Sulfuric Acid Agitator

We are designing an agitator for a sulfuric acid process containing 75-80% sulfuric acid near the boiling point of 160-170C. We are interested in Ultramet CPT's tantalum surface but wanted to understand the corrosion resistance of tantalum how it would hold up in an agitator environment as I am concerned about erosion corrosion effects.

Hello John,

From a corrosion resistance point of view, tantalum metal will have a nil corrosion rate in sulfuric acid at 75-80% at 160-170C. The sulfuric acid corrosion curve below shows the corrosion rate of tantalum in those H2SO4 conditions.

Now the 2nd part of your question regarding the erosion corrosion of an agitator is an excellent question. Typically the affects of flow or turbulence increases the corrosion rate of most materials. The reason being, the protective oxide layer is eroded away before a fresh protective oxide layer could be generated. As a result you get what is known as erosion corrosion.

What makes tantalum different than most other materials is that the tantalum protective oxide is extremely tenacious. It is more easily formed, extremely well bonded and can instantaneously self repair (as long as O2 is present in virtually any quantity). As result the affects of erosion corrosion are minimized because tantalum metal is less susceptible to them.