Carbon Monoxide From Hot Cast Iron

[briand2]

Can anyone please suggest what temperature cast iron needs to be heated to before the free carbon in it combines with oxygen in the air to start producing carbon monoxide?

Thanks,

Brian

 

[orenda1168]

Briand2:

To begin with, carbon in cast iron, generally at or above 2%, is heterogeneously dispersed throughout the bulk of the iron and therefore not subject to oxidation from exposure to the air, with the possible exception of that minor quantity at the outer surface. Assuming the presence of sufficient heat and air (oxygen), it's reasonable to believe that surface carbon, if it oxidizes at all, will form CO2, not CO.

Orenda

Orenda

 

[briand2]

Orenda,

Thanks for the reply.

The reason for my question is that I've come across two reports (one here in the UK, on in the USA)that suggest the amount of Carbon Monoxide given off by an overheated "lump" of cast iron (in an electric storage heater with defective / bypassed high-temperature safety cut-out) was sufficient to cause ill effects to room occupants. Although I can see that this is possible in theory, I'm wondering if in practice it really could occur.

Brian

 

[tomwalz]

I would think there must have been another carbon source than just cast iron to produce enough CO2. Of course it depends on what was meant by "cast iron"

From wikipedia
Cast iron usually refers to grey cast iron, but can mean any of a group of iron-based alloys containing more than 2% carbon (alloys with less carbon are carbon steel by definition). It is made by remelting pig iron, often along with substantial quantities of scrap iron and scrap steel, and taking various steps to remove undesirable contaminants such as phosphorus and sulfur, which weaken the material. Carbon and silicon content are reduced to the desired levels, which may be anywhere from 2% to 3.5% for carbon and 1% to 3% for silicon depending on the application. Other elements are then added to the melt before the final form is produced by casting.

From Wikipedia
Industrially, iron is extracted from its ores, principally hematite (nominally Fe2O3) and magnetite (Fe3O4) by a carbothermic reaction (reduction with carbon) in a blast furnace at temperatures of about 2000°C. In a blast furnace, iron ore, carbon in the form of coke, and a flux such as limestone are fed into the top of the furnace, while a blast of heated air is forced into the furnace at the bottom.

In the furnace, the coke reacts with oxygen in the air blast to produce carbon monoxide:

6 C + 3 O2 ? 6 CO
The carbon monoxide reduces the iron ore (in the chemical equation below, hematite) to molten iron, becoming carbon dioxide in the process:

6 CO + 2 Fe2O3 ? 4 Fe + 6 CO2

Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessor.com

 

[unclesyd]

Hit with one of the those brain things. I can’t say whether the gas is CO or Water Gas (CO + H2) but I can say there is a combustible gas when you spray H20 on hot CI.
In our lab we had a small heat treating furnace where at time we used oil free cast iron shavings to provide protective atmosphere on small heat treating jobs where we did want to use the gas generator.
The procedure was to wrap a part to be heat treated in brown paper and bury it in the oil free cast iron shavings and charge it into the furnace. We immediately got a gas burning above the heat treating pot, this was the shielding gas. This flame usually lasted about 10 minutes. Upon removal of the pot from the furnace and removing the part from the shavings we got few hot spots of the cast iron oxidizing. At this point if you would spray a small amount of water on the hot CI shavings you would form a gas that would burn with a blue flame above the hot shavings. I took this to be water gas form the very small amount of residual carbon in the hot CI or possibly H2 form steam and iron reacting. This gas would be evolved and burn until the shavings lost color. The shavings are one shot deal as they offer no protection to part on a second pass.

You could do the same thing with spent pitch coke except you got a slightly bluish yellow flame which we took to be water gas also.

It would be an easy experiment to heat up some CI chunks and spray with a little water at temperature.