World's Lightest Material?

UC Irvine, HRL Laboratories and the California Institute of Technology have announced that they have succeeded in making the world's lightest material, with a density of 0.9 mg/cm³.

This material is made up of a metallic lattice of interconnected hollow tubes with walls a thousand times thinner than a human hair. Because of this open lattice structure, the material is actually made up mostly of air, 99.99% air .

But what is the metal making up this new material?

We know the density of the new material, so we can calculate the mass of a 1cm cubed volume of this material:

1cm³ of the new material would have a mass of 0.9 mg = 0.0009g.

If 99.99% of the mass of this material is made up of air, then

the mass of air = 99.99/100 x 0.0009 = 8.991 x 10^-4g (0.8991 mg)

and the mass of metal in the new material = 0.0009 - 8.991 x 10^-4 = 9 x 10^-7g (9 x 10^-4 mg)

If we assume that 0.00001% of the volume of the new material is metal, then

the volume of metal = 0.00001/100 x 1cm³ = 1 x 10^-7cm³

So, the density of the pure metallic solid would be 9 x 10^-7g/10^-7cm³ = 9g/cm³

If we compare this calculated density of the metal to a list of common metals as shown below,

Pure Substance	State	Density (g/cm3) at 25oC and 1atm
gold	solid	19.3
mercury	liquid	13.6
lead	solid	11.4
silver	solid	10.5
copper tin	solid solid	9.0 7.3
zinc	solid	7.1
aluminium	solid	2.7

then we see it is possible that the new material is made up of copper.

Reference

T. A. Schaedler, A. J. Jacobsen, A. Torrents, A. E. Sorensen, J. Lian, J. R. Greer, L. Valdevit, W. B. Carter.Ultralight Metallic Microlattices. Science, 2011; 334 (6058): 962 DOI: 10.1126/science.1211649

Further Reading

Density Calculations

Suggested Study Questions

1. Using the table of densities above, calculate the mass in grams of a
   • cubic centimetre of gold
   • a cubic metre of copper
   • a cubic millimetre of silver
   • a cubic kilometre of zinc
2. Using the table of densities above, calculate the volume in cubic centimetres of
   • 1g of copper
   • 100mg of lead
   • 4500μg of aluminium
   • 2kg of silver
3. Brass is a mixture of copper and zinc. A sample of brass has a density of 8.5g/cm³
• What is the mass a cubic centimetre volume of this brass sample?
• If the sample were made up of equal masses of copper and zinc, what is the mass of copper in the sample?
4. A sample of brass was produced using 500cm³ of each of copper and zinc.
• What mass of copper is present in the brass?
• What mass of zinc is present in the alloy?
• Assuming additivity of volumes, what is the density of this brass sample?
5. Cymbals are commonly made of bronze which is a mixture of about 10% (by mass) tin and 90% (by mass) copper. For a 100g sample of bronze, calculate
• the mass of copper present in the sample
• the volume of copper this mass represents
• the mass of tin present in the sample
• the volume of tin this mass represents
• the density of the bronze sample assuming additivity of volumes
6. Typically, bronze contains copper and about 12% (by mass) tin. Calculate the density of a sample of this bronze.
7. Bronze coins often contain copper and about 5% tin. Calculate the density of the bronze used to make coins.
8. The brass used to make springs and screws is often 65% (by mass) copper and 35% (by mass) zinc. Calculate the density of the alloy in a brass screw.