Structural characteristics of alkali borate flux liquids
1969; Elsevier BV; Volume: 6; Issue: 1 Linguagem: Inglês
10.1016/0022-0248(69)90090-6
ISSN1873-5002
AutoresJohn S. Berkes, William B. White,
Tópico(s)Crystal Structures and Properties
ResumoAnalysis of the role of flux liquids in controlling nucleation and crystal growth requires an understanding of the way in which the cations to be grown are bound in the parent liquid. The nature of the alkali borate family of fluxes was examined by measuring the deviation of the solution from ideality utilizing the growth of NiO as a probe. Precise liquids relations were determined for the systems NiO-Na2O · 2B2O3, NiO-K2O · 2B2O3, and NiO-Rb2O · 2B2O3. The experimental liquidus curves were fitted to a model using regular solution theory. The deviations from ideal solution lead to a liquid model involving a di-borate molecular aggregate. The thermodynamic results were combined with results from optical spectroscopy to deduce the environment of the Ni++ ion in solution prior to crystallization. It was shown that Ni++ (and therefore by inference, other transition metal ions) is in a large network-modifying site with a very weak bonding to its surroundings. This situation accounts at least in part for the low-energy barriers to crystal growth in the borate fluxes.
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