Silica Glass from Aerogels
Figure 1: Ordered SiO2 structure
Silica glass in the other hand is made from the same elemental
tetrahedron except that there is no apparent regularity
in the construction of this network as shown below.
Figure 2: Random network of SiO2
One needs to go up to more than 1800°C in order to melt the quartz crystal and transform one structure to another. In addition
-due to the high viscosity of silica- successive melting is required before achieving
optical quality. Glass chemists overcame the difficulty by building the amorphous silica network at room temperature using liquid silicon precursors known as Silicon alkoxides. The general formula of this molecular precursors is Si (OR)4
An amorphous 3D silica network is those progressively formed by chemical reactions at room temperature. The viscosity of the solution is continuously increasing up to the point were the entire solution is
Although simple in its illustration the system is rather complex. A
number of parameters can change the reactivity scheme and ultimately
the properties of the final product.
Hopefully all these parameters, give additional degree of freedom to tailor specific properties such as pore volume, pores size, specific surface area etc.