TDS and XPS study of oxygen diffusion into subsurface layers of Pd(110)

Summary The interaction of O₂with Pd(110) has been studied by TDS and XPS at T = 400 K and at pressures P_{O2 from 2.6x10}^-6to 10 Pa. At low exposures in O₂(e￡1-5 L), an adsorption layer withqof ca.0.5 and with the O1s peak at BE = 529.3 eV has been found to form on the surface. Whenegrows from 5 to 10⁸L, the position and intensity of the oxygen O1s peak remain practically constant. At the same time, as much as 5 mL of oxygen is absorbed according to the TDS data. The results obtained by TDS and XPS indicate that oxygen penetrates deep into the subsurface layers of palladium (315-20 ?) and is distributed in its bulk in a low concentration.     

Chemical diffusion of oxygen in tin dioxide: Effects of dopants and oxygen partial pressure

Tin dioxide SnO_2−δ is a pronounced n-type electron conductor due to its oxygen deficiency. This study investigates the rate of chemical diffusion of oxygen in SnO_2−δ single crystals, which is a crucial step in the overall stoichiometry change of the material. The chemical diffusion coefficient D^δ was determined from conductivity- and EPR-relaxation methods. The temperature dependence was found to be . The dependence on crystal orientation, dopant content and oxygen partial pressure was below experimental error. The latter observation leads to the conclusion that the chemical diffusion coefficient is close to the diffusion coefficient of oxygen vacancies. Along with the relaxation process resulting from the chemical diffusion of oxygen, additional processes were observed. One of these was attributed to complications in the defect chemistry of the material. The relevance of the results for the kinetics of drift processes of Taguchi sensors is discussed.     

锡铅银等低熔点合金中氧的测定方法研究

研究了锡铅银等低熔点合金中杂质氧的测定方法。针对这些金属高温下易挥发、分解的特点，选择适宜的加热温度，使用铜和石墨粉作为浴料，选择标准坩埚，以电流920A加热进行试验。对氧的质量分数为0.017%的试样，分析精密度为5.9%，加标回收率为91％－108％。     

Effects of Oxygen and Water Vapor on Volatile Organic Compounds Decomposition Using Gliding Arc Gas Discharge

The combined effects of oxygen and water vapor on three typical volatile organic compounds, i.e. tetrachloromethane, n-butane and toluene, decomposition efficiency under gliding arc gas discharge conditions are studied. The electron density and the density of the reactive radicals such as O and OH are modified by addition of oxygen and water vapor. Consequently, the decomposition process can be enhanced or suppressed, depending on the involved chemical structures and reaction channels. The addition of oxygen and water vapor suppresses the tetrachloromethane decomposition which indicates that this process is mainly controlled by the electron dissociation reactions. By contrast, the n-butane and toluene decompositions are enhanced, which shows that they can be mainly ascribed to the radical induced reactions. Especially, in a moist atmosphere the OH radicals are supposed to play the most important role in the n-butane decomposition process.     

Low volume sampling device for mass spectrometry analysis of gas formation in nickel-metalhydride (NiMH) batteries

Rechargeable nickel-metalhydride (NiMH) batteries have major advantages with respect to environmental friendliness and energy density compared to other battery systems. Research on thermodynamics and reaction kinetics is required to study the behaviour of these batteries, especially under severe operating conditions such as overcharging and (over)discharging. During these processes several reactions take place resulting in the formation of oxygen and hydrogen gas. Hence, the recombination processes should be well controlled to guarantee that the partial oxygen and hydrogen pressure inside the battery are kept low.Mass spectrometry is one of the analytical techniques capable of measuring the composition of gases released inside the battery during the charge and discharge processes. However, the sample gas needs to be withdrawn from the battery during the experiment. The gas consumption must be kept to a minimum otherwise the equilibrium inside the battery will be disturbed. A bench-top quadrupole mass spectrometer with a standard capillary by-pass inlet cannot be used for this purpose as its gas consumption is in the 1-10 ml/min range. In this paper, a new gas inlet device is presented that reduces gas consumption to a value <50 μl/h. The use of a capillary by-pass splitter and a discontinuous sampling procedure allow mass spectrometry to be used as a gas analysis tool in many applications in which small amounts of sample gas are involved.Experiments with standard AA-size NiMH batteries show that hydrogen release dominates during (over)charging at increased charging rates. Beside mass spectrometry, evolved gases are also analysed using Raman spectroscopy. Although some differences are observed, the results of similar experiments show a good agreement.     

The systems Zr(Nb,Ti)(R)O2−δ, R=Yb, Ca—optimization of mixed conductivity and comparison with results of other systems (R=Y and Gd)

In this work we address the optimization of mixed conductivity in fluorite compounds based on zirconia. Phase relations of the new systems YbO_1.5-NbO_2.5-ZrO₂, and CaO-NbO_2.5-ZrO₂ are presented. The limit of the cubic defect fluorite phase in YbO_1.5-NbO_2.5-ZrO₂ closely resembles that of the system YO_1.5-NbO_2.5-ZrO₂, whilst in CaO-NbO_2.5-ZrO₂ is narrow extending to include composition Ca_0.255Nb_0.15Zr_0.595O_1.82 at 1500°C. The influence of dopant ion size, charge and composition on ionic conduction is assessed and parallels are drawn with the systems YO_1.5-NbO_2.5-ZrO₂ and YO_1.5-TiO₂-ZrO₂. Comparison of these results with published data on the Ti containing systems CaO-TiO₂-ZrO₂, GdO_1.5-TiO₂-ZrO₂ shows that the highest mixed conducting compositions can only be offered in the system YO_1.5-TiO₂-ZrO₂ out of all the systems here studied.     

Xyloccensin L, a novel limonoid from Xylocarpus granatum

The isolation and structure elucidation of xyloccensin L from the stem bark of Xylocarpus granatum is described. Xyloccensin L is a highly oxidized heptacyclic A, B, D-seco limonoid with an α-8, 30-epoxy ring and a rare 1, 29 oxygen bridge.     

Hole doping and superconductivity characteristics of the s=1, 2 and 3 members of the (Cu,Mo)-12s2 homologous series of layered copper oxides

Superconductivity characteristics have been systematically evaluated for a two-CuO₂-plane copper oxide system, (Cu,Mo)-12s2, upon increasing the number of fluorite-structured layers, s, between the two CuO₂ planes. Essentially single-phase samples of (Cu_0.75Mo_0.25)Sr₂YCu₂O_7+δ (s=1), (Cu_0.75Mo_0.25)Sr₂(Ce_0.45Y_0.55)₂Cu₂O_9+δ (s=2) and (Cu_0.75Mo_0.25)Sr₂(Ce_0.67Y_0.33)₃Cu₂O_11+δ (s=3) were synthesized through a conventional solid-state route in air. To make the samples superconductive an additional high-pressure oxygenation (HPO) treatment was required. Such treatment (carried out at 5 GPa and 500 °C in the presence of 75 mol% Ag₂O₂ as an oxygen source to maximize the T_c) compressed the crystal lattice for the three members of the (Cu_0.75Mo_0.25)-12s2 series equally, i.e., by 0.01 Å for the a parameter and by 0.07 Å for the c parameter per formula unit. From both Cu L-edge and O K-edge XANES spectra the s=1 sample was found to possess the highest overall hole-doping level among the HPO samples. Accordingly it exhibited the best superconductivity characteristics. With increasing s, both the T_c (s=1: 88 K, s=2: 61 K, s=3: 53 K) and H_irr values got depressed, being well explained by the trend of decreasing CuO₂-plane hole concentration with increasing s as revealed from O K-edge XANES spectra for the same samples. Hence, the present results do not suggest any significant (negative) impact on the superconductivity characteristics from the gradually thickened fluorite-structured block itself.     

纳米Ce1-xCoxO2-δ固溶体的水热合成及表征

采用水热方法, 在络合剂及氧化剂的辅助下合成出传统方法难以合成的Ce1-xCoxO2-δ固溶体. XRD结果表明, Ce1-xCoxO2-δ固溶体具有立方萤石结构; 产物的平均粒度约为4 nm. 小半径、低价态Co离子的掺杂导致晶格收缩. 结合XRD和Raman表征结果确定固溶体的固溶限约为x=0.06. 紫外光谱分析结果表明, Co离子以混合价态(+2, +3)存在于CeO2晶格中, 随着钴掺杂量的增大, 带隙逐渐蓝移. 低于固溶限样品的室温体相电导率随着钴含量增大而提高.     

氟化锶／氧化钕催化剂的甲烷氧化偶联性能及其吸附氧物种的原位FTIR光谱研究

氟化锶／氧化钕催化剂的甲烷氧化偶联性能及其吸附氧物种的原位ＦＴＩＲ光谱研究龙瑞强，万惠霖，赖华龙，蔡启瑞（厦门大学化学系固体表面物理化学国家重点实验室，厦门，３６１００５）关键词甲烷氧化偶联，氟化锶／氧化钕，吸附氧物种近年来，甲烷氧化偶联（ＯＣＭ）的...