Doping homogeneity in co-doped materials investigated at different length scales

Doping homogeneity is important for the properties of co-doped phosphors, as it can affect the energy transfer between sensitizer and activator ions. In a case study we apply different methods, that is scanning electron microscopy (SEM) combined with energy dispersive X-ray spectroscopy (EDX) mapping, SEM combined with cathodoluminescence (CL) and solid-state nuclear magnetic resonance (NMR), to study the doping homogeneity of the host system monazite LaPO4 doped with two different lanthanide ions on different length scales. A new criterion for doping heterogeneity in co-doped systems is developed, which is based on the NMR visibility function, which for this purpose is extended to doping with two or more paramagnetic dopants. A deviation from this function is indicative of doping heterogeneity on the length-scale of the blind-spheres of the paramagnetic dopants. A discussion of the advantages and disadvantages of the different methods is presented. The combined approach allows to study doping homogeneity from the nm to the mm scale

Formation of α-Hemihydrate Inside of a Gypsum Crystal during the Dehydration Process

Gypsum (calcium sulfate dihydrate) is one of the most used inorganic binding materials in the world. During calcination, calcium sulfate subhydrates are formed and, for technical reasons, are mixed with water to form dihydrate again. Therefore, the dehydration process of gypsum and the rehydration of hemihydrate were investigated. This dehydration process is technically performed in three different ways. Heating up, i.e., in a rotary kiln, leads to a preferred formation of β-hemihydrate, which crystallizes in comparatively small crystals. Similar results can be achieved by recrystallization from gypsum slurry around 100 °C in an autoclave or under a water steam atmosphere. However, in contrast, the recrystallization process here leads to the formation of a larger, needle-like morphology and sometimes branched α-hemihydrate crystals. The synthesis of β-hemihydrate was investigated in detail with a special thermal stage for optical microscopy on natural single gypsum crystals. It was observed that the crystal loses transparency because of the breaking surface of the crystals due to water evaporation. Furthermore, within a deeper layer of the crystal, new crystals become visible but disappear during dehydration of the upper layers. These are expected to be α-hemihydrate. This theory of the formation of α-hemihydrate inside of a gypsum crystal is experimentally proven in the present work. This work firstly shows that the observed crystallization inside of gypsum during dehydration is the formation of alpha-hemihydrate

Strategy facilitating the transfer of zirconium-oxide nanotubes onto zirconia-based ceramic implants

We report on the synthesis route for metal-oxide nanotubes via electro-chemical anodization of zirconium foil resulting in the formation of zirconia nanotubular (ZrNT) films, subsequently transferred onto pre-formed zirconia (ZrO2) implant material. The approach was based on a direct transfer of ZrNT films onto the ceramic implant via an acetone bath. The ZrNT film was detached from the metal-foil using regular adhesive-tape prior to transfer. This simple technique allows to impart a robust micro-nanoscale structure to bulk-ceramics that can potentially offer enhanced surface-reaction sites and functionality in the field of ceramic-biomaterial applications

Flavonoid intake and cardiovascular disease risk

Emerging evidence from epidemiological and randomized controlled trials (RCTs) support protective effects of foods and dietary supplements rich in flavonoids against cardiovascular disease (CVD). Epidemiological studies provide valuable information in this field but the estimation of flavonoid intake is still prone to bias due to limitations of food-frequency-questionnaires and lack of biomarkers. Advancements in mass spectrometry led to more accurate flavonoid quantification in foods and biological fluids and development of comprehensive metabolomic databases. Current research is still struggling with the establishment and validation of new biomarkers of flavonoid intake. Efforts to create adequate standardized materials and well-matched controls used in RCTs have also improved data robustness. However, the relationship between flavonoid intake and CVD is still not fully established

Flavonoid intake and cardiovascular disease risk

Emerging evidence from epidemiological and randomized controlled trials (RCTs) support protective effects of foods and dietary supplements rich in flavonoids against cardiovascular disease (CVD). Epidemiological studies provide valuable information in this field but the estimation of flavonoid intake is still prone to bias due to limitations of food-frequency-questionnaires and lack of biomarkers. Advancements in mass spectrometry led to more accurate flavonoid quantification in foods and biological fluids and development of comprehensive metabolomic databases. Current research is still struggling with the establishment and validation of new biomarkers of flavonoid intake. Efforts to create adequate standardized materials and well-matched controls used in RCTs have also improved data robustness. However, the relationship between flavonoid intake and CVD is still not fully established

Nanodentistry aspects explored towards nanostructured ZrO2: Immobilizing zirconium-oxide nanotube coatings onto zirconia ceramic implant surfaces

We report on a facile strategy to impart nanostructured morphology to commercially available ceramic-preforms used for biomedical applications in the field of dentistry. This process involves the deposition of nanotubular zirconium-oxide (ZrNT) membranes onto zirconia (ZrO2) ceramic discs at ambient conditions. ZrNTs are fabricated via electrochemical anodization of zirconium foil in a one-pot synthesis. The ZrNT film is detached from the metal-foil using office-adhesive tape and freestanding ZrNT films were obtained via dissolution of adhesives in a solvent bath, which also facilitate the transfer of ZrNT film onto the ceramic. This simple technique allows to impart a robust micro-nanoscale structure to bulk-ceramics that can potentially offer insights into designing ‘smart’ implants in the field of ceramic-biomaterial applications

Preparation and characterization of transferable encapsulated dye-sensitized solar cells

The increasing demand for sustainable energy as a means to combat the impact of climate change is addressed via a novel concept in the present work. Herein, the development of encapsulated dye-sensitized solar cells, canonically “solar capsules”, for photovoltaic applications on alternative surfaces, such as facades, is presented. The solar capsule assembly houses all components necessary for photovoltaic energy conversion, enclosed within a semiconductor nanotubular array, making them truly unique in their construction. This capsule-style unit enables an easy transfer and draft onto a wide range of materials and surfaces for photovoltaic functionalization and applications. This type of dye-sensitized solar cell typically consists of transferred solar capsules and two additional electrodes. The design and construction of solar capsules have high economic viability as they can seamlessly be up-scaled using commercially established techniques such as anodization and subsequent functionalization. This work demonstrates a working model of such a capsule by fabricating TiO2 nanotubes that are functionalized via facile dip- and spin-coating techniques in a wet lab at ambient conditions. These prototype solar capsules are characterized in bulk and are thoroughly investigated at the nanoscale for information on the chemical distribution of the constituents, as they may be influenced during the manufacturing process

Synthesis and characterization of methylammonium phosphates as crystalline approximants for anhydrous, low melting phosphate glasses

Finanziert aus dem DFG-geförderten Open-Access-Publikationsfonds der Universität Siegen für ZeitschriftenartikelLow-melting methylammonium phosphate glasses are synthesized from crystalline starting agents. To this end crystalline tris(methylammonium) cyclotriphosphate [CH3NH3]3P3O9, was synthesized by a novel and simple synthesis route from P4O10 and N-methylformamide. It, undergoes an irreversible phase transition to methylammonium catena-polyphosphate [CH3NH3]PO3. The crystal structure of the catena-polyphosphate was solved and refined from X-ray powder diffraction data by the Rietveld method using constraints obtained by solid-state 31P and 1H NMR spectroscopy. This compound crystallizes in a triclinic space group with a = 13.2236(9), b = 7.8924(6), c = 4.6553(2) Å, α = 91.068(4), β = 87.840(5) and γ = 106.550(3)°. Quantum chemical calculations confirm that the obtained structure lies at an energetic minimum. Finally the reaction of tris(methylammonium) cyclotriphosphate and P4O10 into methylammonium phosphate glass is presented. The synthesized, water-free phosphate glass shows a very low glass transition temperature Tg of 33 °C, which was verified by dynamic scanning calorimetry and NMR. The chain-like crystal structure of the high-temperature methylammoniumphosphate [CH3NH3]PO3 serves as an approximation for the short-range order of the glass

Effect of Iron-Doped TiO₂ Nanotubes on the Hydration of Tricalcium Silicate

Environmental pollution is one of the most serious and global problems for humans. Photocatalysis is a promising technology to control environmental pollution via the utilization of semiconductor materials as a photocatalyst. In this study, iron-doped TiO2 nanotubes (Fe/TiNTs) with an increased photocatalytic effect at longer wavelengths compared to undoped TiNTs were used, and the effect on the early hydration and mechanical properties of the main clinker phase tricalcium silicate (C3S) was investigated for the first time. Prior to the incorporation of nanotubes into C3S, it was treated with a supersaturated Ca(OH)2 solution. The addition of 1 and 2 wt.% of Fe/TiNTs into the C3S system significantly accelerated the course of hydration. The degree of hydration for the hydration products after 8 h, 1 d and 7 d have improved. The enhancement of compressive strength after 7 d, 14 d and 28 d were observed compared to normal TiO2 nanotubes (TiNTs). Treating Fe/TiNTs with a supersaturated Ca(OH)2 solution revealed a stronger interaction between Ca2+-ions and nanotubes. Fe/TNTs were synthesized via a modified hydrothermal process. The study shows that Fe/TiNTs can be used as a nanomaterial in cement-based building materials due to their enhanced interaction with the system