Editing Phase diagram (section)

===Binary mixtures===
[[Image:Eutektikum new.svg|class=skin-invert-image|thumb|right|250px|A phase diagram for a binary system displaying a [[eutectic point]].]]Other much more complex types of phase diagrams can be constructed, particularly when more than one pure component is present. In that case, [[concentration]] becomes an important variable.  Phase diagrams with more than two dimensions can be constructed that show the effect of more than two variables on the phase of a substance. Phase diagrams can use other variables in addition to or in place of temperature, pressure and composition, for example the strength of an applied electrical or magnetic field, and they can also involve substances that take on more than just three states of matter.

One type of phase diagram plots temperature against the relative concentrations of two substances in a [[wikt:binary|binary]] mixture called a ''binary phase diagram'', as shown at right. Such a [[mixture]] can be either a [[solid solution]], [[eutectic point|eutectic]] or [[peritectic]], among others. These two types of mixtures result in very different graphs. Another type of binary phase diagram is a ''boiling-point diagram'' for a mixture of two components, i. e. [[chemical compound]]s. For two particular [[volatility (chemistry)|volatile]] components at a certain pressure such as [[atmospheric pressure]], a [[boiling point|boiling-point]] diagram shows what [[vapor]] (gas) compositions are in [[Vapor–liquid equilibrium|equilibrium]] with given liquid compositions depending on temperature. In a typical binary boiling-point diagram, temperature is plotted on a vertical axis and mixture composition on a horizontal axis.[[Image:Binary Boiling Point Diagram new.svg|class=skin-invert-image|thumb|250px|right|Boiling-point diagram]]

A two component diagram with components A and B in an "ideal" solution is shown. The construction of a liquid vapor phase diagram assumes an [[ideal solution|ideal liquid solution]] obeying [[Raoult's law]] and an ideal gas mixture obeying [[Dalton's law of partial pressure]]. A tie line from the liquid to the gas at constant pressure would indicate the two compositions of the liquid and gas respectively.<ref>{{cite journal |last1=David |first1=Carl W. |title=The phase diagram of a non-ideal mixture's p − v − x 2-component gas=liquid representation, including azeotropes |url=https://opencommons.uconn.edu/chem_educ/107/ |journal=Chemistry Education Materials |publisher=University of Connecticut |access-date=9 April 2022 |date=2022}}</ref>

A simple example diagram with hypothetical components 1 and 2 in a non-[[Azeotrope|azeotropic]] mixture is shown at right. The fact that there are two separate curved lines joining the boiling points of the pure components means that the vapor composition is usually not the same as the liquid composition the vapor is in equilibrium with. See [[Vapor–liquid equilibrium#Boiling-point diagrams|Vapor–liquid equilibrium]] for more information.

In addition to the above-mentioned types of phase diagrams, there are many other possible combinations. Some of the major features of phase diagrams include congruent points, where a solid phase transforms directly into a liquid. There is also the [[peritectoid]], a point where two solid phases combine into one solid phase during cooling. The inverse of this, when one solid phase transforms into two solid phases during cooling, is called the [[eutectoid]].

A complex phase diagram of great technological importance is that of the [[iron]]–[[carbon]] system for less than 7% carbon (see [[steel]]).

The x-axis of such a diagram represents the concentration variable of the mixture. As the mixtures are typically far from dilute and their density as a function of temperature is usually unknown, the preferred concentration measure is [[mole fraction]]. A volume-based measure like [[molarity]] would be inadvisable.