universe said:
sterose - I'm not sure who you're referring to, but good to see your messages.
Water is H2O or H-OH -> giving (H+ plus OH-) which is the basis for corrosion.
Hydrogen ions (H+) drive corrosion in water (acidic conditions).
Hydroxide ions (OH-) drive corrosion in water (alkaline conditions).
ie, acidity/alkalinity determine the corrosion direction, as explained above - eg acidic solutions, more hydrogen ions, more corrosion.
Hydrogen gas (H2) is generated by corrosion in water - because watever aggressive chemical element is driving the corrosion, its excess electrons are taken up by hydrogen ions (H+) to form hydrogen gas (H2).
Oxygen is an agressive element, so more dissolved oxygen, more corrosion - it drives the (OH-) chain reaction.
Dissolved carbon dioxide (CO2) enhances corrosion - drives the H+ reaction, it combines with H+ from water, changes to carbonic acid (pepsi/coke) - very mild acidic pH of 5.5 but can go through steel like butter - severe pitting/pin-hole corrosion under temperature and with flow - eg oil/gas well & transport pipelines are very susceptible to this.
Iron hydroxide is the corrosion product (rust) in water/aqueous solutions - its build up may eventually reduce corrosion as in old sunken ships.
Hydrochloric acid is HCl - it drives the H+ reaction side, but it also adds a lot of H+ of its own therefore also reduces the pH - anything below 5.
Chloride (Cl-) also enhances corrosion (eg from salts or acids), particularly damaging to Stainless or Aluminium, gives pitting/pin-hole corrosion.
Flux may produce acidic conditions - I don't know flux composition, but I guess because of Cl which combines with H+ of water to result in hydrochloric acid (HCl), giving fast localised corrosion - Sentinel litrature says chloride relates to flux.
I do not know if the water in this system is neutral, acidic or alkaline.
Anyway the test will tell us more . . . I hope.
"I'm not sure who you're referring to"
You wrote a message; the one before mine.
Although the 'gist' of your message seems to show understanding, you do in fact wildly
misunderstand the science.
"Water is H2O or H-OH -> giving (H+ plus OH-) which is the basis for corrosion."
This does not occur in water
on its own. H+ is present in acids. OH- is present in alkalis. Whe combined they
produce water (neutralisation) again; they do not seperate
from it. By definition, for the 'water' (i.e. water and another substance) to be corrosive, it must have an element that creates the H+ or OH-. Think of it like a magnet. In the prescence of the magnet, the H+ and OH- ions seperate, when the magnet is removed, the ions join again. Chlorine is a good 'magnet', it is very electronegative. Without the magnet, it is, literally, water; not corrosive.
"Hydrogen ions (H+) drive corrosion in water (acidic conditions).
Hydroxide ions (OH-) drive corrosion in water (alkaline conditions)."
Correct.
"Hydrogen gas (H2) is generated by corrosion in water"
Yes, in the presence of a substance that creates acidic (or alkaline) conditions, not by the water itself.
"because watever aggressive chemical element is driving the corrosion, its excess electrons are taken up by hydrogen ions (H+) to form hydrogen gas (H2)."
No. Hydrogen exists where is can as a diatomic molecule: H2. The process from H to H2 involves no change in number of electrons. And there is no such thing as 'excess' electrons.
H+ is basically a proton. H is a proton and electron. If H+ exists, where did its electron go in the first place. H+ was 'stolen' by another molecule (i.e. Hydrogen Chloride dissolved into water: the chlorine atom attracts the H atom (creating H+), but leaves the electron behind with the water which forms OH-).
"Dissolved carbon dioxide (CO2) enhances corrosion - drives the H+ reaction, it combines with H+ from water, changes to carbonic acid (pepsi/coke) - very mild acidic pH of 5.5 but can go through steel like butter"
When CO2 dissolves in water, the H (i.e. not H+) part of the water is attracted to the CO2, and this produces H+ ions and OH- ions. It does not 'combine with H+'.
"Iron hydroxide is the corrosion product (rust) in water/aqueous solutions"
Again, I dont think it is correct. Rust is iron
oxide.
"Hydrochloric acid is HCl - it drives the H+ reaction side, but it also adds a lot of H+ of its own therefore also reduces the pH - anything below 5.
Chloride (Cl-) also enhances corrosion (eg from salts or acids)"
It does not 'add' H+. IT ACTUALLY
MAKES IT FROM THE WATER. It is the negative attraction of chlorine that attracts the H away from the water. It leaves its electron behind and therefore creates H+, and OH- respectively.
I would be very keen to carry on this debate if you wish. Seriously.