Aluminum anodizing is a surface hardening process in which electrolytic passivation is used to thicken the oxide layer found naturally on aluminum alloys. Used to increase corrosion and wear resistance, anodizing can be performed on a variety of metals, such as anodizing titanium; however, among anodizers, aluminum is typically the metal of choice as it is naturally prone to corrosion due to alloying elements such as copper and iron. Say no to plagiarism. Get a tailor-made essay on "Why Violent Video Games Shouldn't Be Banned"? Get an original essay There are three main processes used in anodizing aluminum: chromic acid anodizing (Type I), sulfuric acid anodizing (Type II), and sulfuric anodizing acid hard anodizing (Type III), also known as hard anodizing. Other subprocesses fall into these three main categories, including clear anodizing and colored anodizing, such as black anodizing. Titanium anodization, closely related to aluminum anodization, is also known for its variety of colors, although it achieves different shades without the use of dyes. Additionally, custom anodizing processes are available. These main processes are specifically methods for anodized aluminum; sometimes it is necessary to use other processes to obtain other types of anodized metal. Some processes, such as chromate conversion, have similar methods and results to anodizing, but still have key differentiating factors that separate them, such as whether or not electrical conductivity is maintained. Anodizing aluminum is used in a wide range of applications, in sectors such as: electronics, for external casings to protect objects such as cameras, mp3 players and satellites; food and drink, for heavy-duty cookware such as pots, mixers and pans; architecture, for structural durability in areas such as window frames, roofs and external surface panels; automotive, for aesthetic purposes such as finishing and protective housings of exposed parts in automotive workshops; and industrial manufacturing, for plant equipment such as scales, electrolytic capacitors, and conveyors. Aptly named Type I, chromic acid anodizing is the oldest and most common anodizing process. An electrolytic process using chromic acid, which is a corrosive and oxidizing acid compatible with most aluminum alloys, anodizing occurs when a reactive metal to which an anode is attached is immersed in an electrolyte solution and a direct current is passed through the solution. the anode produces oxygen, creating the oxide film, a cathode attached to the solution-filled tank simultaneously produces hydrogen. A disadvantage of the Type I process is that it can reduce the thickness of aluminum by 0.02 to 0.4 mil; however, Type II and Type III can reduce the thickness by several times that much. Additionally, the Environmental Protection Agency (EPA) limits the use of chromic acid emissions because they can be harmful to the environment. Type I also differs from Types II and III not only in the type of acid solution used, but also because in Type I the DC voltage increases throughout the process. Both Types II and III use a sulfuric acid solution, which is a corrosive, thick, oily acid formed from sulfur dioxide. Type III differs from Type II in that it runs at lower temperatures and with a higher electrical current density, which provides greater anodic growth while making the surface much harder. With so many sub-processes,.