Theory
The science is not particularly well understood. It has been known for years that silica sols (also known as colloidal silica, silicic acid, polysilicic acid) will gel when exposed to temperatures around 0°C (32°F). The theoretical mechanism is quite simple:
Colloidal silica is produced by the polymerisation of monosilicic acid, Si(OH)4, until the chains of polysilicic acid become so long they form silica particles with hydroxylated surfaces. On freezing of the sol, the silica particles are rejected away from the solidifying interface and forced into the interstices between the ice crystals. Here, they come into contact with each other, and link via the condensation of their surface hydroxyl groups into siloxane bonds. This, happening throughout the sol, forms a gel.
In a filled sol, the ceramic powder is trapped within the gel, and forms a monolith.
Read more about this topic: Freeze Casting
Famous quotes containing the word theory:
“... liberal intellectuals ... tend to have a classical theory of politics, in which the state has a monopoly of power; hoping that those in positions of authority may prove to be enlightened men, wielding power justly, they are natural, if cautious, allies of the “establishment.””
—Susan Sontag (b. 1933)
“By the “mud-sill” theory it is assumed that labor and education are incompatible; and any practical combination of them impossible. According to that theory, a blind horse upon a tread-mill, is a perfect illustration of what a laborer should be—all the better for being blind, that he could not tread out of place, or kick understandingly.... Free labor insists on universal education.”
—Abraham Lincoln (1809–1865)
“Every theory is a self-fulfilling prophecy that orders experience into the framework it provides.”
—Ruth Hubbard (b. 1924)