PHASE FORMATION IN THE Na2O-B2O3-CaSi2O5 SYSTEM
E.P. Shvanskii and N.I. Leonyuk
Moscow State University, Moscow 119899, Russia
Keywords: crystal growth, spontaneous nucleation, borates, borosilicates
This work was undertaken as a part of a program to gain an understanding of structural principles and device potential of anhydrous borates and silicates. As a consequence of the earlier results [1], here the main attention was paid to the phase formation in the borosilicate system CaO-B2O3-SiO2 in the field near stoichiometric danburite, CaB2Si2O8 which have never been synthesized in laboratories and/of the available structural data for further refinement.
Solid phases were grown from melt, fluxed melts and were also prepared by solid state reaction. The x-ray powder patterns of synthesized products were obtained on a DRON-1UM diffractometer (CoKa - radiation, Fe-filter) in the 2 theta region of 15 - 80o angles.
The phases Na2CaSiO4 and Na2SiO3 dominate in the (3.0-4.0)Na2O/(1.75-1.5)CaO /(1.75-1.5)B2O3/(3.0-3.5)SiO2 system. An increase contain of Na2O up to 50 mole% leads to form of Na2SiO3-phase. The replacement of Na2O by Li2O cause formation of Li2SiO3 compound. The region of glassy solidification is detected for danburite compositions with 10 to 20 mole% of Na2O.
Likewise as an flux was used Bi2O3. At 30 mole% Bi2O3 mixture not react practically. At 50 mole% Bi2O3 occurred caking but melt has not formed. Main detected phases are SiO2 and Bi2B8O15 (into second accident).
More details and the numerical results will be presented in the full-length paper.