What Is an Alpha Case?

An alpha case is an unwanted byproduct of working with titanium. It occurs when heated titanium is exposed to oxygen. Alpha case is very brittle and not usable in most industrial or commercial functions.

Titanium is a durable metal that is commonly found throughout the earth’s crust. This metal is very useful to engineers as it is both strong and relatively light. It can be used in circuits because it resists corrosion, and in airplanes due to its light weight. Titanium bonds readily with oxygen and can be very brittle in its natural state. There is a form of titanium/oxygen alloy called rutile that retains the more desirable features of the pure metal, however.

Generally, titanium is most useful if it has not reacted with oxygen. There are many ways to avoid or remedy this situation in an industrial setting where titanium must be heated to a high temperature. A frequently impractical but obvious solution is to conduct metallurgy involving titanium in a vacuum. This would prevent oxygen from reaching the heated titanium and allow the workers to combine the heated titanium with iron, making it more stable. Creating a vacuum is not always possible in an industrial setting, however, so other methods are more commonly used.

The usual method for removing unwanted oxygen from titanium involves a chemical reaction using electricity. The alpha case is submerged in liquid calcium chloride. An electrical charge is then run through this mixture. The result of this is that the oxygen is released and the workers are left with pure titanium and another titanium alloy that can also be used in some industrial applications.

A metallurgical process called pickling can also be used to remove unwanted elements from titanium. Submerging the titanium in a solution of hydrogen and fluorine or hydrogen, nitrogen, and oxygen can cause it to shed the unwanted oxygen molecules, creating useful titanium. This process is less commonly used because it is expensive and creates hazardous waste products that are difficult to dispose of.

The use of titanium today is somewhat limited due to the difficulty and high costs of avoiding or reversing the creation of alpha case. The durability, strength, and lightweight features of refined titanium are appealing, especially for use in microchips and aeronautics. With improved methods of avoiding alpha case, other applications for pure titanium may be discovered as well.