Features of the mechanical properties of phosphate glasses doped with rare earth elements under indentation

The microstructure, as well as the mechanical and thermal properties, of phosphate glasses (PhGs) doped with rare earth elements (REEs), namely, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, and Yb, were studied in the present paper. The strength parameters of the PhGs and their dependence on the load value modification were estimated by the dynamic indentation method. Three specific stages were revealed in the deformation process, including nano-, submicro-, and microdeformation. The factors responsible for each stage were determined. It was shown that the strength properties (Young’s modulus and hardness) and the thermal characteristics (the lower and upper annealing temperature, the softening temperature, and the vitrification temperature) exhibit no evident relationship with the atomic mass and ionic radius of an REE. An assumption was made that the elastic and plastic properties of PhGs can be determined by the internal structure of the glasses.     

Surface properties of aromatic polymer film during thermal treatment

Aromatic polyimide films are processed from polyamic acid solutions. This process involved the simultaneous loss of solvent and chemical conversion of polyamic acid to polyimide, and implied structural reorganization which led to changed physical properties. Polymer films generated from benzophenonetetracarboxylic dianhydride and 4,4′-diamino-3,3′-dimethyl diphenylmethane have been investigated at different stages of thermal treatment. The surface polarity, which was determined by the presence of polar COOH and CONH groups, changed during polyamic acid thermal treatment. These polar groups were removed step by step by imidization process leading to the modification of the physical properties of the polymer film.     

Preparation method and thermal properties of samarium and europium-doped alumino-phosphate glasses

The present work investigates alumino-phosphate glasses from Li₂O–BaO–Al₂O₃–La₂O₃–P₂O₅ system containing Sm³⁺ and Eu³⁺ ions, prepared by two different ways: a wet raw materials mixing route followed by evaporation and melt-quenching, and by remelting of shards. The linear thermal expansion coefficient measured by dilatometry is identical for both rare-earth-doped phosphate glasses. Comparatively to undoped phosphate glass the linear thermal expansion coefficient increases with 2 × 10⁻⁷ K⁻¹ when dopants are added. The characteristic temperatures very slowly decrease but can be considered constant with atomic weight, atomic number and f electrons number of the doping ions in the case of T_g (vitreous transition temperature) and T_sr (high annealing temperature) but slowly increase in the case of T_ir (low annealing temperature–strain point) and very slowly increase, being practically constant in the case of T_D (dilatometric softening temperature). Comparatively to undoped phosphate glass the characteristic temperatures of Sm and Eu-doped glasses present lower values. The higher values of electrical conductance for both doped glasses, comparatively to usual soda-lime-silicate glass, indicate a slightly reduced stability against water. The viscosity measurements, showed a quasi-linear variation with temperature the mean square deviation (R²) being ranged between 0.872% and 0.996%. The viscosity of doped glasses comparatively to the undoped one is lower at the same temperature. Thermogravimetric analysis did not show notable mass change for any of doped samples. DSC curves for both rare-earth-doped phosphate glasses, as bulk and powdered samples, showed T_g values in the range 435–450 °C. Bulk samples exhibited a very weak exothermic peak at about 685 °C, while powdered samples showed two weak exothermic peaks at about 555 °C and 685 °C due to devitrification of the glasses. Using designed melting and annealing programs, the doped glasses were improved regarding bubbles and cords content and strain elimination.     

Effect of cooling rate on structure and mechanical properties of monotectoid zinc-aluminium alloys

The cooling curves of a number of monotectoid zinc-aluminium allows have been obtained during casting at different pouring and mould temperatures using thermocouples and an analogue-digital converter in a computer. The average cooling rate for each ingot of the allows was determined by taking the derivative of the cooling curves. The effect of cooling rate on the structure and properties of the alloys was investigated. It was observed that as the cooling rate increased the secondary dendrite arm spacing of the alloys decreased but their hardness, tensile strength and percentage elongation increased. Correlation of the experimental results showed that the cooling rate of the alloys could be related to their secondary dendrite arm spacing, hardness, tensile strength and percentage elongation using first and second degree mathematical equations. In addition, the Skenazi equation was found to be applicable to these alloys. As a result of this work, the optimum range of cooling rate for the alloys was found to be between 4·40?4·56 K s^-1.     

Synthesis and thermal behavior of some anthracene‐based copolymers obtained by Diels–Alder cycloaddition reactions

New polymer structures have been synthesized via Diels–Alder cycloaddition of bisdiene compounds bearing two anthracene groups and different bisdienophiles, all containing bismaleimide or biscitraconimide functions. The monomers and polymers were characterized by FTIR, UV, and ¹H NMR techniques and compared with two models having a cycloadduct structure. The polymers were studied by thermogravimetric analyses. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Thick lead-free ferroelectric films with high Curie temperatures through nanocomposite-induced strain

Ferroelectric materials are used in applications ranging from energy harvesting to high-power electronic transducers. However, industry-standard ferroelectric materials contain lead, which is toxic and environmentally unfriendly. The preferred alternative, BaTiO(3), is non-toxic and has excellent ferroelectric properties, but its Curie temperature of ～130 °C is too low to be practical. Strain has been used to enhance the Curie temperature of BaTiO(3) (ref. 4) and SrTiO(3) (ref. 5) films, but only for thicknesses of tens of nanometres, which is not thick enough for many device applications. Here, we increase the Curie temperature of micrometre-thick films of BaTiO(3) to at least 330 °C, and the tetragonal-to-cubic structural transition temperature to beyond 800 °C, by interspersing stiff, self-assembled vertical columns of Sm(2)O(3) throughout the film thickness. The columns, which are 10 nm in diameter, strain the BaTiO(3) matrix by 2.35%, forcing it to maintain its tetragonal structure and resulting in the highest BaTiO(3) transition temperatures so far.     

Formation of guaiacol from vanillin by<Emphasis Type="Italic"> Alicyclobacillus acidoterrestris</Emphasis> in apple juice: a model study

In this study, the formation of guaiacol from vanillin by Alicyclobacillus acidoterrestris in apple juice was investigated. Apple juices spiked with 10 and 100 mg/L of vanillin were inoculated with 1×10³ CFU/mL and 1×10⁵ CFU/mL spores of A. acidoterrestris and incubated at 25 and 46 °C. A. acidoterrestris started to form guaiacol from vanillin when the spore count exceeded the critical level of 1×10⁴ CFU/mL. Increasing the vanillin concentration also increased the concentration of guaiacol formed, especially at 46 °C. The growth of A. acidoterrestris was not favorable at 25 °C. Thus, the formation of guaiacol is strongly limited at room temperature.     

Interaction of silicon-based quantum dots with gibel carp liver: oxidative and structural modifications

Quantum dots (QDs) interaction with living organisms is of central interest due to their various biological and medical applications. One of the most important mechanisms proposed for various silicon nanoparticle-mediated toxicity is oxidative stress. We investigated the basic processes of cellular damage by oxidative stress and tissue injury following QD accumulation in the gibel carp liver after intraperitoneal injection of a single dose of 2 mg/kg body weight Si/SiO₂ QDs after 1, 3, and 7 days from their administration.QDs gradual accumulation was highlighted by fluorescence microscopy, and subsequent histological changes in the hepatic tissue were noted. After 1 and 3 days, QD-treated fish showed an increased number of macrophage clusters and fibrosis, while hepatocyte basophilia and isolated hepatolytic microlesions were observed only after substantial QDs accumulation in the liver parenchyma, at 7 days after IP injection.Induction of oxidative stress in fish liver was revealed by the formation of malondialdehyde and advanced oxidation protein products, as well as a decrease in protein thiol groups and reduced glutathione levels. The liver enzymatic antioxidant defense was modulated to maintain the redox status in response to the changes initiated by Si/SiO₂ QDs. So, catalase and glutathione peroxidase activities were upregulated starting from the first day after injection, while the activity of superoxide dismutase increased only after 7 days. The oxidative damage that still occurred may impair the activity of more sensitive enzymes. A significant inhibition in glucose-6-phosphate dehydrogenase and glutathione-S-transferase activity was noted, while glutathione reductase remained unaltered.Taking into account that the reduced glutathione level had a deep decline and the level of lipid peroxidation products remained highly increased in the time interval we studied, it appears that the liver antioxidant defense of Carassius gibelio does not counteract the oxidative stress induced 7 days after silicon-based QDs exposure in an efficient manner.