Phase diagrams of one substance and binary phase diagrams.

1. This project has received funding from the European Union’s Horizon 2020
research and innovation programme under grant agreement No 869993.
Phase diagrams

2. Phase diagrams of single substance
• Phase diagrams have the lines of equilibrium,
where multiple phases can coexist.
• The simplest phase diagrams present the
phases of a single substance in
different temperature and pressure
conditions.
• From the phase diagram, you can read the
phase of the substance in specific conditions.
• The blue line marks the boiling point and the
solid green line marks the melting point in
particular pressure-temperature conditions.
• The dotted green line shows the special
behaviour of water.
Picture: Brews ohare CC BY-SA 3.0

3. Triple point and critical point
• The red line points the conditions where
sublimation and desublimation may occur.
• In the triple point the lines of equilibrium
intersect. All three phases may occur
simultaneously in those conditions.
• At the end of the phase equilibrium curve is
a critical point. In those conditions liquid
and vapor phases become
indistinguishable.
• Critical point is defined by critical
temperature Tc and critical pressure Pc. At
higher temperatures, gas cannot be
liquefied by pressure.
Picture: Brews ohare CC BY-SA 3.0

4. Phase diagram of water
• Pressure increases the
boiling point of water. That
is typical for most of the
substances.
• Pressure decreases the
melting point of water,
which makes water an
unusual substance.
• Triple point of water:
273.16 K and 611.657 Pa
• Critical point of water:
647 K and 20.064 MPa
Picture: Cmglee CC BY-SA 3.0

5. Binary phase diagrams
• In a binary system there are three
variables that can affect the phase
equilibrium: temperature, pressure
and concentration.
• There are many kinds of binary
phase diagrams. Here is a simple
example.
• Pressure is usually atmospheric in
crystallization processes, so the
phase changes can be represented
on a temperature-concentration
diagram.
Picture: Kati Jordan CC BY-SA 4.0

6. Simple example
• x-axis: composition of two subtances
• If concentration is 10
%, it means that there is 10 %
of the substance B and 90 %
of substance A.
• y-axis: temperature
• From the diagram, you can read
present phases as a function of
concentration and temperature.
• Above the liquidus line, substance
is in liquid phase. Below the solidus
line, substance is in solid phase.
Picture: Kati Jordan CC BY-SA 4.0

7. This project has received funding from the European Union’s Horizon 2020
research and innovation programme under grant agreement No 869993.
References
Beckmann, W (ed.) 2013. Crystallization: Basic Concepts and Industrial Applications. Weinheim:
Wiley‐VCH Verlag GmbH & Co. KGaA. Pp. 36-38.
Mullin, J. W. 2001. Crystallization. Oxford: Elsevier Science & Technology, pp. 135-141.
Videos:
• Binary phase diagrams explained: https://youtu.be/7Ym-QyLpsiE
• Basic information about phase changes: https://youtu.be/oc0ypeDELb0