Heating rate effect on the thermal behavior of ammonium nitrate and its blends with limestone and dolomite

The effect of heating rate on the thermal behavior of ammonium nitrate (AN) and on the kinetic parameters of decomposition of AN and its blends with limestone and dolomite was studied on the basis of commercial fertilizer-grade AN and several Estonian limestone and dolomite samples. Experiments were carried out under dynamic heating conditions up to 900 °C at heating rates of 2, 5, 10 and 20 °C min⁻¹ in a stream of dry air using Setaram Labsys 2000 equipment. For calculation of kinetic parameters, the TG data were processed by differential isoconversional method of Friedman. The variation of the value of activation energy E along the reaction progress α showed a complex character of decomposition of AN—interaction of AN with limestone and dolomite additives with the formation of nitrates as well as decomposition of these nitrates at higher temperatures.     

Interactions of ammonium nitrate with different additives Thermodynamic analysis

In order to elucidate the influence of Ca and Mg carbonates with or without the presence of boron, manganese and copper compounds on the thermal stability of ammonium nitrate (AN), thermodynamic analysis of different reactions between AN and additives was carried out. Temperature dependency of Gibbs free energy changes ∆G _T and equilibrium composition of reaction products were calculated for a set of reactions using the HSC software. Main solid compounds that can form in the systems of AN and carbonates, were Ca(NO₃)₂ and Mg(NO₃)₂, Ca(OH)₂ and Mg(OH)₂, CaO₂ and MgO₂, CaO and MgO, and N-containing gaseous compounds NO, N₂O and NO₂. As a result of H₃BO₃, MnO₂ and CuSO₄ addition, the content of CuO, Cu₂O and MnO as solids and SO₂, SO₃ and HBO as gaseous reaction products reached the same level. Thereby, their equilibrium concentrations did not depend on the carbonate origin of CaCO₃, MgCO₃ or CaMg(CO₃)₂. Small amount of CuSO₄, H₃BO₃ or MnO₂ additive (0.01–0.05 mol) in the system, practically, did not influence the temperature dependencies of ∆G _T of the reactions between AN and CaCO₃ or CaMg(CO₃)₂. The influence of additives taken in the larger amount (0.5 mol) was evident and, depending on the additive and reaction, shifted their proceeding temperatures in either direction by more than 300–400 K.     

Thermal behaviour of ammonium nitrate prills coated with limestone and dolomite powder

The thermal behaviour of ammonium nitrate (AN) and its prills coated with limestone and dolomite powder was studied on the basis of commercial fertilizer-grade AN and six Estonian limestone and dolomite samples. Coating of AN prills was carried out on a plate granulator and a saturated solution of AN was used as a binding agent. The mass of AN prills and coating material was calculated based on the mole ratio of AN/(CaO + MgO) = 2:1. Thermal behaviour of AN and its coated prills was studied using combined TG-DTA-FTIR equipment. The experiments were carried out under dynamic heating conditions up to 900 °C at the heating rate of 10 °C min⁻¹ and for calculation of kinetic parameters, additionally, at 2, 5 and 20 °C min⁻¹ in a stream of dry air. A model-free kinetic analysis approach based on the differential isoconversional method of Friedman was used to calculate the kinetic parameters. The results of TG-DTA-FTIR analyses and the variation of the value of activation energy E along the reaction progress α indicate the complex character of the decomposition of neat AN as well as of the interactions occurring at thermal treatment of AN prills coated with limestone and dolomite powder.     

Kinetics of the thermal decomposition of dinitramide

The kinetic regularities of the heat release during the thermal decomposition of liquid NH₄N(NO₂)₂ at 102.4–138.9 °C were studied. Kinetic data for decomposition of different forms of dinitramide and the influence of water on the rate of decomposition of NH₄N(NO₂)₂ show that the contributions of the decomposition of N(NO₂)₂ ⁻ and HN(NO₂)₂ to the initial decomposition rate of the reaction at temperatures about 100 °C are approximately equal. The decomposition has an autocatalytic character. The analysis of the effect of additives of HNO₃ solutions and the dependence of the autocatalytic reaction rate constant on the gas volume in the system shows that the self-acceleration is due to an increase in the acidity of the NH₄N(NO₂)₂ melt owing to the accumulation of HNO₃ and the corresponding increase in the contribution of the HN(NO₂)₂ decomposition to the overall rate. The self-acceleration ceases due to the accumulation of NO₃ ⁻ ions decreasing the equilibrium concentration of HN(NO₂)₂ in the melt. For Part 2, see Ref. 1. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 3, pp. 395–401 March 1998.     

Influences of aging on thermal decomposition mechanism of high performance oxidizer ammonium dinitramide

Ammonium dinitramide (ADN) is one of the several promising new solid propellant oxidizers. ADN is of interest because its oxygen balance and energy content are high, and it also halogen-free. One of the most important characteristics of a propellant oxidizer, however, is stability and ADN is known to degrade to ammonium nitrate (AN) during storage, which will affect its performance. This study focused on the effects of aging on the thermal decomposition mechanism of ADN. The thermal behaviors of ADN and ADN/AN mixtures were studied, as were the gases evolved during their decomposition, using differential scanning calorimetry (DSC), thermogravimetry–differential thermal analysis-infrared spectrometry (TG–DTA-IR), and thermogravimetry–differential thermal analysis-mass spectrometry (TG–DTA-MS). The results of these analyses demonstrated that the decomposition of ADN occurs via a series of distinct stages in the condensed phase. The gases evolved from ADN decomposition were N₂O, NO₂, N₂, and H₂O. In contrast, ADN mixed with AN (to simulate aging) did not exhibit the same initial reaction. We conclude that aging inhibits early stage, low temperature decomposition reactions of ADN. Two possible reasons were proposed, these being either a decrease in the acidity of the material due to the presence of AN, or inhibition of the acidic dissociation of dinitramic acid by NO ₃ ^? .     

Similarities and differences of thermal behaviour of 2-hydroxymethylbenzimidazole complexes with Zn(II) and Cd(II) ions

For a comparison of structural data and thermal behaviour of Zn(II) and Cd(II) complexes with biologically important ligand, 2-hydroxymethylbenzimidazole (L) the complex of the formula [ZnL₃](NO₃)₂L_0.67L′_0.33 was prepared and characterized by elemental analysis, infrared (IR) spectra, single-crystal X-ray diffraction and thermal analysis (where L′ = 2-carbaldehydebenzimidazole). IR and X-ray studies have confirmed a bidentate fashion of coordination of the 2-hydroxymethylbenzimidazole to Zn(II) ion (through the nitrogen atom of heteroaromatic ring and oxygen atom of hydroxymethyl group). The zinc ion is hexacoordinated and the shape of polyhedron can be described as pseudo-octahedron (N₃O₃ chromophore type). The decomposition process of studied Zn(II) and Cd(II) benzimidazole complexes in the air atmosphere proceeds in three or four main stages and traces structures of complexes. On the basis of the first DTG_max of the decompositions the thermal stability of the complexes follows the order: [CdL₃](NO₃)₂LEtOH_0.25 < [CdL₂(NO₃)₂] < [ZnL₃](NO₃)₂L_0.67L′_0.33. As the final solid products of thermal decomposition suitable metal oxides are formed.     

Influence of some lime-containing additives on the thermal behavior of urea

Urea is one of the main nitrogen fertilizers used in agriculture. But being well soluble in water, hardly 50% of its nitrogen is assimilated by plants. One possibility to eliminate this disadvantage is to use coating agents for modification of urea to obtain a controlled-realized fertilizer. The aim of this research was to study the influence of different lime-containing additives on the thermal behavior and decomposition kinetics of urea in oxidizing atmosphere. Commercial fertilizer-grade urea (46.4% N) and analytical-grade CaO, MgO, CaCO₃, MgCO₃ were used in the experiments. In addition, one Estonian limestone and one dolomite sample were used as additive or coating material. The experiments with a Setaram Setsys 1750 thermoanalyzer coupled to a Nicolet 380 FTIR Spectrometer by a heated transfer line were carried out under non-isothermal conditions up to 900 °C at the heating rate of 5 °C min^?1 and to calculate kinetic parameters, additionally, at 1, 2, and 10 °C min^?1 in the atmosphere containing 80% of Ar and 20% of O₂. The differential isoconversional method of Friedman was used to calculate the kinetic parameters. The results obtained indicate that thermooxidative decomposition of urea as well as the blends of urea with lime-containing materials and urea prills coated with limestone or dolomite powder follows a complex reaction mechanism.     

Identification of Thermal Decomposition Products and Reactions for Liquid Ammonium Nitrate on the Basis of Ab Initio Calculation

This work analyzed the thermal decomposition of ammonium nitrate (AN) in the liquid phase, using computations based on quantum mechanics to confirm the identity of the products observed in past experimental studies. During these ab initio calculations, the CBS‐QB3//ωB97XD/6–311++G(d,p) method was employed. It was found that one of the most reasonable reaction pathways is HNO₃ + NH₄⁺ → NH₃NO₂⁺ + H₂O followed by NH₃NO₂⁺ + NO₃^– → NH₂NO₂ + HNO₃. In the case in which HNO₃ accumulates in the molten AN, alternate reactions producing NH₂NO₂ are HNO₃ + HNO₃ → N₂O₅ + H₂O and subsequently N₂O₅ + NH₄⁺ → NH₂NO₂ + H₂O. In both scenarios, HNO₃ plays the role of a catalyst and the overall reaction can be written as NH₄⁺ + NO₃^– (AN) → NH₂NO₂ + H₂O. Although the unimolecular decomposition of NH₂NO₂ is thermodynamically unfavorable, water and bases both promote the decomposition of this molecule to N₂O and H₂O. Thus AN thermal decomposition in the liquid phase can be summarized as NH₄⁺ + NO₃^– (AN) → N₂O + 2H₂O.     

Three-parametric equation in evaluation of thermal dissociation of reference compound

Further considerations concerning thermal decomposition of reference material — CaCO₃, described by three-parametric equation in version (3), have been presented. It was established that in linear relationship between coefficients of Eq. (3) a ₂ is the argument of a ₁, which reaches minimal value of thermodynamic character (δH/vR) when a ₂=0 (equilibrium relationship). During thermal decomposition connection between system atmosphere — rich in CO₂ or vacuum, caused by fast evacuation of gaseous products — and activation energy value, as well as maximal temperature of reaction process. Conditions of this kind may be explained by Zawadzki-Bretsznajder law.     

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.

     

Preparation,X-ray crystallography and thermolysis of transition metal nitrates of 2,2′-bipyridine (Part 63)

Recent work has described the preparation and characterization of the two complexes [Fe₂(C₁₀H₈N₂)₄O(OH₂)₂](NO₃)₄ and [Co(C₁₀H₈N₂)₃]₂[Co(OH₂)₆]·7(OH₂) (NO₃)₈ in which both the nitrogen atoms of 2,2′-bipyridine are directly bonded with the metals. Their structures were determined by single-crystal X-ray diffraction at 296 K. Thermolysis of these complexes has been detailed by the use of TG–DTA and ignition delay measurements. Kinetics of thermal decomposition has also been established. Model free isoconversional and model fitting kinetic approaches have been applied to isothermal TG data for the decomposition of these complexes.     

Thermal decomposition of cobalt nitrato compounds: Preparation of anhydrous cobalt(II)nitrate and its characterisation by Infrared and Raman spectra

The thermal decomposition of Co(NO₃)₂·6H₂O (1) as well as that one of NO[Co(NO₃)₃] (Co(NO₃)₂·N₂O₄) (2) was followed by thermogravimetric (TG) measurements, X-ray recording and Raman and IR spectra. The stepwise decomposition reactions of 1 and 2 leading to anhydrous cobalt(II)nitrate (3) were established. In N₂ atmosphere, cobalt oxides are finally formed whereas in H₂/N₂ (10% H₂) cobalt metal is produced. Rapid heating of cobalt(II)nitrate hexahydrate causes melting (formation of a hydrate melt) and therefore side reactions in the hydrate melt by incoupled reactions and evolution/evaporation of different species as, e.g., HNO₃, NO₂, etc. In case of larger amounts in dense packing in the sample container, the formation of oxo(hydoxo)nitrates is possible at higher temperature. For 2, its thermal decomposition to 3 was followed and its decomposition mechanism is proposed.     

Synthesis and characterization of polyvinyl butyral–Al(NO<Subscript>3</Subscript>)<Subscript>3</Subscript> composite sol used for alumina based fibers

The polyvinyl butyral–Al(NO₃)₃ composite sol used for alumina based fibers was synthesized by the sol–gel process in an aqueous solution using the polyvinyl butyral (PVB) and Al(NO₃)₃ · 9H₂O (AN). The alumina fibers with smooth surface and uniform diameter were prepared. PVB, AN, PVB–AN composite sol and alumina fibers have been studied by X-ray diffraction (XRD), derivative thermo-gravimetric/differential scanning calorimetry (DTG/DSC), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM). The interaction between PVB and AN was reported. The presence of a new weak peak at low angle and deviation of diffraction angle in XRD patterns implied that the reaction between PVB and AN took place. DTG/DSC curves showed the decomposition temperatures of AN increased and that of PVB decreased in the PVB–AN composite sol, which was considered to be caused by the interaction between PVB and AN. FTIR spectroscopy of PVB–AN gel showed a new absorption peak due to the COOH group, which implied the presence of new reaction product. The schematic reaction formula was shown in this paper. The XRD pattern of fibers sintered at 1,200 °C showed the formation of α-alumina and the fibers showed smooth surface and uniform diameter.     

Kinetics of thermal decomposition of dinitramide

Kinetic regularities of thermal decomposition of dinitramide in aqueous and sulfuric acid solutions were studied in a wide temperature range. The rate of the thermal decomposition of dinitramide was established to be determined by the rates of decomposition of different forms of dinitramide as the acidity of the medium increases: first, N(NO₂)⁻ anions, then HN(NO₂)₂ molecules, and finally, protonated H₂N(NO₂)₂ ⁺ cations. The temperature dependences of the rate constants of the decomposition of N(NO₂)⁻ (k _an) and HN(NO₂)₂ (k′_ac) and the equilibrium constant of dissociation of HN(NO₂)₂ (K _a) were determined:k _an=1.7·10¹⁷ exp(−20.5·10³/T), s⁻¹,k′_ac=7.9·10¹⁶ exp(−16.1·10³/T), s⁻¹, andK _a=1.4·10 exp(−2.6·10³/T). The temperature dependences of the decomposition rate constant of H₂N(NO₂)₂ ⁺ (k _d) and the equilibrium constant of the dissociation of H₂N(NO₂)₂ ⁺ (K _d) were estimated:k _d=10¹² exp(−7.9·10³/T), s⁻¹ andK _d=1.1 exp(6.4·10³/T). The kinetic and thermodynamic constants obtained make it possible to calculate the decomposition rate of dinitramide solutions in a wide range of temperatures and acidities of the medium. In this series of articles, we report the results of studies of the thermal decomposition of dinitramide performed in 1974–1978 and not published previously. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2129–2133, December, 1997.     

Effect of metal oxide additives on the thermal decomposition kinetics of potassium metaperiodate

The effect of additives (CuO, MnO₂ and TiO₂) on the thermal decomposition kinetics of potassium metaperiodate (KIO₄) to potassium iodate (KIO₃) has been studied in air by thermogravimetry under isothermal conditions. Irrespective of whether p- or n-type, the metal oxides show only a little or no influence on the rate of the decomposition except for the small decrease when the oxide concentration is as high as 10 wt%. The rate law for the decomposition of KIO₄ (Prout–Tompkins model) remained unaffected by the additives.     

Manganese(II), cobalt(II), nickel(II), copper(II) and zinc(II) complexes with 4-oxo-4H-1-benzopyran-3-carboxaldehyde

The complexes Mn(II), Co(II), Ni(II) and Zn(II) with 4-oxo-4H-1-benzopyran-3-carboxaldehyde were synthesized and characterized by elemental analysis, infrared and UV spectroscopy, X-ray diffraction patterns, magnetic susceptibility, thermal gravimetric analysis, conductivity and also solubility measurements in water, methanol and DMF solution at 298 K. They are polycrystalline compounds with various formula and different ratio of metal ion:ligand. Their formula are following: [MnL₂(H₂O)](NO₃)₂·2H₂O, [CoL₂](NO₃)₂·3H₂O, [NiL₂](NO₃)₂·3H₂O, [CuL₂](NO₃)₂·H₂O and [ZnL₃](NO₃)₂, where L = C₁₀H₆O₃. The coordination of metal ions is through oxygen atoms present in 4-position of γ-pyrone ring and of aldehyde group of ligand. Chelates of Mn(II), Co(II), Ni(II) and Cu(II) obey Curie–Weiss law and they are high-spin complexes with the weak ligand fields. The thermal stability of analyzed complexes was studied in air at 293–1,173 K. On the basis of the thermoanalytical curves, it appears that thermal stability of anhydrous analysed chelates changed following: Cu (423 K) < Zn (438 K) ~ Co (440 K) < Ni (468 K). The gaseous products of thermal decomposition of those compounds in air atmosphere are following: CO₂, CO, NO₂, N₂O, hydrocarbons and in case of hydrates also water. The molar conductance data confirm that the all studied complexes are 1:2 electrolytes in DMF solution.     

ZnS and ZnSe Nanoparticles via Solid-State and Solution Thermolysis of Zinc Silylchalcogenolate Complexes

The thermolysis of the zinc trimethylsilylchalcogenolate complexes (N,N′-tmeda)Zn(ESiMe₃)₂ (E = S, 1; E = Se, 2) and (3,5-Me₂-C₅H₃N)₂Zn(ESiMe₃)₂ (E = S, 3; E = Se, 4) has been investigated. Solid-state thermal decomposition of complexes 1–4 above 250°C results in the formation of hexagonal ZnS and cubic ZnSe, respectively, via the liberation of TMEDA (1–2) or 3,5-lutidine (3–4) and E(SiMe₃)₂. Solid-state or solution thermolysis of these complexes up to 200°C produces nanocrystalline ZnS and ZnSe materials whose surface is protected by either coordinated TMEDA or 3,5-lutidine ligands. The progress of the step-wise solid-state decomposition of these complexes was monitored by thermogravimetric and single differential thermal analysis and volatile decomposition products in both solution and solid-state experiments were identified by GC/MS.Dedicated to Professor Brian F. G. Johnson on the occasion of his retirement.     

Studies on the Thermal Decomposition of Benzoic Acid and its Derivatives

The thermal decomposition of benzoic acid and its derivatives containing —OH, —NH₂, —COOH and —SO₃H functional groups as substituents in ortho, meta and (or) para position together with sulphanilic acid was investigated. The analyses were performed using derivatograph, sample mass ranged from 50 to 200 mg, heating rates from 3 to 15 K min⁻¹ and static air atmosphere. It has been established that thermal decomposition of these aromatic acids proceeds through three common stages. In the first stage the phase transformations occur. The following two stages are due to the formation of intermediate products of the thermal decomposition and their combustion. Principal component analysis (PCA) was applied for evaluation of the results. Thanks to this method the influence of specific functional groups and their positions on the benzene ring on the thermal decomposition of the compounds under investigation was determined. This revised version was published online in July 2006 with corrections to the Cover Date.     

Kinetics of the thermal decomposition of dinitramide

The kinetic regularities of the thermal decomposition of dinitramide in aqueous solutions of HNO₃, in anhydrous acetic acid, and in several other organic solvents were studied. The rate of the decomposition of dinitramide in aqueous HNO₃ is determined by the decomposition of mixed anhydride of dinitramide and nitric acid (N₄O₆) formed in the solution in the reversible reaction. The decomposition of the anhydride is a reason for an increase in the decomposition rates of dinitramide in solutions of HNO₃ as compared to those in solutions in H₂SO₄ and the self-acceleration of the process in concentrated aqueous solutions of dinitramide. The increase in the decomposition rate of nondissociated dinitramide compared to the decomposition rate of the N(NO₂)₂ ⁻ anion is explained by a decrease in the order of the N−NO₂ bond. The increase in the rate constant of the decomposition of the protonated form of dinitramide compared to the corresponding value for neutral molecules is due to the dehydration mechanism of the reaction. For Part 1, see Ref. 1. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 41–47, January, 1998.     

Kinetics of heat release during the reaction ofn-decane with nitrogen dioxide in the liquid phase

The rates of heat release in the nitrogen dioxide—n-decane system at a molar ratio of nitrogen oxides ton-decane (β) from 2.4·10⁻³ to 3.1 and gaseous volumes per mole ofn-decane (V(g)) equal to 0.05–4.5 were studied in the 55.2–92.8 °C temperature range. The initial rate of the process is determined by the interaction of NO₂ withn-decane. The equilibrium constants of dissociation of N₂O₄ inn-decane and Henry's constants of NO₂ and N₂O₄ in ann-decane solution were determined by complex analysis of the thermodynamic equilibrium in the NO₂—n-decane system and dependences of the initial rates onV(g) and β. The experimentally observed self-acceleration of the process in the region of high β and lowT values was suggested to be due to the reaction of N₂O₄ with intermediate oxidation products. The rate constants of the reaction of NO₂ withn-decane were compared with analogous values determined in its mixtures with HNO₃ solutions. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1789–1794, October, 1997.