Ag-Bi-Sb-Te四元合金的热电性能

以Ag、Bi、Sb、Te为原料在1373K真空熔炼合成了AgxBi0.5Sb1.5-xTe3(x=0～0.5)合金.微观组织和结构分析显示,真空熔炼的合金具有层状组织特征,属R3m晶体结构,当x≥0.2时出现面心立方AgSbTe2相.电学性能测试表明,在300～580K温度范围内合金的电导率随温度升高而下降,掺Ag后合金的电导率明显提高,掺Ag量为x=0.1试样的最大值达到2.3×105S/m.材料的Seebeck系数均为正值,表明掺Ag合金为p型半导体.     

K、Al共掺杂Bi0.5Sb1.5Te3热电材料的制备及性能

采用真空熔炼及热压方法制备了K和Al共掺杂P型Bi0.5Sb1.5Te3热电材料。XRD分析结果表明,K0.04Bi0.5Sb1.5-x Alx Te3块体材料的XRD图谱与Bi0.5Sb1.5Te3的图谱完全对应,SEM形貌分析表明材料具有一定的层状结构和微孔。K和Al共掺杂提高了Bi0.5Sb1.5Te3在室温附近的Seebeck系数。除了K0.04Bi0.5Sb1.34Al0.12Te3样品的300K和400K以上的高温区,以及共掺杂样品的500K高温附近之外,K和Al共掺杂均使Bi0.5Sb1.5Te3材料的电导率降低。在300~500K温度范围内,K0.04Bi0.5Sb1.42Al0.04Te3样品的热导率均小于Bi0.5Sb1.5Te3的热导率。在300~350K温度范围内,K0.04Bi0.5Sb1.42Al0.04Te3样品的热电优值较Bi0.5Sb1.5Te3有较大幅度的提高。     

Ag_2Te掺杂对p型Bi_(0.5)Sb_(1.5)Te_3块状合金热电性能的影响

采用真空熔炼、机械球磨及放电等离子烧结技术(SPS)制备得到了(Ag2Te)x(Bi0.5Sb1.5Te3)1-x(x=0,0.025,0.05,0.1)系列样品,性能测试表明,Ag2Te的掺入可以显著改变材料的热电性能变化趋势,掺杂样品在温度为450~550K范围内具有较未掺杂样品更优的热电性能.适当量的Ag2Te掺入能够有效地提高材料的声子散射,降低材料的热导率.在测试温度范围内,(Ag2Te)0.05(Bi0.5Sb1.5Te3)0.95具有最低的晶格热导,室温至575K范围内保持在0.2~0.3W/(m·K)之间,在575K时,(Ag2Te)0.05(Bi0.5Sb1.5Te3)0.95试样具有最大热电优值ZT=0.84,相较于未掺杂样品提高了约20%.     

机械球磨-热压法制备Bio.5Sb1.5Te3热电材料

用机械球磨-热压法制备了Bi0.5Sb1.5Te3热电材料,分别研究了机械球磨时间对合成Bi0.5Sb1.5Te3合金相的影响和烧结温度对其热电性能的影响.结果表明Bi、Sb、、Te原始混合粉末高能球磨10 h以后,就可以完全合金化,生成Bi0.5Sb1.5Te3相.球磨10h的粉末分别在400、450和520℃下热压烧结成型,烧结样品的密度随烧结温度的增大而增加,Seebeck系数和电阻率随烧结温度的升高而降低     

Ba填充方钴矿化合物的高压合成及热电性能

利用高压固相反应方法成功合成了Ba填充型方钴矿化合物BaxCo4Sb12(0.2≤x≤0.8),并探讨了Ba填充及合成压强对化合物电学性能的影响.采用XRD和SEM确定了相组成和晶体形貌,并在室温下测试了材料的电阻率及Seebeck系数.实验结果表明:高压可有助于提高Ba在CoSb3中的填充含量;化合物BaxCo4Sb12的晶粒直径处于微纳米级而且样品中含有大量的微气孔;在合成压强为4.25GPa时,样品BaCoSb获得最高的功率因子13.19μW/(cm.K2).     

Co4Sb12-xSex的高温高压合成及电学输运性能研究

利用高压(2～5GPa)固相反应法合成了单相的方钴矿多晶体化合物Co4Sb12-xSex(0≤x≤1.2).室温下对其电阻率(ρ),Seebeck系数(S)以及微观形貌(SEM)进行了测试分析.结果表明,高压固相反应法合成的样品Co4Sb12-xSex具有细小的晶粒和大量的晶界,晶粒直径处于微纳米级.样品的Seebeck系数绝对值随Se置换浓度(x)而增大,电阻率随Se置换浓度x的升高而显著增大.在合成压强为4.25GPa时,样品Co4Sb10.8Se1.2具有绝对值最大的Seebeck系数501.59μV/K,Co4Sb11.9Se0.1获得最大的功率因子值为3.77μW/cm·K2.     

Te掺杂方钴矿CoSb3的溶剂热合成及电学性能

以CoCl2,SbCl3和Te粉为原料,NaBH4为还原剂,用溶剂热方法合成了Te掺杂方钴矿CoSb（3-x）Tex（x=0,0.05,0.1,0.2,0.4）纳米粉末.研究发现,Te含量较高的样品（x≥0.2）有明显的CoTe2等杂相存在.CoSb（3-x）Tex合成粉末的粒径大小在40nm左右,热压后晶粒发生长大,平均晶粒尺寸约为300nm.电学性能测试表明Te掺杂方钴矿CoSb（3-x）Tex的导电类型为n型,Seebeck系数的绝对值随着Te含量的增加而变小,电导率随着Te含量的增加而增大.在测试温度范围内,CoSb（2.8）Te（0.2）具有最高的功率因子,在773K温度下达到2.3×10^-3W·m^-1·K^-2.     

压力对CoSb_(2.750)Te_xGe_(0.250-x) n型方钴矿化合物的电输运性能的影响

采用高温高压方法,在900K的温度条件下,成功合成出CoSb2.750 TexGe0.250-x(x=0.125,0.175,0.200)n型方钴矿化合物,并考察了不同的压力对其电输运性能的影响规律。室温下对样品的电阻率(ρ),Seebeck系数(S)进行了测试分析。电学性能测试表明,方钴矿CoSb2.750 TexGe0.250-x化合物的导电类型为n型,电阻率和Seebeck系数的绝对值随着压力的升高而增加,随着Te掺杂量的增加而降低。功率因子随合成压力增大而降低,随Te掺杂量的增加而升高。CoSb2.750Te0.200Ge0.050在2GPa时具有最大的功率因子为7.59μW/(cm.K2)。     

非晶Ag11In12Te26Sb51薄膜的结晶行为

采用初始化仪使非Ag11In12Te26Sb51薄膜结晶，利用差分扫描量热仪、X射线衍射和光学透过率的测量研究了非晶Ag11In12Te26Sb51薄膜的结晶行为，结果表明，非晶Ag11In12Te26Sb51膜结晶温度约为210℃，熔化温度为481.7℃，结晶活化能Ea=2.07eV/atom；Ag11In23Te26Sb51膜的结晶力学遵循成核和生长机理；在激光致相变过程中可能出现的晶相有AgSbTe2、AhInTe2、Sb和Ag2Te等相；Ag11In12Te26Sb51薄膜的结晶程度受初始化功率和转速的影响。     

Te掺杂方钴矿CoSb3的溶剂热合成及电学性能

以CoCl₂, SbCl₃和Te粉为原料, NaBH₄为还原剂, 用溶剂热方法合成了Te掺杂方钴矿CoSb_3-xTe_x(x=0, 0.05, 0.1, 0.2, 0.4)纳米粉末. 研究发现, Te含量较高的样品(x≥0.2)有明显的CoTe₂等杂相存在. CoSb_3-xTe_x合成粉末的粒径大小在40nm左右, 热压后晶粒发生长大, 平均晶粒尺寸约为300nm. 电学性能测试表明Te掺杂方钴矿CoSb_3-xTe_x的导电类型为n型, Seebeck系数的绝对值随着Te含量的增加而变小, 电导率随着Te含量的增加而增大. 在测试温度范围内, CoSb_2.8Te_0.2 具有最高的功率因子, 在773K温度下达到2.3×10³W·m^-1·K^-2.     

Piezoelectric composites with high sensitivity and high capacitance for use at high pressures

A type of piezoelectric composite has been developed for oceanographic applications. The composites have a large figure of merit (d(h)xg(h) or d(h )xg(h)/tan delta, where d(h ) is the hydrostatic piezoelectric voltage coefficient), a large dielectric constant (K) and low dielectric loss, and great mechanical strength. A shallow cavity between the PZT ceramics and thick metallic electrode is designed to convert a portion of the z-direction stress into a large radial and tangential stress of opposite sign. thereby causing the d(33) and d(31) contributions to d(h) to add rather than subtract, and raising the figure of merit. Theoretical stress analysis was carried out using an axisymmetric finite element method. Experimental results show that the d(h)x g(h), K, and withstandable pressure are extremely high.     

Fracture of high carbon high strength anchor rods

During a heavy windstorm, there was failure of anchors supporting transmission towers. We were given the mandate to examine the reasons for the failure of the anchor rods and suggest measures to prevent such failures from occurring. The study involved the in-depth examination of the chemical composition, microstructures, mechanical properties and fracture morphologies of specimens from failed anchors. Results indicated that the chemical composition, yield and tensile strengths of the anchor rods are within the norm of ASTM standard A722. The chemical composition corresponds to that of AISI 1070 with slightly higher manganese and silicon levels. Microstructure is ferrite–pearlite with dominance of pearlite due to the relatively high carbon content. Fracture surfaces of failed anchor rods exhibited pronounced cleavage facets (cleavage steps and river pattern) indicating that failure mode is brittle and the mechanism of fracture is cleavage. There were no signs for the occurrence of fatigue – any beach mark or striations. Final area of fracture showed traces of ductility (small shallow dimples). To prevent brittle failure of anchor rods, their toughness has to be improved. To achieve this, the potentiality of applying HSLA steel technology of micro alloying and TMCP (thermo mechanical control process) has been suggested.     

Repetitive waveform high frequency, high precision digitizer

A digitizing technique for measuring high-speed phenomena with very high precision is described. A commercially available waveform digitizer using this method is shown to exhibit settling times of less than 5 ns to 0.1% and less than 10 ns to 0.01% after a voltage transition. Also, RMS measurements of sine waves up to 100 MHz show errors on the order of that obtained using a thermal transfer standard     

高刚度高阻尼结构试验研究

利用预置变形碳纤维梁、螺旋弹簧、碟簧和橡胶块构成一种高刚度高阻尼结构,其承载刚度和阻尼均较大。为了便于对高刚度高阻尼结构的力学性能进行评价,提出技术指标,即:等效弹性模量、等效阻尼系数和等效刚度系数。在此基础上,设计静动态力学试验,验证高刚度高阻尼结构设计方法的有效性并评价其力学性能。试验结果表明,高刚度高阻尼结构的等效弹性模量显著大于单个预置变形碳纤维梁;等效阻尼系数随着频率增大而减小,等效刚度系数随着频率增大而增大,分别大于104 Ns/m和107 N/m。由此证明,高刚度高阻尼结构的设计方法有效,且实现了输出刚度和阻尼均较大的设计目标。     

Intermittent bonding for high toughness/ high strength composites

High strength and high toughness are usually mutually exclusive in brittle filament/brittle matrix composites. The high tensile strength characteristic of strong interfacial filament/matrix bonding can, however, be combined with the high fracture toughness of weak interfacial bonding, when the filaments are arranged to have alternate sections of high and low shear stress (and low and high toughness). Such weak and strong areas can be achieved by appropriate intermittent coating of the fibres. The strong regions ensure that the filament strength is picked up; weak areas randomly in the path of running cracks serve to blunt them by the Cook/Gordon mechanism which, in turn, produces long pull-out lengths with an associated large contribution to toughness. Boron-epoxy composites of volume fraction 0.20 to 0.25 have been made in this way which have fracture toughnesses of over 200 kJ m^?2, whilst retaining rule of mixtures tensile strengths (～ 650 MN m^?2). At the volume fractions used, this apparently representsK _IC values greater than 100 MN m^?3/2. An analysis is presented for toughness and strength which demonstrates, in broad terms, the effects of varying the coating parameters of concern. Results show that the “toughness” of interfaces is an important parameter, differences in which may not be shown up in terms of interfacial “strength”. The choice of coating material is crucial in getting the desired effect. Some observations are made upon methods of measuring the components of toughness in composites.     

Behaviour of B-N-Si under high pressure and high temperature

The phase relations of the B-N-Si system have been studied using a quenching method up to 10GPa and 2000 °C using a high-pressure apparatus of the octahedral anvil type. Pressure-temperature conditions for obtaining z-BN (diamond analogue of boron nitride) were delineated for turbostratic BN (t-BN), t-BN/amorphous Si₃N₄ and t-BN/-Si₃N₄. These conditions shift toward higher regimes of temperature as amorphous Si₃N₄ or -Si₃N₄ is incorporated into t-BN. Spontaneous sintering occurringin situ at high pressure yields z-BN-based composite compacts.     

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.     

无钴高强韧钢力学性能研究

本文利用人工神经网络方法研究了化学成分和热处理条件对G50钢力学性能的影响,通过电镜观察分析了合金元素间交互作用形成的组织和第二相的作用,结果C、Cr、Mo提高钢强度,Ni、Mo、Si降低钢强度,C,Mn降低韧性,Cr,Mo,Ni提高韧性.