Advanced Materials Research Vols. 39-40

Abstract: Novel low melting glasses in the MoO3-La2O3-Nd2O3 system were obtained at different cooling rates (102 K/s and 104-105 K/s). Characterization of the amorphous samples was made by differential thermal analysis (DTA) and X-ray absorption fine structure (XAFS) method. According to DTA data of the glass samples, the glass transition temperatures are at 325-330 0C, the crystallization started above 410 0C and the melting temperatures are at 660-720 0C. A structural model of glasses was suggested on the basis of XAFS and IR investigations. It was shown that the predominant structural units in the amorphous network of glasses containing 90 -80 mol% MoO3 are MoO6 groups. The appearance of MoO4 groups deteriorates the glass formation ability.

Abstract: Spatial distribution of heavy metal ions (HMI) in inorganic glass forming melts was studied by measuring HMI distribution coefficient between two unmixable melts: sodium-borate glass forming melt and non-glass forming molten sodium sulfate. Combining the data on glass host composition dependence of HMI distribution coefficient with the data of Rayleigh and Mandel’shtam-Brillouin scattering (RMBS) spectroscopy of glasses doped with HMI and undoped ones made it possible to evidence the segregation of HMI into alkali-enriched inhomogeneities of glass hosts and offer the approach to choosing compositions of glass host in which HMI segregation will be minimized.

Abstract: Selenite glasses are a new class of amorphous materials which are interesting mainly from a scientific point of view and they are not yet fully examined. Selenite glasses containing other non-traditional glass formers (TeO2, V2O5 and MoO3) as well as network modifiers (Ag+, Cu2+, Zn2+, etc.) were obtained. The aim of the present study is to explain the glass formation ability in selenite systems with the participation of modifiers (Ag+ and Cu2+) and MoO3.

Abstract: The specific features of the dynamics of oxygen ions in Ме2O · SiO2 (Ме = Li, Na, K, Cs) and Na2O·ZnO·P2O5 melts at а temperature of 2000 K were investigated bу the molecular dynamics method. It is demonstrated that, as in the systems studied earlier, the formation of defect complexes is а necessary condition fог an oxygen diffusion event to bе successful. The scenarios of generating defect соmplexes аrе described, and the lifetimes of these complexes are calculated. The structure of the defect complexes is determined. It is shown that two-membered rings, free and threefold-coordinated oxygen ions сап also bе involved in the formation of defect complexes.

Abstract: The main purpose of the present work is the sol-gel synthesis, structure and application of hybrid inorganic–organic hybrids based on different silica precursors and addition of the organic compound sepharose (SP). The structural evolution of the hybrid materials containing different amounts of SP is examined. Formation of silica nanocomposites by self-assembling processes was studied by AFM and roughness analysis. The average size of nanoparticles on the sample surface is about 7 to 14 nm and the formation of their self-organized structures is observed. The hybrids are used for immobilization of bacterial cells, producers of thermostable nitrilase. The biocatalysts show good operational stability for a long period-18 days, as well as high thermostability. The degradation capability is greater for the encapsulated cells in the hybrid matrix with 5% SP.

Abstract: In the light of environmental perspective, clay minerals attract special interest because of their capability to absorb and chemically stabilize heavy metals in their structure [1, 2]. The absolute suppression of heavy element leakage from clay structures to the environment, which is obviously a strict demand, can be achieved with clay vitrification. This work is related to the influence of the addition of (0-50 wt%) of montmorillonite to a borate glass with composition of 0.33Na2O-0.67B2O3 on its structure. This influence has been studied with Raman and FT-IR spectroscopies, Archimedean density measurements, chemical durability in 90°C water and finally by studying of the ultrasonically measured elastic properties, such as Young’s and shear modulus and Poisson’s ratio, of the resultant glasses. The experimental results showed that the glass structure is predominantly comprised from tetrahedral and trigonal borate units and silicon and/or aluminium tetrahedral units. The results of density and chemical durability are fairly well correlated with structure. Higher amounts of montmorillonite lead to glasses of higher mechanical strength and chemical durability.

Abstract: A wet non-conventional method for preparing aluminophosphate glasses is presented. Aluminophosphate glasses belonging to the oxide system Li2O-BaO-Al2O3-La2O3-P2O5, doped with rare-earth ions (Pr3+, Er3+, Gd3+, and Yb3+) were obtained. The influence of the doping ions on the optical properties of the phosphate glasses has been investigated in relation with micro-structural and local electronic phenomena The optical behavior of Li2O-BaO-Al2O3-La2O3-P2O5 glasses doped with 3% mol. rare-earth ions has been studied by ultra-violet-visible-near-infra-red (UV-VISNIR) spectroscopy. The transmission spectra revealed electronic transitions between 4f and 6s inner orbital of the rare-earth ions. Structural information via optical phonons was provided by infra-red (IR) absorption spectra in the range 400-4000 cm-1. IR optical phonons are characteristic for the vitreous phosphate network, showing out the glass network-forming role of P2O5. The absorption spectra present the main PO2 and P-O-P symmetrical stretch modes besides P-O-P bend mode, P-OH, P=O, PO3 2-, asymmetrical and symmetrical vibration modes. Fluorescence spectra of the rareearth- doped aluminophosphate glasses, in the visible range, were obtained by laser excitation at 514.5 nm. The fluorescence signals revealed specific electronic transitions, which provide visible and near-infra-red emission. Glasses containing rare-earth ions exhibit luminescence at the following wavelengths: Pr3+ ions at 820 nm and 880 nm, Er3+ ions at 520 nm, 550 nm and 560 nm, Gd3+ ions at 530 nm, 540 nm, 550 nm 820 and 880 nm, Yb3+ions at 530 nm, 540 nm, 550 nm and 980 nm.

Abstract: Alkali-silicate glass irradiated with electrons of the medium energy becomes to be fully depleted of alkali ions after some time. The chemical changes are expected to be accompanied with significant changes of glass structure. The changes in structure of 15K2O•85SiO2 glass were simulated by ab-initio MD. Experimental conditions were imitated by the following procedure. First, glass was prepared by the numerical cooling from the high-temperature melt. Second, alkali ions were removed. Third, silica structure was relaxed at temperatures 300 K and 1000 K. Structural changes are characterized in terms PP RDF’s and coordination numbers. It was found peroxide bonds were created from the dangling bonds, coming from non-bridging oxygen.

Abstract: An increase of the Ge–O coordination numbers (NGeO) from 4 to 5 with decreasing GeO2 content is obtained by diffraction on K2O-GeO2-P2O5 glasses of GeO2 fractions ≥ 50 mole%. First sharp diffraction peaks (FSDP) appear at small scattering vectors Q of 7.5 nm-1. A structural model is already reported which explains this behaviour for that sample (25K2O-50GeO2-25P2O5) with the FSDP reaching maximum intensity and NGeO = ~5. Here, this model gets support by considering the detailed fractions of the structural groups which exist at the corresponding glass stoichiometry. Structures similar to this model are not known of the crystalline germanophosphate compounds.

Abstract: Low melting glasses in the MoO3-Nd2O3-Bi2O3 system were obtained at slow (102 K/s) and high cooling rates (104-105 K/s). The amorphous state of the samples was proved by X-ray diffraction. Comparative analysis of the infrared spectra of the obtained glasses and other available molybdate spectral data was carried out. The structure of glasses with a high MoO3 content was found to consist of corner shared MoO6 units. The increasing of Nd2O3 and Bi2O3 lead to partial transformation of MoO6 to MoO4 units, due to breaking of Mo-O-Mo linkage.