The Stovebolt Site Forums The Shop Area Paint and Body Shop RUST Poll - Cast your vote!

Effectively sealing out moisture from mild steel will prevent any FURTHER rusting of the metal (metal already has slight corrosion).

TRUE or FALSE

If False, why?

False. I'm nit-picking here. Sealing out moisture won't do it but sealing out oxygen will (rust encapsulator and like products).

the answer is no, if by 'prevent further rusting' you're talking of the long term, yes in the short run - "effectively" sealing out moisture and/or air is a short term solution because most surface preperations like paint, won't hang on to rust long, and the rusting process is actually an organic growth that is somewhat self-sustaining, so the surface will lose it's seal before long, unless done using a rust converter that will convert the existing iron oxides [rust] to more stable componds that are bound to the base metal, that can then hold a surface protector like paint

Bill

Mmmm, I'm not so sure about the self contained organic growth. Isn't corrosion kinda like fire in that if you take away one of the elements/factors that make it exist, it no longer CAN exist?

Good point Mugsy...water without air will not rust

"...... once rust is formed, there is mobile oxygen in the metal, and the oxygen can move deeper into the metal causing further rust."
the result of a thing called cation exchange, which us master composters are very familiar with rusting is definitely an organic process

see this about rust - rust never sleeps, once it starts the only way to kill/stop/cause-it-to-not-exist, it is remove it, either mechanically or w/ a converter - your question was to do w/ further rusting, which will happen to a degree that will cause further expansion and damage the coating

Bill

shooper, what is water? an electrolyte composed of hydrogen and oxygen - no air? what kinda water they got in Illinois?

Bill

Technically rust is an inorganic oxidation process and it needs both moisture, oxygen, and steel of course to occur. [Organic chemistry is the study of compounds that contain mostly carbon and hydrogen. Iron oxide (rust) only contains iron and oxygen and is therefore discribed as an inorganic compound]. For a long term fix you need to either physically remove the rust and then seal the metal with primer/paint, convert the rust (after first removing all loose rust and dirt) from iron oxide to zinc phosphate (Eastwoods - Oxisolve) and then prime and paint, or you can use a rust encapsulation product (Eastwoods - Rust Encapsulator or POR-15). If you could effectively seal the metal from moisture and oxygen you could stop the rust, but the problem is that regular primer and paint needs to make a mechanical bond to the surface to make a good seal. A rusty surface is not a stable surface in which to make this mechanical bond, it would be like achoring a new deck railing into rotten wood.

exactly
and in Chemistry an organic compound is a carbon compound, including carbon steel?

Bill

Like Joker says...Just Drive It

cujo8,
I'm with you mostly except you kinda contradict yourself. At first you say rust needs moisture AND oxygen to occur on steel and then later you say "If you could effectively seal the metal from moisture and oxygen you could stop the rust".
Red58 says removing moisture is not enough, that rust only needs oxygen to occur.
So which is it? Rust needs both to occur or just one of the two?
I'm still thinking if you take one of the sides of the triangle away, corrosion doesn't occur. Fact or fiction?

mugsy, if you could totally eliminate one of the 2, you might stop further rusting, but what I'm saying is that you can't totally eliminate the oxy [ which is the critical element ] because it has become part of the rust that's there, and the oxidizing process can continue w/ very minimal moisture, which also will prolly be there unless you bake the piece before you coat it [called ambient humidity, and salty air like in your area works especially well] - the oxygen becomes part of the material - when you coat it w/ something you will supply a bit more moisture to maintain the electrolysis, and how long it will be before it pops the paint may vary, but it'll happen - that's why good shops use a metal prep like phosphoric acid, to convert any stray iron oxide in the little pits and crannies to an inert form that can't continue growing under the paint - you can inhibit rust by encapsulating it, but you won't 'prevent any further rusting'

Bill

Here is some information I got from the HowStuff Works website:
"Rust is the common name for a very common compound, iron oxide. Iron oxide, the chemical Fe2O3, is common because iron combines very readily with oxygen -- so readily, in fact, that pure iron is only rarely found in nature. Iron (or steel) rusting is an example of corrosion -- an electrochemical process involving an anode (a piece of metal that readily gives up electrons), an electrolyte (a liquid that helps electrons move) and a cathode (a piece of metal that readily accepts electrons). When a piece of metal corrodes, the electrolyte helps provide oxygen to the anode. As oxygen combines with the metal, electrons are liberated. When they flow through the electrolyte to the cathode, the metal of the anode disappears, swept away by the electrical flow or converted into metal cations in a form such as rust.

For iron to become iron oxide, three things are required: iron, water and oxygen. Here's what happens when the three get together:

When a drop of water hits an iron object, two things begin to happen almost immediately. First, the water, a good electrolyte, combines with carbon dioxide in the air to form a weak carbonic acid, an even better electrolyte. As the acid is formed and the iron dissolved, some of the water will begin to break down into its component pieces -- hydrogen and oxygen. The free oxygen and dissolved iron bond into iron oxide, in the process freeing electrons. The electrons liberated from the anode portion of the iron flow to the cathode, which may be a piece of a metal less electrically reactive than iron, or another point on the piece of iron itself.

The chemical compounds found in liquids like acid rain, seawater and the salt-loaded spray from snow-belt roads make them better electrolytes than pure water, allowing their presence to speed the process of rusting on iron and other forms of corrosion on other metals."

When you paint a rusty piece of metal you can trap some moisture and oxygen under the paint and the rusting process will continue until one of the three required elements (iron, water, oxygen)are used up and then the reaction stops. If the paint seal stays intact the rust is still there, but the rusting process has stopped. If the seal is broken (Paint Chips off)the process will begin again. Remember that to effectly protect the metal from rusting you need to seal both sides of the metal. Painting just one surface leaves the back door open to rust (Bubbled paint w/ rust underneath). Remember also that two of the required elements (water & Oxygen) are present in the air, so the rusting process can continue on our cars parked in our garages. That is why cars last so long w/o rusting in really dry climates like Arizona due to low humidity, we all know they have plenty of oxygen in AZ.

Mugsy, To answer your question:

"I'm with you mostly except you kinda contradict yourself. At first you say rust needs moisture AND oxygen to occur on steel and then later you say "If you could effectively seal the metal from moisture and oxygen you could stop the rust."

A good paint seal Will protect the surface from both water and oxygen, but if you could provide a seal that say excluded the water, but allowed oxygen the rusting process would not occur. This type of seal is called a semi-permeable membrane and it would cost you quite a bit to coat your car with one. It is simply easier and cheaper to seal your car with a compound that eliminates both water and oxygen exposure. Also remember that water can exist as a solid, liquid, and a gas. The gaseous form of water is what rusts our cars in our so called dry garages.

Bill: If I put rusty car parts in the compost, will the vegetables grown with that compost be iron fortified?

as a matter of fact putting rusty nail or a chain under a apple tree helps it produce better apples