Corrosion Protection for Lead Acid Battery Systems – a new solution for a 154-year-old problem

Writer:  Ron Knight (Chemist)

Objective:

To provide long-term corrosion protection for the external metal parts of the rechargeable lead acid battery electrical system.  The external battery case contains a number of cells, each containing electrodes of lead and lead oxide with sulfuric acid as the electrolyte.  (The internal corrosion known as a softening and shedding of lead off the plates cannot be avoided because the shedding is a natural phenomenon caused by the reaction of the electrodes with the sulfuric acid.)

Background:

The lead acid battery is the oldest but is still the most widely used rechargeable electric storage device.  The lead acid battery was invented in 1859 by Gaston Plante and remained unchanged until Camile Alphonse Faure improved it in 1881.  The next notable improvement came in the 1970’s with the introduction of the valve regulated (sealed) gel electrolyte battery.  The lead acid battery is simple, relatively inexpensive and portable but the other metallic parts of the system are subject to corrosion due to the chemical reaction of those parts with the acid, acid vapors and hydrogen that are produced during the recharging process.

System Ingredients/Materials

In addition to the lead, lead oxide, sulfuric acid and battery case that make-up the actual battery most if not all of the following are found in the recharging system:  copper, aluminum, zinc, a variety of connector plating materials and steel.

Identifying the Problem

Upon inspection of the recharge system, it is probable that the effects of corrosion will be present.  Aluminum connectors corrode to aluminum sulfate, which is a white crystalline/granule; zinc corrodes to a white powder and copper corrodes  leaving blue/white crystals.  Copper and Iron reacts to produce iron sulfate (a green or blue greenpowder) and/or a brown-yellow coating, which is ferric sulfate.  If a white powder is found on the lead positive battery terminal, it is because the terminal is a lead/zinc alloy.  The above sulfates are a result of :  over-filling the battery with either water or electrolyte (thermal expansion of the liquid will force some of the liquid out of the battery vents onto the top of the battery causing a chemical reaction with the other materials); the electrolyte can weep from the plastic-to-lead seal in the battery case; if the battery is overcharged, sulfuric acid fumes will vaporize through the vent caps and react with the other metals.

Understanding the Problem

All atoms are comprised of a nucleus and 1 (in the case of hydrogen) or more electrons orbiting the nucleus and the total number of electrons in an atom constitute the elements’ atomic number.  There are one or more “levels” of orbits and these are called valence shells and each shell has a maximum number of electrons that can occupy a given shell. The number of valence electrons of an element determines its periodic table grouping.  There are 18 groups (vertical columns) and groups 3-12 are classified as “transition metals”.  It can be stated that a transition metal is an element whose atom has an incomplete valence shell(s) in its atomic structure” and the number of electrons in an atom’s outermost valence shell governs its bonding behavior.  An atom with only one or two valence electrons in its outer-most shell is highly reactive, because the extra electrons are easily removed to form a positive ion.  Iron (atomic number 26), Copper (atomic number 29) and Zinc (atomic number 30) are all highly reactive transition metals.  Aluminum (atomic number 13) is in group 13 has 3 electrons in its outer shell is still reactive but not as reactive as the other three elements.  Pure lead is considered a stable element but the addition of zinc makes the lead battery terminal less stable.  Equilibrium is the natural state of matter.  In order to gain equilibrium elements attach (bond) with each other until the outermost valence shell is complete (i.e. a closed shell).  That is why the most active elements (such as sodium) are never found in its “pure” state.

Chemical reactions in which atoms are lost or gain are called “redox” reactions.  These reactions can be simple or complex but in all cases involve the transfer of electrons.  If electrons are lost the oxidation number increases and  it is called an oxidation process.  If electrons are gained, the oxidation number decreases and it is a reduction process.  A visual way of determining the type of reaction is by the color of the resulting material.  Red is associated with oxidizing conditions while green and white are typically associated with reducing conditions.

The reaction of sulfuric acid on metal depends on a number of factors:  the metal, the concentration of the acid and temperature.  Dilute sulfuric acid (like that found in lead-acid batteries) will react with any metal by displacing hydrogen from the acid.  The result

is H2 + the sulfate of the metal (as noted above with the various colored powders and crystals).

Metal + H2SO4  yields  H2 + Metal sulfide

The understanding of the problem is that most elements are not found in nature in the “pure” state.  Over time the elements bond with other elements and/or compounds to achieve the natural state of equilibrium.  Through a variety of manufacturing process man has taken these compounds out of equilibrium and into an unnatural pure unstable state.

As reasons and causes for corrosion were understood, it was found that there were a number of causes and forms of corrosion.  The end result is the same but the causes were much more complex than previously thought.  The forms of corrosion now include:

Forms of Corrosion

Uniform

Galvanic

Concentration Cell

Pitting

Crevice

Filiform

Intergranular

Stress

Corrosion Fatigue

Fretting

Erosion

Dealloying

Hydrogen damage

Corrosion in Concrete

Microbial

To make matters even worse, most of the time corrosion is caused by several of the above with the ultimate result being failure of the part or piece of equipment.

Historical Solutions

The discovery of iron predates 5000 BC and the oxidation of iron, commonly called rusting, has been a problem since man first used iron (even the bible mentions rust 8 times, Matthew 6:19-21 says that “rust destroys—“).  Throughout time a variety of solutions have been tried.  Iron items have been made thicker and heavier so they would last longer.  At some point someone noticed that water had an adverse effect on iron so a light oil was used to help keep moisture away from the iron.  It was found that animal fat (lard) was more effective than oil because it could be put on thicker and last longer.  In the early to mid 20th century cosmoline was applied as a rust preventive.  cosmoline is a mixture of oily and waxy long-chain non-polar hydrocarbons and proved to be an effective coating for equipment on long sea voyages during WWII.  The problem with cosmoline was that once the volatile hydrocarbons evaporated, the solid wax that was deposited was extremely difficult to remove.

In the early to mid 1950’s new improved versions of cosmoline type products were introduced as corrosion preventative compounds (CPC’s).  The generic name for the major ingredient is “slack wax”.  Slack wax is a soft, oily crude wax obtained from the pressing of petroleum paraffin distillate or wax distillate containing 2-35% oil.  Slack wax is easier to remove than cosmoline but it still is a preventative barrier helping to keep oxygen and water from the treated area.  Neither cosmoline nor slack wax products remove or drive-off moisture that is already on or in the treatment area.  They trap the moisture under the coating allowing the trapped moisture to start/continue the corrosion process.  Another concern for the slack wax type of products is that as the waxy barrier heats up, they soften and can sag because they remain in place by gravity or by the slight vacuum (similar to what holds paint on a wall) that occurs when it is applied.  Any sagging or drooping can create a gap allowing moisture and other contaminates into the protected area.

Probably the first time that corrosion prevention compounds were looked at closely was in 1987 when a flameout of an Air Force F-16 nearly resulted in a crash.  It was found that the flameout was due to corrosion in the aircraft’s fuel control valve.  The Department of Defense contracted with Battelle of Columbus, Ohio to find out exactly why the fuel control valve was malfunctioning and to provide a solution.  Battelle worked with Bell Labs and the AFRL to identify the problem.  In August 1996 Battelle submitted their final report for this contract.  Battelle’s findings were that the failure was due to fretting corrosion on the tin plated pins in the main fuel shutoff valve.  Battelle preformed extensive testing on 12 lubricants/corrosion preventative compounds and found 10 of the CPC’s failed (six of the formulations were found to actually accelerate corrosion) and two of the products passed.  One of the products that passed was Super Corr (now known as Super Corr A) and it assigned to military specification MIL-L-87177A.  Super Corr and the other product were then subjected to extensive flight tests on F-16 aircraft.  The final report on phase two testing was submitted by Battelle in March 1999.  The summary of the report was that 150 aircraft at 9 bases were involved in the study and that “gold-plated connectors without any protection can corrode rapidly and that the best lubricants/corrosion preventative compounds can totally inhibit corrosion.  It was also determined that the money spent on the lubricants/corrosion preventative compounds equates to $1000 in savings for each $1.00 spent on corrosion preventative compounds.

Changing Technology

As time passes both the understanding of the causes of corrosion and the materials/ingredients available to combat corrosion improve.  Because of environmental concerns the carrier solvent in Super Corr has been changed twice (for a total of 3 different solvents) and each time Battelle tested and re-approved Super Corr.  Each time Battelle not only tested the newest version against other corrosion preventative compounds, they tested it against previous versions of Super Corr. In the most recent testing (completed October 2010) the newest version of Super Corr A outperformed the previous version, which had outperformed the original version.

Providing the most effective CPC possible is a constantly changing process.  The current solvent was chosen from 20 different solvents. The original ingredient for extended salt spray performance has been replaced with a newer ingredient that is 2.5 times as effective against salt.  Neither the solvent(s) nor the new corrosion preventative compound was available in earlier versions of Super Corr.  Science and technology allows us to outperform even the earlier versions of Super Corr.

21st Century Solutions for Lead Acid Recharging Systems

The development of Corrosion Zero is based on the past experiences and lessons learned from the ongoing improvement of Super Corr A.  For example:  Because of need to prevent fretting corrosion in vibrating in “mobile” recharging systems and closer manufacturing tolerances (in electrical connectors), the lubricant used in Corrosion Zero is from the same family as the lubricant in Super Corr a but is 40% of the molecular size.  Because of new availability, the ingredient to protect against salt (the newer ingredient in Super Corr A) has been replaced with an ingredient that is 5 times as effective as the one in Super Corr A.  The solvent in Corrosion Zero was selected because it is also non-flammable, is a heavy hydrophobic to displace water and is a very good cleaner/degreaser.  These are the minor changes.  The most noticeable change from past CPC’s is that because we now have a much better understanding of the problems associated with the chemically active electrical charging systems components, we have included ingredients that bond with the “outer shell active electrons” thus making the core electrons more chemically inert (non-reactive).  The final addition to Corrosion Zero is a newer ingredient that has proven to be very effective against acid vapors.

Corrosion Zero is an engineered product that addresses and solves all currently known problems with lead-acid batteries and the recharging system components.

Corrosion Protection and Solutions in 2013

Combating corrosion is a dynamic and ongoing process.  Products that were best available yesterday may not be the best available tomorrow.  Realizing “one size” does not fit all, CP&S is constantly looking for new and better ingredients to improve and develop current and future products.  Microbial influenced corrosion has recently been recognized as a problem on aircraft.  Since last July, Battelle has been testing a version of Super Corr A containing a biocide that will stop or at least slow down the corrosion effects due to the presence of microbes on aircraft.  The results look very promising.  A private company has ongoing testing on a new CP&S product that is showing to be very effective on copper in a hydrogen sulfide environment.  The research has been funded to test a new CPC for aluminum in both solvent and water bases.  In the 4th quarter of 2012, CP&S started work on a line of corrosion preventive compounds that will contain nanotubes and also a line of products that will purposely vaporize with the vapors filling and protecting otherwise unreachable voids.  Samples of both of the new product lines will be available for testing in 2013.

Leave a Reply

Your email address will not be published. Required fields are marked *