Magnetocaloric effect in Er-Al-Co bulk metallic glasses

A series of Er-Al-Co bulk metallic glasses (BMGs) have been prepared by the copper mold casting method. The glass forming ability and magnetocaloric effect (MCE) for these alloys have been investigated. The second-order magnetic transition from para-magnetic to ferromagnetic states takes place at about 9 K. These BMGs exhibit excellent MCE because of their large effective magneton number; Er56Al24Co20 BMG has a maximum entropy change and refrigeration capacity of 16.06 J kg-1 K-1 and 546 J kg-1,respectively,under the field of 50 kOe (10 kOe=795.775 kA/m) indicating that these BMGs are potential candidate magnetic materials for hydrogen liquefaction.     

Transition-metal-based magnetic refrigerants for room-temperature applications.

Magnetic refrigeration techniques based on the magnetocaloric effect (MCE) have recently been demonstrated as a promising alternative to conventional vapour-cycle refrigeration. In a material displaying the MCE, the alignment of randomly oriented magnetic moments by an external magnetic field results in heating. This heat can then be removed from the MCE material to the ambient atmosphere by heat transfer. If the magnetic field is subsequently turned off, the magnetic moments randomize again, which leads to cooling of the material below the ambient temperature. Here we report the discovery of a large magnetic entropy change in MnFeP0.45As0.55, a material that has a Curie temperature of about 300 K and which allows magnetic refrigeration at room temperature. The magnetic entropy changes reach values of 14.5 J K-1 kg-1 and 18 J K-1 kg-1 for field changes of 2 T and 5 T, respectively. The so-called giant-MCE material Gd5Ge2Si2 (ref. 2) displays similar entropy changes, but can only be used below room temperature. The refrigerant capacity of our material is also significantly greater than that of Gd (ref. 3). The large entropy change is attributed to a field-induced first-order phase transition enhancing the effect of the applied magnetic field.     

室温磁制冷材料的研究现状

本文简要介绍了磁制冷的原理、历史,简述了磁热效应的表征,概述了近年来各室温磁制冷材料的研究进展及最新研究成果,展望了室温磁制冷材料的发展趋势。     

Designing metallic glass matrix composites with high toughness and tensile ductility

The selection and design of modern high-performance structural engineering materials is driven by optimizing combinations of mechanical properties such as strength, ductility, toughness, elasticity and requirements for predictable and graceful (non-catastrophic) failure in service. Highly processable bulk metallic glasses (BMGs) are a new class of engineering materials and have attracted significant technological interest. Although many BMGs exhibit high strength and show substantial fracture toughness, they lack ductility and fail in an apparently brittle manner in unconstrained loading geometries. For instance, some BMGs exhibit significant plastic deformation in compression or bending tests, but all exhibit negligible plasticity (<0.5% strain) in uniaxial tension. To overcome brittle failure in tension, BMG-matrix composites have been introduced. The inhomogeneous microstructure with isolated dendrites in a BMG matrix stabilizes the glass against the catastrophic failure associated with unlimited extension of a shear band and results in enhanced global plasticity and more graceful failure. Tensile strengths of approximately 1 GPa, tensile ductility of approximately 2-3 per cent, and an enhanced mode I fracture toughness of K(1C) approximately 40 MPa m(1/2) were reported. Building on this approach, we have developed 'designed composites' by matching fundamental mechanical and microstructural length scales. Here, we report titanium-zirconium-based BMG composites with room-temperature tensile ductility exceeding 10 per cent, yield strengths of 1.2-1.5 GPa, K(1C) up to approximately 170 MPa m(1/2), and fracture energies for crack propagation as high as G(1C) approximately 340 kJ m(-2). The K(1C) and G(1C) values equal or surpass those achievable in the toughest titanium or steel alloys, placing BMG composites among the toughest known materials.     

Zr_(55)Al_(10)Ni_5Cu_(30)大块金属玻璃的晶化行为研究

分别在603 K、653 K、683 K、723 K、753 K、793 K和0.5 h、1 h、2 h、3 h、5 h的保温时间下对Zr55Al10Ni5Cu30大块金属玻璃进行了退火热处理.采用x射线衍射(XRD)法分析了退火后Zr55Al10Ni5Cu30大块金属玻璃的弛豫和晶化相析出的过程,计算了不同温度下结晶度和纳米晶粒尺寸的大小.通过差示扫描量热(DSC)法分析了Zr55Al10Ni5Cu30大块金属玻璃的热稳定性.Kjssinger曲线分析表明,Zr55Al10Ni5Cu30大块金属玻璃弛豫后晶化激活能高于其淬态的晶化激活能,退火温度对大块金属玻璃热稳定性有显著影响.     

Effect of Mo on properties of the industrial Fe-B-alloy-derived Fe-based bulk metallic glasses

The experimental results concerning the effects of Mo on the glass-forming ability (GFA), thermal stability, and mechanical, anticorrosion, and magnetic properties of an (Fe71.2B24Y4.8)96Nb4 bulk metallic glass (BMG) were presented. An industrial Fe-B alloy was used as the raw material, and a series of Fe-based BMGs were synthesized. In BMGs with the Mo contents of approximately 1at%-2at%, the cast alloy reached a critical diameter of 6 mm. The hardness and fracture strength also reached their maximum values in this alloy system. However, the anticorrosion and magnetic properties of the BMGs were not substantially improved by the addition of Mo. The low cost, good GFA, high hardness, and high fracture strength of the Fe-based BMGs developed in this work suggest that they are potential candidates for commercial applications.     

Influence of Cu content on the mechanical properties and corrosion resistance of Mg-Zn-Ca bulk metallic glasses

(Mg_66.2Zn_28.8Ca₅)_100?xCu_x (at%, x = 0, 1, 3, and 5) bulk metallic glasses (BMGs) of 2 mm in diameter were prepared by the conventional copper mold injection casting method. Besides, the influence of Cu content on the microstructure, thermal stability, mechanical properties, and corrosion behavior of Mg-Zn-Ca BMGs was investigated. It is found that the addition of Cu decreases the glass-forming ability of Mg-Zn-Ca BMGs. Crystalline phases are precipitated at a higher Cu content, larger than 3at%. The compressive fracture strength of Mg-Zn-Ca BMGs is enhanced by the addition of Cu. With the formation of in-situ composites, the compressive strength of the Mg-Zn-Ca alloy with 3at% Cu reaches 979 MPa, which is the highest strength among the Mg-Zn-Ca alloys. Furthermore, the addition of Cu also results in the increase of corrosion potential and the decrease of corrosion current density in Mg-Zn-Ca BMGs, thereby delaying their biodegradability.     

块体非晶合金的室温力学行为研究新进展

块体非晶合金由于具有优异的力学性能、物理性能、化学性能,从而得到广泛研究.本文综述了块体非晶合金室温力学行为研究的最新进展,详细介绍了块体非晶合金的室温塑性、屈服行为以及变性机制.     

Room temperature plastic deformation behavior of ZrCuNiAl bulk metallic glasses

The Zr_62.55Cu_17.55Ni_9.9Al₁₀ bulk metallic glass (BMG) was prepared by using copper-mold suction-casting. X-ray diffraction and differential scanning calorimetry were utilized to determine its structure and thermal stability. Uniaxial compression and Rockwell indentation tests were adopted to study the plastic deformation behavior at room temperature. The results show that the glass transition temperature and the onset temperature of exothermic reaction of the BMG are 651.5 and 748 K, respectively. During the compression test, the BMGs undergo an engineering strain of about 2.5%, i.e., true strain of 2.8%, and then fracture. The BMGs deform via the formation and propagation of shear bands. Under indentation loading, the BMGs deform through the formation of radiation-like and circular shear bands. The circular shear bands form earlier than the radiation-like ones. The formation mechanism of shear bands in the BMGs was analyzed and discussed.     

解淀粉芽孢杆菌GSBa-1产凝乳酶培养基组成的优化

从甜酒曲中分离筛选得到1株解淀粉芽孢杆菌菌株GSBa-1,为了提高该菌株液态发酵产凝乳酶的能力,采用单因素实验和响应面法优化其产酶培养基组成。通过单因素实验分析了碳源、氮源、金属盐、磷源对菌株GSBa-1产凝乳酶的影响,并采用响应面法对产酶培养基中麦芽糖、蛋白胨和酵母浸粉含量3个主要因素的优化组合进行了定量研究,确定解淀粉芽孢杆菌GSBa-1产凝乳酶的优化培养基组成为:麦芽糖1.93g/L、蛋白胨10.89g/L、酵母浸粉2.15g/L。在此优化培养基培养条件下,该菌株产凝乳酶活力可达(562.57±7.67)Su/mL,接近理论预测值537.10Su/mL,且平均误差为4.53%。优化后解淀粉芽孢杆菌GSBa-1产凝乳酶活力比基础培养基提高了1.88倍。     

Deformation behavior during nanoindentation in Ce-based bulk metallic glasses

Recently, bulk metallic glasses (BMGs) have at- tracted a great deal of attention due to their extremely high strength, improved wear resistance and excellent corrosion resistance[1-7]. However, it is known that their structural applications are currently…     

基于最小分类错误训练的神经网络分类器设计

提出了一种基于最小分类错误（MCE）训练的采用多层感知器（MLP）结构的模式分类器设计方法。这是一种以分类错误率最小化为目标的模式分类器设计方法，将它用于MLP分类器设计能够进一步提高分类器的性能。采用MLP实现MCE训练中的分类损失计算，从而将MCE训练过程与MLP分类器设计统一在一个神经网络结构中，通过BP算法予以实现。这不仅能达到提高MLP分类器性能的目的，而且简化了它的设计过程。     

大豆磷脂对大鼠实验性高脂血症的预防

研究了大豆磷脂的降血脂作用,大鼠在食用高脂饲料的同时灌服大豆磷脂0.75g.kg^-1.d^-1-3.00g.kg^-1.d^-1,并于实验前,实验15d和21d时分别测血清总胆固醇（TC),甘油三酯（TG）,高密度脂蛋白－胆固醇（HDL－C）,低密度脂蛋白－胆固醇（LDL－C）的浓度,结果表明,大鼠在食用高脂饲料的同时,灌服大豆磷脂3.00g.kg^-1.d^-115d时,血清HDL－C浓度显著升高（P＜0．05）,LDL－C浓度显著降低（P＜0．05）;21d时,0.75g.kg^-1.d^-1-3.00g.kg^-1.d^-1大豆磷脂均能使血清TC浓度降低（P＜0．05）,降幅28．8％－49．6％,说明大豆磷脂对大鼠实验性高脂血症有预防作用。     

不完全投影据图像重建的最小交叉熵算法

提出图像重建的最小交叉熵算法,详细推导了算法的有关公式,并给出程序实现框图.计算机模拟结果表明:最小交叉熵算法的性能优于最大熵算法.     

Itinerant-electron metamagnetic transition and giant magnetic entropy change in La0.8Ce0.2Fe11.4Si1.6 compound

Iron-based rare-earth intermetallic compounds LaFe13?xSix (1.2≤x≤2.6) and CeFe13?xSix (2.4≤x≤2.6) both have the cubic NaZn13-type structure with Fm3c(Oh6) space-group symmetry[1―3]. Fujita et al. [4] demonstrated that the cubic NaZn13-type LaFe13?xSi     

Chemical composition dependence of atomic oxygen erosion resistance in Cu-rich bulk metallic glasses

The effect of atomic oxygen(AO) on the surface oxidation of several typical Cu-based bulk metallic glasses(BMGs) was studied in the present work.The AO source using in this study is generated by discharge plasma type ground simulation equipment.The AO erosion/oxidation resistances of the amorphous alloy samples were assessed based on the analysis of mass loss,surface color and microstructure.It is found that these Cu-based BMGs possess good AO erosion/oxidation resistance and their resistance to AO erosion/oxidation strongly depends on the chemical composition.For the samples containing more Ag and/or Cu,the AO erosion/oxidation resistance is weaker.The present result is important for designing new metallic glasses using as space materials.     

甘草中甘草酸的多级逆流提取技术研究

研究利用多级逆流技术提取甘草酸的新方法.采用正交试验考察提取温度、提取时间、级数和液固比对提取效率的影响,确定多级逆流提取甘草酸的最佳工艺条件;在优选出的最佳工艺条件下,考察了提取溶剂对提取率的影响,并与室温冷浸法、超声波法、索氏提取法和微波提取法做了比较.结果表明:多级逆流提取甘草酸的最佳条件为提取温度70℃,单级提取时间60 min,液比6,提取级数为5.在此最佳条件下,多级逆流提取的提取率高于室温冷浸44.3 h、超声波提取40 min、索氏提取4 h、微波萃取54 min的提取率.多级逆流提取具有快速、高效、节能、节约溶剂的特点,用于中草药有效成分的提取,值得推广应用.     

拟环的Jacobson根

Betsch[1]将结合环的Jacobson根引入到拟环N上,得到三种类型的Jacobson根,分别记为(?)_o(N),(?)_1(N),(?)_2(N).Holcombe[2]引入另一种类型的Jacobson根,记为(?)_8(N).本文给出一种介于(?)_2(N)与(?)_3(N)之间的Jacobson根,并证明其一系列的性质。     

EDTA对Cd及Cd-Mn复合污染处理下藜生长的影响

采用盆栽实验方法,研究了在Cd及Cd-Mn复合污染土壤中添加EDTA对藜生长的影响以及对Cd的转运和富集作用.结果表明:单一Cd污染处理下最佳的EDTA添加水平为2.5mmol.kg-1,Cd-Mn复合污染处理下EDTA的添加水平为5.0mmol.kg-1,这时EDTA可以促进藜地下部分的重金属元素向地上部分迁移,藜地上部分含Cd量分别是对照值的1.8倍、3.7倍,同时对Cd的富集系数也有明显提高.     

典型工业区杂草对土壤中重金属吸收特性研究

以沈阳冶炼厂厂区及其附近周围分布的一些常见植物为研究对象，探明其对重金属的吸收特性。结果表明，马齿苋、龙葵、艾蒿和酸浆的地上部分对Cd的吸收能力较强，Cd含量均接近或超过20mg．kg^-1，富集系数接近或超过1，其中艾蒿对Cd和Zn的转运系数分别为173和2．09。植物中Pb的含量均未超过130mg．kg^-1，且富集系数均在0．15以下。20种植物的地上部分Cu含量都在65mg.kg^-1以下，富集系数最大值也仅为0．15。水芹地上部分Zn含量为647．57mg．kg^-1，且富集系数为0．81，转运系数大于1。研究发现的具有潜在应用前景的重金属污染土壤修复植物，均是在自然环境采样分析测试的结果，其对重金属的最大忍耐浓度还需在实验室进一步深入研究。