Mechanochemistry or mechanical chemistry is the coupling of mechanical and chemical phenomena on a molecular scale and includes mechanical breakage, chemical behaviour of mechanically stressed solids (e.g., stress-corrosion cracking or enhanced oxidation), tribology, polymer degradation under shear, cavitation-related phenomena (e.g., sonochemistry and sonoluminescence), shock wave chemistry and physics, and even the burgeoning field of molecular machines. Mechanochemistry can be seen as an interface between chemistry and mechanical engineering. It is possible to synthesize chemical products by using only mechanical action. The mechanisms of mechanochemical transformations are often complex and different from usual thermal or photochemical mechanisms. The method of ball milling is a widely used process in which mechanical force is used to achieve chemical processing and transformations. The special issue of Chemical Society Review (vol. 42, 2013) is dedicated to the theme of mechanochemistry. Fundamentals and applications ranging from nano materials to technology have been reviewed.
Mechanochemistry is radically different from the traditional way of dissolving, heating and stirring chemicals in a solution. Because it eliminates the need for many solvents, mechanochemistry could help make many chemical processes used by industry more environmentally friendly. For example, the mechanochemical process has been used as an environmentally preferable way to synthesize pharmaceutically-attractive phenol hydrazones.
The term mechanochemistry is sometimes confused with mechanosynthesis, which refers specifically to the machine-controlled construction of complex molecular products.
Mechanochemical phenomena have been utilized since time immemorial, for example in making fire. The oldest method of making fire is to rub pieces of wood against each other, creating friction and hence heat, allowing the wood to undergo combustion at a high temperature. Another method involves the use of flint and steel, during which a spark (a small particle of pyrophoric metal) spontaneously combusts in air, starting fire instantaneously.