The Temperature-Composition Relations of the Binary System Magnesium Nitrate—Water

The decomposition mechanism of Mg(NO3) 2 . 6H20 was studied by means of simultaneous TG, DTG and DTA method combined with EGA technique under conventional and quasi isothermal~luasi isobaric conditions. It has been found that Mg(NO3) 2 9 6H20 melts at 89 ~ in a congruent way. The solution formed begins to boil at 147 ~ The water loss process of the salt hydrate and the decomposition process of the Mg(NO3)2 always overlap to some extent. Accordingly, Mg(NO3) 2 of stoichiometric composition cannot be prepared thermally, because the compound always contains some basic salt. The last part of water departs in the vicini;.y of 270 ~ with extreme rapidity. In contrast to expectations the compound decomposes in pure "self-generated" atmosphere at a temperature lower by about 80 ~ than in the presence of air which contains a small amount of the gaseous decomposition product.

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“…4) is also demonstrated [15] in the phase diagram of the Mg(NOa)2-H20 system [19,20]. This is curve 1 (points a, b, c,…”

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confidence: 67%

Investigation on the thermal behaviour of Mg(NO3)2·6H2O I. The decomposition behaviour

Paulik

Arnold

et al. 1988

Journal of Thermal Analysis

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“…30 "C), Mg(NO,), 6 H 2 0 , and Mg(NO,),~PH,O. Sieverts and Petzold (1) reported the existence of a metastable tetrahydrate which has a small field of exlsteuce betvieen 50 and 58 "C In the vlclnlty of an apparent eutectlc point which occurs at a composition of 4 inoles water per mole salt Zw~ng et a1 (2) were not able to confiim the existence of thls hydrate H n thls study we report confirmation of the tetral-rydrate and report ~t s Raman and Infrared spectra. The spectra of the hexa-and d~hydratec are also reported Spectra of the hexahydrate have been, in part, Interpreted In terms of the space group deterlnined in X-ray studies by Braibarltl et a1 (3).…”

Section: Introductionmentioning

confidence: 98%

Raman and Infrared Studies of Hexa-, Tetra-, and Dihydrates of Crystalline Magnesium Nitrate

Chang¹,

Irish²

1973

Can. J. Chem.

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Raman and infrared spectra of Mg(N03)2.6H20, Mg(N03)2.6D20 and partially dehydrated products have been obtained and assigned. As the water content is reduced a different set of lines appears and maximizes at the coinposition Mg(hTQ3),4H,0. On further dehydration a third set of lines characteristic of Mg(NO,)2.2H2Q appears. The existence of the metastable tetrahydrate had not been confirmed since it was reported in 1932. The spectra suggest that four equatorial sites aroung Mg2+ in the tetrahydrate are occupied by four water molec~lles and two axial sites by nitrate ions, oriented in monodentate fashion. The spectra suggest that in the dihydrate approximately octahedral coordination is maintained by having two nitrate ions oriented in bidentate fashion and two water molecules trans to each other on the remaining sites.Nous avons obtenu et assign6 les spectres Raman et infrarouge de Mg(NO3),,6H2O, et de leurs derives partiellement deshydrates. Si la teneur en eau dinlinue. un ensemble diirerent de bandes apparait et devient maxium a la conjonction Mg(NQ3),.4H,0. Si la molec~~le est deshydralee Lln peu plus un troisikme groupe de bandes, caracteristiq~~es de Mg(N03),.2H20 apparait. L'existence du composk tetrahydrate metastable n'a pas Ct C confirnike depuis sa dicouverte en 1932. Lcs spectres suggerent que les quatre sites equatoriaux, autour de Mg2+, dans le tetrahydrate, sont occupes par quatre rnolCcules d'eau et les deux sites axiaux par des ions nitrates, orientes de faqon monodentee. On tire aussi des spectres que dans le dihydrate, une coordination approxin~ativerl~ent octaedrique est maintenue au moyen de deux ions nitrates orientis de faqon bidentie, et de deux molecules d'eau, rratls une par rapport a I'autre sur les sites restants.

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“…[9] Ae utectic compositiono f8 2% magnesium nitrate/18% water has been found to melt congruently at 130 8C. [10] In the solid state,i tw as calculated that this compositionc orresponds to 90 %d ihydrate and1 0% anhydrous salt. Interestingly,1 30 8Ci se asily achievable with available sources of low-grade thermal energya nd it is a useful temperature for residential and humanitarian applications.…”

Section: Introductionmentioning

confidence: 99%

“…However, research examining the slow dehydration of magnesium nitrate hexahydrate has shown stable lower hydrate states before eventually decomposing at 400 °C . A eutectic composition of 82 % magnesium nitrate/18 % water has been found to melt congruently at 130 °C . In the solid state, it was calculated that this composition corresponds to 90 % dihydrate and 10 % anhydrous salt.…”

Section: Introductionmentioning

confidence: 99%

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Reactive Phase‐Change Materials for Enhanced Thermal Energy Storage

2018

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Effective storage and release of low‐to‐moderate temperature thermal energy (e.g., solar thermal or geothermal) could be transformational for applications such as space heating/cooling, domestic hot water, or off‐grid cooking. Good candidates for thermal energy storage in this temperature range include latent heat storage (LHS) systems and thermochemical energy storage (TCES) systems using reversible salt‐hydrate dehydration reactions. Here, we propose that an energy‐storage system by use of magnesium nitrate hexahydrate can potentially improve upon independent TCES or LHS systems by utilizing both the thermochemical hydration reaction and the latent heat available through the solid–liquid phase change of one magnesium nitrate hydrate eutectic. This chemistry is investigated through thermogravimetric analysis (TGA)/differential scanning calorimetry (DSC) analysis and shows a total energy density of approximately 1170±94 kJ kg−1 when dehydrating the material up to 145 °C. Reversible latent heat cycling at a eutectic melting temperature of 130 °C is shown by the DSC signal and estimated to be on the order of 115±9.2 kJ kg−1—a 10 % increase over the thermochemical energy storage alone. Although the latent energy release was found to decrease slightly over several cycles, the mass was found to stabilize near an asymptotic value corresponding to the published eutectic composition. These results suggest the concept of reactive phase‐change materials could be a promising solution to increasing the stored volumetric energy density.

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The Temperature-Composition Relations of the Binary System Magnesium Nitrate—Water

Cited by 20 publications

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Investigation on the thermal behaviour of Mg(NO3)2·6H2O I. The decomposition behaviour

Investigation on the thermal behaviour of Mg(NO3)2·6H2O I. The decomposition behaviour

Raman and Infrared Studies of Hexa-, Tetra-, and Dihydrates of Crystalline Magnesium Nitrate

Reactive Phase‐Change Materials for Enhanced Thermal Energy Storage

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