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Study on Synthesize、characterization and Thermal Decomposition Kinetics of Ammonium Niobium Oxalate

Author: XuXiaoZuo
Tutor: JiangHeng
School: Liaoning University of Petroleum \u0026 Chemical Technology
Course: Analytical Chemistry
Keywords: Niobium oxalate Synthesis Thermal gravimetric analysis Thermal decomposition Dynamics
CLC: TQ251
Type: Master's thesis
Year: 2010
Downloads: 161
Quote: 1
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Abstract


Niobium oxalate as a white crystalline solid, is a soluble compound can be used as catalyst, iron oxide agents, the dielectric material additives. In recent years, the niobium oxalate as a catalyst in terms of environmental, catalytic activity, the use of cycle greater advantage of a wide range of applications. Oxalic acid, niobic acid, ammonium oxalate into a mixed solution was prepared according to a certain molar ratio, followed by filtration, crystallization, recrystallization, drying, and other processes to obtain relatively pure niobium oxalate. By elemental analysis, X-ray diffraction analysis, infrared spectroscopy and thermal gravimetric analysis characterized niobium oxalate synthesis, clear structure and composition of niobium oxalate, formula NH 4 · [NbO (C 2 O 4 ) 2 (H 2 O) 2 ] · 3H 2 O. Calcined at different temperatures by thermal gravimetric analysis and niobium oxalate product analysis, and learned that the process of thermal decomposition of niobium oxalate in three stages. The first stage (30 2 00 C) weight loss percentage of 22.68%, the niobium oxalate dehydration process, the weight loss is mainly caused by the contained water of crystallization calculated crystalline water number 5; second stage weight loss percentage of 40.96%, is the niobium oxalate thermal decomposition process, due to the decomposition of niobium oxalate in NH4 oxalate ions; (200 3 50? C) The third stage (550 < sup> 6 30? C) weight loss percentage of 4.15%, and the weightlessness of substances as carbon dioxide. The thermal decomposition of the remaining product of niobium oxalate as niobium pentoxide. As far as we know, niobium oxalate thermal decomposition kinetics study has not yet reported in the literature. In this paper, in the air thermal decomposition kinetics under different heating rates (1,2,3,5,10? C / min). Divided into three steps: (1) use of the FWO law, the KAS method, iterative method, Friedman method to calculate the the niobium oxalate three-step thermal decomposition activation energy; (2) the use of the Coats-Redfern integral equation and Achar-Bridly-Sharp Differential infer appropriate reaction mechanism. (3) The results obtained through the calculation of the pre-exponential factor. By calculation shows that, in order to ln [β / H (x)] 1 / T, and the LN [β / h (x) T2] versus 1 / T, the iteration proceeds Ea value of almost the same, so obtained by the iterative method, EA The value is more reliable. Activation energy to take the average of the four methods to get the the niobium oxalate three-step thermal decomposition activation energy were 88.97kJ · mol -1 the 134.60kJ · mol -1 206.23kJ · mol -1 . The 41 kinds mechanism functions corresponding to the G (α), and f (α) substituting into the equation: In the first step of thermal decomposition function 15 is the most likely mechanism, i.e. G (α) = [-ln (1-α) 3/4 and f (α) = (3/4) (1-α) [-LN (1-α)] 1/4, the kinetic parameters lnA was 2.55s -1 ; in the second step thermal decomposition in the function 19 is the most likely mechanism, i.e. G (α) = Ln (1-α) 3, and f (α) = (1/3) (1-α) [-ln (1 -α)] -2, kinetic parameters lnA of 2.85s -1 . The third step of the thermal decomposition is off the process of adsorption of carbon dioxide on the surface of niobium oxalate, calculated using the above two methods are not suitable kinetic model. The study provides a theoretical basis for this thesis, the data obtained for the the niobium oxalate thermal stability and thermal decomposition kinetic mechanism. Concluded of the niobium oxalate provides the basis for the application of the relevant aspects.

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