Enhanced thermoelectric performance of dual-element-filled skutterudites BaxCeyCo4Sb12

Single-phase polycrystalline dual-element-filled skutterudites Ba_xCe_yCo₄Sb₁₂ (0 < x < 0.4, 0 < y < 0.1) are synthesized by the melting–quenching–annealing and spark plasma sintering methods. The electrical conductivity, Seebeck coefficient, thermal conductivity and low-temperature Hall data of these compounds are reported. Our results suggest that there is essentially no difference in electrical transport properties between the dual-element-filled Ba_xCe_yCo₄Sb₁₂ and single-element-filled Ba_yCo₄Sb₁₂ systems. The Ba–Ce co-filling is more effective in lattice thermal conductivity reduction than Ba single filling in the temperature range of 300–850 K. Very low lattice thermal conductivity values less than 2.0 W m^?1 K^?1 are obtained at room temperature. Consequently, enhanced thermoelectric figure of merits (ZT) for these dual-element-filled CoSb₃ skutterudites are achieved at elevated temperatures, in particular ZT = 1.26 at 850 K for Ba_0.18Ce_0.05Co₄Sb_12.02.     

放电等离子烧结原位合成CeyFe1.0Co3.0 Sb12热电材料

以Co、Sb、Fe及Ce为起始原料,采用放电等离子烧结(SPS)技术原位反应合成了填充式Skutterudite化合物Cey Fe1.0 Co3.0 Sb12,并研究了该化合物的合成条件及热电性能.实验结果表明:当y为0～0.30时,用放电等离子烧结法在573 K开始生成Cey Fe1.0 Co3.0 Sb12且在673～873 K时,Cey Fe1.0 Co3.0 Sb12化合物为主晶相,并伴有极少量的FeSb2和Sb相.晶格常数和Seebeck系数随Ce填充分数的增加而呈线性增加,电导率和热导率随Ce填充分数的增加而降低.Cey Fe1.0 Co3.0 Sb12化合物表现为P型传导,Cey Fe1.0 Co3.0 Sb12化合物中Ce的填充分数y为0.30时,Ce0.30 Fe1.0 Co3.0 Sb12化合物具有较高的热电性能,其中在773 K时具有最大的热电优值(ZT值)0.45.     

Effects of Ag doping on thermoelectric properties of Zn4Sb3 at low temperatures

The thermoelectric properties of Ag-doped compounds (Zn_1?xAg_x)₄Sb₃ (x = 0, 0.0025, 0.005, 0.01) have been studied at the temperatures from 15 to 300 K. The results indicate that low-temperature (T < 300 K) thermal conductivity of the moderately doped (Zn_1?xAg_x)₄Sb₃ (x = 0.0025 and 0.005) reduced remarkably as compared with that of Zn₄Sb₃ due to enhanced impurity (dopant) scattering of phonons. Electrical resistivity and Seebeck coefficient were found to increase first and then decrease obviously with the increase in the Ag content, which could be ascribed to the change of carrier concentration presumably due to different Zn positions occupied by Ag upon increasing doping content. Moreover, the lightly doped compound (Zn_0.995Ag_0.005)₄Sb₃ exhibited the best thermoelectric performance due to the improvement in both its electrical resistivity and thermal conductivity, whose figure of merit (at 300 K), ZT, is about 1.3 times larger than that of β-Zn₄Sb₃ obtained in the present study. Present results suggest that proper Ag doping in Zn₄Sb₃ is a promising way of improving its thermoelectric properties.     

High-pressure synthesis of phonon-glass electron-crystal featured thermoelectric LixCo4Sb12

Li-filled CoSb₃, which is inaccessible under ambient pressure, was successfully synthesized with a high-pressure synthesis technique, demonstrating a fast and effective way to broaden elemental species that can be filled into voids of skutterudites. The optimized Li_0.36Co₄Sb₁₂, with a greatly enhanced thermal power factor and much reduced thermal conductivity, has a ZT value of 1.3 at 700 K, the highest among all single elemental filled CoSb₃ materials at this temperature. In addition, an instructive linear relationship between the Einstein temperatures of the distinct rattling fillers and their ionic radii is revealed, which as a reference can easily be applied to the multiple elemental filling strategy for selecting suitable filling elemental species to reduce the lattice thermal conductivity more effectively.     

Enhanced thermoelectric performance of ternary compound Cu3PSe4 by defect engineering

The diamond-like compound Cu₃PSe₄ with low lattice thermal conductivity is deemed to be a promising thermoelectric material,which can directly convert waste heat into electricity or vice versa with no moving parts and greenhouse emissions.However,its performance is limited by its low electrical conductivity.In this study,we report an effective method to enhance thermoelectric performance of Cu₃PSe₄ by defect engineering.It is found that the carrier con...     

Anticorrosive performance of epoxy/clay nanocomposites pretreated by hexafluorozirconic acid based conversion coating on St12

Abstract

In this research, epoxy composites were prepared using different loadings (0.5, 0.8, 1, 2 and 3 wt-%) of clay nanoparticles. Fourier transform infrared spectroscopy was utilised to investigate the curing behaviour of epoxy resin. The quality of dispersion and the distribution structure of nanoclays in coating were studied by visual observations and X-ray diffraction in detail. Corrosion resistance behaviour of epoxy coating containing various clay percentages was investigated on steel by electrochemical impedance spectroscopy. Moreover, the modification of substrate was accomplished using conversion coating based on hexafluorozirconic acid. The electrochemical results revealed that the pretreated coating with 3 wt-% nanoclays possesses the best anticorrosive performance (2.5×10⁸ Ω cm²) after 2 weeks immersion in 3.5 wt-%NaCl solution. The morphological properties of conversion coating were observed by a field emission scanning electron microscope. In addition, pull-off technique was employed to measure the adhesion strength of coatings to metallic substrate. Experimental results exhibited that optimum clay loadings and conversion coating impressively increased the corrosion resistance and coating adhesion as well.     

爆炸喷涂WC-12Co/MoS_2复合涂层的摩擦磨损性能

为进一步提高爆炸喷涂WC-12Co涂层的耐磨性,在WC-12Co合金粉末中添加不同比例的MoS2粉末,利用爆炸喷涂技术在Q235钢表面制备了系列WC-12Co/MoS2复合涂层.采用金相显微镜、扫描电子显微镜、X射线衍射仪、显微硬度计及摩擦磨损试验机对WC-12Co/MoS2复合涂层的微观组织形貌、结构、显微硬度、摩擦磨损性能进行了研究.结果表明,MoS2均匀的分布于复合涂层中,当MoS2含量为2%时,复合涂层的硬度、致密度变化不大,但摩擦系数和磨损率大幅度下降,分别为WC-12Co涂层的50%和36%.随着MoS2含量的增加,复合涂层的摩擦系数和磨损率均呈上升趋势.     

Li4Ti5O12/TiN复合材料的制备及电化学性能

以尿素为氮源,采用高温热处理方法在Li4Ti5O12表面自生长一层纳米尺寸厚度的TiN导电包覆膜。利用DSC-TG、Raman、TEM、FT-IR、XRD及恒流充放电等测试手段,研究热处理工艺对材料结构、形貌及电化学性能的影响。结果表明:使用适中的尿素原料含量可以获得均匀连续、厚度适中的TiN导电膜,较高的热处理温度有利于促进TiN的生成,而较短的热处理时间可以保持材料物相的纯净和较高结晶度。在尿素含量10%(质量分数)、热处理温度800℃、热处理时间20 min的工艺条件下,所制备的复合材料的容量和倍率性能最优,0.2C和3C初始放电比容量分别达到162.4和130.2 mA.h/g。     

Synthesis and electrochemical performance of Co3O4/C composite anode for lithium ion batteries

The Co3O4/acetylene black composite anodes were successfully prepared by combination of oxalate precipitation and pyrolysis of the precipitate. The composite and its precursor were characterized by thermo-gravimetric analysis(TGA), differential thermal analysis(DTA), X-ray diffractometry(XRD), scanning electronic microscopy(SEM) and electrochemical measurements. The effects of carbon content and calcination temperature on properties of the composite were investigated in detail. The cycling performance of the Co3O4 anode is improved remarkably by the addition of carbon. As the calcination temperature rises in the range of 300-450 ℃, the crystallinity of the composites increases, but their reversible capacity and cycling stability decrease. Being charged/discharged at a current density of 0.1C rate, the optimized Co3O4/C composite anode shows a large initial reversible capacity of 757 mA-h/g, and a capacity of 743 mA-h/g is observed after 10 cycles.     

High temperature thermoelectric properties and energy transfer devices of Ca3Co4−xAgxO9 and Ca1−ySmyMnO3

The high temperature oxide thermoelectric materials of p-type Ca₃Co_4−xAg_xO₉ (denoted as p-Co349/Ag_x) and n-type Ca_1−ySm_yMnO₃ (denoted as n-Mn113/Sm_y) were prepared by the self-ignition method combined with a sintering technique. The influence of doping Ag and Sm on the thermoelectric properties of the corresponding materials was evaluated. The figures of merit, ZT, for the p-Co349/Ag_0.2 and n-Mn113/Sm_0.02 materials reached maxima of 0.20 and 0.15 at 973 K, respectively. The performances of thermoelectric devices constructed with the p- and n-type pairs were evaluated in terms of the maximum output power (P_max) and manufacturing factor. The P_max and volume power density for the four-leg devices reached 36.8 mW and 81.9 mW cm⁻³ at ΔT of 523 K, respectively.     

Synthesis of BaFe12O19/MFe2O4 (M=Co,Mn) by sol-gel method

Composites of M-type hexaferrite BaFe12O19 and spinel ferrites MFe2O4 (M=Co, Mn) were directly synthesized by sol-gel method. The structure of composites was analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The formation of BaFe12O19 /CoFe2O4 composite was proved by XRD patterns with coexistence of diffraction peaks of the two kinds of ferrites, BaFe12O19 and CoFe2O4. Compared with BaFe12O19 , the diffraction peaks of CoFe2O4 are fairly weak, revealing the dominant structure of hexaferrite in the composite. SEM micrographs provide further evidence and the particle size of composites is about several hundred nanometer, meaning that the co-synthesizing sol-gel method can be in favor of the formation of finer particles. However, the diffraction peaks of MnFe2O4 can be hardly found in BaFe12O19 /MnFe2O4 composite, revealing the synthesis conditions are not favorable for the formation of MnFe2O4. Substitution reaction of Ba or Fe by Mn may be proposed.     

六方-BN对非晶前驱体制备不含添加剂的Si3N4/SiC复合材料相变的影响（英文）

Si3N4/SiC纳米复合材料由于具有优良的力学和热性能,广泛应用于涡轮发动机、热交换器和其他复杂情况中。然而,不添加添加剂很难制备出Si3N4/SiC复合材料。添加剂在烧结过程形成液相从而促进复合材料的致密化。然而,添加剂的存在降低了复合材料的高温力学性能。通常在不添加添加剂的情况下,采用电场辅助烧结,利用聚合物前体路线制备Si3N4/SiC复合材料。本研究中,在无添加剂、温度1700°C、真空50MPa条件下,热压烧结2h,利用非晶前体路线成功制备了六方-BN致密化的Si3N4/SiC复合材料。聚合物前驱体和BN的作用减少了的SiC含量。并对相变、致密化、微观组织和力学性能进行了讨论。     

Sol-gel synthesis and electrochemical performance of Li4Ti5O12/graphene composite anode for lithium-ion batteries

Li₄Ti₅O₁₂/graphene composite was prepared by a facile sol-gel method. The lattice structure and morphology of the composite were investigated by X-ray diffraction (XRD) and scanning electronic microscopy (SEM). The electrochemical performances of the electrodes have been investigated compared with the pristine Li₄Ti₅O₁₂ synthesized by a similar route. The Li₄Ti₅O₁₂/graphene composite presents a higher capacity and better cycling performance than Li₄Ti₅O₁₂ at the cutoff of 2.5-1.0 V, especially at high current rate. The excellent electrochemical performance of Li₄Ti₅O₁₂/graphene electrode could be attributed to the improvement of electronic conductivity from the graphene sheets. When discharged to 0 V, the Li₄Ti₅O₁₂/graphene composite exhibited a quite high capacity over 274 mAh g⁻¹ below 1.0 V, which was quite beneficial for not only the high energy density but also the safety characteristic of lithium-ion batteries.     

Pt/Co双金属纳米溶胶的制备及催化制氢性能

采用化学共还原法制备了聚乙烯吡咯烷酮(PVP)稳定的Pt/Co双金属纳米溶胶,利用UV-Vis、TEM等对所合成的Pt/Co双金属纳米溶胶进行了表征,并系统研究了PVP用量,还原剂用量,双金属比例对该溶胶型纳米双金属催化剂活性的影响。结果表明:所制备的Pt/Co双金属纳米溶胶的平均粒径在2~3 nm之间,大部分双金属纳米溶胶催化剂催化NaBH4制氢的活性都优于单金属Pt和Co纳米溶胶,Pt10Co90双金属纳米溶胶的催化活性最高,其催化NaBH4制取氢气的活性可以达到8800 mol-H2·mol-催化剂-1·h-1,该双金属纳米溶胶催化NaBH4水解反应的活化能为61.8 kJ/mol。所制备的Pt/Co双金属纳米溶胶催化剂具有很好的稳定性,即使在4次催化试验后该催化剂仍然保持着较高的催化活性。     

Precipitation of a-Fe from Fe84-xSi4B12+x (x=1,3) Amorphous Alloys Under High Magnetic Field Annealing

This work aims to investigate the effects of high magnetic field annealing (HMFA) on the precipitation of α-Fe from Fe84-xSi4B12+x (x =1,3) amorphous precursors.Isothermal annealing process for Fe81Si4B15 and Fe83Si4B13 amorphous ribbons has been performed with and without the magnetic field.The magnetic field shows the effects of increasing the nucleation rate and decreasing the grain size of α-Fe crystals simultaneously,during the crystallization processes of the investigated amorphous alloys.By applying HMF,α-Fe crystals with more homogeneous distribution and smaller grain size are achieved in the amorphous matrix,which is crucial helpful to improve the magnetic properties for Fe-Si-B amorphous alloys.The mechanism of HMFA affecting the crystallization microstructure is also discussed in the present work.     

Hot corrosion of a novel (Ni,Co)O/(Ni,Co)Fe2O4 composite coating thermally converted from an electrodeposited Ni–Co–Fe2O3 composite coating

Ni–Co–Fe₂O₃ composite coatings were successfully developed by sediment co-deposition. In order to improve their hot corrosion resistance, a pre-oxidation treatment was conducted at 1000 °C for 6 h. The corrosion behaviour of the oxidised composite coating was investigated at 960 °C in an atmosphere consisting of a mixture of Na₃AlF₆–AlF₃–CaF molten salts and air. They exhibited good hot corrosion resistance due to not only the pre-formed oxide scale with (Ni,Co)O and (Ni,Co)Fe₂O₄ phases after pre-oxidation, but also the formation of (Ni,Co,Fe)Al₂O₄ phases in the outer layer and a well-distributed NiFe₂O₄-enriched phase along the grain boundaries in the subscale area during the corrosion process.     

氨基功能化CoFe2O4-SiO2 磁性复合材料的制备及其在去除水中重金属离子的吸附性能

钴-铁氧体纳米粒子(CoFe₂O₄ NPs)通过改良的共沉淀法制备,CoFe₂O₄-SiO₂磁性复合材料通过st?ber法合成,为了吸附重金属离子CoFe₂O₄-SiO₂进行了氨基功能化。这种吸附剂的晶体结构、形貌、颗粒尺寸、化学组成和分子结构采用X射线衍射图谱(XRD)、扫描电子显微镜(SEM)以及傅里叶变换红外光谱(FTIR)进行表征。此复合材料具有优良的磁性能,由于其高的饱和磁化强度,磁铁可以将其在30秒内快速分离。同时,CoFe₂O₄ NPs的磁性能可以通过烧结温度进行调节,随烧结温度提高,磁性能增强。溶液的pH及反应时间对重金属离子吸附的影响进行了研究,此外此吸附剂对Cu (II)、Cd (II)、Mn (II) 和Zn (II)具有较高的吸附容量和去除率,这一结果使此复合材料可以潜在应用于废水中重金属离子的吸附上。     

The in situ synthesis and wear performance of a metal matrix composite coating reinforced with TiC-TiB2 particulates, formed on Ti-6Al-4V alloy by a low oxygen partial pressure fusing technique

A metal matrix composite coating reinforced with TiC-TiB₂ particulates has been successfully fabricated utilizing the in situ reaction of Al, Ti and B₄C by the low oxygen partial pressure fusing technique to improve the wear resistance of Ti-6Al-4V alloy. The results show that increasing the B₄C content is adverse to forming the coating for the formation of interfacial stress; however, the addition of TiC powder as a diluent can favor the formation of this coating and the addition of small amounts of Y₂O₃ can greatly improve the adhesion of the coating. After a pin-on-disc wear test, the wear mass loss of the coating is only about 1/12 that of the Ti-6Al-4V alloy and the wear mechanism of coating is a mixed type of slight peeling-off, adhesion and abrasion.