Kinetics and mechanism of thermal decomposition of hydroxylammonium nitrate

The kinetics of thermal decomposition of melted hydroxylammonium nitrate have been investigated by the rate of heat production in the temperature range 84.8–120.9°C. The decomposition proceeds with autocatalysis and up to 60 % of conversion the rate of the process increases proportionally to the square of the degree of decomposition. The initial rate is proportional to the square of the concentration of HNO₃ formed due to dissociation of the salt. The activation energy of this process is 15.3±1.8 kcal/mol. It is suggested that the initial stage the process proceeds via interaction between N₂O₃ and NH₃OH⁺, whereas the subsequent acceleration is due to oxidation of NH₃OH⁺ by nitrogen oxides formed as well as by nitrous acid.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1897–1901, November, 1993.     

The thermal decomposition of cerium(III) nitrate

The thermal decomposition of anhydrous Ce(NO₃)₃ has been studied. The thermal decomposition reaction is described by the second order kinetic equation, [1/(1–)]–1=kt. The apparent activation energy was determined asE _a=104 kJ mol^–1 while the enthalpy of the reaction was estimated asH _r=111.1 kJ mol^–1. The decomposition reaction differs from that observed for Nd(NO₃)₃.

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Zusammenfassung Die thermische Zersetzung von wasserfreiem Ce(NO₃)₃ wurde untersucht. Die thermische Zersetzung wird durch die Geschwindigkeitsgleichung zweiter Ordnung[1/(1–)]–1=kt, beschrieben. Für die scheinbare Aktivierungsenergie wurde ein Wert von 104 kJ mol^–1 und für die Enthalpie der Reaktion ein Wert von 111,1 kJ mol^–1 ermittelt. Die Zersetzungsreaktion unterscheidet sich von der für Nd(NO₃)₃.

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. : [1/(1–)]– 1=kt. a, 104 · ^–1, H _r, 111.1 · ^–1. .

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The authors wish to thank the Council for Scientific and Industrial Research and the University of Pretoria for financial assistance.     

Mechanism of thermal decomposition of hydrated copper nitrate in vacuo

The general scheme of three-stage thermal decomposition of Cu(NO₃)₂·3H₂O to CuO has been refined based on evolved-gas-analysis data with a quadrupole mass analyzer (Jackson et al., Spectrochim. Acta Part B, 50 (1995) 1423). Quantitative evaluation of the composition of the gaseous products shows that the first stage involves primarily deaquation, and the second stage, primarily denitration of the original hydrated nitrate. The basic nitrate formed in the second stage most probably has the formula Cu(NO₃)₂·3Cu(OH)₂. It has been established that the molecular oxygen observed in the third stage of decomposition is produced by catalytic decomposition of NO₂ on the surface of CuO. The presence of Cu-containing ions in all stages of the process is consistent with the gasification mechanism of thermal decomposition.     

Kinetics of autocatalytic thermal decomposition of perchlorates in molten nitrate solutions

The rates of perchlorate decomposition in various molten salt solvents have been studied. Activation energies of both catalytic and noncatalytic processes are close and the differences between the rates of these two processes are due to the variations of pre-exponential factors.

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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.

     

The thermal decomposition of aqueous manganese (II) nitrate solution

The thermal decomposition of commercially available aqueous solutions of manganese(II) nitrate was investigated using the conventional thermal analytical techniques of thermogravimetry (TG), differential thermal analysis (DTA), and evolved gas analysis (EGA). Infrared spectra and X-ray diffraction patterns were used to help characterize intermediate species.     

Physico-chemical characterization of thermal decomposition course in zinc nitrate-copper nitrate hexahydrates

This study reports experimental investigations by non-isothermal TG/DSC analysis of Zn(NO₃)₂·4H₂O, Cu(NO₃)₂·4H₂O and their mixtures of known compositions in the temperature range 30–1200°C. Solid/liquid transitions in the sealed samples of the hexahydrate salts and their mixtures were also studied by DSC in the temperature range 0–60°C. The mixture with composition 0.85Zn(NO₃)₂·6H₂O+0.15Cu(NO₃)₂·6H₂O showed single melting peak at 29°C. This mixture was chosen for detailed studies. Melting temperature and heat of fusion of single salt hexahydrates and of the mixture were calculated from DSC endotherms. The different stages in the thermal decomposition processes have been established. The intermediate and the final solid products of the thermal decomposition were analyzed by XRD. The scheme and the decomposition temperature depended on the composition of the starting material. The final decomposition products were CuO (monoclinic), Cu₂O (cubic), ZnO (hexagonal) and their mixtures with the defined crystalline structures. Possible influence of the addition of CuCl₂·2H₂O into the mixture 0.85Zn(NO₃)₂·6H₂O+0.15Cu(NO₃)₂·6H₂O and a gel combustion technique of the precursor preparation, on the composition and morphology of the solid decomposition products, were also studied. The gel combustion technique, using citric acid added to a mixture of 0.85Zn(NO₃)₂·6H₂O+0.15Cu(NO₃)₂·6H₂O, was applied in an attempt to obtain mixed Zn/Cu oxides of a particular mole ratio. The morphology of the solid decomposition products was examined by SEM.     

Gas-phase thermal isomerization of hexachlorocyclopropane

The gas-phase thermal isomerization of hexachlorocyclopropane to hexachloropropene at 208–283°C is first order and unaffected by changes in the surface-to-volume ratio or by the addition of iodine, tetrachloroethylene, and oxygen. The first-order rate constants fit the Arrhenius equation The reaction was interpreted as an unimolecular process taking place with chlorine atom migration. A comparison of the reactivities of several chlorocyclopropanes is made.     

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.     

The effect of γ-irradiation on the thermal decomposition of strontium nitrate

The thermal decomposition of -irradiated strontium nitrate was studied by dynamic thermogravimetry. The reaction order, activation energy, frequency factor and entropy of activation were computed by means of the Coats-Redfern method and were compared with those for the unirradiated salt. It has been suggested that NO₂ formed under irradiation catalyzes the decomposition.     

Kinetics of the thermal decomposition of anhydrous cobalt nitrate by SCRT method

It has been shown the ability of the Sample Controlled Reaction Temperature (SCRT) method for both discriminate the kinetic law and calculate the activation energy of the reaction. This thermal decomposition is best described by a Johnson–Mehl–Avrami kinetic model (with n = 2) with an activation energy of nuclei growth which fall in the range 52–59 kJ mol^?1. The process is not a single-step because the initial rate of decomposition is likely to be limited by nucleation. The results reported here constitute the first attempt to use the new SCRT method to study the kinetic of the thermal decomposition of cobalt nitrate.     

Kinetic analysis of thermal decomposition of praseodymium(III) nitrate hexahydrate

The kinetics of thermal decomposition of praseodymium(III) nitrate hexahydrate was studied by using isothermal and dynamic thermogravimetric techniques. Kinetic analysis of the isothermal data with respect to various solid-state reaction models showed that the reaction is best described by phase boundary-controlled and random nucleation models. Kinetic analysis of the dynamic TG curves was discussed and a critical comparison was made of two integral methods, that of Coats and Redfern and that of Ozawa. The results showed that the Ozawa method gives a better correlation, and the results are in good agreement with those obtained under isothermal thermogravimetric conditions.

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Zusammenfassung Mittels isothermer und dynamischer thermogravimetrischer Methoden wurde die Kinetik der thermischen Zersetzung des Hexahydrates von Praseodymnitrat untersucht. Eine kinetische Auswertung der isothermen Meßdaten unter Anwendung verschiedener Feststoffreaktionsmodelle ergab, daß die Reaktion am besten durch ein phasengrenzenkontrolliertes Randomkeimbildungsmodell beschrieben werden kann. Die kinetische Auswertung der dynamischen TG-Kurven wurde diskutiert und ein kritischer Vergleich zwischen zwei Integriermethoden, der von Coats und Redfern und der von Ozawa, angestellt. Die Betrachtungen ergaben, daß die Methode von Ozawa eine bessere Korrelation liefert und daß die Resultate gut mit denen der isothermen thermogravimetrischen Messungen übereinstimmen.

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The effect of gamma-irradiation on the thermal decomposition of anhydrous cadmium nitrate

The thermal decomposition of -irradiated anhydrous cadmium nitrate was studied by dynamic thermogravimetry. The reaction order, activation energy, frequency factor and entropy of activation were calculated by the Coats-Redfern method and were compared with those of the unirradiated salt. Irradiation enhances the decomposition and the effect increases with the irradiation dose. The activation energy decreases on irradiation. The mechanism of the decomposition of unirradiated and irradiated anhydrous cadmium nitrate follows the Mampel equation: -ln(1-) for g() and the rate-controlling process is random nucleation with the formation of a nucleus on every particle.     

The agent of the autocatalytic thermal decomposition of aliphatic nitrate ester explosives

The condensed-phase thermal decomposition of aliphatic nitrate ester explosives is generally autocatalytic. The object of this article is to show that the agent of the autocatalysis is not the product NO₂, as is generally believed, but to suggest that it may be the product formaldehyde.     

Synthesis and thermal decomposition of antimony(III) oxide hydroxide nitrate

The thermal decomposition of the only known antimony nitrate antimony(III) oxide hydroxide nitrate Sb₄O₄(OH)₂(NO₃)₂, whose synthesis routes were reviewed and optimized was followed by TG-DTA under an argon flow, from room temperature up to 750°C. Chemical analysis (for hydrogen and nitrogen) performed on samples treated at different temperatures showed that an amorphous oxide hydroxide nitrate appeared first at 175°C, and decomposed into an amorphous oxide nitrate above 500°C. Above 700°C, Sb₆O₁₃ and traces of -Sb₂O₄ crystallized.Author to whom all correspondence should be addressed     

Computerized modeling of intermediate compounds formed during thermal decomposition of gadolinium nitrate hydrate

It was shown that after partial dehydration occurs a simultaneous condensation of four mol of initial monomer Gd(NO₃)₃ · 6H₂O into a tetramer Gd₄O₄(NO₃)₄. The heterocycle containing 4 gadolinium atoms gradually loses N₂O₅ and, through the formation of unstable oxynitrates, is transformed into Gd₂O₃. The interatomic distances and angles were calculated using the molecular mechanics method. The comparison of the potential energies of consecutive oxyphosphates permitted an evaluation of their stability. The models of intermediate oxynitrates represent a reasonably good approximation to the real structures and a proper interpretation of experimental data.     

Reactivity of amorphous aluminas prepared by the thermal decomposition of aluminum chloride and nitrate

The physicochemical properties and reactivity of amorphous aluminas, Al₂O₃(C1) and Al₂O₃(N), which were prepared by the thermal decomposition of AlCl₃ · 6 H₂O and Al(NO₃)₃ · 9 H₂O at 600°C for 2–300 h, were investigated by means of TG, DTA, X-ray diffraction, SEM and IR. The reactivity of Al₂O₃(Cl) for ZnAl₂O₄ formation was, in general, higher than that of Al₂O₃(N) and was influenced by the content of residual chlorine in Al₂O₃(Cl). The rate of ZnAl₂O₄ formation followed the Avrami—Erofeev equation in the ZnOAl₂O₃(Cl) system and the Jander equation ZnOAl₂O₃(N) system, respectively.     

Isothermal decomposition of urea nitrate

The kinetics of isothermal decomposition of urea nitrate, an organic secondary explosive with monoclinic structure and chemical formula CO(NH₂)₂ · HNO₃, which melts with decomposition at 152°C, was studied in open air in the temperature range 106-150°C, using a gravimetric method. Gas chromatographic analysis of product gases indicate CO₂, N₂O and traces of water vapor as product gases. A pasty amorphous product on the basis of wet chemical and infrared analysis was found to be cyanourea. The weight loss-time curve exhibited an acceleratory region extending almost to the end of the main reaction (35% decomposition) and followed a three-dimensional nucleation model obeying the relation x^1/3 = K(t—t₀ where α = fraction of sample reacted at time t, K = reaction rate constant, and t₀ = induction time. On the basis of this model, an enthalpy of activation of 27.6 ± 1.2 kcal/mole was calculated at 95% confidence range. The rate of decomposition was slightly accelerated in He atmosphere and slightly retarded in N₂O and CO₂ atmospheres, while water vapor drastically reduced the rate. The reaction 3CO(NH₂)₂ · HNO₃ → CNNHCONH₂ (cyanourea) + 6H₂O+3N₂O+CO₂ is presented as the most likely one for decomposition of urea nitrate in open air.     

Kinetics of the thermal decomposition of cellulose nitrate over a wide range of nitrogen contents

We have studied the kinetics of the thermal decomposition of cellulose nitrate at 167.4°C in a vacuum for the range of nitrogen contents from 0.09 to 13.45%. The rate constants of the initial and autocatalytic stages have been determined. The method of nitrating cellulose with a mixture of the vapors of water and nitric acid in a previously evacuated sealed vessel has no special effect on the thermal kinetic properties of the cellulose nitrate produced. It is shown from the experimental results that at 167.4°C the rate constant for the loss of NO₂ groups in the primary position is about 14 times less than for those in the secondary position.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1273–1279, June, 1990.