Advanced Materials Research Vols. 284-286

Abstract: ZnO₂ nanoparticles were synthesized via hydrothermal reaction between Zn₅(CO₃)₂(OH)₆ powder and 30 mass% H₂O₂ aqueous solution at 80 °C for 24 h, and ZnO powders with granular and rodlike morphologies were synthesized via hydrothermal decomposition of the as-synthesized ZnO₂ nanoparticles in water at 150-170 °C for 24 h. The obtained products were characterized by X-ray diffraction, Raman and Field emission scanning electron microscopy.

Abstract: This research applied molecular dynamics method to micro Couette flow of nanofluids, in order to examine the absorption layer near solid surfaces, and propose mechanisms of heat transfer enhancement due to flow. The model of nanofluids consisted of 4 nm Cu nanoparticles and liquid argon as base liquid, Lennard-Jones potential function was adopted to deal with the interactions between atoms. Through visual observation and analysis, it was found that the even-distributed liquid argon atoms near solid surfaces could be seemed as a reform to base liquid and had contributed to heat transfer enhancement. In the process of Couette flow, nanoparticles were rotating and vibrating besides moving translationally. The micro-motions of nanoparticles could disturb the continuity of fluid and strengthen partial flow nearby nanoparticles, and enhance heat transfer in nanofluids.

Abstract: Silica-based aerogels doped with nano-ITO powder were synthesized using sol–gel process followed by supercritical drying. The main factors were studied including dosage of compling agent KH570 and ITO. The result shows that thermal radiation conductivity is 0.02659 W/(m•K) with ITO of 44.44% after 10 g ITO powder is modified with 1 mL KH570. The microstructure and physical characteristic of the SiO₂–ITO aerogels were characterized by FTIR, SEM, TG-DSC and BET. Their specific surface was in the range of 513–775m²/g and their average pore size was mainly 20 nm. Nano-ITO powders are physically embedded by SiO₂ aerogels.

Abstract: The synthesis of hexagonal phase Mn-doped CdS (Cd_1-xMn_xS) nanorods was achieved by solvothermal treatment of a class of easily obtained, air-stable single-source molecular precursors (cadmium manganese diethyldithiocarbamates, Cd_1-xMn_x-(DDTC)₂) in ethylenediamine at 180 °C for 12 h. The structures and compositions of the as-synthesized products were characterized by X-ray diffraction, energy dispersive X-ray spectroscopy and transmission electron microscopy.

Abstract: Cracking behaviors of oxide films on A3, 30CrMnSiA steel under applied stress were investigated in this paper. Theoretical deductions confirmed that critical cracking conditions for oxide films on A3 and 30CrMnSiA steel did exist. Electrochemical tensile experiments in 3%NaCl aqueous solution showed that the critical cracking stress for oxide film on A3 steel is about 220MPa,the critical cracking stress for oxide film on 30CrMnSiA steel is about 80MPa.In-situ dynamic tensile experiments verified the correctness of the experiments results in the electrochemical tensile experiments.

Abstract: MoB/CoCr, a novel material for thermal spraying, with high durability is used to resist erosion by molten Al-12.07wt.%Si alloy. The durability of the MoB/CoCr coating prepared by low pressure plasma spraying (LPPS) has been investigated using a molten-metal immersion tester. The test revealed that the MoB/CoCr coating has much higher durability without dissolution in the molten Al-12.07wt.%Si alloy. Little change of crystal structure, mainly composed of ternary borides of Co₂MoB₂ and CoMoB, is observed after the immersion test, suggesting that the ternary borides have much higher durability.

Abstract: The Se/Te alloys nanorods have been synthesized through spontaneous oxidation of NaHE (E = Se and Te) by dissolved oxygen at room temperature. Phase structures and morphologies of the Se/Te products are investigated by XRD, EDS, SEM, and TEM. The composition of Se/Te alloys could be tuned via simply changing the value of n (n denoted as molar ratio of the starting reagent Se to Te). In order to obtain pure Se/Te alloys nanorods, the value of n should be higher than 3. Otherwise, by-product t-Te would be formed. A possible nucleation and growth mechanism of the Se/Te nanorods was discussed.

Abstract: Without using any templates or surfactants, flowerlike α-nickel hydroxide (Ni(OH)₂) was successfully synthesized by homogeneous precipitation method. The prepared products were characterized by X-ray powder diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and N₂ adsorption-desorption. The prepared Ni(OH)₂ is α-phase with specific surface area of 245.0 m²/g and shows flowerlike structure with 4-6 um in diameter.

Abstract: In a neutral environment, Chrysotile nanotubes have been synthesized by hydrothermal method, with MgO and SiO₂ powder as the starting materials. X-Ray Diffraction(XRD), Scanning Electron Microscopy(SEM), Transmission Electron Microscopy(TEM) are used to characterize the crystal structure and morphology of the as-prepared samples. We found that the diameter of Chrysotile is uniform. Their outer diameter is about 30~50 nm and the inner diameter is about 6~8 nm. The length of them is a few hundred nanometers. The XRD analysis indicates that the as-prepared Chrysotile is a Rhombohedral structures. The results of HRTEM and SAED showed that the {006} planes of serpentine roll up along the [600] direction to form the tubular structure. In addition, the curves of temperature and pressure with time showed that the water might participate in the reaction.

Abstract: Oxidative dehydrogenation of cyclohexane was studied over three pure Mg-V-O catalysts, which are Mg₃(VO₄)₂, Mg₂V₂O₇ and MgV₂O₆, respectively. Catalysts were prepared via citric acid complexation and characterized by N₂-adsorption, XRD, FT-IR, NH₃-TPD and H₂-TPR techniques. Among the pure magnesium vanadates, Mg₃(VO₄)₂ has the isolated active sites, weakly basic surface and lower reducibility of the metal cations, and could be recognized as the catalytic active phase. Mg₃(VO₄)₂ catalyst exhibited a better catalytic performance, on which a cyclohexene selectivity of 41.5% at cyclohexane conversion of 15.5% was obtained.