Merzhanov Institute of Structural Macrokinetics and Materials Science, Russian Academy of Sciences, Chernogolovka, Russia

M. I. Alymov, Director, Professor, Doctor of Technical Sciences, Corresponding Member of the Russian Academy of Sciences
Yu. V. Levinskiy, Lead Researcher, Professor, Doctor of Technical Sciences, e-mail: levinsky35@mail.ru

D. Mendeleev University of Chemical Technology of Russia, Moscow, Russia
E. V. Vershinina, Associate Professor, Candidate of Technical Sciences

Studying and analyzing the Au – Zn system is currently relevant for manufacturing soft solder alloys, prosthetic dentistry, and jewelry. Adding a small amount of zinc reduces melting temperature, decreases hardness, increases workability, and changes the color of gold alloys from red shades to yellow shades; and zinc is also used for manufacturing white gold. As a rule, zinc content in such alloy reaches 8 % (wt.). Generally, manufacturing finished products from the stated alloy includes stages of melting and casting in vacuum or inert atmosphere. In view of a considerable difference in volatilisation and melting temperatures of gold and zinc (T^Au_melt = 1064 ^оC, T^Zn_melt = 420 ^оC), when conducting technological processes, including the system under study, it is mandatory to factor into both the composition (с), and temperature (Т), and external pressure (p). Thus, in addition to the diagram in axes с – Т, we need the p – Т diagram. It should be noted that the Au – Zn diagram shows complex nature in axes с – Т: crystallization occurs with forming solid solutions, intermediate and ordered (when decreasing temperature) phases at peritectic and eutectic transformations. When plotting the p – Т diagram for the Au – Zn alloy, the authors of the article used experimental data of thermodynamic properties and equilibrium of condensed phases in the system under study, as well as principles of plotting similar diagram stated in a monograph of one of the authors. The state diagram of the Au – Zn system in axes p – Т resulted from research was used as a basis for determining coordinates of points of four-phase equilibriums, plotting isobaric and isothermal sections within a temperature range of 300–800 ^оC and a pressure range of 10^–5–10⁵ Pa. In spite of complexity of such state diagrams, they are of practical interest, when conducting technological processes and using products from the Au – Zn system.

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