In situ synthesis of Al2O3–SiC powders via molten-salt-assisted aluminum/carbothermal reduction method

Al₂O₃–SiC composite powder (ASCP) was successfully synthesized using a novel molten-salt-assisted aluminum/carbothermal reduction (MS-ACTR) method with silica fume, aluminum powder, and carbon black as raw materials; NaCl–KCl was used as the molten salt medium. The effects of the synthesis temperature and salt-reactant ratio on the phase composition and microstructure were investigated. The results showed that the Al₂O₃–SiC content increased with an increase in molten salt temperature, and the salt–reactant ratio in the range of 1.5:1–2.5:1 had an impact on the fabrication of ASCP. The optimum condition for synthesizing ASCP from NaCl–KCl molten salt consisted of maintaining the temperature at 1573 K for 4 h. The chemical reaction thermodynamics and growth mechanism indicate that the molten salt plays an important role in the formation of SiC whiskers by following the vapor-solid growth mode in the MS-ACTR treatment. This study demonstrates that the addition of molten salt as a reaction medium is a promising approach for synthesizing high-melting-point composite powders at low temperatures.     

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.     

Early hydration properties and microstructure evolutions of MgO-activated slag materials at different curing temperatures

This study reports on the early hydration properties and microstructure evolutions of MgO-activated slag at five curing temperatures (20 °C, 40 °C, 50 °C, 60 °C, and 80 °C) and three MgO types (S-MgO, M ? MgO, and R-MgO). The results indicated that high-temperature curing substantially increased the compressive strength of the specimens. Particularly, the highest strength was obtained at 40 °C and 60 °C for the S-MgO and M-MgO-activated slag specimens, respectively, and the high curing temperature for the R-MgO-activated slag specimen was 40 °C. We focused on the relationship between the mechanical properties, pore structure characteristics, and hydration products. The combination of calcium-silicate-hydrate (C-S-H) gel and Al increased under high-temperature curing conditions. XRD, FT-IR, TG-DTG, and ²⁷Al MAS-NMR results showed a high Al content in the formation of calcium silicate hydrate with Al in its structure (C-A-S-H gel) for the R-MgO-activated slag pastes under high-temperature curing; however, the microstructure was loose owing to the formation of excessive brucite. For the S-MgO-activated slag specimen, the Ca/Si ratio was high, with more Mg²⁺ penetrating the C-S-H gel interlayer, forming more hydrotalcite-like phases and increasing the chain length of the C-S-H gel. The microstructure showed good compatibility of the hydration products interweaving to form dense microstructures.     

A Complexing Agent to Enable a Wide-Temperature Range Bromine-Based Flow Battery for Stationary Energy Storage

Bromine-based flow batteries (Br-FBs) are considered one of the most promising energy storage systems due to their features of high energy density and low cost. However, they generally suffer from uncontrolled diffusion of corrosive bromine particularly at high temperatures. That is because the interaction between polybromide anions and the commonly used complexing agent (N–methyl–N–ethyl–pyrrolidinium bromide [MEP]) decreases with increasing temperatures, which causes serious self-discharge and capacity fade. Herein, a novel bromine complexing agent, 1–ethyl–2–methyl–pyridinium bromide (BCA), is introduced in Br-FBs to solve the above problems. It is proven that BCA can combine with polybromide anions very well even at a high temperature of 60 °C. Moreover, the BCA contributes to decreasing the electrochemical polarization of Br⁻/Br₂ couple, which in turn improves their power density. As a result, a zinc–bromine flow battery with BCA as the complexing agent can achieve a high energy efficiency of 84% at 40 mA cm⁻², even at high temperature of 60 °C and it can stably run for more than 400 cycles without obvious performance decay. This paper provides an effective complexing agent to enable a wide temperature range Br-FB.     

The thermochromic characteristics of Zn-doped VO2 that were prepared by the hydrothermal and post-annealing process and their polyurethane composite films

In this paper, Zn-doped VO₂ nanoparticles have been successfully fabricated by a two-step hydrothermal-annealing process, and the thermally induced visible light transmittance enhancement of Zn-doped VO₂ has been studied for the first time. It is found that Zn-doped VO₂ not only exhibits excellent solar modulation ability (ΔT_sol = 15.27%) but also can reduce the phase transition temperature and increase the visible light transmittance after the heat-induced phase transition (ΔT_lum=+5.78%). Moreover, with the increase of Zn doping concentration, the phase transition temperature (T_c) and phase transition hysteresis (ΔT) both decrease. It is shown that the Zn-doped VO₂-PU films not only have good solar light modulation ability and properties of improving visible light transmission after phase transition, but also have good durability. The research result is of great significance for improving the visible light transmittance after phase transition and realizing the practical application of VO₂ in the field of smart windows.     

Anisotropic effects of oxygen vacancy defects on the electrical properties of highly oriented bismuth titanate ferroelectric ceramics

Bismuth titanate (Bi₄Ti₃O₁₂, BIT) exhibits a high Curie temperature and anisotropic electrical performance owing to its layered perovskite structure, and hence, it is an important ferroelectric material for high-temperature piezoelectric applications. It is crucial to understand the effects of the anisotropy in BIT-based ferroelectrics for developing novel high-temperature piezoelectric materials. In this study, a highly textured BIT ceramic was fabricated using the tape-casting technique from highly grain-oriented BIT platelets prepared by the molten salt method. The textured BIT ceramic showed a dense microstructure and high grain orientation along the (00l) plane with a texturing degree F_00l = 0.86. It exhibited significant anisotropy in the electrical properties along the directions parallel and perpendicular to the axis of the tape-casting plane. Double ferroelectric hysteresis P–E loops and normal ferroelectric P–E loops were observed in the parallel and perpendicular samples, respectively. In addition to the layered crystal structure and domains, the anisotropy in the arrangement of the oxygen vacancy defects and their transport in the structure led to a significant anisotropy in the ferroelectric properties of the textured BIT ceramics. This work demonstrates the anisotropic arrangement of the oxygen vacancy defects and its effect on the electrical properties of high-temperature bismuth layer-structured ferroelectrics.     

Dual-mode optical thermometry based on Bi3+/Eu3+ co-activated BaGd2O4 phosphor with high sensitivity and signal discriminability

A series of BaGd₂O₄:Bi³⁺,Eu³⁺ phosphors with dual-emitting centers were prepared by high-temperature solid-state method. X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), fluorescence spectroscopy, lifetime decay curve and variable temperature emission spectroscopy were used to systematically study the structure, luminescence performance and temperature characteristics. Under ultraviolet (UV) excitation, the BaGd₂O₄:Bi³⁺,Eu³⁺ phosphor showed a broad-band emission in the blue region corresponding to transitions of Bi³⁺ ions and the sharp red light emission corresponding to Eu³⁺ ions. The Bi³⁺ and Eu³⁺ ion emission peaks were well-separated, which meets a prerequisite for efficient temperature signal resolution measurement. The fluorescence intensity ratio (FIR) technique was used to measure the different temperature response characteristics between Bi³⁺ blue emission and Eu³⁺ red emission. When the temperature varies from 293 K to 473 K, the relative temperature sensitivity (S_r) of BaGd₂O₄:Bi³⁺,Eu³⁺ phosphors is obtained, was determined as 1.0182%K⁻¹. In addition to calculating the relative sensitivity by FIR technology, we can also obtain the value of S_r through experiments and formulas related to the decay life, and found to be 1.0651%K⁻¹. Therefore, BaGd₂O₄: Bi³⁺,Eu³⁺ phosphor is an excellent non-contact optical temperature measurement material.     

气藏型储气库注气期试井分析探讨

针对气藏型储气库注采井注采过程中储层物性参数影响因素不明确、注采能力不对称的问题。基于相国寺储气库井下连续油管试井测试结果,提出储气库注气期“温降效应”、“变表皮效应”的概念,分析了储气库注采过程中温降效应、变表皮效应以及储层应力敏感对注采的影响。通过气藏型储气库注气期试井分析技术,研究各因素在试井曲线上的响应特征以及对试井解释参数的影响。结果表明:①相对于采气期试井测试,注气期测试得到的储层物性参数具有同样的参考价值;②储气库温降效应对于试井解释结果的影响可忽略不计,而在不同注采运行周期内,变表皮效应以及应力敏感效应影响差异较大;③编制储气库注采运行方案时应充分考虑变表皮效应与应力敏感的影响,在不同注采运行周期内开展试井测试获取准确的储层参数值。研究成果为储气库试井测试与解释提供了重要的研究依据和理论指导。     

Influence of substrate temperature on the microstructure of YSZ films and their application as the insulating layer of thin film sensors for harsh temperature environments

Thin film sensors are employed to monitor the health of hot-section components of aeroengine intelligence (for instance, blades), and electrical insulating layers are needed between the metal components and thin film sensors. For this purpose, the electrical insulation characteristics of an yttria-stabilized zirconia (YSZ)/Al₂O₃ multilayer insulating structure were investigated. First, YSZ thin films were deposited by DC reactive sputtering at various substrate temperatures, and the microstructural features were investigated by scanning electron microscopy and X-ray diffraction. The results indicate that the micromorphology of the YSZ thin film gradually became denser with increasing substrate temperature, and no new phases appeared. The compact and uniform topography of the YSZ thin film improved the insulation properties of the multilayer insulating structure and enhanced the adhesion of the thin film sensors. In addition, the electrical insulation properties of the YSZ/Al₂O₃ multilayer insulating structure were evaluated via insulation resistance tests from 25 to 800 °C, in which the YSZ thin film was deposited at 550 °C. The results show that the insulation resistance of the multilayer structure increased by an order of magnitude compared with that of the conventional Al₂O₃ insulating layer, reaching 135 kΩ (5.1 × 10^?6 S/m) at 800 °C. Notably, the insulation resistance was still greater than 75 kΩ after annealing at 800 °C for 5 h. Finally, the shunt effect of the YSZ/Al₂O₃ multilayer insulating structure was estimated using a PdCr thin film strain gauge. The relative resistance error was 0.24%, which demonstrates that the YSZ/Al₂O₃ multilayer insulating structure is suitable for thin film sensors.     

Zirconium-diboride silicon-carbide composites: A review

Zirconium diboride (ZrB₂) and silicon carbide (SiC) composites have long been of interest since it was observed that ZrB₂ improved the thermal shock resistance of SiC. However, processing of these materials can be difficult due to high and different sintering temperatures and differences in the thermodynamic stability of each material. ZrB₂–SiC composites have been processed in a variety of ways including hot-pressing, spark-plasma sintering, reactive melt infiltration, pack cementation, chemical vapor deposition, chemical vapor infiltration, stereolithography, direct ink writing, selective laser sintering, electron beam melting, and binder jet additive manufacturing. Each manufacturing method has its own pros and cons. This review serves to summarize more than 60 years of research and provide a coherent resource for the variety of methods and advancements in development of ZrB₂–SiC composites.