Mechanochemistry: The Science of Crush

Investigating the science of crush may lead to greener chemistry, requiring less energy use and fewer toxic chemicals in the future.

Crushing can make familiar substances into something new. 

Crushing has also helped us to better understand matter: what it is, how it changes, and what we can do with it.

Crushing and grinding food are common techniques that have been used for thousands of years and in almost every human culture. They make grains and nuts more palatable and easier to digest, unlocking extra nutrition and different flavors.

How many tools for crushing or grinding can you find in a kitchen near you?

For centuries, apothecaries made medicines by blending together specific ratios of crushed ingredients or “simples,” including medicinal plants, minerals, and even gemstones. Breaking down the structure of simples by crushing or grinding made them more effective when swallowed or spread upon the skin of a patient.

Women as well as men ran pharmacies. Nuns were important providers of medical care, and women learned the practices of pharmacy in convents and while working in charity hospitals.

Chemists sometimes used mechanical force to initiate chemical reactions. The young Michael Faraday wrote about extracting pure silver by grinding together silver chloride powder and zinc filings in 1820.

Faraday casually referred to this as “the dry method” since it did not require a liquid solvent to induce a chemical reaction, implying this technique was well known among chemists in the first decades of the 1800s. The field was eventually named “mechanochemistry” by Wilhelm Ostwald in 1891.

Trituration: to reduce to powder by rubbing. (Lippincott’s Pocket Medical Dictionary, 1897)

Trituration was slow and tedious work that required considerable arm strength and skill.

“In many cases success depends upon the exertion of great pressure on the pestle,” Mathew Carey Lea wrote in 1893. The pestle must be “rotated with the utmost force that can be exerted.”

Beginning in the 1920s, laboratory mortars and pestles were supplemented by new kinds of milling machines.  Ball mills and vibration mills could crush materials to ever more exacting standards.

Finely ground materials enabled chemists to use new instruments that measured the physical properties of molecules. Instrument analysis made possible new products, better quality control, and intensified production.

The Beckman Vibromill used an electromagnet to vibrate a beryllium copper blade, which accelerated two or three grinding spheres made of agate or stainless steel. The device could prepare a wide range of hard and soft materials for infrared spectroscopy, x-ray diffraction, powder metallurgy, and other laboratory applications.

New ways to reduce climate change could come from tribology, the study of friction and lubrication. Mechanochemistry helps scientists discover why lubricants reduce the damage that occurs as two surfaces slide past each other.

Tools like the atomic force microscope let chemists study the action of common motor oil additives like zinc dialkyldithiophosphate (ZDDP). Understanding how the behavior of atoms leads to friction and wear may lead to motor oils that reduce energy consumption, prolong vehicle life, and lower harmful emissions.