THE ENTHALPIES OF FORMATION AND MIXING OF NH4MI 1−xMII xPO4⋅H2O (M = Mn, Fe, Co) SOLID SOLUTIONSтезисы доклада

Дата последнего поиска статьи во внешних источниках: 22 ноября 2015 г.

Работа с тезисами доклада


[1] The enthalpies of formation and mixing of nh4mi 1−xmii xpo4⋅h2o (m = mn, fe, co) solid solutions / L. A. Tiflova, A. S. Monayenkova, V. A. Alyoshin, P. P. Yakovlev // Abstracts of the XX International Conference on Chemical Thermodynamics in Russia (RCCT-2015, June 22-26, 2015, Nizhni Novgorod). — Lobachevsky State University of Nizhni Novgorod Nizhni Novgorod, 2015. — P. 313–313. This work is a part of systematic investigations of the thermodynamic properties of new materials synthesized on the basic of compounds of transition elements. It is carried out at Luginin’s Laboratory of Thermochemistry and Inorganic Synthesis Laboratory of Inorganic Chemistry division. It is devoted to the study of thermochemical properties of substitution solid solutions: NH4Fe1−xMnxPO4⋅H2O and NH4Co1−xMnxPO4⋅H2O. The choice of reasearch object is caused by its application as precursors for synthesis of cathode material in Li-ion batteries. The reproducible synthesis of such compounds and application of materials based on them require knowledge of thermodynamic properties of double lithium and transition elements phosphates and its precursors. There is no literature data on thermochemical properties of NH4Fe1−xMnxPO4⋅H2O and NH4Co1−xMnxPO4⋅H2O solid solutions. Only one work [1] was concerned with the determination of the NH4FePO4⋅H2O enthalpy of formation. According to the IUPAC classification, the data obtained in single work can be considered only as preliminary. The samples of NH4Fe1−xMnxPO4⋅H2O and NH4Co1−xMnxPO4⋅H2O (х = 0, 0.25, 0.5, 0.75, 1) were prepared by coprecipitation method. The ammonium and phosphates groups are introduced in the M(OH)2 matrices. The precipitates were washed out by the distilled water and dried up. The synthesized samples were checked by X-ray, ICP-MS and TG analysis. The X-ray examination supported the single-phase nature of samples. It state by using X-ray and TG analysis that investigated solid solutions are monohydrates. To determinate the enthalpies of formation of studied solid solutions, the enthalpies of reactions of NH4Fe1−xMnxPO4⋅H2O and NH4Co1−xMnxPO4⋅H2O with 1 M hydrochloric acid were measured at 298.15 K in a hermetically sealed swinging calorimeter with an isothermal coat. Temperature rise in each run was measured by platinum resistance thermometer. Thermometric sesitivity of circuit was 3⋅10−5 K. The energy equivalent of calorimeter was determined by electric technique. The enthalpies of formation of specified solid solution were calculated on basis of experimental data and the reliable literature data on thermochemical properties of ammonium, iron, cobalt, manganese chlorides and phosphoric acid solutions. The enthalpies of formation of studied systems depend on type of transition element. These values decrease by an increase of x (the degree of Mn substitution for Fe and Co). The enthalpies of mixing are negative for Fe−Mn system and the dependence of these values on x has the minimum at x = 0.5. The solid solution of NH4Fe1−xMnxPO4⋅H2O can be considered as regular solution. The enthalpies of mixing are not near from 0 within measurement errors for Co−Mn systems. The entropy factor can play the role in thermodynamic stability of NH4Co1−xMnxPO4⋅H2O solution. The NH4FePO4⋅H2O enthalpy of formation found by us coincides with data [1] within measurement errors. All of other thermochemical parameters were obtained for the first time in this work.

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