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[Skywalker]

- identify data, choose equipment, plan and perform a first-hand investigation to compare the corrosion rate, in a suitable electrolyte, of a variety of metals, including named modern alloys to identify those best suited for use in marine vessels

Don't think I've seen this one answered anywhere...do you guys know what materials should be used besides iron, steel, galvanised iron, etc and what the most suitable for building ships would be?

 

[mon_mon]

well, i assume this is from Shipwrecks and Salvage? the ones you've listed sound like the best from my uneducated-in-the-ways-of-the-module brain. unless you want to use stuff like titanium or gold . Anything that doesn't react with either water or salt should work i would think.

 

[Frigid]

Originally posted by Skywalker
Before Frigid says anything about his summary - no, you didn't address this dot point completely.

mr. skywalker doesn't seem to like me... hahaha...

but yeah, you can also say magnesium or aluminium stripes of the same size. and if you ask me, we only sort of covered this prac in class by comparing the corrosion rates of nails... lazy teacher.

 

[mon_mon]

surely not. wouldn't they react with water over time?

 

[freaking_out]

Originally posted by Frigid

mr. skywalker doesn't seem to like me... hahaha...

or doesn't like u bragging on abt. your summaries.

 

[mon_mon]

oooh....i can forsee a mexican style standoff. or maybe not.

 

[Frigid]

if anyone has a better idea i'm happy to comply...

i'm not here to be arrogant and sell my summary... fuck.

 

[mon_mon]

ok ok ok. calm down. and step away from the edge! nah, its all good everyone, we all apreciate your insight frigid.

 

[Skywalker]

Originally posted by Frigid

mr. skywalker doesn't seem to like me... hahaha...

Whoops didn't mean for you to take it that way, soz. Edited out.

I just called Advice line, and they once again demonstrated their ineptness by blabbering on about how "it depends on salt concentrations".

 

[mon_mon]

i love how the advice line just quotes from the textbooks. w00t. thanks guys. thats just so helpful.

 

[Frigid]

Originally posted by Skywalker
I just called Advice line, and they once again demonstrated their ineptness by blabbering on about how "it depends on salt concentrations".

oh which reminds me!

aluminium oxide, the protective passivating layer of aluminium, actually can be corroded in acidic conditions (i think), so aluminium can corrode in low pH. similarly, iron is protected in pH >7.

 

[P.I.M.P.]

i thought it was basic solutions which AlO corrods???
correct me if im wrong

 

[Frigid]

you're right and i'm right. Al2O3 corrodes in very alk or acidic conditions.
see this page.

 

[Skywalker]

I managed to find a list of metals to be used in this prac..

Aluminium, bronze, brass, copper, magnesium, zinc, mild steel, tool steel, structural steel, stainless steel and chromium-plated steel can all be used.

So assuming you keep the pH at around 7 and everything else constant, what would corrode the least?

 

[Frigid]

skywalker, you gotta use a NaCl salt solution to simulate seawater... or you could just use plain sea-water...

salt solutions also attack the oxide layer of passivating metals, so i guess in the end you have just got to look at their oxidation potential and negate their oxide protection... i dunno... gotta do this prac properly to find out... =\

 

[Inhuman]

Originally posted by Frigid
skywalker, you gotta use a NaCl salt solution to simulate seawater... or you could just use plain sea-water...

The NaCl is to be a 3% salt solution, apparently this best mimics seawater.

If they ask about this as a prac you need to mention how impossible it is to get identical-sized pieces of metal, therefore experiment isn't very valid because variables haven't all been controlled

 

[Skywalker]

Originally posted by Frigid
skywalker, you gotta use a NaCl salt solution to simulate seawater... or you could just use plain sea-water...

Yep yep I know that...so I guess no one has a proper answer to this? I guess i'll bs and say stainless steel works the best in salt water and pH7.

 

[Frigid]

basically in ships, i think they would use mild steel and then chuck loads of cathodic protection on it... so cannot corrode anyway...

and seawater is slightly acidic (i think) bcoz of aerobic respiration and stuff like coral...