determination of phase diagram of lead-tin system
The Use of Cooling Curves in the Determination of the Phase Diagram for a Lead-Tin System
V.O.L.Tabell
Department of Mining, Metallurgical and Materials Engineering
University of the Philippines, Diliman vo_tabell@yahoo.com Abstract
This paper discusses the use of the cooling curves in the determination of the phase diagram of a Lead-Tin system. The inflection points of these cooling curves were obtained by melting a series of mixtures of lead and tin at varying compositions. These critical points were used on a temperature versus percent tin plot, thus obtaining the experimental phase diagram.
Comparing the theoretical critical temperatures to the experimental data, percent deviations that ranged from 0.04% to 19.15% were calculated. This large difference in error was due to many factors on the way the experiment was conducted. Errors contributed by the instruments used and the difficulty in determining inflection points from the cooling curves, were all considered. It was analyzed that the reconsideration of such errors could prevent some of the erroneous readings and a better phase diagram can be obtained.
1. Introduction
A phase diagram is a graphical representation of chemical equilibrium. Since chemical equilibrium is dependent on the composition of the system, the pressure, and the temperature, a phase diagram should be able to tell us what phases are in equilibrium for any composition at any temperature and pressure of the system [1].
In the phase diagrams of eutectic systems, the first addition of either component metal to the other causes lowering of the melting point, so that the liquidus curve passes through a temperature minimum known as the eutectic point [2].
Three two-phase regions are designated in the figure above namely, L + α, L + β and α + β. The three two-phase regions meet at a special kind of tie-line that is common to all the regions and that joins the compositions of three conjugate phases
that
V.O.L.Tabell
Department of Mining, Metallurgical and Materials Engineering
University of the Philippines, Diliman vo_tabell@yahoo.com Abstract
This paper discusses the use of the cooling curves in the determination of the phase diagram of a Lead-Tin system. The inflection points of these cooling curves were obtained by melting a series of mixtures of lead and tin at varying compositions. These critical points were used on a temperature versus percent tin plot, thus obtaining the experimental phase diagram.
Comparing the theoretical critical temperatures to the experimental data, percent deviations that ranged from 0.04% to 19.15% were calculated. This large difference in error was due to many factors on the way the experiment was conducted. Errors contributed by the instruments used and the difficulty in determining inflection points from the cooling curves, were all considered. It was analyzed that the reconsideration of such errors could prevent some of the erroneous readings and a better phase diagram can be obtained.
1. Introduction
A phase diagram is a graphical representation of chemical equilibrium. Since chemical equilibrium is dependent on the composition of the system, the pressure, and the temperature, a phase diagram should be able to tell us what phases are in equilibrium for any composition at any temperature and pressure of the system [1].
In the phase diagrams of eutectic systems, the first addition of either component metal to the other causes lowering of the melting point, so that the liquidus curve passes through a temperature minimum known as the eutectic point [2].
Three two-phase regions are designated in the figure above namely, L + α, L + β and α + β. The three two-phase regions meet at a special kind of tie-line that is common to all the regions and that joins the compositions of three conjugate phases
that
References: New York: McGraw-Hill, 1956. Print.