Estimation of the parameter of interaction of boron in melts of the iron–bor

P. G. Ovcharenko, E. V. Kuzminykh, V. I. Ladyanov

ABSTRACT:

Concentration dependence of the interaction parameter in melts εBB of the system Fe – B is considered. For calculations we used the experimental data summarized in the phase diagram of Fe – B. The phase diagram was been taken from literature. We received the expression for the boron activity coefficient in the melt: YB=1/KFe2Bx2FeY2FexB considering the eutectic point ( xB= 0.17, Т = 1177°С) where the melt to be in equilibrium with the solid boride Fe2B. The equilibrium constant of reaction of boride (KFe2B) formation was calculated on the Δ GoT of reaction. Using the first approximation of Ulica the Δ GoT of reaction was estimated according to the standard heat ΔHo298 and entropy ΔSo298 of the process with a reduction to the standard conditions “pure liquid iron and liquid (metastable) Bor”. To calculate the activity coefficient of iron in the melt (YFe) we took into account in the eutectic point the melt to be in equilibrium with the solid solution of boron in iron.  From the equilibrium condition of the solid and liquid solutions of Fe – B (YFe) is believed to be equal one due to the very low concentration of boron in solid solution we got that in liquid solution YFe=0.95.   Using the values YFe and KFe2B we calculated value YB in the melt of eutectic composition. It is equal 0.017 with standard condition “pure liquid Bor”. To recalculate YB with temperature of 1177 at the temperature of 1600 we used the ratio lnYi,T2=T1/T2*lnYi,T1 , getting 0.043, that corresponds to the parameter value εBB  equal to 6.0. εBB is assumed to be liner function of xBB and take into account that in an infinitely dilute solution εBB=2.5 so at 1600: εBB=2.5 + 21xBB. The getting dependence is proved to be very close to the dependence that known from the literature obtained theoretically on the basis of a statistical model of the solution.

KEY WORDS: 

melts, state diagram, iron–boron system, iron boride, equilibrium, activity coefficient, interaction parameter