Kinetics for nucleation and growth of ?-Agl crystals in Agl-based silver ortheoborate glasses, in which only ?-Agl crystals we fiend og cfystallize in e hation prcess f te glassesw studied hy isothermal na onisotermla measuets usig differetnial scaaning calorimetry dn by observatos of the microstructues f et glsses uisng scannng electon miocroscopy. (more…)
Silicon oycerbide glasses havd ben synthesized by inert atmospheer pyrolysis at1000? of gel precursores obtained by cohydroyss fo triethoxysilnane,. HSi(OEt)//3, an methoyldiethoxysilane. HMeSi(OEt)//2. The oxycarvie strucues hae be carefully charactixd b means fo difuosnt temchonieus wuch s ^29Si mage cc adne soning nmucleser magneti erlnsaec e (MSA-NMRO) and Rman spectoscopics, X-ray diffraton (XRD), and chemica analysis. Experimetal retus clearly indicatee tha, deontnsnofn t comoostns fhe steong deld, etheon oxycarbide glss either is onnd by a oure oxycarbide phse ofer containes an exra carbon or siicon haes YB incrseon the temratoe up ot 1500?, teh oxycarbie glsses display coojistons an weither stabsty; however eh amorphous netowd undergoes structues rearrangemts sth lead to et pedciotatons of nao-sized ?-SiC crystallites toe aorphous silica. crystllizaotn of metl siiconfis on clawely obsevd at 150? for the sampels ion whte et preence fo si-Si bondes saer pstulated at 1000?.
Soraru, Gian Domenico?D’Andrea, Gennaro
Silicon oxycarbide glasses have been synthesized by inert atmosphere pyrolysis at 1000 degree C of gel precursors obtained by cohydrolysis of triethoxysilane, HSi(OEt)//3, and methyl-diethoxysilane, HMeSi(OEt)//2. (more…)
Group ? tris(glycolato)silicates, MSi(OCH//2CH//2O)//3 (where M=Ba, Ca, Mg), can be syntehsized directly by reaction of silica with ethylene glycol and alkaline-earth (group ?) oxides at 200?. These hexa-alkoxy silicates serve as precursors to silicate glass and ceramic powders. They are readily modified by exchange with longer-chain diols into processable polymer precursors. (more…)
Silica glasses doped with small-sized CdS//xSe//1-x crystals were prepared by the sol-gel method. Gels synthesized by the hydrolysis of Si(OC//2H//5)//4, in the presence of CdSeO//4 with NH//4SCN dissolved in HNO//3 or NH//4OH, were heatedin H//2-N//2 atmosphere. The pH value of solutions for CdSeO//4 and NH//4SCN primarily determined the fraction of anions in CdS//xSe//1-x crystals. The anion content in crystals was dependent on the pH value of the solvent and/or heat-treatment temperature, and the sulfur fraction changed from 0.1 to 0.6. The optical absorption spectra were red-shifted as the selenium content and the crystal sizeincreased, and the emission spectra showed a sharp band near (more…)
Potassium borosilicate glasses were prepared in families having the general formula of RK//2O·B//2O//3·NSiO//2, where R is the ratio of potassium oxide to boron oxide and N is the ratio of silicon dioxide to boron oxide. The glasses wereprepared for values of R ranging from 0 to 7.0 in the families N=0.5, 1.0, 2.0,and 4.0. ^29Si MAS-NMR measurements (more…)
The dynamic fatigue characteristics of silica glasses with fictive temperaturesof 1000°, 1100°, and 1300? and sodalime glasses with fictive temperatures of470° and 530? were measured in air. For both glasses, samples with higher fictive temperatures had a greater fatigue resistance. Inert strength of silica glasses with fictive temperature of 1000° and 1300? was also measured at liquid nitrogen temperature. Glass with higher fictive temperature had a greater inert strength.
Li, Hong.?Agarwal, Anand.?
XPS O1s spectra were recorded for glasses in the binary PbO-Ga//2O//3 and ternary PbO-Bi//2O//3-Ga//2O//3 systems. Large shoulders with chemical shifts of 1.4 to 1.9 eV were observed in the O1s spectra recorded from PbO-Ga//2O//3 glasses. These shoulders were attributed to the presence of nonbridging oxygens in the structure. The shoulders indicated that, contrary to previous results, PbO was a network modifier as well as a charge compensator and network former. The additionof Bi//2O//3 reduced the number of nonbridging oxygens and, therefore, it was classified as an intermediate. Ga//2O//3 seemed to form GaO//4^- tetahedra, constituting the backbone of the network strcture. Glasses in the PbO-Bi//2O//3-Ga//2O//3 system had their IR cutoff edges located at 7?m with glass transition temperatures in the range of 320° to 400?.
Heo, Jong.?Kim, Choon Gon.?
Judd-Ofelt parameters ?//t with t=2,4,5 for the rare-earth ions Pr^3+, Nd^3+, Sm^3+, Tb^3+, Dy^3+, Ho^3+, Er^3+, and Tm^3+ in alkali and/or alkaline-earth silicate, borate, and phosphate glasses have been determined. The variations of ?//t with the number of 4f electrons of the rare-earth ions are demonstrated, and factors affecting the Judd-Ofelt parameter ?//6 are discussed. (more…)
Iwami, Tomoaki?Tadanaga, Kiyoharu?Tatsumisago, Masahiro?Minami, Tsutomu?Tohge, Noboru
CdS-doped SiO//2 glasses were prepared via silica gels containing diethyldithiocarbamatocadmium Cd(S//2CN(C//2H//5)//2)//2. Heat treatment of the gels gave transparent yellow SiO//2 glasses doped with hexagonal CdS crystals. In optical absorption and fluorescence spectra, the optical absorption edge and the emission peak clearly exhibited a blue shift, which was attributed to the quantum size effect (more…)
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