Fluoride glass

Mercury(II) fluoride has been used in the process for manufacture of fluoride glass (qv) for fiber optics (qv) appHcations (11) and in photochemical selective fluorination of organic substrates (12). It is available from Advance Research Chemicals, Aldrich Chemicals, Johnson/Matthey, Aesar, Cerac, Strem, and PCR in the United States. The 1993 annual consumption was less than 50 kg the price was 800—1000/kg. 

TaF has been characterized by ir, Raman, x-ray diffraction, and mass spectrometry (3,11,12). TaF has been used as a superacid catalyst for the conversion of CH to gasoline-range hydrocarbons (qv) (12) in the manufacture of fluoride glass and fluoride glass optical fiber preforms (13), and incorporated in semiconductor devices (14). TaF is also a catalyst for the Hquid-phase addition of HF to polychlorinated ethenes (15). The chemistry of TaF has been reviewed (1,16—19). Total commercial production for TaF is thought to be no more than a few hundred kilograms aimuaHy. 

Hafnium tetrafluoride [13709-52-9] is one component in the cladding layer of a proposed zirconium fluoride glass optical waveguide fiber composition which is expected to have a lower intrinsic light absorption than fused quart2 optical fiber (see Glass Fiber optics Fluorine compounds, inorganic-zirconium). 

Halide Glasses. Fluoride glasses are the most important of the haUde glasses. The only primary fluoride glass former is beryUium fluoride,... 

Hydrogen fluoride Glass Etching, becoming opaque... 

In fluoride glasses, calcium fluoride is an essential constituent, but generally cryolite, NajAlFg, is also added as a flux to lower the temperature of fusion. Aluminium orthophosphate is also generally added to the fusion mixture for various reasons. Of course, the various elements may be added in different ways. Thus, calcium orthophosphate, aluminium fluoride and sodium carbonate are often used in the preparation of fluoride glasses. 

Fluoride glasses are difficult to classify because the various constituents can be added to the fusion mixture in several ways. However, glasses of the Laboratory of the Government Chemist (Wilson Kent, 1973 Kent, Lewis Wilson, 1979 Wilson et al., 1980 Hill Wilson, 1988a), which form the basis of many commercial cements, can be represented as... 

Table 5.8. Composition of fluoride glasses used in studies on polyalkenoate cements, parts by mass Kent, Lewis Wilson, 1979 Wilson et al., 1980)...

Cement formation with fluoride glasses - - -)-tartaric acid The presence of (+)-tartaric acid in a cement formulation exerts a profound effect on the cement-forming reaction. The nature of the underlying chemical reaction is changed and this is reflected in time-dependent changes in viscosity. 

Effect of glass composition on cement properties As we have indicated previously, two types of glass have been used in dental silicate cements the obsolete oxide glass and the modem fluoride glass. Only four studies on glass composition and its relationship to cement property have been published (Wright, 1919 Crepaz, 1951 Manly et al.. 

It was left to Kent Wilson (1968), in unpublished observations, to discover that in glasses based on Si02-Al203-CaF2 compositions the Al/Si ratio controlled the rate at which the cement paste set. These observations laid the foundation for the development of the glass-ionomer cement, during which most of the work on fluoride glasses was done. This topic is covered in detail in Section 5.9.2. 

A number of other up-conversion processes are known. The blue emission from a Yb3+/Tm3+ couple in which the active emitters are defect Tm3+ centers is mainly due to the efficient excitation ET process from Yb3+ centers. Two-frequency up-conversion has been investigated using Pr3+ defects in a fluoride glass matrix. Illumination with one pump wavelength results in GSA, while simultaneous irradiation with a second pump wavelength further excites the GSA centers via ESA. The doubly excited defects emit red light. Up-conversion and visible output only takes place at the intersection of the two beams. 

V. Ruddy, S. McCabe and B.D. MacCraith, Detection of propane by IR-ATR in a Teflon-clad fluoride glass optical fibre, Appl. Spectrosc., 44(9) (1990) 1461. 

Hydrogen fluoride Glass etching, removal of High... 

In spite of the usually low cooling efficiencies (see the exercise above), recent experiments have demonstrated an anti-Stokes cooling from room temperature to 77 K within a certain internal volume of Yb + doped fluorochloride and fluoride glasses under high photon irradiances (Fernandez et ai, 2000). Future practical applications of optical cooling of solids include cooling systems for spacecraft electronics and detectors, as well as for superconductive circuits. 

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