Specific trends in phosphate glass crystallization

This paper focusses on investigating and comparing the congruent crystallization of phosphate glasses with different degrees of polymerization. The study was performed both on powders, with different size fractions, and coarse particles which can be assimilated to bulk. From DSC experiments, corroborated by SEM analysis, it was demonstrated that LiPO3 crystallizes from surface whereas LiGe2(PO4)3 crystallizes in the whole volume. Sn2P2O7 presented both phenomena, the nucleation time lag being short enough to observe internal crystallization at the laboratory time scale. Using the non-isothermal Ozawa method, the kinetic parameters of the overall devitrification process were determined in terms of the Avrami exponent and of the activation energy for crystallization. The temperature of the maximum nucleation rate was calculated by using the nucleation adiabatic theory. For the achievement of this calculation, the heat capacity temperature dependence up to melting was determined from DSC experiments. The results were found in a good agreement with the SEM observation and the results of the non-isothermal crystallization study.acceptedVersionPeer reviewe

Time-resolved Thermal Lens Measurements Of Thermo-optical Properties Of Fluoride Glasses

We present measurements of the temperature coefficient of optical path change, ds/dT, thermal diffusivity, D, and conductivity, K, using time-resolved mode-mismatched thermal lens method for fluoride (mol%) 53ZrF 4-4.5LaF 3-3.5AlF 3-29BaF 2-10NaF (ZBLAN), fluoroaluminate 20YF 3-40AlF 3-20CaF 2-20BaF 2 (YABC) and fluoroindates 20GaF 3-15InF 3-20CaF 2-15ZnF 2-30PbF 2 (PGIZCa), 6GaF 3-34InF 3-20SrF 2-16BaF 2-20ZnF 2-4NaF (ISZn), 2GdF 3-40InF 3-20SrF 2-16BaF 2-20ZnF 2-2%NaF (InSBZnGdN). All the samples were crystal free, as verified by X-ray diffraction (XRD), and were at least 3 mm thick. The ds/dT of our samples was negative, the thermal diffusivity, D, was found to vary between 2.5 and 3.3×10 -3 cm 2/s, and the thermal conductivity, K, varied between 7.4 and 10.3×10 -3 W/K cm.256337342Hirao, K., Todopoki, S., Soga, N., (1992) J. Non-Cryst. Solids, 143, p. 40Tran, D.C., Siger G.H., Jr., Bendow, B., (1984) J. Lightwave Tech., 2, p. 566Drexhage, M.G., (1985) In: Treatise on Materials Science Technology, 26, p. 151. , Academic Press, New YorkJewell, J.M., Aggarwal, I.D., (1992) J. Non-Cryst. Solids, 142, p. 260Parker, J.M., (1989) NATO on Fluoride Glasses, p. 123. , in: A.E. Comyns (Ed.) Wiley, New YorkGordon, J.P., Leite, R.C.C., More, R.S., Porto, S.P.S., Whinnery, J.R., (1965) J. Appl. Phys., 36, p. 3Baesso, M.L., Shen, J., Snook, R.D., (1992) Chem. Phys. Lett., 197, p. 255Baesso, M.L., Shen, J., Snook, R.D., (1994) J. Appl. Phys., 75, p. 3732Catunda, T., Baesso, M.L., Messaddeq, Y., Aegerter, M.A., (1997) J. Non-Cryst. Solids, 213, p. 225Baesso, M.L., Bento, A.C., Andrade, A.A., Catunda, T., Sampaio, J.A., Gama, S., (1997) J. Non-Cryst. Solids, 219, p. 165Baesso, M.L., Bento, A.C., Andrade, A.A., Sampaio, J.A., Pecoraro, E., Nunes, L.A.O., Catunda, T., Gama, S., (1998) Phys. Rev. B, 57, p. 10545Powell, R.C., Neikirk, D.P., Sardar, D., (1980) J. Opt. Soc. Am., 70, p. 486Sheldon, S.J., Knight, L.V., Thorne, J.M., (1982) Appl. Opt., 21, p. 1663Hatta, I., (1979) Rev. Sci. Instrum., 50, p. 292Azechi, L.S., Costa, R.F., Medina, A.N., Gandra, F.C.G., (1995) Rev. Fís. Apl. Instrum., 10, p. 70(1960) Prod'homme, Phys. Chem. Glasses, 1, p. 119Izumitani, T., Yamashita, T., Tokida, M., Miura, K., Tajima, H., (1987) Mater. Sci. Forum, 19, p. 1

Elaboration of chalcogenide microstructured optical fibers preform by 3D additive manufacturing

International audienceFor several years, chalcogenide glasses have been studied as good candidates for numerous applications in the midinfrared region. Indeed, these glasses are transparent from 1 to 20 μm (depending on the composition), a mid- IR windows well-suited for sensing molecules whose optical signatures are located in the 2-16 μm range. In addition, thanks to appropriate thermal properties, chalcogenide glasses can be drawn into fibers, including microstructured optical fibers. In this work, a new method based on 3D-printing process is investigated to produce hollow chalcogenide glass preforms, which are then drawn into hollow-core fibers. The transmission of the "printed"hollow-core fiber has been measured and compared to the initial glass. A significant, but still manageable, increase by a factor of 2.5 is observed. This works opens a promising way for the fabrication of chalcogenide MOFs, more particularly for the elaboration of hollow core fibers. © 2021 SPIE

SrTi1-xSnxO3 Thin Films as Photocatalysts for Organic Dye Degradation: Influence of the Composition, Deposition Method, and Growth Orientation

International audienceAlkaline earth titanates and stannates with perovskite structure—A(Ti/Sn)O3, A = Ca, Sr, Ba—have appeared as emerging materials for photocatalysis applications due to their outstanding physicochemical properties. Particularly, SrTiO3 and SrSnO3 have been widely applied for hydrogen production and degradation of organic pollutants. Despite this, little is known about photocatalysis using these materials in thin film form. In this chapter, polycrystalline SrTi1-xSnxO3 films were grown on amorphous silica substrate by chemical solution deposition (CSD) and pulsed laser deposition (PLD), and their photocatalytic activity was investigated towards an organic dye degradation. Sn content has a strong influence on the photocatalytic efficiency of the films. The higher photocatalytic photodegradation of the azo dye was achieved for SrSnO3 films, whatever the deposition method, with the highest efficiency for the film deposited by CSD with 55 and 90% of degradation and discoloration of the dye, respectively. Oriented and epitaxial SrSnO3 thin films were also grown on R-sapphire and (100) LaAlO3 single crystal substrates, respectively, and the photocatalytic behaviour was investigated as a function of the growth orientation. In addition, the feasibility to reuse the films in the photocatalytic process was evaluated. Our findings demonstrate the high potential use of SrSnO3 thin film materials in photocatalysis

Characteristics of PbO-BiO1.5-GaO1.5 glasses melted in SnO2 crucibles

PbO-BiO 1.5-GaO 1.5-based glasses are good candidates for optical applications, because of some of their interesting characteristics, such as high refraction indices and high transmission in the ultraviolet (UV), visible (VIS), and infrared (IR) regions. A limited stage in the processing of these glasses is the corrosion that is caused by the melt in all currently used conventional crucibles, such as noble metals (platinum or gold) and Al 2O 3. The absorption of crucible material by the glass composition may reduce the transmission level, the cutoff in the UV-VIS, and IR regions, and the thermal stability. In this study, a SnO 2 crucible has been tested for PbO-BiO 1.5-GaO 1.5 molten glass. Optical and thermal analyses show, in some cases, advantages over the use of platinum and Al 2O 3 crucibles. A visible cutoff value of 474 nm has been measured, and a longer melting time (850°C for 4 h) results in a significant reduction of the O-H absorption band at 3.2 μm

Sinterização ultra-rápida de materiais cerâmicos usando radiação laser Ultra-fast laser sintering of ceramic materials

Nessa comunicação apresentamos nossos primeiros resultados de sinterização ultra-rápida em materiais cerâmicos óxidos usando a radiação de um laser de CO2 como fonte de aquecimento. Os compostos Bi4Ti3O12 (BIT) e Bi4Ge3O12 (BGO) foram sintetizados via reação do estado sólido, conformados em corpos cerâmicos cilíndricos de 12 mm de diâmetro e 2 mm de espessura e, posteriormente, levados ao laser para o processo de sinterização. A análise dos pós reagidos, efetuada por difratometria de raios X, confirmou a presença de fase cristalina única em cada um dos sistemas investigados. A potência máxima do laser necessária para a sinterização apresentou forte dependência com a estratégia usada na irradiação. A análise da microestrutura, realizada por microscopia eletrônica de varredura (MEV), revelou um alto grau de eficiência do processo desenvolvido. Em alguns casos, pudemos verificar que a sinterização ocorreu a uma profundidade de até 1 mm, apontando para a viabilidade de obtenção de corpos cerâmicos sinterizados como um todo.<br>In this communication we present our first results on ultra-fast laser sintering of oxide ceramics employing a CO2 laser as the heating source. The Bi4Ti3O12 (BIT) and Bi4Ge3O12 (BGO) compounds were synthesized following a solid state route in air atmosphere. Cylindrical ceramic bodies with 12 mm in diameter and 2 mm in thickness were shaped and sintered under laser irradiation. The X-ray diffraction of the calcined powders confirmed the presence of single phase in each of the investigated systems. The maximum laser power required to the sintering process showed to have a strong dependency on the strategy used for irradiation. The microstructure analysis of the samples, performed by scanning electron microscopy (SEM), revealed the high efficiency of the process. In some cases we could verify that the sintering occurred until a depth of 1mm, indicating the feasibility of obtaining the ceramic bodies sintered as a whole

Microwave synthesis and physical characterization of tin(II) phosphate glasses

Tin phosphate glasses in the SnO-P2O5 binary diagram have been prepared by using a domestic microwave-heating device. Microwaves provide an extremely facile and automatically temperature-controlled route to the synthesis of glasses due to the specific dielectric properties of each chemical composition. Typical melting time is no longer than 10 min, limiting the oxidation of Sn2+ and the melt can be quenched into glass. The glass transition temperature increases with the SnO content confirming the depolymerization of the vitreous network, as expected by the relative fraction of the different Q n structural units deduced from NMR experiments. Concerning the mechanical properties, the Vickers hardness and the fracture toughness decrease while the thermal expansion coefficient and the different elastic moduli remain constants. These results confirm that those characteristics are not very sensible to structural considerations. On the contrary, the chemical durability of Sn2P2O7, determined from the weight loss method, is 300 times higher than that of Sn(PO3)2. Furthermore, Sn2P2O7 is the only glass composition that exhibits a devitrification phenomenon leading to the low-temperature phase of the crystalline tin(II) pyrophosphate