The Effect of Heating on Humic Acid Structure and Electronic Spin Resonance Signal1
- I. M. Eltantawy2
ESR and IR spectra were recorded and weight loss measured on soil humic acid after subjecting the humic acid to heat over the temperature range 25° to 600°C. Heating to 200°C enhanced the ESR signal (g = 2.0024), indicating an increase in the free radical content. No changes were observed in the g value, suggesting that the thermally generated and the original free radicals had similar structures. IR spectra indicated that structural modifications during heating include partial dehydroxylation and/or decarboxylation, vaporization of low-boiling volatiles, oxidation, and solid state transition. The maximum weight loss was 20% after heating to 200°C.
Heating humic acid from 200 to 400°C caused great structural changes and a loss of weight of about 90%. These structural changes slightly increased the free radical content, the increase occurring within the temperature range 25 to 400°C. It was due to structural modification of the heated substance and not due to increase in the percentage of carbon in the humic acid char.
Humic acid residue was burnt off at 600°C with a 95% loss of weight.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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