[benjster85]

I was very surprised to find out that nitric acid can be more corrosive at lower concentrations than at higher ones.

Regarding safety gloves (http://www.grainger.com/Grainger/static/chemical-resistance-guide-gloves-166.html):

"You should never assume that different concentrations will have the same effect on gloves as the test data. In fact, Nitric Acid is more corrosive at 10% than it is at 50%."

And when acting on lead (Handbook of Corrosion Data, by B. Craig and D. Anderson)
"Although nitric acid rapidly attacks lead when dilute, it has little effect at strengths of 52-70%."

Why does this happen?!?! It it true for all materials' interactions with nitric acid, or only some?

[curiouscat]

HCl and H2SO4 have similar behavior I seem to recall. Not sure.

[Schrödinger]

I don't about about the applicability of this universally to all substances. But for one instance (Cu, i believe), I remember seeing two different chemical reactions (equations) being written for the concentrated and diltue acids.

http://www.angelo.edu/faculty/kboudrea/demos/copper_HNO3/Cu_HNO3.htm

As you would expect and can see in the link above, amount of HNO₃ used per Cu is lesser in the dilute case as compared to the concentrated one. Yet, the amount of Cu(NO₃)₂ produced per Cu is the same. Basically, the product formed in the dilute acid is in the same ratio with the metal, even though you're using lesser acid-per-metal. Which means, it's more 'potent'. Atleast this was my interpretation. The by-products vary.