Dominique de Ligny

Femtosecond laser induced density changes in GeO 2 and SiO 2 glasses: fictive temperature effect [Invited]

Density changes of GeO2 and SiO2 glasses subjected to irradiation by tightly focused femtosecond pulses are observed by Raman scattering. It is shown that densification caused by the void formation in GeO2 glass is very similar to the changes under hydrostatic pressure. In contrast, the experimental observations in SiO2 glass could be explained by pressure effect or by the fictive temperature anomaly, i. e., a resultant smaller specific volume of the glass (a denser phase) at a high thermal quenching rate. Density changes of GeO2 and SiO2 glasses are opposite upon close-to-equilibrium heating; this gives new insights into the mechanisms of densification under highly non-equilibrium conditions: fs-laser induced micro-explosions, heating and void formation. The pressure and temperature effects of glass modification by ultra-short laser pulses are discussed considering applications in optical memory, waveguiding, and formation of micro-optical elements.

Observation of O 2 inside voids formed in GeO 2 glass by tightly-focused fs-laser pulses

This work was supported by CNRS, CECOMO and LLP - Leonardo da Vinci. SJ is thankful for the visiting professorship at Lyon-I University.

Experimental study of dissolution rates of hedenbergitic clinopyroxene at high temperatures: dissolution in water from 25 °C to 374 °C

Steady-state pyroxene dissolution rates in aqueous solutions have been measured at temperatures from 25 to 374 °C at a pressure of 23 MPa and at neutral pH. The pyroxene is hedenbergitic clinopyroxene, of composition Na 0.04 Ca 0.95 Mg 0.3 Fe 2+ 0.64 Fe 3+ 0.06 Al 0.04 Si 1.97 O 6 . All experiments were performed at conditions far from equilibrium in Ti-alloy mixed-flow reactors. In most runs, the reactive solutions were undersaturated with respect to pyroxene and secondary minerals were rarely found at the reacted surface. The dissolution is non-stoichiometric in most cases, while the different chemical elements of the pyroxene are released at different rates. Stoichiometric steady-state dissolution was obtained in neutral solution at 100 °C. The release rates of the different elements vary with temperature and solution chemistry. The dissolution rates (r Si ) in neutral pH conditions increase with temperature from 25 to 300 °C, reach a maximum at 300 °C, and then decrease with continued temperature increase. At a given temperature, the rates decrease significantly with increasing pH of the reactive fluid and are also affected by the activities of Ca, Mg, Fe in the solution. At neutral pH, the dependence of the pyroxene dissolution rates on activities of Ca, Mg, Fe and H + in the fluid can be expressed by the relation: log r + ( T , a i ) = log ( A - E a / ( 2.303 R T ) + α log ( a H + ) Z i / a M i Z i + ) where r + is the far-from-equilibrium dissolution rate, R the gas constant, T the absolute temperature, Z i valence of metal M i and a i represents the activity of the subscript aqueous species. E a equals 22.667 kJ/mole/K and A = 2.011 × 10 −7 mole/cm 2 /s; α is the empirical reaction rate order, which can be derived from the experimental results. At temperatures below 300 °C, the exchange reactions 2H + ↔M i 2+ , where M i 2+ refers to divalent cations Mg 2+ , Fe 2+ or Ca 2+ , dominate in the dissolution. The following evolution of the dissolution with temperature is proposed: at 300 °C, the tetrahedral Si–O bonds break after the M i 2+ –O bonds in adjacent octahedral positions have been removed by proton exchange reaction, whereas, above 300 °C, the breaking of the octahedral M i 2+ –O bonds occurs after adjacent tetrahedral Si–O bonds have been broken.

Relaxation processes of densified silica glass

Densified SiO2 glasses, obtained from different pressure and temperature routes, have been annealed over a wide range of temperatures far below the glass transition temperature (500 °C-900 °C). Hot and cold compressions were useful to separate the effects of pressure and the compression temperature. In situ micro-Raman spectroscopy was used to follow the structural evolution during the thermal relaxation. A similar glass structure between the non-densified silica and the recovered densified silica after the temperature annealing demonstrates a perfect recovery of the non-densified silica glass structure. While the density decreases monotonically, the structural relaxation takes place through a more complex mechanism, which shows that density is not a sufficient parameter to fully characterize the structure of densified silica glass. The relaxation takes place through a transitory state, consisting in an increase of the network inhomogeneity, shown by an increase in the intensity of the D2 band which is as...

Luminescent centres in pezzottaite, CsBe2LiAl2Si6O18

Pezzottaite, CsBe 2 LiAl 2 Si 6 O 18 , is a rare new pink mineral found in central Madagascar and Afghanistan, exhibiting a beryl-like trigonal reduced symmetry ( R 3 c ). Numerous data on its optical properties, Raman, IR, absorption spectra as well LIBS data are available, while it is described as a non-luminescent mineral under UV light. However, pezzottaite shows several laser-induced red emissions and a particular unusual blue luminescence. LIBS analysis reveals the presence of Sc, Ca, Sr, Na, K and Rb as substituted trace elements, but these elements cannot be considered as the centres responsible for the observed emissions. Time-resolved analyses under different excitations (266, 355, 514 and 532 nm) at room and liquid nitrogen temperatures allow the identification of Fe 3+ (730 nm) and Cr 3+ (699 nm) as red emitting centres, while Tl + is considered responsible for the blue fluorescence (420–425 nm). Photoluminescence proves effective for identifying the presence of these luminescent trace elements even below the LIBS detection limit (a few ppm), but without yet attaining a quantitative resolution.

Effect of thermally induced structural disorder on the chemical durability of International Simple Glass

While the influence of silicate oxide glass composition on its chemical durability is increasingly known, the contribution of structure only is less well understood, yet is crucial for an accurate description of aqueous alteration mechanisms. The effect of structural disorder can be investigated by varying the thermal history of the glass. Furthermore, the structural changes generated by self-irradiation in nuclear glasses can be compared with those induced by fast quenching. In the context of deep geological disposal of vitreous matrices, it is then challenging to address the structural impact on glass durability. Here, a borosilicate glass, the International Simple Glass, was fiberized to obtain a rapidly quenched sample. The quenching rate and fictive temperature were evaluated from in situ Raman and Brillouin spectroscopies. Multinuclear nuclear magnetic resonance was used to obtain insight into the effect of quenching on the pristine and altered glass structure. Higher bond angle distribution and lower mixing of alkalis were observed in the fast quenched glass. Some of AlO4 groups are then Ca-compensated, while a part of BO4 is transformed into BO3 units. The structural modifications increase the hydrolysis of the silicate network occurring in the forward rate regime at 90 °C by a factor of 1.4–1.8 depending on the pH value. Residual rate regime is similarly affected, more significantly at the beginning of the experiments conducted in silica saturated solutions. These findings prove that the reactivity of glass remains controlled by its structure under the various alteration regimes.Glass durability: Studying structureThe structural changes induced by the rapid quenching of borosilicate glasses and their effects on chemical durability have been studied. Understanding how, and how fast, borosilicate glasses degrade is of great importance because they are often used as containment matrices for the disposal of radioactive waste. However, understanding how glass structure affects durability can be troublesome because both structural and compositional factors must be accounted for and are difficult to deconvolute. Now, a team, led by Frédéric Angeli at the CEA, Marcoule, France, have shown, using various spectroscopic techniques, how the effects of structural disorder can be investigated by varying the thermal history of a glass. The results show that this methodology can be used to investigate radiation damage in nuclear glasses, the effects of which are similar to those of quenching.

Investigation of Aluminate and Al2O3 Crystals and Melts at High Temperature Using XANES Spectroscopy

Using X‐ray absorption at the Al K‐edge at high temperature, structural information was determined on Al2O3, CaAl2O4 (CA), Ca3Al2O6 (C3A) and CaAl2Si2O8 (anorthite) in the crystalline and liquid states (2380 K). Important changes are observed for Al2O3 where all oscillation in the XANES spectra disappear above the liquidus temperature. For the three other compositions some modifications of the XANES spectra can be attributed to changes in the Al coordination.

An In Situ High Temperature Investigation of Cation Environments in Aluminate and Silicate Glasses and Liquids at the LUCIA Beamline

The structure of crystals and melts were obtained at high temperature using X‐ray absorption at the Ca K‐edge on CaMgSi2O6 (diopside), CaAl2Si2O8 (anorthite), Ca3Al2O6 (C3A) and CaAl2O4 (CA) compositions. Important changes are observed above the liquidus temperature particularly for the C3A composition where all oscillations in the XANES spectra disappear. Important changes in the Ca K‐edge XANES are also visible in the pre‐edge region, with increasing temperature, for crystalline CaMgSi2O6.