Thermal behaviour and photoluminescence properties of Er- and Nd-doped yttrium aluminate glasses

Journal of Thermal Analysis and Calorimetry - Yttrium aluminate glasses (76.8 mol% of Al2O3, 23.2 mol% of Y2O3) doped with Er3+ and Nd3+ ions at different concentration levels...     

One-step synthesis and structure of an oligo(spiro-orthocarbonate)

The reaction of pentaerythritol and tetraethylorthocarbonate at 260 degrees C for 12 h yields a white crystalline material that was characterized by 13C CPMAS NMR, CHN analysis, FT-IR, electron and X-ray powder diffraction, and Rietveld analysis. The white crystalline material was found to have the formula C6H8O4 and a crystal structure with a monoclinic cell [a = 9.167 A, b = 5.681 A, c = 5.880 A, beta = 90.0 degrees , space group I2] of hexagonally arranged spiro-oligomeric chains.     

Transformation of n- hexane on PtAl/MCM-41 and PtAl/SBA-15

PtAl/MCM-41 and PtAl/SBA-15 materials were prepared by post-synthesis alumination followed by introduction of platinum by ion exchange. The samples were characterized by pyridine adsorption followed by FTIR and TPR of hydrogen. The catalytic behavior was explored in the transformation of n-hexane. This revised version was published online in August 2006 with corrections to the Cover Date.     

A relativistic meson-baryon description ofpp-Bremsstrahlung

We describe a relativistic approach to the calculation of nucleon-nucleon Bremsstrahlung, where all meson-baryon and meson-baryon-photon interactions can be calculated consistently and microscopically. In this first relativistic approach to the problem, we present numerical results including both single-scatter and rescatter contributions with a relativistic current density, within a model where the explicit photon coupling to meson-exchange currents are small. The need for high precision(p, pγ) measurements is stressed.     

Preface: Contributions of OR to solve agricultural problems

Annals of Operations Research -     

Fast and highly regioselective allylation of indole and pyrrole compounds by allyl alcohols using Ru-sulfonate catalysts

New Ru-sulfonate catalysts have been synthesized and shown to very rapidly allylate indole and pyrrole compounds using allyl alcohols as substrates. The observed regioselectivity is exceptionally high (up to 100% of the branched isomer). Density functional theory calculations explain these results.     

Decomposition of Fluorinated Graphene under Heat Treatment

Fluorination modifies the electronic properties of graphene, and thus it can be used to provide material with on‐demand properties. However, the thermal stability of fluorinated graphene is crucial for any application in electronic devices. Herein, X‐ray photoelectron spectroscopy (XPS), temperature‐programmed desorption (TPD), and Raman spectroscopy were used to address the impact of the thermal treatment on fluorinated graphene. The annealing, at up to 700 K, caused gradual loss of fluorine and carbon, as was demonstrated by XPS. This loss was associated with broad desorption of CO and HF species, as monitored by TPD. The minor single desorption peak of CF species at 670 K is suggested to rationalize defect formation in the fluorinated graphene layer during the heating. However, fluorine removal from graphene was not complete, as some fraction of strongly bonded fluorine can persist despite heating to 1000 K. The role of intercalated H₂O and OH species in the defluorination process is emphasised.     

A review on the thermal stability of calcium apatites

High temperature processing is essential for the preparation of apatites for biomaterials, lighting, waste removal and other applications. This requires a good understanding of the thermal stability and transitions upon heating. The most widely used is hydroxyapatite (HAp), but increasing interest is being directed to fluorapatite (FAp) and chlorapatite (ClAp). The structural modifications for substitutions are discussed to understand the temperature processing range for the different apatites. This is based on a review of the literature from the past few decades, together with recent research results. Apatite thermal stability is mainly determined by the stoichiometry (Ca/P ratio and structural substitutions) and the gas composition during heating. Thermal stability is lowered the most by a substitution of calcium and phosphate, leading to loss in phase stability at temperatures less than 900?°C. The anions in the hexagonal axis, OH in HAp, F in FAp and Cl in ClAp are the last to leave upon heating, and prevention of the loss of these groups ensures high temperature stability. The information discussed here will assist in understanding the changes of apatites during heating in calcination, sintering, hydrothermal processing, plasma spraying, flame pyrolysis, and other high-temperature processes.     

Effects of some admixtures on the decomposition of calcium sulphate

The by-product phosphogypsum contains CaHPO₄, H₃PO₄, Ca₅(PO₄)₃F, Al₂O₃, Fe₂O₃, SiO₂ etc. besides the main product CaSO₄. By means of TG-DTA the thermochemical decomposition of pure phosphogypsum and phosphogypsum containing CaO, Al₂O₃, Fe₂O₃ and SiO₂ in a reductive atmosphere was studied. The solid phase was examined by high-temperature thermomicroscopy, scanning electronmicroscopy, X-ray diffraction and other methods. It could be confirmed, that most of the admixtures undergo secondary reactions with CaO and CaS, modifying the decomposition rate of CaSO₄.

---

Zusammenfassung Das Abfallprodukt Phosphatgips enthält neben dem Hauptbestandteil CaSO₄ noch CaHPO₄, H₃PO₄, Ca₅(PO₄)₃F, Al₂O₃, Fe₂O₃, SiO₂ und anderes. Die thermochemische Zersetzung von Phosphatgips bzw. Phosphatgips mit Zusätzen von CaO, Al₂O₃, Fe₂O₃ und SiO₂ wurde in reduzierender Atmosphäre mittels TG-DTA untersucht. Die feste Phase wurde durch Hochtemperatur-Thermomikroskopie, Rasterelektronenmikroskopie, Röntgenbeugung und andere Methoden untersucht. Dabei wurde bestätigt, dass die meisten Beimengungen mit dem Calciumoxid bzw. -sulfid Sekundärreaktionen eingehen, wodurch auch die Zersetzungsgeschwindigkeit des CaSO₄ beeinflusst wird.

---

, , ₄, Ca₅(PO₄)₃F, Al₂O₃, Fe₂O₃, SiO₂ . - , , , . , , . , , .