，标题为 Hot Corrosion
Hot Corrosion
Introduction
Hot corrosion is a form of corrosion that occurs when certain conditions are present. It is an aggressive form of accelerated corrosion caused by combining high temperatures (313-843 K) and water or moisture within the atmosphere, often containing combustible gases or particulate matter. Hot corrosion is common in industrial settings, such as gas turbine engines, due to the extreme heat, high temperatures, and presence of contaminants.
History
Hot corrosion was first studied by Patrice Simard in 1922, who charted out the conditions for which the corrosion appeared, and monitored the resultant effects. In a paper published in the Annals of the Chemical Society of Belgium, Simard described the sequence in which hot corrosion first became visible and then eventually spread, thus establishing a system for studying hot corrosion.
In the 1950s, hot corrosion became a significant issue in the aviation industry, as jets are more prone to hot corrosion due to their faster speeds and higher temperatures. Scientists experimented with various corrosion inhibitors, leading to the use of chromate inhibiting paints for reducing hot corrosion incidents.
Hot corrosion in gas turbines appeared in the 1990s, leading to a whole new field of study. It is typical of airbreathing engines, and experiments have been conducted in order to better understand and reduce the affects of hot corrosion.
What Causes Hot Corrosion
Hot corrosion is caused by certain conditions in the atmosphere, as well as the environment of the object it is impacting. Oftentimes this corrosion is caused by the presence of particulate or vapor contaminants that are found in industrial or combustion environments. Objects in these types of environments are exposed to high temperatures that can reach up to 843K. When water or other reactive species are present, it can lead to the accelerated corrosion of the material.
Metals commonly subjected to hot corrosion include Nickel, Nickel-based superalloys, and aluminum-magnesium alloys.
Metals can also promote hot corrosion when their surface is exposed to hot gases containing aggressive species such as NO, SO2, CO2, H2O, H2S, and hydrocarbons, for extended periods of time. Hot corrosion is accelerated as a result of oxidation and sulfidation, as well as from the build-up of silica, lead, potassium, and other compounds in the atmosphere. Hot corrosion can also be exacerbated when the affected material has a porous structure or surface.
The Effects of Hot Corrosion
Hot corrosion can have destructive effects on the materials it impacts. In gas turbines, the accelerated corrosion can lead to pitting and cracking of the blades, which can lead to increased levels of vibration and stress, increasing the risk of blade breakage and engine failure.
Materials that have undergone hot corrosion can become brittle and flaky, while certain components may completely disappear as a result of the corrosion. Not only can this lead to a decrease in efficiency, but also an increase in emissions and fuel consumption due to the weakened material.
Preventing Hot Corrosion
There are several methods of preventing hot corrosion from occurring, and steps one can take in order to protect material from the effects of hot corrosion.
First and foremost, it is important to maintain proper ventilation in an environment with potential hot corrosion, as this can keep the temperature of the surrounding air down, as well as minimize the levels of contamination that may lead to hot corrosion.
Second, one should monitor and measure the temperatures of the machined materials, ensuring they remain within a safe operating temperature range. Additionally, using a corrosion inhibitor system can be beneficial in reducing the frequency of hot corrosion occurring, as well as proper surface protection from paints or thin film metals.
Conclusion
Hot corrosion is an aggressive form of accelerated corrosion that can severely damage materials as well as lead to decreased efficiency and increased emissions. The causes of hot corrosion are largely based on the environment and atmosphere of the material, namely temperature and the presence of contaminate species. Proper ventilation, operating temperature monitoring, and corrosion inhibitor systems can help reduce instances of hot corrosion and protect against it.
