Tag: phosphoric acid

Hastelloy: Fasteners for phosphoric and sulfuric acid process

Q: I’m using a pretty corrosive wet process to produce phosphoric acid. It involves taking phosphate rock and the addition of concentrated (93%) sulfuric acid in a series of well-stirred reactor. Any ideas on bolting that won’t corrode my bolts and fasteners?

A: Since your process is exposed to both sulfuric and phosphoric acid, I would suggest Hastelloy C276 bolts. C276 performs very well in phosphoric acid at all temperatures below boiling and concentrations to 65%. In addition, Hastelloy bolts also protect against sulfuric acid corrosion even in high temperatures and concentrations.

Tantalum bolts for hot phosphoric acid

Q: I’m running a semiconductor wet chemical etching process that utilizes 85 % phosphoric acid at around 150-160°C. I need a material that can withstand this process. Super Duplex hex bolts are not cutting it.

A: At that particular concentration and temperature high performance nickel alloys like Hastelloy C276 bolts as well as Zirconium fasteners will have a corrosion rate most likely greater than 25 mils/year (0.025″/yr).  The only metal that is commercially available in the form of fasteners and will not have any corrosion rate is Tantalum. Furthermore for semiconductor processing tantalum has an advantage of not contaminating sensitive materials because of its high level of inertness. However tantalum fasteners are not that strong so the mechanical requirements of the application need to be considered as well.