高温超导体磁悬浮轴承在低温液体泵中应用的可行性分析

目前低温液体泵用轴承一般为机械轴承,由于机械磨损其工作寿命有限;工作在低温环境下,该轴承润滑条件恶劣,不能满足高转速、重载荷条件下的长期连续应用.高温超导体磁悬浮轴承则直接工作在低温条件下,没有机械接触且无源自稳定,是代替机械轴承的一种选择.近年来关于高温超导磁悬浮轴承的应用研究很多,其承载能力等性能参数提升很多,并在...     

焦炭与CO2和水蒸气气化后孔隙结构和高温抗压强度研究

通过焦炭气化反应装置和高温抗压强度测定装置,研究了焦炭与CO₂和水蒸气气化后孔隙结构变化规律及溶损率、温度和孔隙结构对焦炭高温抗压强度的影响。结果表明,与CO₂气化相比,水蒸气气化后焦炭平均孔径较小,比表面积和100 μm以下气孔数量增加,且整体高温抗压强度更高。焦炭气化后高温抗压强度随溶损率增加而降低,随温度升高而降低。温度为1 200 ℃时,随溶损率增加压缩过程焦炭承受压缩功(WOC_u)逐渐降低,水蒸气气化后的WOC_u高于CO₂条件,随溶损率增加焦炭压缩过程形变量呈降低趋势。在相同溶损率下,水蒸气气化后焦炭的孔隙结构对焦炭强度损害相对较小,抗变形能力更强。     

Alkali Lithosilicates: Renaissance of a Reputable Substance Class with Surprising Luminescence Properties

A hitherto unknown synthetic access to alkali lithosilicates, a substance class first described by Hoppe in the 1980s, is reported. With the synthesis and characterization of NaK₇[Li₃SiO₄]₈, a new representative has been discovered, expanding the family of known alkali lithosilicates. Astonishingly, NaK₇[Li₃SiO₄]₈ and the already established alkali lithosilicates Na[Li₃SiO₄] as well as K[Li₃SiO₄] display unforeseen luminescence properties, when doped with Eu²⁺. Na[Li₃SiO₄]:Eu²⁺ exhibits an ultra‐narrow blue, K[Li₃SiO₄]:Eu²⁺ a broadband, and NaK₇[Li₃SiO₄]₈:Eu²⁺ a yellow‐green double emission upon excitation with near‐UV to blue light. Consequently, all of the investigated substances of this class of compounds are highly interesting phosphors for application in phosphor converted LEDs.     

SiC MOSFET栅极电参数退化机理及耦合关系

栅极一直是SiC MOSFET可靠性研究的重点,栅极老化过程中电参数之间的耦合关系对栅极可靠性研究有至关重要的作用。为此,搭建了能够同时监测阈值电压和栅极漏电流的高温栅偏(HTGB)试验平台。研究了HTGB下阈值电压和漏电流的退化趋势和影响,基于氧化层注入电荷量深入分析了两者之间的耦合关系。结果表明,热应力对载流子隧穿影响较为明显,对陷阱捕获的载流子影响相对较小,而场强则对两者均具有显著的影响。此外,提出了减小阈值电压漂移对SiC MOSFET均流特性影响的方法,指出了栅极漏电流下降现象的本质是栅极陷阱充电,并给出了栅极老化过程中漏电流失效基准值选取的方法。该研究结果为深入理解SiC MOSFET的栅极失效机理提供了理论指导。     

Ultrathin Titanium Carbide (MXene) Films for High-Temperature Thermal Camouflage

Thermal camouflage has attracted increasing attention owing to the rapid development of infrared (IR) surveillance technologies. Various materials and systems have been developed to date, but the realization of high-temperature thermal camouflage using ultrathin film/coating remains a great challenge; this is of great significance, especially for IR stealth in military equipment. This work demonstrates a series of ultrathin Ti₃C₂T_x MXene films (as low as 1 µm) with superior high-temperature indoor/outdoor thermal camouflage performance: wide camouflage temperature range (from below −10 °C to over 500 °C), large reduction in radiation temperature (exceeding 300 °C for objects with temperatures over 500 °C), long-term high-temperature or fire stability, multifunctionality including disguised Joule heating capability, and high electromagnetic interference shielding efficiency. The superior high-temperature thermal camouflage performance of the ultrathin MXene film is attributed to its low mid-IR emissivity (0.19), which is comparable to that of stainless steel but far below that of other 2D nanomaterials, such as graphene. The multifunctional ultrathin MXene films prepared through simple vacuum-assisted filtration provide a feasible method for efficient high-temperature thermal camouflage using ultrathin films, demonstrating the great promise of MXene materials for thermal camouflage, IR stealth, counter-surveillance, and security protection.     

Hydrothermal “Disproportionation” of Biomass into Oriented Carbon Microsphere Anode and 3D Porous Carbon Cathode for Potassium Ion Hybrid Capacitor

The comprehensive utilization of biomass to obtain energy-storage carbonaceous materials with special microstructures is of great significance. Herein, a universal method is proposed to fabricate oriented carbon microspheres (OCMSs) and 3D porous carbon (3DPC) block at the same time via high-temperature hydrothermal “disproportionation” of biomass including but not limited to basswood, pinus sylvestris, red walnut, beech, bamboo, and sorghum straw. Through nuclear magnetic resonance, gas chromatography mass spectrometry, as well as various morphologic and structural characterizations, it is demonstrated that OCMS with (002) orientation originates from the carbonization of organic matters produced by the successive decomposition of hemicellulose, cellulose, and lignin during the high-temperature hydrothermal process, while the 3DPC blocks exhibit abundant sp³ defects and micropores with a surface area of 855.12 m² g⁻¹ due to the constant loss of organic components from basswood blocks. As a result, the OCMS anode exhibits a high capacity of 201.1 mA h g⁻¹ at 2000 mA g⁻¹ after 2000 cycles, 3DPC cathode delivers a capacity of 95.7 mA h g⁻¹ at 1.0 A g⁻¹ after 5000 cycles. Remarkably, the as-assembled OCMS//3DPC potassium ion hybrid capacitor exhibits an energy of 140.7 Wh kg⁻¹ at 643.8 W kg⁻¹, with a long cycle life over 8500 cycles.     

高功率单高阶模倒置表面浮雕结构垂直腔面发射激光器

提出并研究了一种带有环形出光孔的倒置表面浮雕结构垂直腔面发射激光器.该器件最突出的结构特点在于,支持稳定的单高阶横向模式激射.在输入电流为六倍阈值电流时,输出功率高达9.8 m W,边模抑制比将近30 d B.在外界为360 K高温时,输出功率仍可达4 m W.且其远场表现出的高斯光束发散角较小.     

Noncatalytic organic rearrangement using supercritical water

Abstract

Significant acceleration of Beckmam and pinacol rearrangements can be achieved by using supercritical water (scH₂O), especially just near the critical point even in the absence of any acid catalysts. A high-pressure, high-temperature flow reactor system with FTlR operable at 500°C and 50 MPa was suaxssfdy developed, wherein the non-catalytic Beckmam and pinacol rearrangements using scH₂O were carried out and monitored. It has been demonstrated that scH₂0 itself acts very effectively in the place of conventional acid catalysts for both the rearrangements. The rate of the pinacol rearrangement using scH₂O is 28,200-fold rate of that in 0.871 M HCl solution at 46.7 MPa under distillation conditions. The high rate of reaction may be attributed to a great increase in the local proton concentration around the organic reactants.     

High-temperature/high-pressure X-ray diffraction: Recent developments

Abstract

We have developed two Merrill-Bassett diamond-anvil cells for specialized high-temperature uses. The first is constructed largely of rhenium to provide uniform, constant P and T on the order of 20 GPa at 1200 K for extended periods. The second is for single-crystal x-ray diffraction, but can be heated to 630 K at 20 GPa to grow single-crystal samples which cannot be produced at room temperature. With this cell, the crystal structure of ?-O₂ was shown to be monoclinic with a = 3.649 A, b = 5.493 A, c = 7.701 A, and β = 116.11° at 19.7 GPa.