33

Let's divide the steel world into two classes: 1) rusting steel and 2) stainless steel. Rusting steel, in the presence of oxygen and moisture, will oxidize, forming hydrated iron oxides/hydroxides which have a greater volume than the original iron, and which have relatively little adhesion to the metal. They curl up and continue to expose bare metal, and so ...


21

It is usually a bulk property though you would need to know exact regulations for your country to be certain. Stainless steel is steel (i.e. iron + a little bit of carbon) alloyed with another metal (usually chromium) which makes it resistant to oxidation by atmospheric oxygen, but not to strong acids (e.g. concentrated hydrochloric acid) or strong oxidizers....


15

In general, salt (particularly NaCl) will increase the rate of corrosion (rusting). To understand why, consider metallic iron $\ce{Fe}$ which rusts (oxidises) to iron(II) oxide $\ce{Fe2O3}$ in the presence of oxygen $\ce{O2}$ and water $\ce{H2O}$. $$\ce{4Fe +3O2 +6H2O->4Fe(OH)3}$$ Corrosion (rust) is a 'redox' reaction, which means it involves ...


12

Yes it is corrosive to skin. The Safety Data Sheet identifies it as Category 1A for skin corrosion, which means: A substance that, according to animal data acquired from a scientifically validated method, produces irreversible damage to the skin after an exposure of three minutes or less, and within one hour of observation, in at least one of three animals....


11

"Stainless" is not a specific definition. The stainless steel with the least alloy is $5\% \; \ce{Cr}$ ( grade 501) according to AISI (It can't be cut with an oxygen/acetylene torch-like regular steel). API considers $\ce{Cr :Mo}$ (9:1) as stainless for oil well tubulars. SAE consider $12\% \; \ce{Cr}$ as stainless (most modern auto exhaust pipe). Stainless ...


9

Quick and simple: Steel = iron + carbon (less than 2%; also called "forgeable iron") Adding chromium (min. 12 %) makes it stainless. These chromium atoms are spread over the full volume of your block, also on the surface of it. There they create a thin layer of oxygen atoms. This layer makes the steel stainless. So when you cut your block in half, a new ...


8

Very good question and thought provoking too. It appears that the nail somehow knows or is it is able to decide which part will be a cathode and which part will be an anode! Why is that so? Why one end was not a cathode and the other end an anode, just the one shown in the cartoon taken from here Imaging metal corrosion So the fact you should keep in mind ...


7

Cast iron has considerable free carbon as graphite, but carbon steel has iron carbide in cementite, $\ce{Fe3C}$ in a ferrite ($\ce{α-F}$e) matrix, along with other phases and additives. In a corrosive environment, the ferrite and cementite form a galvanic couple, causing increased corrosion of the $\ce{α-F}$e while effectively protecting the $\ce{Fe3C}$. ...


5

In $\ce{SiO2}$ etching, there are two active fluorine-containing species, $\ce{HF}$ and $\ce{HF2-}$. The rate of etching at 25 degrees C in Angstroms per second is: $$9.66[\ce{HF2-}] + 2.50 [\ce{HF}] -0.14$$ according to A Study of the Dissolution of SiO2 in Acidic Fluoride Solutions J. Electrochem. Soc. vol. 118, pp. 1772-1775. The relavent equilibrium ...


5

The corrosion of metals like iron is essentially an electrochemical process. In corrosion, a metal is oxidised by loss of electrons to oxygen and formation of oxides. Corrosion of $\ce{Fe}$ (commonly known as rusting) occurs in presence of water and air. The chemistry of corrosion is quite complex, but it may be considered essentially as an electrochemical ...


5

Judging from the location and colour, it is most likely residue from liquid polish that was not properly rubbed/polished off. Quite a few types of liquid polish for brass turn white when they dry, and any folds and creases in the design is where they would be most likely to accumulate if the person doing the polishing is not very thorough. Depending on how ...


4

Short answer — none. Hastelloy C276 or C22 are the best alloys, also considering availability, presumably cost is no object. At that high temperature there is no readily available data. At 500 °C for a limited time experiment, other nickel alloys like 625 or 201 and even 316 SS have some limited life. But for 900 °C, I expect the Hastelloy C family was ...


4

Yes, the aluminum oxide coating is generally protective, but not always. For example, in the presence of $\ce{NaCl}$ (like in spray from ocean water), it is reported that aluminum alloys in coastal communities undergo significant corrosion. Here is a reference to quote: When salt air and salt water come into contact with aluminum they can cause both the ...


4

No. Aluminium stops corroding once a strong oxide layer is formed. Aluminium is a fairly reactive metal. The reason why it usually survives in air and water under normal conditions is because the aluminium oxide layer on the surface is very strong and normally protects the metal from further attack. Even if the layer is disrupted, it reforms quickly ...


4

Wikipedia lists many corrosive compounds. While a lot of them function as strong acids or bases, there are also these (not an exhaustive list): Strong oxidizers including concentrated hydrogen peroxide Fluorides (they say "fluoride ion", so salts as well as the acid are meant) Organic compounds that can act as alkylating agents such as methyl sulfate The ...


4

Rebar for concrete is frequently stored in heaps, and rusts. It actually develops a stronger bond if it is not too rusty, because the rebar surface is rougher and better able to adhere to the hardened cement. It's interesting to see a pile of old rebar with a fresh delivery on top - silvery, not a trace of rust - on top of a pile of rebar that looks almost ...


4

If you have a plastic bowl or container large enough to accommodate your item, fill it with water with with some salt (e.g., kitchen salt). Then you need Aluminum foil lightly wrapping your rusty piece of iron which altogether are immersed in this said solution (luke warm is enough). One important detail is that the foil is in mechanical contact to the ...


3

Zinc chemistry is overwhelmingly that of the +2 oxidation state, it does not go higher. For ZnO to reduce Pd+2, the Zn has to go up from +2 which it cannot. If you are getting reduction of Pd+2, Zn is not responsible.


3

Rusting is a redox reaction. $\ce{4 Fe + 3 O2 -> 2 Fe2O3}$ Redox reactions mean one chemical is being reduced and one is being oxidized. Reduction = electron gain, oxidation = electron loss. The reason it is called oxidation is because oxygen is so good at reducing other chemicals (it wants electrons). How do you tell what gets electrons in a compound? ...


2

Well there are also many different kinds of steels with different galvanic characteristics are well. For example, all of these metals have a higher reduction potential than copper: 1. Red Brass 2. Stainless steel 347 (active) 3. Molybdenum, Commercial pure 4. Copper-nickel 715 5. Admiralty brass 6. Stainless steel 202 (active) 7. Bronze, Phosphor 534 (B-1) 8....


2

It is an open ended question. What is meant by corrosion to begin with? Corrosive is very general term which literally meant to "gnaw into pieces" like the worms. Do you know pure supercritical water is quite a corrosive substance. It will attack many metals. Others have given you examples. Fluorine gas is corrosive. Who said that only acid and bases can ...


2

Operatively, the most corrosive substance on planet earth is likely seawater (which has a pH of 7.5 to 8.4). Ordinary pure aqueous NaCl also does a very good job on corroding Aluminum alloys, being able to attack the protective Al2O3 coating. Part of the explanation is likely due to the ability of NaCl to be an excellent electrolyte serving in a variety of ...


2

A traditional softener has a zeolite resin that "holds" positive ions. When it is charged the Na ions fill the resin. Then in service , the positive ions - Ca , Mg , etc , exchange places with the Na ions, putting Na in the water . In theory the back flush of the softener after charging, removes the Cl ions. So that in service the only Cl present would be ...


2

Your alloy should be sufficient. For one, cupronickel alloys are very corrosion resistant and is used to make many different coins across the world. occasionally yes, a nickel or dime will tarnish but this is usually from exposure to soda, salt or some other corrosive liquid, other wise they can sit in a fountain for weeks without tarnishing. AS long as the ...


2

You can setup a situation where one metal is acting as a cathode and the other metal acting as an anode. There will be a small potential difference due to their differences in Fermi Levels much like a thermocouple but the alloy will be at an electrochemical potential that is constant. This is not that different than a single metal(like a piece of iron) in ...


2

If you are trying to observe corrosion in a specific area, agar is a convenient way to prevent convection currents from obscuring what caused the corrosion and for localizing the indicator.


2

First off, read carefully: Different metals will increase the likelihood of corrosion. It doesn't say: Different metals will increase the likelihood of corrosion of gold With that in mind, it's called galvanic corrosion and occurs when contact between two (or more) dissimilar metals causes the more reactive one to corrode when it normally would not ...


2

I upvoted the question because it seems so simple, but allows so much discussion about special cases, all of which can and do happen. First, copper pipe was used for house plumbing because it is so easy to work. Then copper became too expensive, or plastic became cheaper, I'm not sure which. So copper must pass the test of non-corrodability. Now stainless ...


1

"it usually doesn't matter if the steel used in reinforced concrete gets rusty" isn't exactly accurate. It is good if the rebar used in concrete is slightly rusty, for a better bond. But loose rust results in a poor bond. And if the steel "gets" rusty (rustier), the corrosion produces ferric oxide/hydroxides which have a larger volume than the original iron, ...


1

An extremely wide variety of plant extracts have been shown to serve as corrosion inhibitors, including black tea, chamomile, orange peels, black pepper, mustard seed, neem, the list goes on an on. I have skimmed almost 100 papers so far and handfuls of review papers, and it is not clear to me that any of these "results" can be trusted. Most of these ...


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