ISSN 1070-4272, Russian Journal of Applied Chemistry, 2014, Vol. 87, No. 7, pp. 837−852. © Pleiades Publishing, Ltd., 2014.
Original Russian Text © A.G. Morachevskii, 2014, published in Zhurnal Prikladnoi Khimii, 2014, Vol. 87, No. 7, pp. 841−857.
Liquid Alloys of the Mercury–Sodium System:
Thermodynamics, Structure, and Applications
A. G. Morachevskii
St. Petersburg State Polytechnical University, ul. Politekhnicheskaya 29, St. Petersburg, 195251 Russia
Received July 16, 2014
Abstract—Published data on thermodynamic properties, structure, and applications of liquid mercury–sodium
alloys are discussed.
115 years ago, N.S. Kurnakov published in Russian,
German, and French chemical journals the ﬁ rst and, at
the same time, the basic paper, “On Mutual Compounds
of Metals” . In this paper, he analyzed the results of
studying the phase diagrams of sodium and potassium
amalgams and of sodium alloys with cadmium, lead,
and bismuth. Such previously unknown compounds
as HgNa and Hg
Na were discovered. Their existence
could not be rationalized from the standpoint of the
classical valence theory. Kurnakov noted: “…Alkali and
alkaline earth metals exhibiting the most pronounced
base or metal properties show particularly pronounced
tendency to form compounds. Their combinations with
Hg, Zn, Pb, Sn, Cd, Bi, and other heavy metals are
undoubtedly the most characteristic and the best deﬁ ned
group of mutual combinations of metals known by now.
As could be expected from the position of alkali metals
in the periodic table, this group is characterized by
extraordinary diversity of forms” .
Paper  initiated broad-scale studies of variable-
composition phases in metal systems in Russia. In
subsequent papers, Kurnakov and his closest coworkers
and disciples formulated the concept of bertollides and
daltonides, developed the doctrine of composition–
property diagrams, and laid the groundwork for a major
section of general chemistry, physicochemical analysis
The logical continuation of studies on phase
diagrams of metal systems was studying the nature,
thermodynamic properties, and structure of liquid alloys.
Such studies were performed particularly actively in the
second half of the XX century. Liquid mercury–sodium
alloys ﬁ nd diverse applications in technology, which has
been noted in a number of special monographs [5–9].
The production of chlorine and alkali by electrolysis
with a liquid mercury cathode remains an important
application ﬁ eld of sodium amalgam [7, 10]. Certain
problems related to the use of sodium amalgam are
discussed in the concluding part of this review.
According to published data, mercury forms with
sodium a congruently melting compound Hg
(mp 353°C) and a series of compounds melting with
, and Hg
Na (Fig. 1) [11–14]. Some authors
[15–20] report somewhat different compositions of
incongruently melting compounds: HgNa
, HgNa, and Hg
Na. Also, a different value is
reported for the melting point of Hg
Na, 340°C .
Hoch and Simon  discuss the structure of the
possible compound Hg
. Crystallographic studies
of mercury compounds with sodium are summarized
in . For discussing the properties and structure of
liquid alloys of the Hg–Na system, only the compounds
Na, HgNa, and Hg
Na play an important role.
The thermodynamic properties and structure of liquid
sodium–mercury alloys were not discussed previously
in full combination, in spite of numerous experimental
and calculation studies published on this matter.