Fundamental investigations on the material flow at combined sheet and bulk metal forming processes

The class of combined sheet and bulk metal forming (SBMF) processes denotes the forming of sheet metals with typical bulk forming operations. As a consequence, simultaneous 2D and 3D stress and strain states are present. Furthermore the local shape elements formed out of the sheet plane are in the magnitude of the sheet thickness. This paper deals with process combinations upsetting/lateral extrusion and deep drawing/upsetting. It has been shown that an insufficient mould filling is nearly inevitable using conventional tooling systems. Hence, the prospect of newly developed forming approaches will be discussed.     

Binary [Cu2O/MWCNT] and ternary [Cu2O/ZnO/MWCNT] nanocomposites: formation, characterization and catalytic performance in partial ethanol oxidation

Cuprous oxide agglomerates composed of 4-10 nm Cu2O nanoparticles were deposited on multiwalled carbon nanotubes (MWCNTs) and on ZnO/MWCNTs to give binary [Cu2O/MWCNT] and ternary [Cu2O/ZnO/MWCNT] composites. Di-aqua-bis[2-(methoxyimino)propanoato]copper Cu[O2CCCH3NOMe](2)·2H2O 1 in DMF was used as single source precursor for the deposition of nanoscaled Cu2O. The precursor decomposes either in air or under argon to yield CuO2 by in situ redox reaction. Thermogravimetric coupled mass spectroscopic analysis (TG-MS) of 1 revealed that methanol formed during the decomposition of 1 acts as a potential in situ reducing agent. Scanning electron microscopy (SEM) of the binary [Cu2O/MWCNT] nano-composite shows an increase of cuprous oxide loading depending on the precursor amount, along the periphery of the MWCNTs as well as formation of larger particle agglomerates. Transmission electron microscopy (TEM) of the sample shows crystalline domains of size 4-10 nm surrounded by an amorphous region within the larger particles. SEM and TEM of ternary [Cu2O/ZnO/MWCNT] clearly reveal that Cu2O nanoparticles are primarily deposited on ZnO rather than on MWCNTs. The catalytic activities of the [Cu2O/MWCNT] and [Cu2O/ZnO/MWCNT] binary and ternary composites were studied for the selective partial oxidation of ethanol to acetaldehyde with molecular oxygen. While using binary [Cu2O/MWCNT] (13.8 wt% Cu) as catalyst, acetaldehyde was obtained with a yield of 87% at 355 °C (selectivity 96% and conversion 91%). When nanoscale ZnO is present, the resulting [Cu2O/ZnO/MWCNT] composite shows preferential hydrogen and CO2 formation due to the fact that the dehydrogenation and total oxidation pathway is more favoured compared to the binary composite. Significant morphological changes of the catalyst during the catalytic process were observed.     

Self-standing nanoparticle membranes and capsules

We perform coarse-grained molecular dynamics simulations of self-standing nanoparticle membranes observed in recent experiments (K. E. Mueggenburg et al., Nat. Mater., 2007, 6, 656). In order to make our simulations feasible, we model 2-3 times smaller gold nanoparticles (core radius of r(core) ≈ 0.8 nm) covered with alkanethiol ligands (length of l(ligand) ≈ 0.5-2.6 nm). We study the structure, stability, and mechanical properties of these membranes and show that these characteristics are controlled by the ratio of R(LC) = l(ligand)/r(core). For R(LC) ≈ 0.6, the ligated nanoparticles form well ordered monolayers with hexagonal packing, in agreement with the experiments (R(LC) ≈ 0.44). For R(LC) ≈ 1.6, the nanoparticles form less organized multilayers, which are more stable and flexible. We show that these membranes could potentially form stable capsules for molecular storage and delivery.     

Facile preparation of water-soluble fluorescent gold nanoclusters for cellular imaging applications

We report a facile strategy to synthesize water-soluble, fluorescent gold nanoclusters (AuNCs) in one step by using a mild reductant, tetrakis(hydroxymethyl)phosphonium chloride (THPC). A zwitterionic functional ligand, D-penicillamine (DPA), as a capping agent endowed the AuNCs with excellent stability in aqueous solvent over the physiologically relevant pH range. The DPA-capped AuNCs displayed excitation and emission bands at 400 and 610 nm, respectively; the fluorescence quantum yield was 1.3%. The effect of borohydride reduction on the optical spectra and X-ray photoelectron spectroscopy (XPS) results indicated that the AuNC luminescence is closely related to the presence of Au(I) on their surfaces. In a first optical imaging application, we studied internalization of the AuNCs by live HeLa cells using confocal microscopy with two-photon excitation. A cell viability assay revealed good biocompatibility of these AuNCs. Our studies demonstrate a great potential of DPA-stabilized AuNCs as fluorescent nanoprobes in bioimaging and related applications.     

Nanoporous artificial proboscis for probing minute amount of liquids

We describe a method of fabrication of nanoporous flexible probes which work as artificial proboscises. The challenge of making probes with fast absorption rates and good retention capacity was addressed theoretically and experimentally. This work shows that the probe should possess two levels of pore hierarchy: nanopores are needed to enhance the capillary action and micrometer pores are required to speed up fluid transport. The model of controlled fluid absorption was verified in experiments. We also demonstrated that the artificial proboscises can be remotely controlled by electric or magnetic fields. Using an artificial proboscis, one can approach a drop of hazardous liquid, absorb it and safely deliver it to an analytical device. With these materials, the paradigm of a stationary microfluidic platform can be shifted to the flexible structures that would allow one to pack multiple microfluidic sensors into a single fiber.     

Study of hybrid PVD–PECVD process of Ti sputtering in argon and acetylene

Hybrid PVD–PECVD process of target sputtering in hydrocarbon containing atmosphere combines aspects of both conventional reactive magnetron sputtering (PVD) and plasma enhanced chemical vapour deposition (PECVD). Such process is being typically used for deposition of metal carbides embedded in hydrogenated carbon matrix. Compared to the conventional co-sputtering of metal and carbon targets, in the hybrid deposition process the source of the carbon is dissociated hydrocarbon vapour in plasma. The aim of this paper is to study the extent of similarities or differences between this hybrid process and the conventional reactive magnetron sputtering. We have chosen the sputtering of titanium target in acetylene containing atmosphere as a representative of the hybrid processes. We focused on experimental measurements of the hybrid PVD–PECVD process behaviour, the time necessary for the process to achieve steady-state conditions and basic modelling of the process.     

Mechanism and kinetics of wollastonite fibre dissolution in the aqueous solution of acetic acid

The dissolution of fibrous wollastonite (CaSiO₃) in the aqueous solution of acetic acid (3 mol dm^− 3) was investigated in the temperature interval from 25 to 50 °C using mixed batch-type reactor. An incongruent dissolution of wollastonite proceeds under applied acidic condition. The pH of solvent was increasing during leaching of calcium and its actual value depended on the concentration of Ca²⁺ ions in the solution according to the Henderson buffer equation. That enabled the monitoring of dissolution kinetics via concentration of Ca in the dispersion medium of suspension of wollastonite measurement. The kinetic parameter of the process was evaluated from measured dissolution rates of wollastonite at constant temperature using the empirical Arrhenius equation. The apparent activation energy and pre-exponential factor estimated from the Arrhenius plot are 47 ± 1 kJ mol^− 1 and (1.8 ± 0.9) × 10³ s^− 1. The kinetics analysis of the process indicates that the process is driven by the stationary two-dimensional diffusion (D₂).     

EXTRACTION SYSTEMS USING BIS-1,2-0ICARBCILYLC0BALTATE ANO POLYOXONIUM COMPOUNDS FOR LANTHANIOE SEPARATIONS

ABSTRACT

The extraction of rare earths (lanthanides, Y, Sc) by voluminous bis-1,2-dicarbollylcobaltate anions disolved in nitrobenzene and in a nitrobenzene - carbon tetrachloride mixture has been investigated and the exchange extraction constants for both solvents, individual extraction constants anddG for ion transfer across the water - nitrobenzene phase boundary has been determined. Extraction decreases with increasing atomic number of the lanthanide.

The influence of several polyoxonium compounds on the distribution ratios and the extraction selectivity has been investigated. In the extraction systems with bis-1,2-dicarbollylcobaltate - 18-crown-6 in nitrobenzene, synergism was found for the light lanthanides but antagonism was observed for the heavy ones. The overall separation factor is Ctla/10 compared to in the absence of crown la/²     

Heterodera schachtii Nematodes Interfere with Aphid-Plant Relations on Brassica oleracea

Aboveground and belowground herbivore species modify plant defense responses differently. Simultaneous attack can lead to non-additive effects on primary and secondary metabolite composition in roots and shoots. We previously found that aphid (Brevicoryne brassicae) population growth on Brassica oleracea was reduced on plants that were infested with nematodes (Heterodera schachtii) prior (4 weeks) to aphid infestation. Here, we examined how infection with root-feeding nematodes affected primary and secondary metabolites in the host plant and whether this could explain the increase in aphid doubling time from 3.8 to 6.7 days. We hypothesized that the effects of herbivores on plant metabolites would depend on the presence of the other herbivore and that nematode-induced changes in primary metabolites would correlate with reduced aphid performance. Total glucosinolate concentration in the leaves was not affected by nematode presence, but the composition of glucosinolates shifted, as gluconapin concentrations were reduced, while gluconapoleiferin concentrations increased in plants exposed to nematodes. Aphid presence increased 4-methoxyglucobrassicin concentrations in leaves, which correlated positively with the number of aphids per plant. Nematodes decreased amino acid and sugar concentrations in the phloem. Aphid population doubling time correlated negatively with amino acids and glucosinolate levels in leaves, whereas these correlations were non-significant when nematodes were present. In conclusion, the effects of an herbivore on plant metabolites were independent of the presence of another herbivore. Nematode presence reduced aphid population growth and disturbed feeding relations between plants and aphids.