Graft copolymerization of poly(methyl methacrylate) with some alkyl methacrylates by atom transfer radical polymerization method and thermal properties

The preparation of graft copolymers of poly(methyl methacrylate) with some alkyl methacrylates were carried out via atom transfer radical polymerization method catalyzed by CuCl/2,2′-bipyridine and using a macroinitiator, poly[(methyl methacrylate)-co-(3,5-bis(chloroacetoxy)phenyl methacrylate)], including an amount of 1 mol % having α-halogeno carbonyl group in the side groups. Although the number-average molecular weights of a graft copolymer series of n-butyl methacrylate (n-ButMA) ended at different times increased from 55,700 to 99,500, the polydispersities decreased from 1.85 to 1.39 with time. The thermal degradation kinetics of macroinitiator and a two-armed graft copolymer of n-ButMA with this macroinitiator, PMMA-g-PnButMA: 4% (by mol), were carried out at different heating rates by thermogravimetric analysis and the results were compared. Using both the Flynn–Wall–Ozawa and Kissinger methods, the decomposition activation energies for macroinitiator were determined as 168 and 162 kJ/mol, respectively; they were also calculated as 233 and 239 kJ/mol for PMMA-g-PnButMA: 4%. The solid state thermodegradation mechanisms of both macroinitiator and PMMA-g-PnButMA: 4% are R₁-type mechanism, a phase boundary-controlled reaction, and F₁-type mechanism, a random nucleation with one nucleus on the individual particle, respectively. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Microscopic and electrochemical characterization of lead film electrode applied in adsorptive stripping analysis

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.     

Factors controlling the time evolution of the corrosion potential of aluminum in alkaline solutions

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.     

Zur Messung der Oberfläche von Spanplatten

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.

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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.

     

Comparison of natural convection flows under VHTR type conditions modeled by both the conservation and incompressible forms of the Navier-Stokes equations

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.     

Schnittplanoptimierung durch Computer

Ohne Zusammenfassung