查看更多>>摘要：Solid-state refrigeration based on electrocaloric effect (ECE) is a high efficiency and eco-friendly refrigeration technique, which has attracted increasing attention. However, it is still a challenge to realize a large adiabatic temperature change (?T) accompanied by wide operating temperature range (Tspan). Herein, enhanced room temperature ECE was realized in lead-free (1-x)Na0.5Bi0.5TiO3-xSr0.85Bi0.10TiO3 (NBT-xSBT) by a synergistic effect of forming relaxor ferroelectric and constructing multilayer ceramic capacitor (MLCC). It is found that the maximum ?T of NBT-0.50SBT ceramic is 0.31 K at 80 kV/cm, and Tspan is up to 60 K. To further improve the breakdown strength (BDS), NBT-0.50SBT MLCC was fabricated by a tape-casting method. A large ECE of MLCC reached 2.59 K at 60 °C with excellent temperature stability from 35 °C to 95 °C. These results indicate that NBT-based material is a promising electrocaloric material for solid-state cooling applications.
查看更多>>摘要：Constructing heterostructure and N-doping are two effective methods to improve gas sensing performance. Herein, a facile novel solution calcination strategy has been proposed to synthesize N-doped carbon sheets-zinc oxide (NC-ZnO) hybrids for low concentration NO2 detection. The formation of NC is accompanied by generation of ZnO particles on its surface to construct heterostructure. Intriguingly, NO3- acts as an expanding agent and N source in the calcination process, wherein the N elements are directly doped into carbon sheets. As expected, the prepared heterostructural NC-ZnO-63 hybrids exhibit 74.9 times enhancement of response as well as high sensitivity (~ 265.8–20 ppm NO2), excellent repeatability and selectivity compared with pure ZnO. Importantly, the measured detection limit of the NC-ZnO-63 sensor to NO2 is about 100 ppb (~ 0.3) and the calculated detection limit is 2.65 ppb. Furthermore, the influences of humidity on testing NO2 gas have been researched systematically which would provide guidance for practical use of similar sensors. In this work, ZnO and derived carbon are low-cost, eco-friendly, and the synthesis strategy presented here is simple and repeatable, which provides new idea for mass fabricating other-type metal oxides-NC hybrids for various applications.
查看更多>>摘要：Powders of heat-resistant NiAl-8Cr-6Co-xMo-1 Nb-0.9Hf (x = 0, 2, 4 and 6 at% Mo) alloys were successfully obtained by high-energy ball milling (HEBM) and combustion synthesis. Powders with the grain size of 10–55 μm were characterized by high flowability (up to 30 s) and bulk density (up to 3.1 g/cm3) due to the absence of submicron-sized particles. Compacted samples having a finer-grained (<5 μm) structure were produced from the combustion-synthesized powders by hot isostatic pressing (HIP). Molybdenum doping gave rise to a duplex structure consisting of NiAl and (Cr, Mo) grains. High-resolution electron microscopy (HRTEM) and selected area electron diffraction studies of the fine structure of the alloys detected that there are nanoparticles of refractory compounds (Co2Nb, Cr2Nb, (Hfx, Nby)C, and Ni2AlHf) along the grain boundaries and in grain bulk, which improve resistance to viscoplastic strain at temperatures above 800 °C. Molybdenum was shown to affect the mechanical properties of the base alloy in compression tests at 500–1100 °C. Two predominant mechanisms of alloy deformation were identified: glide of matrix dislocations and mechanical twinning.
查看更多>>摘要：This article investigated microstructure, phase transformation and mechanical property of porous NiMnGa alloy and its composite with epoxy resin. The porous NiMnGa alloys with large pores and different porosity exhibited a similar martensitic transformation behavior but with reduced martensitic transformation temperature as compared to that of the original powder. The porous alloys exhibited low mechanical strength and ductility due to the existence of large size pores. After compositing with epoxy resin, the mechanical strength and ductility of the porous alloy had been apparently enhanced due to the synergistic effect between the polymer and porous alloy. In addition, the composite demonstrated a martensitic transformation behavior similar with that of the porous alloy, indicating that the constraint effect of polymer matrix on the phase transformation of the porous alloy could be neglected. The combination of porous NiMnGa alloys with continuous structure and polymer could provide a promising way to make NiMnGa/polymer composites with better performance than the composites consisting of NiMnGa particles and polymer.
查看更多>>摘要：Based on high temperature solid state technique, a series of Pb2+/Sm3+ doped CaZrO3 perovskite phosphors have been successfully synthesized. Comparing with CaZrO3 host, the absorption edge of CaZrO3:x%Pb2+ samples exhibits a red shift with the increase of Pb2+ ions doping concentration. Analysis shows that the red shift of absorption edge can be attributed to the 1P1 level of Pb2+ ions which is just below the bottom of conduction band. By comparing the absorption and excitation spectra of CaZrO3:x%Pb2+ samples, it is found that the excitation band at 286 nm should be composed of two parts, MMCT and 1S0→3P1 transitions, respectively. The normalized excitation and emission spectra of CaZrO3:x%Pb2+ samples also confirm that the excitation band at 286 nm should be composed of MMCT and 1S0→3P1 transitions, and the emission band at 370 nm should come from the 3P1→1S0 transition. Based on the analysis of the absorption and excitation spectrum of CaZrO3:Sm3+, it indicates that the excitation band of CaZrO3:Sm3+ sample at 231 nm should be the O2--Sm3+ charge transfer state. In addition, the characterization of the temperature sensing properties demonstrates that the relative sensitivities of CaZrO3:Pb2+ and CaZrO3:Pb2+/Sm3+ samples have high stability. In the temperature range of 303–443 K, the relative sensitivity for CaZrO3:Pb2+ and CaZrO3:Pb2+/Sm3+ materials is in the range of 1.03%?1.32% K?1 and 0.89%?1.13% K?1, respectively. Therefore, the CaZrO3:Pb2+/Sm3+ material has great potential and application value in temperature sensing.
查看更多>>摘要：This study reports the effect of hydrogen behaviors on the tensile properties of an equiatomic FeCrNiMnCo high-entropy alloy. We reveal that the hydrogen at the interfaces (including grain boundaries and twin boundaries, etc.) is the main factor affecting the mechanical properties of the materials. We found that hydrogen alloying with a proper concentration makes the alloy resistant to hydrogen embrittlement and improves the strength and ductility of the material. This beneficial effect is positively correlated with the hydrogen concentration at the interface of the alloy, with hydrogen promoting the formation of stacking faults / nanotwins, which are excessively compensatory to the surface cracks introduced by the hydrogen. The influence of hydrogen at the interface of 316NG stainless steel on the tensile behavior has also been discussed. Although hydrogen embrittlement occurred at the same hydrogen-charged conditions, the deterioration of the ductility of the deformed 316NG with a high hydrogen concentration at the interface was significantly reduced. AIMD simulation has been used to study the diffusion of interstitial hydrogen in the HEA and FeCrNi model alloy. It was found that the diffusion barrier and diffusion coefficient of hydrogen in the two alloys were very close at different temperatures.
NSTL
Elsevier