Mystery Metal

March 11, 2011

When I had some builders do some work the other year, they left me some metal. Thin sheet approx 0.3mm folded into a L shape approx 15x15x15cm. I had assumed it was zinc and something to do with the roof. Some people on the Mig Welding forum also suggested that it might be a coated metal e.g. galvanised steel.

How to test this?

Metals have various properties that can be examined easily in a workshop laboratory.

• Colour
• Specular reflection aka shininess
• Hardness
• Reaction with chemicals
• Melting point
• Flame test
• Magnetism
• Spark Test

Well the colour was easy, it was a silver colour. This rules out a few materials such as copper and brass. It could of course be silver although I doubt that my pile of metal is a load of silver sheet.

Shininess, yup, quite shiny. The material had been in a damp shed for some time so the fact it was still shiny eliminates steel and iron as that would have likely rusted over the autumn and winter. The surface texture of my metal is even not grainy as is typically seen with galvanised sheets. Also when I cut the metal the colour and shine goes all the way through there is no change in material meaning it’s not likely to be a composite.

Comparing hardness to some known metals, I can’t push a finger nail into the metal so it’s not likely to be lead. Lead typically is greyer on the surface so that’s a couple of reasons. The metal can also be easily marked using a steel fork so again it’s unlikely to be steel. In the workshop testing hardness is often done by filing the metal as this can identify the difference in mild steel vs tool steel vs hardened steel.

By this point I’d come to the conclusion that it was probably aluminium but just to eliminate zinc competely I though I’d test it against an acid. I dropped my strip into my favourite acidic cleaning product and there was no reaction at all. With a pH of about 2, I would expect something to happen. I tried it on a galvanised nail, nothing with that either so perhaps the acid is just not strong enough, I’ve nothing stronger to hand so will have to skip this test.

There’s a few other tests that I could have done.

I could look at the melting point in comparison to known samples. The flame test is a test used in laboratories, the metal is placed into a flame and the colour is noted.

It’s possible to identifiy different types of steel by looking at it’s magnetic properties and the identification of cast iron vs steel and the steel’s carbon content can be done using a spark test. See references below for more details.

Reference

Flame Test
Weld Procedures – Metal Identification
Engineering toolbox – identify stainless steel
Whats in Cillit Bang?

By Andy from Workshopshed One Comment

  Posted in: Uncategorised Materials: Aluminium, Zinc Tags: Chemicals, Materials Science, Metal