Relationships between silicate melt structure and petrologic processes

The role of P2O5 in silicate melts

An exhaustive review of compositional and thermal extents of miscibility gaps in 41 binary silicate systems permits identification of three groups of cations exhibiting different immiscibility behaviours. The first group comprises network-modifier cations with an ionic radius larger than about 87.2 pm. They have coordination numbers equal to, or higher than, 5 and their miscibility gap size increases linearly with increasing ionic potential. The second group involves cations with an ionic radius larger than 26 pm and smaller than about 87.2 pm (in octahedral coordination). They have at least two coordination numbers: the first one is always 4 and the other 5 (or more). For this reason they are called amphoteric. Their miscibility gap sizes do not increase linearly with an increase of the ionic potential, but follow curves. The third group includes cations with variable crystal field stabilization energies. They are characterized by larger miscibility gap sizes than expected when they are compared with cations with similar ionic radii despite the fact that some of them (e.g. Cr3+) may behave as an amphoteric element because their ionic radii in octahedral coordination are smaller than about 87.2 pm. The origin of phase separation in binary silicate systems is due to coulombic repulsions between poorly screened cations bounded by bridging oxygen strongly polarized towards the silicon, and by non-bridging oxygen.

The nature of phase separation in binary oxide melts and glasses. I. Silicate systems

Over the past two decades, fiber laser technologies have matured to such an extent that they have captured a large portion of the commercial laser marketplace. Yet, there still is a seemingly unquenchable thirst for ever greater optical power to levels where certain deleterious light-matter interactions that limit continued power scaling become significant. In the past decade or so, the industry has focused mainly on waveguide engineering to overcome many of these hurdles. However, there is an emerging body of work emphasizing the enabling role of the material. In an effort to underpin these developments, this paper reviews the relevance of the material in high power fiber laser technologies. As the durable material-of-choice for the application, the discussion will mainly be limited to silicate host glasses. The discussion presented herein follows an outward path, starting with the trivalent rare earth ions and their spectroscopic properties. The ion then is placed into a host, whose impact on the spectroscopy is reviewed. Finally, adverse interactions between the laser lightwave and the host are discussed, and novel composition glass fiber design and fabrication methodologies are presented. With deference to the symbiosis required between material and waveguide engineering in active fiber development, this review will emphasize the former. Specifically, where appropriate, materials-based paths to the enhancement of laser performance will be underscored.

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Materials for optical fiber lasers: A review

Oxide solution mechanisms in silicate melts: Systematic variations in the activity coefficient of SiO2

Phase relations in the binary system between SiO2-P2O5 and SiO2 were investigated by the quenching method using sealed platinum tubes to prevent the loss of P2O5. The compound Si02-P2O5 exists in two forms, the low-temperature β form inverting sluggishly but reversibly to the high-temperature β form at 1030°C. The β form melts congruently at 1290°C. The compound 2SiO2-P2O5 melts incongruently at 1120°C to a silica-rich liquid and SiOa-P2O5. In the region between 5 and 25 mole % PO2, reactions were so sluggish that no data could be obtained by quenching.

The System SiO2–P2O5

As a preliminary to the investigation of the ternary systems Li/sub 2/O- B/sub 2/O/sub 3/-P/sub 2/O/sub 5/ and Li/sub 2/O-SiC/sub 2/-P/sub 2/O/sub 5/, the existence of the previously reported lithium ortho-, pyro-, and metaphosphate compounds was confirmed. A rapid, reversible inversion takes place in Li/sub 4/P/ sub 2/O/sub 7/ at 630 deg C. New data on the melting points, optical properties, and x-ray diffraction patterns of each of the compounds were obtained. (auth)

Studies in Lithium Oxide Systems: X, Lithium Phosphate Compounds

Recent studies have shown that opaque white glasses can be obtained in the systems Li2O-TiO2-SiO2 and CaO–TiO2–SiO2, owing to the separation of immiscible liquids. The two phases in the lime system are easily observed under the petrographic microscope, but the dispersion of spheres in the matrix glass in the lithia system can be seen only with the higher resolutions available with the electron microscope. The two systems have been combined to yield a base for opaque glaze compositions which can be fired in the usual maturing range of vitrified whiteware bodies around 1250°C. The thermal expansion behavior of four-component oxide glazes is discussed in the light of some glaze-fit problems which might arise. A brief picture of the effect of other oxides such as Na2O, ZnO, BaO, and ZrO2 on the texture and opacity of these immiscible liquid glasses is presented.

T. Y. Tien

Papers

The System SiO2–P2O5

Studies in Lithium Oxide Systems: X, Lithium Phosphate Compounds

Studies in Lithium Oxide Systems: VIII, Application of Silicate Liquid Immiscibility to Development of Opaque Glazes