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hy is the phenomenon of "segregation" in materials so mysterious and can affect the properties of materials
In materials science, the phenomenon of segregation still leaves many unanswered questions for scientists and engineers. Even the enrichment of atoms, ions and molecules at the microscopic scale in material systems shows its influence on the properties of materials, which triggers the necessity of in-depth exploration.
What is segregation?
Segregation refers to the enrichment of atoms, ions or molecules in microscopic areas in a material system. The term is in some cases synonymous with adsorption, but it is usually used to describe the partitioning of molecular constituents in solid solutions to defects. This phenomenon is distinct from other material phenomena such as particle separation or phase separation, in which molecules become segregated into macroscopic regions of different composition.
Segregation phenomena can affect the entire process of a material from its microstructure to its final performance.
Historical background of segregation
The history of segregation can be traced back to the mid-20th century. Equilibrium segregation is closely related to lattice defects, which allow solute atoms to aggregate at interfaces or surfaces to reduce the overall free energy. The first scholar to predict this phenomenon was McLean, who proposed an explanation in 1957.
In contrast, non-equilibrium segregation, a concept proposed by Westbrook in 1964, is related to the coupling of solutes to vacancies during the so-called "annealing" process or stress application process, and exhibits different thermodynamic properties. . In a non-equilibrium state, as the temperature increases, the degree of segregation will also increase, which is exactly the opposite of the equilibrium state.
The importance of segregationWhen solutes accumulate at the surfaces and grain boundaries of a solid, they create portions of the material with different compositions, which can affect the overall material properties. In other words, these "areas" of higher concentration are like the cement of a building; the overall structure of the building depends not only on the material of the bricks, but also on the properties of this cement.
For example, segregation of grain boundaries may lead to grain boundary fracture due to brittleness, which is a serious problem in many engineering applications.
How segregation in materials affects performance
In many cases, segregation has a significant impact on the properties of materials, especially when applied to industrial materials such as structural steels, where it may lead to phenomena such as environmentally induced fatigue or hydrogen embrittlement. Furthermore, as material recycling rates increase, we may also see interfacial disruption issues that we have not seen before.
Understanding of segregation mechanism
To further control the effects of segregation, scientists are currently developing modeling capabilities and experimental techniques to explain the operation of these segregation mechanisms in increasingly complex systems. This will not only aid in the design of future materials, but also predict their performance in various industrial applications.
Several theories provide descriptions for the segregation behavior, such as the Langmuir–McLean theory, the BET theory, etc., in which the distribution model of the solute atoms becomes crucial.
Thinking about the future of materials science
Although the complexity of the segregation phenomenon means that many problems remain unresolved, with the advancement of technology in the future, it is necessary for us to continue to invest in the study of this phenomenon. Understanding how to control these segregate phenomena, especially in the development of new materials, may be the key to our progress. As technology develops and industry needs continue to change, the ultimate question becomes: Can we effectively predict and control these material properties?
