#msedefinitions

For the rest of this month, posts will be about the applications of sound and the study of acoustics in the field of materials science and engineering (or adjacent field), including (but not limited to) going into more detail on the speed of sound, nondestructive evaluation methods using sound, and acoustic levitation.

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A triple point ( 2 ) on a phase diagram is a point at which three phases coexist simultaneously. Triple points exist at a single temperature and pressure.

A colloid ( 2 ) ( 3 ) is a mixture of particles suspended in another substance, usually a liquid, though the definition is sometimes expanded to include gases. Colloids are also sometimes known as colloidal suspensions, to refer to the entire mixture, but they are separate from suspensions overall (though, like suspensions, they are not a distinct phase). Colloids are stable, and the particles do not settle out of the fluid. The particles in a colloid are also often defined by their size, between 1-1000nm in diameter.

The third method of heat transfer is known as radiation, or thermal radiation ( 2 ) ( 3 ) and involves the transfer of energy (heat) by the electromagnetic spectrum. Radiation is how the Earth is warmed by the sun, even with the vacuum of space between them, and how fire spreads warmth. The radiation of everyday objects is typically in the infrared region of the spectrum, but as objects get warmer they can shift their energy to emit in the visible spectrum - which is how objects get 'red hot'.

There are three different modes of heat transfer: thermal conduction ( 2 ) ( 3 ), or heat conduction, is the transfer of energy through physical contact by means of molecular motion. When molecules on one surface bump into molecules of another surface, they exchange energy, the higher energy molecule (higher temperature substance) transferring energy (heat) into the lower energy molecule.

Exsolution ( 2 ) ( 3 ) is the decomposition of a single, homogeneous solution phase into two separate and distinct phases which are not soluble. It is sometimes referred to as demixing.

A suspension ( 2 ) ( 3 ) in chemistry is a heterogeneous mixture of solid particles in a liquid, in which the solid particles are large enough that they will eventually settle out of the liquid (at which point it will no longer be classified as a suspension). Suspensions do not count as distinct phases. The particles in a suspension are often defined as needing to be larger than a specific size, usually 1 micron or 1000 nm. If liquid droplets or fine solid particles are present in a gas, the suspension is known as an aerosol.