钆基分子基低温磁制冷材料的最新研究进展

分子基低温磁制冷材料因其可能替代稀缺昂贵的3He实现低温制冷而备受关注。由于GdIII具有较大的自旋基态、低自旋激发态和单离子各向同性,Gd基分子基低温磁制冷材料近年来发展迅速。结合本课题组近年来的工作及国内外相关的研究报道,介绍四类Gd基低温磁制冷材料的构筑策略:Gd簇分子基磁制冷材料、Gd基配位聚合物分子基磁制冷材料、Gd-过渡金属簇合物磁制冷材料、Gd-异金属聚合物分子基磁制冷材料;同时也对Gd基低温磁制冷材料的发展趋势予以展望。     

氦

随着原子能研究的发展,近年来低温科学的研究,也跟着产生,的确它的重要性并不在原子核物理学的研究之下。氦元素现除常被利用作为供给实验原子的中子的原料外(由放射体元素蜕变中获得),它的重要用途,便是供作低温测验用的冷却媒介,有了氦的酷冷温度圈,我们才能看到原子在绝对零度左右所产生的物理化学变化和其他物质构造的奇妙现象。     

磁制冷

在当今世界,制冷起着非常重要的作用。如果没有制冷技术,我们要想获得新鲜的食物,依然要受季节以及地域的限制。调节环境温度使生活环境变得舒适也将成为不可能的事情。而且,一些医疗方面的前沿技术,如核磁共振成像,器官移植,器官和组织的低温储藏,以及低温外科手术等都将不复存在。制冷技术自100多年前被发明以来基本上没有本质上的改变。现代制冷技术基本上都是基于气体压缩/膨胀的制冷循环过程,这一过程是一个高能耗过程,每年大约会消耗109kW的电能。现有制冷技术的制冷效率已经接近了它的理论极限,而这个极限远远小于根据卡诺循环计算得到的最大理论效率。此外,那些被用作制冷工质,且最终会进入环境中的液态化学物质,不仅可以破坏臭氧层,使得全球气候变暖,还有一些本身就是有害的气体(如NH3气)。1997年的两个巨大突破向人们展现了一种新的制冷方式———磁制冷,这种制冷技术是一种绿色环保制冷技术,效率高,而且能进行循环交替制冷。第一个突破是1997年2月往复式结构磁制冷样机的成功研制[1]。这台机器利用超导磁体产生磁场(最大5 T)。在5 T的磁场强度下,最大制冷量可达600 W,COP值最大可达15,效率接近卡诺循环的60%,温跨...     

分子基低温磁制冷材料的研究进展

磁制冷技术是以磁性物质为工质,通过等温磁化和绝热去磁达到制冷目的的一种极具开发潜力的高新制冷技术．相比于传统的气体压缩制冷,磁制冷以其高效、节能、环保的特点得到研究者越来越多的青睐．近年来研究发现,与合金、纳米磁制冷材料相比,分子基磁制冷材料在超低温制冷领域表现出较大的优势．本文针对分子基低温磁制冷材料的研究报道及本实验室的相关工作进行总结和讨论,并探究了其发展趋势．     

热扩散法浓缩~3He工艺研究简介

惰性气体氦由~3He和~4He两种稳定同位素组成。大气中氦的含量为 7×10~(-7)(重量),其中~3He与~4He之比为1.2×10~(-6)。因此想从自然界获得有实用价值的~3He十分困难。现在各国都不再从大气氦中波集~3He,而是从生产氚的副产物中获得~3He。近年来,~3He在各个研究领域里的应用日益重要,如~He中子计数管,以~3He作工作物质的氦-氖激光器,以及~3He在低温物理中的应用需要大量的高纯,高浓度的~3He。热扩散法是分离气体同位素的基本方法之一。由于~He、~He分子量的相对差较大,有比较大的热扩散     

理化检验工作者的良师益友——向您推荐《机械工程材料测试手册》(化学卷)

世界性的科学技术进步,促进理化检验技术的迅速发展.在工业发达国家,理化检验工作与工农业生产和国防建设等许多重要领域的联系十分紧密.在工业生产中,理化检验的重要性主要表现在对产品的质量监测,生产工艺流程的控制以及商品的进出口检验等方面.产品的质量控制是生产质量管理的主要手段,也是占领商品市场的一项重要因素,更是企业保持持久活力的基础.当今世界上一些工业发达国家,每年用于产品质量控制的测试费用有高达数百亿美元者,每天进行的分析测试工作量达几亿次之多.事实表明工业发达国家的工业生产中,理化检验工作的严格执行保证了它们的产品质量保持在国际一流水平.鉴于理化检验工作的重要性,中国机械工程学会理化检验分会受有关部委的委托,主持组织编写一套大型理化测试技术的工     

欢迎订阅《理化检验-物理分册》杂志

《理化检验-物理分册》杂志创刊于1963年,系中国机械工程学会理化检验分会和失效分析分会会刊,是国内理化测试专业领域最早、且具权威的一本应用类技术刊物,多次获得国家机械行业和上海市优秀期刊奖,并被列为中国科技论     

离子色谱法测定制冷吸收剂溴化锂溶液中的阴离子

正溴化锂制冷机是目前世界上最常用的吸收式制冷机种,是一种以热能为驱动力,水为制冷剂,溴化锂溶液为吸收剂的耗热型制冷设备[1]。该制冷机利用水-溴化锂溶液二元组分的沸点差异及热力学状态变化规律实现制冷循环[2-4]。其能源利用范围广,对废气、废热、太阳能和低温位热能的利用具有重要作用[5-7]。此外,由于机内的制冷剂为水,避免了传     

低温微波技术在化学研究中的应用

低温微波技术可用于降低微波反应时体系的温度,减少或消除微波辐射时速热效应带来的副反应,具有快速高效、反应均匀、安全环保等优势,在化学研究中得到了广泛关注和应用。本文介绍了低温微波技术的实现方法,综述了近年来该技术在蛋白质研究、合成反应、天然产物研究和微波化学机理研究等领域中的应用,并展望了低温微波技术的发展方向。     

磁制冷材料实用化研究进展

作为新一代的制冷技术,磁制冷技术已经进入到实用化研究阶段.主要评述了最有希望实用化的La-Fe-Si系磁制冷材料的研究进展,总结了材料的成相机制,以及热处理时间、温度、不同元素等因素对成相规律的影响,介绍了最新的制备加工工艺和氢化工艺,并讨论了 La-Fe-Si材料在磁制冷机中的应用进展,展望了磁制冷材料的发展趋势.     

Adirectly Coupled Microwave-Induced Plasma Atomic Emission Liquid Chromatograpy Detector for Nonmetals: Preliminary Characterization with Halides and Oxohalogen Salts

Abstract

A liquid chromatography system is directly coupled to a moderate power helium microwave induced plasma for the selective determination of no metals in aqueous solutions. The detector is a large volume helium microwave-induced plasma operated at 500 watts with a helium support gas flow of 21L/min. A sample set of halides and oxohalgen salts are separated by ion exchange chromatography and introduced into the plasma as mist generated with an ultrasonic nebulizer. Detection limits range from 1.5 to 6 μg. Calibration plots are presented. Selectivity is observed when monitoring the elemental signals of co-eluting peaks.     

The eigenenergies for ~3S excited states of the helium atom with CFPHGLF method

The matrix elements of the correlation function between symmetric potential harmonics were first simplified into the analytical summation of the grand angular momentum. The correlation-function potential-harmonic and generalized Laguerre function method (CFPHGLF) proposed by us recently was then applied to directly solve the Schrodinger equation for n3S(n=2-5) excited states of the helium atom. With only 12 PHs, the convergent eigenenergies of 23S, 33S, 43S and 53S states were 2.17427, 2.06849, 2.03644, 2.02257 Eh, respectively. The errors only were 0.00096, 0.00020, 0.00007, 0.00005 Eh, when compared with the exact Hylleraas variational results respectively.     

Optical emission spectroscopy of electron-cyclotron-resonance-heated helium mirror plasmas

In this experiment emission spectroscopy in the 3000–5000 Å range has been utilized to determine the electron temperature (15–60 eV) and ion density (2–5 x 10¹¹ cm^–3) of helium plasmas produced by the Michigan mirror machine⁽¹⁾ (MIMI). The plasma is generated and heated by whistler-mode electron-cyclotron resonance (ECR) waves at 7.43 GHz with 400–900 W power in 80-ms-long pulses. Gas fueling is provided at the midplane region by a leak valve with a range in pressure of 3 x 10 to 2 x 10⁴ Torr. Emission line intensities are interpreted using a model of the important collisional and radiative processes occurring in the plasma. The model examines secondary processes such as radiation trapping, excitation transfer between levels of the carne principle quantum number, and excitation front metastable states for plasmas in the parameter range of MIMI (n _c = 1–6 x 10¹¹ cm^–3). Front the analysis of line intensity ratios for neutral helium, the electron temperature is measured and its dependence upon the gas pressure and microwave power is determined. These temperatures agree with those obtained by Langmuir probe measurements. Art analysis of the line intensity ratio between singly ionized helium and neutral helium yields a measurement of the ion density which is in good agreement with electron density measurements made by a microwave interferometer.     

氦气置换过程中未知杂质分析

用美国GOW—MAC公司的气相色谱仪和Agilent公司的气相色谱仪对某卫星气体贮箱在氦气置换化验过程中发现的未知杂质进行试验分析,经分析未知杂质的来源可能是所用气体贮箱处理时的残留物。试验发现,氧化剂贮箱氦气和燃烧剂贮箱氦气经3次氦气置换后未知杂质的色谱峰消失。提出了消除未知杂质的的建议。     

The one-dimensional extended Bose-Hubbard model

We use the finite-size, density-matrix-renormalization-group(DMRG) method to obtain the zero-temperature phase diagram of the one-dimensional, extended Bose-Hubbard model, for mean boson densityρ = 1, in theU-V plane (U andV are respectively, onsite and nearest-neighbour repulsive interactions between bosons). The phase diagram includes superfluid (SF), bosonic-Mott-insulator(MI), and mass-density-wave (MDW) phases. We determine the natures of the quantum phase transitions between these phases. Dedicated to Professor C N R Rao on his 70th birthday     

氦离子化气相色谱仪的实验条件及其应用

论述了氦离子化气相色谱仪的原理、构造以及与该仪器用密切相关的多种影响因素。同时还介绍了该仪器的广泛应用以及在分析测试中的一些技巧,尤其是在气体工业和半导体制造工业所用化学品的分析。     

Energy-transfer processes in decaying helium-cadmium plasmas

Light absorption and emission spectroscopy were used in studies of the time dependences of the CdII spectral emission and He^m(2³S) number density in the stationary afterglow of helium-cadmium mixtures. Transitions from 12 CdII energy levels were monitored in the afterglow. The five CdII states below 20 eV are produced, either directly or via cascading, by the Penning ionization of Cd by He^m(2³S). The remaining CdII states studied are produced by the chargeexchange excitation of Cd by He⁺. No evidence was found for the production of CdII energy levels by charge transfer between Cd and He ₂ ⁺ or by Penning ionization of Cd by He ₂ ^m (2³ _u ⁺ ). A value of (5.4±0.3)×10^–10 cm³ sec^–1 was measured for the reaction rate coefficient for the Penning ionization of Cd by He^m(2³S), and a value of (2.1±0.2)×10^–10 cm³ sec^–1 was measured for the reaction rate coefficient for charge exchange between He⁺ and Cd at a gas temperature of 200°C.     

On the validity of complete basis set extrapolation formula optimized for the equilibrium distance applied to the potential energy surface for the correlation energy of the helium dimer

Full configuration interaction calculations are performed for He₂ using various orbital basis sets of the aug‐cc‐pVXZ type, with the correlation energies being extrapolated to the complete basis set (CBS) limit. A two‐point CBS extrapolation formula has been utilized for such a purpose. It is shown that the extrapolation formula with the offset parameter k(R) optimized for the equilibrium distance is not uniformly applicable to He He distances in the very short region of the potential energy curve. The offset parameter k(R) in the repulsive region of the potential energy curve can be largely different with the one in the long‐range distances especially in the cases of basis‐sets with large cardinality number. It is also noticed that the accuracy of this extrapolation scheme may not be improved with the increasing of the cardinality number.