Thermal decomposition of decavanadates of bivalent metals

Abstract

The thermal decomposition of CdaVloOzs " 16HaO and MgaV100~s " 18H:O has been investigated. It was found by means of IR spectroscopy and X-ray phase analysis that the final products of decomposition of the given compounds are V.On, the corresponding metavanadates and the vanadium bronzes of cadmium and magnesium. Present and previous results allow conclusions on the thermal decomposition of decavanadates of bivalent metals.The thermal reactivity of deeavanadates has become the subject of thorough research only in the last few years. Recent results have brought not only new information but also stimuli for further research.Analysis of the thermal properties of decavanadates of bivalent metals has been carried out in the cases of ZnaVi0028 " 16H20 [1], CaaV1002s " 16H~.O, SraVloO2~' 24 H,,O and BaaVl002 a 9 19 H20 [2]. Further research into decavanadates proved to be necessary for the explanation of certain phenomena connected with the thermal decomposition of the given compounds and also for purposes of obtaining a larger number of experimental data.The present paper deals with the problem of dehydration and thermal decomposition of CdaVmO,~ 8 " 16 H,,O and MgaVmO2s " 18 H20. ExperimentalCdaVloO:, ~ " 16 H20 and MgaVloOzs 9 18 HzO were prepared by the reaction of HaV1002s with the corresponding acetates [3].The cadmium or magnesium content was determined complexometrically [4]. Vanadium(V) was determined volumetrically by titrating with a 0.1 N solution of iron(II) sulphate using diphenylamine as indicator [5], and vanadium(IV) by titrating with a 0.01 M solution of potassium permanganate [5], but also qualitatively by using e.p.r, spectra. The amount of crystal water was estimated by drying the substances at 350 ~ as well as by DTA.For CdaVloO28 The thermal analysis of the compounds was performed on the Paulik-PaulikErdey derivatograph (MOM, Budapest), sample weight 200 mg. Gaseous products were sucked off by a water pump. For the study of the processes connected with heating of the compounds, products obtained by interrupted DTA, by drying over silica gel, and by isothermal heating at definite temperatures in a crucible furnace, were used. The samples obtained isothermally were always heated to constant weight and investigated by means of IR spectroscopy and X-ray phase analysis.The infrared spectra were taken on a Perkin-Elmer type 221 instrument, with the Nujol technique.X-ray diffraction patterns were taken on a Philips PW 1058 diffractograph equipped with a copper anticathode and a nickel filter.The e.p.r, spectra were taken on a Varian instrument of the Strong Pitch type (modulation amplitude 10 G, frequency 9.5 GHz, power of microwave radiation 25 mW, sensitivity 5 " 10a-2 9 105). Results and discussionThe results of differential thermal analysis of CdaVloO2s 9 16 HzO are shown in Fig. 1. The DTA curve indicates two r processes within the temperature range 75-240 ~ These are immediately followed by an r protess (max. at 265~ By long-term drying of CdaV1002s " 16 1-120 over silica gel, it is possible to ob...

The pseudo-orthorhombic structure of caesium dihydrogendecavanadate tetrahydrate

“…The reaction is reversible without appreciable thermolysis of the anion, in contrast to the situation in other decavanadates which are known to be destroyed by heating after the loss of a certain number of water molecules (depending upon the bonding properties of the cation). This reaction, which leads to lower condensed vanadates and oxides of vanadium (Ulicka, 1980;Ulicka & Zfirkova, 1981), shows the stabilizing role of water of crystallization in crystalline decavanadate hydrates. [However, the existence of zinc and magnesium anhydrous decavanadates with relatively high thermal stabilityhas been reported (Ulicka, 1980).]…”

“…This reaction, which leads to lower condensed vanadates and oxides of vanadium (Ulicka, 1980;Ulicka & Zfirkova, 1981), shows the stabilizing role of water of crystallization in crystalline decavanadate hydrates. [However, the existence of zinc and magnesium anhydrous decavanadates with relatively high thermal stabilityhas been reported (Ulicka, 1980).] We have observed that controlled thermal dehydration of the compound leads to an anhydrous non-crystalline solid, which in the presence of water vapour, turns back to the original crystalline hydrate.…”

Synthesis and 3D Network Architecture of 1- and 16-Hydrated Salts of 4-Dimethylaminopyridinium Decavanadate, (DMAPH)6[V10O28]·nH2O

“…In this stage there is an oxidization of the 4-dimethylaminopyridinium cations and decomposition of [V 10 O 28 ] 6´a s can be corroborated by an endothermic peak in the DSC curve at 210˝C. Comparing the IR spectrum of 2 with the intermediate (black amorphous product) obtained at 250˝C ( Figure S4) changes in signals of [V 10 O 28 ] 6´c luster can be observed, which is indicating the breakdown of cage and the consequent formation of products possibly containing mixed valence oxides [48][49][50][51]. At 340˝C a loss of about 30% occurs for the total sample.…”