Crystalline vs. amorphous structures: their role in corrosion resistance

Introduction

In materials science, the comparison between the differences in crystalline vs. amorphous structures is fundamental to understand their influence on the corrosion resistance of metallic materials. The mechanical and chemical properties of materials are directly related to their internal structure, which determines their behavior in corrosive environments. While crystalline structures offer order and stability, amorphous structures present disorder that can improve their resistance in certain applications.

This article aims to explore how crystalline and amorphous structures affect the corrosion performance of materials, highlighting their applications in industry, providing technical information that allows the selection of optimal materials according to operating conditions.

Solid materials present a structural organization that defines their mechanical, chemical and physical properties. This organization can be crystalline, characterized by an ordered and periodic arrangement of its components, or amorphous, where there is no defined pattern. In this article, we will explore the main differences between crystalline vs. amorphous structures, and their implications in the resistance of metallic materials, and how understanding these configurations impacts the development of technological applications.

Differences between crystalline and amorphous structures

The atomic structure determines the vulnerability to corrosion: The ordered arrangement of atoms in crystalline materials, with grain boundaries and defects, facilitates the initiation at specific points. In contrast, amorphous materials, lacking these weak points, offer greater resistance to uniform corrosion.

Corrosion resistance varies depending on the type of material: Amorphous materials, due to their more homogeneous structure, have a higher corrosion durability compared to crystalline materials. This makes them more suitable for applications in aggressive environments where widespread exposure to corrosive agents is expected.

Crystalline structures

Crystalline materials are made up of unit cells, three-dimensional patterns that are repeated in a uniform manner. These cells can adopt specific configurations such as simple cubic, body-centered cubic (BCC) or face-centered cubic (FCC). Each cell type directly affects properties such as density, conductivity and mechanical strength of the material.

For example:

• Simple cubic: Lower density due to its low space occupation.
• Body centered cubic (BCC): Stronger but less ductile.
• Face-centered cubic (FCC): Higher density and ductility, ideal for metallurgy applications.

The atomic organization of crystalline solids makes them suitable for structural and electronic applications, where regularity influences thermal and electrical conductivity.

Amorphous structures

Unlike crystals, amorphous materials do not have a defined pattern in the arrangement of their atoms. This structural disorder can be an advantage in certain applications, such as metallic coatings and metallic glasses, where high corrosion resistance and unique magnetic properties are required.

• High corrosion resistance: Due to the absence of grain boundaries that favor corrosive processes.
• Isotropic mechanical behavior: Ideal for components subjected to multidirectional loads.

However, its production requires specialized methods such as rapid solidification, which limits its availability for mass applications.

Implications for corrosion

Atomic arrangement directly influences mechanisms. Crystalline solids have specific sites, such as grain boundaries and defects, where can initiate. In contrast, amorphous materials, lacking this ordered structure, offer greater resistance to uniform corrosion.

The atomic arrangement of materials has a fundamental impact on their behavior, since the internal structure determines how stresses and interactions between atoms are distributed. In crystalline solids, the ordered arrangement of atoms generates certain structural characteristics that directly influence their susceptibility to corrosion. One of the most relevant aspects are the grain boundaries, which act as zones of weakness where the atoms are not as organized as in the interior of the crystal.

These grain boundaries are points where stresses can accumulate, facilitating corrosive attack in specific areas. In addition, defects such as dislocations, vacancies, or inclusions can also be sites prone to the onset of corrosion, as free electrons or charges in these imperfections can interact with the corrosive environment, accelerating the degradation process.

On the other hand, amorphous materials, lacking an ordered crystalline structure, have a more random and homogeneous atomic configuration. This lack of well-defined grain boundaries or defects means that there are no clearly identifiable areas of weakness where This can initiate. As a result, amorphous materials generally offer greater resistance to uniform corrosion.

The random distribution of atoms in these materials facilitates greater stability against corrosive agents, since there are no points of stress concentration or chemical interactions that favor the initiation of the corrosion process. This behavior is particularly advantageous in environments where this is widespread, since amorphous materials tend to be more resistant to degradation across their entire surface.

Corrosion resistance depends not only on the atomic structure, but also on other factors such as chemical environment, temperature, and the presence of mechanical stresses. However, the atomic arrangement remains a crucial factor that can significantly influence the lifetime of materials, especially under severe corrosive conditions. Therefore, the choice between crystalline and amorphous materials will depend on the specific conditions of the application and the type of corrosion expected.

Impact on the development of technological applications

New properties of crystalline structures

Crystalline structures have evolved through the engineering of their microstructures. One notable advance is the creation of ultrafine-grained and nanostructured materials, which decrease the size of crystalline grains down to nanometer scales. This innovation significantly reduces sites susceptible to intergranular corrosion by decreasing grain boundaries, which are often preferential attack zones. In addition, the manipulation of crystallographic orientation on exposed surfaces has enabled the development of specific coatings, such as those based on metal nitrides, which provide a more uniform and resistant barrier to corrosive agents.

In this video, information about metals, microstructure and various techniques such as grain boundary strengthening, solid solution strengthening, precipitation hardening and work hardening that can be used to improve their properties are shown. Courtesy of: The Efficient Engineer.

Another advance is the incorporation of alloying elements, such as chromium, molybdenum and nickel, in controlled proportions. These elements strengthen the formation of passive films in crystalline alloys, such as stainless steels and superalloys, improving their resistance in acidic and saline environments. Through techniques such as physical vapor deposition (PVD) and ion implantation, it is possible to reinforce these properties in a localized manner, optimizing performance against localized corrosion, such as pitting and crevices.

Innovations in amorphous structures and their corrosion resistance

Amorphous structures play an important role in materials science for uniform corrosion resistance. These structures lack grain boundaries and possess a homogeneous chemical composition, which eliminates common weaknesses in crystalline materials. In recent years, research has developed amorphous metallic alloys with specific formulations, such as metallic glasses, which combine elements such as iron, nickel, zirconium and lanthanum. These alloys not only show greater resistance to corrosion in harsh chemical environments, but also superior mechanical properties, such as high hardness and elasticity.

An important innovation is the development of amorphous coatings using techniques such as sputtering and thermal spraying, which allow these properties to be applied to conventional components. In addition, the addition of elements such as phosphorus and boron has improved the passivation characteristics of amorphous alloys, creating more durable chemical barriers under extreme conditions. These properties have made them ideal for applications in the chemical industry, such as reactors and pipelines in contact with highly corrosive acids, and in biomedical components, such as implants exposed to aggressive body fluids.

Synergy between crystalline and amorphous structures: New hybrid approaches

One of the most innovative trends is the combination of crystalline and amorphous structures in hybrid materials. This approach seeks to integrate the advantages of both configurations, such as the mechanical stability of crystalline materials and the uniform corrosion resistance of amorphous ones. For example, the creation of multilayer coatings that alternate crystalline and amorphous layers has been shown to significantly improve performance in marine and chemical environments.

In addition, composites based on high-entropy alloys, which combine multiple metallic elements in equimolar proportions, are redefining structural and corrosion resistance properties. These alloys can be designed to have crystalline and amorphous regions, optimizing the balance between hardness, toughness and chemical resistance.

Conclusions

The study of crystalline vs. amorphous structures continues to drive significant advances in corrosion resistance. Innovations in ultra-fine grain alloys, amorphous coatings and hybrid materials are redefining the ability of materials to withstand highly aggressive environments. The understanding and manipulation of these structures are not only improving component lifetimes, but also promoting more sustainable solutions in sectors such as energy, chemicals and biomedicine.

The integration of hybrid approaches and advanced manufacturing technologies promises to take the anti-corrosion properties of materials to an unprecedented level, marking a milestone in materials engineering. The choice between crystalline and amorphous structures depends on the end use of the material. While crystalline solids stand out for their high mechanical strength and ductility, amorphous solids are ideal for applications that demand chemical resistance and unique properties.

Delving into the relationship between structure and behavior allows the design of materials optimized for specific industrial challenges. The choice between crystalline and amorphous materials must consider the specific environmental conditions. While crystalline materials may be more susceptible in environments with high concentration of local stresses, amorphous materials are preferable in conditions where high chemical resistance and unique properties are required.

References

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