Solid Power

Solid is a state of matter in which atoms are closely packed and are difficult to move past each other. Solids resist compression, expansion, or external forces that would alter its shape, with the degree of resistance being dependent upon the specific material under consideration. Solids also always possess the least amount of kinetic energy per atom/molecule relative to other phases or, equivalently stated, solids are formed when matter in the liquid / gas phase is cooled below a certain temperature. This temperature is called the melting point of the substance and is an intrinsic property; i.e. independent of how much of the matter there is. The vast majority of substances, when in the solid state, can be arranged in one of a few ubiquitous structures. Solids are characterized by structural rigidity and resistance to applied external forces and pressure. Unlike liquids, solids do not flow to take on the shape of their container, nor do they expand to fill the entire available volume like a gas. Much like the other three fundamental phases, solids also expand when heated, the thermal energy put into increasing the distance and reducing the potential energy between atoms. However, solids do this to a much lesser extent. When heated to their melting point or sublimation point, solids melt into a liquid or sublimate directly into a gas, respectively. For solids that directly sublimate into a gas, the melting point is replaced by the sublimation point. As a rule of thumb, melting will occur if the subjected pressure is higher than the substance's triple point pressure, and sublimation will occur otherwise. Melting and melting points refer exclusively to transitions between solids and liquids. Melting occurs across a great extent of temperatures, ranging from 0.10 K for helium-3 under 30 bars (3 MPa) of pressure, to around 4,100 K at 1 atm for the composite refractory material hafnium carbonitride. The atoms in a solid are tightly bound to each other in one of two ways: regular geometric lattices called crystalline solids (e.g. metals, water ice), or irregular arrangements called amorphous solids (e.g. glass, plastic). Molecules and atoms forming crystalline lattices usually organize themselves in a few well-characterized packing structures, such as body-centered cubic. The adopted structure can and will vary between various pressures and temperatures, as can be seen in phase diagrams of the material (e.g. that of water, see left and upper). When the material is composed of a single species of atom/molecule, the phases are designated as allotropes for atoms (e.g. diamond / graphite for carbon), and as polymorphs (e.g. calcite / aragonite for calcium carbonate) for molecules. Non-porous solids invariably strongly resist any amount of compression that would otherwise result in a decrease of total volume regardless of temperature, owing to the mutual-repulsion of neighboring electron clouds among its constituent atoms. In contrast to solids, gases are