A porous glass-ceramic in the CaO–TiO2—P2O5 system has been prepared by crystallization and subsequent chemical leaching of the corresponding glass. By applying a two-step heat treatment to 45CaO · 25TiO2· 30P2O5 glasses containing a few mol% of Na2O, volume crystallization results in the formation of dense glass-ceramics composed of CaTi4(PO4)6 and β-Ca3(PO4)2 phases. By leaching the resultant glass ceramics with HCI, β-Ca3(PO4)2 is selectively dissolved out, leaving a crystalline CaTi4(PO4)6 skeleton. The surface area and mean pore radius of the porous glass-ceramics were approximately 40 m2/g and 13 nm, respectively.

Porous Glass‐Ceramic in the CαO–TiO2–P2O5 System

Optical Absorption of Glasses

Optical absorption spectra of reduced synthetic Fe, Ti silicate glasses were measured at elevated temperatures and results correlated with information from Mossbauer spectra in order to resolved several controversies concerning the species and coordination environment causing each absorption. Crystal field (CF) bands were resolved due to Fe2+ in octahedral coordination (9500 ± 300 cm−1, 1.05 μm), Fe2+ in tetrahedral coordination (5300 ± 200 cm−1, 1.89 μm), and Ti3+ in octahedral coordination (17 700 ± 300 cm−1, 0.56 μm) as well as the Fe2+ → Ti4+ charge transfer (CT) transition (24 000 ± 300 cm−1, 0.42 μm). Several oxygen-cation CT transitions contribute to the near-ultraviolet absorption edge usually extending into the visible region. Mossbauer spectra show asymmetry common to other glass studies and have been assigned to Fe2+ in octahedral coordinations. The asymmetry is shown to be due to multiple overlapping doublets of slightly varying quadrupole splitting. No evidence of two distinguishable octahedral glass sites has been found in either set of spectra. Only minor amounts of tetrahedral Fe2+ are present in the glasses, observed in the optical spectra due to the two orders of magnitude difference between octahedral and tetrahedral extinction coefficients.

Optical absorption and Mössbauer spectra of Fe, Ti silicate glasses

The non-linear optical properties of Li2O–TiO2–P2O5 glasses were measured by Z-scan technique using a nanosecond pulsed laser. The non-linear refractive index (γZ) estimated from Z-scan normalized transmittance was considered to include the optical Kerr effect (γK), the thermo-optic effect (γT) and the resonant non-linearity (γR) related to Ti3+ ions of which content was increased with TiO2 content. The sign of γZ for glasses with 5 and 10 mol% TiO2 was positive, whereas for glasses with 15 and 20 mol% TiO2 it was negative. The γT of all the glasses in the present work was negative due to the negative temperature coefficient of linear refractive index (dn/dT), and decreased with increasing TiO2 content, and was considered to be dominated by the two-photon absorption. For Ti3+-containing 50Li2O · 15TiO2 · 35P2O5 glass with negative γZ (−1.78 × 10−18 m2 W−1), each of these three contributions was evaluated. The thermo-optic γT of the Ti3+-containing glass was determined to be −22.11 × 10−18 m2 W−1. Using the γZ and γT for the Ti3+-free glass made by remelting the Ti3+-containing glass at 1000 °C under O2 atmosphere, the optical Kerr γK of the Ti3+-containing glass was found to be positive (11.87 × 10−18 m2 W−1). The resonant γR of the Ti3+-containing glass was found to be positive (8.46 × 10−18 m2 W−1). As a result, it was concluded that negative γZ of the Ti3+-containing glass resulted from negative thermo-optic γT.

Non-linear optical properties of Li2O–TiO2–P2O5 glasses

The state of Ti 3+ ions in reduced sodium silicate glasses was investigated by optical absorption and ESR spectroscopies. From the observation of three optical absorptions, especially the absorption near 9000 cm −1 , it is concluded that Ti 3+ ions in these glasses are in an octahedral environment with a tetragonality less than unity. The conclusion is inconsistent with the observation of a resonance near g = 1.93. A Ti 3+ -Ti 4+ redox equation using Ti complex ions was proposed and it is suggested that Ti 3+ O 4 − O 2 2− and Ti 3+ O 3 − O 3 2− complex ions are most probable in the reduced sodium silicate glasses.

State of Ti3+ ion and Ti3+−Ti4+ redox reaction in reduced sodium silicate glasses

The bleaching of bulk titania-silica glasses in the annealing temperature range is investigated. The sample-size kinetics can be predicted from the hydrogen diffusion coefficient. Hydrogen gas is evolved from both titania-silica and silica glass but in larger amount from the former. In the bleaching process, Ti 3+ ions disappear from the titania-silica glass. These results are consistent with the coloration caused by Ti 3+ which is oxidized by OH- in the glass to produce gaseous hydrogen.

D.S. Carson

Papers

Optical attenuation in titania-silica glasses