Kinetics of iron oxidation with water vapour at temperatures between 1300 and 1450°C

In this paper measurements of the kinetics of iron oxidation in H₂O-containing gas mixtures of various compositions in the temperature range of 1300 to 1450°C, and metallographic examinations are described. The reaction product is solid wustite below and liquid iron saturated iron oxide above 1377°C, this temperature being the incongruent melting temperature of iron saturated wustite. The experiments were carried out by measuring the weight increase during the oxidation of an iron specimen connected to a thermo-balance with a platinum wire. The water vapour was generated by means of a water vapour saturator. The rate law is linear in the beginning of the single experiment and later becomes parabolic. The linear law was interpreted as being caused by two resistances connected in series: the transport of the oxidising gas through the adjacent gas boundary layer, and the phase boundary reaction at the oxide interface. The parabolic law was interpreted as being determined by the transport of iron ions and vacancies through the growing oxide layer. The resistance of gas transport becomes negligible above a certain critical gas velocity which is, for example, 23 cm/s at 1342°C. The temperature-dependent values of the phase boundary reaction rate constant were calculated with the help of known theories from the results of those experiments in which the gas velocities were above the critical value for gas transport at the respective temperatures. The parabolic law did not apply, when the oxidation product was liquid as under these circumstances the formed oxide dropped off the specimen during the experiment and hence, became no thicker than 22 μm. For all the experiments the oxide layer was composed of wustite, even when the oxygen potential of the reaction gas was far higher than that for equilibrium of the gas with wustite and magnetite. The surface structure of the oxide layer and the grain sizes varied with temperature. At lower temperatures the grains were relatively small while at higher temperatures they became extremely large up to a diameter of 6 mm.     

Oil taxation in the presence of consumer adjustment costs and volatile prices: The case of small countries

Politicians in various countries (e.g. in the USA, Switzerland and Austria) have suggested the levy of different forms of taxes or duties on crude oil. One of the major (normative) arguments behind all these proposals seems to somehow smooth oil prices after observing the dramatic oil price collapse and because of the conjecture of another, future oil price hike. Hence, these arguments refer (implicitly or explicitly) to adjustment costs to justify government intervention. This paper analyses whether the instrument of a tax on crude oil may improve welfare if oil prices are volatile and adjustment costs are important. It will be shown that these proposals are only defensible if the government is smart (uses foresight) and when the consumers are myopic. However, the optimal commodity tax should be zero if consumers and the government use the same forecast (perfect foresight).     

Reaction kinetics of the CO2 reforming of methane

The kinetics of the CO₂ reforming of methane was investigated in the temperature range 700–850°C at normal pressure with a 1:1 mixture of CH₄ and CO₂ on Ir/Al₂O₃ catalysts. The feed composition was kept constant to avoid a change in mechanism associated with composition changes. Various rate models were fitted to the experimental data by numerically integrating the rate equations. All rate models included the reverse water gas shift reaction as the most important side reaction at these reaction conditions. The best agreement was obtained with a rate model based on the stepwise mechanism, where in the rate-determining step methane is decomposed to hydrogen and active carbon followed by the direct and fast conversion of this active carbon with CO₂ to 2 CO. This model is also the first and only one containing a complete subset of reactions necessary to describe the network of reactions known to occur at these reaction conditions. Comparable fit quality was obtained with a simple first order model and with a model based on a Langmuir-Hinshelwood rate expression, where the latter provided physically meaningless parameters. Values of the reaction parameters are given for the 5 best rate models studied.     

Low threshold current MOVPE grown GaInAs-Al(Ga)InAs separateconfinement heterostructure multiquantum well metal-clad ridge-waveguidelasers emitting at 1585 nm

GaInAs-Al(Ga)InAs separate confinement heterostructure (SCH) multiquantum-well (MQW) metal-clad ridge-waveguide (MCRW) laser diodes were successfully fabricated for the first time from layer structures grown by atmospheric pressure (AP) metalorganic vapor-phase epitaxy (MOVPE) on InP substrate without any use of phosphine. CW operation of 2.9-μm-wide and 400-μm-long MCRW laser diodes emitting at 1585 nm was demonstrated with a minimum threshold current of 38 mA     

Brommethan- und Bromidgehalte in Samenkernen nach Vorratsschutz-Begasung und verschiedenen Verarbeitungsverfahren

Zusammenfassung Im Anschluß an eine 24stündige Brommethan-Begasung mit 30 g/m³ wurden Mandel-, Haselnuß-, Erdnuß- und Kakaokerne bis zu 14 Tage nach der Behandlung einigen Bearbeitungsprozessen der Süßwarenindustrie unterworfen. Anschließend erfolgte eine gaschromatographische Bestimmung der Brommethanund Bromidgehalte. Anteilig entstandenes Bromid wurde mit einer ionensensitiven Elektrode erfaßt. Brommethan diffundierte nach Zerkleinerung schneller aus den Produkten heraus. Wärmeeinwirkung bei Verarbeitungsprozessen wie Brühen und Rösten führte zu schneller Verminderung der Brommethangehalte. Beim Rösten erhöhten sich aber die Bromidrückstände. Der Bromidgehalt wurde lediglich durch Brühen der begasten Produkte vermindert und blieb nach Zerkleinerung sowie Schälen unverändert. In Kakaobohnen wurde der überwiegende Anteil des Bromids in den Schalen gefunden.

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Residues of methyl bromide and bromide in fumigated seed kernels following different industrial processes

Summary Almonds, hazelnuts, ground-nuts and cocoa beans were treated with methyl bromide for one day at about 30 g/m³. The produce was stored and treated by a process derived from the food processing industry. The measurement of methyl bromide was carried out using gas chromatography. Bromide contents were determined by an ion-specific electrode technique. Methyl bromide desorption was enhanced by grinding the fumigated produce. Heat treatment, such as scalding, peeling or roasting, lead to pronounced reduction of the methyl bromide content but with the disadvantage of an increase in bromide ion content. Of all the tested processes, only the application of (hot) water reduced the amount of residual bromide. Most of the residual bromide in fumigated cocoa beans could be found in the shells.

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Diese Arbeit ist ein Teil der Dissertationsarbeit (D 83, FB 13 Nr. 289) von A. Franz an der Technischen Universität Berlin, Fachbereich 13 (Lebensmittel- und Gärungstechnologie)     

On the constitution of the system Al-Mn-Si

The constitution of the ternary system Al-Mn-Si over the entire composition range is investigated using metallography, X-ray diffraction (XRD), and differential thermal analysis (DTA). Ten stable ternary phase are identified and characterized. Isothermal sections for 550 °C and 700 °C, the liquidus projection, and a reaction scheme linking them are presented.