Theme: Двухкомпонентные of system. Elements of a structure and rule of job with the diagrams of a condition двухкомпонентных of systems.

Lecture № 20

Правило определения пути кристаллизации двухкомпонентной системы с образованием твердых растворов.

Выше кривой t_А в t_B находится однофазная область ненасыщенной жидкой фазы. Между кривыми ликвидуса и солюдуса t_А С₂ t_B двухфазная область жидкость твердого раствора между компонентом АВ обозначенного SАВ и ниже кривой солюдуса t_А С₂ t_B однофазная область твердого раствора SАВ. Путь изменения состава жидкой фазы а – в - в₂ твердая фаза с- с₂ – d.

 

 

 

The diagrams двухкомпонентных of systems with эвтектикой without firm solutions and chemical connections with a stratification in a liquid phase with polymorphic transformations of components and education of firm solutions.

 

Figure. The diagram of a condition двухкомпонентной of system with эвтектикой.

 

In figure the type of the diagram of a condition двухкомпонентной of system А-В with эвтектикой (without binary chemical connections and firm solutions) is submitted. Let's consider a way кристаллизации расплава of structure and. Final phases кристаллизации of any binary structure in this system will be components And and In, and кристаллизация will come to an end at эвтектической to temperature, that is in a point эвтектике. At downturn to temperature from a point and up to in there will be only cooling расплава, at achievement of temperature ликвидуса tB a liquid phase (расплав) of structure In will appear sated in relation to a component And (in area tА, tе - Е) in balance with a liquid there are crystals And. The structure of a liquid phase will be will change thus on curve ликвидуса from a point in up to Е (system моловариантна). In a point Е the crystals And and In are simultaneously allocated, hence liquid of structure Е is sated in relation to both components. Thus, for structure of a point and way of change of structure of a liquid phase at cooling it is possible schematically to represent as follows:

Let's consider a way of change of structure of a firm phase at кристаллизации same расплава. The first crystals of a component And begin to be allocated at temperature from tB up to tе, the firm phase will consist only of crystals А. at кристаллизации эвтектической of a liquid structure of a firm phase begins to be enriched by a component В.

 

 

Rule of definition of ways кристаллизации in двухкомпонентных systems with chemical connections decomposed конгруэнтно and инконгруэнтно.

 

In figure the diagram of a condition двухкомпонентной of system with individual chemical connection АВ плавящимся without decomposition (конгруэнтно) is given. According to a rule of definition of final phases кристаллизации all structures laying to the left from a vertical tАВ - АВ comes to an end to crystallize Е1, and laying in the right in a point Е2. As the connection АВ is individual chemical connection structure precisely adequate(precisely answering) to this connection completely закристаллизуется or расплавиться at constant tАВ.

 

 

In figure the diagram of a condition двухкомпонентной of system with chemical connection АВ плавящимся with decomposition (инконгруэнтно) is given. A characteristic point of this diagram is the invariant point n (point перитектики). Let's consider ways кристаллизации some расплавов in this system. Structure а1. At cooling structure а1 on a site а1 в1 there is a downturn of his(its) temperature. At temperature to the appropriate point в1 on a curve ликвидуса begins кристаллизация of a component In, and the structure of a liquid phase will change till a curve ликвидуса в1 n at simultaneous кристаллизации In. In a point перитектики n at constant tn there is перитектическая a reaction: as a result of which is allocated АВ. For the given initial structure расплава кристаллизация in a point перитектики will be finished can not, as final phases кристаллизации а1 is the connection And and АВ. The vertical of structure а1 d1 gets between points of structure of connections And and АВ, and the component And in products кристаллизации at перитектической to temperature is absent. Therefore in result перитектической of reaction a component In completely disappears, and the liquid remains. In the further structure of a liquid phase changes till a curve ликвидус Е with allocation of crystals АВ and at last in a point Е кристаллизация comes to an end with simultaneous allocation of final phases кристаллизации of crystals And and АВ. Below эвтектической of a point will occur at downturn of temperature only cooling of a mix of crystals And and АВ on a surface of structure с1d1. Thus way of change of a liquid phase at cooling расплава а1 can be represented as follows: а1 - в1 - n - Е

For structure а2: а2 - в2 - n.

For structure а3: а3 - в3 - n

 

Rule of definition of ways кристаллизации двухкомпонентных of systems with ликвацией and polymorphic transformations.

 

The area ликвации в1в3в5 area of polymorphic transformations (connection Ав exists in three polymorphic forms АВ, А'B ', And " B "). The structure of a point а1 at cooling расплава up to tB when a figurative point в2 reaches(achieves) n on the further curve в1в3в5. an initial homogeneous liquid is decomposed to two liquids, which structures is defined(determined) by the ends канода в2в4. At the further downturn of temperature the structure of a liquid changes till a curve ликвидуса в5 Е. A way of change of structure of a liquid phase for structure а1:

 

в₂ - в₁

а₁ – в₂ в₄ – в_{5 -} в₅ - Е

 

 

The structure а2 of connection АВ has three polymorphic forms низкотемпературной АВ, stable up to t3, form A'B ' with area of stable existence from t3 up to t2 and high-temperature And " B " existing above t2.