Home / Iodine Number
Iodine Number Explained
The number buyers check first: what it measures, how it is tested, and which values count as good.
What it measures
The iodine number is the amount of iodine adsorbed by one gram of activated carbon under standard conditions, expressed in mg/g. The iodine molecule is small, so the figure mainly reflects micropore volume — pores below 2 nm.
In practice it is the fastest answer to "how much will this carbon hold?". It is not directly proportional to surface area, but it correlates strongly and has become the industry's common language.
How it is measured
Testing follows ASTM D4607: an iodine solution of known concentration is contacted with ground carbon, the remaining iodine is found by titration, and the difference gives the adsorbed amount.
Grinding and drying of the sample affect the result, so figures are only comparable when obtained by the same method. We test per batch; documents are on the technical data sheets page.
What counts as good?
Roughly: below 600 mg/g is low, 800–900 mg/g is the commercial middle, and 1000 mg/g or above is high grade. Coconut shell carbons typically sit in the 1000–1100 band.
Akarbon's hazelnut shell products carry an iodine number of 1000 mg/g — the same band as imported coconut carbons. The figure holds for both the granular and powdered forms.
Is it enough on its own?
No. The iodine number only describes micropores. Large molecules — colour bodies, humic acids — are held in mesopores, and that is what methylene blue indicates: ours is >250 mg/g.
Read the three together when deciding: iodine number, methylene blue and ash. To see how the pores actually work, visit what is activated carbon.