Phase Transition Of Ammonium Nitrate Research Articles

Differential scanning calorimetric and Raman studies of phase transition V ⇌ IV of ammonium nitrate

Differential scanning calorimetry, alone and in conjunction with Raman spectrophotometry for simultaneous calorimetric and spectral measurements, was used to study the solid state phase transitions of ammonium nitrate between − 50 and 100 °C. On heating, two transition paths were observed between − 40 and 0 °C: one showing two separate peaks in DSC and the other showing a single peak. The latter path became dominant when samples were thermally cycled. The double transition was followed by transition IV →II at 51 °C and the single transition by transitions IV → III → II at about 50 and 87 °C. Raman spectra showed that there were two phases present between the two DSC peaks at low temperature. The first peak was attributed to a transition from the phase here designated as V to phase IV, and the second peak to a transition from V to IV. The single peak under 0 °C was the transition V → IV.

Phase transitions of ammonium nitrate doped with alkali nitrates studied with fast X-ray diffraction

Dried samples of ammonium nitrate (AN) containing 1, 3, 5 mol% KNO3, RbNO3 and CsNO3 were investigated with temperature resolved X-ray diffraction. The samples were cycled with 2 temperature programs from −70° to 100° and −70° to 150°C, resp. DSC measurements were made for comparison.KNO3 extends the stability range of phase III. The supercooling observed with the transitions II/III and III/IV was so severe that the phases III and IV could be skipped leading to the transitions II/IV and III/V. No hindered nucleation was observed on heating.RbNO3 gives dried AN the properties of the humid nitrate. Phase III appeared on heating but was skipped on cooling, when the sample had been heated to 150°C. Hindered nucleation was observed.CsNO3 stabilizes the phases II and V. No strong hysteresis or supercooling was observed.

Investigation of factors affecting caking tendency of calcium ammonium nitrate fertilizer and coating experiments

Caking of fertilizers is an important problem both to manufacturers and users. Manufacturers must recycle the caked fertilizer to the process resulting in an extra cost and users may have difficulties during the application of the fertilizer to the soil. In the first part of this study major factors which influence caking of a commercial grade calcium ammonium nitrate (CAN) fertilizer were investigated with a laboratory caking apparatus kept in a controlled atmosphere. It was observed that the caking tendency of CAN fertilizer increases almost linearly with pressure exerted on the fertilizer and with moisture content of the fertilizer at a temperature of 35 °C. The results indicate that the phase transition of ammonium nitrate between crystalline forms IV and III plays a significant role in caking of CAN since caking tendency is greatly reduced below the phase transition temperature which occurs at about 32 °C. In the second part of the study, the effectiveness of some coating materials to reduce the caking tendency of CAN fertilizer were tested. Among the materials tested, kieselguhr gave the most satisfactory result under the experimental conditions employed.

On the chemical and thermal stabilization of NH 4NO 3(IV)

The authors present the results of a DTA and X-ray diffraction investigation of the changes induced in the phase transitions of ammonium nitrate by the addition of ammonium sulphate and water and by repeated heating and cooling through the NH 4NO 3(IV)⇌ NH 4NO 3(III) phase transition point.

Investigation of phase transitions in ammonium nitrate by nitrogen–15 nuclear magnetic resonance

Abstract Exploratory Nitrogen-15 nuclear magnetic resonance (NMR) studies of ammonium nitrate (AN) have been undertaken using both conventional and magic angle spinning (MAS) methods. The chemical shift anisotropy is measured by two different methods at room temperature, and a precise measurement of the difference in isotropic chemical shift occurring at the phase transition IV to III is reported. Finally, the activation energy for the motion of both ions in the room temperature phase are obtained. No evidence in discontinuity of nitrogen relaxation times across the phase boundary at 32°C was observed.

Solid-state studies. Part 26.—Raman spectroscopic evidence for a phase II-like intermediate during the course of the IV–III phase transition in ammonium nitrate

Raman evidence is presented which supports the view that the intermediate occurring in the IV → III phase transition of ammonium nitrate has a structure similar to that of phase II.

Electron paramagnetic resonance study of the role of CuO additives in altering phase transition behavior of ammonium nitrate

The role of CuO in reducing the volume change and altering the transition temperature of structural phase transitions in ammonium nitrate is studied by electron paramagnetic resonance (EPR). At room temperature, two distinct EPR spectra, indicative of two chemical forms of copper were observed in ammonium nitrate heated from the melt containing 5% by weight of CuO and through which NH3 gas was bubbled. One spectrum having an orthorhombic g tensor with principle components g1 = 2.185, g2 = 2.109, and g3 = 2.055 is assigned to the Cu(NH3)2+4 complex. The other spectrum, also having orthorhombic symmetry, with g1 = 2.315, and g2 = 2.264, is tentatively assigned to a Cu2+ ion either interstitial or substitutional in the lattice. The g values of this spectrum were quite sensitive to temperature and change substantially during the structural phase transition at 60 °C. Heating ammonium nitrate to 160 °C for an hour changed the tetramine copper complex into a new spectrum which is identified as the diamine complex of copper. At room temperature this spectrum slowly returned to the tetramine complex. The role of these forms of copper in reducing the volume change associated with the above room-temperature phase transition is discussed.

Phase transitions in ammonium nitrate

The phases of ammonium nitrate, NH4NO3, doped with small amounts of NiO or CuO have been studied by X-ray and neutron diffraction at various temperatures from 80 to 423 K. NH4NO3 with metal-oxide additives, which are believed to form complexes, exists as a solid solution. Phase IV is stable down to 140 K in the NiO-doped samples and 210 K in the CuO-doped sample. The thermal expansion of this phase is extremely anisotropic, with the b axis expanding rapidly with increasing temperature while the a axis contracts slightly. At higher temperatures the doped samples transform directly from phase IV to phase II, bypassing phase III, starting at about 328 K. The structure of phase II, which is disordered, was refined in the space group P4/mbm. The structure of phase III contains hydrogen-bonded chains parallel to the b axis.

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 NO 3 − 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.

Misroscopic observation of phase transitions of ammonium nitrate

Phase transitions IV ⇌ II, IV ⇌ V and II ⇌ V of ammonium nitrate were observed through a polarizing microscope by using thin single crystals of various orientations. In the transition II ⇀ IV, a single crystal is split into two kinds of crystals, in which the direction of the c-axes is common but the a- and b-axes are interchanged. A composite pattern appears which is characteristic of the orientation of the initial crystal. The crystal composites have boundaries of {110} planes, which may be twinning planes. On the reserve transition, the composites are unified again. In both transformations, the new phase grows in a specified direction in the mother crystal in conformity with a minimum strain postulate. The IV ⇌ V transitions are very similar to the IV ⇌ II transitions except for the appearance on occasions of a faint chiaroscuro pattern of phase V. This pattern is probably due to the formation of microtwins. The II ⇌ V transitions occur as a second order transition in minute crystals within a temperature range from about 44°C to 41 °C. The transformation has been detected only by the same chiaroscuro pattern of phase V in some crystals as in the case of the IV ⇀ V transition. The observed transition phenomena are discussed on the basis of the crystal structures of the polymorphs of ammonium nitrate.

硝酸アンモニウムの誘電的性質と相転移

硝酸アンモニウムの誘電的性質と相転移

硝酸アンモニウムの相転移におよぼす添加剤の効果

硝酸アンモニウムの相転移におよぼす添加剤の効果