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101.
102.
采用浸渍法和共沉淀法制备了CrOx/ZrO2样品.制备过程中所得沉淀都经100 ℃碱液回流老化24 h.通过X射线衍射、X射线光电子能谱、氮吸附、差热-热重分析等手段对样品进行了表征.结果证实,碱液回流过程中会有SiO2从所用的玻璃器皿进入样品, SiO2的表面修饰作用提高了载体的热稳定性.氧化铬的引入进一步提高了所得样品的比表面和热稳定性.与浸渍法相比,共沉淀法制备的样品具有更好的性能.其中铬锆摩尔比为0.15时,用NaOH作沉淀剂, pH值为13的条件下制备的样品在1000 ℃焙烧后比表面仍达到121 m2•g-1. 相似文献
103.
R. Rodríguez S. Jiménez-Sandoval M. Estevez S. Pacheco S. Vargas 《Journal of Sol-Gel Science and Technology》2007,44(2):97-104
The quenching process of the laser-induced luminescence of Co(II)-doped zirconia samples prepared by the sol–gel method is
reported. Zirconia monoliths doped with Co(II) at different concentrations, were laser irradiated producing fluorescence;
its intensity, measured by the slope at the low energy side of the Raman spectra, is reduced with the irradiation time. The
rate the fluorescence decays can be modeled as a double exponential function of the irradiation time; the characteristic times
involved in this quenching process are in the range of seconds. The suppression of the luminescence has been associated to
the local heating produced when the laser beam is focused in a small area (≈2 microns in diameter) on the sample. This heating
process reduces physical (such as grain boundaries and surface states) and chemical (oxygen vacancies) defects; however, some
residual fluorescence still remains after long periods of illumination.
R. Rodríguez is on sabbatical leave at Cinvestav, Unidad Queretaro. 相似文献
104.
Iraj Mohammadpoor-Baltork Majid Moghadam Shahram TangestaninejadValiollah Mirkhani Arsalan Mirjafari 《Polyhedron》2008
A wide variety of primary and secondary alcohols were efficiently converted to their corresponding methoxymethyl (MOM) and ethoxymethyl (EOM) ethers in the presence of catalytic amounts of supported H3PW12O40 on silica gel and zirconia at room temperature and under microwave irradiation at solvent-free conditions, whereas, phenols and tertiary alcohols remained intact under the same reaction conditions. Deprotection of these ethers to their parent alcohols was also achieved using these heterogeneous catalysts in ethanol, as a green solvent, under reflux conditions and microwave irradiation. Selective deprotection of primary and secondary MOM- and EOM-ethers in the presence of phenolic and tertiary ones, methyl and benzyl ethers, esters and trimethylsilyl ethers was achieved by these reagent systems. The present methodology offers several advantages such as short reaction times, high yields, simple procedure, heterogeneous reaction conditions, selectivity, non-toxicity and reusability of the catalysts. 相似文献
105.
Liping Liang Yao Xu Lei Zhang Dong Wu Yuhan Sun 《Journal of Sol-Gel Science and Technology》2008,47(2):173-181
Polyvinylpyrrolidone (PVP)/ZrO2-based hybrid thin films, with suitable properties for application in the high power lasers, have been prepared combining
the advantages of both the sol–gel route and the organic-inorganic hybrid materials. By virtue of light scattering analysis,
the chemical composition of the reaction system was fully optimized, endowing the films with good optical properties and high
laser-induced damage threshold (LIDT). Light scattering studies also provided valuable structural information about the hybrid
sols, which offered a better understanding of the structure and performance of the hybrid films. Our experiments showed that,
in the hybrid sols, the incomplete substitution for the chelating ligands by the hydroxyls might considerably conceal and
weaken the effect of PVP on the nucleation and growth of ZrO2 particles. Thus, the incorporation of PVP only resulted in slight decreases in the refractive index and LIDT of the films.
By energy relaxation through their flexible polymer chains, however, the addition of PVP could easily enhance the stress compatibility
between the high- and low-index layers and then facilitate the deposition of the multi-layer highly reflective mirrors. 相似文献
106.
107.
采用共沉淀法制备了Fe掺杂的ZrO2样品,并采用X射线衍射、N2吸附-脱附、紫外漫反射光谱、扫描电镜-电子能谱、氨程序升温脱附、X射线光电子能谱和原位红外光谱进行了表征。结果表明, Fe进入ZrO2晶格中有效稳定了其晶相结构为单一的四方相。这些样品可很好地催化苯酚气相甲基化反应,其催化活性取决于Fe含量,并与样品中L酸有关。 相似文献
108.
109.
S. El Hajjaji S. Manov J. Roy T. Aigouy A. Ben Bachir L. Aries 《Applied Surface Science》2001,180(3-4):293-301
Conversion coatings modified by deposits of electrolytic alumina added or not with yttria and/or zirconia, have been studied which are well known for their resistance to chemical attack and high temperature. Conversion coating, characterised by a particular morphology and strong interfacial adhesion with the substrate, facilitate the electrochemical deposition of ceramic layers and enhance their adhesion to the substrate. Zirconia–alumina coating behaviour at 1000°C is similar to that of alumina coating; from 800°C, the chromium diffuses from the stainless steel through the electrolytic refractory coating up to the external interface, provokes discontinuities and can modify its protective character. Yttrium stabilises the cubic and the tetragonal form of the zirconia; so, during cooling, the phase transformation near 1000°C of tetragonal zirconia to monoclinic form cannot take place. 相似文献
110.
Polycrystalline tetragonal zirconia fiber was obtained by pyrolysis of precursor fibers from citrate‐acetate‐zirconium complex solution. The viscous zirconia sol with good spinnability was prepared by aging the starting solution of ZrOCl2 · 8H2O (ZOC) in the presence of acetic acid (HA) and citric acid (CA). The effects of molar ratio of zirconium cation to carboxylic acid and the aging time on the formation of spinnable sol were investigated. Thermogravimetric (TG) analysis, x‐ray diffraction (XRD), infrared (IR) spectra, and scanning electron microscope (SEM) techniques were used to characterize the sintered fibers. The results show that the fibers obtained at 1400°C are crack‐free with diameter of ca. 5–10 µm. 相似文献