A Thermodynamic Analysis of the System Anorthite-Åkermanite

E. Christiaan De Wys
International Business Machines Corporation, Kingston, New York, U.S.A.

Summary: From thermodynamic considerations of the system anorthite-åkermanite it appears that the melts in this system are ionic in nature. The liquidus relation in this system would thus seem to afford confirmation of the theory, based on conductivity measurements, that silicate melts such as molten anorthite dissociate into such ions as Ca2+ and (Al2Si2O8)2−.

Further thermodynamic calculations involving no unreasonable assumption lead to a close reproduction of the experimental liquidus curve of åkermanite. This lends added strength to the belief in the stable existence of åkermanite down to the eutectic; no evidence in support of the claim that åkermanes becomes unstable below 1 325° C. (Osborn and Schairer, 1941) was encountered.

According to Osborn et al. (1954) the presence of substantial Ca2+ increases the desulphurizing potential of blast furnace slag. The thermodynamic treatment of the binary system anorthite-åkermanite leads to the conclusion that both phases dissociate in the molten state and in mutual solution to yield Ca2+; it therefore appears probable that a high concentration of these minerals in the slag would have a salutary effect on the slag chemistry.

Mineralogical Magazine; December 1960 v. 32; no. 251; p. 644-649; DOI: 10.1180/minmag.1960.032.251.05
© 1960, The Mineralogical Society
Mineralogical Society (www.minersoc.org)