Thermoanalytische Untersuchungen zur Zersetzung von MgCl2 · 6 H2O unter quasiisobaren Bedingungen

The thermal decomposition of MgCI 2 9 6H20 (non-dried and partly dried) and the kinetics of the process were studied by DTA, TG, DTG, I R, X-ray diffraction'and chemical analysis of Mg and CI. The reactions which occurred in the course of the thermal analysis were identified as dehydration (in steps), thermal hydrolysis of MgC12"H20 and dehydrochloridization of magnesium hydroxy chlorides, Melting of the phases MgCIz-6HzO, MgC/2" 4HzO and MgC12 was also identified in the thermal curves. Thermal weight loss continued up to 800 ~ in flowing air or nitrogen, but only up to 700 "C in static air. MgO was the end-product of thermal treatment in both cases.The kinetic parameters of the reaction, the activation energy E, pre-exponential factor A and apparent order of reaction b, were computed by several methods. The activation energy and the apparent reaction order of dehydration were found to increase with decreasing hydration number of the Mg. The dehydrochloridization process had the highest activation energy, The thermal decomposition of magnesium chloride hexahydrate has recently been the subject of several studies [1-6}. These studies have elucidated some points which were not cleared up in previous work [7][8][9][10], especially concerning the influence of the experimental conditions on the dehydration and hydrolysis processes. Very Iittle has been done to determine the kinetic parameters of the reactions, however. In the present study the kinetics of the processes are investigated by applying three methods of analysis to DTA and DTG curves: (1) the method of Freeman and Carroll, (2) the initial rate method, and (3) Chen's "half-width" method. In each of these methods, the activation energy E, preexponential factor A and apparent order of reaction b are computed. From a comparison of the results, the reliability of the data can be evaluated. In order to identify the products obtained at various stages of the thermal analysis, infrared 1"John Wiley & Sons, Limited, Chichester AkadOmiai Kiad6, Budapest

Section: Meltingsupporting

confidence: 92%

Kinetic analysis of thermal dehydration and hydrolysis of MgCl2·6H2O by DTA and TG

Kirsh

Yariv

Shoval³

1987

“…After the completion of these processes, a saturated MgCI 2 -4H20 melt is attained, whose thermal decomposition to magnesium hydroxide chloride is approximately identical with the decomposition of MgCI2"4H20 from MgCI2 "6H20 [5] as described above. In contrast to this, the thermal decomposition of MgCI 2 9 2C4H802 results in anhydrous magnesium chloride (Fig.…”

Section: Mgci2-h20-c4h802 Systemmentioning

confidence: 96%

“…C4HaO 2 and MgCI 2 9 2C4H802 are presented in comparison with MgCl2" 6H20. Just like the hydrate [5], the dioxane solvates melt incongruently, with the melting point of MgCI2.6H20 at 117 ~ intermediate between that of MgCI2-2C,~H802 at 71 ~ and that of MgCI2"6H20"C4H802 at 127 ~ In the case of the mixed solvate at 130 ~ a solid phase composed of MgCl 2 9 2H20" C4H802 and two liquid phases approximately composed of dioxane and a melt rich in water consisting of MgC12 9 6H20" 0.5C4H802 are present.…”

Section: Mgci2-h20-c4h802 Systemmentioning

confidence: 98%

“…Moreover, in the presoace of 1,4-dioxane (C4H802) the solvates and mixed solvates LiCI.H20.C4HsO2, LiC1. C4H80 2 [1], MgC12 9 6H20" C4H80 2 , MgCl 2 " 2C4HaO 2[2], A1CI3 "9H20" 3C4HaO 2 and AIC13 9 2C4HAO2 [3] can be obtained.From the point of view of coordination chemistry, the incorporation of 1,4-dioxane in the solvates is interesting because this can be coordinated as a bridging ligand between the aquo complexes of the cations, as well as directly to the cation.As a continuation of our thermoanalytical investigations of solid-phase solvates in the salt-water-organic component systems, this paper is intended to demonstrate the influence of 1,4-dioxane on the solvate structure and the coordination of the solvents to the different cations, through an investigation of their thermal behaviour.Detailed results ofthermoanalytical investigations are available only for the pure salt hydrates [4][5][6][7]. As concerns the solvates and mixed solvates, the data published John Wiley & Sons, Limited, Chichester Akad~miai Kiadt, Budapest …”

mentioning

confidence: 99%

See 1 more Smart Citation

The thermal behaviour of solvates in the LiCI(MgCl2, AlCl3) water-1,4-dioxane systems

Emons

Naumann

Köhnke

et al. 1987

Self Cite

The thermal behaviour of the solvates and mixed solvates in the LiCI(MgC12, A1Cla)-water-1,4-dioxane systems was investigated by means of DTA measurements of the melting behaviour and by quasi-isothermal and quasi-isobaric investigations of the thermal decomposition processes.The compounds melt incongruently. The positions of the melting points and the processes of thermal decomposition confirm the assumption that 1,4-dioxane is bonded in the first coordination sphere in the mixed solvate of lithium, but in the cases of magnesium and aluminium chloride it is bonded via hydrogen-bonds and not directly to the cations. Only for the lithium and magnesium compounds does the decomposition of the anhydrous solvates result in anhydrous chlorides.At 298.15 K, LiCI, MgCI 2 and A1C13 form the salt hydrates LiCI-H20 , MgC12 9 6H20 and A1Cl a 9 6H20 in aqueous solution. Moreover, in the presoace of 1,4-dioxane (C4H802) the solvates and mixed solvates LiCI.H20.C4HsO2, LiC1. C4H80 2 [1], MgC12 9 6H20" C4H80 2 , MgCl 2 " 2C4HaO 2[2], A1CI3 "9H20" 3C4HaO 2 and AIC13 9 2C4HAO2 [3] can be obtained.From the point of view of coordination chemistry, the incorporation of 1,4-dioxane in the solvates is interesting because this can be coordinated as a bridging ligand between the aquo complexes of the cations, as well as directly to the cation.As a continuation of our thermoanalytical investigations of solid-phase solvates in the salt-water-organic component systems, this paper is intended to demonstrate the influence of 1,4-dioxane on the solvate structure and the coordination of the solvents to the different cations, through an investigation of their thermal behaviour.Detailed results ofthermoanalytical investigations are available only for the pure salt hydrates [4][5][6][7]. As concerns the solvates and mixed solvates, the data published John Wiley & Sons, Limited, Chichester Akad~miai Kiadt, Budapest

“…Nous n'avons retenu que les mesures isothermes d'6quilibres solide-vapeur [2,5] et les analyses thermogravim6triques et thermiques diff6rentielles [3,12,13] effectu6es sous pression totale constante de HCI et de HzO : les r6sultats obtenus sous courant de gaz inerte ou sous atmosph6re impos6e sont difficiles li exploiter dans le cadre de cette 6tude. La d6composition thermique de chaque hydrate ne s'observe pas fi une temp6rature fixe mais dans un large domaine de temp6ratures qui d6pend du d6bit de gaz inerte, de la vitesse de chauffage, de la masse de l'6chantillon et sa granulom&rie.…”

Section: Comparaison Avec Les R~sultats Exp~rimentauxunclassified

Etude thermodynamique de la decomposition thermique des hydrates du chlorure de magnesium

Danès

Saint‐Aman²,

Coudurier

1988

The thermodynamic study of the different compounds of the system MgCI z, HzO, HCI allows to draw the stability diagram of the 8 solid phases into a three-dimensional space (temperature, total pressure and ratio of HCl and H20 partial pressures). The evolution of the composition of solid and gaseous phases during an isobaric heating is described. The conclusions of this study are in good agreement with the experimental results obtained in laboratory and with the industrial requirements set for the different steps of the dehydration of MgCI 2.