# Testing a nickel band material

Jul 25, 2019

I recently purchased a “pure nickel” band for use in building a battery pack.

However, from various forum posts, I’ve learned that it’s unlikely that these strips are really made up of what they claim to be made up of, so I decided to test the product.

## By weight

When measured on a scale, the product I received was $$156\mathrm{g}$$.

The volume, as calculated from the vendor’s measurements, should be $$10\mathrm{m} \times 10\mathrm{mm} \times 0.2\mathrm{mm} = 20\mathrm{cm}^3$$.

$20\mathrm{cm}^3 \times 8.9\frac{\mathrm{g}}{\mathrm{cm}^3} = 178.16\mathrm{g}$

So clearly something is off. I either received too little product, or it was not actually made of nickel.

$20\mathrm{cm}^3 \times 7.75\frac{\mathrm{g}}{\mathrm{cm}^3} = 155\mathrm{g}$

The low end of this range ends up being exactly what my band weighs, a point of evidence towards my band being made up mostly of steel.

## Flame test

One way to find out what it’s actually made up of is to conduct a flame test.

The flame isn’t silver-white, so it’s clearly not coming from nickel. It’s orange, which indicates either iron or sodium.

### Potential contamination

Sodium is a common component or contaminant in many compounds and its spectrum tends to dominate over others[1]

At first, I didn’t realize that sodium contamination could be a problem. After careful reading though, I decided to try cleaning my strip in hydrochloric acid before applying the flame. This mimics the procedure used when placing flame test samples on a platinum wire:

Samples are usually held on a platinum wire cleaned repeatedly with hydrochloric acid[1]

After doing this, the results were very different:

This flame is much more clearly orange, and has no yellow tint to it, like it did before. The orange here clearly indicates the presence of iron.

However, when I then touched the band with my fingers and applied the flame again, I’d get an orange flame. This shows that the tiny amount of sodium contamination from my fingers has a drastic result on the color of the flame–and it’s a neat, intuitive, way of seeing why sodium was chosen for sodium-vapor lamps.

## Conclusion

Both the orange glow from the acid-cleaned band and the density of the band indicate that this product is not made of nickel.