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[en] Energy conversion technologies, especially for power generation and refrigeration technologies driven by the low temperature heat, are gathering the momentum recently. This paper presents a novel resorption system for electricity and refrigeration cogeneraion. Compared with adsorption refrigeration system, resorption refrigeration is characterized as safety and simple structure since there is no ammonia liquid in the system. The cogeneration system is mainly composed of three HTS (high temperature salt) unit beds; three LTS (low temperature salts) unit beds, one expander, three ammonia valves, two oil valves, four water valves and connection pipes. Chemical working pair of MnCl_2–CaCl_2–NH_3 is selected. Since scroll expander is suitable for small type power generation system, it is chosen for expansion process. 4.8 kg MnCl_2 and 3.9 kg CaCl_2 impregnated in expanded natural graphite treated with sulfuric acid (ENG-TSA) are filled in the cogeneration system. Experimental results show that maximum cooling power 2.98 kW is able to be obtained while maximum shaft power is about 253 W with 82.3 W average value. The cogeneration system can be utilized for the heat source temperature lower than 170 °C. Total energy efficiency increases from 0.293 to 0.417 then decreases to 0.407 while exergy efficiency increases from 0.12 to 0.16. - Highlights: • A resorption system for power and refrigeration cogeneration is established and investigated. • ENG-TSA as the additive improves the heat and mass performance of composite adsorbent. • The highest shaft power and refrigeration power are 253 W and 2.98 kW, respectively. • Total energy efficiency of the system increases from 0.293 to 0.417 then decreases to 0.407.
[en] Lead-free eutectic SnBi and SnAgCu solder alloys were studied by nanoindenter. Eutectic SnPb solder was also examined for comparative purpose. Their mechanical properties including hardness, reduced modulus and creep rate sensitivity coefficient m values were obtained. It was found that eutectic SnAgCu solder is stiffer than both eutectic SnBi solder and SnPb solder, while eutectic SnBi is the hardest among these solder alloys. For eutectic SnAgCu alloy, its m value obtained by nanoindenter was in excellent agreement with that by uniaxial tensile test. Both lead-free solders showed more creep resistance than eutectic SnPb solder. Nanoindenter is a useful way to characterize the small sized materials of electronic components
[en] In this study, friction and wear of a body-centered cubic equiatomic TiZrHfNb high-entropy (HE) alloy were investigated using a nanoscratch method. Scratch tests, under both ramping and constant load modes, were conducted to evaluate the coefficient of friction (COF) and wear rate of the alloy. The effects of scratch rate on the friction and wear were also studied. The morphology such as the surface profile and depth of scratched tracks was examined using scanning electron microscopy (SEM) and scanning probe microscopy (SPM). It was found that, whilst wear behavior, including wear rate and wear resistance, could be described by Archard equation, friction of the alloy appeared to be more complicated. Experimental results revealed that the friction of the alloy could be divided into two distinct regimes - elastic and plastic. The COF decreased rapidly with increasing normal load in the elastic regime, but became essentially constant in the plastic regime, indicating a transition of friction mechanism. In this study, scratch tests were also performed on pure Nb and a solid-solution strengthened Nb-based C103 alloy to make a direct comparison. The TiZrHfNb HE alloy apparently exhibited an improved wear resistance and lower COF as compared to its traditional alloy counterparts. The better wear resistance and lower COF were discussed in lights of the acting plowing and adhesion mechanisms during wear.
[en] Ca2+ and Ba2+ ions co-doped BiFeO3 nanoparticles, Bi0.8Ca0.2−xBaxFeO3 (x=0–0.20), were prepared by a sol–gel method. The phase structure, grain size, dielectric and magnetic properties of the prepared samples were investigated. The results showed that the lattice structure of the nanoparticles transformed from rhombohedral (x=0) to orthorhombic (x=0.07–0.19) and then to tetragonal (x=0.20) with x increased. The dielectric properties of the nanoparticles were affected by the properties of the substitutional ions as well as the crystalline structure of the samples. The magnetic properties of the nanoparticles were greatly improved and the TN of the nanoparticles was obviously increased. All the Ca2+ and Ba2+ ions co-doped BiFeO3 nanoparticles presented the high ratio of Mr/M from 0.527 to 0.571 and large coercivity from 4.335 to 5.163 KOe. - Highlights: ► Ca2+ and Ba2+ ions co-doped BiFeO3 nanoparticles were prepared using a sol–gel method. ► The magnetic properties of the nanoparticles are greatly improved. ► The Neel temperature (TN) of the nanoparticles is greatly increased. ► Doped ions and crystal structure affect the dielectric properties of the nanoparticles.
[en] Highlights: • Mg–Al–Zn sheets were friction stir spot welded (FSSW) with addition of Zn interlayer. • Complex alloying reactions occurred between Mg sheets and Zn interlayer during FSSW. • Alloying reactions increased the area of bonded zone and eliminated the hook defects. • Tensile–shear load of FSSW joints increased from 2.4 to 4 kN by adding Zn interlayer. - Abstract: 2.4 mm thick Mg–Al–Zn alloy sheets were friction stir spot welded (FSSW) without and with the addition of 0.1 mm thick Zn interlayer. The influence of interlayer addition on the microstructural features and mechanical properties of FSSW joints was investigated by optical microscope, scanning electron microscope, transmission electron microscope, X-ray diffraction and tensile testing. The results show that the addition of Zn interlayer resulted in complex alloying reactions between Mg substrate and Zn interlayer, forming a bonded zone composed of α-Mg, (α-Mg + MgZn) eutectoid structure and a mixture of Mg_4Zn_7 and unreacted Zn, thereby increasing the area of bonded zone and reducing the hook defects. This results in a significant increase in tensile–shear load from 2.4 kN to about 4 kN
[en] Highlights: • Al-containing Zn coating improved Mg–steel interfacial wettability during friction stir spot welding (FSSW). • Pre-existing Al5Fe2 phase in coating on steel surface promoted Mg–steel metallurgical bonding. • A high tensile-shear load of 4.3 kN was obtained in FSSW AZ31–steel joint. - Abstract: 2.4 mm thick AZ31 Mg alloy sheet and 1.5 mm Q234 steel sheet with a hot-dipped Al-containing Zn coating were friction stir spot welded (FSSW) using a pinless tool. It was shown that the Al-containing Zn coating played a crucial role in joining the Mg alloy and steel during FSSW. The Zn coating observably improved the Mg–steel interfacial wettability during FSSW, and the Al5Fe2 phase in the Zn coating on the steel substrate surface promoted the metallurgical bonding of Mg alloy and steel. It was confirmed that the Al5Fe2 phase on the steel surface resulted from the reaction between the steel substrate and the Al in the Zn coating during hot-dipping, and was not related to the Al-containing Mg alloy substrate. The tensile-shear load of the FSSW Mg–steel joint reached 4.3 kN. The fracture of the joint occurred along the interface on the steel substrate side. The interface between the Al5Fe2 layer and Mg alloy substrate was the weakest region of the Mg–steel joint.