We report a study of nanophases in the Lasub.2Osub.3–MOsub.3 (M = Mo, W) systems, which are known to contain a variety of good oxygen-ion and proton conductors. Mechanically activated Lasub.2Osub.3 + ...MOsub.3 (M = Mo, W) mixtures and the final ceramics have been characterized by differential scanning calorimetry (DSC) and X-ray diffraction (XRD) with Rietveld refinement. The microstructure of the materials has been examined by scanning electron microscopy (SEM), and their conductivity in dry and wet air has been determined using impedance spectroscopy. In both systems, the formation of hexagonal Lasub.15Msub.8.5Osub.48 (phase II, 5H polytype) (M = Mo, W) nanophases is observed for the composition 1:1, with exothermic peaks in the DSC curve in the range ~480–520 °C for Lasub.15Mosub.8.5Osub.48 and ~685–760 °C for Lasub.15Wsub.8.5Osub.48, respectively. The crystallite size of the nanocrystalline tungstates is ~40 nm, and that of the nanocrystalline molybdates is ~50 nm. At higher temperatures (~630–690 and ~1000 °C), we observe irreversible reconstructive phase transitions of hexagonal Lasub.15Mosub.8.5Osub.48 to tetragonal γ-Lasub.2MoOsub.6 and of hexagonal Lasub.15Wsub.8.5Osub.48 to orthorhombic β-Lasub.2WOsub.6. We compare the temperature dependences of conductivity for nanoparticulate and microcrystalline hexagonal phases and high-temperature phases differing in density. Above 600 °C, oxygen ion conduction prevails in the coarse-grained Lasub.18Wsub.10Osub.57 (phase I, 6H polytype) ceramic. Low-density Lasub.15Wsub.8.5Osub.48 and Lasub.15Mosub.8.5Osub.48 (phase II, 5H polytype) nanoceramics exhibit predominantly electron conduction with an activation energy of 1.36 and 1.35 eV, respectively, in dry air.
Due to their ability to form white light by mixture of blue emission and yellow emission from Dy.sup.3+ ions, Dy.sup.3+-doped phosphors have attracted much attention recently. For the sake of ...obtaining white-emitting phosphors excited by near-UV (ultraviolet) chip, a series of Gd(III)-MOF: xDy.sup.3+ (Gd(III)(BTC):xDy.sup.3+) (where MOF = metal-organic framework, and BTC = 1,3,5-benzenetricarboxylate) phosphors have been prepared by hydrothermal method, and Gd(III)-MOF: 0.0125Dy.sup.3+ is the optimal sample. When compared to that of normal Dy.sup.3+ doped inorganic compound phosphors, some new luminescent performances inducing by Gd(III)-MOF were presented: (a) CT band is redshifted by about 26 nm and is much stronger than f right arrow f transition band. (b) In the PL spectra, the blue emission bands have two split peaks, and the right peak is stronger than the left one. The chromaticity coordinates value of Gd(III)-MOF: 0.0125Dy.sup.3+ indicated that the optimal sample is greenish white-emitting phosphor under UV excitation. Kinetics of thermal decomposition of the Gd(III)-MOF: 0.0125Dy.sup.3+ was explored. Activation energies were determined by the KAS iterative method. The mechanism function of the decomposition was g(alpha) = (1 - alpha)^(- 1/2) - 1 determined by the Z(alpha) masterplots method, which was attributed to the chemical reaction mechanism.
A Co-Mn/Ni foam catalyst and alkali metal K-poisoned catalyst were prepared by an impregnation method using foamed Ni metal as a carrier. Mn was the active component, and Co was a trace auxiliary. ...The effects of different levels of alkali metal K poisoning and different concentrations of Co auxiliaries on the K poisoning resistance of the catalyst were studied. The results showed that the number of Brønsted acid sites on the surface of the catalyst, the reduction capacity and the number of unsaturated Ni atoms decreased after the addition of K. The interaction between the active Mn and the metallic Ni decreased, and the activity of the catalyst decreased. As the addition amount of added K increased, the catalyst alkali metal poisoning phenomenon became more significant. The kinetic studies showed that the activation energy increased after the addition of K, whereas the activation energy of K.sub.0.3Co.sub.0.5/Fresh catalyst decreased after Co modification. The amounts of Brønsted acid and Lewis acid sites on the surface of the K-poisoned catalyst were improved dramatically by Co modification of the Mn/Ni foam catalyst. K destroys the extremely important Brønsted acid sites that adsorb and activate NH.sub.3, reducing the performance to less than half. Additionally, NH.sub.3-TPD and in situ DRIFT analyses showed that Co, K, Mn and Ni synergistically improved the acid sites. The number of Brønsted acid sites and Lewis acid sites on the catalyst surface were greatly increased in the K.sub.0.3Co.sub.0.5/Fresh catalyst, whose reduction performance increased substantially compared with the K.sub.0.3/Fresh catalyst.
Four catalysts were prepared in our previous work using the solution combustion method, incipient-wetness impregnation method, colloid mill circulating impregnation method, and ...hydrothermal-precipitation method, respectively, labeled as SCM, IMP, T310, and HTP. And the performance (stability) of the four catalysts for COsub.2 reforming of CHsub.4 was investigated at 800 °C. In this paper, the composition and structure characteristics of the deposited carbon on the above four catalysts were tested through TEM, Raman, TPH, and TG-DTG technologies. The results showed that filamentous carbon was the primary type of carbon deposition on the catalysts, and a large amount of accumulated carbon would block the catalyst pores, affecting the catalytic performance. The carbon deposited on the catalyst prepared using the hydrothermal-precipitation method calcined at 800 °C exhibited a high degree of graphitization, and the proportion of graphitized carbon was considerable, which is harmful to the stability of the catalyst. The decarburization temperature of the deposited carbon on the four catalysts was mainly in the range of 500–700 °C. Using the Coats–Redfern model, as the reaction order was set as 1, 2, 3, 4, and 5, the decarburization activation energy ranged between 50 and 80 kJ/mol.
Moslae herba is considered to be a functional food ingredient or nutraceutical due to its rich bioactive components. The present research was carried out to investigate the effects of different ...temperatures (40 °C, 50 °C and 60 °C) on the drying characteristics, textural properties, bioactive compounds, flavor changes and final quality attributes of Moslae herba during the hot air-drying process. The results showed that the Midilli model could effectively simulate the drying process of Moslae herba. The effective moisture diffusivity ranged from 3.14 × 10sup.−5 msup.2/s to 7.39 × 10sup.−5 msup.2/s, and the activation energy was estimated to be 37.29 kJ/mol. Additionally, scanning electron microscopy (SEM) images of Moslae herba samples showed the shrinkage of the underlying epidermal layers and glandular trichomes. In total, 23 volatile compounds were detected in Moslae herba. Among them, the content of thymol increased from 28.29% in fresh samples to 56.75%, 55.86% and 55.62% in samples dried at temperatures of 40 °C, 50 °C and 60 °C, respectively, while the other two components, p-cymene and γ-terpinene, decreased with an increase in the temperature. Furthermore, both radar fingerprinting and principal component analysis (PCA) of the electronic nose (E-nose) showed that the flavor substances significantly altered during the drying process. Eventually, drying Moslae herba at 60 °C positively affected the retention of total phenolics, total flavonoids and the antioxidant capacity as compared with drying at 40 °C and 50 °C. The overall results elucidated that drying Moslae herba at the temperature of 60 °C efficiently enhanced the final quality by significantly reducing the drying time and maintaining the bioactive compounds.
Nonmetallic doping can induce oxygen vacancies on semiconductor surfaces to form local gaps and subsequently regulate semiconductor absorption band edge. However, the existence and instability of ...these holes challenge the activity and stability of the semiconductor catalysts. In this work, we demonstrate a molten salt homogeneous doping method of non-metallic doping involving double doping, on the surface and bulk phase of the catalyst, thereby NiO.sub.x/B-TiO.sub.2@CdS core-shell nanowires achieving high photocatalytic hydrogen evolution activity. The double doping function of the homogeneous method is realized by the fact that B.sub.2O.sub.3 acts as both molten salt and doping precursor. The dual-doping of B reduced exciton binding energies and improves the stability and density of oxide vacancies resulting in high light utilization rate. The results showed that the oxygen vacancy density of the catalyst remained at 83.3% after 10 h of reaction. In addition, the construction of a heterojunction enhances the separation efficiency of photogenerated carriers, and the loading of group catalyst reduces the activation energy of reaction, thus improving the catalytic efficiency of the catalyst. As a result, the photocatalytic performance of the B-TiO.sub.2@CdS core-shell structure photocatalyst is significantly better than that of bare CdS. The H.sub.2 evolution rate is increased to 8.11 mmol/g with NiO.sub.x/B-TiO.sub.2@CdS, which is 5.7 times greater than CdS (1.42 mmol/g). The research furnishes a new strategy for the design of stable oxygen vacancies within heterojunction-based photocatalysts to produce H.sub.2 from photocatalytic water splitting.
We have investigated the space-charge-limited conduction (SCLC) in two different metal-insulator-metal junctions of the form: Au/BaTiO.sub.3 (BTO)/Nb:SrTiO.sub.3 (Nb:STO) and ...Au/BTO/La.sub.0.67Ca.sub.0.33MnO.sub.3 (LCMO) at various temperatures. The SCLC model has been employed to determine various parameters relevant to the charge conduction in these systems. While the trap density increases with decreasing temperature, the ratio of free to trapped carriers (theta) reduces for both the junctions, which can be understood as the thermally activated process. The extracted activation energies of 0.071 eV for Au/BTO/Nb:STO and 0.154 eV for Au/BTO/LCMO indicate the presence of shallow trap level. Moreover, the Fermi level at thermal equilibrium approaches the intrinsic limit with increasing temperature. Comparing both the junctions, we observe lower theta and deeper trap level in BTO/LCMO junction.
The mixed ionic and electronic oxide LaNisub.0.6Fesub.0.4Osub.3−δ (LNF) is a promising ceramic cathode material for solid oxide fuel cells. Since the reaction rate of oxygen interaction with the ...cathode material is extremely important, the present work considers the oxygen exchange mechanism between Osub.2 and LNF oxide. The kinetic dependence of the oxygen/oxide interaction has been determined by two isotopic methods using sup.18O-labelled oxygen. The application of the isotope exchange with the gas phase equilibrium (IE-GPE) and the pulsed isotope exchange (PIE) has provided information over a wide range of temperatures (350–800 °C) and oxygen pressures (10–200 mbar), as each method has different applicability limits. Applying mathematical models to treat the kinetic relationships, the oxygen exchange rate (rH, atom × cmsup.−2 × ssup.−1) and the diffusion coefficient (D, cmsup.2/s) were calculated. The values of rH and D depend on both temperature and oxygen pressure. The activation energy of the surface exchange rate is 0.73 ± 0.05 eV for the PIE method at 200 mbar, and 0.48 ± 0.02 eV for the IE-GPE method at 10–20 mbar; for the diffusion coefficient, the activation energy equals 0.62 ± 0.01 eV at 10–20 mbar for the IE-GPE method. Differences in the mechanism of oxygen exchange and diffusion on dense and powder samples are observed due to the different microstructure and surface morphology of the samples. The influence of oxygen pressure on the ratio of contributions of different exchange types to the total oxygen exchange rate is demonstrated. For the first time, the rate-determining step in the oxygen exchange process for LNF material has been identified. This paper discusses the reasons for the difference in the mechanisms of oxygen exchange and diffusion.
The spectral distribution of the photoconductivity and the temperature dependence of the photocurrent of MnIn.sub.2S.sub.4 single crystals were investigated. The intrinsic and impurity ...photoconductivities as well as a maximum at energy 2.69 eV, which is associated with the intracenter transition of Mn.sup.2+ ions (sup.6A.sub.1 right arrow sup.4A.sub.1), were found in the photoconductivity spectrum. The wavelength region 600-1000 nm appears with an excess of manganese in the crystals and is caused by a donor defect. The increase in the photocurrent at 80-145 K is associated with thermal depletion of the adhesion levels. The activation energy of the adhesion levels was determined. Keywords: MnIn.sub.2S.sub.4, single crystal, spectral distribution, photoconductivity, photocurrent, activation energy.
Thermal characterization of different compositions of Ge.sub.30-xSb.sub.xTe.sub.10Se.sub.60 (x = 0, 5, 10, 15, 20 at.%) glassy materials has been investigated through differential scanning ...calorimetry (DSC). The tested glasses have been synthesized by melt-quench technique. Glassy materials display compositional phase separation at x = 0, 5, 10, 15 at.%. For additional increase in Sb content at x = 20 at.%, the separation of phases combines in the glass matrix. The glass transition temperature (T.sub.g), initial temperature of crystallization (T.sub.c), peak crystallization temperature (T.sub.p) and melting temperature (T.sub.m) were found to be affected by both heating rate and composition. It is noticed that the increasing of antimony mass percentage in the glassy matrix is leading to decrease in T.sub.g, T.sub.c, T.sub.p and T.sub.m values. The melting temperature (T.sub.m) of these glasses was found in the range 733-746 K for the first phase and in the range 740-792 K for the second phase. The activation energy of glass transition (E.sub.g), activation energy for crystallization (E.sub.c), Avrami index (n) and fragility index (F.sub.i) were calculated using these specific temperatures. E.sub.g decreases with increasing Sb content in all studied samples, but E.sub.g is increasing in the sample with Sb content of 20%, and hence, it varies between 102.7 and 110.6 kJ approximately, whereas (E.sub.c) decreases with the increase in the Sb content in all the tested samples and varies between 283 and 339 kJ. The fragility index varies between 10 and 26 indicating that the melts of these glasses are strong, and the fragility is minimum. The results were discussed in terms of the average coordination number N.sub.C and chemical bond approach.
