Research Progress of Non-Chrome Passivation
Abstract
As a process of protecting the surface of metal or alloy materials, passivation plays an important role in application industries due to its low cost and high efficiency. Chromium-based passivation is commonly used in various industrial applications, however, due to its toxic nature, alternatives to chromium have been actively investigated in recent decades. In this review paper, the recent progress in non-chrome passivation technologies and its applications in various industries have been summarized and analyzed.
Keywords: passivation, chromium-free, alternative
1 Introduction
Passivation is a process that increases the corrosion resistance of the surface of a metal or alloy by forming a protective coating. Reactive metals, such as iron and aluminum, can be passivated by chemical or electrochemical methods. In the chemical process, an acidic or alkaline solution is used to form an oxide film on the surface of the metal. In the electrochemical technique, a current passes through the oxide layer on the surface to form a protective layer. Passivation increases the corrosion resistance of the metal surface by making it less susceptible to corrosion from external factors, such as water and air.
Passivation has been widely used in industrial applications since it is a relatively simple and cost-effective process. Chromium passivation, for example, is a popular technique due to its low cost and high efficiency. However, chromium-based compounds are toxic, and their use is tightly regulated. In order to replace chromium, researchers have been investigating alternative passivation technologies that are viable and cost-effective.
2 Non-Chrome Passivation Technologies
In recent years, numerous non-chrome passivation techniques have been developed and studied. Titanium passivation, anodizing, and vapor deposition are the most commonly used techniques.
2.1 Titanium Passivation
Titanium passivation is an environmentally friendly method of passivation that uses titanium nitride (TiN) as the barrier material. Titanium nitride is deposited on the surface of the metal in a vacuum. It serves as a corrosion-resistant barrier that prevents corrosion by blocking oxygen, water, and other corrosive gases from reaching the metal surface.
The process is carried out in a vacuum chamber, where a titanium target is evaporated onto the metal surface in a highly reactive plume of nitrogen and oxygen. Titanium nitride is formed on the surface and serves as a protective coating. The process is cost-effective and environmentally friendly, as it does not use any hazardous chemicals.
2.2 Anodizing
Anodizing is a process of passivating metal surfaces by electrochemically forming an oxide layer on them. Anodizing has been traditionally used on aluminum, but in recent years, it has been used on other metals too. During the process, a metal surface is submerged in an electrolyte solution and a voltage applied to it. This causes oxygen to be released from the electrolyte solution and deposit on the metal surface, forming an oxide layer. The thickness of the oxide layer can be controlled by the voltage and duration of the process.
Anodizing is a popular alternative to chromium passivation as it is environmentally friendly and cost-effective. In addition, anodized surfaces have better wear resistance than chromium-passivated surfaces due to the thicker oxide layer.
2.3 Vacuum Vapor Deposition
Vacuum vapor deposition is a process of depositing a protective coating on a metal surface by depositing a film of material, such as titanium or aluminum, on it while in a vacuum. The coating is created by vacuum-evaporating the materials, which condense on the metal surface and form a protective layer.
Vacuum vapor deposition is a simple, cost-effective, and environmentally friendly method of passivating metal surfaces and is often used in place of chromium passivation.
3 Applications
Non-chrome passivation technologies have a wide range of applications in industries such as automotive, electronic, and medical.
3.1 Automotive Industry
Non-chrome passivation technologies, such as anodizing and titanium passivation, are used in the automotive industry for preventing corrosion of automotive components, such as brake calipers, engine blocks, and exhaust manifolds. Anodizing is used on aluminum alloys for its excellent corrosion resistance, while titanium passivation is used for its enhanced wear resistance.
3.2 Electronics Industry
Vacuum vapor deposition is used in the electronics industry for the passivation of circuit boards and components. The passivation process ensures a uniform and reliable bond between the components and the circuit board, preventing shorts and head-on collisions between components.
3.3 Medical Industry
Non-chrome passivation technologies are also being used in the medical industry for the passivation of medical implants, such as pacemakers and prosthetic devices. Titanium passivation has been found to be an ideal method for these medical implants as it is highly corrosion and wear resistant, and also non-toxic.
4 Conclusion
Non-chromium passivation technologies have become more widely used in recent years due to their environmental and cost advantages. Anodizing and titanium passivation are the most commonly used techniques, while vacuum vapor deposition is also finding applications in the electronics and medical industries. This review paper summarized and analyzed the various non-chromium passivation technologies and their applications in various industries.
