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Letter 9549
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There is a reference to BLACK RUST protective coating in the lower left-hand table of http://amgoz.freeservers.com/chain.htm so maybe those people can supply info. I've never heard of the term being applied to rust on steel to distinguish it from ordinary brown rust.
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Bill Reynolds |
I don't think so, Bill. I believe that chain-maker was talking about a BLACK rust-protective-coating, not a BLACK RUST protective-coating.
If you disagree, we have an even bigger problem 
because
someone is going to want to know about another color of rust listed
on that page: a GOLD PASSIVATED RUST protective-coating.
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 Ted Mooney finishing.com Brick, New Jersey |
A wild guess--They might be referring to the black "mill scale" that is an oxide on steel, when it is quite hot and exposed to air.
James Watts
- Navarre, Florida
Yes, Ted Mooney ... After reviewing the amgoz page of chain data, I agree with you. I previously interpreted the phrase "BLACK RUST" as being some trade or proprietary name for a coating, but the reference to gold rust on the same page certainly does cast doubt on such an interpretation. So still nobody knows what the original reference is to.
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Bill Reynolds |
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+ I ran across this web page in reference to "Black Rust". http://www.nacecorrosionnetwork.com/archive/9812/0257.html This page refers to converting Red Rust Fe2O3 to Black Rust Fe3O4. Bill Boatright
+ I may be wrong but from my days at school I remember iron as having a "salt" which is black in colour. Ferric chloride or something similar. Darren Marchant
+ Not to further add to the confusion but... could you be describing the actions of a rust "converter/remover"? ( Rust Converter [link is to product info at Amazon]) These products will convert/dissolve red rust and leave behind a "passive" surface. In heavily rusted areas the rusted area once converted will appear black. Richard Newman |
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The common chemical name for rust is Iron Oxide(s). It can actually be separated into different chemicals. The three most common are:
a) FeO = ferrous oxide
b) Fe2O3 = ferric oxide, hematite, and red iron oxide
c) Fe3O4 = ferrous ferric oxide, magnetite, and black iron oxide
They are widely used in the cosmetic and pharmaceutical industries as colorants. The shade ranges from a dull yellow through various oranges and reds to a deep black. Magnetite, or black iron oxide is also used to make recording media:audio and video tapes, floppy and hard disks, etc.
I'm not aware that "black rust" has any significantly different properties chemically than any of the other forms of Iron Oxides.
Bob Zonis
cosmetic pencil manufacturing - Bohemia, New York
Not much progress! Some context from the original document would be helpful. That might indicate whether we're looking for a processing byproduct or a weathering/corrosion product or a deliberately applied coating or whatever.
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Bill Reynolds |
I assume you have probably already attained the answer you were looking for, but if not here is some more information for you.
The "rust" converter concept does exist, but there is another possibility. In thermal processing of metal there is a process called blackening. This is a high temperature process used on (in my specific case) steel. The process promotes the "rusting" of the metal. The oxidizing of iron initially goes to FeO it then further oxides to Fe2O3 (your red rust). Another possibility is to hinder the formation of Fe2O3 and promote further oxidization to Fe3O4. This skips the layering effect. I mean red oxide (Fe2O3) which is then is oxided to Fe3O4 (black oxide). Instead you are attempting to have a larger % of FeO going to Fe3O4 than Fe2O3. Why is this important? Well Fe3O4 is more adherent and it has nice magnetic properties (very good for TV tubes). It also then inhibits red rust. So it is a "good" rust.
Regards,
Doreen Fulmer
- Lancaster, Pennsylvania
The context in which you have encountered the term "black rust" would be helpful, but I have also encountered the term recently as it relates to the a black, marbleized discoloration on corrugated metal roof panels that have been galvanized with zinc. It appears that the panels were stored outside for a period of time, and some water got in between the stacked corrugated sheets. The prolonged exposure to the water (so the theory goes) created the discoloration as the water could not evaporate quickly. In my case, both the terms "black rust" and "white rust" have been used to describe this condition. It is unclear whether this discoloration is merely aesthetic or whether it has impaired the rust-inhibiting properties of the zinc galvanization. A prior letter in this chain referred to "white rust" as the result of oxidized zinc. Does anyone know whether this condition impairs the zinc coating or the underlying steel?
Robert Dunn
- Farmington, Connecticut
Hi, Robert. "White rust" is the corrosion product of zinc, not the underlying steel. However, it is often associated with poor storage conditions. In use, galvanized coatings "see" carbon dioxide in the air and form a more stable corrosion product; but when stacked and stored wet, they suffer this "white rust" wet storage stain.
Regards,
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Ted Mooney finishing.com Brick, New Jersey |
The black rust could possibly be a coating, which is a form of rust. There is black rust which is good, and red/brown rust which is bad! The black rust is applied through a process of heat treatment (sort of a controlled rust)...its purpose is to reduce corrosion rate and its also a form of lubrication...its used in aviation parts as a break-in period.
San
- Norm, Oklahoma
If this is still an active enquiry, I would like to add my own experience.
My understanding of the term "Black Rust" is the corrosion products that form when iron or steel corrodes under conditions of limited oxygen availability. It is a sticky material that rapidly turns to the more conventional red/brown rust if it encounters a more oxygen rich environment.
Such black rust might be encountered on steel or cast iron under layers of aquatic growth or marine fouling, or on reinforcing steel in concrete immersed in sea-water. It may also be present on the surface of pipelines underneath disbonded but otherwise impermeable coatings. I suspect that black rust forms at the anode of macro corrosion cells in oxygen poor environments, and therefore does not encounter the cathode reaction products which under more normal conditions would allow the formation of conventional rust, Fe2O3.H20.
I am not sure of the composition of this black rust, but suspect that when it forms on steel immersed in sea-water it is a colloidal mixture of FeO (black) and FeCl2 since it sometimes has a greenish hue to it.
Since corrosion of steel to form black rust does not produce a crystalline material, it will occupy voids in concrete or other available spaces in concrete without exerting expansive pressures on the surrounding material, and therefore has the ability to dissolve substantial amounts of reinforcing steel without the concrete cracking and spalling. This can result in gross underestimation of the severity of corrosion and the weakening of RC structures.
I have heard of failures in the UK involving prestressed concrete beams due to black rust, but I do not have any more details. I would also welcome more information about black rust.
Fred Salome
- Sydney, NSW, Australia
Ed. note: All inquiries remain "active", Fred, and the discussion remains interesting for other readers even if the original inquirer has moved on. Per google, 147 people read this page each month, spending over 6 minutes on it. Your reply is a good part of that -- thanks!
Dear Sir,
Black rust is the ferric tannate formed by the reaction of tannic acid with iron. All forms of rust are converted to the ferric salt and passivated. It is also the classical ink which lasts very long.
Bye,
Ashok Surana
- Chennai, India
I live in an area where road salts are used a lot and rust is a constant problem. I have done a bit of research on rust prevention and will answer your question about BLACK RUST.
Black Rust on steel or Iron is Fe3O4. The red rust you normally see is Fe2O3. Black Rust is protective in nature as it's molecules are not as large as Red Rust. Black rust will coat the iron/steel and prevent oxygen from reaching the underlying metal. Red Rust on the other hand puffs up because of it needs more room than in it's previous unoxidized state. This expansion exposes bare metal to oxygen and causes the Red Rust to spread.
There are many products on the market that will convert Fe2O3 (red) to Fe3O4 (black). The resulting Black Rust will protect the metal and can be painted but does not offer a smooth surface. It's not too practical for auto body but for the underbody, inside wheel wells, etc it's perfect. Black Rust conversion is also perfect for marine applications, steel fences, towers, or anything else outside that has rusted and does not require a smooth finish.
David Zimmerman
- London, Ontario, Canada
Hello, perhaps I would be able to answer this question since I majored in Chemistry. First off, as was already explained, rust as you probably are familiar with it is an iron oxide. The red/brown stuff is Fe2O3, or Iron III Oxide with a +3 charge on the iron. However, being a transition metal, iron may also exist with a +2 charge. Oxygen under ordinary conditions only exists with a -2 charge. This means that you can have FeO or Fe2O3. In certain mineral structures you can also have Fe3O4 (This is also an Iron III Oxide.) FeO and Fe3O4 are usually black. Unfortunately, this is not the whole story. Sometimes, molecules of the same chemical can be arranged in different ways or in different structures. Usually one of a few of these forms will predominate, however atoms arranged in different ways will effect light in different ways. For example, you are probably familiar with diamonds and graphite. Technically, they are both made of nothing but carbon atoms. But most people would rather wear a diamond on their finger than a chunk of graphite. Actually, Fe2O3 can exist in a black state, the structure known as Black Alaskan diamond. If I am not mistaken it also plays a role in giving color to other precious gems but since these gem structures involve more than a single type of molecule I will avoid further discussion. If you want to know if you have FeO or Fe3O4, you can try to put a flame to it. FeO should become rust like you know it if it is forced to react with more Oxygen. Fe3O4 on the other hand already has given up all the electrons it can and actually there is something else going on with it that I will not explain. Suffice it to say that 2 of the irons in Fe3O4 are +3 while one is +2, but due to something called resonance the charge is distributed.
Hope this answers your question.
Daniel Villageliu
- Iowa City, Iowa
Black rust is caused by heat.
Nicholas Ross Clements
- Gainesville, Florida
I hope this will help. I found it posted online on the MadSci Network: Chemistry site hope it helps.
"When iron rusts quickly and is kept wet, the first product is usually Fe3O4, the mineral with this formula is called Magnetite. It is magnetic, colored grey to brownish-black. When finely divided it is black."
Date: ++
Posted By: Charlie Crutchfield, Retired
Ginger Botzi
- Sooke, BC, Canada
Wait....if you keep the rust in water the whole time, it will turn into black rust, and if you put it in water, then take it out, its normal rust?????????
Samuel Freedman
- Jenkintown, Pennsylvania
Hi - I am doing some R&D; but just for interest -
Circ 1700 Guns were made - then they discovered brown rust (red
rust) protected the metals - as used on guns like the brown bess
a thin coating usually polished and oiled protected the surface from
further rusting -
Circ 1900 the gun trade discovered that if you boil in water the
brown rust - you ended up with a nice black rust - known as blacking
/ blueing - hence blacking of steel -process is still used today .
Andy T
- Kent, UK
Fe3O4 is Black Magnetite
a black colored corrosion product
This came off of:
METHODS OF CONSERVING ARCHAEOLOGICAL MATERIAL FROM UNDERWATER
SITES
The primary anodic reaction of electrochemical corrosion of iron is
the production of ferrous ions. The secondary stage, the oxidation of
the ferrous ion compounds to a ferric state, is modified in anaerobic
environments. Intermediate oxidation products of ferrous hydroxide,
such as hydrated magnetite and black magnetite, are formed (Potter
1956:236-237; Evans 1963:28-29, 75):
6Fe(OH)2 + O2 >> 4 H2O +
2Fe3O4 . H2O
(green hydrated magnetite)
Fe3O4 . H2O >> H2O
+ Fe3O4
(black magnetite)
Depending on the environment, the corrosion products can take on a
variety states of division and hydration, as well as a variety of
physical forms. It is common to find corroded iron from marine sites
with an outer layer of hydrated ferric hydroxide (common rust), which
has restricted the supply of oxygen to the ferrous hydroxide briefly
formed at the surface of the metal. Laminated corrosion layers
consisting of an inner layer of black magnetite, a thin layer of
hydrated magnetite, and an outer layer of hydrated ferric hydroxide
are formed:
Fe3O4 /2 Fe3O4 .
H2O or 2 Fe2O3 . H2O
Jesse Meisterling
- East Hampton, Connecticut
Black rust forms during high temperatures in a reducing atmosphere.
Tristan pope
- Coventry, England
I am in Year 9 at School, and I Make Chainmail. We mailsmiths use
lemon juice or a similar acid to turn galvanized iron or steel
darker.
I don't know if this is any help.
Ben B
Student, Turramurra High School - Sydney, NSW, Australia
Fe3O4 is not black magnetite.
Fe3O4 . H2O is black magnetite. The
difference is marked, and the two should not be confused.
In any event, Fe3O4 occurs in low moisture
environments when iron is heated substantially. As far as I know,
black rust does not occur naturally.
Fe2O3 (the bad kind) occurs when iron hydrides
are formed during the partial oxidization of iron.
Fe2O3 flakes off and exposes more of your
metallic crystal iron/steel to be oxidized.
Fe3O4 does not.
James Saunders
- Odessa, Texas
Daniel et al.,
Sorry that I did not see this posting earlier. There is a quite
excellent article on anhydrous (5 types) and hydrated (10 types) of
iron oxide authored by Mr. Douglas Godfrey. It appears (pages 33-37)
in the February 1999 edition of
Lubrication Engineering Magazine (a.k.a. The
Journal of the Society of Tribologists and Lubrication
Engineers).
Three of the anhydrous types are black. All other types are
red-yellow-brown.
Charles Bice
- Saxonburg, Pennsylvania
In the coil coating industry, black rust is the oxide that
forms on zincalume coated steel. It is the product of wet storage
similar to white rust formed on galvanized coating. It is
aesthetically displeasing and if allowed to continue to be exposed to
moisture will eventually result in perforation of the steel substrate
(iron oxide will begin).
For more information visit galvinfo.com.
Gary Preisendorfer
- Kalama, Washington
You refer to a what seems to be a coating on metal.
there is not enough information in your request to confirm that
conclusion
perhaps the reference in the document does not mean a
coating...
black rust is a component in manufacturing thermite:
from wikipedia:thermite entry:
Black or blue iron oxide (Fe3O4), produced by
oxidizing iron in an oxygen-rich environment under high heat, is the
most commonly used thermite oxidizing agent because it is inexpensive
and easily produced.
Helios Higgins
- Lubbock, Texas
++++++
Well I am doing a project on rust and I must find out how many types of rust there is and what they are so can anyone help me?
Sarah Bruno
University of Chicago - Chicago, Illinois
Red rust is the oxidation of iron with water
Blue rust is the oxidation that occurs after you burn iron(light a
match and hold to some
Steel Wool [link is to product info at Rockler], be careful I'm
not responsible if you burn your hand off!)
Black rust occurs when you run electricity through steel wool hook a
- and a + current up to it and after it sorta burns it leaves behind
black rust
black rust is much more explosive
I don't know much about blue rust and red rust is a much better
oxidizing agent which is why its used in thermite.
Lukas Schulz
- Pville, Iowa
Sorry this is so late but I came across it as I was researching for a project. The "black rust" you mentioned may be caused by the solution that the steel came into contact with. Sulfur, sulfide, and sulfamic acid (used in construction to dissolve concrete) contain Sulfur, Hydrogen, Oxygen, and Nitrogen, all of which react with the steel to create a rust which is black in color. I am unsure of its official name, however I also know that it is common with Sulfamic acid and occurs at low pH. There are probably other instances where the "black rust" can occur, but this is the one I am familiar with.
John Reddings
- Sacramento, California
I'm 13 years old and I'm working on a science fair project. I encountered that "Black Rust" on mild steel which was immersed in Coca Cola, Gatorade and vinegar. I did some research on it. I think its some kind of residue or salts of something. And about that lest post about the sulfur, its called "mackinawite" .
Nikki C
- Abbotsford, British Columbia, Canada
I believe that the original question was referring to corrosion in
buildings (or other structures) which is detrimental to that
structure. It seems most of the replies have been hung-up on the
colour, the chemical formulae, and methods of creating same.
I agree with Fred Salome as what Fred described is exactly what I
found recently in an ocean-side block of home units
(apartments).
As well as the marine atmosphere, this particular building had floors
that were topped with "magnesite:, a fibrous topping that is
self-levelling and provides a degree of sound dampening. It is a good
product until water, from any source, reaches the topping. The
chloride salts are leached from the magnesite and seep into the
underlying concrete. At that time, the protective patina
(Fe2O3)on the steel rebars is dissolved and
corrosion begins.
This building has several sources of water ingress - leaking windows
and doors, leaking water heaters and bathroom showers.
We identified the 'black rust' by stains (aka 'blooms') on the
magnesite and then later on the concrete top surface after removing
the magnesite.
When the steel bars were exposed, we fond exactly what Fred had
described. The outer surface of the steel was dark gray to black, and
the core was a black hard jelly like substance. All quickly turned to
red rust after exposure to the air.
The bars were 12 and 16 diameter (1/2" and 3/4"). Typically the 12
diameter bars had only about a 1 mm annulus around their periphery,
while the 16 diameters bars had 1.5 - 2.0 mm annuluses. That is,
effectively no structural capacity remaining.
Keith Wilson
Structural Engineer - Sydney, Australia
Aug 12, 2008
I'm curious about the reason that black rust is the preferred rust
for thermite. Is it the extra oxygen atom? I made black rust quite by
accident when I was trying to get red. I simply put some fine steel
wool in a small amount of water and let the capillary action pull the
moisture up into the rest of the "wool". It all turned into very fine
black rust, no other chemicals were added.
John Wagner
- Bonham, Texas
Black Rust, without discussing the chemistry, has been a common phenomenon with bridge painters for at least a few centuries. The common terms in this industry is; Red Rust (surface rust red/orange in color). Black Rust- commonly called Pack Rust (Black/ grey/yellow in color and stratifying- Layers). You can find this phenomenon on older bridges in the North Eastern US. Common terminology Ferric Oxide -red surface rust and Ferrous Hydroxide black stratifying rust. Contact NACE International; www.nace.org and ask for a CIP level 3 instructor for more detailed information.
John Brown PE
- Luanda, Angola
On a current archaeological dig in Ottawa, Ontario, many of the iron items dug have had a bright blue rust just like the toolbar & browser frame on this pc computer.
Ted Stewart
- Rideau Lakes, Ontario, Canada
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October 19, 2008 Black rust isn't rust but a phosphric reaction so look that up. William Nefr
October 30, 2009 First of all this has mostly been answered correctly, "Black Rust" is not rust as most people would think, it is formed at high temperatures and is not significantly damaging to the bulk material, however it is not Fe3O4, but rather FeO. Fe3O4 is a common term denoting the what you have is not pure "black rust" but rather a combination of Fe2O3 (red rust) and FeO. Fe2O3+FeO=Fe3O4, technically inaccurate, but not all that important. What is important is knowing how much of the "black rust" is actually "red rust". Also, for the person I saw asking about thermite, FeO is better because it unstable at low (room) temperature, so it reacts better. David McDonald
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