Enhancing the strength of granules and thermal stability of ammonium nitrate

The effect of sulfate ions on the physicochemical properties of ammonium nitrate with a dolomite additive was examined. Changes in the rate of the IV → III phase transition, granule strength, number of thermal cycles, and content of ammonium nitrate aerosol in air after the granulation tower were evaluated.     

Studies on the thermal dissociation of some carbonate minerals

Differential thermal investigations with pure synthetic carbonate minerals revealed a general lowering of the dissociation peak for magnesite, dolomite or calcite when present together in an artificial mixture. The presence of siderite did not affect the dissociation curves of these carbonates. A systematic study of this phenomenon using pure compounds with controlled grain size and other affecting parameters may help in understanding the dissociation curves of natural carbonate aggregates.

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Zusammenfassung Differentialthermoanalytische Untersuchungen an reinen synthetischen Karbonatgemischen von mineralischer Zusammensetzung zeigten im allgemeinen eine Verminderung in der Temperatur der Dissoziationsspitze von Magnesit, Dolomit und Kalzit, wenn sie gemeinsam zugegen waren. Siderit beeinflu\te den Verlauf der Dissoziation der Karbonate nicht. Eine systematische Untersuchung dieser Erscheinung mit Hilfe von reinen Verbindungen mit kontrollierter Korngrö\e und anderen beinflu\baren Parametern trÄgt zur KlÄrung der Dissoziationserscheinungen von natürlichen Karbonataggregaten bei.

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Résumé L'étude par ATD de carbonates minéraux synthétiques purs a montré un abaissement du pic de dissociation de la magnésite, de la dolomie, ou de la calcite, quand ils coexistent dans le mélange artificiel. La présence de sidérite n'affecte pas le mode de dissociation de ces carbonates. L'étude systématique de ce phénomène avec des composés purs, en contrÔlant la granulométrie et les autres paramètres, a permis de comprendre le mode de dissociation des agrégats des carbonates naturels.

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The thermal dissociation of some carbonate minerals

Detailed differential thermal studies on mixtures ofnatural carbonate minerals have confirmed the peak-temperature shifts recently reported for mixtures ofsynthetic carbonates and have established that such shifts can be attributed entirely to dilution effects. The exception, where magnesite in the presence of siderite maintains its peak position, is due simply to the fact that both minerals give similarly sized peaks at approximately the same temperature.

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Zusammenfassung Eingehende differentialthermische Untersuchungen von Gemischen natürlicher Karbonatmineralien zeigten ähnliche Spitzentemperaturverlagerungen wie kürzlich bei Gemischen von künstlichen Karbonatgemischen beobachtet wurden. Solche Verlagerungen sind ausschließlich Dilutionserscheinungen zuzuschreiben. Magnesit behielt zwar in Gegenwart von Siderit seine Spitzenpositionen, wofür jedoch der Umstand verantwortlich ist, daß beide Mineralien ähnliche und bei gleichen Temperaturen erscheinende Spitzen besitzen.

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Résumé L'étude de mélanges de carbonatesnaturels par les procédés thermiques différentiels a confirmé l'observation faite récemment d'un déplacement de la température au sommet du pic pour des mélanges de carbonatessynthétiques. On attribue ces déplacements entièrement aux effets de dilution. La magnésite en présence de sidérite constitue une exception. Dans ce cas, la position du pic reste inchangée du fait que ces deux minéraux donnent des phénomènes sensiblement identiques presque à la même température.

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Influence of lime-containing additives on the thermal behaviour of ammonium nitrate

Ammonium nitrate (AN) is one of the main nitrogen fertilizers used in fertilization programs. However, AN has some serious disadvantages — being well soluble in water hardly 50% of the N-species contained are assimilated by plants. The second disadvantage of AN is associated with its explosive properties. The aim of this paper was to clarify the influence of different lime-containing substances — mainly Estonian limestone and dolomite — as internal additives on thermal behaviour of AN. Commercial fertilizer grade AN was under investigation. The amount of additives used was 5, 10 or 20 mass%, or calculated on the mole ratio of AN/(CaO, MgO)=2:1 in the blends. Experiments were carried out under dynamic heating condition up to 900°C (10°C min⁻¹) in a stream of dry air or N₂ by using Setaram Labsys 2000 equipment coupled to Fourier transform infrared spectrometer (FTIR). The results of analyses of the gaseous compounds evolved at thermal treatment of neat AN indicated some differences in the decomposition of AN in air or in N₂. At the thermal treatment of AN’s blends with CaCO₃, MgCO₃, limestone and dolomite samples the decomposition of AN proceeds through a completely different mechanism — depending on the origin and the content of additives, partially or completely, through the formation of Mg(NO₃)₂ and Ca(NO₃)₂.     

The influence of dissociation reaction on ammonium nitrate thermal decomposition reaction

In order to investigate the influence of dissociation reaction on thermal decomposition of ammonium nitrate (AN), biochar was selected as an adsorbent to interfere with the dissociation of AN. The TG-DSC results showed that the notable exothermic reaction of AN with the presence of 2% or 7% biochar took place. The decomposition temperature of AN decreased with increasing amount of biochar. The notable knee point was found in the TG curves. The activation energy of AN with biochar in the initial stage was higher than that of AN itself. Remote sensing Fourier transform infrared experiments found biochar induced AN decomposition at about 190 °C, which was also confirmed by the TG-MS results. After dissociation reaction, HNO₃ (g) and NH₃ (g) were adsorbed and crystalline of AN was formed on the surface of biochar. With the increasing temperature, NH₃ escaped from the surface of biochar, while HNO₃ (g) was stayed in biochar. HNO₃ (g) catalyzed the thermal decomposition of AN and also reacted with biochar. The results indicated that dissociation reaction of AN played an important role during AN thermal decomposition process. When dissociation reaction was changed, the thermal decomposition reaction of AN would also change, catalysis or inhibition AN thermal decomposition. It is a useful reference to guide the AN additives selection and to understand the mechanism for the AN decomposition accident.

     

Phase transformation of ammonium nitrate by thermal factors and inoculation

The reason for the special thermal behaviour of ammonium nitrate (AN) has been examined. Under certain experimental conditions more transition temperatures were obtained than hitherto found (37–42°, 50° and 86°). With Du Pont DSC curves several exothermic peaks or exothermic oscillations were shown after the endothermic peak at 51°, indicating that phase IV had been transformed to metastable phase III, as a consequence of which the IIIII transformation at 86° also became possible. On repeated cycling the exothermic peak decreased or disappeared if the IIIII transformation had developed to a greater extent. A successful IVIII transformation was induced by inoculation of AN with phase III, an unusual procedure in investigating the phase transformation of AN. The use of the method is obvious with regard to the fact that all transformations are controlled by the rate of nucleation.

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Zusammenfassung Die Ursachen des besonderen thermischen Verhaltens von Ammoniumnitrat (AN) wurden untersucht. Unter gewissen Versuchsbedingungen wurden mehrere Übergangstemperaturen erhalten als bisher gefunden wurden (37°–42°, 51° und 86 °C). An Du Pont DSC Thermogrammen wurden mehrere exotherme Peaks oder exotherme Oszillationen nach dem endothermen Peak bei 51 °C nachgewiesen, welche zeigen, daß die Phase IV in die metastabile Phase III umgewandelt wurde. Infolgedessen wurde die Umwandlung IIIII bei 86 °C ebenfalls möglich. Bei wiederholtem Meßzyklus nahm der exotherme Peak ab oder verschwand, wenn die Umwandlung IIIII sich in größerem Maße entwickelte. Eine erfolgreiche IV III Umwandlung wurde durch Inokulierung mit der Phase III von AN induziert, was ein ungewöhnliches Verfahren bei der Untersuchung der Phasenumwandlung von AN ist. Die Vorteile dieser Methode sind offensichtlich, da sämtliche Umwandlungen durch die Geschwindigkeit der Nuklierung geregelt werden.

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Résumé On a étudié les causes du comportement thermique spécial du nitrate d'ammonium. Dans certaines conditions d'expériences, on a obtenu des températures de transition en plus grand nombre qu'il n'avait été trouvé auparavant (37–42 °C, 51 °C et 86 °C). On a mis en évidence sur des enregistrements obtenus à l'aide d'un appareil d'analyse calorimétrique différentielle DSC Dupont, plusieurs pics exothermiques ou oscillations exothermiques après le pic endothermique à 51°C, ce qui indique que la phase IV a été transformée en phase métastable III. Par conséquent, la transformation IIIII à 86 °C devient également possible. Lors du cyclage répété, le pic exothermique diminue ou disparaît si la transformation IIIII s'est développée dans une plus grande mesure. On induit avec certitude une transformation IVIII en inoculant le nitrate d'ammonium avec la phase III, procédure insolite dans l'étude des transformations de phases du nitrate d'ammonium. L'avantage de la méthode est évident, puisque toutes les transformations sont contrôlées par la vitesse de nucléation.

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The author is grateful to Prof. Z. G. Szabó for helpful criticism and for valuable discussions.     

Effect of metal oxides on the gamma radiolysis of ammonium nitrate

The studies of radiation decomposition of ammonium nitrate in the presence of MnO₂, PbO and V₂O₅ with the absorbed dose reveal that MnO₂ retards while PbO and V₂O₅ accelerate the rate of radiolysis. G/NO ₂ ^– / values were found to increase with the mole% of V₂O₅ in an admixture. The results are explained on the basis of electron donor-acceptor properties of oxides affecting the equilibrium concentration of electrons present in pure ammonium nitrate in the presence of the added oxides.     

Effect of polymer addition amount and type on thermal decomposition behavior of spray-dried particles comprising ammonium nitrate,potassium nitrate,and polymer

Certain properties of ammonium nitrate (AN), such as high hygroscopicity and the thermal transformation of the crystal structure accompanied by volume changes, pose problems for industrial applications of AN. To solve these problems, we previously prepared AN-based particles by spray-drying. The particles contained potassium nitrate (PN) as a phase stabilizer and a polymer (e.g., PVA, CMCs, and Latex) to produce a moisture-resistant material. Herein, we investigate the thermal decomposition of spray-dried AN/PN/polymer particles by differential scanning calorimetry and Thermogravimetry–Differential thermal analysis. Comparison of the thermal decomposition of AN/PN/polymer materials with different amounts and types of polymers suggested that thermal decomposition at lower temperatures resulted from the reaction of AN with the molten polymer or decomposition products derived from the polymer. Therefore, it can be concluded that the thermal stability of the AN/PN/polymer was exclusively determined by the thermal properties of the polymer components.     

The influence of titanium dioxides,alumina and calcium carbonate on the thermal stability of barium carbonate

Using static oxygen-bomb calorimetry, the standard enthalpies of combustion of the 2,4-and 2,6-isomers of dinitrophenol have been determined as ?2697.22 and ?2723.08 ± 3.18 kJ mole^?1, respectively. Standard enthalpies of formation have been calculated as ?235.50 and ?209.64 ± 3.27 kJ mole^?1, respectively.     

The influences of combinative effect of temperature and humidity on the thermal stability of pyrotechnic mixtures containing strontium nitrate as oxidizer

The influences of combinative effect of temperature and humidity on the thermal stabilities of three pyrotechnic compositions are investigated in the study. The thermal behavior for each pyrotechnic is analyzed by SETARAM thermal analyzer. Activation energy is determined by Kissinger method and critical temperature of thermal explosion (T _b) of pyrotechnic compositions is also calculated. The results of thermal analysis revealed that relative humidity could decrease the thermal stability of pyrotechnic mixtures. The critical temperature of thermal explosion (T _b) of each pyrotechnics decreased as the relative humidity increasing. Based on the value of T _b, the thermal stabilities of the pyrotechnic mixtures are in the order of S_r(NO₃)₂/Mg₄Al₃/PVC/PF > S_r(NO₃)₂/S_rCO₃/KClO₄/Mg₄Al₃/PVC/PF > S_r(NO₃)₂/KClO₄/Mg₄Al₃/PVC/PF. The thermal stability of S_r(NO₃)₂/Mg₄Al₃/PVC/PF show the best thermal stability than other two mixtures whether it is in the condition of humidity or not.     

Effect of the cation structure on the thermal stability of ionic liquids,quaternary ammonium tetrachloroferrates(III)

New ionic liquids, tetrachloroferrates(III) of quaternary ammonium salts [(CH₃)₂NR₁R₂]FeCl₄ [R₁ = CH₃; C₄H₉; (CH₂)₃CN. R₂ = C₁₀H₂₁; C₁₆H₃₃; CH₂CH₂OH; CH₂C₆H₅], were synthesized and their thermal stability was investigated in air in the range 25–600°С. The mechanism of thermal decomposition of the investigated ionic liquids is suggested in agreement with Hofmann’s rule as β-E2-elimination.     

Kinetics and mechanism of thermal decomposition of ammonium nitrate and sulfate mixtures

Fundamental kinetic aspects of the decomposition of mixtures and double salts of ammonium nitrate and ammonium sulfate were studied. The effect of water and sulfuric acid additives on the thermal decomposition rate of ammonium nitrate and sulfate mixtures was examined. The constant of proton exchange between nitric acid and the sulfate anion in molten ammonium nitrate was estimated.     

聚缩水甘油硝酸酯的热安定性和相容性研究

采用DSC、TG热分析方法研究了聚缩水甘油硝酸酯(PolyGLYN)的热安定性和与1,3,5-三硝基-1,3,5-三氮杂环己烷(RDX)间的相容性.结果表明,PolyGLYN在100℃以前较为稳定.当加热速率趋于零时PolyGLYN的热分解峰温为196.4℃,由Ozawa法计算的热分解表观活化能为182.0 kJ·mol-1,分别比RDX的低15.1℃和高22.2 kJ·mol-1.PolyGLYN热稳定性与RDX接近,两者之间的相容性较好.     

Preparation and thermal studies of chloride containing cerous carbonate compounds

Two chloride containing cerous carbonate compounds, formulated as Ce₃Cl(CO₃)₄ and Ce₄Cl(OH)₃(CO₃)₄, have been synthesized by carbonation of cerous oxychloride in pyridine/H₂O mixtures at elevated temperatures. Pyridinium chloride has been identified as a reaction product. These compounds have been characterized by IR spectral and X-ray diffraction techniques. Thermal decomposition studies indicate that the final solid product at 873 K in the absence of steam is a mixture of ceric oxide and cerous oxychloride, the amount of each being dependent upon the Cl⁻/Ce ratio in the initial compound. The thermal reaction pathway of both compounds involves initial decomposition to cerous dioxymonocarbonate and cerous oxychloride with concomitant carbon dioxide evolution. The cerous dioxymonocarbonate subsequently oxidizes at higher temperature to ceric oxide via carbon monoxide evolution. The utility of these new cerium(III) chlorocarbonate phases in heat cycles for water splitting is discussed.     

Effect of zinc borate on the thermal degradation of ammonium polyphosphate

The thermal behaviour of a mixture containing an ammonium polyphosphate based compound (AP760) and zinc borate (ZB) is investigated. After an investigation of the degradation of the pure components, the interactions between them are examined by thermogravimetry. Then, X-ray diffraction (XRD) and ¹¹B and ³¹P solid-state nuclear magnetic resonance (NMR) measurements have been carried out on residues of mixtures of AP760 and FBZB heat treated at different characteristic temperatures. It reveals the nature of the interactions taking place between the two components. It is demonstrated that reactions lead to the formation of zinc phosphate and of borophosphates. Mechanisms of thermal degradation are proposed.     

Effect of electric fields on the thermal decomposition of calcium carbonate

The thermal decomposition of CaCO₃ powder and single crystal samples to CaO has been shown by X-ray diffraction and ESCA to be assisted by the application of external DC electric fields during the reaction. The effect is particularly marked at the positive electrode. The results are discussed in terms of both ionic migration effects and the field-induced electro-adsorption/electro-desorption of gaseous CO₂ at the surface of a semiconductor. Approximate calculations based on both theories show that ionic migration cannot account for the magnitude of the observed effects, but a reasonably satisfactory explanation is provided by the application of semi-conductor surface theory to the system.     

Effect of grinding on thermal reactivity of ceramic clay minerals

The effect of grinding on thermal behavior of pyrophyllite and talc as commonly used ceramic clay minerals was investigated by DTA, TG, emanation thermal analysis (ETA), B.E.T. surface area (s.a.) measurements, X-ray diffraction (XRD) and scanning electron microscopy (SEM). A vibratory mill was used in this study, grinding time was 5 min. It was found that the grinding caused an increase in surface area and a grain size reduction of the samples. From TG and DTA results it followed that grinding caused a decrease of the temperature at which the structure bound OH groups released. The formation of high temperature phases was enhanced with the ground samples. For the ground talc sample the crystallization of non-crystalline phase into orthorhombic enstatite was observed in the range of 800°C. For ground pyrophyllite a certain agglomeration of grains was observed in the range above 950°C. Moreover, for both clays the ETA characterized a closing up of subsurface irregularities caused by grinding as a decrease of the emanation rate in the range 250–400°C. The comparison of thermal analysis results with the results of other methods made it possible to better understand the effect of grinding on the ceramic clays.     

Catalytic effect of lithium titanate oxide doped with praseodymium on thermal decomposition of ammonium nitrate

Journal of Thermal Analysis and Calorimetry - In this work, lithium titanate oxide (Li4Ti5O12) (LTO) and praseodymium ion doped in lithium titanate oxide (Pr-LTO) were synthesized in a...     

Polypropylene fabrics padded with microencapsulated ammonium phosphate: Effect of the shell structure on the thermal stability and fire performance

Three types of microcapsules of di-ammonium hydrogen phosphate (DAHP) with different polymeric shells were evaluated as flame retardants in commercial polyurea padding for textiles. Encapsulated FR agent has the advantage of being compatible with the polymer matrix. The thermal degradation for the three types of DAHP microcapsules shows that our microcapsules act as intumescent fire retardants. The reaction to fire of polypropylene fabrics padded with FR polyurea loaded with neat DAHP or microencapsulated DAHP was studied with the cone calorimeter as a fire model.     

Synthesis and thermal stability of hydrotalcites containing manganese

The hydrotalcite based upon manganese known as charmarite Mn₄Al₂(OH)₁₂CO₃·3H₂O has been synthesised with different Mn/Al ratios from 4:1 to 2:1. Impurities of manganese oxide, rhodochrosite and bayerite at low concentrations were also produced during the synthesis. The thermal stability of charmarite was investigated using thermogravimetry. The manganese hydrotalcite decomposed in stages with mass loss steps at 211, 305 and 793 °C. The product of the thermal decomposition was amorphous material mixed with manganese oxide. A comparison is made with the thermal decomposition of the Mg/Al hydrotalcite. It is concluded that the synthetic charmarite is slightly less stable than hydrotalcite.