Re: What makes carbon fibres so strong and light weight ?

What makes carbon fibers used in high strength composites stronger than 
the carbon in charcoal?  They're both carbon, right?  Well, yes, they are,
but to answer this question, we need to understand what gives a material
it's "strength."   


As we all know, matter is made up of atoms, and these atoms are arranged 
(in solids) into a lattice structure.  The lattice is a regular arrangement
of atoms and its shape is determined by the constitutive atoms.
Within the lattice, the atoms are held together through atomic bonds. 
These
bonds each have a strength which is dependent on many factors, but let's 
just say that they are joined together with bonds that have a
characteristic
strength.

When a material is put under stress, these atomic bonds stretch.  (This is
the theoretical basis for Young's Modulus)  If you stretch the bonds
enough, eventually they will break.  So you can see that the strength of a
material is directly related to the strength of the atomic bonds between
the individual atoms.  (Actually, this defines the theoretical maximum
strength of the material... the actual strength is much much lower due to
imperfections in the lattice)

This explains why the carbon in charcoal is 'weaker' than high strength
carbon fibers.  Carbon has many many forms, and will bond with many
different types of elements.   These microscopic details affect the
macroscopic behavior of the material and how strong it could possibly be.  

There are many other factors which influence the strength of a material,
but on the core level, this is where it all begins. 

I hope that answers your question!

Michael