Surface micromachining via solid electrochemical reaction on oxide ion conductors

We propose a simple and novel route for the surface microstructuring of tough materials (glassy carbon, SiC, W and Mo) through a solid electrochemical reaction at a microcontact between the oxide ion conductor and target substrate. More specifically, the surface of materials was locally oxidized by an anodic electrochemical reaction with the oxide ion conductor via the microcontact under a dc bias. Since the oxidation products of the targets were gaseous or sublimable, a fine-patterned surface was obtained as a result of the continuous consumption of the oxidation products formed at the microcontact. The success of the proposed method may stimulate such conventional applications of oxide ion conductors.     

Effect of alkali content on AC conductivity of borate glasses containing two transition metals

Sodium borate glasses containing iron and molybdenum ions with the total concentration of transition ions constant and gradual substitution of sodium oxide (network modifier) by borate oxide (network former) was prepared. Densities, molar volume, DC and AC conductivities are measured. The trends of these properties are attributed to changes in the glass network structure. Their DC and AC conductivity increased with increasing NaO concentration. The increase of AC conductivity of sodium borate glasses is attributed to the chemical composition and the hopping mechanism of conduction. Measurements of the dielectric constant (ε) and dielectric loss (tan δ) as a function of frequency (50 Hz–100 kHz) and temperature (RT—600 K) indicate that the increase in dielectric constant and loss (ε and tan δ) values with increasing sodium ion content could be attributed to the assumption that Fe and Mo ions tend to assume network-forming position in the glass compositions studied.The variation of the value of frequency exponent s for all glass samples as the function of temperature at a definite frequency indicates that the value of s decreases with increasing the temperature which agrees with the correlated barrier-hopping (CBH) model.     

EPR and UV studies of VO ions in potassium d-gluconate monohydrate single crystals

Electron paramagnetic resonance (EPR) of VO²⁺ doped potassium hydrogen d-gluconate single crystals and powder have been examined at room temperature. Single crystal rotations in each of the three mutually orthogonal crystalline planes namely ac, ba and ca indicate two different VO²⁺ complexes. Each complex is located in different chemical environments, each environment containing two magnetically inequivalent VO²⁺ sites in distinct orientations occupying substitutional positions in the lattice and showing a very large angular dependence. The powder spectrum also clearly indicates four different VO²⁺ complexes, confirming the single crystal analysis. Crystalline field around the VO²⁺ ion is nearly axial. The optical absorption spectrum of VO²⁺ ions in the crystal lattice is also studied at room temperature. The characteristic spectrum of the VO²⁺ ions has two absorption bonds. The bond positions are at 17 857 and 11 235 cm^-1. Spin Hamiltonian parameters and molecular orbital coefficients are calculated from the EPR and the optical data, and results are discussed.     

Enhanced cyclability of triple-metal-doped LiMn2O4 spinel as the cathode material for rechargeable lithium batteries

To improve the cycle performance of spinel LiMn₂O₄ as the cathode of 4-V-class lithium secondary batteries, spinel phases LiM _x Mn_2 − x O₄ (M=Li, Fe, Co; x = 0, 0.05, 0.1, 0.15) and LiFe_0.05M _y Mn_{1.95 − y} O₄ (M=Li, Al, Ni, Co; y = 0.05, 0.1) were successfully prepared using the sol–gel method. The spinel materials were characterized by powder X-ray diffraction (XRD), elemental analysis, and scanning electron microscopy. All the samples exhibited a pure cubic spinel structure without any impurities in the XRD patterns. Electrochemical studies were carried out using the Li|LiM _x Mn_2 − x O₄ (M=Li, Fe, Co; x = 0, 0.05, 0.1, 0.15) and LiFe_0.05M _y Mn_{1.95 − y} O₄ (M=Li, Al, Ni, Co; y = 0.05, 0.1) cells. These cathodes were more tolerant to repeated lithium extraction and insertion than a standard LiMn₂O₄ spinel electrode in spite of a small reduction in the initial capacity. The improvement in cycling performance is attributed to the stabilization in the spinel structure by the doped metal cations.     

催化动力学分光光度法测定痕量双酚A

在盐酸介质中,双酚A对溴酸钾氧化罗丹明B具有促进作用,据此建立了动力学分光光度测定痕量双酚A的方法。方法的线性范围是0.1—0.4mg·L-1,检出限为0.01mg·L-1,回收率在84.0%—115.0%之间。该方法用于塑料包装杯、地表水中双酚A的测定,结果满意。     

Effect of local environment and Sm-codoping on the luminescence properties in the Eu-doped potassium tungstate phosphor for white LEDS

The luminescence properties of Eu³⁺- and Sm³⁺-doped potassium tungstate phosphors were investigated. The K_4−3(x+y) (WO₄)₂:Eu_x³⁺,Sm_y³⁺ phosphor was produced by solid-state reactions, followed by re-firing with a flux. The phosphor showed a strong absorption in the near-UV to green region due to 4f-4f electron transitions of the Eu³⁺ and Sm³⁺ ions, generating a red emission. The excitation spectrum could be adjusted by Sm³⁺-codoping. A small amount of Sm³⁺, acting as a sensitizer, increased the energy absorption peak at 405 nm. The crystal structure and local environment around the Eu³⁺ ions were determined using the Rietveld method. The crystal structure of this phosphor was determined to be monoclinic with a space group of C2/c. The small Eu-0 distance in the crystal led to high energy-level splitting at the ⁵D₀→⁷F₂ transition of the Eu³⁺ ions, resulting in more emission peaks.     

A PdO(1 0 1) thin film grown on Pd(1 1 1) in ultrahigh vacuum

We present experimental results demonstrating that a high quality PdO(1 0 1) thin film can be grown on Pd(1 1 1) in ultrahigh vacuum by oxidizing the metal at 500 K using an oxygen atom beam, followed by annealing to 675 K. Low energy electron diffraction (LEED) images show that the [0 1 0] direction of the PdO(1 0 1) thin film aligns with the [−1 1 0] direction of the Pd(1 1 1) substrate, and that the PdO film grows in three degenerate domains, rotated 120° relative to one another. Based on excellent agreement between the experimental and simulated LEED patterns, we conclude that the surface structure of the PdO thin film deviates minimally from bulk-terminated PdO(1 0 1). Recent temperature programmed desorption (TPD) experiments also provide evidence that the PdO(1 0 1) thin film on Pd(1 1 1) is terminated by the stoichiometric surface in which half of the Pd atoms are coordinatively unsaturated (cus), corresponding to a cus-Pd atom density equal to about 35% of the surface density of Pd(1 1 1). The ability to generate a well-defined PdO(1 0 1) surface in ultrahigh vacuum should provide new opportunities for conducting model surface science studies of PdO, particularly studies aimed at elucidating the reactivity of PdO(1 0 1) toward species important in commercial applications of Pd catalysis.     

Effect of superficially applied ZrO2 inhibitor on the high temperature corrosion performance of some Fe-, Co- and Ni-base superalloys

High temperature corrosion is an acute form of corrosion occurring at elevated temperature in the presence of an oxidizing gas and is associated with a thin electrolytic deposit (salt or ash) on alloy. Inhibitors and fuel additives have been used with varying success to combat oil ash corrosion. In this paper, the effect of an oxide additive namely ZrO₂ on the hot corrosion behaviour of some superalloys, viz. Superfer 800H (alloy A), Superco 605 (alloy B) and Superni 75 (alloy C) has been investigated in an Na₂SO₄-60%V₂O₅ environment at 900 °C for 50 cycles. Each cycle consisted of 1 h heating in a Silicon Carbide Tube furnace followed by 20 min cooling in ambient air. Weight change measurements after each cycle were taken by an electronic balance having an accuracy of 0.01 mg. XRD, SEM and EPMA analyses of the exposed specimens were carried out to characterize the oxide scales. In the Na₂SO₄-60%V₂O₅ environment, the corrosion rate for the Co-base alloy was found to be highest, whereas that for the Ni-base Superni 75 a lowest. Whereas, with ZrO₂ superficial coating, the overall weight gains got reduced for the alloys B and C, however the inhibitor was marginally effective in the alloy A. A thick scale was observed in the latter case, which was rich in Cr, Ni, Fe and V. Absence of protective continuous chromia layer and presence of less protective NiO was probably the main reason for more corrosion rate in this case.     

Effect of Potassium Addition on Coprecipitated Iron Catalysts for Fischer-Tropsch Synthesis Using Bio-oil-syngas

以生物油基合成气的模拟气H2/CO/CO2/N2(62/8/25/5,体积比)为原料,采用固定床反应器,在1.5 MPa、300 o C、W=F=12.5 gcath/mol的条件下,研究了钾助剂及钾的添加量对沉淀铁催化剂费托合成催化活性及产物选择性的影响．生物油基合成气是通过生物油催化蒸汽重整得到．研究发现,钾的添加促进了沉淀铁催化剂费-托反应及逆水气变换反应的活性．此外,钾的加入增加了碳氢产物的平均分子量(链长)．结果表明,随着钾助剂含量的增加,甲烷的选择性降低,液相碳氢产物(C5+)的选择性增加．通过多种方法,例如X射线衍射、X射线光电子能谱及比表面等对不同钾含量的费托合成催化剂进行了表征．通过费托合成实验和催化剂的表征,选出100Fe/6Cu/16Al/6K(质量比)作为生物油基合成气费-托合成最适宜的催化剂．     

K_3Dy(PO_4)_2晶体的生长

二磷酸钕钾作为新型的化学计量比激光材料已有报导.由于二磷酸稀土钾盐具有独特的结构性质,即PO_4四面体与LnO_7十面体的相互隔离,使Ln~(3+)-Ln~(3+)之间的相互作用减少,荧光猝灭较小,以及在磷酸盐晶体中有较高的热稳定性,因而引起人们的关注.对K_3Ln(PO_4)_2(Ln:Pr,Nd,Sm,Gd)晶体的生长、结构和光谱已进行了深入的研究,但是Tb-Lu的稀土二磷酸钾盐晶体由于难以生长,至今未见报导.本文参照K_3Nd(PO_4)_2晶体的生长方法,用助熔剂缓冷法从KCl-KF熔体中生长出K_3Dy(PO_4)_2晶体.工艺过程如