1180 and 1220?°C, it exerted excellent macro and micro properties. The optimum parameters were 2% CaSO₄ addition and sintering temperature of 1200?°C, and the corresponding bulk density and compress strength values were 0.98?g/cm³ and 9.84?MPa, respectively. Overall these results indicated that the preparation of foam glass ceramic made up a promising strategy for recycling industrial waste into new kind of building insulation materials.     

METHOD FOR DETERMINING TENSILE PROPERTIES OF REFRACTORY MATERIALS AT ELEVATED TEMPERATURES*

Equipment for testing ceramic materials to temperatures of 2000°F. was developed, and a method was devised for evaluating the bending stresses introduced by the test equipment. With this equipment, the tensile strength, stress-to-rupture characteristics, and modulus of elasticity of a sillimanite refractory were investigated at the Cleveland Laboratory of the National Advisory Committee for Aeronautics. The tensile strength varied from a minimum of 8000 lb. per sq. in. at 500°F. to a maximum of 19,000 lb. per sq. in. at 1800°F. Heat-treating the tensile specimens for one half hour at 1800°F. increased the tensile strength 35% at room temperature and 70% at 500°F. No increase in strength was noted at or above 1400°F. The stress-to-rupture in 1000 hours at 1600°F. was 8500 lb. per sq. in. The modulus of elasticity at room temperature was 20.3 × 10⁶.     

Nanoporous anatase ceramic membranes as fast-proton-conducting materials

Nanoporous anatase ceramic membranes were prepared via particulate sol–gel processes. The calcined xerogels were mesoporous, with a BET surface area of 121 m²/g, an average pore diameter of 5.8 nm and a pore volume of 0.236 cm³/g. Proton conductivity of the membranes was measured as a function of temperature and relative humidity, R.H. When anatase membranes are treated at pH 1.5, the proton conductivity increased in the whole range of temperature and R.H. It indicates that the surface site density (number of water molecules per square nanometer) of these materials has a strong effect on conductivity. The proton conductivity of the studied anatase membranes followed an Arrhenius-like dependence on the temperature (from room temperature to 90 °C), in both treated and untreated membranes. A sigmoidal dependence of the conductivity on the R.H. was observed with the greatest increase noted between 58 and 81% R.H. in both treated and untreated anatase membranes. The highest value of proton conductivity was found to be 0.015 S/cm at 90 °C and 81% R.H., for treated anatase ceramic membranes. An increase of the conductivity could be achieved by means of longer times of treatment.According to the activation energy values, proton migration in this kind of materials could be dominated by the Grotthuss mechanism in the whole range of R.H. The similar values of proton conductivity, lower cost and higher hydrophilicity of these membranes make them potential substitutes for perfluorosulfonic polymeric membranes in proton exchange membrane fuel cells (PEMFCs).     

Materials Challenges in Reverse‐Flow Pyrolysis Reactors for Petrochemical Applications

Currently, the pyrolysis of hydrocarbons for the production of light olefins is almost exclusively carried out in steam crackers operating around 900–1000°C. However, cracking hydrocarbons at much higher temperature results in high selectivity to acetylene, which can be converted into many petrochemical products including ethylene. The desired hydropyrolysis reaction from hydrocarbons to acetylene can be realized in a reverse‐flow reactor at very high temperatures (>1700°C) in a scalable manner. The reactor elements include ceramic components that are placed in the hottest regions of the reactor and must withstand a temperature that is in the range of 1500–2000°C. In addition, the temperature rises and falls with the reverse‐flow cycle; a fluctuation that could be as high as 100–500°C over a period of several seconds. Moreover, the materials in the hot zone are exposed alternately to a regeneration (heat addition) step that is mildly oxidizing, and a pyrolysis (cracking) step that is strongly reducing with a correspondingly high carbon activity. This article addresses the thermodynamic stability of selected ceramic materials based on alumina, zirconia, and yttria for such an application. Results from laboratory tests involving the exposure of these ceramic materials to simulated process conditions followed by their microstructural characterization are compared with expectations from thermodynamic predictions.