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The Characterization of Thermal Decomposition Products of Ammonium Molybdate and The Kinetic Investigation of Decomposition Steps
Molybdenum oxide, formed by the thermal decomposition of ammonium heptamolybdate tetrahydrate (AHM), is usually being used as heteogeneous catalyst in various processes. Molybdenum oxide is obtained by the thermal decomposition of pure AHM or AHM mixed with support material. The non-stoichiometric structure of the formed molybdenum oxide varies with respect to the gas atmosphere used. In this study, the thermal decomposition of AHM in different heating rates and under different air and nitrogen gas flow rates was investigated using analytical techniques such as TGA, DTA and EGA.
In the thermal decomposition of AHM three well-defined steps were observed and the intermediate and final products of each decomposition step were characterized by using XRD and FTIR analysis techniques and their morphologies were determined by SEM analysis.
The characterization of the products and thermogravimetric analyses showed that AHM decomposes as
(NH4)6Mo7O24∙4H2O → (NH4)4Mo5O17 + (NH4)2Mo2O7 →
(NH4)2Mo4O13 → MoO3
in air and as
(NH4)6Mo7O24∙4H2O → (NH4)4Mo5O17 + (NH4)2Mo2O7 →
(NH4)2Mo4O13 → MoO3-x
in nitrogen gas.
The activation energy values of the thermal decomposition of AHM and it’s decomposition products were calculated from TGA diagrams by applying Ozawa method. The activation energy values were found to be 57.86, 74.66, 74.49 and 87.96 kJ∙mol-1 in air and 55.77, 69,85, 71,93 and 88.56 kJ∙mol-1 in nitrogen gas respectively for AHM, (NH4)2Mo2O7, (NH4)4Mo5O17 and (NH4)2Mo4O13.
YAZICI Ozan
Danışman : Doç. Dr. Suat YILMAZ
Anabilim Dalı : Metalurji ve Malzeme Mühendisliği
Mezuniyet Yılı : 2008
Tez Savunma Jürisi : Doç. Dr. Suat YILMAZ
Prof. Dr. Tevfik Osman ÖZKAN
Prof. Dr. İbrahim YUSUFOĞLU
Prof. Dr. Enver Oktay
Prof. Dr. Ercan AÇMA
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