DETERMINATION OF THE TEMPERATURE
OF SOLID–LIQUID PHASE TRANSITIONS
S. A. Suvorov
and V. V. Kozlov
Translated from Novye Ogneupory, No. 10, pp. 42 – 44, October, 2006.
Original article submitted July 21, 2006.
A method for determining the melting point of nonmetallic materials in a wide temperature interval (up to
2000°C) is considered. This method makes it possible to measure the melting points of individual materials, as
well as identify the temperature of the emergence of a liquid phase (start of melting) in a mixture containing
two or more components. The melting temperature interval of a multicomponent mixture can be determined.
The method of differential thermal analysis (DTA) based
on the effect of energy absorption or emission by a material
in the course of phase transformations is extensively used to
determine the temperatures of phase transitions. It is known
that melting is an endothermic process accompanied by heat
absorption and the melting point correlates with the extreme
minimum on the thermogram [1, 2].
Hard nonmetallic materials, as a rule, are dielectrics;
their electric resistivity is very high and decreases with in-
creasing temperature. A melt consisting of charged ions, on
the contrary, is an electric current conductor;therefore, the
conductivity of a material changes at the moment of its melt
ing, and the emergence of a liquid phase is accompanied by a
sharp decrease in resistance.
Crystalline nonmetallic materials in their electrophysical
properties are classified into dielectrics and semiconductors.
Dielectrics, in turn, are classified based on their propensity
for vitrification (formation of supercooled melts) into glass-
forming and non-glass-forming materials . When non-
glass-forming crystalline materials (dielectrics) are heated to
a temperature close to their melting point, we observe a
monotonic exponential decrease in their resistivity, from a
few megaohm to hundreds of ohms or kiloohms. As the melt
ing point is reached, the resistivity sharply drops to a few
ohms. Crystallization of the melt is accompanied by an
abrupt increase in electric resistivity .
Glass-forming crystalline materials, in contrast to non-
glass-forming ones, in cooling exhibit a significant resistance
hysteresis depending on temperature. Materials with an in-
tense glass-forming capacity, such as B
, have no abrupt
changes in their resistance in melting.
Melting semiconductors as well does not involve sharp
changes in their resistance . Multicomponent mixtures be-
come melted within a temperature interval. The temperature
of the formation of a liquid phase is called the solidus and the
minimal temperature under which the mixture is totally
melted is called the liquidus. The emergence of the melt in
a multicomponent system sharply decreases its electric
A method has been developed and a plant has been cre
ated for determining the temperature of transitions from the
solid state to liquid and vice versa. The method is based on
variations in the electrophysical properties of nonmetallic
crystalline materials occurring in their melting and crystalli
The measuring complex (Fig. 1) constitutes a furnace
with a spiral electric heater. It working chamber contains a
measuring cell consisting of two wire electrodes and an iso
metric sample fastened between the electrodes. The size of
the sample has to be no more than 2 mm in order to reduce to
a minimum the heterogeneity of the temperature field of the
sample. Wire electrodes are connected to an ohmmeter to
measure the resistivity of the sample.
The temperature in the working zone is measured by a
thermocouple or based on a preconstructed “heater power –
temperature” graduation plot. If the second variant is chosen,
a wattmeter is included in the circuit with the heater to deter
mine the power of the current in the heater.
Refractories and Industrial Ceramics Vol. 47, No. 5, 2006
1083-4877/06/4705-0314 © 2006 Springer Science+Business Media, Inc.
St. Petersburg Technological Institute (Technical University),