All metals form an oxide at their surface after being exposed to air, water or other oxidizing systems. Rust on steel is an oxide (Ferric Oxide), and the green patina on Copper is an oxide (Cuprous Oxide). Even Stainless Steel forms an oxide coating and this allows it to stay intact when exposed to sea water. Oxides can form when exposed to extreme heat as well, as when cut with a gas torch.

These oxides are temperature-sensitive. Heat enhances oxidation as does the chlorine in seawater. The oxide coatings that form serve to protect the base metal from further corrosion. If the oxide coating is left intact then the base metal will be protected and will have an extended service life. If the oxide coating is disturbed, scratched or washed away (due to high fluid velocity over the metal), then the base metal will begin to corrode and can be destroyed in a very short time.

So, to our question; what is a “Reactive Alloy” and why is it of interest where metals are exposed to seawater (NaCl). Reactive alloys are metals that form oxides in a very short time, in seconds and in both air or water. They are referred to as Reactive Alloys because they “React” so quickly when exposed to oxidizing environments.

The advantage to Titanium Oxide is that it not only forms very quickly, it is also much harder than the oxides on copper, iron and steel. And when it is removed due to abrasion or scuffing or machining; it reforms almost immediately. The new oxide coating protects the base Titanium and provides a long service life in sea water.

Most people don’t realize that stainless steel will quickly disappear if exposed to high-velocity sea water. The mechanism is simple, the seawater continually washes off the surface oxide and in so doing takes a little bit of the base stainless metal as the high-velocity sea water is flowing over it. Stainless steel can wash out in a matter of days. The ends of a heat exchanger can literally ‘disappear’ if exposed to high-velocity sea water.

Titanium, with it’s harder oxide will protect the base metal because it quickly reforms in both air and water, and it is very hard. The oxide acts like a ceramic, and is ‘self-healing’. These characteristics protect Titanium base metal in seawater, acids, and other corrosive environments.