Rust and Decay

Rust is the colloquial term for decayed iron, steel, and other metals. I use "rust" and "corrosion" on this blog because everybody immediately knows what that means, irregardless of how much chemistry one may know. I do want to put a formal explanation of rust because it helps people to understand why we are hopeful for our experiments.

Rusting metal is undergoing an electrochemical reaction.  This means that electrical energy is driving chemical changes to the object. While we don't need to go into too much detail about the atomic level, atoms that chemists group as metals share a couple of traits.  Metal ions are generally positive, in that they seek additional electrons when they are free or in solution.  A chemist would say that metal ions are electron deficient, so that when metal ions bond together into molecules, the group of ions don't have enough elections to form common valence bonds (which tend to be very stable).  Instead, metal molecules are held together through metallic bonds. Metallic bonds enable a few electrons to be shared by all atoms, where one election might facilitate bonds between three individual atoms, for example. But while doing this the electrons move around a lot and this movement is what enables electrical current to move through metals.

Corrosion occurs in metals upon the transfer of electrical charge.  A zap of electrical energy pumps a bunch of new electrons into the metal atoms, ionizing them, and allowing them to form new bonds with other atoms that might be in the neighborhood. During ionization, foreign atoms such as oxygen join with the metallic ions and form covalent bonds. The new substance formed through this process is more stable than the pure metallic material was before the reaction. Most metals exhibit visual changes as a result: silver corrosion appears as black tarnish, copper corrosion forms a green encrustation, and iron breaks down into reddish brown rusts.In short, metallic atoms are very unhappy when they are together by themselves.  Fe (iron) does not like being with just other Fe atoms, nor does Cu (copper) or Ti (tin).  If you pump some electrons into them or simply expose them to other atoms, they will jump at the opportunity to form stable covalent bonds, and once they have done that, it is very hard to reverse that chemical change.  

If you leave your bike out in the rain, the steel parts  will rust, and you will not be able to convince the iron to let go of it's bond with the oxygen ever again.The chemical change also means that the molecules have taken a new shape, one that is generally larger, so these molecular changes have effects that you can see with your naked eye.  Corroded objects swell and warp, discolor, and even change hardness.

There are lots and lots of videos and useful things about this on the Internet, such as these YouTube videos. Why? Because metals are essential to human existence in our environment but the metals don't like staying in the form where we find them useful.  Stopping metals from corroding has been a key human endeavour since humans started making metals in the first place!

In the next post, I will explain the decay of iron and related metals (ferrous metals) in more specific terms.

Project Team: Shubham Borole

My name is Shubham Borole. I am a graduate student at Michigan Technological University pursuing Master's degree in Chemical Engineering and I'm a research team member in MTU's Center for Environmentally Benign Functional Materials. I come from Vapi, Gujarat, India, a city evolving as a chemical & industrial hub. Growing up in such atmosphere, along with some family background, drew me towards chemical engineering studies. I completed my bachelors degree from Government Engineering College, Valsad (Gujarat, India) and worked for a year gaining experience in industry.

At Michigan Tech, I joined Dr. Gerard Caneba for research studies concerning oil spill control using surfactants. This included studies of foaming characteristics, dispersion effects in presence of crude oil and toxicity comparisons. I have just been introduced to Industrial Archaeology, specifically problems concerned with preservation of archaeological artifacts. I will apply my experience with supercritical carbon dioxide extraction at high pressures to museum and archaeology problems. This is a very exciting project since it involves applying chemical engineering to problems in art and history. Also, I get an opportunity to work and communicate with people from different educational disciplines. I hope to play my part in this project and supporting my colleagues to the fullest extent.


Connect with Shubham on LinkedIn.

Project Team: Eric Pomber

My name is Eric Pomber and I am a senior in the SocialSciences Program at Michigan Technological University.  I am originally from Detroit, Michigan, and grew up in a family in which most of my relatives worked in the auto industry. Growing up in an industrial town and seeing it's decline fed my interest in Industrial Archaeology.  I took part in the Cliff Mine Archaeological Project's 2011 Field School and worked as a Cultural Resources Intern for Isle Royale National Park in 2012. 

My first exposure to the problems of iron conservation came while working on old wooden boats.  In the past many shipyards used galvanized iron fasteners as an inexpensive alternative to bronze and this creates serious problems for people that maintain or restore those boats today (like me). The fasteners oxidize, leading to damage in the surrounding wood.  I was able to learn about traditional iron conservation techniques such as electrolysis during a course on Archaeological Sciences taught by Dr. Scarlett. I completed a project conserving iron artifacts from the Cliff Mine as a part of the course work.  That project was a great learning experience drew me into this project.  I look forward to helping develop this new technique to provide conservators a new option for iron conservation.  

Project Team: Stephanie Tankersley

My name is Stephanie Tankersley and I am a fourth year undergraduate student at Michigan Technological University. I am majoring in Materials Science and Engineering and minoring in Polymer Science and Engineering. I'm also completing a concentration in Michigan Tech's Enterprise Program. My interests are in sports and outdoor activities; eco-friendly processes; and textiles, polymers, and composite materials engineering. More about my interests and experience can be found on my LinkedIn account.

I'm new to the Supercritical Team. So far I have done research on polymers in conservation as well as readings about other supercritical treatments. I am very excited to start the process of experimentation with our various artifacts and I will be taking lots of photos and recording my findings along the way!

Project Team: Gerard Caneba

I am pleased to introduce my chief collaborator on this project!  Gerard Caneba and I had not worked together before this study, but when I read an article about the use of supercritical carbon dioxide treatments to dry waterlogged archaeological artifacts, I started looking for someone at Michigan Tech than could help me understand that process. Gerry and I spoke and something in our discussions sparked his interest.

Dr. Caneba is a chemical engineer and is the director of Michigan Tech’s Center for Environmentally Benign Functional Materials.  His expertise includes both polymer composites and precipitation polymerization.  Dr. Caneba’s main research involves the process of free-radical retrograde-precipitation polymerization (FRRPP) and the use of these polymers in oil recovery and remediation, adhesive formulation, wood preservation, copper ore processing, silicone formulation, carbon nanotube/polymer composites, and many other applications.  He has published many research articles and recently two monographs with Springer Verlag: Free-Radical Retrograde-Precipitation Polymerization (FRRPP): Novel Concept, Processes, Materials, and Energy Aspects (Caneba 2010) and Emulsion Free-Radical Retrograde-Precipitation Polymerization (Caneba and Dar 2011).

Gerry and I have assembled a small team of undergraduate and graduate students at MTU to work on this project. Over the next few posts, the students will introduce themselves and I will continue to write updates on aspects of the background for our research project.

Want to connect with Gerry? Try LinkedIn, Pivot (Community of Science)

Conservation of Ferrous Metals for Industrial Heritage and Archaeology

I am reviving this blog so that one of my research teams can report on their work.  We have been working on a project to solve a puzzle for industrial archaeologists and heritage managers, trying to add a new technique to the conservator's tool box for wrought and cast iron, steel, and other ferrous metal objects.

"Rusting" is the colloquial term for the chemical reactions that decay metal artifacts.  Rust causes big problems for archaeologists.  When excavating on a site, archaeologists become excited discovering humble artifacts, such as iron nails. While nails aren't as exciting as coins, armor, bullets, rings, buttons, bottles, and the dramatic artifacts featured on TV shows about digging for treasure, but the unassuming nails teach us a great deal about places.  Did you know that if you sort out and count the nails according to the way they were manufactured, then by comparing those counts, a researcher can estimate when a building was built? This seems to work, even if the building burned, leaving only a soil layer of ash and charcoal (and lots of nails!).

Of course, for industrial archaeologists, ferrous metals don't just include artifacts that were purchased and used in one place or another, but also includes manufacturing waste.  While digging at the West Point Foundry in Cold Spring, New York, our research teams encountered hundreds of gallons of metallurgical waste over the years.  Examples ranged from curls of iron cut while rifling cannon barrels, lathing and boring waste from giving cannon precisely smooth surfaces; blacksmithing waste from forging; ferrous tap slag from the blast furnace; discarded sprues, gates, and risers from the casting house; and tons of scrap iron left around the shops for making rods, bolts, spikes, brackets, and all manner of other hardware.  This list only includes waste products, not the hundreds of other iron and ferrous metal objects manufactured at that site-- including shells and shot; architectural iron; and machinery parts for example.  Most industrial heritage sites have this problem.

These artifacts all teach us a great deal about the past, including issues such as the technical creativity of people at work during their daily lives in the nineteenth century.  Yet they present a difficult problem for long term care and storage once the archaeological fieldwork is over.  Unlike brass, gold, and aluminum, iron does not stabilize once it has developed it's rusty patina.  The process of chemical decay continues underneath the surface rust.  Without some intervention, a bag of ferrous metal objects removed from the ground, cleaned and bagged, then put into storage in a controlled environment, continues to decay.  After a decade passes, the bag will be full of nodules of corrosion product and rusty dust instead of nails, screws, and hardware.

Conservators and museum staff have several tools available to counter iron's tendency toward chemical decay, but most of them are unsatisfactory for different reasons.  My colleagues and I proposed to develop a new technique for stabilization and conservation that will help solve these problems, and we were generously awarded a grant in support of our efforts by the National Park Service's National Center for Preservation Technology and Training.

Over the next few posts, I will introduce our research team members, discuss existing techniques of iron and ferrous metals conservation, the nature of decay, and lay out our proposed technique.  If this subject interests you, please stay tuned!