537 posts
Re: egg yolk
While reduced iron can lead to the phenomenon of brown or yellow centres in clinker nodules as described above, I have come across another phenomenon that also causes something similar.
In some brown cores at our plant I discovered that the core material tested negative to the fairly sensitive Maggotteaux test for Fe2+. This lead me to examine polished sections (imbedded in epoxy) of these nodules under a microscope.
I found that the areas which were yellow-brown to the naked eye were physically different from the darker areas beside them in that they contained mostly closed pores, whereas the darker areas contained open pores. This lead me to believe that the colour phenomenon was related to the amount of light reflected from the clinker surface.
Closed pores would act like small reflectors, wheareas open pores would transmit the light into depths of the nodule where it would not be able to be reflected back to the observer, rather like a fibre optic cable. Thus the area of closed pores would appear lighter (brown) and the areas of open pores would appear dark.
The Maggotteaux test seemed to confirm this hypothesis on almost every nodule I tested.
I would suggest that to confirm whether or not the brown cores in your clinker are due to reducing conditions or this reflected light phenomenon you should perform the Maggotteaux test (reducing conditions) on the brown centers.
Regards,
Ted.
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198 posts
Re: egg yolk
Dear Mr.Ted Krapkat, Thanks for sharing your experience regarding yellow core clinker.Such healthy discussion will raise the standard of the forum.Could you please explain briefly in the forum regarding Maggotteaux Test and instrument used for the test?All forum members will be benifited from your knowledge including myself. With regards, R.M.Sahu, India
537 posts
Re: egg yolk
Hello Raj,
The Magotteaux test is a fairly simple but very sensitive test for the presence of Fe2+ in clinker, although it is qualitative rather than quantitative.
The principle reagent used is an acidic solution of 2,2'-bipyridyl in water. Traces of Fe2+ will produce a pink colouration with the reagent, the intensity of the colour is a measure of the relative amount of Fe2+ present.
In our plant we perform this test daily. I have attached below a short method if you wish to try it out;-
REAGENTS:
Solution A
Weigh 0.25 g of 2,2'-bipyridyl and transfer it to a beaker. Add 90 ml of water and 10 ml of concentrated hydrochloric acid. Stir until the reagent has dissolved and transfer it to an amber glass bottle fitted with a dropper..
Solution B
Dissolve 50 g of tri-sodium citrate in 100 ml of water and transfer it to an amber glass bottle fitted with a dropper.
APPARATUS:
A white porcelain tile, perferably with small circular depressions.
Analytical balance to weigh the reagents.
Timer.
METHOD:
- Place approx. 5 to 10mg of powdered sample into a depression on the tile.
- Add 2 drops of solution A.
- If there is no pink colour after 2 minutes, add 2 drops of solution B.
- Allow to stand for a further 5 minutes. If a pink colour is now apparent then Fe2+ is present, but just above the sensitivity of the test.
- Record the result according to Table 1 below;-
Table 1: Test Results Key
Negative | Produces no discernable pink colour even after the addition of Reagent B |
Very Slightly Positive | Produces no discernable pink colour with Reagent A alone and a light pink colour after the addition of Reagent B |
Slightly Positive | Produces a light pink colour with Reagent A alone |
Positive | Produce a pink colour with Reagent A |
Strongly Positive | Produces a strong pink colour with Reagent A alone. |
Correctly burned clinker should be nagative or very slightly positive.
The sensitivity of 2-2'-bipyridyl to Fe2+ is 1:107
If you wish any further information please let me know,
Best regards,
Ted.
198 posts