Sciencemadness Discussion Board

Oxidation of iron

Devilinajolie - 20-6-2010 at 07:17

Hi everyone , i'd like to test the resistivity of an iron wire using electricity ( the Joule heating effect ) , but the problem is that iron is oxidized very fast after 538 °c , That's why i'm thinking about an inert gas , what do you think about carbon dioxide ? is that the cheapest way to protect iron from oxidation at very high temperature ( between 900 and 1000 °c ) ? thanks a lot for you help my friends .

[Edited on 6/20/2010 by Devilinajolie]

12AX7 - 20-6-2010 at 07:45

CO2 will also oxidize iron.

Hydrogen is traditional, though long-term use may lead to embrittlement.

Incidentially, the resistivity increases so steeply with temperature that the V-I characteristics of iron in hydrogen (with some geometry, at some pressure) approximate a constant current source. These "barreters" were used in the old days to limit turn-on surge current.

Tim

Devilinajolie - 20-6-2010 at 08:19

Thanks Tim , another question , do u think i can reach 1200 °c using an iron wire and an inert gas like argon or nitrogen ?

[Edited on 6/20/2010 by Devilinajolie]

12AX7 - 20-6-2010 at 11:39

Sure. I've certainly reached 1600C in air for short periods (i.e., the damn wire melted).

Tim

Devilinajolie - 20-6-2010 at 13:00

Thanks Tim , i think i'll use nitrogen for my experiment

zed - 21-6-2010 at 20:29

I think I can guarantee, that Iron is quite inert to vacuum, right up to it's melting point.

You do have to take into consideration however, that the Iron will melt with much lower energy input, than it might with other atmospheres. Vacuum is a mighty fine insulator.

Anders Hoveland - 27-6-2010 at 14:04

In New Zealand, I saw the black sand beaches. The black sand is paramagnetic, sticking to a strong magnet to make a spiked formation. It is composed of Magnetite FeO·Fe2O3. It is interesting that all the iron things near the beach were heavily corroded to the orange rust, Fe2O3, or Fe(OH)3. The rail to the case going down to the beach was so corroded that I was able to break it in half, even though it hadf once been a thick steel pipe. In that wet, salty envirorment, it was interesting to see that the sand had not been corroded to orange rust, but all the elemental human-made iron was fast converting. Any thoughts on this?

I put the sand in bleach, in H2O2, mixed the two in the pressence of the black sand, put the sand in chlorine water, even used vinegar and dilute H2O2, but I was unable to turn the black sand to an orange colored rust.

12AX7 - 27-6-2010 at 17:15

Iron rusts because of water. Electrochemical reactions corrode the metal, and the hydrous byproduct flakes away. Fe(OH)2 is not stable so it oxidizes to Fe(OH)3 and associated types (FeOOH, etc.).

Magnetite sands are formed without water, and therefore remain in a quite excellently stable form (the spinel crystal type, well known for physical strength and chemical stability).

Tim

JohnWW - 27-6-2010 at 19:21

Quote: Originally posted by Anders Hoveland  
In New Zealand, I saw the black sand beaches. The black sand is paramagnetic, sticking to a strong magnet to make a spiked formation. It is composed of Magnetite FeO·Fe2O3. It is interesting that all the iron things near the beach were heavily corroded to the orange rust, Fe2O3, or Fe(OH)3. The rail to the case going down to the beach was so corroded that I was able to break it in half, even though it had once been a thick steel pipe. In that wet, salty environment, it was interesting to see that the sand had not been corroded to orange rust, but all the elemental human-made iron was fast converting. Any thoughts on this?

So you have been here to New Zealand? Actually, magnetite, Fe3O4, is ferromagnetic rather than paramagnetic. Haematite, Fe2O3, and limonite, FeOOH, are strongly paramagnetic.

Nearly all the New Zealand "black sand" is on the west coast of the middle North Island and north of the South Island, where it has been formed as the impervious granular residue (along with some silica and ilmenite, FeTiO3, and others) left from the prolonged weathering of the basalt ejected by now-dormant or extinct volcanos, especially Mt. Egmont in the Taranaki region, and carried by wave and wind action for quite some distances northwards and southwards to form huge coastal deposits. The deposit at Glenbrook, near Waiuku, in South Auckland, forms the ore source, after magnetic and electrostatic purification, for the steel smelting mill there, which has supplied mild steel plate and extrusions for New Zealand since 1965. Another deposit, at Waverley near Wanganui, is exported as raw ironsand. The ilmenite content of it is refined for TiO2 for use mainly as white paint and plastic pigment.

There are smaller amounts of black sand on the east coast where basalt volcanos have erupted on the coast, e.g. around Lyttelton and Otago Harbors.