Mechanochemistry: The Science of Crush
Crushing is an ancient technique for transforming materials that remains central to our lives today. Humans have developed ingenious ways to crush things, from simple home grindstones to complex computer-controlled milling machines.
ReadC.C. Dennis Using Mortar and Pestle at Dearborn Laboratory (ca. 1924) by Dearborn Chemical CompanyScience History Institute
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.
Yam Broken Into Small Pieces In Mortar (2019) by The Centenary projectThe Centenary Project
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?
Untitled (Kachinas in Ceremony of Grinding Meal) (1918 - 1922) by ZuniThe Museum of Fine Arts, Houston
Hint: Look for mortars and pestles, mallets, and heavy bottles. Even a simple spoon can be used to smoosh something.
Alchemist with Monkey (1600–1800) by In the Manner of David Teniers IIScience History Institute
Transforming matter was a central concern of alchemists during the 1500s and 1600s. Every alchemical laboratory had a mortar and pestle for crushing, alongside tools for grinding, heating, melting, and distilling.
Can you find the mortar and pestle among this alchemist’s tools?
Wealthier alchemists had assistants to handle the hard work of grinding materials.
For alchemists, the creation of compounds (called “mixts”) was an act of generation that they compared to human reproduction.
They described a mixt as a “descendant” that carried the qualities of its “parent” substances, which were often described as male and female.
Artists also crushed materials with mortars and pestles to produce pigments and dyes. Smalt was an inexpensive blue pigment produced by grinding cobalt glass. So the window in this oil painting might be made of actual glass.
One way to understand properties of matter and materials is to work with them, hands-on. Historians with Refashioning the Renaissance and the Making and Knowing Project understand the past by recreating recipes and chemical practices used during the Renaissance.
In this video (music and subtitles only), students crush plant roots, minerals, and the shells of beetles to produce natural dyes used in Renaissance clothing.
Early Italian Pharmacy (17th century) by Anonymous and Italian SchoolScience History Institute
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.
Plate 16: Various Chemical Apparatus and Instruments (1824) by Henry AdlardScience History Institute
As modern chemistry emerged from alchemy in the 1700s, mortars and pestles remained essential equipment in chemistry labs. Crushing was often a crucial step in preparing a substance for the reactions and experiments that were reshaping how chemists understood matter.
M. [Michael] Faraday (1851) by Thomas Herbert MaguireScience History Institute
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.
A Cornish Crushing Machine Worked by a Steam Engine from “The Playbook of Metals” (1862) by John Henry PepperScience History Institute
Crushing remained essential for preparing materials during the 1800s, but research into mechanochemistry waned. Instead, most chemists initiated chemical reactions by applying heat or dissolving materials in liquids or gases.
Techniques for precisely controlling heat and solvents contributed to new products like synthetic dyes and metal alloys, making chemistry one of the most important sciences for industry during the 1800s.
One person who remembered the techniques of mechanochemistry was Mathew Carey Lea of Philadelphia. A reclusive chemist who worked out of a private laboratory in his own home, Carey Lea made the first systematic studies of how mechanical action could produce chemical effects.
In a series of experiments between 1892 and 1894, Carey Lea tried to break down various chemical compounds using mechanical force. He found that while static pressure (squishing with a press) could break apart small fractions of various compounds, trituration (shearing with a pestle) initiated chemical reactions much more efficiently.
C.C. Dennis Using Mortar and Pestle at Dearborn Laboratory (ca. 1924) by Dearborn Chemical CompanyScience History Institute
Trituration: to reduce to powder by rubbing. (Lippincott’s Pocket Medical Dictionary, 1897)
“The word triturate may have been entirely foreign to our vocabulary a few months ago, except as used in connection with pharmaceutical manipulation, but after a while we find ourselves using the word triturate in its broader sense and possibly threatening to triturate the customer who refuses to pay his bills…”
—Dr. H. M. Whelpley, Proceedings of the Missouri State Pharmaceutical Association, 1893
McKenna mechanically operated agate mortar and pestle (1908) by Richard K. MeadeScience History Institute
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.”
Beckman Vibromill (1969) by Beckman Instruments, Inc.Science History Institute
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.
Extrusion of Saran Bubbles at Dow Chemical Company (1957) by Dow Chemical CompanyScience History Institute
In the first half of the 1900s, mechanochemistry was largely a matter of individuals and small groups working on specific problems. This began to change in the 1960s.
Chemists who led significant research groups in the Soviet Union and Eastern Europe focused teams of researchers on mineral processing, the study of friction (tribology), and the mechanochemistry of polymers. Polymers are very large molecules made up of repeating subunits, including proteins and the molecules in Saran Wrap.
In Western countries and Japan, understanding of how matter behaved under mechanical force largely came out of research into mechanical alloying, in which metals are combined through crushing rather than melting.
Japanese metallurgists began attending Soviet conferences on mechanochemistry in 1986, and the first fully international meetings of mechanochemists and mechanical alloy researchers began in 1993.
The science of crush is undergoing a renaissance today. Contemporary mechanochemists study how force could initiate reactions that currently require toxic solvents or high levels of heat. Once researchers understand how these reactions happen in laboratories, they will work with engineers and manufacturers to scale up the processes for commercial production.
James Mack and his Research TeamScience History Institute
Mechanochemistry offers ways to create organic molecules that produce less waste.
Chemist James Mack and his research team study how mechanical methods compare to older methods of making molecules in liquid solutions.
Understanding the rules that govern each method and modifying the milling machine accordingly will help scientists know where mechanochemical approaches can be used most effectively.
Deborah Crawford and Evelina Colacino with a Twin-Screw Extruder (2020)Science History Institute
Mechanochemistry also offers possibilities for manufacturing pharmaceutical molecules, continuing the long history of connections between crushing and medicine. A twin-screw extruder grinds together solid reactants, triggering a chemical reaction without liquid solvents. Scientists have used extrusion to make muscle relaxants and antibiotics.
Chemists Working with a Raman Microscope and Mechanochemical Reactor (2021) by William C. JarvisScience History Institute
Other mechanochemists are developing new tools to understand how crushing forces drive chemical reactions at the atomic scale. Combining these new instruments with computer simulations may help scientists make chemicals more efficiently.
Atomic Force Microscope at Work (2012) by Kevin Monko for Kelsh WilsonScience History Institute
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.
Written and curated by
Roger Turner, Science History Institute
Research and scientific advice by
James D. Batteas and Nathaniel Hawthorne, Texas A&M University
Robert W. Carpick, University of Pennsylvania
Special thanks to
Sophie Pitman and Paula Hohti Erichsen, Refashioning the Renaissance
Pamela H. Smith, The Making and Knowing Project
Tomislav Friščić, McGill University (Canada)
Evelina Colacino, Université de Montpellier (France)
Deborah Crawford, University of Bradford (UK)
McGill University (Canada)
Funding for this exhibit was provided by the Center for the Mechanical Control of Chemistry under NSF Grant #CHE-2023644, and Texas A&M University.
