熔体缓冷制备Pb9.6SbmTe3Se7合金及其热电性能

采用真空封管熔炼缓冷和热压法制备Pb9.6SbmTe3Se7合金样品(m=0.15,0.2,0.25,0.267,0.3,0.35,0.4),研究Sb的掺杂量对热电性能的影响。结果显示,除m=0.4的样品由于Sb含量过多呈金属特性外,随着Sb含量的增加,载流子迁移率降低,电导率减小,热导率呈减小趋势,且都明显低于PbTe的热导率。HRTEM显示样品中广泛存在着不同形貌的纳米微区,增加了声子散射,有效降低热导,提高热电优值。其中Pb9.6Sb0.3Te3Se7样品在677K时ZT达到的1.14,与目前可复现的n型掺杂PbTe基材料的最大ZT值相比,增长近50%。     

基于分步式双重调控n型(PbTe)1-x-y(PbS)x(Sb2Se3)y体系的热电传输特性

PbTe在中温区热电材料中广受关注, 然而, n型PbTe因其较低的载流子浓度和复杂的能带结构, 其热电性能难以大幅提升。本研究通过分步式添加PbS、Sb₂Se₃组元以调控n型PbTe基体的热、电传输性能。研究发现, PbS与Sb₂Se₃组元可分别提升功率因子和降低热导率。通过扩大带隙、增加点缺陷、第二相弥散等途径可改善能带, 加剧散射, 从而有效提升热电优值ZT。其中(PbTe)_0.94(PbS)_0.05(Sb₂Se₃)_0.01表现出最佳的热电性能, 700 K时ZT最大值为1.7, 且ZT平均值较PbTe基体显著提高, 这表明分步式双组元调控可为改善其它材料体系的热电性能提供技术途径。     

Mg_2(Si,Sn)基热电材料研究进展

热电材料又称温差电材料,是利用固体中载流子和声子的输运及其相互作用实现热电相互转换的新型功能材料。热电材料可以将太阳辐射、工业废热、汽车尾气余热等转换成电能,对缓解污染和能源压力有重要意义。此外,热电制冷器件也具有低噪音、无污染、体积小和反应灵敏等压缩机制冷所不具备的优点,近年来受到研究者的广泛关注。材料的热电转换性能通过热电优值ZT表征,如何提高热电转换效率(即提高ZT值)成为研究者关注的热点。作为最具潜质的中温区热电材料之一,Mg2(Si,Sn)基热电材料由于其低廉的成本和无毒无害等优点,过去十几年被广泛研究。近年来,研究者们尝试了多种方法(如高频感应熔炼、固相反应加热压烧结、两步固相反应加放电等离子烧结和快速凝固加等离子活化烧结等)来获得高质量的Mg2(Si,Sn)块体。除此之外,研究者们还利用能带工程、单元素和双元素掺杂等方法来进一步提高材料的ZT值,这些方法可以使合金的ZT值从0.5提高到1.55。但是这类基于固相反应加烧结来制备纳米级晶粒块体材料的方法存在反应不完全和服役过程中晶粒易发生长大等问题。而且由于Mg元素极高的化学活泼性和挥发性,以及组成合金的各元素之间较大的熔点差,给熔炼法制备Mg2(Si,Sn)块体材料带来了很大的困难,极大地限制了材料热电性能的优化。因此,如何制备高质量的Mg2(Si,Sn)块体材料成为亟待解决的难题。本文综述了Mg2(Si,Sn)基热电材料制备方法的最新研究进展,以及能带工程和掺杂元素的选择等ZT值优化途径,提出存在的问题和未来的发展方向。同时,本文提出采用材料定向凝固方法制备Mg2(Si,Sn)单晶材料,并利用单晶各向异性来优化其热电性能,此方法有望解决纳米级晶粒块体材料服役过程中出现晶粒长大而导致的性能恶化问题,同时为此类合金热电材料的性能优化提供了新的思路。     

不同元素替代掺杂化合物M_(0.04)Ti_(0.96)S_2(M=Ni,Al,Mg)的热电性质

层状结构TiS2具有准二维结构,高热电势(室温时S≈250μV/K)和大的热电功率因子,作为热电材料具有很好的开发和应用前景。通过固相反应法,我们分别用原子量大于和小于Ti的原子部分替代Ti位引入替位缺陷(NiTi″,AlTi′,MgTi″),合成了不同元素替代掺杂化合物M0.04Ti0.96S2(M=Ni,Al,Mg),在5-310K的温度范围内研究了各化合物的电阻率、热导率及热电势率与温度的对应关系。结果表明Ni、Al、Mg三种元素的掺杂均引起了主体材料从金属性到半导体导电性质的转变,且在低温范围内呈现莫特二维变程跳跃电导规律,lnσ∝T-1/3,表明了TiS2的二维导电机制。值得注意的是:①Mg、Al的掺杂引起了热电势绝对值的显著增高,特别是Al掺杂的化合物在310K时热电势率为-500μV/K,达到了纯TiS2的200%;②Ni掺杂也在整个研究温区引起热导率的明显下降,而Mg、Al的掺杂却在整个研究温区引起热导率的明显升高。由于电阻率的增大,Ni、Al的掺杂均没能使得材料的ZT值有所提高,而Mg的掺杂明显地提高了TiS2的ZT值,在310K其ZT值是纯TiS2的1.6倍。这表明元素掺杂是提高材料的热电优值的有效途径之一。     

Sb/Al/Zn多掺杂Mg2Si热电材料的制备及性能研究

采用放电等离子体烧结技术,制备了Sb/Al/Zn多掺杂Mg_2Si热电材料,利用粉末X射线衍射、霍尔效应和标准四探针电导率研究了Mg_2Si热电材料的电输运特性和热电性能。结果表明,Sb/Al/Zn多掺杂Mg_2Si热电材料具有良好的电输运和热电性能。采用放电等离子体烧结技术在880 K时,Sb0.5%Zn0.5%掺杂Mg_2Si热电材料具有最大热电优值为0.964,与PbTe基热电材料相当。根据电导率(σ)、塞贝克系数(S)和热导率(κ)的温度依赖性计算掺杂Mg_2Si热电材料在300～900 K的热电性能和热电图优值(ZT),同时根据霍尔系数确定掺杂Mg_2Si热电材料的电子浓度(N)。     

La掺杂n型Mg2Si基半导体的热电性能研究

采用感应熔炼然后热压的方法制备了La掺杂Mg2Si基热电材料Mg2-xLaxSi(x=0、0.002、0.005、0.010、0.015).La在Mg2Si中占Mg位,当x≥0.005时,出现第二相LaMg.性能测试表明,Mg2-xLaxSi的导电类型为n型,Seebeck系数的绝对值随La含量的增多而减小,电导率和热导率均随La含量的增多而增大,在测试温度范围内,Mg1.995La0.005Si具有最高的ZT值,在774K温度下达到0.42.     

硅化镁热电材料的一步合成法制备及性能表征

采用MgH2代替Mg粉,与Si粉和Bi粉按照一定比例混合后,在FAPAS(电场激活压力辅助合成)炉中,用一步合成法制备Bi(1%(摩尔分数))掺杂的硅化镁(Mg2Si)块体热电材料。系统研究了一步合成法烧结制备Mg2Si基热电材料的工艺过程,对试样进行了成分和热电性能分析,并且与管式炉+FAPAS(T+F)法制备出的样品进行比较。实验结果表明,一步合成法制备块体Mg2Si基热电材料效率高,产物具有纯净和纳米的特征,有效降低了热导率,从整体上改善了材料的热电性能。同时,适度过量的Si有助于提高材料的热电性能,配比为1.95∶1的样品在热电性能上要优于配比为2∶1的样品,在725K时,前者的ZT值可达0.54。     

PbTe基合金的热压制备与热电性能

以Pb粉,Te粉和PbI2粉为原料,采用固相合成方法合成了掺杂PbI2(0.03,0.05,0.1,0.3at%)N型PbTe合金,XRD分析表明,合金具有NaCl型面心立方结构。采用热压烧结法将PbTe合金粉末烧结成块体材料,运用XRD,SEM方法对材料的物相组成和形貌进行了表征,表明热压烧结后材料仍保持NaCl型面心立方结构,出现偏析现象,分为富Te相和富Pb相,其中富Pb相呈现片状。通过材料热电性能参数的测试,研究了20MPa下不同热压烧结温度,不同含量PbI2掺杂对材料热电性能的影响,结果表明合理热压烧结温度对材料的热电性能提高起到关键作用,当PbI2含量为0.1at%时,PbTe合金在350℃具有最高的功率因子2.48mW/(m.K2)。     

Na、Ga共掺杂对n型Bi_2Te_(2.7)Se_(0.3)电热输运性能的影响

采用真空熔炼及热压烧结方法制备了Na和Ga共掺杂n型Bi2Te2.7Se0.3热电材料。XRD结果表明,Na0.04Bi1.96-xGaxTe2.7Se0.3块体材料的XRD图谱与Bi2Te2.7Se0.3的图谱对应一致。通过EDAX技术对Na0.04Bi1.96-xGaxTe2.7Se0.3块体材料的成分进行了分析,无氧化现象。在298~523K温度范围内,在垂直于热压方向对样品的电热输运性能进行了测试分析,结果表明Na和Ga共掺杂可以有效地提高Bi2Te2.7Se0.3的载流子浓度,从而使电导率得到明显改善,但同时Seebeck系数有不同程度的损失。由于晶格热导率减小,Na掺杂及共掺杂样品Na0.04Bi1.96-xGaxTe2.7Se0.3(x=0.04)均使热导率降低。当Na掺杂浓度为0.04时,随着Ga掺杂浓度的增加,热导率呈现递增的现象,Na和Ga共掺杂样品Na0.04Bi1.96-xGaxTe2.7Se0.3(x=0.04)的热电优值获得了较明显的提高,在398K时的最大ZT值为0.75。     

化工新型材料

美国新型热电材料性能跨越重要里程碑热电材料把热能直接转化为电能,是人类梦寐以求的明星材料。理想的热电材料应具有较高的热电势和电导率、较低的热传导系数。由这3个指标加上热源温度形成了衡量热电材料品质的热电优值——ZT值。一般认为ZT达到2.0以上方有实际应用价值,但过去热电材料的最高ZT只有1.6～1.8。     

Insertion of triangulated surfaces into a meccano tetrahedral discretization by means of mesh refinement and optimization procedures

In this paper, we present a new method for inserting several triangulated surfaces into an existing tetrahedral mesh generated by the meccano method. The result is a conformal mesh where each inserted surface is approximated by a set of faces of the final tetrahedral mesh. First, the tetrahedral mesh is refined around the inserted surfaces to capture their geometric features. Second, each immersed surface is approximated by a set of faces from the tetrahedral mesh. Third, following a novel approach, the nodes of the approximated surfaces are mapped to the corresponding immersed surface. Fourth, we untangle and smooth the mesh by optimizing a regularized shape distortion measure for tetrahedral elements in which we move all the nodes of the mesh, restricting the movement of the edge and surface nodes along the corresponding entity they belong to. The refining process allows approximating the immersed surface for any initial meccano tetrahedral mesh. Moreover, the proposed projection method avoids computational expensive geometric projections. Finally, the applied simultaneous untangling and smoothing process delivers a high‐quality mesh and ensures that the immersed surfaces are interpolated. Several examples are presented to assess the properties of the proposed method.     

Certification Institutions Expected to Update and Transfer Information on Present Standards

Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.……     

Flow calorimeter for enthalpy increment measurements on condensed gases

A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa.     

Refrigerators Enter a New Era of Health Preservation Frestech initiates the establishment of China's first standard for household sterilization refrigerators

On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.……     

Optimum-Simulation von Ernteprozessen

Zusammenfassung Bei der Gestaltung von Ernteprozessen — beispielsweise des Prozesses Mähdrusch, Körnertransport und -abnahme — als transportverbundene Fließarbeitsverfahren mit mindestens zwei verschiedenen Arbeitsmitteln gibt es einen großen Optimierungsspielraum. Solche Prozesse sind mehrstufige Bedienungsprozesse mit gemischter Anordnung der Bedienungseinrichtungen. Außerdem besitzen sie stark ausgeprägte räumliche Aspekte. Es wird vor allem gezeigt, welche Merkmale solcher Prozesse in Simulationsmodellen abgebildet sein müssen, welche Zielgrößen in Abhängigkeit von welchen Einflußgrößen unter Berücksichtigung welcher Prozeßbedingungen ermittelt werden sollten und wie der Bewertungsprozeß zur Ermittlung der gewünschten Informationen gestaltet werden muß.     

A study of centrifugal cast high boron high speed steel

In the present study a high‐boron high speed steel (HSS) roll material was designed. Many expensive alloy elements have been substituted by cheap boron alloy, and high‐boron high speed steel roll has been manufactured by centrifugal casting method. The microstructures, mechanical properties and wear resistance of centrifugal casting high‐boron high speed steel roll have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), and X‐ray diffraction (XRD) analysis, hardness test, impact test and wear test. The results indicated that the solidification microstructures of high‐boron high speed steel roll consisted of M₂(B,C), (W,Mo)₂(B,C), M₃(B,C), M₂₃(B,C)₆ type borocarbides and martensite, a small amount of retained austenite. Borocarbides were continuously distributed over the grain boundary. After quenching from 1050 °C, local broken network appeared in partial borocarbides, and fine secondary borocarbide precipitated from the matrix. After tempering from 525 °C, the amount of precipitated borocarbide increased significantly. After heat treatment, the hardness of high‐boron high speed steel roll excelled 60 HRC, and its impact toughness excelled 8.0 J/cm². The single groove steel rolling amount of high‐boron high speed steel rolls increases by 500% than that of bainite cast iron roll, when the rolls are used in K₁ mill housing of bar mill.     

Thixotropy of Systems with Shear Thinning and Plastic Flow Behavior

The definition of the thixotropy is a decrease in viscosity with time in shear and a subsequent recovery of viscosity after the shear deformation is removed.We ...     

Brainstorming for ISO Strategy 2016-2020

正Responding to ISO’s appeal for survey for the to-be-developed ISO Strategy Plan for 2016-2020,SAC hosted a special workshop over the needs and comments of various fi elds on June 8 in Beijing.The workshop was attended by ISO President-elect and Ansteel General Manager Zhang Xiaogang,SAC Vice-Administrator Yu Xinli,and 30 experts from     

CNAS Passes APLAC's PTP Review

正The review group of Asia Pacific Laboratory Accreditation Cooperation(APLAC)carried out a 4-day peer review of the proficiency testing provider(PTP)for China National Accreditation Service for Conformity Assessment(CNAS)from July 28 to 31,2014.CNAS passed the PTP review with excellent performance.Two senior peer reviewers of APLAC made a comprehensive,rigorous and detailed review of CNAS’s PTP accreditation activities,and made the on-spot inspection of the review groups in Shanghai and Shenzhen respectively.