Solid

Solid
NASA/Marshall · Public domain · source
Name	Solid
Category	State of matter
Density	Variable
Melting point	Variable
Conductivity	Variable

Solid

A solid is a state of matter characterized by structural rigidity and resistance to shape or volume change under standard conditions. Solids appear across contexts from planetary Earth and Mars geology to engineered materials used by NASA and Siemens, and their study connects laboratories at Max Planck Society, MIT, Stanford University, CERN, and National Institute of Standards and Technology. Investigations of solids have led to landmark developments recognized by awards such as the Nobel Prize in Physics and institutions including the Royal Society.

Definition and Properties

A solid exhibits a fixed shape and near-constant volume at given temperature and pressure, distinguishing it from gases and liquids; classical descriptions by Isaac Newton and later formulations in James Clerk Maxwell's era evolved into modern treatments by Albert Einstein and Niels Bohr. Key macroscopic properties include density, hardness, elastic modulus, thermal expansion, electrical conductivity and optical transparency; these properties are central to applications by Boeing, General Electric, Toyota, Apple Inc., and Lockheed Martin. Phenomena such as anisotropy, brittleness and plasticity are quantified using standards from International Organization for Standardization and tests developed at institutions like TÜV Rheinland.

Types and Classification

Solids are classified by bonding, order, and electronic structure into categories including crystalline solids exemplified by Diamond, Quartz, Sodium chloride, and Graphite; amorphous solids such as Glass and certain polymers used by Dow Chemical; metallic solids like Iron, Copper, Aluminum alloys used by ArcelorMittal; ionic solids such as Magnesium oxide; covalent network solids including Silicon carbide; and molecular solids like Ice and Solid carbon dioxide. Electronic classification distinguishes conductors found in Gold and Silver, semiconductors exemplified by Silicon and Gallium arsenide, and insulators such as Mica. Advanced categories include superconductors discovered in compounds like YBa2Cu3O7 and topological insulators studied at Princeton University and University of Cambridge.

Structure and Bonding

Atomic and electronic arrangements in solids are governed by bonding frameworks developed in works by Linus Pauling and formalized in band theory by Felix Bloch and Sir Nevill Mott. Crystalline solids adopt lattice systems named within the Bravais lattices and common space groups cataloged at International Union of Crystallography; prototypes include the face-centered cubic lattice of Copper and the body-centered cubic lattice of Iron. Bonding types—metallic bonding in Aluminium, ionic bonding in Sodium chloride, covalent bonding in Diamond, van der Waals interactions in Graphite—determine cohesion and defect behavior. Point defects studied by Walter Schottky and dislocations described by G. I. Taylor and Egon Orowan control plastic deformation and diffusion.

Mechanical and Thermal Behavior

Mechanical response such as elasticity, plasticity, creep and fracture mechanics traces to foundational work by Augustin-Jean Fresnel and fracture theories advanced by A. A. Griffith. Stress–strain relations in engineering contexts reference standards from American Society for Testing and Materials and design codes used by American Institute of Steel Construction. Thermal properties—specific heat, thermal conductivity, and thermal expansion—are crucial in technologies from Intel microprocessors to Siemens turbines; low-temperature behavior invoking Debye theory relates to experiments at Los Alamos National Laboratory and Argonne National Laboratory.

Phase Transitions and Crystallography

Phase transitions between solid, liquid and gas were central to thermodynamic treatments by Sadi Carnot and formalized in phase diagrams used in metallurgy by William Hume-Rothery. Solid–solid transitions such as martensitic transformations underlie shape-memory alloys developed at Brown University and Oak Ridge National Laboratory. Crystallography techniques—X-ray diffraction pioneered by Max von Laue and refined by William Lawrence Bragg and William Henry Bragg—map crystal structures of minerals like Feldspar and synthetic compounds used in Semiconductors.

Applications and Examples

Solid materials enable skyscrapers by firms like Skidmore, Owings & Merrill and transportation by Boeing and Toyota, form electronic devices by Intel and Samsung, and serve medical implants developed at Mayo Clinic and Johns Hopkins Hospital. Examples span natural minerals such as Granite and Basalt, industrial ceramics like Alumina, polymers from DuPont and BASF, and composite materials used by Airbus. Research into functional solids drives photovoltaics at National Renewable Energy Laboratory, battery electrodes by Tesla, Inc. and Panasonic, and quantum materials explored at Harvard University and IBM Research.

Experimental Methods and Characterization

Characterization employs techniques including X-ray diffraction developed at Royal Institution, electron microscopy advanced at Brookhaven National Laboratory and Lawrence Berkeley National Laboratory, neutron scattering at Oak Ridge National Laboratory and Institut Laue–Langevin, and spectroscopy methods (Raman, infrared, nuclear magnetic resonance) used at Max Planck Institute for Solid State Research. Mechanical testing uses universal testing machines standardized by ASTM International, while surface analysis via scanning probe microscopy originates from Nobel-recognized work at IBM Zurich Research Laboratory. Computational methods in density functional theory trace to theoretical foundations at University of Cambridge and Cornell University.

Category:States of matter