Heavy Metal Fluoride Research Articles

Reaction of NF3 and SF6 with some oxides connected with heavy-metal fluoride glass processing

The fluorinating properties of NF3 and SF6 in heavy-metal fluoride glass processing were investigated between 200 and 1100 °C. Using infrared (IR) absorption spectroscopy the reactions of NF3 with ZrO2 and Al2O3 and the reactions of SF6 with ZrO2, SiO2, and Ni were studied. The reaction of NF3 with zirconia and alumina starts at 300 and 650 °C, respectively (yielding nitrogen oxides, nitrogen oxyfluoride, and presumably the metal fluorides). The reaction of SF6 and zirconia starts at 600 °C, yielding SO2F2. Sulfur hexafluoride and silica yield (above 900 °C) SiF4, SO2F2, and SOF2. Nickel and SF6 react above 700 °C yielding SF4 (and presumably NiF4). The results indicate that both gases are effective in oxide conversion at typical fluoride glass melting temperatures (800–900 °C). In addition NF3 can be used as a low-temperature fluorinating source for both oxide containing fluoride and pure oxide precursors. This offers great advantages over the use of solid NH4HF2, which is typically used and which forms an additional source of contamination.

Light scattering in fluoride glass

A heavy metal fluoride glass (HMFG) (1,2) known as ZBLAN, an acronym for a formulation composed of ZrF 4, BaF 2, LaF 3, AlF 3, and NaF was prepared under a variety of atmospheric environments to determine their role in influencing optical scatter. Glasses were evaluated using a focused He-Ne laser beam through the test sample, which was immersed in an index matching liquid. The atmospheres investigated were argon, CCl 4, SF 6, C 2Cl 2F 4 (Freon 114), CF 4 O 2 , and CCl 4 O 2 . The study indicates that lowest scattering glasses are those prepared with either SF 6 or C 2Cl 2F 4. These glasses show scattering losses comparable to Suprasil grade silica glass.

Efficient frequency upconversion of Tm3+ ions in Yb3+ doped barium-thorium fluoride glass

If infrared light can be efficiently changed to visible light it would have important implications for optical detection and display devices. In this paper the efficiency of the two-photon upconversion process between Yb3+ and Tm3+ ions in BaF2/ThF4 heavy metal fluoride glass is investigated as a function of Tm3+ concentration and temperature. It is found that for the concentration of 0.05-mol % TmF3 and a projected incident infrared intensity of 1 W/cm2, the projected efficiency at 300 K would be 1.2%.

Interaction of NF3 with melt confinement materials in fluoride glass processing

Nitrogen trifluoride (NF3) was recently used by others as a reactive atmosphere during the melting of heavy metal fluoride glasses. This compound fluorinates oxide impurities, dehydrates the melt, and controls the oxidation state of both glassformer and impurity cations. The reaction of NF3 with nickel, silica, platinum, and vitreous carbon between 200 and 1100°C using IR absorption spectroscopy was investigated. This is an important issue, since reaction products (impurities) from the crucible and containment vessel walls may be incorporated in the melt. All materials, except for nickel, reacted below 600°C yielding corresponding fluorides (and oxides in the case of silica). The results indicate that, directly heated, vitreous carbon crucibles are preferred for melting of fluoride glasses in a NF3 atmosphere.

Effects of Composition and Environment on the Fracture of Fluoride Glasses

Indentation‐crack‐length procedures were used to determine the critical fracture toughness (KIC) and the sensitivity to environmentally enhanced crack growth in heavy‐metal fluoride glasses of varying chemical composition. The data show that while KIC was more or less invariant with composition, some glasses were more susceptible to subcritical crack growth than others. The results are interpreted in terms of existing crack‐growth models. A technique for predicting KIC from fundamental atomic bonding and crystal‐structure data for these glasses is discussed.

Infrared Spectroscopic Studies of the Hydrolysis Reaction During Leaching of Heavy‐Metal Fluoride Glasses

In this work, the interfacial reactions of heavy‐metal fluoride glasses with water have been investigated by Fourier transform infrared spectroscopy. High dilution and stirring conditions were maintained to prevent any influence of pH drift and reprecipitation. From comparisons of the integrated absorption peak areas for the O‐H stretching and H‐O‐H bending vibrations in the glass with those for molecular water, the contributions of metal hydroxyls formed in the corrosion layer can be separated from the total O‐H band. The comparison between the infrared spectra for leached samples and hydroxides of the glass components show the presence of Zr‐OH and La‐OH groups in ZrF4‐based glasses after leaching and drying and of Th‐OH groups in ThF4 glass, indicating the existence of F.‐/OH‐ ion exchange between the glass surface and water.

Matrix isolation and mass spectrometric studies on the vaporisation of OsO2F3: characterisation of molecular OsO2F3

The vapour species produced by heating solid osmium trifluoride dioxide in vacuo have been isolated in low-temperature matrices and also studied by mass spectrometry. Both studies indicate a complex mode of decomposition, and in addition to the identification of OsOF4(C4v) and OsO3F2(D3h) the i.r. spectra show additional features at 907 and 655 cm–1 which are assigned as v(Os;O) and v(Os–F) respectively in molecular OsO2F3. A D3h structure is proposed for this species by comparison with other heavy-metal oxide fluorides.

Radiation-induced paramagnetic defects in heavy metal fluoride glasses

Ionizing radiation-induced defects in heavy metal fluoride glass have been studied by electron paramagnetic resonance (EPR) and electron spin echo (ESE) modulation techniques. Both pristine as well as water-contaminated glass samples were investigated. EPR measurements indicate that the radiation-induced defect observed after annealing at 393 K is not an oxide-related center introduced by water corrosion. ESE modulation data was used to probe the structure of the hole trap responsible for the so-called “central line”. From the observed aluminum modulation it is concluded that the defect site is located near an aluminum cation in the glass structure.

Laser emission of Er+3 in ZrF4-based fluoride glass

Laser emission is reported in an Er+3-doped ZrF4-based fluoride glass often referred to as ‘heavy metal fluoride glass’ (HMFG). The laser operates at room temperature at a wavelength of 2.78μm. The glass is a standard ZBLAN formulation in which all of the LaF3 (4 mol%) is replaced by ErF3. Glass preparation, spectroscopy, and laser data are presented and discussed.

INFRARED LIGHT TO VISIBLE LIGHT UPCONVERSION IN HEAVY METAL FLUORIDE GLASSES

INFRARED LIGHT TO VISIBLE LIGHT UPCONVERSION IN HEAVY METAL FLUORIDE GLASSES

EPR of VO 2+ ions in heavy metal fluoride glasses

The EPR spectra of VO2+ ions in glasses of composition (mol%) 58ZrF4-6LaF3-32BaF2-4AlF3 (ZL glasses) are investigated in the temperature range from 77 to 473 K. The spectrum is similar to that observed for VO2+ in many oxide glasses and can be described by the axial spin Hamiltonian. The spectral parameters estimated by computer simulation of the spectrum are: gII =1.916, g⊥ =1.976. VAII =194 × 104cm−1 and VAtT = 76.6 × 10−4 cm−1. An additional weak structure due to the superhyperfine (SHF) interaction of an unpaired vanadyl electron with 19F nuclei is observed for some hyperfine components. The principal values of the SHF structure are Faz = (14 ) Oe, Fax = (10 ) Oe and Fay = (35±2) Oe. It was assumed that vanadyl complexes formed in ZL glasses contain at least four fluorine ligands which form a square in the equatorial plane.

Bubbles in heavy metal fluoride glasses

Theoretically, light transmission losses as low as 0.001 dB/km are possible in optical fibres made from heavy metal fluoride glasses. One reason this has not yet been achieved is scattering due to bubbles in the glass. Such bubbles can be reduced in size, if not completely eliminated, by heat treatment of the glass preform before fibre drawing.

Optical absorption characteristics of neutron irradiated heavy metal fluoride glasses

Samples of ZBLA and HBLA glasses were subjected to various fluences of neutron irradiation, and the spectral dependence of optical absorption was measured before and after irradiation. The IR edge was found to be unaffected by neutron irradiation for the fluences used. However, a red shift occurred at the UV edge which slightly recovered after three weeks.

Fluoride glass starting materials: Characterization and effects of thermal treatment

The production of heavy metal fluoride (HMF) glasses, and the effects of thermal treatments on the HMF glasses are investigated. ZrF4, BaF2, AlF3, LaF3, and NaF were utilized in the synthesis of zirconium-barium-lanthanum-aluminum-sodium fluoride glass. The purity of these starting materials, in particular ZrF4, is evaluated using XRD analysis. The data reveal that low temperature heating of ZrF4-H2O is effective in removing the water of hydration, but causes the production of ZrF4 and oxyfluorides; however, dehydration followed by sublimation results in the production of monoclinic ZrFe without water or oxyfluoride contaminants.

Chemical Durability of Fluoride Glasses: III, The Effect of Solution pH

The aqueous corrosion behavior of glasses from two heavy‐metal fluoride families (ZrF4‐based and BaF2‐ThF4‐based) was studied as a function of controlled solution pH and of glass composition. Leach test results demonstrate a profound pH dependence of corrosion over the range pH 2 to 13. Whereas the glasses readily undergo congruent matrix dissolution in acidic media, they exhibit a marked increase in chemical durability in neutral and basic solutions, with the optimum aqueous environment occurring near pH 7. Results of this study are discussed and compared with results reported earlier for leach tests of these two compositional families in unbuffered de‐ionized water. In addition, several testing methods, both static and dynamic, are described and point to the importance of appropriate test selection in predicting the corrosion resistance of these glasses over prolonged periods.

The effects of hydrated raw materials upon heavy metal fluoride glass quality

The consequences of using hydrated raw materials for the preparation of ZBLAN glass were qualitatively assessed in terms of effect upon 1) general appearance, 2) hydroxyl content, 3) oxide content and 4) presence of inclusions. Glasses were prepared using ZrF 4·H 2O and sublimed ZrF 4 and dry N 2 and dry N 2 + CCl 4 atmospheres. The resulting glasses were examined with the aid of IR spectroscopy and optical microscopy. It was found that the use of hydrated raw materials did not significantly enhance the OH- or O--concentration of the glass, but did produce a degradation of glass quality.

Heavy metal fluoride glass (HMFG) equation of state

Two HMFG constants, associated with the fluoride ion, the molar volume, and heat capacity, are demonstrated. This constancy of the specific heat per unit volume of the fluoride network yields an equation of state that links the stoichiometry, density, and specific heat of HMFG.

Material dispersion in heavy metal oxide glasses containing bi 2o 3

The refractive index of PbO-Bi2O3-Ga2O3 and CdO-Bi2O3-Ga2O3 glasses has been measured between 0.5 and 5.0 μm, and their material dispersion has been evaluated. The cross-over wavelengths are near 3 μm. Electronic and lattice dispersion parameters have been obtained, and compared with those of heavy metal fluoride glasses. The material dispersion values at 3.5 μm are comparable for the oxide and fluoride glasses, while the cross-over wavelength is larger in the oxide glass.

New zirconium free multicomponent fluoride glasses

Systematic investigations of indium based heavy metal fluoride glasses have led to the discovery of a fluoride composition with a low devitrification rate. The glass BIZYbT with the composition 30 BaF 2−30 InF 3−20 ZnF 2−10 YbF 3−10 ThF 4 is characterized by a difference Tc−Tg = 123° C and an I.R. multiphonon edge lying in the 8 μm region, about 1 μm longer than for the fluorozirconate. Investigations of the T.T.T. curve and various optical properties indicate that this composition is a good candidate for I.R. fluoride fibers of wide transmission range.

DSC studies of melting behavior of heavy metal fluoride glass compositions

Differential scanning calorimetry (DSC) studies of a number of heavy fluoride glasses have been carried out while heating from below the glass transition up to 950K. The glasses first crystallize and then remelt. The final stage of melting is generally marked by a small, high temperature endotherm, whose location allows assignment of a liquidus temperature T L to the glass composition. The ratio T L T g of the liquidus to the glass transition temperature is roughly constant and equal to about 1.5 for a wide variety of glass compositions.