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Journal of Thermal Analysis and Calorimetry
Authors: Imre Miklós Szilágyi, Eero Santala, Mikko Heikkilä, Marianna Kemell, Timur Nikitin, Leonid Khriachtchev, Markku Räsänen, Mikko Ritala and Markku Leskelä

appropriate annealing conditions for polymer/inorganic nanofibers prepared by electrospinning. We use the PVP/AMT fibers as a model system, as we have recently developed a new electrospinning process for preparing WO 3 nanofibers (detailed results about the

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Abstract  

DTA runs and flux growth experiments have shown that the crystallization temperatures of WO3 from NaF flux are in the range of 1020–1090°C. Addition of Pb2+ influences the crystal growth and the crystallization temperatures are altered (within this range). A thermal effect giving rise to an exothermal DTA peak was observed above the crystallization temperature. This peak occurs at a higher temperature when lead ions are present. We propose an explanation based on pre-crystallization clustering and on the number of nucleation sites on the surface of the platinum crucible.

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Abstract  

This paper presents the synergetic effect of Te2MoO7 and MoO3 (WO3) in the partial oxidation of propylene to acrolein. The study found that the addition of MoO3 (or WO3) to Te2MoO7 greatly promoted the propylene conversion and acrolein yield. As the results of the investigation revealed, the higher catalytic performance could be attributed to the increased acidity, which is beneficial for the adsorption of propylene.

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oxide. WO 3 is harmless and stable semiconductor in acidic and oxidative environments. WO 3 is a visible light-responsive photocatalyst that can absorb up to ca. 480 nm. However, there are very few reports concerning the degradation of organic

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2 [ 10 , 11 ], TiO 2 /V 2 O 5 [ 12 , 13 ], and TiO 2 /WO 3 [ 14 – 17 ]. The bicomponent system TiO 2 /WO 3 seems rather promising for photocatalysis with visible illumination due to the stability of these oxides and the suitable combination of

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The chlorination kinetics of alkali-added (K and Li) tungsten trioxide were studied by thermogravimetry, using gaseous CCl4 as chlorinating agent. The reactivity of the modified samples was compared to the results on the chlorination of pure WO3. Similar apparent activation energies were found for the pure and alkali-added samples. However, potassium additive resulted in a strong decrease of the initial reaction rate, while surface lithium has no influence on it.

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Journal of Thermal Analysis and Calorimetry
Authors: Latifa Al-Hajji, Muhammad Hasan and Mohamed Zaki

Abstract  

The formation of Barium monotungstate (BaWO4) particles in equimolar powder mixtures of BaCO3 and WO3 was examined under isothermal and non-isothermal conditions upon heating in air at 25–1200 °C, using thermogravimetry. Concurrence of the observed mass loss (due to the release of CO2) to the occurrence of the formation reaction was evidenced. Accordingly, the extent of reaction (x) was determined as a function of time (t) or temperature (T). The xt and xT data thus obtained were processed using well established mathematical apparatus and methods, in order to characterize nature of reaction rate-determining step, and derive isothermal and non-isothermal kinetic parameters. Moreover, the reaction mixture quenched at various temperatures (600–1,000 °C) in the reaction course was analyzed by various spectroscopic and microscopic techniques, for material characterization. The results obtained indicated that the reaction rate may be controlled by unidirectional diffusion of WO3 species across the product layer (BaWO4), which was implied to form on the barium carbonate particles. The isothermally determined activation energy (118–125 kJ/mol) was found to be more credible than that (245 kJ/mol) determined non-isothermally.

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Abstract  

The phase equilibria established up to the solidus line in the system Fe2V4O13−WO3, one of the intersections of the three-component system Fe2O3−V2O5−WO3, have been studied. The system appears not to be a real two-component system.

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Abstract  

Thermodynamic calculations predict the formation of hydrochloric acid gas and alkali tungstates during hydrogen reduction of WO3 doped with alkali chlorides MCl (M=Li, Na, K). The formation of HCl was proved experimentally by simultaneously coupled TG-MS measurements from RT to 1200C. The formation of HCl is the result of the reaction between MCl, WO3 and water. Ubiquitous traces of moisture in the gas are sufficient for reaction according to WO3+(2+2n)MCl +(1+n)H2O→M2+2nWO4+n+(2+2n)HCl (n=0, 1, 2). Laboratory reduction tests showed that the formed tungstates differ. NaCl and KCl form monotungstates (n=0), while LiCl produces more lithium-rich compounds (n=1, 2). Temperature and humidity, among other process factors, control subsequent reduction of the tungstates to metals.

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