The thermal decompositions of mechanically activated and nonactivated galenas were studied by thermogravimetry analysis (TGA)
at the heating rate of 10 K min−1 in argon. Results indicate that the initial temperature of thermal decomposition (abbreviated as Tdi) in the TGA curves for different galenas decreases gradually with increased grinding time. The specific granulometric surface
area (SG), the structural disorder, and the content of elemental sulfur of mechanically activated galenas were analyzed by an X-ray
diffraction (XRD) laser particle-size analyzer, XRD analysis, and the gravimetric method, respectively, which shows that the
specific granulometric surface area of mechanically activated galenas remains almost constant after a certain grinding time,
but the lattice distortions (ε) rise, the crystallite sizes (D) decrease, and the elemental sulfur contents of mechanically activated galenas increase with increased grinding time. The
results imply that the decrease of the initial temperature of thermal decomposition in the TGA curves for mechanically activated
galenas is mainly caused by the increase of lattice distortions, and the formation of new dangling bonds resulted from the
production of elemental sulfur of mechanically activated galenas with increased grinding time. Finally, the differences in
the thermal-decomposition reactivity between nonactivated and mechanically activated galenas were also discussed. 相似文献
Al-doped LiVPO4F cathode materials LiAlxV1-xPO4F were prepared by two-step reactions based on a car-bothermal reduction (CTR) process. The properties of the Al-doped LiVPO4F were investigated by X-ray diffraction (XRD),scanning electron microscopy (SEM),and electrochemical measurements. XRD studies show that the Al-doped LiVPO4F has the same triclinic structure (space group p-↑1 ) as the undoped LiVPO4F. The SEM images exhibit that the particle size of Al-doped LiVPO4F is smaller than that of the undoped LiVPO4F and that the smallest particle size is only about 1 μm. The Al-doped LiVPO4F was evaluated as a cathode material for secondary lithium batteries,and exhibited an improved reversibility and cycleability,which may be attributed to the addition of Al^3+ ion by stabilizing the triclinic structure. 相似文献
The leaching kinetics of willemite in ammonia-ammonium chloride solution was investigated. The effects of the ammonia-ammonium
ratio, particle size, temperature, and total ammonia concentration on the leaching rate of willemite were determined. The
results show that the optimum ammonia-ammonium ratio is 1:2 over the studied range. The zinc extraction increases with the
reduction of particle size and with the increase of temperature and the total ammonia concentration. Leaching kinetics indicate
that the grain pore model could be adopted to describe the leaching process, and diffusion is the main rate-controlling step.
The apparent activation energy was determined to be 54.47 ± 6.39 kJ/mol and a reaction order with respect to NH3(aq) was 3.16 ± 0.40, both of which are likely a result of the parallel nature of the chemical reaction and diffusion in porous
solids, even if the chemical reaction is not the rate-controlling step. 相似文献
The thermoelectric power of Rh and Ir was redetermined between 100 K and 1400 K. It varies almost linearly from +1.7 μV K−1 to −3.8 μV K−1 for Rh and from +1.5 μV K−1 to −2.2 μV K−1 for Ir. The diffusive part of the thermopower could be calculated from the density of states. It is approximately equal to
the temperature dependence of the electrochemical potential of the electrons divided by the electronic charge. This is attributed
to the approximate establishment of local equilibrium between electrons and lattice atoms above 400 K—a condition not fulfilled
in the phonon-drag regime below 300 K. 相似文献
Porous graphitic carbon nanorings (PGCNs) are proposed by smart catalytic graphitization of nano-sized graphene quantum dots (GQDs). The as-prepared PGCNs show unique ring-like morphology with diameter around 10 nm, and demonstrate extraordinary mesoporous structure, controllable graphitization degree and highly defective nature. The mechanism from GQDs to PGCNs is proven to be a dissolution-precipitation process, undergoing the procedure of amorphous carbon, intermediate phase, graphitic carbon nanorings and graphitic carbon nanosheets. Further, the relationship between particles size of GQDs precursor and graphitization degree of PGCNs products is revealed. The unique microstructure implies PGCNs a broad prospect for energy storage application. When applied as negative electrode materials in dual-carbon lithium-ion capacitors, high energy density (77.6 Wh·kg−1) and super long lifespan (89.5% retention after 40,000 cycles at 5.0 A·g−1) are obtained. The energy density still maintains at 24.5 Wh·kg−1 even at the power density of 14.1 kW·kg−1, demonstrating excellent rate capability. The distinct microstructure of PGCNs together with the strategy for catalytic conversion from nanocarbon precursors to carbon nanorings opens a new window for carbon materials in electrochemical energy storage.
The effect of mannitol and 1,2-octanediol on gibbsite crystallization from seeded sodium aluminate liquor was investigated and compared. The inhibitory effect of mannitol increases with its concentration, in good agreement with other strong inhibitors. Low concentrations of 1,2-octanediol have no apparent influence on crystallization but above 1.0 mmol/L severe inhibition occurs with crystallization rate rapidly decreasing until completely stopped 2.0 mmol/L. Unlike with mannitol, the inhibition cannot be alleviated by doubling the seed amount or by adding oleic acid. Unseeded experiments also show that a high concentration of 1,2-octanediol inhibits Al(OH)3 nucleation while the influence of low concentration of 1,2-octanediol is negligible. 1,2-octanediol appears to be a unique inhibitor for alumina crystallization. The effect is evident below the critical micelle concentration of 1,2-octanediol in sodium aluminate solution indicating it is a molecular effect. Infrared spectroscopy indicates that the structure of the solution might be changed when the concentration of 1,2-octanediol is relatively high. Clearly the inhibition by mannitol derives from adsorption on the active surface sites, while inhibition by 1,2-octanediol appears to be due to changing the characteristic of sodium aluminate liquor. 相似文献
Forming core–shell-structured phosphor particles is an effect way to improve the properties of the rare-earth-doped inorganic luminescent systems, as well as to achieve a reduction in the amount of expensive rare earth metal. Heterogeneous nucleation processing is a commonly used method to prepared core–shell-structured particles. A nanocomposite BaSO4/Y2O3:Eu3+ powder was prepared by coating BaSO4 submicrospheres with nano-Y2O3:Eu3+ particles via heterogeneous nucleation processing. Thermogravimetric analysis and differential scanning calorimetry (TGA/DSC) were utilized to reveal the mechanism of the homogenous precipitation reaction process. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS) were utilized to characterize the BaSO4/Y2O3:Eu3+ core–shell-structured phosphor particles. By controlling the hydrolysis of urea, BaSO4 particles are well coated with the shell of Y2O3:Eu3+, and the nucleation of coating materials is predominantly heterogeneous rather than homogeneous. Photoluminescence spectra were utilized as well. The BaSO4/Y2O3:Eu3+ particles show a red emission corresponding to 5D0–7F2 of Eu3+ under the excitation of ultraviolet. 相似文献