The phase diagram of ammonium nitrate

The pressure-temperature (P-T) phase diagram of ammonium nitrate (AN) [NH(4)NO(3)] has been determined using synchrotron x-ray diffraction (XRD) and Raman spectroscopy measurements. Phase boundaries were established by characterizing phase transitions to the high temperature polymorphs during multiple P-T measurements using both XRD and Raman spectroscopy measurements. At room temperature, the ambient pressure orthorhombic (Pmmn) AN-IV phase was stable up to 45 GPa and no phase transitions were observed. AN-IV phase was also observed to be stable in a large P-T phase space. The phase boundaries are steep with a small phase stability regime for high temperature phases. A P-V-T equation of state based on a high temperature Birch-Murnaghan formalism was obtained by simultaneously fitting the P-V isotherms at 298, 325, 446, and 467 K, thermal expansion data at 1 bar, and volumes from P-T ramping experiments. Anomalous thermal expansion behavior of AN was observed at high pressure with a modest negative thermal expansion in the 3-11 GPa range for temperatures up to 467 K. The role of vibrational anharmonicity in this anomalous thermal expansion behavior has been established using high P-T Raman spectroscopy.     

Raman scattering study of the low temperature phase transitions in ammonium nitrate

The phase changes in polycrystalline ammonium nitrate and its fully deuterated analogue have been studied by Raman scattering. The phase V and IV transition was found to be associated with the softening and intensity decrease of a NO₃^? librational mode. The Raman line-width data suggest that the VII to V phase transition involves a change in the degree of orientational order of the ions without incurring a change in lattice structure.     

Pressure induced isostructural metastable phase transition of ammonium nitrate

The energetic material ammonium nitrate (AN, NH(4)NO(3)) has been studied under both hydrostatic and nonhydrostatic conditions using diamond anvil cells combined with micro-Raman spectroscopy and synchrotron X-ray powder diffraction. The refined powder X-ray data indicates that under hydrostatic conditions AN-IV (orthorhombic, Pmmn) is stable to above 40 GPa. In one nonhydrostatic compression experiment a volume collapse was observed, suggesting an isostructural phase transition to a "metastable" phase IV' between 17 and 28 GPa. The structures of phase IV and IV' are similar with the subtle difference in the hydrogen-bonding network; that is, a noticeably shorter N1···O1 distance seen in phase IV'. This hydrogen bond has a significant component along the b-axis, which proves to be the most compressible until cell axis over the entire pressure range. It is likely that the shear stress of the nonhydrostatic experiment drives the phase IV-to-IV' transition to occur. We compare the present isotherms of phase IV and IV' in both static and nonhydrostatic conditions with the previously obtained Hugoniot and find that the nonhydrostatic isotherm approximately matches the Hugoniot. On the basis of this comparison, we conjecture that a chemical reaction or phase transition may occur in AN under dynamic pressure conditions at 22 GPa.     

Determination of water,ammonium nitrate and sodium nitrate content in ‘water-in-oil’ emulsions using TG and DSC

The main component of an emulsion explosive is a water-in-oil emulsion consisting of a supersaturated ammonium nitrate (AN) water phase, finely dispersed in an oil phase. Quantitative determination of nearly all the components in a W/O emulsion is possible using thermogravimetry (TG) and differential scanning calorimetry (DSC). Isothermal TG measurements enable determination of water content, while cycled DSC measurements allow the amount of ammonium nitrate to be determined. In the case that sodium nitrate (SN) is also added to AN as an oxidizing agent, it is necessary to quantitatively separate both salts from organic matter with diethyl ether. On the basis of the TG curve of the precipitated salts, the amount of AN can then be calculated, and that of SN is obtained from TG measurement of the original sample.     

Control over phase transformations in the crystal lattice of ammonium nitrate by modification of the system of intermolecular interactions via addition of organic substances

Methods for phase stabilization of ammonium nitrate were sought for to substantially extend the application fields of this oxidizing agent in self-combustible formulations for various purposes, including the new generation of gas-generating formulations for automobile safety bags. The phase state of ammonium nitrate alloys with minor additions of organic substances with crystallographic parameters close to those of ammonium nitrate was studied.     

A study of phase transformations in the surface layer of titanium dioxide

The capabilities of the diffuse reflectance spectroscopy in a study of the state of the surface layer of anatase in anatase-rutile phase transformations in successive thermal treatments of anatase in the temperature range 200–900°C and in analysis of titanium dioxide of P25 brand (Degussa) containing anatase and rutile in a 80: 20 ratio, respectively, are demonstrated for the example of dispersed titanium oxide.     

Kinetic study of the solid phase reaction of ammonium nitrate and copper oxide by the use of fast x-ray diffraction

The solid state reaction of ammonium nitrate and copper oxide was studied by the use of energy dispersive and angle dispersive x-ray diffraction. The reaction takes place within the temperature interval 110 to 150 °C and consists of two steps. The product of these consecutive reactions is the diammine copper complex. The relative concentrations of the species involved were evaluated by summing up difference x-ray spectra. The resulting curves were analyzed by a computer program to obtain the kinetic constants of the reactions.

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Zusammenfassung Mittels Röntgendiffraktionsverfahren wurde die Feststoffreaktion von Ammoniumnitrat mit Kupferoxid untersucht. Die Reaktion verläuft im Temperaturbereich 110–150°C und besteht aus zwei Schritten. Das Produkt dieser Polgereaktionen ist der Diamminkupferkomplex. Die relative Konzentration der daran beteiligten Spezies wurde durch Aufsummieren von Röntgendifferenzspektren ermittelt. Anhand der resultierenden Kurven wurden die kinetischen Konstanten der Reaktionen mittels eines Rechnerprogrammes bestimmt.

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. 110–150°. . . .

     

A differential scanning calorimetric study on phase transformations of HgI2

The influence of stoichiometry on the mercuric iodide to transformation temperature was studied in a limited region around the exact stoichiometry. It is concluded that although this influence is small, the transformation temperature has its highest value at the exact stoichiometry composition.

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Zusammenfassung In einem begrenzten Intervall in der Nähe der exakten Stöchiometrie von Quecksilberjodid wurde der Einfluß der Stöchiometrie auf die/ß Umwandlungstemperatur untersucht. Es konnte festgestellt werden, daß dieser Einfluß zwar gering ist, die Umwandlungstemperatur ihren größten Wert jedoch bei der exakten Stöchiometrie erreicht.

     

A differential scanning calorimetric study on phase transformations of HgI2

A quantitative study of the different factors that influence the- transformation of mercuric iodide was carried out with differential scanning calorimetry. The transformation temperature and the peak width during the heating of the material were followed. An attempt was made to explain the experimental results.

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Zusammenfassung Mittels Differential-Scanning-Kalorimetrie wurde der Einfluss verschiedener Faktoren auf die- Umwandlung von Quecksilberjodid quantitativ untersucht. Dabei wurde die Umwandlungstemperatur und die Signalbreite beim Erhitzen der Substanz beobachtet. Es wurde ein Versuch unternommen, die experimentellen Ergebnisse zu erklären.

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, - . . .

     

Thermal properties of ammonium nitrate

The reproducibility of the DTA curves of ammonium nitrate as functions of its grain size and the atmosphere during the measurements was studied with a derivatograph. The temperatures and the areas of the peaks assigned to the modification transitions IV → III (peak 1), III → II (peak 2) and II → I (peak 3) were evaluated. It was found that for some unground samples the area of peak 2 decreases markedly. It has been verified that in an atmosphere of moist air the temperature of peak 1 is lowered. The temperatures of lumpy and loose samples do not differ appreciably. Statistical methods evidenced the mutual dependence of the areas of peaks 1 and 2. The possible causes of this are discussed.     

Application of simultaneous thermomicroscopy/DSC to the study of phase diagrams

The correlation between morphological changes and DSC recordings gives valuable information on the mechanism of phase transformations. The present paper describes a new instrument for simultaneous DSC and thermomicroscopy in transmitted light, where a DSC device is placed in a commercially available hot-stage. The application of this DSC/thermomicroscopy is exemplified by study of the phase diagrams for KNO₃-NaNO₃, diphenylamine-benzophenone and a liquid crystal system.

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Zusammenfassung Die Korrelation zwischen morphologischen Veränderungen und DSC-Kurven ergibt wertvolle Informationen über den Mechanismus von Phasenumwandlungen. Es wird ein neues Gerät zur simultanen DSC und Thermomikroskopie im durchfallenden Licht beschrieben, in dem die DSC-Einheit in einem im Handel erhältlichen hot-stage untergebracht ist. Die Anwendbarkeit dieses DSC/Thermomikroskops wird durch Untersuchung der Phasendiagramme KNO₃-NaNO₃, Dyphenylamin-Benzophenon und eines Flüssigkeitskristallsystems demonstriert.

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. , . KNO₃-NaNO₃, - .

     

Phase transformations of ammonium tungsten bronzes

This article discusses the formation and structure of ammonium tungsten bronzes, (NH₄) _x WO_3−y . As analytical tools, TG/DTA-MS, XRD, SEM, Raman, XPS, and ¹H-MAS NMR were used. The well-known α-hexagonal ammonium tungsten bronze (α-HATB, ICDD 42-0452) was thermally reduced and around 550 °C a hexagonal ammonium tungsten bronze formed, whose structure was similar to α-HATB, but the hexagonal channels were almost completely empty; thus, this phase was called reduced hexagonal (h-) WO₃. In contrast with earlier considerations, it was found that the oxidation state of W atoms influenced at least as much the cell parameters of α-HATB and h-WO₃, as the packing of the hexagonal channels. Between 600 and 650 °C reduced h-WO₃ transformed into another ammonium tungsten bronze, whose structure was disputed in the literature. It was found that the structure of this phase—called β-HATB, (NH₄)_0.001WO_2.79—was hexagonal.     

Sequential flow injection analysis of ammonium and nitrate using gas phase molecular absorption spectrometry

A flow injection method on the basis of gas phase molecular absorption is described for the sequential determination of ammonium and nitrate. Two hundred microliters of sample solution is injected into the flow line. For ammonium determination, the sample zone is directed to a line in which reacts with NaOH (13 M) and produces ammonia. But for nitrate determination, the sample zone is passed through the on-line copperized zinc (Zn/Cu) reduction column and produces ammonium ion and in the follows ammonia. The produced ammonia in both cases is purged into the stream of N₂ carrier gas. The gaseous phase is separated from the liquid phase using a gas-liquid separator and then is swept into a flow through cell, which has been positioned in the cell compartment of an UV-Vis spectrophotometer. The absorbance of the gaseous phase is measured at 194 nm. Under selected conditions for sequential analysis of ammonium and nitrate, linear relations were found between the peak heights of absorption signals and concentrations of ammonium (10-650 μg ml⁻¹) and nitrate (20-800 μg ml⁻¹). The limit of detections for ammonium and nitrate analysis were 8 and 10 μg ml⁻¹, respectively. The relative standard deviations of repeated measurements of 50 μg ml⁻¹ of ammonium and nitrate were 2.0, 2.9%, respectively. Maximum sampling rate was about 40 samples/h. The method was applied to the determination of ammonium in pharmaceutical products and the sequential determination of ammonium and nitrate in spiked water samples.     

DSC studies of binary inorganic ammonium compound systems

The thermal behaviour of the binary systems HNH₂SO₃-NH₄NH₂SO₃ (I), HNH₂SO₃-(NH₄)₂SO₄ (II), HNH₂SO₃-NH₄HSO₄ (III), NH₄NH₂SO₃-(NH₄)₂SO₄ (IV), NH₄NH₂SO₃-NH₄HSO₄ (V), (NH₄)₂SO₄-NH₄HSO₄ (VI) was investigated with a Du Pont Thermal Analyzer supplied with a DSC module. The corresponding single compounds and freshly prepared (NH₄)₂S₂O₇ were examined under the same conditions in preliminary experiments. The ΔH _f values of HNH₂SO₃, NH₄NH₂SO₃, (NH₄)₂S₂O₇ and (NH₄)₂SO₄ · NH₄HSO₄ determined in the absence of air were 11.9, 16.8, 11.7 and 11.7 kJ/mole. Due to the moisture content of the atmosphere, an repeated heating in air the DSC curves showed more endothermic peaks than under air-free conditions. Exothermic additive reactions took place for binary systems (I) and (III), resulting in the formation of (NH₄SO₃)₂NH and (NH₄)₂S₂O₇, respectively, and for systems (II) and (VI), producing a new compound on melting.     

Anharmonic effects in ammonium nitrate and hydroxylammonium nitrate clusters

The covalent and ionic clusters of ammonium nitrate and hydroxyl ammonium nitrate are characterized using density functional theory and second-order vibrational perturbation theory. The most stable structures are covalent acid-base pairs for the monomers and ionic acid-base pairs for the dimers. The hydrogen-bonding distances are greater in the ionic dimers than in the covalent monomers, and the stretching frequencies are significantly different in the covalent and ionic clusters. The anharmonicity of the potential energy surfaces is found to influence the geometries, frequencies, and nuclear magnetic shielding constants for these systems. The inclusion of anharmonic effects significantly decreases many of the calculated vibrational frequencies in these clusters and improves the agreement of the calculated frequencies with the experimental data available for the isolated neutral species. The calculations of nuclear magnetic shielding constants for all nuclei in these clusters illustrate that quantitatively accurate predictions of nuclear magnetic shieldings for comparison to experimental data require the inclusion of anharmonic effects. These calculations of geometries, frequencies, and shielding constants provide insight into the significance of anharmonic effects in ionic materials and provide data that will be useful for the parametrization of molecular mechanical force fields for ionic liquids. Anharmonic effects will be particularly important for the study of proton transfer reactions in ionic materials.     

Ammonium nitrate-polymer glasses: a new concept for phase and thermal stabilization of ammonium nitrate

Dissolving of ammonium nitrate in highly polar polymers such as poly(vinylpyrrolidone) and/or poly(acrylamide) can result in the formation of single-phase glassy solid materials, in which NH 4 (+) and NO 3 (-) are separated through an ion-dipole interaction with the polymer matrix. Below the glass transition temperature of the polymer matrix the resulting materials remain phase and thermally stable as demonstrated through the absence of decomposition as well as the solid-solid transitions and melting of ammonium nitrate. The structure of the materials is explored by Fourier transform infrared spectroscopy and density functional calculations. Differential scanning calorimetry, thermogravimetry, and isoconversional kinetic analysis are applied to characterize the thermal behavior of the materials.     

DSC study of phase transitions of cephalin pseudo-binary systems in excess water

The gel-liquid crystal phase transitions of the pseudo-binary systems of cephalins DMPE and DHPE in excess water were studied by differential scanning calorimetry. The phase diagram of the pseudo-binary systems has been given. The experiments showed that the partial phase separation in gel phase might occur at least at the mole fractions of DHPE below 0.1. The analysis by the model of ideal solution showed that both the cephalins were non-ideally miscible both in the gel phases and in the liquid crystal phases. The analysis by the model of regular solution showed that all the non-ideality parameters in the gel phases were larger than those in the liquid crystal phases at the same temperature. All the non-ideality parameters were not constant, but rather dependent on temperature.     

Thermal decomposition of ammonium nitrate dispersed in a multicomponent nitrate system

To obtain the kinetic curves of thermal decomposition of ammonium nitrate occurring together with decomposition of metal nitrates contained in a mixture, the ammonia contents evolved from samples heated under thermoanalytical conditions were determined by the Kjeldahl method.

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Zusammenfassung Der aus unter thermoanalytischen -Bedingungen erhitzten Proben freigesetzte Ammoniakgehalt wird durch das Kjeldahlverfahren bestimmt, um die kinetischen Kurven der thermischen Zersetzung von Ammoniumnitrat zusammen mit der Zersetzung von Metallnitraten in Gemischen zu erhalten.

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