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calcium oxide-boron oxide eutectic.

updated tue 7 jan 03


iandol on sun 5 jan 03

Dear Linda Arbuckle,=20

I have often wondered why Dr Lawrence deleted that list of Eutectics =
from the Second Edition of his book. The information is preserved in =
Handbook for Australian Potters.

That Eutectic cannot be obtained just by using Boron Oxide and Calcium =
Oxide. If you think about the facts, this would make the definition of a =
Eutectic used by Potters (see Hamer, Rhodes, Cooper and Royle etc) =
complete nonsense. Boron Oxide has a melting point of 450=B0Celsius and =
by the definitions of the authors I mention, eutectics have to melt =
below the melting point of any of the contributing materials.=20

The Equilibrium Phase Diagram of the CaO-B2O3 system is quite complex. =
It shows that there is a Liquid at temperatures lower than 900=B0C mixed =
with solid CaO.2(B2O3) in the region of the values you quote. The =
commentary by the Author of this phase diagram might make interesting =
reading. The ref is E. T. Carlson, Bur. Standards J. Research, 9, 830 =
(1932);R. P. 516. As show in the ACS "Phase Diagrams for Ceramists".

But you are correct in the sense that compounds made from these two =
oxides make a valuable contribution as low melting point fluxes.

Best regards and a Happy New Year to you.

Ivor Lewis, Redhill, South Australia=20