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Pinacone hexahydrate, a glycol hydrate, has a comparably high melting enthalpy of about (316 ± 16) J·g−1 at 45.5 °C. Based on results of a previous study and to further assess the applicability of pinacone hexahydrate to be used as phase change material in latent heat storage systems, additional investigations were carried out in this work. First, the influence of a deviation of the water content around the stoichiometric hexahydrate composition on the melting enthalpy was investigated. It was less pronounced compared with typical inorganic salt hydrates. Second, the crystallization velocity was measured as a function of temperature with a maximum value of about 0.5 cm·min−1 at 27 °C. Third, tests of the thermal cycling stability were carried out. Within 110 conducted cycles between 20 °C and 60 °C, the melting enthalpy and temperature remained stable.

Thermochemical energy storage using salt hydrates is a promising concept to bridge the gap between supply and demand for solar thermal energy in residential buildings. Using a suitable thermochemical material such as a salt hydrate, a thermal energy storage device, also known as a heat battery, can be created to supply low-temperature thermal energy during colder periods. To generate adequate power from a heat battery for the production of domestic hot tap water or space heating, the hydration rate of the salt hydrate needs to be sufficiently fast. It is hypothesized that the hydration rate of the material increases over multiple charge and discharge cycles due to crack formation and volume increase of the salt hydrate particles. This hypothesis is tested by performing two kinds of experiments: optical microscopy experiments using a micro-climate chamber to evaluate the particle size, and Thermo Gravimetric Analysis (TGA) experiments to determine the hydration rate of the particles. The hydration rate and particle size are input for a nucleation and growth model that takes into account crack formation and particle growth. Optical microscopy experiments show a particle expansion of approximately 30 % over 12 cycles. Typical hydration rates are increased by a factor 15 comparing the first and the 12th TGA cycle. It is shown that particle growth and crack formation significantly contribute to the improvement of the hydration rate. Finally, taking into account crack formation and particle growth in the numerical model results in a good agreement between model and experiments. Such a numerical model can be used for heat battery design.

The nucleation of methane hydrate in water – methane and two-layer water – decane – methane systems was studied using thermal analysis under methane pressure. The nucleation processes in the systems under consideration were represented as empirical survival curves. The effect of aggregate state of guest-rich phase on the methane hydrate nucleation process was evaluated. The experiments were carried out at constant supercooling (19.7 °C). The two-step shape of experimental survival curves was observed in the both studied systems. Based on the data obtained and literature data, it was assumed that in the case of Teflon containers steady-state methane hydrate nucleation occurred at interfaces of water – methane and water – decane saturated with methane while non-isothermal nucleation with a higher rate may be caused by the presence of a small quantity of microimpurities in the initial samples or two-step mechanism of the methane hydrate nucleation process. The comparison of the observed periods of non-stationarity during which nucleation rate takes constant value and calculated nucleation rates showed that the presence of a liquid phase rich with the hydrate-forming component promotes a steadier nucleation of the methane hydrate in the quiescent reactor and facilitates the formation of clusters in the surface layer (water – decane).

The multistep thermal decomposition behavior and kinetic feature of magnesium nitrate hydrate (MNH) were studied systematically in this study. Firstly, the multistep reaction processes in MNH pyrolysis were identified by Thermogravimetry-Fourier Transform Infrared analysis. Then, a common method of data processing, mathematical peak deconvolution, was used to separate such complex multistep reaction processes. Additionally, kinetic triplets of each separated process were determined by Friedman isoconversional method and Ozawa kinetic equation. Finally, kinetic features of each separated process were interpreted in terms of the physico-geometrical reaction mechanism. The results showed that MNH pyrolysis was a complex multistep reaction, including three reaction processes. The first two reaction processes were characterized by evolution of H2O, whereas the third reaction process was characterized by evolution of NO2. Three processes obeyed diffusion, order-based and nucleation and growth mechanisms, with E(apparent activation energy) = 80 ± 1, 137 ± 2, 227 ± 4 kJ/mol and A(pre-exponential factor)=(2.5 ± 0.2)×109, (1.5 ± 0.1)×1011 and (8.8 ± 0.2)×1015 s−1, respectively.

In this study, the impact of a deviation from the stoichiometrically correct hydrate concentration of a salt hydrate on the melting enthalpy is investigated exemplarily via 10 samples of CaCl2 + H2O around semicongruent melting CaCl2·6H2O by using differential scanning calorimetry (DSC). While the melting enthalpy of CaCl2·6H2O is determined to be (185 ± 19) J g−1, a trend of decreasing melting enthalpy with increasing deviation in the CaCl2 concentration from CaCl2·6H2O is observed. Three out of the 10 samples of CaCl2 + H2O were measured via DSC and T‐History. The determined enthalpy changes agree within the standard deviation of the DSC measurements. However, the value of the enthalpy change determined for consecutive heating cycles of the same sample via T-History is more stable than for consecutive heating cycles measured via DSC. This observation is attributed to the different sample volume of DSC and T-History and indicates a volume dependent behaviour of semicongruent melting CaCl2·6H2O. Statistical investigations into the high randomness of measured values for the melting enthalpy of consecutive heating cycles of CaCl2·6H2O were conducted via DSC. These reveal a strong negative correlation between the crystallisation temperature of CaCl2·4H2O and the melting enthalpy determined for the succeeding heating cycle. By adding 1 wt% of Sr(OH)2·8H2O as nucleating agent for CaCl2·6H2O, the crystallisation of CaCl2·4H2O in the DSC measurements is suppressed and reproducible values for the melting enthalpy of consecutive heating cycles are obtained.

In the current work, we reported the size effects of rutile TiO2 nanoparticles on the latent heat recovered of eutectic hydrate salt (EHS) phase change material (PCM). The nanoparticles modified EHS composites were prepared with different volume loadings (0.1 %, 0.3 % and 0.5 %) of TiO2 nanoparticles with two different sizes of 25 and 100 nm. The rheological behaviour analysis was carried out to demonstrate the dispersion stability of TiO2 nanoparticles in EHS. The factorial experiment method has been developed to evaluate the size effects of TiO2 nanoparticles. Meanwhile, the characterization technique, DSC was used to investigate the thermal properties. The results showed that the nanoparticles modified EHS composites incorporated with TiO2 nanoparticles in diameter of 25 nm achieved an optimal latent heat recovered, of which the mechanism analyses were validated by SEM and FT-IR. This study will provide insights into the further improvement of thermal properties of nanoparticles modified PCM composites by means of tailoring the size of nanoparticles.

A little known compound of the type Mg 2 KH(PO 4 ) 2 ·15H 2 O which is a rare example of highly hydrated salt containing H(PO 4 ) 2 symmetric dimers has been studied with a particular focus on its spectroscopic and thermal features. The infrared spectra have been recorded at room and liquid nitrogen temperatures and assignment of the observed vibrational bands has been proposed. The thermal behavior of Mg 2 KH(PO 4 ) 2 ·15H 2 O has been examined by simultaneous TG/DTA/mass spectrometry technique in a broad temperature interval up to 1000 °C. New insights on the processes of thermal decomposition as well as on the solid state transformations up to 1000 °C have been obtained by combination of the TG/DTA/MS analyses with IR spectroscopic and XRD studies.

In large latent heat storages based with the phase change material (PCM) being a salt hydrate, it is difficult to assure the stoichiometrically correct hydrate concentration of the salt hydrate. In this study the impact of the concentration of CaBr2 + H2O in a concentration range of about 2.6 wt% around the congruent melting CaBr2·6H2O on the melting enthalpy and the maximum storage capacity is exemplary investigated via differential scanning calorimetry (DSC) and via a model. The melting enthalpy of CaBr2·6H2O is found to be 142.1 J g−1, which is significantly larger than the value indicated in literature (115.5 J g−1). For a CaBr2 concentration around 0.8 wt% lower than the concentration of CaBr2·6H2O, a decrease of over 17% is found for both the melting enthalpy and the maximum storage capacity. A good agreement is found for the maximum storage capacity between the experimentally determined values and the values determined by the model.

Many synthesis procedures have been worked out to prepare CaSnO3. A great deal of them resort to the classical ceramic method that implies a very high temperature treatment (1300–1500 °C) of the component oxides mixture. To avoid such high temperature treatment, many alternative routes have been proposed. In this paper stoichiometric mixtures of Ca citrate tetrahydrate and Sn(II) oxalate have been mechanically activated by high energy milling. The reactions taking place in the mixtures during annealing have been studied by coupled TG–DSC measurements, XRPD and diffuse reflectance FT-IR spectroscopy. It has been established that the stage of mechanical activation allows the synthesis to be completed by 3 h-annealing at 850 °C.

International audience; In the present study, the chemo-physical modeling of time dependent hydration phenomenon of the cement-based concrete materials has been achieved using the finite element method. For this study, two identical concretes have been considered with different aggregate size distribution, i.e. one contains small aggregates, 4–8 [mm] and the other contains larger aggregates, 8–12 [mm]. The experimental measurements about the heat release rate and total hydration heat have been taken into account for the numerical modeling using the modified Arrhenius's law. The numerical results confirm that the initially homogeneous hydration phenomenon across the cement paste matrix is disturbed by the existence of aggregates during the hydration period. This induced heterogeneous hydration field strongly depends on the size of aggregates. Afterwards, the hydration gradient has been scrutinized. This can readily explain not only the gap space creation which can be generally observed around the aggregates but also the particular mechanical properties and the induced hydrate product concentration at ITZ (Interfacial Transition Zone) next to the aggregates.

The hydration products and thermal decomposition mechanism of hydrated CaAl 2 O 4 and Ca 7 ZrAl 6 O 18 compounds were investigated by X-ray diffraction, SEM/EDS and thermal analysis. The processes of crystal hydrate nucleation and precipitation were preceded by the evolution of the X-ray amorphous phase during the first 24 h of hydration. DTA–TGA–EGA techniques allowed the study of the detailed decomposition and identification of intermediate and stable to be performed. The differential thermal analysis (DTA) curves of hydrated CaAl 2 O 4 and Ca 7 ZrAl 6 O 18 compounds show five similar endothermic peaks due to crystal water desorption. According to the quantitative TGA–EGA analyses performed on hydrated CaAl 2 O 4 and Ca 7 ZrAl 6 O 18 compounds, it was found that C 2 AH 8 , C 3 AH 6 and Al(OH) 3 phases are the main hydration products of CaAl 2 O 4 . Under the same laboratory conditions, the hydration of Ca 7 ZrAl 6 O 18 proceeds with the formation of mainly CAH 10 and AH 3 -gel phases. We provide the original illustrations of the hydrate crystals formation via amorphous phases.

The synthesis of magnesium silicate hydrate (MSH), which has wide applications in both construction and environmental fields, has been studied for decades. However, it is known that the characteristics of magnesia (MgO) vary significantly depending on their calcination conditions, which is expected to affect their performance in the MgO–SiO2–H2O system. This paper investigated the effect of different MgO and silica sources on the formation of magnesium silicate hydrate (MSH) at room temperature. The hydration process was studied by mixing commercial reactive MgO and silica powders with water and curing for 1, 7 and 28 days. The hydration products were analysed with the help of X-ray diffraction (XRD) and thermogravimatric analysis (TGA). The results showed the continuous consumption of MgO and the existence of MSH and brucite and other minor phases such as magnesite and calcite. It is found that the Mg and Si sources have significant effect on the hydration process of MgO–SiO2–H2O system. The reaction degree is controlled by the availability of dissolved Mg and Si in the solution. The former is determined by the reactivity of MgO and the latter is related to the reactivity of the silica as well as the pH of the system.

International audience; After mixing of the cement with water, most of the anhydride products sustain the hydration process and this leads to the hydrate products, e.g. CSH, Ca(OH)2, Afm and Aft. The mentioned hydration process is a highly complex phenomenon involving the chemically based thermo-activation inside the cement mortars during the early age hydration process. The chemo-thermal hydration reactions drasticaly increase at the early age of hydration after the mixing action and then it becomes less important and turns to be nearly asymptotic. The progress of the hydration phenomenon drives the material properties change during the very early age of cement hydration. Regarding the mortar and concrete, such hydration process would not be homogeneous through the cement matrix due to the aggregates presence. These inclusions will affect the temperature distribution as well as degree of hydration. In the current contribution, the chemical and thermal hydration have been firstly investigated by means of SEM observations using replica method and secondly by the 3D-FEM numerical experiments including two different case studies using glass beads as aggregates. The numerical experiments match fairly good the experimental measurements obtained using a pseudo-adiabatic testing setup for the case studies herein. The scanning electron microscopy (SEM) images observation demonstrates the gap spaces around the glass beads next to the external surfaces. These gaps can be essentially seen for the multi-glass beads case study. The role of the temperature and degree of hydration gradients are clearly obtained using the numerical samples. Some fresh routes and outlooks have been afterwards discussed.

A series of hydrazinated mixed nickel manganese zinc ferrous hydrazine fumarate complexes were synthesized from aqueous mixed metal chloride solutions and sodium fumarate-hydrazine hydrate mixture. The detailed characterization was carried out by chemical analysis, infrared spectroscopy and isothermal mass loss studies. The hydrazine ligand in these complexes shows bidentate bridging nature while fumarate anion exhibit monodentate behavior. These complexes act as single source precursors for nanosize ferrites. Thermal decomposition of these precursors was studied upto 800 °C in static air using simultaneous TG/DTA. The thermal decomposition study indicates 3-step decomposition of these precursors into nanosize mixed metal oxides. The nanosize mixed metal oxides were then characterized by X-ray diffraction, transmission electron microscopy and infrared spectral studies.

In this study, TGA–DTA–MS and TGT techniques were used to investigate the thermal decomposition of ammonium phosphotungstate hydrate ((NH 4 ) 3 (PW 12 O 40 )· x H 2 O, APhT) in inert gas (Ar) atmosphere. The thermal decomposition products of APhT obtained in Ar atmosphere at various temperatures were characterized by using XRD, FT-IR and SEM analyses. APhT losses its crystal water in the first step and forms anhydrous ammonium phosphotungstate ((NH 4 ) 3 (PW 12 O 40 ), anhydrous APhT). Anhydrous APhT is stable up to 640 K and it is transformed into cubic structured, dark blue colored phosphotungstate bronze ((PO 2 ) 2 (WO 3 ) 24 , PhTB) which is stable up to 1250 K. PhTB is then decomposed gradually into light black colored WO 3 and (PO) 2 (WO 3 ) 16 mixture. This mixture does not vaporize until 1423 K. After this temperature, sublimation takes place followed by melting at 1545 K and weight loss is observed due to evaporation. At 1573 K the samples are transformed into light black colored tungsten suboxide (WO 3− y ).

The single phase NH 4 CoPO 4 ·H 2 O with layered structure was prepared via solid-state reaction at 60 °C. Based on the iterative isoconversional calculation procedure, the values of activation energy E a associated with the first, second and third stages of the thermal decomposition of NH 4 CoPO 4 ·H 2 O were obtained, which demonstrate that the three stages are all a single-step kinetic process and can be adequately described by a unique kinetic triplet. The most probable reaction mechanisms of the three stages were estimated by comparison between experimental plots and modeled plots. The values of pre-exponential factor A of the three stages were obtained on the basis of E a and the reaction mechanisms.

In this study, hydration behaviour of prazosin hydrochloride polyhydrate was assessed using differential scanning calorimetry, thermogravimetric analysis, powder X-ray diffraction and dynamic vapour sorption techniques. Differential scanning calorimetry and thermogravimetric analysis at faster heating rate (20 °C/min) showed single step water loss, attributed to both dihydrate and unbound water. In contrast, thermogravimetric analysis at slower heating rate (1 °C/min) showed unbound and dihydrate lattice water separately, with unbound water being lost initially, followed by loss of dihydrate water. Variable vacuum and variable humidity PXRD study revealed shift in diffraction peaks to higher values on removal of unbound water. Initial PXRD patterns were regained when kept again at ambient conditions. Dynamic vapour sorption depicted type I sorption isotherm with interstitial water, indicating that polyhydrate form show reversible behaviour with change in humidity. Correlation between thermal, sorption and crystallographic data established hydration behaviour to be characteristic of expanded channel type (non-stoichiometric) hydrate.

Mayenite was synthesized using the conventional solid-state reaction and two low temperature synthesis methods a self-combustion method and a polymeric precursor process. Using the low temperature methods the metastable phase 5CaO·3Al2O3 (C5A3) crystallizes at 1173 K (2 h) instead of C12A7. After forming pure crystalline 12CaO·7Al2O3 (C12A7) at 1373 K (2 h) the hydration was monitored at 283 K, 288 K, 293 K, 298 K and 301 K by heat flow calorimetry. During hydration the first calorimetric peak correlates with the formation of layers around the C12A7 grains and the second peak corresponds to further hydration reactions and crystallization of lamellar calcium aluminate hydrates C2AH8±x showing different hydration steps of 8.2H2O, 8.0H2O and 7.5H2O depending on temperature. At higher temperatures the formation of hydrate shells is increased and consequently the further hydration reaction is hindered.

Sustainable air conditioning systems require heat reservoirs that operate between 4 and 20 °C. A systematic search for binary and ternary eutectics of inorganic salts and salt hydrates with melting temperatures in this temperature regime and with high enthalpies of fusion has been performed by means of differential scanning calorimetry (DSC). Promising results were obtained for the pseudo-ternary system Zn(NO3)2·6H2O, Mn(NO3)2·4H2O, and KNO3 with the melting temperature range 18–21 °C and the enthalpy of fusion of about 110 kJ kg−1. Suitable nucleating and thickening agents have been found and tested to prevent the mixture from supercooling and phase separation.

Crystallographic characteristics of congruent melting 18-crown-6 crystalline hydrates were specified using X-ray structure analysis. Melting enthalpies of 18-crown-6 tetra- and hexahydrates have been determined; melting points of these compounds have been specified. Liquidus of 18-crown-6–water system has been calculated in the concentration range x H 2 O = 0.750 – 0.935 by using the received data and known thermodynamic properties of the solution.

The interaction between uranyl nitrate hexahydrate (UNH) and rubidium nitrate in solid state at elevated temperatures has been studied for several compositions using simultaneous thermal analysis techniques (TG–DTA–EGA), X-ray diffraction and IR spectral measurements. The formation of rubidium uranyl nitrate has been observed in rubidium nitrate rich mixtures even at ambient temperature during mixing of the two nitrates in solid state. The reaction at room temperature was incomplete in mixtures containing higher than 30 mol% uranyl nitrate hexahydrate. Thermal and XRD data on equimolar mixture indicate complete dehydration of uranyl nitrate hexahydrate by 300 °C to form rubidium uranyl nitrate, Rb[UO 2 (NO 3 ) 3 ], which decomposes on further heating to the polymerised structures, Rb 2 [(UO 2 NO 3 ) 2 (O) 2 ] and Rb 4 [(UO 2 ) 3 (O) 4 (NO 3 ) 2 ] above 360 °C and 460 °C, respectively. Rb 4 [(UO 2 ) 3 (O) 4 (NO 3 ) 2 ] reacts with UO 3 above 550 °C to form rubidium diuranate, Rb 2 U 2 O 7 , when the initial nitrate mixture is prepared from compositions containing UNH at 50 mol% or lower levels. In the case of initial nitrate mixtures containing a higher amount of UNH, however, Rb 2 U 4 O 13 and U 3 O 8 are formed above 550 °C.

Current studies on thorium oxalate hexahydrate and its decomposition intermediates are being presented using a combination of thermal, X-ray diffraction and IR spectral methods. It has been shown here that thorium oxalate dihydrate formed by the thermal dehydration of thorium oxalate hexahydrate undergoes partial thermal decomposition to form a polynuclear complex at 165 °C, which further decomposes at higher temperatures to a hydroxyoxalate, a carbonate and finally to thorium oxide. Formation of thorium oxalate monohydrate and/or anhydrous thorium oxalate could not be seen here.

The dihydrate of barbituric acid (BAc) and its dehydration product, form II were investigated by means of moisture sorption analysis, hot-stage microscopy, differential scanning calorimetry, thermogravimetry, solution calorimetry, IR- and Raman-spectroscopy as well as powder X-ray diffraction. The dihydrate desolvates already at and below 50% relative humidity (RH) at 25 °C whereas form II is stable up to 80% RH, where it transforms back to the dihydrate. The thermal dehydration of barbituric acid dihydrate (BAc-H2) is a single step, nucleation controlled process. The peritectic reaction of the hydrate was measured at 77 °C and a transformation enthalpy of Δ trs H H2-II = 17.3 kJ mol −1 was calculated for the interconversion between the hydrate and form II. An almost identical value of 17.0 kJ mol −1 was obtained from solution calorimetry in water as solvent (Δ sol H H2 = 41.5, Δ sol H II = 24.5 kJ mol −1 ). Additionally a high-temperature form (HT-form) of BAc, which is enantiotropically related to form II and unstable at ambient conditions has been characterized. Furthermore, we observed that grinding of BAc with potassium bromide (KBr) induces a tautomeric change. Therefore, IR-spectra recorded with KBr-discs usually display a mixture of tautomers, whereas the IR-spectra of the pure trioxo-form of BAc are obtained if alternative preparation techniques are used.

New data on the dehydration and rehydration processes of calcium, manganese and copper dichlorides are presented that reveal surprising, in a certain sense, behaviour difficult to be explained for the last two chlorides in terms of the usual conception of thermodynamic equilibrium. A substantial role of a super disperse phase at studying the equilibrium of the thermal decomposition of a hydrate is postulated to explain the experimental results for manganese and copper dichlorides. It is shown that the formation of such a phase of the hydrate is able to change appreciably the experimental results, causing the increase of water vapour pressure and the decrease of the derived enthalpy of a reaction. The results obtained allow to understand the reasons for considerable differences of some literature data. They enable to receive more precise and reliable data for thermal dehydration and probably for some other decomposition processes.

We studied the dehydration behavior of iron(II) sulfate heptahydrate (FeSO 4 ·7H 2 O) as part of NASA's in situ resource utilization program for the recovery of water on Mars. We examined the effect of the variables important in using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The temperatures at which waters of hydration are removed and the enthalpy values for the various dehydration steps were measured using DSC. For the dehydration of FeSO 4 ·7H 2 O, a particle size As discussed above, proper selection of DSC and TGA operating parameters and baseline analysis technique is required to obtain accurate thermal results.

It was found that during thermal decomposition of hydrates of d -metal nitrates nitrous oxide (N 2 O) is always present among the other gaseous products: H 2 O, HNO 3 , NO, NO 2 and O 2 . In all studied decomposition reactions the nitrous oxide formed contains approximately 5–8% of total nitrogen coming from nitrate. Two new mechanisms of N 2 O formation, based on the reaction between NO or NO 2 and nitrate ion, have been proposed. The discussed third possible mechanism: (a) 2NO = N 2 O 2 and (b) N 2 O 2 + NO = N 2 O + NO 2 is unlikely.

The heterocyclic amines 2,6-lutidine, pyrazine, piperazine and piperidine were intercalated into layered crystalline hydrated barium phenylphosphonate, Ba(HO 3 PC 6 H 5 ) 2 ·H 2 O, through a batch method in ethanolic solution, to give the maximum amounts 0.39, 0.82, 2.80 and 5.50 mmol g −1 , respectively. The original host interlayer distance ( d ) of 1532 pm increased after intercalation for piperazine (1752 pm) and piperidine (2112 pm) molecules, while for 2,6-lutidine and pyrazine molecules d values were maintained. The enthalpy of intercalation gave −5.60 ± 0.10, −1.00 ± 0.02, −9.55 ± 1.00 and −30.70 ± 0.68 kJ mol −1 for the sequence of heterocyclic amines. The Gibbs free energies are negative and entropies are positive for intercalation.

The solid copper l -threonate hydrate, Cu(C4H6O5)·0.5H2O, was synthesized by the reaction of l -threonic acid with copper dihydrocarbonate and characterized by means of chemical and elemental analyses, IR and TG-DTG. Low-temperature heat-capacity of the title compound has been precisely measured with a small sample precise automated adiabatic calorimeter over the temperature range from 77 to 390 K. An obvious process of the dehydration occurred in the temperature range between 353 and 370 K. The peak temperature of the dehydration of the compound has been observed to be 369.304 ± 0.208 K by means of the heat-capacity measurements. The molar enthalpy, ΔdHm, of the dehydration of the resulting compound was of 16.490 ± 0.063 kJ mol−1. The experimental molar heat capacities of the solid from 77 to 353 K and the solid from 370 to 390 K have been, respectively, fitted to tow polynomial equations with the reduced temperatures by least square method. The constant-volume energy of combustion of the compound, ΔcUm, has been determined as being −1616.15 ± 0.72 kJ mol−1 by an RBC-II precision rotating-bomb combustion calorimeter at 298.15 K. The standard molar enthalpy of formation of the compound, Δ f H m ° , has been calculated to be −1114.76 ± 0.81 kJ mol−1 from the combination of the data of standard molar enthalpy of combustion of the compound with other auxiliary thermodynamic quantities.

A pure calcium borate Ca2[B2O4(OH)2]·0.5H2O has been synthesized under hydrothermal condition and characterized by XRD, FT-IR and TG as well as by chemical analysis. The molar enthalpy of solution of Ca2[B2O4(OH)2]·0.5H2O in HC1·54.582H2O was determined. From a combination of this result with measured enthalpies of solution of H3BO3 in HC1·54.561H2O and of CaO in (HCl + H3BO3) solution, together with the standard molar enthalpies of formation of CaO(s), H3BO3(s) and H2O(l), the standard molar enthalpy of formation of −(3172.5 ± 2.5) kJ mol−1 of Ca2[B2O4(OH)2]·0.5H2O was obtained.

The thermal decomposition of Co(NO3)2·6H2O (1) as well as that one of NO[Co(NO3)3] (Co(NO3)2·N2O4) (2) was followed by thermogravimetric (TG) measurements, X-ray recording and Raman and IR spectra. The stepwise decomposition reactions of 1 and 2 leading to anhydrous cobalt(II)nitrate (3) were established. In N2 atmosphere, cobalt oxides are finally formed whereas in H2/N2 (10% H2) cobalt metal is produced. Rapid heating of cobalt(II)nitrate hexahydrate causes melting (formation of a hydrate melt) and therefore side reactions in the hydrate melt by incoupled reactions and evolution/evaporation of different species as, e.g., HNO3, NO2, etc. In case of larger amounts in dense packing in the sample container, the formation of oxo(hydoxo)nitrates is possible at higher temperature. For 2, its thermal decomposition to 3 was followed and its decomposition mechanism is proposed.

The solid–liquid equilibrium diagrams of binary mixtures involving magnesium nitrate hexahydrate with cobalt nitrate hexahydrate, nickel nitrate hexahydrate (partly), manganese nitrate tetrahydrate, and iron(III) nitrate nonahydrate and of magnesium chloride hexahydrate with cobalt and nickel chlorides hexahydrates and manganese chloride tetrahydrate, and the of two manganese salts were determined. Those diagrams that showed a simple eutectic were fitted by the Ott equation and where the required BET parameters were available, the magnesium salt rich parts of the liquidus were modeled by means of this method.

Two commercial magnesium stearate powders in two well-characterised structural states are investigated using DSC and coupled TGA–DTA under dry nitrogen flow. They consist of either a mixture of crystalline hydrates or a poorly crystallised so-called anhydrate. Following the degassing of unbound water, 1 or 3 weight-loss peaks are observed below about 100 °C, each associated with one heat loss peak at the same temperature. The present results and a review of graphical data from literature show that the so-called anhydrate always contains a significant amount of water. At the beginning of the dehydration process, the heat loss is the same as the standard heat of vaporisation of water and then gradually departs from it by positive values. The idea according to which the mixture of dihydrate and trihydrate loses water to form the anhydrate cannot be quantitatively reconciled with the present and other gravimetric results.

Magnesium phthalate dihydrate was synthesized by rheological phase reaction. The crystal structure was determined by XRD. Its thermal decomposition mechanism in N 2 was studied by TG DTA. The thermal decomposition products were characterized by XRD, GC–MS. The thermal decomposition of magnesium phthalate dihydrate in N 2 proceeded in two stages; it first lost two crystal water to form anhydrate salt, then magnesium phthalate decomposed further, the last product was MgO. The organic compounds are mainly benzophenone and anthraquinone.

The thermal decomposition of a suite of synthetic agardites of formula ACu6(AsO4)2(OH)6.3H2O where A is given by a rare earth element has been studied using thermogravimetric analysis techniques. Dehydration of the agardites occurs at low temperatures and over an extended temperature range from ambient to around 60 degrees Celsius. This loss of water is attributed to the loss of zeolitic water. The mass loss of water indicates 3 moles of zeolitic water in the structure. Dehydroxylation occurs in steps over a wide range of temperatures from 235 to 456 degrees Celsius. The mass loss during dehydroxylation shows the number of moles of hydroxyl units is six. There is a linear relationship between the first dehydroxylation temperature and the electronegativity of the REE.

A pure calcium borate 2CaO·B2O3·H2O has been synthesized under hydrothermal condition and characterized by XRD, FT-IR and TG as well as by chemical analysis. The molar enthalpy of solution of 2CaO·B2O3·H2O in HCl·54.579H2O was determined. From a combination of this result with measured enthalpies of solution of H3BO3 in HCl·54.561H2O and of CaO in HCl+H3BO3 solution, together with the standard molar enthalpies of formation of CaO(s), H3BO3(s), and H2O(l), the standard molar enthalpy of formation of −(3041.8±2.5) kJ mol−1 of 2CaO·B2O3·H2O was obtained.

The course of conventional DTA or DSC curves is rather characteristic of the experimental conditions then of the transformation itself. The course of Q-TA T curves taken by the Q-DTA measuring technique is not deteriorated by these factors when using the “transformation-governed heating control” (TGHC). In this technique, namely, the temperature of the sample is governed by the transformation itself based on the feed-back principle so that the relay-switch system of the Q-DTA apparatus sensing the change of the Q-DTA t signal governs the heating control unit in a way, in which the transformation proceeds with a predetermined, very small and strictly constant rate by providing the suitable difference between the temperatures of the sample and the furnace. In order to normalise the experimental conditions, for decomposition reactions a particular, so-called “labyrinth crucible” should also be used, which provides a “self-generated atmosphere” already at the beginning of the reaction, and keeps the partial pressure of gaseous decomposition products constant at their maximum value of 100 kPa till the end of the transformation. This way, the unique normal characteristic temperature of reactions and transformations, together with reaction heat belonging to them can be measured, and the course of transformations free of every foreign influence can also be recorded.

The thermal behavior and magnetic properties of two manganese(II) oxalates crystallohydrates are studied and compared. MnC 2 O 4 ·2H 2 O crystallizes in monoclinic syngony, while the MnC 2 O 4 ·3H 2 O—in orthorhombic. The difference in the crystal lattice is responsible for the different thermal behavior of the samples. This fact is proved by in situ measurement of the magnetic properties, TGA, DTA, DSC, and X-ray diffraction. The dehydration proceeds in one step with MnC 2 O 4 ·2H 2 O (Δ H =86 kJ/mol) and in three steps with MnC 2 O 4 ·3H 2 O (Δ H =132 kJ/mol). The exchange interaction between the manganese ions in MnC 2 O 4 ·3H 2 O is changing from antiferromagnetic to ferromagnetic during the entire dehydration process, while in the case of MnC 2 O 4 ·2H 2 O the same interaction remains almost constantly antiferromagnetic. The two crystallohydrates reveal different initial and final temperatures of dehydration, thus changing the region where the anhydrous oxalate exists. The oxidative decomposition of the anhydrous oxalate leads not only to Mn(III) but also to Mn(IV) and an oxidation process is much weaker when starting from MnC 2 O 4 ·3H 2 O. This fact shows that the orthorhombic crystal lattice stabilizes the lower oxidation states of manganese. The annealing of the monoclinic MnC 2 O 4 ·2H 2 O at 450 °C leads to its complete transformation into Mn 3 O 4 with hausmanite structure. At the same temperature, the orthorhombic MnC 2 O 4 ·3H 2 O gives not only Mn 3 O 4 but also a great quantity of cubic Mn 2 O 3 .

Yb(NO3)3·6H2O was used as a parent compound for the formation of Yb2O3 at up to 800 °C in atmosphere of air. Thermal processes occurring during the decomposition course were monitored by means of differential thermal analysis (DTA), thermogravimetry (TG), and the gaseous decomposition products were identified by mass spectrometry (GC–MS). The intermediates and final solid products were characterized by IR-spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that, Yb(NO3)3·6H2O decomposes completely through 11 endothermic mass loss processes. The dehydration occurs through the first six steps at 95, 145, 165, 175 and 200 °C, forming crystalline nitrate Yb(NO3)3, which decomposes to YbO0.5(NO3)2 at 250 °C. The latter, decomposes to non-stoichiometric unstable intermediate YbO0.75(NO3)1.5 at 335 °C, which decompose immediately to a stable and crystalline YbONO3 at 365 °C, then to a non-stoichiometric unstable intermediate Yb(O)1.25(NO3)0.5 at 470 °C. Finally, Yb2O3 was formed at 510 °C. The decomposition course and surface morphology were supported and followed by SEM and textural studies (SBET).The final product Yb2O3 at 600 °C has a large irregular sheet shaped particles containing a large pores, voids and cracks and has SBET=45 m2/g. The gaseous decomposition products are water vapor, nitric acid and nitrogen oxides (NO, NO2 and N2O5). The activation energy (ΔE in kJ/mol) was calculated non-isothermally for each thermal processes.

Some new hydrazinium salts of benzene tricarboxylic and tetracarboxylic acids have been prepared by neutralisation of these acids with hydrazine hydrate in aqueous medium and characterised by conductance measurement, IR spectral and thermal analyses. Hemimellitic acid (H 3 hml) forms monohydrazinium salt, trimellitic acid (H 3 tml) and trimesic acid (H 3 tms), mono and dihydrazinium salts, and pyromellitic acid (H 4 pml) all the four salts with hydrazine hydrate. Conductance study indicates their electrolytic nature. IR spectra of all the salts show NN stretching frequencies of the N 2 H 5 + in the region of 960–990 cm −1 . The hemimellitate salt undergoes endothermic dehydrazination at 154 °C, trimellitates and pyromellitates in the range of 191–271 °C, and trimesates in the range of 267–332 °C. Trimesates decompose to give CO 2 around 337 °C. All the salts then undergo strong exothermic decomposition in the range of 517–595 °C via the formation of respective acid intermediates first, then arenes, yielding carbon residue. A comparison of the thermal behaviour of pure acids with that of their salts reveals the fact that the acids do not withstand high temperature like salts. They show sharp endotherms at their melting points and then they decompose exothermally before 400 °C to give carbon residue.

Low-temperature heat capacities of the solid coordination compound Zn(His)SO 4 ·H 2 O(s) were precisely measured by a precision automated adiabatic calorimeter over the temperature range between T =78 and 373 K. The initial dehydration temperature of the coordination compound was determined to be, T d =324.20 K, by analysis of the heat-capacity curve. The experimental values of molar heat capacities were fitted to a polynomial equation of heat capacities ( C p,m ) with the reduced temperatures, x ( x = f ( T )), by least square method. Enthalpies of dissolution of the ZnSO 4 ·7H 2 O(s)+His(s) (Δ d H ° m,1 ) and the Zn(His)SO 4 ·H 2 O(s) (Δ d H ° m,2 ) in 100.00 ml of 2 mol l −3 HCl(aq) at T =298.15 K were determined to be, Δ d H ° m,1 =−(13.129±0.013) kJ mol −1 and Δ d H ° m,2 =−(11.271±0.012) kJ mol −1 , by means of a homemade isoperibol solution-reaction calorimeter. The standard molar enthalpy of formation of the compound was determined as: Δ f H ° m ( Zn ( His ) SO 4 · H 2 O , s , 298.15 K )=−(1827.61±2.31) kJ mol −1 from the enthalpies of dissolution and other auxiliary thermodynamic data through a Hess thermochemical cycle by using the homemade isoperibol calorimeter. Furthermore, the reliability of the designed Hess thermochemical cycle was verified by comparing between UV/Vis spectra and the refractive indexes of Solution A (from dissolution of the [ZnSO 4 ·7H 2 O(s)+His(s)] mixture in 2 mol l −3 hydrochloric acid) and Solution A′ (from dissolution of the complex Zn(His)SO 4 ·H 2 O(s) in 2 mol l −3 hydrochloric acid).

New solid heavy metal complexes with 4-chloro-2-methylphenoxyacetic acid (MCPA) of the general formulae: Pb(MCPA) 2 ·H 2 O and Cd(MCPA) 2 ·2H 2 O have been prepared. Diffractometric, IR spectroscopic and thermal analyses of these complexes and the previously described Cu(MCPA) 2 have been performed. The complexes have different structures, a low level of crystallinity and exhibit a tendency to form polymers. An attempt has been made to explain the mode of the ligand molecule coordination on the basis of the position of the bands of the characteristic ν asym and ν sym vibrations of the carboxylate group. The course of the TG, DTG and DTA curves indicates that the compounds decompose in two (the copper salt) or three stages. The decomposition of the cadmium complex is preceded by dehydration. The basic gaseous products of decomposition are H 2 O and CO 2 . HCOOH, HOCH 2 COOH, HCl and trace amounts of compounds containing an aromatic ring were also detected. The final solid decomposition product is a metal oxide.

The TG/DSC curves of K 3 [Cr(C 2 O 4 ) 3 ]·3H 2 O, K 3 [Al(C 2 O 4 ) 3 ]·3H 2 O, K 3 [Fe(C 2 O 4 ) 3 ]·3H 2 O and K 2 [Cu(C 2 O 4 ) 2 ]·2H 2 O in nitrogen were determined at the heating rate of 15, 10, 5, and 2 °C min −1 , respectively. A non-linear optimization was applied for different reaction models to perform single and overall steps optimizations. Kinetic parameters were given, and the most probable mechanism functions were suggested.

Thermal decomposition of Zn(NO 3 ) 2 · n H 2 O ( n =4 and 6) was studied using TG, DTA and QMS techniques. Measurements were performed in helium and in dry air. It was found that the examined reaction is a multi-step process with overlapping stages. The whole process depends on the rate of heating. Degradation of nitrate(V) groups starts before all water of crystallisation is removed from the system. Zn(NO 3 ) 2 ·2Zn(OH) 2 was identified as intermediate product of decomposition of Zn(NO 3 ) 2 · n H 2 O.

Experimental data on the heat capacities, enthalpies of formation from the oxides and elements of the natural pollucites: Cs 0.77 Na 0.14 Rb 0.04 Al 0.91 Si 2.08 O 6 ·0.34H 2 O (Minas Gerais, Brazil) (I) and Cs 0.84 Na 0.11 Al 0.88 Si 2.10 O 6 ·0.17H 2 O (East Siberia, Russia) (II) have been determined. The heat capacities of the pollucite (II) were measured by differential scanning calorimetry (DSC) method from T =250 to 810 K. A value of C° p, m (298.15 K )=172.2 J K −1 mol −1 was obtained and the resultant C ° p ,m ( T ) equation in the interval T =298.15–610 K was calculated: C° p ,m =131.37+181.97×10 −3 T−11.84×10 5 T −2 J K −1 mol −1 (±0.36%). The standard enthalpies of formation were determined by a set of thermochemical cycles using decomposition and subsequent dissolution of the dehydration products in molten lead borate at T =973 K. Values of Δ f H° m (298.15 K ) are found to be −3104±13 kJ mol −1 (pollucite I) and −3090±14 kJ mol −1 (pollucite II). The values of Δ f G° m (298.15 K ) were calculated as −2921 kJ mol −1 (pollucite I) and −2911 kJ mol −1 (pollucite II).

A new magnesium borate MgO·3B 2 O 3 ·3.5H 2 O has been synthesized by the method of phase transformation of double salt and characterized by XRD, IR and Raman spectroscopy as well as by TG. The structural formula of this compound was Mg[B 6 O 9 (OH) 2 ]·2.5H 2 O. The enthalpy of solution of MgO·3B 2 O 3 ·3.5H 2 O in approximately 1 mol dm −3 HCl was determined. With the incorporation of the standard molar enthalpies of formation of MgO(s), H 3 BO 3 (s), and H 2 O(l), the standard molar enthalpy of formation of −(5595.02±4.85) kJ mol −1 of MgO·3B 2 O 3 3.5H 2 O was obtained. Thermodynamic properties of this compound was also calculated by group contribution method.

Sm(NO3)3·6H2O and Sm2(C2O4)3·10H2O were used as precursors for the formation of Sm2O3. Thermal processes involved in the decomposition course of both salts up to 800 °C in air were monitored by nonisothermal gravimetry and differential thermal analysis. Intermediates and final solid products were characterized by IR-spectroscopy, X-ray diffraction and scanning electron microscopy. The results showed that Sm(NO3)3·6H2O decomposes completely through nine endothermic mass loss processes. The dehydration occurs through the first four steps at 90, 125, 195, and 240 °C, culminating in a crystalline nitrate monohydrate, which subsequently decomposes to Sm(OH)(NO3)2 at 355 °C. The latter decomposes rapidly to form a stable and crystalline SmO(NO3) at 460 °C, through nonstoichoimetric unstable intermediates. Finally Sm2O3 forms at 520 °C. For the oxalate, the dehydration occurs in five steps: the anhydrous oxalate is thermally unstable and immediately decomposes to Sm2O3 at 645 °C through two unstable intermediates. The crystalline oxide obtained from the nitrate contains larger pores than the oxide obtained from the oxalate, as indicated from scanning electron microscopy (SEM) results.