Influence of reactant characteristics on the microstructures of combustion-synthesized titanium carbide

The influence of reactant characteristics on morphological development through the stages of combustion synthesis was investigated using a titanium-carbon system. The effect of the characteristics of a variety of carbons (carbon blacks, graphites, and cokes) and a variety of titanium powders on the density and microstructure of combusted and uncombusted sample compacts was studied. The size of the titanium particles had a relatively small influence on the density of the final (TiC) product but had a significant effect on its microstructure. The structure of the carbon blacks (as judged by the n-dibutyl phthalate absorption number, DBP) had a direct influence on the density of the uncombusted and combusted samples: low-structure carbon blacks resulted in higher densities for both cases. Products made with natural graphites had higher densities than those made with synthetic graphites. The surface area of carbon and graphite reactant powders had less influence on the density of the product than on its network morphology. Cored structures in TiC products made from certain carbon and graphite powders were observed and are explained in terms of their ash (oxide) content.     

Zeitlicher Druckverlauf bei Explosionen als Grundlage zur Auslegung von Behältern und Apparaten

Time-dependent behaviour of pressure in cases of explosions: A basis for design of pressure vessels and apparatus . The knowledge of the maximum explosion pressure is important for design of pressure vessels subject to danger of explosion. Especially for non-spherical geometries or plant-internal pressure relief, the maximum explosion pressure has to be calculated from the time-dependent pressure caused by a chemical reaction in the vessel. Therefore, a set of ordinary differential equations was solved numerically by means of the method of differences. Examples are drawn from known experimental studies. Turbulence effects are also considered. As a result, an analytical relationship is derived which gives the necessary pressure relief area. Finally the results are compared with those of available formulas. Deviations are explained in detail.     

Formation and properties of magnesium–ammonium–phosphate hexahydrate biocements in the Ca–Mg–PO<Subscript>4</Subscript> system

Calcium substituted trimagnesium phosphate with the general formula Ca_xMg_(3−x)(PO₄)₂ (0 < x < 1.5) was synthesized by calcination of powder mixtures with the appropriate stoichiometry and reacted with 3.5 M diammonium hydrogenphosphate solution to form a cementitious matrix of magnesium ammonium phosphate hexahydrate (struvite). The degree of ionic substitution was shown to influence physical cement properties; clinically suitable cement formulations with setting times in the range 5–15 min and compressive strengths of >50 MPa were obtained for x ≤ 0.75 together with a grinding time ≥1 h and a powder to liquid ratio ≥2.5 g/ml. The cement cytocompatibility was investigated by culturing human osteoblast cell line MG63 on cement surfaces demonstrating pronounced cell growth during 13 days cultivation.     

Theoretical principles for the indirect determination of the total glucosinolate content in rapeseed and meal quantifying the sulphur concentration via X-ray fluorescence (X-RF method)

The introduction of double low oilseed rape cultivars into common crop production will require the development of methods for a precise, rapid and simple determination of the total glucosinolate content in rapeseed. Recent methods are often inappropriate for plant breeding work, and also for the trade and oil mills in separating parcels of seed according to their glucosinolate contents. In contrast to the methods commonly used (chromatography, enzymic and colorimetric tests) an indirect method is described here which is based on the very close correlation between the total sulphur and glucosinolate content in rapeseed. The sulphur content of the samples can be determined precisely and non-destructively by means of X-ray fluorescence spectroscopy (X-RF). This new method, which is suitable for rapeseed and meal, requires simple preparation of the seed samples by grinding and compressing. The whole analytical procedure (sample preparation and measurement) takes 2-4 min. If necessary, moist seed samples can be quickly dried by microwave heating, because the method does not require intact glucosinolates. The steps of the X-RF method are fairly insensitive to errors. The method shows an excellent repeatability (r = 1.9 μmol g^?1) and reproducibility (R = 3.8 μmol g^?1). The results obtained with this X-RF method correlate closely with the conventional reference methods (r² = 96-99%).     

Microbiological Quality of Raw Dried Pasta from the German Market,with Special Emphasis on Cronobacter Species

The microbiological quality of 132 dried pasta products available on the German market, originating from 11 different countries, was studied. Sample materials included soft or durum wheat products, some of which produced with other ingredients such as eggs, spices, or vegetables. Parameters included hygiene indicators (aerobic plate count, mold count, the presence of Enterobacteriaceae) and pathogenic/toxinogenic bacterial species (Salmonella spp., Staphylococcus aureus, presumptive Bacillus cereus, and Cronobacter spp.). The overall results of hygiene parameters indicated a satisfactory quality. Salmonella was not found in any sample. Three samples were positive for S. aureus (10² to 10⁴ colony forming unit (CFU)/g). Presumptive B. cereus at levels of 10³ to 10⁴ CFU/g were detected in 3 samples. Cronobacter spp. were isolated from 14 (10.6%) products. Of these, 9 isolates were identified as C. sakazakii, 2 each as C. turicensis and C. malonaticus, and 1 as C. muytjensii. The isolates were assigned to 9 multilocus sequence typing (MLST) sequence types and to 14 different PFGE profiles. Although pasta products are typically cooked before consumption, some consumers, and children in particular, may also eat raw pasta as nibbles. Raw pasta seems to be a relevant source of exposure to dietary Cronobacter spp., although health risks are probably restricted to vulnerable consumers. High numbers of presumptive B. cereus as found in some samples may be a risk after improper storage of cooked pasta products because toxinogenic strains are frequently found within this species.     

C60Con complexes as hydrogen adsorbing materials

An active line of contemporary research is dedicated to the adsorption and storage of hydrogen on metal-doped carbon materials. Using density functional theory and van der Waals corrections we have studied molecular and dissociative adsorption of H₂ on neutral and cationic C₆₀Co_n complexes with n = 1–8. The Co atoms form compact clusters on the surface of the fullerene. Dissociative chemisorption of one H₂ molecule is more stable than molecular adsorption on neutral C₆₀Co_n, with the only exception of C₆₀Co. When C₆₀Co_n is ionized, the electronic charge deficit remains localized in the cobalt cluster. The molecular and dissociative adsorption features on cationic C₆₀Co_n⁺ and neutral C₆₀Co_n complexes are in general similar, but some differences can be highlighted. Molecular and dissociative H₂ adsorption on C₆₀Co₂⁺ are competitive; in fact, molecular adsorption is slightly more stable as a result of the localized electronic charge deficit on the Co dimer. Another difference is that the dissociative adsorption energies on some of the neutral C₆₀Co_n complexes are substantially larger than the dissociative adsorption energies on the corresponding C₆₀Co_n⁺ cationic complexes by amounts between 0.2 and 0.5 eV. Activation barriers for dissociation of the adsorbed H₂ molecule strongly depend on the charge state and cluster size. These barriers help to interpret the adsorption state (molecular or dissociated) of experimentally produced hydrogenated C₆₀Co_n⁺ complexes. Hydrogen saturation has been studied in two cases. C₆₀Co adsorbs three H₂ units in molecular form, and C₆₀Co_n adsorbs up to thirteen H₂ units, four dissociated and nine in molecular form.     

Regelung eines redundant aktuierten Steer-by-Wire-Systems

Forschung im Ingenieurwesen - Im Rahmen des autonomen Fahrens gewinnen Steer-by-Wire (SbW) Systeme wieder an Bedeutung, da ein permanent mitdrehendes Lenkrad im Fahrzeug unerwünscht ist. Zudem...     

Hochtemperatur-Verschleißverhalten von Ein- und Mehrphasenwerkstoffen

In many industries combined erosion, impact and abrasive wear at high temperatures play a dominating role regarding lifetime of tools and wearing parts. In view of the above an austenite, a high speed steel (HSS) and a Fe-Cr-C-B complex alloy were investigated at different temperatures and loading situations to examine their wear resistance. The dependence of hardness of these materials on temperature was investigated by an especially designed hot hardness test rig (HHT) from room temperature up to 800 °C. 2-body particle erosion and 3-body impact/abrasion were investigated at elevated temperatures, and wear results were correlated with the hot hardness results. The austenite shows ductile behaviour in all tests and a formation of a mechanically mixed layer (MML) at higher temperature entailing a wear decreasing effect. The tool steel reveals a significant drop in hardness at 500 °C which leads to increased wear rate and the formation of a MML due to ductile surface regions. The complex alloy shows brittle wear behaviour. Softening of the matrix above 500 °C leads to significant fracture of the hard phases.     

Polarization and phase control of remote surface-plasmon-mediated two-photon-induced emission and waveguiding

We report here on the control of remote surface-plasmon-mediated two-photon-induced luminescence of dendritic silver nanoparticle aggregates as observed by femtosecond laser microscopy. With a focal spot diameter approximately 1 microm, polarized remote emission has been observed 99 microm from the focal spot. We show control over the regions of emission by changing the polarization of the incident beam and by changing the spectral phase of the laser pulse.     

Pre‐ or post‐harvest applications of putrescine and low temperature storage affect fruit ripening and quality of ‘Angelino’ plum

BACKGROUND: Plum has a very short storage life. The role of pre‐ or post‐harvest applications of putrescine (PUT) and low temperature storage on fruit ripening and quality was investigated in plum fruit (Prunus salicina Lindl. cv. Angelino). RESULTS: Pre‐ or post‐harvest PUT treatments [(0.1, 1.0 or 2.0 mmol L^?1) + 0.01% Tween‐20 as a surfactant] delayed and suppressed the climacteric ethylene production and respiration rate irrespective of the method used to apply PUT. PUT‐treated fruit following low temperature storage (0 ± 1 °C; 90 ± 5% RH), at the ripe stage exhibited higher fruit firmness and titratable acidity (TA), while soluble solids content (SSC), levels of ascorbic acid, total carotenoids and total antioxidants were lower than in untreated fruit. Fruit both sprayed with PUT and stored in low temperature for 6 weeks, at the ripe stage showed reduced respiration rate, delayed changes in the SSC:TA ratio and levels of total carotenoids compared to post‐harvest PUT application. CONCLUSION: Pre‐harvest application of 2.0 mmol L^?1 PUT 1 week before the anticipated commercial harvest was more effective in delaying plum fruit ripening and can be used to extend the storage (0 ± 1 °C) life of plums for up to 6 weeks with minimum losses in fruit quality. Copyright © 2008 Society of Chemical Industry