[DoctorBeaver (OP)]

Is there such a thing? Or any corrosive substance in solid form? If not, why not?

[eric l]

Many organic acids are crystalline solids in pure form (and at room temperature), e.g. citric acid, oxalic acid, benzoic acid...
By the way, some acids are gasses in their pure form (like hydrochloric acid or hydrofluoric acid).

[Bored chemist]

Sulphamic acid is a solid inorganic acid. There are others too. Equally, while sulphuric acid is a liquid at room temperature, it freezes to a solid at about 10 degrees C.

[DoctorBeaver (OP)]

Sulphamic acid is a solid inorganic acid. There are others too. Equally, while sulphuric acid is a liquid at room temperature, it freezes to a solid at about 10 degrees C.

I should have specified "solid at room temperature"

[lightarrow]

Sulphamic acid is a solid inorganic acid. There are others too. Equally, while sulphuric acid is a liquid at room temperature, it freezes to a solid at about 10 degrees C.

I should have specified "solid at room temperature"

Ok, but, then, you should also have specified "not in an Esquimese room"  []

[lightarrow]

Is there such a thing? Or any corrosive substance in solid form? If not, why not?

Even if solid, such a substance usually require water or other solvents to act easily.
Other such substances: AlCl₃, NaHSO₄, P₄O₁₀.

[Yucky]

so complicated they are!! -.-{"

[eric l]

The whole point of course is that these products only act as an acid (setting free H⁺-ions) when dissolved in water. 
Though liquid, concentrated sulfuric acid behaves as an oxidant and dehydrating agent before it works as an acid.

[Bored chemist]

There's nothing magical about water or protons. It's perfectly possible to have acids (and bases) without water or H+. Conc H2SO4 is indeed an oxidant and dehydrating agent but that doesn't stop it being a strong acid.

[DrDick]

Technically, pure H₂SO₄ is neutral, just as pure water is neutral.  Acidity and basicity and "strong" and "weak" are relative concepts.  In sulfuric acid, water acts as a very strong base.  In this case, sulfuric acid acts as an acid, but in the same way that water acts as an acid when introduced to a very strong base such as alkoxides.  If treated with a stronger acid, sulfuric acid can act as a base, too.

Strictly speaking, there is (almost) nothing that can be absolutely called an acid or base.  In general, when we say something is an acid or base, we're comparing it to water.

Dick

[eric l]

If you read the initial question, DoctorBeaver was looking for the corrosive properties associated with acid, and I think you'll need a more or less dilute acid for that.
I have used a mix of oxalic acid and water to remove rust (in a 1 to 1 ratio by weight).  In this way I could use both the acidity and the reducing properties together with the grinding properties of the "paste".
Using a dry acid without any water and/or a lot of friction will give you poor results.
Btw, isn't the sand in sandpaper also an acid ?

[Bored chemist]

It's true that liquids can do a better job of being corrosive than solids- not least because they can react easilly with whatever they are corroding and the used stuff can diffuse away afterwards. Also liquids can sometimes dissolve away the products of corrosion exposing a fresh surface to attack.
There's a nice introduction to acids and acidity here
http://aic.stanford.edu/sg/bpg/annual/v10/bp10-01.html
(though they cant spell Hammett)
OK I accept that "In general, when we say something is an acid or base, we're comparing it to water." and that " In sulfuric acid, water acts as a very strong base.  In this case, sulfuric acid acts as an acid, but in the same way that water acts as an acid when introduced to a very strong base such as alkoxides."
which leads me to conclude that sulphuric acid, in forcing water to behave as a strong base, is a strong acid which is exactly what I said earlier. (Of course, in sulphuric acid even sulphuric acid acts as a weak base.)
Depending on what deffinition you take, sulphuric acid can be viewed as neutral but I think that most people would accept that, as a very proficient proton donor, it's an acid.

[lightarrow]

Is there such a thing? Or any corrosive substance in solid form? If not, why not?

In this moment I can only think to salts like NaCl or CaCl₂ which are "corrosive" for solid ice (or the opposite: solid ice corrosive for those salts).

[loucasa]

If you're looking for protic acids (i.e. Bronsted acids), then acetic acid, the main ingredient in vinegar, in its pure form is called "glacial" acetic acid because its freezing point is about 15 C, which would be room temperature on a slightly chilly day. It is quite corrosive.

[DoctorBeaver (OP)]

Thinking about it, I'm sure my mum used to have a pot of boracic acid in the cupboard & I seem to remember it was a white powder.

[lightarrow]

Thinking about it, I'm sure my mum used to have a pot of boracic acid in the cupboard & I seem to remember it was a white powder.

Yes it is, it's sold in pharmacies. I use it to make green flames: H3BO3 + CH3OH --> methylborate B(CH3O)3 which burns with a green flame; this is also exploited to colour the flame in microfusion laboratories.

[Bored chemist]

"this is also exploited to colour the flame in microfusion laboratories"
What is a  microfusion laboratory?

[lightarrow]

"this is also exploited to colour the flame in microfusion laboratories"
What is a  microfusion laboratory?

I didn't know how to translate it into english. It's a small firm where they work precious metals (Au, Ag) by hands with (also) little, pointy flames for soldering. Those flames use H2 as fuel, often made from water electrolysis (with KOH)and use methyl borate for 2 purposes: make the little flame more visible and release borum oxide to remove the metal oxides formed.

[Bored chemist]

You learn something new every day, is this in making jewelry?

[lightarrow]

You learn something new every day, is this in making jewelry?

Exactly. You don't imagine how many new little firms of this kind start every day (often from indian or pakistan people).