Ce_(0.7)Zr_(0.3)/γ-Al_2O_3纳米固溶体的制备及其结构

以氯氧化锆、硝酸铈、硝酸铝为原料,按n(Ce)∶n(Zr)=0.7∶0.3的比例,采用化学共沉淀法与有机物共沸蒸馏法,将CeO2、ZrO2分散到γ-Al2O3表面上使其形成Ce0.7Zr0.3O2/γ-Al23固溶体。用XRD考察纳米固溶体在不同温度下焙烧后的相结构。结果表明:Ce0.7Zr0.3O2/γ-Al2O3纳米固溶体为立方晶型,且随着焙烧温度的升高,样品的衍射峰依次变强,峰宽变窄。     

Si/Zr mesoporous catalysts for the vapour phase synthesis of alkylindoles

Si/Zr mesoporous MCM-41 catalysts were investigated in the vapour phase synthesis of 7-ethylindole (7-ETI) starting from 2-ethylaniline (2-ETAN) and ethylene glycol (EG). The catalysts were prepared from the corresponding alkoxides in the presence of a cationic surfactant, which acts as a structure-directing agent. After removal of the surfactant, the resulting mesoporous solids were characterised by X-ray diffraction, N₂ adsorption–desorption, temperature programmed desorption (TPD) of NH₃ and pyridine adsorption coupled with FTIR spectroscopy. As the amount of ZrO₂ increased in the catalysts, the BET surface area decreased, while an enhancement of the acidity took place. The activation of EG to 2-hydroxyacetaldehyde and its attack on 2-ETAN, leading to the formation of 7-ETI, was favoured by increasing the amount of ZrO₂ The maximum yield for the catalyst was obtained with ca. 50 wt.% of ZrO₂, which promoted the presence of Lewis and Brönsted acid sites of suitable strength and concentration, although mesoporous catalysts exhibited very good regenerability.     

Correlation between the milling time and hydrogen storage properties of ZrCrFe ternary alloy

Laves phases with AB₂ compositions are common type of topologically close packed structure. Furthermore, lave phases are capable of dissolving considerable amounts of ternary alloying additions. ZrCr₂ crystallized in the hexagonal C14 type of structure is one of interesting candidate among them, but it is not used as storage compound due to its excessive stability, at 323 K the equilibrium pressure is only 1.2 kPa. However the substitution of chromium by other elements can modify the crystal structure, the hydriding capacity and dissociation pressure of hydrogen. In this work Fe has been chosen as a substitute material for Cr and ZrCrFe ternary alloy is prepared using arc furnace. The mechanical alloying process has been introduced to produce nanocrystalline material. This paper presents comprehensive study on structural aspects of ball milled ZrCrFe alloy. On comparison of the XRD data, the broadening was found in the peak width with the increase of milling time which is clear indication of refinement of crystallite size. This refinement could also be confirmed from the SEM analysis also. PCT measurements were performed for a temperature range 303 K–373 K.     

Fabrication of ZrB2-Zr cermet using laser sintering technique

A combination of laser sintering/melting and induction heating techniques is used to fabricate ZrB₂-Zr ceramic-metal composite (cermet) 3-D structures using layer by layer deposition. It is shown that the interface between layers comprises an ~ 20 µm thick Zr-rich phase near the remelted zone. The starting powder mixtures consist of 30-50 wt.% Zr, which is used to assist binding of ZrB₂ particles. Sintered objects have densities > 95% of theoretical values and have microhardness values up to 16.0 GPa. ZrB₂-Zr cermet may reduce the likelihood of mechanical failures by increasing toughness and impact resistance contributed from the continuous Zr matrix, yet preserve good abrasive characteristics provided by ZrB₂ grains. The proposed method allows fabricating complex-shaped structures, and joining or repairing objects made from analogous ultra-high temperature materials.     

Research on intercrystalline corrosion,exfoliation corrosion,and stress corrosion cracking of Al–Zn–Mg–Sc–Zr alloy

The intercrystalline corrosion, exfoliation corrosion (EXCO), and stress corrosion cracking (SCC) of Al–Zn–Mg–Sc–Zr alloy were investigated by means of constant temperature immersion corrosion method, optical microscopy, transmission electron microscopy (TEM), and electrochemical impedance spectroscopy (EIS). The results show that intercrystalline corrosion, and EXCO susceptibility of Al–Zn–Mg–Sc–Zr alloy decrease gradually with increasing of aging time. Corrosion susceptibility order from low to high is as follows: OA > PA > UA > NA. The SCC susceptibility index of PA temper is more than OA temper at the same strain rate. According to TEM observation, with aging time prolonging, a part of η′ phases transform to η equilibrium phases, which become coarse gradually. The distribution discontinuity of the grain boundary precipitates increases. In addition, for Al–Zn–Mg–Sc–Zr alloy without EXCO, the EIS is comprised by a capacitive impedance arc at high frequency and an inductive impedance arc at low frequency. Once EXCO occurs, the EIS is composed of two capacitive impedance arcs at high frequency and at low frequency, respectively.     

Effect of Mn on the Magnetostriction and Magnetic Properties in Zr_(0.1)Tb_(0.9)(Fe_(1-x)Mn_x)_2 and Y_(0.1)Tb_(0.9)(Fe_(1-x)Mn_x)_2

Effect of Mn substitution for Fe in cubic Laves Zr_(0.1)Tb_(0.9)(Fe_(1-x)Mn_x)_2 and Y_(0.1)Tb_(0.9)(Fe_(1-x)Mn_x)_2 com-pounds is presented.Similar results in both systems are obtained: The structure and the magnetism of TbFe_2 areboth influenced slightly by a small amount of Y or Zr substitution for Tb;With increasing x value,the latticeconstant increases monotonously;the Curie temperature decreases linearly;while saturation magnetizationincreases linearly.For the small amount of Mn substitution for Fe in both systems,magnetostriction issignificantly larger than that in the pure iron alloys.The largest magnetostriction of|γ_‖-|γ_|=2200×10~(-6)at magnetic field of 2×10~7/4π A/mis obtained for Y_(0.1)Tb_(0.9)(Fe_(0.95)Mn_(0.05)_2.     

Microstructure and domain configurations in ferroelectric PbTiO3 and Pb(Zr,Ti)O3 thin fims

Ferroelectric domain configurations in PbTiO₃ and Pb(Zr_xT_1−x)O₃ (PZT, x = 0.3 or 0.5) thin films have been studied by transmission electron microscopy. The PbTiOg and PZT thin films have been deposited by the ionized cluster beam technique and radio frequency sputtering, respectively. The grain size in these thin films is typically less than 0.5 μm. Lamellar 90°-domain features have been observed in both PbTiO₃ and PZT (30/70) samples. The domain walls correspond to the {011} twin boundaries. La-doping and Ca-modification are shown to affect the microstructure of the PZT films. No clear domain feature occurs in the PZT thin film that has composition near the morphotropic phase boundary. The effects of grain sizes are briefly discussed.     

Effects of Sn on the oxidation and oxide characteristics of Zr alloys in water and a LiOH solution

To investigate the Sn effects on the oxidation and oxide characteristics of Zr-xSn (x=02.0wt%) binary alloys, autoclave tests were performed in pure water and LiOH solutions containing 2.2 and 70 ppm Li. Corrosion behavior of the Zr-xSn binary alloys was found to be highly dependent on the Sn content and test environment. Corrosion resistance of the Zr-xSn alloys decreased with increasing Sn content in pure water, but increased with increasing Sn content in the LiOH solution. In pure water, a high Sn content accelerated transformation of the oxide microstructure from a columnar grain to an equiaxed grain and the oxide crystal structure from tetragonal to monoclinic. However, this trend was not maintained in the LiOH solution because Li-penetration into the oxide played a more important role than Sn in the transformation of the oxide properties. It is suggested that high Sn content tends to retard Li-penetration into the oxide in LiOH solution.     

Memory characteristics of Au/PZT/BIT/p-Si ferroelectric diode

A ferroelectric memory diode consisting of Au/PZT/BIT/p-Si multilayer configuration has been fabricated by pulsed laser deposition (PLD) technique. The ferroelectric properties and the memory characteristics are investigated. The P-E curve of the PZT/BIT/p-Si films system had an asymmetry saturated hysteresis loop with P, = 15 μC/cm2 and Ec = 48 kV/cm, and the decay in remanent polarization was only 10% after 109 switching cycles, meanwhile the increase in coercive field was 12% . The C-V hysteresis loop and the I-V curve showed a memory effect derived from the ferroelectric polarization of PZT/BIT films, and the current density was 6.7 × 10-8 A/cm2 at a voltage of + 4V. Our diode had nonvolatile and nondestructive memory readout operation. There was a read current disparity of 0.05 μA for logic "1" and logic "0" at a read voltage of + 2V, and the stored logical value ("1" or "0") could be read out in 30 min.