Two Phase Materials
Date: December 2004
What is meant by a two phase material?
A two phase material is one in which there are distinct parts of the
material that have different chemical or physical structure. Many metal
alloys are two phased (or even more). A cloud is a two phase material
consisting of air and water droplets.
This is a term used in Materials Science, a branch of science/engineering
that studies materials. The materials that are studied might be ceramics,
plastics, metals, carbon nanotubes, ice, concrete, and so on.
In materials science, the word "phase" usually refers to the particular
arrangement of atoms in a material. For example, the atoms in a piece of
iron can form different arrangements, depending on its temperature and
purity. A piece of iron that contains a mixture of these phases could be
called a two-phase material. A fiber reinforced piece of plastic could be
called a two-phase or two-component material, one "phase" is the fibers, and
the other "phase" is the plastic into which the fibers are embedded.
There is also something called "two phase flow." In science, the word
"phase" can also refer to solid, liquid, or gas. In industrial processes,
it is common to have both liquid and vapor flowing through a pipe, for
example, steam and water
In materials science terms, a "phase" is a homogenous bit of substance with a particular chemical formula and crystal structure.
So a new phase can be made by a change in formula, or a change in structure, or both.
Ice crystals are one phase of water, and liquid water is another. So a "Slurpee" is a two-phase fluid material.
A sugar&water solution is considered only one phase.
If you froze your sugar-water at well below 0 degrees C,
the sugar and water would separate, making pure-water crystals and a mostly-sugar solid.
That would be a two-phase solid material.
Solder is Tin and Lead. When melted it's a single-phase liquid solution,
but as solids they are insoluble in each other, so when it freezes it's microscopically a two-phase metal.
Maybe he Lead has 10% tin dissolved in it, and maybe the tin has 1% lead dissolved in it. (Or maybe not.)
But there is a sharp boundary where one formula of crystal stops and the other kind starts.
Dull, grainy looking solder joints happen when the two kinds of micro-crystals have a chance to grow visibly big before freezing is finished.
Sand and cement is a two-phase building material.
Epoxy-Fiberglass PC board is a two-phase material.
I think both solid phases, the epoxy glue and the glass fibers,
have amorphous, non-crystalline, randomized stacking of molecules.
Carbon-carbon composite in rocket nozzles is a two-phase material.
It's all carbon and all solid, but it is mostly fibers of graphite-crystal,
glued together with a smaller amount of non-crystal glassy-carbon.
Soapy water, or emulsified oil & vinegar, are two-phase liquids.
Everything you would consider a "composite material" has two or more phases in it.
Every mixture that is not a true solution has two or more phases in it.
If a bulk of it stays together long enough to be handled together in some way, then it is a "material".
Hence, "two-phase material".
Please don't ask me what wood is. I wouldn't quite figure out what to tell you.
Life can do fancy structures, funny fractal things.
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Update: June 2012