Search results for "engineering.material"
showing 10 items of 2352 documents
Surface composition analysis during the oxidation of ferrites: A necessity
1998
The cationic composition of a titanium ferrite (Fe 2.5 Ti 0.5 O 4 ) has been followed by XPS during its oxidation in cation deficient phases (without crystallographic transformation) in order to reveal a dynamic segregation phenomenon. Indeed, during this oxidation, an important modification of the chemical composition of the first layers of the material has been revealed: below 350 °C, the titanium ferrites surface becomes richer in iron and poorer in titanium. But, if the reaction is extended above 400 °C, some titanium can move to the surface. This phenomenon has been interpreted on the basis of the differences of mobility of the different ions which are present in the material. Finally,…
Improving the photocatalytic H2 evolution activity of Keggin polyoxometalates anchoring copper-azole complexes
2021
Eliminating the use of precious metals as cocatalysts and using visible light are two important aspects in the field of photocatalytic H2 evolution with polyoxometalates (POMs) as photosensitizers. Here we present two new POM-based materials: [CuII5(2-ptz)6(H2O)4(GeW12O40)]·4H2O (1) and [CuI2(ppz)4][H2GeW12O40]·8H2O (2) (2-ptz = 5-(2-pyridyl) tetrazole, ppz = 3-(pyrid-4-yl) pyrazole) synthesized with the Keggin type [GeW12O40]4− (GeW12) polyanion and copper-azole complexes. The optimum photocatalytic H2 evolution rate of compound 1 without a noble metal cocatalyst is 3813 μmol g−1 h−1, which is 7.6 times higher than that of compound 2 and more than 27 times higher than that of bare GeW12 po…
Formation, diffusion, and aggregation of radiation-induced defects in MgO and α-Al 2 O 3
1997
MgO and M2O3 (corundum) are important ceramic materials with several technological applications including theirpossible use in fusion reactors' . Weare therefore studying the properties ofpoint defects (vacancies, interstitials, andtheir aggregates) and electronic defects (trapped holes and electrons) in these materials. Pair-potential (PP) calculationswere carried out using the Mott-Littleton (ML) two-region strategy, as implemented in the computer code CASCADEdue to Leslie. Details ofthe method, including the construction ofPPs, are in the literature3. For semi-empirical INDO(intermediate neglect ofdifferential overlap) calculations computer codes developed at the University of Riga were …
Tracing anthropogenic thallium in soil using stable isotope compositions.
2014
Thallium stable isotope data are used in this study, for the first time, to apportion Tl contamination in soils. In the late 1970s, a cement plant near Lengerich, Germany, emitted cement kiln dust (CKD) with high Tl contents, due to cocombustion of Tl-enriched pyrite roasting waste. Locally contaminated soil profiles were obtained down to 1 m depth and the samples are in accord with a binary mixing relationship in a diagram of Tl isotope compositions (expressed as e(205)Tl, the deviation of the (205)Tl/(203)Tl ratio of a sample from the NIST SRM 997 Tl isotope standard in parts per 10(4)) versus 1/[Tl]. The inferred mixing endmembers are the geogenic background, as defined by isotopically l…
Layered composite based on halloysite and natural polymers: a carrier for the pH controlled release of drugs
2019
We have prepared new biohybrid materials based on halloysite nanotubes and natural polymers (alginate and chitosan) for the controlled and sustained release of bioactive species. A functional nanoarchitecture has been designed allowing us to generate a layered tablet with a chitosan/halloysite nanocomposite film sandwiched between two alginate layers. The assembly of the raw components and the final structure of the hybrid tablet have been highlighted by the morphological and wettability properties of the prepared materials. Since the biohybrid has been designed as a smart carrier, halloysite nanotubes have been first loaded with a model drug (sodium diclofenac). The effect of the tablet th…
Core/Shell Gel Beads with Embedded Halloysite Nanotubes for Controlled Drug Release
2019
The use of nanocomposites based on biopolymers and nanoparticles for controlled drug release is an attractive notion. We used halloysite nanotubes that were promising candidates for the loading and release of active molecules due to their hollow cavity. Gel beads based on chitosan with uniformly dispersed halloysite nanotubes were obtained by a dropping method. Alginate was used to generate a coating layer over the hybrid gel beads. This proposed procedure succeeded in controlling the morphology at the mesoscale and it had a relevant effect on the release profile of the model drug from the nanotube cavity.
Chlorinated and methylated dibenzothiophenes in sediment samples from a river contaminated by organochlorine wastes
2001
Eleven sediment samples from the lower Kymijoki River were analyzed for the occurrence of polychlorinated and polymethylated dibenzothiophenes (PCDT and PMeDTs). The area was heavily polluted by wastes from a pulp chlorobleachery and by leakage from a factory producing wood preservative chlorophenol formulation Ky-5. Levels in the sediments were from <5 to 400, 200 and 50 pg g-1 dw for tetra, penta and hexa-CDT, respectively. The concentrations of mono, di, tri and tetra-MeDTs were in the range of 1–5, 5–85, 5–500 and 15–2300 ng g-1 dw, respectively. PCDT contents in surface sediment (0–3 cm layers) decreased by distance downstream from the bleachery and Ky-5 factory similar to those of the…
Changes of Photosynthesis-Related Parameters and Productivity of Spring Oilseed Rape under Different Nitrogen and Sulphur Fertilizers Supply
2015
Fertilization with essential mineral elements is important to get high quality yield results. The lack of necessary mineral elements in soil can affect oilseed rape plant physiological functions, photosynthesis and plant productivity. Oilseed rape plants have high requirements for nitrogen and as oil crop – for sulphur. The aim of the investigation was to explain changes of chlorophyll a fluorescence parameters in spring oilseed rape leaves and yield changes under nitrogen and sulphur supply. During laboratory experiments changes of chlorophyll a fluorescence parameters and during field experiments changes of yield parameters under different nitrogen and sulphur supply were observed. Labora…
Physiological Aspects of Nitrogen Fertilizer Impact on Latvian Origin Cannabis Sativa L .
2015
The aim of the present study was to evaluate nitrogen fertilizer impact on photosynthesis and yield of hemp, applying modern non-destructive methods. The main object of the investigation – hemp cultivar of Latvian origin ‘Pūriņi’. Laboratory and field experiments showed diverse effects of different nitrogen fertilizer doses on various parameters. Additional nitrogen fertilizer dose of 60 kg ha-1 is most effective as evaluated by chlorophyll content in hemp leaves and changes of chlorophyll a fluorescence parameters. Nitrogen fertilizer negatively affected fiber content in hemp stems, therefore while cultivating hemp only for fiber production use of nitrogen fertilizer should be reduced. Acc…
Humite- and scapolite-bearing assemblages in marbles and calcsilicates of Dronning Maud Land, Antarctica: new data for Gondwana reconstructions
1999
This study investigates marbles and calcsilicates in Central Dronning Maud Land (CDML), East Antarctica. The paleogeographic positioning of CDML as part of Gondwana is still unclear; however, rock types, mineral assemblages, textures and P–T conditions observed in this study are remarkably similar to the Kerala Khondalite Belt in India. The CDML marbles and calcsilicates experienced a Pan-African granulite facies metamorphism at c. 570 Ma and an amphibolite facies retrogression at c. 520 Ma. The highest grade assemblage in marbles is forsterite+spinel+calcite+dolomite, in calcsilicates the assemblages are diopside+spinel, diopside+garnet, scapolite+wollastonite+clinopyroxene±quartz, scapol…