Corrosion
[: Rust is a general term
for a series of iron oxides. The term is applied to red oxides, formed by the
reaction of iron and oxygen in the presence of water or air moisture. Rust
consists of hydrated iron oxides Fe2O3·nH2O
and iron oxide-hydroxide (Fe O (OH), Fe (OH) 3). Given sufficient
time, oxygen, and water, any iron mass will eventually convert entirely to rust
and disintegrate]
Iron
(or steel) rusting is an example of corrosion, which is an electrochemical
process 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. For
iron to become iron oxide (FeO), three things are required: the iron itself, moisture and
oxygen.
Road Salt
One
of the surest signs of winter in cold-weather regions of the United States is
the build-up of salt in tire treads and on roads (and on your boots, and in
your house…). The concept of salt-lining roads is easily explained: when you
add salt to water, its freezing point dips below the normal 32 degrees
Fahrenheit, so the outdoor temperature has to dip even lower than that for ice
to form on the roads.
Although
dry salt is inert 15 – 20.oF (9 – 29.oC) is considered
the lower limit for salt to melt snow and ice but once H2O, even in the form of moist air (i.e. humidity) is added the
freezing point is lowered and the sprayed brine solution (pH 8.5) used on roads
will have an adverse effect (the formation of rust and/or corrosion) on the
vehicles paint and undercarriage.
Magnesium Chloride (MgCl2) attracts moisture from the air making it more aggressive than
salt because it is active even when “dry”. Magnesium Chloride is basically
‘liquid rust’. It clings to everything and it attracts moisture – and it does
not wash off easily”.
When
washing the vehicle ensure that all salt removed to avoid a brine solution
remaining on the paint finish. Using a durable protection (Collinite Insulator Wax) will provide a
sacrificial and renewable protection to the vehicles paint finish.
Nearly
all highway de-icers on the market are made from one, or a blend of, five
materials — calcium chloride (CaCl2) sodium chloride (NaCl) potassium chloride, magnesium chloride (MgCl2) and urea.
What makes these products
different is how quickly they work and at what temperatures. This is determined
by whether the deicer releases or absorbs heat upon contact with snow and ice.
Magnesium
Chloride and Calcium Chloride are used as deicing agents these materials are
especially destructive because of their ability to cling to the under body of a
vehicle and re-crystallize as they slowly dry out.By nature they attract and
absorb moisture from the surrounding environment, keeping them in a
semi-solution state for extended periods of time, which multiplies their corrosiveness
Exothermic
de-icers, which release heat to melt the ice, work the quickest and are
effective at a broader range of temperatures. For example, solid calcium
chloride releases heat and is effective down to –25.oF. Endothermic
deicers, which absorb the sun’s heat and use it to break ice down to liquid
brine, work more slowly and are effective at a smaller range of temperatures
For example, solid sodium chloride absorbs heat and is effective down to about
20.oF. The predominant chemical in a blended product will determine
its performance.
The
salts (salt CI and water H2O produce oxides, which cause corrosion) used for freezing point
depression in a sprayed brine solution (often mixed with grit / sand for tyre
adhesion) commonly used are;
Brake
dust or rail dust is very small, almost microscopic particles of steel, iron or
their alloys. These particles carry a positive charge (due to friction) while
the vehicles they land on are carrying a negative charge. The vehicle surface
becomes a magnet, attracting and bonding the ferrous metal particles to the
vehicle’s paint surfaces.
The corrosive
chemical compounds generated then proceed to etch (corrode) the clear coat, the
metallic particles (brake dust) penetrate and act as a conduit spreading the
corrosives through the paint film system (and the sheet metal), which results
in erosion of the paint surface, that shows on the surface as tiny rust spots
(rust blooms)
Environmental
damage to paint comes in a varied range of threats; acid rain, road salt, tree
sap, hydrazine an extremely active acid that is found in jet fuel, industrial
fallout, ultra violet radiation (UV) and other airborne contaminants are very
detrimental to a vehicles paint film surface. They are all forms of
environmental contamination and given the right catalyst; reactivity (heat)
plus moisture, they will become acidic. During this process the metal absorbs
oxygen from the water and forms iron oxide (rust).
Given the porosity of paint they permeate the
paint matrix down to body metal.
Although
present on all paint surfaces, sintered brake / rail dust is most noticeable on
light coloured paint surfaces, especially white. These contaminants are
invisible to the naked eye, once they start to oxidise, and turn orange; this
is when the problem will be brought to your attention, even on brand new
vehicles.
Stages of Corrosive Paint Damage
Stage One- Iron particulates causing
surface staining leading to substrate corrosion
Stage Two - Contaminants have
permeated the paint matrix causing discoloration and corrosion damage
Stage Three - Particulates and
corrosive compounds causing severe damage to the paints resin (binder) system
Signs of Paint Surface
Contamination
•
Dark coloured specks
•
Brown or Orange (rust) coloured stains or specks
•
Yellow stains
•
Small metal coloured flecks
•
Rough texture
•
‘Water spots’ or marks
•
Surface etching
•
Oxidation
•
Paint ‘stains
Acidic Contaminants Identification
Ferrous
Metal -
·
Light colored vehicles: Small rust orange dots with black in
center of stain.
·
Dark colored vehicles: Small white or silver dots with a
"rainbow hue" around the particle. The surface will also feel rough
to the touch.
Industrial
Fallout
·
The surface feels rough to the touch and may exhibit crystalline
deposits.
·
Usually ferrous metal is present, as well as water spots.
Acid
Rain
·
Surface will exhibit irregular discoloured spotting.
·
Dark colored vehicles will show cloudy or grey spots where the
acids have started to etch the paint.
Rust
Removal / Treatment
Careful
sand blasting is the best method for removing medium to heavy rust but you need
to be careful not to warp the sheet metal. The metal can be sanded to remove
surface rust but if it's pitted you'll need to use a metal conditioner/rust
converter to stabilize the surface before priming.
Phosphoric acid may be used as a rust
converter; by direct application to rusted iron, steel tools, or surfaces. The
phosphoric acid converts reddish-brown iron oxide (rust) to black ferric
phosphate (FePO4)
"Rust converter" is sometimes a
greenish liquid suitable for dipping (in the same sort of acid bath as is used
for pickling metal), but it is more often formulated as a gel, commonly called
naval jelly. It is sometimes sold under other names, such as "rust
remover" or "rust killer". As a thick gel, it may be applied to
sloping, vertical, or even overhead surfaces.
After treatment, the black ferric-phosphate
coating can be washed off, leaving a fresh paint surface. Multiple applications
of phosphoric acid may be required to remove all rust. The black phosphate
coating can also be left in place, where it will provide moderate further
corrosion resistance
Follow up with a rust
protection aerosol can of ValuGard Rust Inhibitor and/or some Eastwood Heavy Duty Anti-Rust. If
you use a product like Picklex 20 to stabilize the rust you want to make sure you work it into
the surface with a scuff pad then wipe it off after a minute or two.
Coat with an acid free, direct to metal primer like epoxy primer
that doesn’t’ contain any acids. If you plan on leaving the metal without
primer for any length of time the Picklex 20 will protect it from flash rusting as long as it doesn't get
wet.
Neutralizing -
Washing
the paint film surface with a slightly alkaline car wash concentrate and
thoroughly rinsing will neutralize the contaminants and remove them from the
paints surface Detailer's clay removes embedded brake dust and other
contaminants by encapsulation, thereby eliminating the primary cause
Treatment-
By
applying a suitable cleaner and then a rust inhibitor (POR-15® Products) it will arrest corrosion on contact without
leaving a sticky residue that would attract dirt, dust or grime. Corrosion
attacks metal by an electrochemical (galvanic) reaction with water as the
catalyst. It penetrates the corrosion cells, emulsifying the moisture and
separating it from the metal, leaving an ultra-thin barrier to protect from
further damage.
Since
most corrosion begins in crevices, (seams), it is important to have the
capability to penetrate these crevices in order to form a protective barrier.
Many heavier or more viscous products don't penetrate crevices, instead they
form a `bridge', and while this may isolate the crevice from further contact
with the electrolyte it does nothing to eliminate the presence of existing
moisture or surface corrosion. Injection into a seam or crevice with an aerosol
or spray eliminates this problem Por-15®
Products Marine Clean
After
the paint surface has been subjected to a chemical cleaning its protective
layer (s) have been removed and the paint surface left without protection, so
it is very important that a wax or polymer protection be applied immediately.
Rust Inhibitor Treatment
A
three-part rust inhibitor treatment by POR-15®
1. Marne Clean ™
cleans and degreases in one application without leaving residues, noxious fumes
or flammable solvents. Its water not solvent-based and it cleans without
leaving residues, no other cleaner works as fast or as well. It makes
petroleum-based cleaners almost obsolete because it can be diluted 5:1with
distilled water, thoroughly rinse with clean water after completing your
cleaning job.
2. POR-15™ Metal Ready provides the best adhesion for POR-15® on any metal surface,
including aluminium and shiny polished metal surfaces.
3. POR-15® is a
high-tech, high performance rust-preventive coating designed for application
directly on rusted or seasoned metal surfaces. It dries to an incredible
rock-hard, non-porous finish that won't chip, crack, or peel, and it prevents
rust from recurring by protecting metal from further exposure to moisture.
Rust
Prevention
A
British company Bilt-Hamber Laboratories has a new product - Dynax UC new high-performance anti-corrosion wax provides a touch-dry
firm wax film that's virtually invisible, a low film thickness see-through
protective shield. Its firm wax like film is rich in unique metal seeking
corrosion inhibitors that stop existing and prevent new corrosion. It can be applied to bare metal or painted
surfaces in fact anywhere where a discrete and powerful inhibitor is
needed.
This
product is aimed at those that want a see-through tack-free film that adds a
lot of corrosion protection but preserves the factory look of the underside or
lower panels, it’s removable too, so after winter it can be stripped if
required, or left in situ and topped up every couple of years, or more if you
wish; very easy to use.
Completely
safe to use on the vast majority of paint coatings and is ideal where dark colored
waxes or under seal would detract from the painted finish of vehicle bodywork
or underside.
The
touch dry tough wax film also provides mechanical protection to the protected
surface too. The ideal product to
provide high levels of protection during the winter months; to apply -clean any
loose dirt, rust flakes or other debris and then clean with a power-washer,
allow product to dry and then apply thin even coating
I
would like to think that these articles become an asset to anyone who is new to
detailing and to professionals alike, as well as industry experts who seek to
advance their knowledge.
I hope the
above article was informative. By having some understanding of the ‘What’ and
‘Why’ as well as the ‘How’ along with a little science to help you understand
how the chemicals we use react, you can achieve the results you desire.
I would appreciate it if you would share
this article as it helps other detailers further their knowledge.
Questions and/ or constructive comments
are always appreciated.
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