Sondermetalle und ihre Anwendung im Chemieapparatebau

Refractory Metals and their Application in the Chemical Process Industry Special metals, such as titanium, zirconium and tantalum, are being used increasingly for chemical plant. The exceptional resistance of special metals to many corrosive chemicals - they show it even at high temperatures and pressures - arises not from natural immunity but from the formation of a protective oxide passive layer on the metal surface. Special metals are well suited for welding. Their reactions with gases of the atmosphere must be taken into account though. Welding is therefore possible only under inert gas or a high vacuum. Similarly, alloying with iron-based materials during welding must be avoided under all circumstances. It should be taken into consideration that the melting point of tantalum, for example, is about twice as high as that of steel. Tantalum and niobium are machined with high-speed cutting steels; the cutting speed and cutting angle are similar to those used for stainless steels. In detail, the outstanding properties of special metals in chemical plant are as follows:

• — the stability of titanium under oxidizing conditions
• — the stability of zirconium under reducing and alkaline conditions
• — the resistance of molybdenum to hydrofluoric acid and fluoride
• — the stability of tantalum under oxidizing and reducing conditions.

In pure mineral acids the passive behaviour generally improves in the order titanium - zirconium - tantalum. Except where molybdenum is concerned, the medium should not contain fluoride. The material with the widest range of applications is tantalum. The addition of niobium as an alloying element leads to favourably priced but similarly resistant materials whose prospects of becoming established in the chemical industry and playing a part similar in importance to that of tantalum itself are good.     

Metal-Organic Framework Thin Films Grown on Functionalized Graphene as Solid-State Ion-Gated FETs

The unique properties of 2D-materials like graphene are exploited in various electronic devices. In sensor applications, graphene shows a very high sensitivity, but only a low specificity. This shortcoming can be mastered by using heterostructures, where graphene is combined with materials exhibiting high analyte selectivities. Herein, this study demonstrates the precise deposition of nanoporous metal-organic frameworks (MOFs) on graphene, yielding bilayers with excellent specificity while the sensitivity remains large. The key for the successful layer-by-layer deposition of the MOF films (SURMOFs) is the use of planar polyaromatic anchors. Then, the MOF pores are loaded with ionic liquid (IL). For functioning sensor devices, the IL@MOF films are grown on graphene field-effect transistors (GFETs). Adding a top-gate electrode yields an ion-gated GFET. Analysis of the transistor characteristics reveals a clear Dirac point at low gate voltages, good on-off ratios, and decent charge mobilities and densities in the graphene channel. The GFET-sensor reveals a strong and selective response. Compared to other ion-gated-FET devices, the IL@MOF material is relatively hard, allowing the manufacturing of ultrathin devices. The new MOF-anchoring strategy offers a novel approach generally applicable for the functionalization of 2D-materials, where MOF/2D-material hetero-bilayers carry a huge potential for a wide variety of applications.     

Comparing neural networks: a benchmark on growing neural gas,growing cell structures, and fuzzy ARTMAP

Compares the performance of some incremental neural networks with the well-known multilayer perceptron (MLP) on real-world data. The incremental networks are fuzzy ARTMAP (FAM), growing neural gas (GNG) and growing cell structures (GCS). The real-world datasets consist of four different datasets posing different challenges to the networks in terms of complexity of decision boundaries, overlapping between classes, and size of the datasets. The performance of the networks on the datasets is reported with respect to measure classification error, number of training epochs, and sensitivity toward variation of parameters. Statistical evaluations are applied to examine the significance of the results. The overall performance ranks in the following descending order: GNG, GCS, MLP, FAM.     

Joint modelling of obstacle induced and mesoscale changes—Current limits and challenges

Obstacles considerably influence boundary layer processes. Their influences have been included in mesoscale models (MeM) for a long time. Methods used to parameterise obstacle effects in a MeM are summarised in this paper using results of the mesoscale model METRAS as examples. Besides the parameterisation of obstacle influences it is also possible to use a joint modelling approach to describe obstacle induced and mesoscale changes. Three different methods may be used for joint modelling approaches: The first method is a time-slice approach, where steady basic state profiles are used in an obstacle resolving microscale model (MiM, example model MITRAS) and diurnal cycles are derived by joining steady-state MITRAS results. The second joint modelling approach is one-way nesting, where the MeM results are used to initialise the MiM and to drive the boundary values of the MiM dependent on time. The third joint modelling approach is to apply multi-scale models or two-way nesting approaches, which include feedbacks from the MiM to the MeM. The advantages and disadvantages of the different approaches and remaining problems with joint Reynolds-averaged Navier-Stokes modelling approaches are summarised in the paper.     

Endocrine disrupting nonylphenols are ubiquitous in food

4-Nonylphenols (NPs) are common products of biodegradation of a widely used group of nonionic surfactants, the nonylphenol ethoxylates (NPEs). These compounds are known to be persistent, toxic, and estrogen active. There is a worldwide scientific and public discussion on the potential consequences of human long term dietary exposure to such endocrine disrupters. Despite numerous determinations of NPs in environmental samples no systematical reports exist relating to concentrations of NPs in food. We analyzed NPs in 60 different foodstuff commercially available in Germany. The results indicate that NPs are ubiquitous in food. The concentrations of NPs on a fresh weight basis varied between 0.1 and 19.4 microg/kg regardless of the fat content of the foodstuff. Based on data on German food consumption rates and these first analyses of NPs in food, the daily intake for an adult was calculated to be 7.5 microg/day NPs. For infants exclusively fed with breast milk or infant formulas daily intakes of 0.2 microg/day and 1.4 microg/day NPs, respectively, can be estimated.     

Diffusion of n-butane/iso-butane mixtures in silicalite-1 investigated using infrared (IR) microscopy

Adsorption and diffusion of n-butane/iso-butane mixtures in individual silicalite-1 crystals has been investigated using infrared (IR) microscopy. The equilibrium sorption isotherm for an equimolar gas phase mixture is calculated using Configurational Bias Monte-Carlo simulations. The comparison between simulation results and the experimental data enabled the determination of absolute values of concentration in the IR experiments.n-Butane uptake under presence of iso-butane and, vice versa, iso-butane uptake under presence of n-butane have been studied experimentally. It is shown that the n-butane counter-uptake is not limited by the n-butane diffusivity, but by the availability of free sites, which is, in turn, determined by the mobility of iso-butane. A site-percolation threshold, given by the number of iso-butane molecules blocking the ‘traffic junctions’ of the channel network, has been employed for explaining the occurrence of network regions which are initially inaccessible for n-butane in the counter-uptake process.