Influence of Aging Time on the Properties of Precursors of CuO/ZnO Catalysts for Methanol Synthesis

The aging process of pure copper precursors and copper-zinc binary precursorswere studied by XRD, TG-DTG and TPR techniques. The catalytic activity and stability of CuO/ZnOwere tested using fixed-bed flow reactor, and the physical properties of the catalysts and Cuspecies were characterized with N_2 adsorption and N_2O passivation method, respectively. For theCu-Zn binary system prepared at the precipitating condition of pH=8.0 and temperature=80℃, theinitial phase was a mixture of copper nitrate hydroxide Cu_2(NO_3)(OH)_3, georgeite and hydrozinciteZn_5(CO_3)_2(OH)_6. By increasing the duration of its aging time, the phase of Cu_2(NO_3)(OH)_2first transited to georgeite, and then interdiffused into Zn_5(CO_3)_2(OH)_6 and resulted in two newphases: rosasite (Cu,Zn)_2CO_3(OH)_2 and au-richalcite (Zn,Cu)_5(CO_3)_2(OH)_6. The former phasewas much easier to be formed than the latter one, while the latter phase was more responsible forthe activity of methanol synthesis than the former one. It is found that the composition andstructure of the precursors altered obviously after the colour transition point. The experimentalresults showed that methanol synthesis is a structure-sensitive catalytic reaction.

Effects of precipitate aging time on the cerium-zirconium composite oxides

Cerium-zirconium composite oxides with high performance were synthesized by a co-precipitation method, using zirconium oxychloride and rare earth chloride as raw materials. The effects of precipitate aging time on the properties of cerium-zirconium composite oxides were investigated. The prepared cerium-zirconium composite oxides were characterized by X-ray diffraction（XRD）, BET specific surface area, pulsed oxygen chemical adsorption, H2 temperature-programmed-reduction（H2-TPR）, scanning electron microscopy（SEM）, etc. The results showed that the precipitate aging time caused great effects on the properties of cerium zirconium composite oxides. With the increase of aging time, the cerium zirconium composite oxides showed enhanced specific surface area, good thermal stability, and high oxygen storage capacity（OSC）. The best performance sample was obtained while the precipitate aging time up to 48 h, with the specific surface area of 140.7 m2/g, and OSC of 657.24 μmolO2/g for the fresh sample. Even after thermal aged under 1000 oC for 4 h, the aged specific surface area was 41.6 m2/g, moreover with a good OSC of 569.9 μmolO2/g.

Influence of synthesis parameters on the crystallinity and Si/Al ratio of NaY zeolite synthesized from kaolin

Well-crystallized high-silica NaY zeolites （Si/Al〉2.5） were prepared from a reaction mixture consisting of metakaolin, sodium silicate solution and seed solution via optimization of the mixture composition and reaction conditions. The transformation from kaolin to high-silica NaY zeolite was confirmed by XRD, SEM and IR techniques. Subsequently, the influence of synthesis parameters, i.e. initial SIO2/Al2O3, initial Na2O/SiO2, initial H2O/SiO2, aging time of the seed solution, crystallization temperature and crystallization time, on the NaY growth was investigated in terms of crystallinity and Si/Al ratio. The results showed that the effects of initial SiO2/Al2O3, initial Na2O/SiO2 and initial H2O/ SiO2 on the crystaIlinity and Si/Al ratio of NaY zeolite are similar to those observed in the conventional syntheses of NaY zeolites only using sodium silicate solution as silicon source. However, due to the use of metakaolin as the main silicon and aluminum sources in the present study, a long crystallization induction period of 20 h was achieved, which can be attributed to the dissolution of metakaolin. In addition, different from the conventional syntheses of zeolite NaY, pure NaY zeolites （i.e. without NaP zeolite impurity） were still obtained even at 120℃ because of the use of a large quantity of seed solution （23 wt%） in the reaction mixture. As the aging time of the seed solution increased from 3.5 h to 22 h, the relative crystallinity of the NaY zeolite first increased sharply and then reached a plateau, while the Si/Al ratio first increased rapidly up to a maximum value of 2.75 corresponding to an aging time of 6.5 h, and then decreased sharply with the aging time.

Aging process design based on the morphological evolution ofγprecipitates in a 4th generation nickel-based single crystal superalloy

In order to meet the design requirements of the aging treatment process of a 4th generation nickel-based single crystal superalloy(Ni-SX)developed independently,the effects of aging temperatures and aging times on the precipitation and morphological evolution ofγprecipitates are studied.The morphological evolution behavior ofγprecipitates during the aging process is summarized subsequently and the coarsening behavior ofγprecipitates is discussed by comparing with the Lifshitz-Slyozov-Wagner model(LSW)and the trans-interface diffusion-controlled model(TIDC).It is demonstrated that primary aging temperature and secondary aging time dominate the size and squareness ofγprecipitates respectively,a narrow primary aging temperature range and a suitable secondary aging time are allowed to obtain the optimized morphology ofγprecipitates.The optimal aging process of the Ni-SX investigated in the present work is obtained for 1100-1120°C/4 h and 870°C/16 h,confirmed by the corresponding creep tests.The coarsening growth ofγprecipitates in short-term aging also conforms to the LSW model well.Besides,the aging process design rules of various Ni-SXs of different generations are also summarized.

Morphology Controlling of the Ultrafine Cerium Dioxide (CeO_2) Precursor

The synthesis of ultrafine cerium dioxide precursor via homogeneous precipitation was studied. Mixed aqueous solution of anhydrous cerium nitrate and urea was first heated to 85℃ for 2 h, and the prepared suspension was then aged at room temperature for various periods of time. White precipitate was finally collected by centrifuging and washed with distilled water and anhydrous ethanol. The obtained cerium dioxide (CeO2) precursor was observed with SEM. It was found that the morphology and size of the precursor were strongly affected by aging time and stirring conditions (with or without stirring). The precipitated fine spherical particles of the precursor changed their shape from ellipse to slice or directly to slice. Fine spherical monodispersed (300 nm) precursor powders could be obtained by controlling the aging time. Stirring the solution also could change the reaction process and thus the morphology and size of the precursor were changed.

MORPHOLOGY CONTROL OF ULTRAFINE CeO_2 AND ITS POLISHING EFFICACY

Homogenous precipitation and subsequent calcination has been used tosynthesize ultrafine ceria from cerium nitrate and urea solution. The ceria calcined from theprecursor inherit the size and morphology of it. The size and morphology of the precursor areclosely related to the preparation process. The morphology, size and distribution of the precursorcould be tailored by changing the reaction condition and the ageing time. Monodispersed 200 nm sizedspherical particles is prepared by this method. The powder is used in the chemical-mechanicalpolishing of Si wafer. The average surface roughness of the polished Si wafer is 0.171 nm measuredby AFM.

Effect of Zr addition on precipitates in K4169 superalloy

In order to investigate the effect of Zr addition on the precipitations of K4169 superalloy,a manual electric arc furnace was used to prepare the superalloy with different Zr addition from 0.03wt.% to 0.07wt%.After standard heat treatment and long-time aging,the microstructures of the alloys were observed using XRD,SEM and TEM.The results show that Zr not only inhibits the precipitation of Laves phase at the grain boundary,but also significantly promotes the precipitation of earlobe-like γ' and γ″ phases.After long time aging at 680℃ for 500 h,the γ″ phase grows up obviously and forms a γ'/γ'' clad microstructure when the Zr addition is 0.03 wt.%.A large number of fine orbed γ' particles precipitate in the grains and some γ″ phase transforms to disk-like δ phase when the Zr addition increases to 0.05wt.%.The nano-polycrystalline γ' phase precipitates in the grains and there is a little δ phase when the Zr addition is 0.07wt.%.As the Zr addition increases,the amount of Laves phase at the grain boundary decreases at first,and then increases and forms flaky morphology.

The Study on the Mechanical Properties of Optical Fiber With Long-Term Time Aging

The fiber properties depending on the coating thickness and long-term time aging were investigated. The coating strip forces of optical fiber were strongly increased with secondary coating thickness. But it did not change with time aging up to 90 days. The tensile strength and stress corrosion parameters of coated fiber were increased with time aging also but the increasing rate was quite different depending on the coating

胶体陈化时间对TiO_2致密层及钙钛矿太阳电池性能的影响探究（英文）

钙钛矿太阳电池的光伏性能有赖于对材料的化学组分、晶体以及微观结构的精细调控和对工艺条件和制备过程的控制.本工作针对不同陈化时间的溶胶制备的TiO_2致密层与太阳电池性能之间的关联性进行了研究.研究中,通过溶胶-凝胶法制备了致密、均匀的TiO_2薄膜,并研究了其表面形貌及厚度对钙钛矿太阳电池性能的影响.通过调节溶胶的陈化时间可以实现对TiO_2表面形貌和厚度的控制,由于陈化后的溶胶会提高TiO_2致密层的覆盖度,粗糙度及光的折射率,并有效阻挡电子的复合,从而导致钙钛矿太阳电池中短路电流密度和填充因子提升.钙钛矿薄膜的吸收光谱,光致发光谱,TiO_2薄膜的循环伏安测试及整个电池的交流阻抗谱的测试结果,也进一步论证了该结论.结果显示使用陈化时间为4h的溶胶制备的钙钛矿电池获得了15.7%的能量转化效率,比使用0h陈化的溶胶制备的太阳电池效率高出50%,是使用陈化时间为8h的溶胶制备的太阳能电池效率的3倍.