Phase equilibriumPhase equilibrium

PlanPlan

1.1. Phase equilibriumPhase equilibrium. . Gibb’s phase ruleGibb’s phase rule..

2.2. Diagram of the state for a one Diagram of the state for a one component systemcomponent system .

3.3. Phase diagrams of a two components Phase diagrams of a two components systemssystems

Prepared by assistant Kozachok S.S.

Phase equilibriumPhase equilibrium. . Gibb’s phase ruleGibb’s phase rule Equilibrium in the Equilibrium in the Heterogeneous systems is described by Gibb’s phase ruleGibb’s phase rule

С = К С = К - - ФФ + 2,+ 2,

wherewhere СС – – degree of freedomdegree of freedom,,

ФФ – – the number of phasesthe number of phases,,

КК – – the number of componentsthe number of components

22 – – the number of changing parametersthe number of changing parameters ((рр і і ТТ).). It’s true for gases It’s true for gases

С = К С = К - - ФФ + + 11

For the systems that contains only solid and liquid phases, pressure doesn’t influence on the system.

Phase: a state of matter that is uniform throughout, not only in chemical composition but also in physical state.

Constituent: any chemical species present in the system.

Component: a chemically independent constituent of the system. It is best understood in relation to the phrase 'number of components' which is the minimum number of independent species necessary to define the composition of all the phases present in the system.

Degree of freedom (or variance): the number of intensive variables that can be changed without disturbing the number of phases in equilibrium.

Specify the number of independent ways in which an atom or molecule can take up energy.

Diagram of the state for a one component systemDiagram of the state for a one component system ((waterwater))

The number of changing parameters that influence The number of changing parameters that influence on the equilibrium state in the two components on the equilibrium state in the two components systems p, T, C1, C2, where C1 and C2 are the systems p, T, C1, C2, where C1 and C2 are the concentration of the components.concentration of the components.But the diagram is plotted between T and C, cause But the diagram is plotted between T and C, cause the condensed systems have a small value of the condensed systems have a small value of vapour pressure that’s why atmospheric pressure vapour pressure that’s why atmospheric pressure doesn’t have the great influence on the system.doesn’t have the great influence on the system.At this case At this case Gibb’s phase ruleGibb’s phase rule isisC = K-C = K-Ф+1Ф+1

Thermo analysis of the two Thermo analysis of the two components system with simple components system with simple

eutecticeutectic

Diagram of the two components Diagram of the two components system with simple eutecticsystem with simple eutectic

concentratioconcentrationn

С

D

F

G

tem

per

atu

rete

mp

erat

ure

TA is fusion temperature for the pure A component

TB is fusion temperature for the pure B component

E is eutectic point

Eutectic mixture A solid solution consisting

of two or more substances and having the lowest freezing point of any possible mixture of these components. The minimum freezing point for a set of components is called the eutectic point.

Low-melting-point alloys are usually eutectic mixtures.

Аntipyrin Мenthol

Mass percentage of the menthol, %

Діаграма плавкості системи антипірин-ментол

A diagram of the fusibility of the system is an antipyrine-Mentholum

Phase diagrams of a two components systemsPhase diagrams of a two components systems

That kind of diagrams gives the That kind of diagrams gives the components with simple eutectic. components with simple eutectic. Components are unisomorphs thus Components are unisomorphs thus don’t create chemical compound don’t create chemical compound ( the components don’t react which ( the components don’t react which each other)each other)

Diagram of the two component Diagram of the two component systemsystem ( (solubility is limitedsolubility is limited) ) with with

the formation of the solid liquidthe formation of the solid liquid

concentrationconcentration

tem

per

atu

rete

mp

erat

ure

Diagram of the two component system Diagram of the two component system ((unlimited solubilityunlimited solubility) ) with formation of with formation of

the solid solutionthe solid solution

isomorphism The existence of two or

more substances (isomorphs) that have

the same crystal structure, so that they

are able to form *solid solutions.

For instance: Ni and Cu

Diagram of the two component system with Diagram of the two component system with the formation of stable chemical compound the formation of stable chemical compound

(created by unisomorphs components)(created by unisomorphs components)

ConcentrationConcentration

Diagram of the two component system with Diagram of the two component system with the formation of non stable chemical the formation of non stable chemical

compoundcompound

concentrationconcentration

Equilateral Equilateral triangle of triangle of

compositions of compositions of Gibbsa-RozebumGibbsa-Rozebum

Spatial diagrams of Spatial diagrams of the triple systemsthe triple systems

Diagram of the limited Diagram of the limited solubility liquidssolubility liquids

ТТ

ТТ

ТТ

ТТ