Hello Steve,
There is not much data in low pH-fluoride chemistry which can be attributed to incompatibility of (commonly-used) glass reactor/beakers in a lab set-up and the safety risks associated with fluoride. Below are some of the articles which you may find interesting,
(1) Materials for Hydrofluoric Acid Service in the New Millennium - Jennings (NACE CORROSION 2021). Some of the cross-references are relevant to this topic.
(2) The Effect of Velocity on Corrosion in H2SO4 + HF Mixtures - Sridhar (NACE CORROSION 1990). I remember seeing corrosion data by Sridhar on 316L in 93% sulfuric acid + HF (probably 1% or higher) at different temperatures. You can plan to reach out to Haynes International.
(3) Corrosion Behavior of 904L in Hydrofluoric Acid - Zou (RSC Advances, 2018) - A pdf copy of this article is available online at no cost
(4) Recent progress on the corrosion behavior of metallic materials in HF solution - Dai (Corrosion Rev., 2021) - A pdf copy of this article is available online at no cost
Additional comments:
(1) What is the temperature range of your interest?
(2) Flow rate can play a big role, with or without fluoride (lots of good information on this topic in MS-1)
(3) There are some literature that suggests fluoride ion act as an inhibitor in an acidic chloride solution. However, 20ppm seems too low to provide an inhibition.
(4) Fluoride (like, chloride) can lead to localized corrosion attack to 316L in an acidic solution at an elevated temperature. I've seen rapid pitting corrosion attack (in headspace) in an acidic solution containing fluoride (no chloride) in stressed region. However, the process condition was complex and other parameters would have played a role.
Thanks
Ajit
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Ajit Mishra
Materials Engineering Consultant
Corteva Agriscience
Midland MI
7654162879
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Original Message:
Sent: 04-21-2022 05:19 PM
From: Stephen Clarke
Subject: Fluoride in Concentrated Sulfuric Acid
Hi:
I am looking for any data on the effect of low concentrations of fluoride ion in concentrated sulfuric acid (93% and up) on stainless steels. I have all the data - and first hand experience- on the effects on high silicon austenitic SS (it's bad) but I am looking for similar data on other stainless steels. Ideally I'd like data on 316L, superduplex and superaustenitic.
I'm interested in low concentrations of F- below 20 ppm.
Thanks.
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Steve Clarke
SJC Materials Engineering
Vancouver BC
604 417 9126 (M)
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