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111.
Lead film electrodes (PbFEs) deposited in situ on glassy carbon or carbon paste supports have recently found application in adsorptive stripping voltammetric determination of inorganic ions and organic substances. In this work, the PbFE, prepared in ammonia buffer solutions, was investigated using scanning electron microscopy, atomic force microscopy and various voltammetric techniques. The microscopic images of the lead films deposited on the glassy carbon substrate showed a considerable variability in microstructure and compactness of the deposited layer depending on the selected experimental conditions, such as the concentration of Pb(II) species, the nucleation and deposition potential, and the time applied. The catalytic adsorptive systems of cobalt and nickel in a solution containing 0.1 ammonia buffer, 2.5 × 10−5 M nioxime and 0.25 M NaNO2 were employed to investigate the electrochemical characteristics and utility of the in situ prepared lead films.The optimal parameters, i.e. the lead concentration in the solution, the procedure of film removal, and the time and potential of lead nucleation and film deposition for the adsorptive determination of metal traces, were selected, resulting in the very good reproducibility (RSD = 4.2% for 35 scans) of recorded signals. The voltammetric utility of the lead film electrode was compared to that of glassy carbon, mercury film and bismuth film electrodes, and was subsequently evaluated as superior. 相似文献
112.
The mechanism of corrosion of 99.99% purity aluminum in alkaline solutions was investigated, through detailed examination of open-circuit potential transients. These transients displayed a characteristic time dependence, in which the potential first decreased over a few seconds to a minimum of −1.7 to −1.9 V vs. Ag/AgCl, and then slowly increased over a period of hours. The value of the minimum potential of electropolished foils, along with its dependence on pH and aluminate ion concentration, indicated that it was determined by the Nernst potential for the oxidation of surface aluminum hydride (AlH3). This finding supports the direct role of hydride in the dissolution process. The increase of anodic polarization after the minimum potential occurred in two stages, the first correlated with the buildup of surface hydride, and the second with surface enrichment of Cu and Fe impurities. 相似文献
113.
Zusammenfassung Die Oberfl?chen von Spanplatten sind für deren Weiterverarbeitung von Bedeutung. Die Frage der Technik zur Messung der Oberfl?chengüte
von Spanplatten wird er?rtert. Im Zusammenhang mit eigen Untersuchungen werden Vorschl?ge für die Oberfl?chenmessungen mit
Hilfe des Tastschnittverfahrens gemacht. Die zur Durchführung des Verfahrens notwendige Quellung der zu prüfenden Spanplattenobertl?chen
erfolgt bei Wasserlagerung rund hundertmal schneller als bei Lagerung in feuchter Luft. Eine Erh?hung des Hydrophobierungsmittel-Gehaltes
der Decklagenp?ne, zeigt keinen nennenswerten Einflu? auf den Verlauf der Decklagenquellung. Mit hoher Decklagen-Spanfeuchtigkeit
hergestellte Platten weisen nach 24 h Wasserlagerung eine nur geringe Rauhtiefenzunahme auf. Spanplatten, die mit Schleifpapier
feinerer K?rnung geschliffen werden, zeigen auch nach einer Wasserlagerung glattere Fl?chen als mit grober K?rnung gechliffene
Platten. Das Befeuchten der Spanplattenoberfl⇂hen vor dem Schleifen ergibt eine merkliche Verminderung der Rauhtiefenzunahme
gegenüber nicht befeuchteten Oberfl?cher. Für die Untersuchung unbehandelter Spanplatten-oberfl?chen ist das Pastentestverfahren
nach H. Flemming gut geeignet.
Measuring of the surface of particleboard
Summary The surfaces of particleboard are of importance for their finishing. The problem of technics concerning the measurement of surface quality of particleboard is discussed. In connection with own investigations proposals for surface measurements with the tracer method are made. The swelling of the particle-board to be tested necessary for the procedure is, with watering achieed about a hundred times quicker than in humid air. An increase in the content of water-repellent agent in the outer layer does not show any significant effect on the swelling of surface layers. After 24 h of watering, boards produced with a high moisture content of the surface layers show merely a slight increase in roughness. Particleboard sanded with sandpaper of a finer grit even after watering shows a smoother surface than boards sanded with a coarser grit. The wetting of the particleboard surfaces prior to sanding yields a notable diminishing of the roughness increase as against not wetted surfaces. For the investigation of untreated particleboard surfaces the Pastentest procedure according to H. Flemming is well suited.相似文献
114.
Richard C. Martineau Ray A. Berry Aurélia Esteve Kurt D. Hamman Dana A. Knoll HyeongKae Park William Taitano 《Nuclear Engineering and Design》2010,240(6):1371-1385
This paper illustrates a comparative study to analyze the physical differences between numerical simulations obtained with both the conservation and incompressible forms of the Navier-Stokes equations for natural convection flows in simple geometries. The purpose of this study is to quantify how the incompressible flow assumption (which is based upon constant density advection, divergence-free flow, and the Boussinesq gravitational body force approximation) differs from the conservation form (which only assumes that the fluid is a continuum) when solving flows driven by gravity acting upon density variations resulting from local temperature gradients. Driving this study is the common use of the incompressible flow assumption in fluid flow simulations for nuclear power applications in natural convection flows subjected to a high heat flux (large temperature differences). A series of simulations were conducted on two-dimensional, differentially heated rectangular geometries and modeled with both hydrodynamic formulations. From these simulations, the selected characterization parameters of maximum Nusselt number, average Nusselt number, and normalized pressure reduction were calculated. Comparisons of these parameters were made with available benchmark solutions for air with the ideal gas assumption at both low and high heat fluxes. Additionally, we generated specific force quantities and velocity and temperature distributions to provide a basis for further analysis. The simulations and analysis were then extended to include helium at the Very High Temperature gas-cooled Reactor (VHTR) normal operating conditions. Our results show that the consequences of incorporating the incompressible flow assumption in high heat flux situations may lead to unrepresentative results. The results question the use of the incompressible flow assumption for simulating fluid flow in an operating nuclear reactor, where large temperature variations are present. 相似文献
115.
116.
117.
Ohne Zusammenfassung 相似文献
118.
119.
Kurt Hain 《Forschung im Ingenieurwesen》1964,30(2):33-42
Zusammenfassung Das Gelenkviereck kann man am einfachsten durch Lagen?nderungen eines Gestellpunkts, d. h. durch ?ndern der Gestell-L?nge
unter Beibehaltung der L?ngen aller übrigen Glieder verstellen. Dadurch entstehen bei voller Ausnutzung der Gestell-L?ngen?nderung
verschiedene Formen des Gelenkvierecks, die sich durch die Art der Relativbewegungen benachbarter Glieder als umlaufende oder
nur schwingende Bewegungen unterscheiden. In r?umlichen Schaubildern lassen sich s?mtliche Bereiche des Gelenkvierecks umfassend
darstellen.
Mitteilung aus dem Institut für landtechnische Grundlagenforschung der Forschungsanstalt für Landwirtschaft, Braunschweig-V?lkenrode.
Die Untersuchungen bilden einen Teil eines von der Deutschen Forschungsgemeinschaft gef?rderten Programms zum Erstellen verschiedener
Gruppen von Kurventafeln für ungleichf?rmig übersetzende Getriebe. 相似文献
120.