Die Verteilung von Zink zwischen Ferrit und Austenit und die Thermodynamik des Zweistoffsystems Eisen—Zink

Verfahren zur Herstellung sehr reiner Eisen-Zink-Legierungen. Ermittlung der Sättigungsgehalte an Zink im Ferrit und Austenit mit Hilfe der Mikrosonde. Berechnungen zur Beschreibung der thermodynamischen Eigenschaften des zinklegierten paramagnetischen Ferrits und des zinklegierten Austenits unter Zuhilfenahme von thermodynamischen Werten aus dem Schrifttum. Berechnung des Gleichgewichts Austenit/Ferrit, Festlegung der γ-Schleife des Zustandsschaubildes und Vergleich mit den ermittelten Werten. Berechnung der Löslichkeit der Γ-Phase im α-Eisen mit Hilfe der bereits bekannten Thermodynamik der α-Phase. Berechnung einer metastabilen Mischungslücke und deren Spinodale im Ferrit.     

Definitions of terms for a thermodynamic data bank—Part 3

For communication with a thermodynamic data bank, it is important to use terms that have strict definitions. The definitions presented here were prepared for use with a solution data bank developed by SGTE (Scientific Group Thermodata Europe), but should prove useful to others working in this field. Part 1 was included in Vol. 2, No. 2, and Part 2 in Vol. 3, No. 3 of theBulletin.     

The sharpness of melting maxima

The shape of melting maxima for strictly stoichiometric phases is examined by computer calculations. For a simplified case, it is found that such maxima look sharp, in apparent violation of Konovalov’s rule, if the Gibbs energy of formation of the phase is −20T _m J/mole of atoms or lower (more negative).     

An assessment of the CaO-SiO2 system

An evaluation of the CaO-SiO₂ system has been made using a newly developed model, a two-sublattice model for ionic solutions. Two alternatives were tested. In the first one, three anions were assumed, O⁻², SiO₄ ⁻⁴, and SiO₃ ⁻². In the second one, SiO₃ ⁻² was omitted. A set of parameter values describing the Gibbs energy of the liquid phase and solid phases was fixed for each alternative by a computer-operated optimization procedure called PARROT. Satisfactory assessments were achieved over the whole phase diagram range with both alternatives. The main difference between them occurs at the monotectic point. A comparison between calculated properties and experimental data is given. Formerly Research Associate, Royal Institute of Technoloy     

How can calphad develop further as a science?

After a difficult beginning, the Calphad approach today has gained a good scientific reputation. In order to retain its reputation Calphad must develop further. It is no longer sufficient just to produce assessments made with well-known techniques. New frontiers must be opened up. When that happens, the Calphad approach will face a number of difficulties that should be tackled. Such difficulties are discussed, and it is proposed that Calphad assessors should apply modern information technology in order to overcome some of the difficulties. As a first step, the electronic Bulletin Board for Thermodynamic Assessments has been opened on the Web: www. met. kth. se/assessment.