The Thermal Decomposition of Ammonium Meta-Vanadate under Restricted Flow Conditions

Lori R Brock,Jeff W Keister,Nathan Fierro,Thomas C Devore,Michelle France

doi:10.4236/ajac.2017.81003

Lori R Brock, Jeff W Keister + Show 3 more

Open Access

https://doi.org/10.4236/ajac.2017.81003

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Abstract

The products obtained during the thermal decomposition of ammonium meta-vanadate depend on the configuration of the container, the mass of the sample, the heating rate and the composition of the carrier gas. The decomposition in an uncapped container produced (NH4)2V4O11, NH4V3O8, and V2O5 as the apparent stable products while the products in a capped container were NH4V3O8, and V2Ox where x was between 4 and 5. These differences are attributed to the different amounts of the evolved gases in the cell. EGA-FTIR clearly established that the reduced final product in the capped cell resulted from a reaction between NH3 and the V2O5 formed during the decomposition. A pre-equilibrium kinetics model where the rate of the reverse reaction depends on the partial pressure of the gaseous products in the cell could explain the different reaction intermediates. This model provides a possible explanation for the different apparent activation energies that have been reported for the thermal decomposition of other compounds where a reversible step could occur in the decomposition mechanism.

Highlights

Simple reactions are those where one solid compound decomposes to form a second solid compound plus one or more gaseous compound in one step
The dynamics observed for the thermal decomposition of ammonium metavanadate depend upon the rate of transport of the gaseous products away from the reaction zone
The different products observed for factors such as cell design, sample size and packing, and the type and flow rate of the carrier gas most likely result from this effect

Summary

Introduction

Simple reactions are those where one solid compound decomposes to form a second solid compound plus one or more gaseous compound in one step. In 1992, Maciejewski showed that the mass of the solid reactant, the surrounding atmosphere, the carrier gas flow rate, the heating rate, and chemical interactions between the gaseous and the solid products changed the apparent kinetic parameters observed for this reaction [18]. Biedunkiewicz et al [24] have presented evidence for chemical reactions between the surrounding atmosphere and the solid residue that will obviously change the products observed

Experimental

EGA-FTIR

Alternative Kinetic Analysis

Conclusions