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71.
Li Yanhui Li Lianglong Peng Cheng Bai Mingmin Zhao Wei Rao Pinggen 《Journal of the American Ceramic Society》2014,97(3):695-699
Platelike α‐Al2O3 powder was obtained at 850°C by thermal decomposition of ammonium aluminum carbonate hydroxide precursor, which was treated by hydrofluoric acid. The results showed the decomposition of the as‐prepared precursors experienced via three steps, adsorption of physical water, dehydration of crystalline water, and decomposition of the precursor, and the activation energies of the above three steps were calculated using the Coats–Redfern method. Meanwhile, the intermediate of (NH4)3AlF6 obtained played an important role in decreasing activation energy of the decomposition and phase transformation. Moreover, the thermal conductivity of the epoxy resin filled with platelike alumina was improved obviously. 相似文献
72.
《Journal of the European Ceramic Society》2014,34(16):4443-4449
Rhenium diboride (ReB2) powder was prepared by mechanochemical processing of Re–B powder mixtures with subsequent annealing at temperatures of 600 °C to 1200 °C. Reactive evolution during the synthesis was investigated; furthermore, the effects of the amount of excess B on the reactions that occurred during the synthesis were assessed. The substantial reaction of Re with B occurred at 700 °C to form Re7B3 with a small amount of ReB2. At 800 °C, Re7B3 converted into ReB2; this conversion was enhanced with increasing temperature and increasing amount of excess B. At 1000 °C or above, single-phase ReB2 powder without trace quantities of Re7B3 was obtained for compositions with 15 wt% or greater excess B. The synthesized ReB2 powder particles were submicrometer with the vast majority being ∼500 nm. In addition, the resulting ReB2 powders were consolidated by hot pressing or spark plasma sintering to examine the sinterability of the powders. 相似文献
73.
A N,N-dimethylamino substituted tetraphenylethylene derivative (TPE-NMe) was synthesized and characterized, and was successfully applied as hole transport material (HTM) in perovskite solar cells. The methoxy-substituted analogue TPE-4DPA was also studied for comparison. The effect of replacing the para-methoxy substituent with N,N-dimethylamino on photophysical properties, energy levels, and hole transport properties is investigated. Photovoltaic performances of the corresponding devices using the two HTMs are studied. Compared to the methoxy substituent, the N,N-dimethylamino groups in TPE-NMe generates a lower Voc (0.87 V), yet it provides higher Jsc (21.69 mA/cm2) and FF (0.73) values, resulting in an overall power conversion efficiency of 13.78%. 相似文献
74.
Galvanic corrosion of carbon steel coupled to antimony was studied in aerated and N2-purged electrolytes at ambient and 60 °C temperatures. Free corrosion potential of antimony and carbon steel shifts to more active values with increasing temperature and N2 purging of the electrolyte. Under all experimental conditions, antimony remains less electronegative than carbon steels. Aeration and temperature affect potentiodynamic behaviour of both materials. As a consequence, the corrosion current for the antimony–carbon steel couple increases with increasing temperature and with aeration. There was a good agreement between the corrosion currents obtained through the Evans’ experiment and super-imposed potentiodynamic scans. 相似文献
75.
In this study, alkali hydroxides (NaOH, LiOH, KOH) were attempted as new-type catalytic additives to improve the hydrogen storage properties of MgH2 by ball milling. It is shown that the additives readily react with the MgH2 to form perovskite-structured NaMgH3 and KMgH3, but not the LiMgH3. Although the in-situ formed perovskite hydrides remain stable during hydriding/dehydriding cycles, both NaMgH3 and KMgH3 show predominant catalytic role on the hydriding and dehydriding of MgH2. In contrast, the LiOH modified MgH2 presents much inferior sorption kinetics because of the absence of LiMgH3. The catalytic mechanism of perovskite hydrides can be explained by the high hydrogen mobility in the perovskite structure. This study shows that such cheap hydroxides could be used as efficient catalysts to improve the hydrogen storage properties of high-capacity metal hydrides and complex hydrides. 相似文献
76.
Joule heating dominated fracture position transition from the interface between the solder and the intermetallic compound (IMC) layer to the solder matrix occurs in micro-scale Cu/Sn-3.0Ag-0.5Cu/Cu(Ni) joints under electro-thermal coupled loads with a high current density and increasing temperature. The interfacial fracture is triggered by localized-melting of the solder induced by current crowding at grooves of the interfacial IMC grains and driven by the strain mismatch between the solder and the interfacial IMC layer, while fracture in the solder matrix is caused by matrix bulk melting and the constraint effect from the interfacial IMC layer-substrates. 相似文献
77.
《Carbon》2013
Carbon nanotube (CNT)/polymer composites with filler loading close to percolation threshold are demonstrated as sensor materials to monitor the thermal aging of insulation components. In order to represent the real aging conditions of the monitored component, the sensor is made of the same polymer material as the one used in the monitored component and placed in close proximity to the component. During thermal aging, the polymer matrix shrinks, leading to a slight increase of volume percentage of CNTs and a substantial decrease in resistivity of the sensors. The sensors are aged at different temperatures and the resistivity change at each temperature is fitted into the modified Arrhenius equation to yield the activation energy of the aging reactions. The activation energy obtained from the sensor signals is similar to those obtained by conventional elongation measurements and the thermal evaluation of the insulation component according to IEEE standard 275. Therefore, the resistivity value of the sensor can be used to accurately predict the remaining life of the monitored parts. These sensors provide many advantages over conventional conditioning monitoring methods, including no damage to the insulation system, real-time monitoring, facile operation, low cost, and much higher sensitivity. 相似文献
78.
M. Jemmali S. Walha M. Pasturel O. Tougait R. Ben Hassen H. Noël 《Journal of Alloys and Compounds》2010,489(2):421-423
Physico-chemical analysis techniques, including X-ray diffraction and Scanning Electron Microscope–Energy Dispersive X-ray Spectroscopy, were employed to construct the isothermal section of the Er–Fe–Al system at 800 °C. At this temperature, the phase diagram is characterized by the formation of five intermediate phases, ErFe12?xAlx with 5 ≤ x ≤ 8 (ThMn12-type), ErFe1+xAl1?x with ?0.2 ≤ x ≤ 0.75 (MgZn2-type), ErFe3?xAlx with 0.5 < x ≤ 1 (DyFe2Al-type), Er2Fe17?xAlx with 4.74 ≤ x ≤ 5.7 (TbCu7-type) and Er2Fe17?xAlx with 5.7 < x ≤ 9.5 (Th2Zn17-type), seven extensions of binaries into the ternary system; ErFexAl3?x with x < 0.5 (Au3Cu-type), ErFexAl2?x with x ≤ 0.68 (MgCu2-type), Er2FexAl1?x with x ≤ 0.25 (Co2Si-type), ErFe2?xAlx with x ≤ 0.5 (MgCu2-type), ErFe3?xAlx with x ≤ 0.5 (Be3Nb-type), Er6Fe23?xAlx with x ≤ 8 (Th6Mn23-type), and Er2Fe17?xAlx with x ≤ 4.75 (Th2Ni17-type) and one intermetallic compound; the ErFe2Al10 (YbFe2Al10-type). 相似文献
79.
Katrin Hedicke-Höchstötter Goy Teck Lim Volker Altstädt 《Composites Science and Technology》2009,69(3-4):330-334
In this study, the silicate nanotubes of the mineral halloysite will be used as reinforcement in polyamide-6 (PA 6). The nanocomposites based on PA-6 and as-received halloysite were prepared by melt extrusion and an adjacent injection moulding process. Mechanical and thermomechanical properties have been investigated by tensile testing and dynamic mechanical analysis. The results show an increased strength and stiffness as well as an enhanced elongation at break at low halloysite content. To evaluate the potential of halloysite as a new candidate in the class of nanofillers, the properties of the halloysite nanocomposites has been compared to those of conventional nanocomposites based on organically modified montmorillonite. From this comparison it can be seen, that both types of nanocomposites show enhanced tensile properties as well as an increased storage modulus, but the increase in tensile strength is more pronounced in the organoclay nanocomposites, whereas the raise of the storage modulus is more prominent in the halloysite nanocomposites. 相似文献
80.
A new method of manufacturing tubes with nano/ultrafine grain structure by stagger spinning and recrystallization annealing is proposed in this study. Two methods of the stagger spinning process are developed, the corresponding macroforming quality, microstructural evolution and mechanical properties of the spun tubes made of ASTM 1020 steel are analysed. The results reveal that a good surface smoothness and an improved spin-formability of spun parts can be obtained by the process combining of 3-pass spinning followed by a 580 °C × 0.5 h static recrystallization and 2-pass spinning with a 580 °C × 1 h static recrystallization annealing under the severe thinning ratio of wall thickness reduction. The ferritic grains with an average initial size of 50 μm are refined to 500 nm after stagger spinning under the 87% thinning ratio of wall thickness reduction. The equiaxial ferritic grains with an average size of 600 nm are generated through re-nucleation and grain growth by subsequent recrystallization annealing at 580 °C for 1 h heat preservation. The tensile strength of spun tubes has been founded to be proportional to the reciprocal of layer spacing of pearlite (LSP), and the elongation is inversely proportional to the reciprocal of LSP. This study shows that the developed method of stagger power spinning has the potential to be used to manufacture bulk metal components with nano/ultrafine grain structure. 相似文献