Shipwrecks - Surface Alloys (1 Viewer)

[Constip8edSkunk]

Ok, Chromium is unsuitable for protection against corrosion on ships as its passivating oxide layer will be continuously broken down by the chloride ions in the salt water. this is one of the reasons that stainless steel is also unsuitable.

But why Surface alloys produced using laser-induced surface improvements where chromium is bound in a layer on the surface of the metal is described as efficient in preventing corrosion on ships hulls by several text books?

Some of the also said that chromium by itself would be unsuitable but high concentration of nickel is required in the alloy to prevent rusting. Why? Doesn't Nickel only add strength to the steel?

My teacher has no idea, can someone help please?

 

[Darkiris]

i'm in your class...does that help?

 

[BlackJack]

The surface laser remodding of the alloy will change the lattice (actually makes it denser I believe as we 'inject' Cr atoms into the lattice), which makes each atom harder to get to in the water. The interactions between each atom will change.

Don't forget Chromium oxidises in preference to iron, even closer than Zinc on the series. (i.e. it's like Zn)

Zinc oxide is non-passivating in sea water isn't it? Coz it evens out.

About the Nickel, you'll probably have to improvise. Corrosion accelerates where there's wear & tear in the lattice structure, as the atoms are easier to get to. Hence, adding Ni strengthens the ship and slows corrosion by not allowing that to happen over the years of service (pure iron is soft, and Cr doesn't do much better right?).

 

[Constip8edSkunk]

thank you for your help.

hmmm not though of chromium as a sacrificial anode, and would this still b effective when the atoms are bound by metallurgical bonding? cuz if it does, wouldnt that effectively make its first role of preventing iron atoms from being oxidised(using this new binding) useless

and just one more thing,what does the zinc oxide even out?

thanx again