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Do all solids have a melting point? For example, is there a point when a tree, a piece of paper, or other carbon based solid becomes a liquid?
Asked by: Jamie Antoun
No in the sense that a material must maintain an identical chemical makeup and then change from one phase to another, not all solids have a melting point.
Many materials, for example paper, will begin having chemical reactions with surrounding materials as temperature increases, before a phase change, as paper will burst into flame (by combining with atmospheric oxygen) at about 450 degrees F. Even in a vacuum, many materials will begin chemical decomposition before they can change phase. I would expect a complex mixture of large organic molecules like wood to undergo various catabolic reactions as first macromolecules and then smaller molecules gained enough activation energy to break down into simpler, less energetic (i.e. lower enthalpy) constituents, long before these molecules were able to change phase.
Answered by: Rob Landolfi, Science Teacher, Washington, DC
All common solids will typically go through one of three types of transformations when heated:
There are conditions under which some materials can either be caused to sublime instead of melting, or liquefy instead of subliming. Common examples are the sublimation of ice under a vacuum during freeze drying, or the liquefaction (melting) of sulphur under high pressure.
The presence of oxygen will have a dramatic effect on the heating of organic materials. When heated in air, most plant or animal substances will partially decompose and then ignite and be converted to combustion products – mostly water and carbon dioxide. The ashes that remain are a mixture of salts and oxides that will melt at high temperatures.
Answered by: Scott Wilber, President, ComScire - Quantum World Corporation