Investigation of interfacial reactions between metallic substrates and n-type bulk bismuth telluride thermoelectric material

Journal of Materials Science - In practical applications of bismuth telluride thermoelectric materials, the materials need to be connected with a metallic electrode before they can be used;...     

Flexible thermoelectric materials and devices: From materials to applications

With the ever-growing development of multifunctional and miniature electronics, the exploring of high-power microwatt-milliwatt self-charging technology is highly essential. Flexible thermoelectric materials and devices, utilizing small temperature difference to generate electricity, exhibit great potentials to provide the continuous power supply for wearable and implantable electronics. In this review, we summarize the recent progress of flexible thermoelectric materials, including conducting polymers, organic/inorganic hybrid composites, and fully inorganic materials. The strategies and approaches for enhancing the thermoelectric properties of different flexible materials are detailed overviewed. Besides, we highlight the advanced strategies for the design of mechanical robust flexible thermoelectric devices. In the end, we point out the challenges and outlook for the future development of flexible thermoelectric materials and devices.     

Electrical characteristics and detailed interfacial structures of Ag/Ni metallization on polycrystalline thermoelectric SnSe

SnSe is a promising thermoelectric material with a high figure of merit in single crystal form, which has stimulated continuous research on polycrystalline SnSe. In this study, we investigated a metallization techniques for polycrystalline SnSe to achieve highly efficient and practical SnSe thermoelectric modules. The Ag/Ni metallization layers were formed on pristine polycrystalline SnSe using various deposition technique: sputter coating Ni, powder Ni and foil Ni by spark plasma sintering. Structural analysis demonstrated that the microstructure and contact resistance could be different according to the metallization process, despite using the same metals. The Ag/Ni metallization layer using foil Ni acted as an effective diffusion barrier and minimized electrical contact resistance(2.3 × 10~(-4) Ω cm~2). A power loss in the thermoelectric module of only 5% was demonstrated using finite element simulation.     

Wettability and interfacial reaction in SiC/Ni plus Ti system

Wettability and interfacial reactions in both SiC ceramic/pure Ni system and SiC ceramic/Ni plus Ti system were studied. The contact angle was determined by high temperature photography. The microstructure and composition of the interfacial region were analyzed. Under the applied experimental conditions, the contact angle of SiC/pure Ni system at 1350°C in vacuum is about 86°. The contact angle slightly decreases with the prolonging of time of the test at 1350°C. The interfacial reactions take place during the test. The reactions facilitate the wetting. The wettability of the system is improved by adding active element titanium into the metallic phase. The contact angle decreases with the increasing of content of the additive within the tested range. Moreover, this effect becomes more remarkable with the prolonging of reaction time at high temperatures. This can be explained by the fact that titanium accumulates at the wetting interface and facilitates the interfacial reactions, resulting in an increase of the driving force of wetting.     

Microstructural characterization of interfacial reaction products between alumina and braze alloy

The Al₂O₃/STS304, Al₂O₃/Cu and Al₂O₃/Al₂O₃ joints were brazed in vacuum with three types of Cu-Ag-Ti brazing filler metals at 1193 K for 1.2 ks. The effects of adherend metals on the microstructure and microchemistry of reaction products formed at the Al₂O₃/filler metal interface have been investigated. The reaction products of A₂O₃/STS304 joints showed a layered structure consisting of TiO (monoclinic, a ₀=0.585 nm, b ₀=0.934 nm, c ₀=0.414 nm), Cu₂Ti₄O (cubic, a ₀=1.149 nm) and Fe₂Ti₄O (cubic, a ₀=1.1297 nm). The TiO compound is a nonstoichiometric titanium monoxide with composition range of TiO_0.9 to TiO_1.1. Cu₂Ti₄O and Fe₂Ti₄O compounds can be considered as (Cu, Fe)₂Ti₄O because both of them have nearly the same crystal structure and lattice constants. The reaction products of Al₂O₃/Cu and Al₂O₃/Al₂O₃ joints also showed a layered structure consisting of TiO and Cu₂Ti₄O. The TiO compound was formed by redox reaction between Al₂O₃ and segregated titanium, whereas Cu₂Ti₄O and Fe₂Ti₄O compounds formed by solid-state reaction between TiO and copper from the brazing alloy and iron from the adherend metals, respectively.     

Effect of Ti on the interfacial reaction between Sn and Cu

The effect of Ti on the solid state reactions between Sn and Cu has been investigated in this work. Based on the experimental results the following statements about the effect of Ti can be made: Firstly, the presence of Ti does not have measurable effect on the thickness of either Cu₆Sn₅ or Cu₃Sn during solid state annealing. However, the unevenness of both Cu₆Sn₅ and Cu₃Sn layers is increased by the addition of Ti. Secondly, there is no marked solubility of Ti to either Cu₆Sn₅ or Cu₃Sn. Rather Ti reacts with Sn to form large Ti₂Sn₃ platelets inside the solder matrix. These findings were subsequently rationalized with the help of the assessed Cu–Sn–Ti phase diagram. By utilizing this phase diagram information, the absence of any marked effects of Ti on the growth of Cu–Sn intermetallic compound (IMC) formation was rationalized. As there is a very low solubility of Ti to SnAg solder and to Cu–Sn IMC’s, Ti cannot change activities of components in the solder nor influence the stability of the IMC layers. Hence, these results throw significant doubts over the concept of trying to influence the Cu–Sn IMC layer thickness or quality by Ti alloying.     

Brazing temperature-dependent interfacial reaction layer features between CBN and Cu-Sn-Ti active filler metal

CBN/Cu-Sn-Ti (CBN: cubic boron nitride) composites are prepared by active brazing sintering at 1123 K, 1173 K, 1223 K and 1273 K, respectively. The effects of brazing temperature on the wettability, interfacial characteristics, and elemental distribution variations are fully investigated. When the brazing temperature is below 1223 K, completely uncoated and/or partially coated CBN particles with sharp edges can still be observed, and the reaction layer, mainly composed of TiN and TiB2, appears to be thin and uneven. When the brazing temperature is 1223 K, all CBN particles are completely coated, suggesting that adequate wetting has taken place. Besides, as Ti diffuses thoroughly and enriches the interface, the reaction layer, filled primarily by TiN, TiB₂ and TiB, becomes thicker (about 1.30 μm), more uniform, stable and continuous. Further increasing the temperature to 1273 K is unnecessary or even harmful as the reaction layer thickness undergoes negligible change yet some tiny micro-cracks appear on the interface, which may likely deteriorate the grinding capability of the final brazing products.     

Wettability and Bonding between Ni and Ti(C, N) with Multiple Carbide Additions

The wettability and bonding in Ni/Ti(C, N) systems with multiple carbide additions were studied by sessile drop technique and vacuum brazing technique, respectively. The phase characterizations of substrates and fracture surfaces were conducted by XRD. The microstructures at metal/ceramic interfaces and fracture surfaces were observed via SEM in back scattered mode and second electron mode, respectively. Furthermore, an X-ray energy-dispersive spectrometer (EDS) attached to SEM was used to study the elements diffusion in interfacial regions. The results reveal that diffusion and dissolution mechanism controlled reactive wetting takes place in the system in high temperature wetting. Results also show that the contact angles decrease with multiple carbide additions, and the effect of multiple carbide additions is stronger than that of single additions. The contact angle reaches the lowest value in the lowest TiC content case. The enhancement of the wettability is due to alloying procedure during high tempe     

Molecular materials for electronic and optical applications

In the past two years molecular rectification and single electron transistor effects in molecular devices have been demonstrated. Because of the ambiguity of assigning these effects to particular molecules, research has turned to carbon nanotubes which are larger than more classical molecules. For optical applications bright and multicoloured organic light emitting diodes are available.     

Metallurgically and mechanically reliable microsilver-sintered joints for automotive power module applications

Journal of Materials Science: Materials in Electronics - Conventional soldering methods with Pb-containing and Pb-free solder alloys have been extensively used in the manufacturing of the power...     

Detailing interfacial reaction layer products between cubic boron nitride and Cu-Sn-Ti active filler metal

In the present study,we offer an in-depth analysis over the microstructure,thickness and product composition of the interfacial reaction layer generated upon CBN/Cu-Sn-Ti active filler metal at 1223 K.Current findings demonstrate that adequate wettability and satisfactory bonding have been achieved via chemical reactions between Ti and N,B.More importantly,we report,for the first time,the formation of a three-layer juxtaposition of reaction products,namely,TiN,TiB2 and TiB,along the diffusion path of Ti.Meanwhile,we determine the average layer thickness to be 1.24 μm.Through deep etching,we unambiguously present morphologies of the newly formed TiN and TiB2,which are columnar and bulky,re spectively,and constitute the formation of a high strength metallu rgical interfacial bonding layer,and is crucial towards gaining enhanced grinding performance.Finally,we propose a possible reaction sequence and mechanism that govern the nucleation and growth of corre s ponding crystals.     

定向凝固钛铝合金熔体与铸型界面反应研究展望

钛铝合金是性能优异的高温合金,在航空航天领域有广泛的应用前景,但由于其熔体具有较高的活性,制备时熔体与所有已知的铸型材料会发生不同程度的反应,限制了钛铝合金铸件的发展.定向凝固技术作为制备高精度钛铝合金的新工艺,使铸件组织定向排列,可以进一步提高钛铝合金的使用性能,因此如何调控凝固过程中钛铝合金熔体与铸型材料间的界面反应成为目前有关定向凝固钛铝合金研究的一个热点.从目前国内外关于钛铝合金熔体与铸型材料间界面反应的研究出发,综述了定向凝固过程中铸型材料、涂层成分、工艺参数及合金元素等对界面反应的影响,介绍了界面反应的理论水平,系统收集了界面反应的各项研究结果.     

Effect of Ni and TiO2 particle addition on the wettability and interfacial reaction of Sn20Bi lead-free solder

Journal of Materials Science: Materials in Electronics - In this paper, the powder samples are mechanically ball-milled by powder metallurgy, cold pressed and shaped, then melted, and finally, the...     

Electrodeposition of n-type and p-type ZnSe thin films for applications in large area optoelectronic devices

ZnSe layers have been grown by a low temperature (65 °C) electrochemical deposition technique in an aqueous medium. The resulting thin films have been characterized using X-ray diffraction (XRD) and a photoelectrochemical (PEC) cell for determination of the bulk properties and electrical conductivity type. XRD patterns indicate the growth of ZnSe layers with (1 1 1) as the preferred orientation. PEC studies show p-type semiconducting properties for the as deposited layers and n-type ZnSe can be produced by appropriate doping. Annealing at 250 °C for 15 min improves the crystallinity of the layers and the photoresponse of the ZnSe/electrolyte junction. © 1998 Kluwer Academic Publishers     

Magnetic and hydrogel composite materials for hyperthermia applications

Micron-sized magnetic particles (Fe3O4) were dispersed in a polyvinyl alcohol hydrogel to study their potential for hyperthermia applications. Heating characteristics of this ferrogel in an alternating magnetic field (375 kHz) were investigated. The results indicate that the amount of heat generated depends on the Fe3O4 content and magnetic field amplitude. A stable maximum temperature ranging from 43 to 47 degrees C was successfully achieved within 5-6 min. The maximum temperature was a function of Fe3O4 concentration. A specific absorption rate of up to 8.7 W/g Fe3O4 was achieved; this value was found to depend on the magnetic field strength. Hysteresis loss is the main contribution to the heating effect experienced by the sample.