A Comparative Study on the Thermal Decomposition of Ammonium p-Tungstate in Batch and Fluidized-Bed Reactors

Abstract

Thermal decomposition of ammonium p-tungstate (APT) to tungsten trioxide (WO3) was carried out in both batch and fluidized-bed reactors. In a batch reactor, the temperature and holding time for achieving complete decomposition were found to be much higher as compared to the respective values obtained in a fluidized-bed reactor using air as the fluidizing medium. The present studies have shown that fluidized-bed decomposition of APT offers a number of distinct advantages such as lower decomposition temperature as well as time, faster kinetics, and better product morphology. The decomposition kinetics, in the fluidized-bed reactor, was found to fit well into the “Power Law” model, dα/dt = k(1/r)α1- r , where α = fraction decomposed, k = rate constant, and r (a constant) is 1/2. The activation energy of the decomposition reaction suggests the overall process to be surface controlled.

Electronic Properties of MoS2–WS2 Heterostructures Synthesized with Two-Step Lateral Epitaxial Strategy

“…When the growth was terminated, 500 sccm Ar flow was introduced into the furnace to remove the residual reactants and the sample was rapidly cooled to room temperature by pushing out of the hot zone of the furnace. The thermolysis of ammonium tungstate (NH 4 ) 10 W 12 O 41 in an inert gas environment resulted in the conversion of (NH 4 ) 10 W 12 O 41 to WO 3 at above 600 °C, as described by eq . …”

Lateral Built‐In Potential of Monolayer MoS2–WS2 In‐Plane Heterostructures by a Shortcut Growth Strategy

“…When the growth was completed, 500 sccm fl ow of Ar was introduced into the furnace to remove the residual reactants and the sample was rapidly cooled down to ambient temperature by simply pushing the quartz tube out of the hot zone of the furnace. The thermolysis of ammonium tungstate (NH 4 ) 6 Mo 7 O 24 and ammonium tungstate (NH 4 ) 10 W 12 O 41 in an inert gas environment resulted in the conversion of (NH 4 ) 6 Mo 7 O 24 to MoO 3 at temperature above 340 °C [ 33 ] as shown in Equation ( 1) , while the conversion of (NH 4 ) 10 W 12 O 41 to WO 3 at a relatively higher temperature, for example, above 600 °C [ 34 ] as described in Equation ( 2) . Due to the difference between the vapor pressures of MoO 3 and WO 3 at specifi c growth temperature (Section S1 and Figure S1i, Supporting Information), as well as the difference in the distance between the precursors (Mo or W) and growth substrate, by carefully controlling the amount of reactants and growth parameters, lateral WS 2 /MoS 2 heterostructures could be well achieved with a good repeatability.…”

Mask-free patterning and selective CVD-growth of 2D-TMDCs semiconductors

“…On the other hand, the exact conversion mechanism of the WS 2 -precursor ink needs further investigation. Based on a limited number of studies, the thermolysis conversion of the ((NH 4 ) 10 H 2 (W 2 O 7 ) 6 )-precursor into 'WO 3 ' required higher temperatures (>600 °C) [43]. We, therefore, speculate that in our experiment the dot-patterns of the Mo-based ink start converting into MoS 2 islands at lower temperatures, whereas WO 3 dot-patterns likely to remain inactive till 600 °C is reached.…”