The composition and the chemical states of components of Zircaloy-4 (zirconium alloy) surfaces were studied in the temperature range between room temperature and 500°C. Each sample was kept at constant temperature (25, 100, 200, 300, 400, 500°C) for up to 16 hours. The changes of composition and chemical states of the Zircaloy-4 surface during heating were monitored by x-ray photoelectron spectroscopy (XPS). Originally, the components form well-defined layers elucidated by angle-resolved x-ray photoelectron spectroscopy (ARXPS). In contrast to depth profiling using ion sputtering, ARXPS is nondestructive. However, it is applicable for layers of up to a few nanometres thickness only.The experiments showed a decomposition of the ZrO, coverage above 200 "C accompanied by oxygen diffusion into the bulk. These processes lead to the reduction of ZrO, to metallic zirconium on the surface at 300°C and higher temperatures. The oxygen diffusion into the bulk was indicated by A M depth profiles. The layered structure observed up to B heating temperature of 200°C could not be seen at higher temperatures. After Zr metal appears at the surface during the heating process, a reaction with the adsorbed hydrocarbons takes place, leading to the formation of zirconium carbide. Though the depth resolution of an AES depth profile does not permit identification of layers with thicknesses in the nanometre region, the temperature-depeadent behaviour of oxygen is reflected by its AES profiles, showing features in accordance with the results from ARXPS, especially with respect to the fact that well-defined layers vanish above 200 "C. INTRODUCTIONSurface processes between structural materials and fission products in a nuclear reactor are of importance in many fields of reactor safety considerations during normal operation as well as in the case of an accident.In particular, aggressive gaseous fission products, such as molecular iodine or volatile iodine compounds, may severely attack structural materials. In addition, although the quantity of gaseous iodine released in the case of an accident was found to be much less than had been previously adopted, it is of interest to get information on possible retention mechanisms for fission iodine in the (case of a core meltdown accident. '-Surface analytical methods have been widely applied to investigate such mechanisms as well as to study the resistivity of structural and fuel material in the presence of aggressive media under operational conditions. Observation of stress corrosion cracking of the fuel cladding material Zircaloy in the presence of gaseous iodine above a critical concentration at elevated temperatures, ' which may lead to reduced mechanical stability of the fuel cladding tubes, gave rise to the question of what the basic processes of this effect were.Since the attack of iodine on the Zircaloy starts from the surface, the surface analytical methods XPS and AES are suitable for use in the investigation of such processes because the information depths of these methods are only a fe...
A fiber-optic evanescent field absorbance sensor (EFAS) is described, for which the sensing element consists of a commercially available silicone-clad quartz glass fiber, coiled on a Teflon® support. The polydimethylsiloxane cladding fulfills various functions. It protects the brittle fiber core against fracture induced by mechanical stress. Moreover, as a lower-refractive-index medium, it causes total reflection in the fiber and acts as a hydrophobic membrane that enriches nonpolar organic compounds, whereas polar species like water cannot penetrate. Coupled to an NIR spectrometer, the sensor has a potential for remote in situ measurements of organic pollutants in drainage waters originating from contaminated areas. In this study aqueous solutions of typical drainage-water contaminants like dichloromethane, chloroform, and trichloroethylene were measured in the 900–2100 nm spectral range. The influence of refractive index, fiber length and diameter, bend radius, polysiloxane swelling, and ambient temperature on the sensor signal is described and qualitatively compared with theoretical predictions. Kinetics measurements are presented, which allow explanation of the diffusion mechanism of CHC13 enrichment in the polysiloxane cladding. The data show that the rate-determining step for penetration of this substance into the sensor polymer layer can be described mainly by film diffusion through the aqueous boundary layer. In most cases no remarkable influence of gel diffusion in the polysiloxane membrane was observed.
The fabrication of a novel thin film electrode based on radio frequency (RF) magnetron sputtered carbon 10 to 500 nm thick is reported. To minimize problems arising from the ohmic resistance of carbon thin films, a titanium nitride base layer is sputter-deposited onto a silicon substrate. This carbon thin film electrode (CTE) compares very favorably with conventional carbon electrodes such as glassy carbon. The CTE exhibits a low double-layer capacitance, a large electrochemical window, and a relatively high activity toward ferricyanide reduction. The formation of surface functional groups and the resulting pH response is discussed. Due to the smoothness of the surface, the CTE provides an excellent substrate for mercury films. The potentiometric stripping response of the mercury-coated CTE toward cadmium, lead, and copper ions at the ppb concentration level in nondeoxygenated solutions is studied. Furthermore, a comprehensive evaluation of physicochemical properties of RF magnetron sputtered carbon films is presented. InfroductionGlassy carbon is nowadays the most widely used electrode material in electroanalytical applications. Its popularity is mainly due to the robust and smooth surface nature and to the large electrochemical window. Its electroanalytical performance frequently suffers, however, from high, irreproducible background contributions and from gradual loss of surface activity. The growing need for reliable measurements of biologically important compounds and of trace metals for clinical screening and environmental monitoring has stimulated attempts to develop alternative, disposable carbon electrodes being amenable to mass production. Several deposition techniques have been applied, including screen printing, spin casting followed by high-temperature carbonization, chemical vapor deposition, and physical vapor deposition (PVD). Special interest has been devoted to the preparation of optically transparent carbon electrodes1'2 and to the production of microelectrodes36 by PVD techniques such as electron beam evaporation and sputtering.Sputter-deposited carbon films are generally believed to be amorphous and similar to evaporated ones.7 However, depending on the sputtering method and the deposition parameters, a large variety of microstructures can be obtained, ranging from graphitic to diamond-like carbon. This is reflected in the considerable variability of physical parameters measured, including the optical bandgap (0 to 2.7 eV 8-13), the resistivity (10-2 to 101 ft cm 8-18) density (0.5 to 3.1 g cm3 10-13.16-20), and hardness (Vickers, 20 to 2400 kg mm2 7111221), Due to its hardness, low coefficient of friction, and general chemical inertness, coatings of sputtered carbon have been used for several wear and tribological applications, e.g., as cover layers for magnetic-recording disks 17,22,23 and electrophotographic-recording materials.21Moreover, attempts at utilizing sputtered carbon as a coating of the walls of fusion reactors have been reported.24 Because of the favorable dielectric properties...
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