Opals Made of Sand
Russian scientists have come up with a way to make artificial opals from sand.
This new technology is based on being able to create very small silicon dioxide spheres with a diameter varying from tens of nanometer to several thousands of nanometers. Silicon dioxide, of course, is an ordinary material – sand. Sand is generally used to make bricks, glass and some semiconductors.
These items have well arranged atoms of silicon and oxygen in their structure. The new materials are based on amorphous silicon dioxide, where atoms are in “disorder” rather than orderly. But little silicon spheres have equal diameter and are densely packed in a periodic face-centered cubic lattice, like separate atoms in a crystal.
Scientists had to develop a special technique, to allow the production of what they call “bricks”, or spheres made of amorphous silicon dioxide and having set diameter. Chemists then applied a well-known technology called sol-gel processing. During the synthesis, a solution of an organosilicon compound is poured into another solution which, under given conditions and a catalytic agent, results in a silicon dioxide sphere suspension.
But the trick here is in getting spheres of a set diameter, because separating small spheres according their size is a very difficult task. Russian chemists say they have solved this problem by sorting out synthesis conditions, so that reaction results in many identical spheres. Moreover, their diameter can vary from 10 nanometers to two thousand nanometers.
After the “bricks” are synthesized, they can then be arranged in structures of any desired shape and size, from one-layer and multilayer films to three-dimensional structures. All you need to do is allowing the spheres to sink to the bottom under gravity, and they will form the necessary densely packed structure due to self-assembly and, hey presto! You have an opal!
That is a simplified version of course but the end result is opals that can be used in laser technology as well as decorating a ladies neck or hands.
Of course opals made of sand will be somewhat cheaper than the real McCoy, but, when they are flashing and sparkling on your hand, will you really care?