Special Materials Valves:
Titanium Alloy, F2, F5, C2, C5…
Duplex Alloy, F51,4A,5A…
Aluminum Bronze Alloy, C95800…
Inconel, 625, 825…
Monel ,400, K500, M35-1 and so on.

Titanium, zirconium, nickel, copper and more 
The chemical process industry calls titanium, zirconium, tantalum and niobium special materials. They are extremely resistant to acids and alkaline media.Also, many nickel and nickel-chrome-based alloys are classified as special materials due to their high resistance, corrosion-resistance and their suitability for use in aggressive environments in combination with reducing media such as acids.