Phase Transition Of Ammonium Nitrate Research Articles

Alternative solutions for the physicochemical evaluation and improvement of the caking properties of calcium ammonium nitrate fertilizer as a quality problem under atmospheric conditions

ABSTRACT Fertilizers are very sensitive to climatic conditions due to their hygroscopic nature. They tend to absorb moisture, weaken and accordingly lose their free-flowing property depending on the ambient conditions. In this study, the influence of storage conditions on a commercial grade calcium ammonium nitrate (CAN/26) fertilizer was investigated using methods that included simulation of storage and handling. The mechanical properties of CAN/26 fertilizer were observed by friability and crushing strength tests. Granule structure begins to weaken especially above a temperature of 40°C and a pressure of 0.33 kg/cm2. Sudden changes in ambient temperature enhance the caking propensity by 4.8%. Fertilizers above 65% relative humidity start to absorb moisture and degrade at very high temperatures. The phase transition of ammonium nitrate between crystalline forms plays an important role in the caking of CAN/26, as its tendency to agglomerate at about 32°C is greatly reduced. The results show that the granule degradation in CAN/26 fertilizer increases almost linearly with increasing temperature, humidity, and pressure but there is a sharp limit for each parameter for degradation to start. With these limits, it may be possible to carry out the protection and control of the good quality of fertilizers in the sector.

Thermal stability of ammonium nitrate systems containing d-metal nitrate salts under limited mass transfer conditions

The influence of cobalt, copper, iron(III), manganese and zinc nitrate salts on phase transitions and thermal stability of ammonium nitrate (AN) has been studied and discussed. Differential thermal analysis/differential scanning calorimetry coupled with thermogravimetry and mass spectrometry were used to evaluate the stability of analyzed systems. Each nitrate salt was appropriately mixed with ammonium nitrate to create samples with AN:salt mass ratios of 4:1, 9:1 and 49:1. It was concluded that the addition of every studied nitrate influenced phase transitions of AN. Most analyzed salts decreased the stability of AN by accelerating its exothermic decomposition process. Iron and cobalt nitrates were defined as the most hazardous additives, resulting in a creation of a highly destabilized mixture. Copper and manganese nitrates were also defined as catalysts of the AN decomposition process, lowering the initial decomposition temperature and increasing the rate of the observed process. Zinc nitrate hexahydrate was the only salt considered to be relatively neutral in such systems, especially in small amounts. The study allowed to define the influence of selected metal nitrate salts on the thermal stability of AN under conditions that are considered as potentially unsafe for such systems.

Crystalline Phase Transitions and Reactivity of Ammonium Nitrate in Systems Containing Selected Carbonate Salts

Samples of pure ammonium nitrate (AN) and its mixtures with calcium carbonate, potassium hydrogen carbonate and potassium carbonate were investigated with the use of differential thermal analysis with mass spectrometry, powder X-ray diffraction and scanning electron microscopy. The main objective of the study was to determine the influence of selected carbonate materials on phase transitions of ammonium nitrate and to consider a possibility to use such potassium salts as fillers in fertilizer production. It was proven that all carbonate salts caused the absence of a phase transition that normally would occur at around 84–86 °C. Potassium carbonates were too reactive in systems containing AN. Based on the performed study, it was concluded that even though potassium carbonates are not fit to replace mineral fillers in the production process of fertilizers containing ammonium nitrate, they could be used in lesser amounts to remove the presence of low-temperature phase transitions of AN.

Understanding phase transition and vibrational mode coupling in ammonium nitrate using 2D correlation Raman spectroscopy

Ammonium nitrate (AN) is an important component of the chemical industry such as an active ingredient in fertilizers, as an oxidizer in explosive compositions and propellants, and as a blasting agent in civil explosives. Numerous accidents have been reported in the past which concerns its thermal instability and poses a big threat to its processing, transportation, and storage. Despite much literature being reported to understand its thermal instability, a mechanistic view remains unclear. In the present work, we have studied the behavior of AN to temperature change using a mathematical approach called 2D correlation (2D Cos) Raman spectroscopy to provide complete insight into the detailed dynamical nature of the interactions between the species (ionic or molecular) occurring with an increase in temperature. We have analyzed various libration and translational modes of nitrate in the low-frequency region using this mathematical tool. It is observed from 2D maps that the phase transition of AN starts with changes in libration modes followed by various nitrate modes and ammonium modes which further precedes low-frequency translational modes. Further, the 2D correlation could differentiate between modes splitting and shifting based on specific 2D Cos pattern. The changes occurring in the N-O deformation modes, symmetric stretching modes as well as anti-symmetric stretching modes which have been attributed to the weakening of the hetero-ionic coupling between the NH4+ and the NO3– ions could be clearly distinguished in the 2D synchronous and asynchronous plots. Besides, moving window analysis was performed to visualize the transition temperature at which phase change of AN takes place.

Effect of Potassium Nitrate on Anti-Caking Performance of AN-based NPK Granular Compound Fertilizer

Agricultural ammonium nitrate(ANP) is one of the main raw materials for the production of AN-based compound fertilizer. The IV-III phase transition of ammonium nitrate(AN) is one of the main reasons for the caking of AN-based compound fertilizer(NPK). Potassium salts used for the production of compound fertilizers are usually K2SO4(KS). In this paper KNO3(KN) was added to improve the anti-caking properties of AN-based NPK. The IV-III phase transition of ANP and the effects of KN, KS, NH4SO4(NS), and NH4H2PO4(NP) on the solid phase transitions of ANP was investigated by differential scanning calorimetry (DSC) and powder X-ray diffractometer(XRD). The results showed that the phase transformation inhibition effect of KN and KS on ANP was better than that of NS and NP. In this experiment, KN was used to replace part of KS in the formula of AN-based NPK, and the granular fertilizer with different contents of KN were prepared, the anti caking properties and hygroscopicity of the fertilizer were tested. The results showed that although the content of potassium in the compound fertilizer remained unchanged, with the increase of the content of KN and the decrease of the content of KS in the formula, the anti-caking performance and hygroscopicity of the AN-based NPK were obviously improved.

Influence of selected potassium salts on thermal stability of ammonium nitrate

Ammonium nitrate (AN) has proven to be an unstable and hazardous component of mineral fertilizers. In order to analyze the influence of various potassium salts on thermal properties of ammonium nitrate, differential thermal analysis coupled with thermogravimetry and mass spectrometry was used. Each potassium salt was mixed with AN to create samples with AN:salt mass ratios of 4:1, 9:1 and 49:1. It was concluded that an addition of potassium influences phase transitions of AN. Depending on the salt used, an exothermic decomposition of AN was either accelerated (potassium chloride) or inhibited to the varying degree. Carbonate salts and potassium metabisulfite were too reactive to be used in a fertilizer production, while nitrate, sulphate and both phosphates are considered to be appropriate additives and could be used in a multicomponent fertilizer production.

PECULIARITIES OF MANUFACTURING AND APPLICATION OF MIXED EXPLOSIVES OF ANFO TYPE AT MINING ENTERPRISES OF MONGOLIA

Рассмотрены вопросы производства взрывных работ, проводимых в промышленных масштабах c применением аммиачно-селитренных взрывчатых веществ. На основании экспериментальных исследований, выполненных авторами, было определено, что для использования на горных предприятиях Монголии, в первую очередь на угольных разрезах, наиболее рациональными и эффективными являются смесевые взрывчатые вещества на основе аммиачной селитры в твердом состоянии с различными жидкими, а также твердыми дисперсными горючими добавками – смеси типа АСДТ или ANFO. Определены температурные границы для фазовых переходов аммиачной селитры на открытых площадках в течение трех месяцев для различной влажности. Установлены показатели маслопоглощения в зависимости от цикла фазовых переходов для аммиачной селитры.

Ammonium nitrate-MOF-199: A new approach for phase stabilization of ammonium nitrate

In this work we have utilized MOF-199 as a well known copper-based metal-organic framework (MOF), to study the thermal behavior of ammonium nitrate (AN). Our results indicate that MOFs improve thermal behavior of AN through their Lewis/Brønsted acid sites as well as their porous structure. Accordingly, MOF-199 (at least 5% by weight) stabilizes phase transition of AN up to 125 °C while [Cu2(bdc)2(bpy)]n is not a suitable MOF of choice. In addition, DSC studies showed a sharp exothermic peak for AN-MOF-199 composite related to the rapid catalytic combustion of the composite.

Effects of amino acids on solid-state phase transition of ammonium nitrate

The purpose of this study was to obtain a better understanding of the effects of amino acids on the solid-state phase transitions of ammonium nitrate (AN). To this end, AN was combined with various amino acids in equimolar ratios and the phase transitions of the resulting mixtures were studied using differential scanning calorimetry (DSC) and in situ Raman spectroscopy. Compositional analysis was also conducted using X-ray powder diffraction (XRD), and the predicted stabilities of various molecular structures were assessed via quantum calculations. DSC and Raman results indicated that l-glycine and l-alanine inhibited the solid-state phase transitions of AN. Both XRD and calculation results suggested that AN reacts with these amino acids to form nitrate salts and that clusters are also generated by interactions between these compounds.

Phase Stability of Ammonium Nitrate with Organic Potassium Salts

A study has been undertaken on the effect of additives on the phase transition of ammonium nitrate(V) (AN). Results obtained using Differential Scanning Calorimetry (DSC) showed that organic compounds and potassium salts of organic compounds have an effect on the phase transition behavior of AN. The samples were further analyzed using infrared (IR) and powder X-ray diffraction (XRD). The mechanism of phase stabilization of AN by compounds of this kind was examined. The present study showed that the influence of additives on the phase transition of AN occurs through the polar groups that are involved in intermolecular interactions of orbital and electrostatic types that form new hydrogen bonds. AN exists in only one phase in the temperature range from 30 °C to +100 °C, when a potassium salt of organic compounds was added. However, with organic compounds, the III→II phase transition was changed. IR and XRD of composites are characterized by new intermolecular interactions. Compacted samples of AN containing potassium salts of organic compounds exhibited better stability than AN containing organic compounds to multiple cyclic changes within a temperature range. This we named 'freezing and thawing analysis'. Additives have two functions on the AN phase transition. First, solid solutions of AN mixture were formed for K + replacement of NH4 + . Second, hydrogen bonds formed, which caused AN and salts of organic compounds to interact intimately

Nanoconfined Solid–Solid Transitions: Attempt To Separate the Size and Surface Effects

The solid–solid phase transitions in ammonium nitrate, ammonium perchlorate, and sodium nitrite confined to native and organically modified silica nanopores are analyzed by differential scanning calorimetry. The study reveals the effect of nanoconfinement on the transition temperature and links it to the kinetic parameters of the process. It is suggested that the effect of nanoconfinement is primarily the surface interaction effect in the native pores and the size effect in organically modified pores. It has been found that in organically modified pores the transition temperature is always depressed relative to the bulk, whereas in the native pores its behavior is generally unpredictable. Kinetic analysis of the transitions in terms of a nucleation model indicates that the experimentally observed shifts in temperature can be explained by a combination of changes in the free energy of nucleation and preexponential factor of the respective processes.

Rheological Properties and Stability of Highly Concentrated Water-In-Oil Emulsions with Different Emulsifiers

An investigation was performed into the effect of emulsifiers on the rheological properties and stability of highly concentrated water-in-oil emulsions (HCEs). The emulsifiers were oligomers of the polyisobutylene succinic anhydride (PIBSA) based on different head-group and relatively low molecular weight sorbitan monooleate (SMO). The viscosity and storage modulus of HCE depend on the nature of head-groups of PIBSA-based emulsifiers and the ratio of SMO. It was shown that an increase in the SMO concentration results in the increase of viscosity and storage modulus. The stability of HCE with aging is also influenced by the nature of emulsifiers. The results of the precipitation of ammonium nitrate and the change of storage modulus with time show that the increase in the ratio of SMO decreases the stability of HCE. It was found that the phase transition of ammonium nitrate is important for the stability of HCE.

A large‐eddy simulation of the phase transition of ammonium nitrate in a convective boundary layer

Under warm and dry conditions, ammonium nitrate aerosol outgasses to form ammonia and nitric acid in the lower atmospheric boundary layer. In the upper boundary layer, where the temperature is lower and the relative humidity is higher, nitric acid and ammonia condense back to the aerosol phase. Measurements show that aerosol nitrate mixing ratios increase with altitude, confirming this phase transition. Since phase equilibrium is not reached instantaneously, updrafts transport aerosol‐poor air from the surface to high altitudes and aerosol‐rich air subsides from high altitudes to the surface under turbulent conditions. As a result, the partitioning deviates from equilibrium, so the horizontal and temporal variabilities of the aerosol nitrate mixing ratio are enhanced and a continuous downward aerosol nitrate flux emerges. We postulate that observations of this variability and flux should not be interpreted as instrument noise and deposition of nitrate. In an idealized large‐eddy simulation (LES) experiment of a convective boundary layer, we find that the larger variability and flux occurred at about one third of the boundary layer height. Both are largest when the gas‐aerosol partitioning time scale is assumed to be about half the time scale of turbulence. Our LES result shows negatively skewed nitrate mixing ratios. Under colder conditions, a smaller fraction of ammonium nitrate aerosol outgasses at the surface, so the absolute effect of nitrate repartitioning becomes smaller. However, dimensionless statistical properties do not change as long as the turbulent properties of the boundary layer remain similar. This indicates that the identified processes are also present under colder conditions.

Correction to “Pressure-Induced Isostructural Metastable Phase Transition of Ammonium Nitrate”

Correction to “Pressure-Induced Isostructural Metastable Phase Transition of Ammonium Nitrate”

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.

Phase stability in the system constituted by ammonium nitrate, potassium dichromate, and alkaline-earth metal nitrates

Methods for modification of ammonium nitrate as an oxidizing agent for ecologically safe solid propellants were sought for and the influence exerted on phase transitions in ammonium nitrate by three-component inorganic additives in which a synergic effect lowering the transition energy is manifested was determined.

Thermal behaviour of CuO doped phase-stabilised ammonium nitrate

Copper phase-stabilised ammonium nitrate (Cu-PSAN) was prepared by the incorporation of copper(II) oxide (CuO) into the ammonium nitrate (AN) crystal lattice by a melt process. We studied the phase transitions of ammonium nitrate and dimensional changes occurring during this phase stabilisation process. Crystallographic aspects of the solid-state reaction between AN and CuO and thermal behaviour of phase-stabilised ammonium nitrate (PSAN) are discussed. It was found that solid-state reaction occurred by an intermediate solid solution formation. Lattice parameters and unit cell volume are calculated as a function of temperature from XRD patterns. They show a non-linear and anisotropic behaviour with increasing temperature. Lattice expansion along b-axis and contraction along a- and c-axes are observed. Unit cell volume increases with temperature.

Experimental determination of NH4NO3-KNO3 binary phase diagram

The solid-state phase transitions in ammonium nitrate (AN)-potassium nitrate (KN) system, and the equilibrium AN-KN phase diagram have been determined by using differential scanning calorimetry and high-temperature in situ x-ray diffractometry. Sample preparation was performed in a special “dry room” with very low humidity. A single phase region (AN III) with no phase transitions to 373 K was observed in the composition range 5 to 20% KN; this is critical for use in air bag gas generators. The high-temperature KN phase (KN I) has a wide range of stability from 20 to 100 wt.% KN. There are one eutectic, two eutectoid, three peritectoid, and one congruent transformations in this phase diagram. Two new nonstoichiometric phases were found at lower temperatures in the mid-composition range between the AN and KN terminal solid solutions. Details of the phase equilibria are presented.

Molecular dynamics studies of melting and solid-state transitions of ammonium nitrate.

Molecular dynamics simulations are used to calculate the melting point and some aspects of high-temperature solid-state phase transitions of ammonium nitrate (AN). The force field used in the simulations is that developed by Sorescu and Thompson [J. Phys. Chem. A 105, 720 (2001)] to describe the solid-state properties of the low-temperature phase-V AN. Simulations at various temperatures were performed with this force field for a 4 x 4 x 5 supercell of phase-II AN. The melting point of AN was determined from calculations on this supercell with voids introduced in the solid structure to eliminate superheating effects. The melting temperature was determined by calculating the density and the nitrogen-nitrogen radial distribution functions as functions of temperature. The melting point was predicted to be in the range 445 +/- 10 K, in excellent agreement with the experimental value of 442 K. The computed temperature dependences of the density, diffusion, and viscosity coefficient for the liquid are in good agreement with experiment. Structural changes in the perfect crystal at various temperatures were also investigated. The ammonium ions in the phase-II structure are rotationally disordered at 400 K. At higher temperatures, beginning at 530 K, the nitrate ions are essentially rotationally unhindered. The density and radial distribution functions in this temperature range show that the AN solid is superheated. The rotational disorder is qualitatively similar to that observed in the experimental phase-II to phase-I solid-state transition.

A solid-state nitrogen-15 NMR study of the phase transitions in ammonium nitrate

The five solid phases of NH 4 NO 3 and transitions between these phases are studied using solid-state 15 N magic angle spinning (MAS) and static NMR. The thermal behavior of this substance is explored by means of the MAS chemical shifts. A magnetic nonequivalence in the NO 3 - ions of phase V is observed. The principal values of the chemical shift tensors of the NO 3 - in all five phases are determined. The evidence of crystal packing deformations is seen in the static NO 3 - spectra of phases V through II