Thermal decomposition of ammonium paratungstate tetrahydrate: New insights by a combined thermal and kinetic analysis

doi:10.1016/j.tca.2016.05.009

Thermochimica Acta

Volume 637, 10 August 2016, Pages 38-50

https://doi.org/10.1016/j.tca.2016.05.009 Get rights and content

Highlights

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Thermal decomposition of APT·4H₂O: A sequence of consecutive and competing reactions.
•
Quantification of liberated water and ammonia from mass-spectrometric data.
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Stoichiometry of the entire decomposition pathway.
•
Determination of activation energies of all thermal effects.

Abstract

The thermal decomposition of ammonium paratungstate tetrahydrate has been studied in oxidising atmosphere at four heating rates employing the analytical techniques TG, DTG, DSC, and MS. In total, three endothermic and two exothermic effects have been detected. From the combined thermal and kinetic analysis based on the MS curves of water and ammonia, the decomposition path has been characterised as a system of consecutive and competing reactions. The activation energies of the five effects for water and ammonia were discussed. On the basis of the kinetic model and the quantified MS data the stoichiometry for the whole pathway of the thermal decomposition of the title compound was construed.

Graphical abstract

Section snippets

Introduction and historic background

Ammonium paratungstate tetrahydrate, (NH₄)₁₀[H₂W₁₂O₄₂]·4H₂O, which will be referred to as APT·4H₂O, is used worldwide as the industrial feedstock for the production of several tungsten-containing products, mostly tungsten carbides, tungsten filaments and electrodes as well as various tungsten-containing heavy alloys.

Due to its extraordinarily high solubility in water and organic solvents, ammonium metatungstate (AMT), (NH₄)₆[H₂W₁₂O₄₀]·∼3H₂O, is of particular importance for fabricating numerous

Material used

Ammonium paratungstate tetrahydrate (APT·4H₂O) (Global Tungsten & Powders Corp., Towanda, USA) was characterised in detail in reference [6]. As followed from TG analysis the crystal water content amounted to 2.9 mol (see Table 2). The formula (NH₄)₁₀[H₂W₁₂O₄₂]·2.9H2O (APT·2.9H₂O) was used throughout this study. The structure of APT·4H₂O obviously “tolerates” the deficit of 1.1 mol water without any structural changes [6].

Simultaneous techniques

The thermal analysis (TA) was performed by using the highly sensitive

Data measured

For this study two data sets were generated – an original and a re-measured one which differ in recording time – using the instrument Sensys: the original measurements served as basis for the figures and tables presented below. The comparison of original vs. re-measured data are summarised in Tables S2 and S4 (chapter 5, Supplementary material). To study the effect of using a different instrument, a few measurements were performed using the STA 409C analyser (see Table S3, Supplementary

Conclusions

The thermal decomposition of ammonium paratungstate tetrahydrate was studied as 2.9-hydrate (NH₄)₁₀[H₂W₁₂O₄₂]·2.9H₂O under oxidising conditions in the temperature range 25–600 °C at the heating rates 2, 5, 9, and 15 K min⁻¹ applying the simultaneous techniques TG, DTG, DSC, and MS. The decomposition process is characterised by a sequence of three endothermic and two exothermic effects. The MS data of water and ammonia provided the experimental basis for calculating the stoichiometry of the

Acknowledgements

The authors thank Ms. C. Rautenberg for performing the thermoanalytical measurements.

References (33)

M.J.G. Fait et al.
Thermal decomposition of ammonium paratungstate tetrahydrate under non-reducing conditions: characterization by thermal analysis, X-ray diffraction and spectroscopic methods
Thermochim. Acta
(2008)
A.O. Kalpakli et al.
Thermal decomposition of ammonium paratungstate hydrate in air and inert gas atmospheres
Int. J. Refract. Met. Hard Mater.
(2013)
J. Pfeifer et al.
Microwave decomposition of solid crystalline ammonium paratungstate and ammonium metatungstate
J.Solid State Chem.
(1993)
M.S. Marashi et al.
Comparing thermal and mechanochemical decomposition of ammonium paratungstate (APT)
Int. J. Refract. Met. Hard Mater.
(2012)
M.A. Mohamed et al.
Non-isothermal kinetic and thermodynamic parameters of ammonium paratungstate decomposition—a thermoanalytic study
Thermochim. Acta
(1989)
S. Materazzi et al.
Applications of evolved gas analysis Part 2: EGA by mass spectrometry
Talanta
(2006)
J. Madarasz et al.
Comparative evolved gas analyses (TG-FTIR, TG/DTA-MS) and solid state (FTIR XRD) studies on thermal decomposition of ammonium paratungstate tetrahydrate (APT) in air
J. Anal. Appl. Pyrol.
(2004)
M.J.G. Fait et al.
Surface tungsten reduction during thermal decomposition of ammonium paratungstate tetrahydrate in oxidising atmosphere: a paradox?
Thermochim. Acta
(2016)
S. Vyazovkin et al.
ICTAC Kinetics Committee recommendations for collecting experimental thermal analysis data for kinetic computations
Thermochim. Acta
(2014)
V.B. Okhotnikov et al.
Thermal decomposition of materials with layered structures: isothermal dehydration of vermiculite single crystals in vacuum
React. Solids
(1989)

V. Koleva et al.

Kinetic analysis of the dehydration processes in some iodate hydrates

Thermochim. Acta

(1994)

M.A. Laurent

Recherches sur les tungstates

Ann. Chim. Phys

(1847)

E.F. Anthon

Über die Verbindungen der Wolframsäure mit den Alkalien

J. Prakt. Chem. (Leipzig)

(1836)

Z. Muro

X-ray study of tungsten. I. Tungsten trioxide

Bull. Aichi Gakugei Univ. Nat. Sci.

(1956)

J. Neugebauer et al.

Über die Reduktion des Ammoniumwolframates und Wolframtrioxyds mittels Ammoniak. Beitrag zur Kenntnis des Systems W–N

Z. Anorg. Allg. Chem.

(1959)

Y. Ahn

Studies on the formation and reduction of the tungsten trioxide. (I) Studies on the process of the thermal decomposition of ammonium paratungstate

Funtai oyobi Funmatsu Yakin

(1961)

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View full text

Thermal decomposition of ammonium paratungstate tetrahydrate: New insights by a combined thermal and kinetic analysis

Highlights

Abstract

Graphical abstract

Section snippets

Introduction and historic background

Material used

Simultaneous techniques

Data measured

Conclusions

Acknowledgements

Thermochim. Acta

Int. J. Refract. Met. Hard Mater.

J.Solid State Chem.

Int. J. Refract. Met. Hard Mater.

Thermochim. Acta

Talanta

J. Anal. Appl. Pyrol.

Thermochim. Acta

Thermochim. Acta

React. Solids

Thermochim. Acta

Recherches sur les tungstates

Ann. Chim. Phys

Über die Verbindungen der Wolframsäure mit den Alkalien

J. Prakt. Chem. (Leipzig)

X-ray study of tungsten. I. Tungsten trioxide

Bull. Aichi Gakugei Univ. Nat. Sci.

Über die Reduktion des Ammoniumwolframates und Wolframtrioxyds mittels Ammoniak. Beitrag zur Kenntnis des Systems W–N

Z. Anorg. Allg. Chem.

Studies on the formation and reduction of the tungsten trioxide. (I) Studies on the process of the thermal decomposition of ammonium paratungstate

Funtai oyobi Funmatsu Yakin