A. Aronne

Solid state 27Al NMR and FTIR study of lanthanum aluminosilicate glasses

The structure of lanthanum aluminosilicate (LAS) glasses, containing: (15–25) mol% La2O3, (15–35) mol% Al2O3 and (40–70) mol% SiO2, were studied by 27Al nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy (FTIR). The effects of La2O3 and Al2O3 content on the properties and structure of the LAS glasses were evaluated. Al3+ ion enters into the glass structure mainly in fourfold co-ordination, forming (AlO4/2)− tetrahedra, and only in small amounts in fivefold and sixfold co-ordination. La3+ acts as network modifier, producing more non-bridging oxygen atoms as its content increases.

Ftir and dta study of lanthanum aluminosilicate glasses

Abstract Structure and glass transition temperature of lanthanum aluminosilicate (LAS) glasses, containing: (15–25) mol% La2O3, (15–35) mol% A12O3 and (40–70) mol% SiO2, were studied by FTIR spectroscopy and differential thermal analysis. The effects of La2O3 and A12O3 on the properties and structures of LAS glasses were evaluated. The Al+3 ion can assume both four-fold co-ordination, forming (AlO4/2)− tetrahedra, and six-fold co-ordination forming (AlO6/2)−3 octahedra. The amount of these depends on La+3 content; acting as network modifier, it can compensate the charge of three neighbouring (AlO4/2)−units or one (AlO6/2)−3 unit.

Amorphous nanostructuring in potassium niobium silicate glasses by SANS and SHG: a new mechanism for second-order optical non-linearity of glasses

Abstract Potassium niobium silicate (KNS) glasses xK2OxNb2O5(1−2x)SiO2 with x=0.167; 0.182; 0.200; 0.220 and 0.250 have been subjected to prolonged heat treatments in a wide temperature range above Tg. As a result, glasses exhibiting liquid-type phase separation phenomena have been isolated. Moreover for each glass composition, the temperature zones have been determined to produce transparent, opalescent or opaque materials which have been studied by X-ray diffraction (XRD), small-angle neutron scattering (SANS) and second harmonic generation (SHG) techniques. SANS data unambiguously point at nanostructuring of KNS glasses in the scale of 5–20 nm under appropriate heat treatments near Tg. In contrast to initial KNS glasses, nanostructured glasses exhibit SHG activity. For earliest stages of phase separation SHG-active glasses are characterized by fully amorphous XRD patterns. Further development of phase separation in glasses with increasing of their opalescence leads to diminishing SHG, and subsequently partial crystallization takes place giving opaque materials. Since relative maximum of SHG efficiency corresponds to non-crystalline nanostructured glasses, such new transparent second-order non-linear media may be of both scientific and practical interest. With regard to non-crystalline structure of nano-inhomogeneities, SHG mechanism in the glasses is supposed to be due to a combination of third-order non-linearity with a spatial modulation of linear polarizability.

KTiOPO4 precipitation from potassium titanium phosphate glasses, producing second harmonic generation

Abstract Glass formation in the K 2 O–TiO 2 –P 2 O 5 –SiO 2 system, and the structure and crystallization behavior of glasses having compositions near the stoichiometry of KTiOPO 4 (KTP) have been examined by differential thermal analysis (DTA), X-ray diffraction (XRD), fast Fourier transform infrared (FTIR) spectroscopy and second harmonic generation (SHG). Pure glasses may be obtained adding an appropriate amount of P 2 O 5 as well as of SiO 2 to the KTP composition. Transparent and homogeneous glasses were synthesized for the 56(K 2 O·2TiO 2 ·P 2 O 5 )·44P 2 O 5 (KTP–44P) and the 90(K 2 O·2TiO 2 ·P 2 O 5 )·10SiO 2 (KTP–10Si) molar compositions. In contrast, for the 80(K 2 O·2TiO 2 ·P 2 O 5 )·20SiO 2 (KTP–20Si) and for higher SiO 2 contents, the obtained glasses were partially opaque and phase separated. KTP glasses with lower P 2 O 5 content cannot be obtained as they crystallize during quenching. The KTP–10Si glass shows the only exothermic peak connected to KTP phase crystallization whereas the KTP–44P and the KTP–20Si glasses devitrify in two steps. Firstly the same unidentified phase is formed in both these glasses and the KTP phase is formed only at higher temperatures. Transparent and opalescent KTP glasses exhibiting SHG activity may be produced by careful heat treatments at temperatures just above T g . The origin of SHG in transparent glasses is supposed to be connected with either precipitation of KTiOPO 4 nanocrystallites or very early stages of liquid-type phase separation.

FTIR study of the thermal transformation of barium-exchanged zeolite A to celsian

In this study room temperature X-ray diffraction patterns and FTIR spectra of zeolite A in its Na form, Ba-exchanged zeolite A, hexacelsian, monoclinic celsian and Ba-exchanged zeolite A samples thermally treated at temperatures ranging from 200 to 1000 °C are reported. The combined inspection of room temperature X-ray diffraction patterns and FTIR spectra reveals the following points. 1) The thermal collapse of the microporous zeolite structure goes to completion upon thermal treatment at 200–300 °C; in the resulting amorphous phase the presence of the secondary building units of the zeolite A structure may be detected. 2) Thermal treatment in the temperature range 200–400 °C results in a middle-range order which favours the crystallisation of small crystallites of monoclinic celsian at 500 °C. 3) The further evolution of the amorphous phase in the 500–800 °C temperature range of thermal treatment instead of promoting the crystalline growth of monoclinic celsian, creates a middle-range order favourable to the crystallisation of hexacelsian which occurs at 1000 °C.

Sol-Gel Synthesis of Humidity-Sensitive P2O5-SiO2 Amorphous Films

The sol-gel synthesis of silicophosphate gels using phosphoryl chloride and tetraethoxysilane as molecular precursors is reported and discussed. Gel-derived glasses and films having the molar compositions 10P2O5 · 90SiO2 and 30P2O5 · 70SiO2 have been obtained. The structure of the dried gels as well as the structural modifications that occurs during the transformations in gel-derived glasses are analyzed by Fourier transform infrared spectroscopy (FTIR). It has been found that the evidence of the P—O—Si linkages begins to appear only on the FTIR spectra of the bulk gels heat treated up to 400°C while they are well resolved on the FTIR spectra of the bulk gel samples heated up to 1000°C indicating that at this temperature the transformation in the corresponding gel-derived glasses occurs. The humidity sensitive properties of the gel-films have been evaluated by electrochemical impedance spectroscopy (EIS). The phosphorous content as well as the temperature of the heat treatments strongly affect the sensitivity to RH of the gel-derived films.

Glass transition temperature and devitrification study of barium germanate glasses

Abstract The devitrification of barium germanate glasses, examined by differential thermal analysis (DTA), Fourier transform infrared spectroscopy and X-ray diffraction, is reported. The glass compositions are expressed by the general formula: xBaO·(1−x)GeO2 with x=0.05, 0.10, 0.20, 0.30 and 0.40. Glass transition temperature and density values are not linearly changed by the increase of BaO content but pass through a maximum at x=0.20. The composition with x=0.05 exhibits two glass transition temperatures. Phases crystallizing during DTA were identified and the crystallization mechanisms were related to these structures. Bulk crystal nucleation is dominant for the first four compositions of the studied series of glasses. BaGe4O9 is the only crystallizing phase for x=0.05, 0.10, 0.20 and the main one for x=0.30. The composition with x=0.40 devitrifies only from surface and BaGe2O5 and BaGeO3 crystals were found.

Structure and devitrification behaviour of sodium, lithium and barium borophosphate glasses

Thermal properties and devitrification behaviour of sodium, lithium and barium borophosphate glasses have been studied by differential thermal analysis. The results are in good agreement with the hypothesis that BO 4 groups form when a network modifier oxide (Na 2 O or Li 2 O or BaO) is added to B 2 O 3 . The excess of negative charge is compensated by metallic cations or positively charged PO 4 groups. Activation energy for crystal growth and devitrification mechanism under non isotermal condition in sodium, lithium and barium metaphosphate glasses were also evaluated.

Glass-ceramics from fly ash with added Li2O

Abstract The effects of the addition of Li2O to fly ash on the devitrification behaviour of the derived glass are investigated with the aid of differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The phases crystallizing first for the as-quenched glass and the glass sample previously nucleated are different. Solid solutions of lithium-magnesium silicate (Li(2 + 2x)Mg(1 − x)SiO4) and a small quantity of β-eucryptite (LiAlSiO4) solid solution are formed from the as-quenched glass, while only solid solutions of lithium-magnesium silicate are formed from the sample previously nucleated. In both cases, these crystalline phases are then converted, at higher temperatures, into a large amount of β-eucryptite solid solution together with small quantities of diopside crystals (CaMgSi2O6). Kinetic parameters for nucleation and crystal growth were estimated from the DTA curves. The temperature of maximum nucleation rate was 620°C and the activation energy for crystal growth E = 316 kJ mol−1. The crystal morphology was investigated by SEM, and the crystal shape was consistent with the morphological index n calculated by DTA. The glass-ceramic obtained from a previously nucleated glass showed a fine-grained texture.

The non-isothermal devitrification of lithium tetragermanate glass

Abstract The devitrification behaviour of Li2O · 4GeO2 glass examined by differential thermal analysis and X-ray diffraction is reported and discussed. Li2O · 4GeO2 glass was found to devitrify in two steps. In the primary transformation microcrystallites of Li2Ge4O9 are crystallised in an amorphous matrix. In the second transformation well shaped Li2Ge4O9 crystals are formed. The activation energies of the two stages are found to be 698 and 502 kJ/mol respectively.