Kinetics Of Thermolysis Research Articles

Too fast and too furious: thermoanalytical and quantum chemical study of the thermal stability of 4,4'-dinitro-3,3'-diazenofuroxan.

Novel energetic materials (EM) often combine two intrinsically counter trends, viz., a high energy density and mediocre safety parameters, like thermal stability and sensitivity toward mechanical stimuli. A rational design of promising EMs requires a proper understanding of their thermal stability at both macroscopic and molecular levels. In the present contribution, we studied in detail the thermal stability of 4,4'-dinitro-3,3'-diazenofuroxan (DDF), an ultrahigh-performance energetic material with a reliable experimental detonation velocity being very close to 10 km s-1. To this end, we employed a set of complementary thermoanalytical (DSC and TGA in the solid state along with advanced thermokinetic models, optical microscopy, and gas products detection) and theoretical techniques (DLPNO-CCSD(T) quantum chemical calculations). According to the DSC measurements, the solid-state thermolysis of DDF turned out to be a complex three-step process. The decomposition commences at ∼85 °C and the most intense heat release occurs at ∼130 °C depending on the heating rate. In order to properly describe the kinetics of DDF thermolysis beyond the simple Kissinger and Friedman methods, we applied a "top-down" kinetic approach resulting in the formal model comprised of three independent stages. A flexible Kolmogorov-Johnson-Mehl-Avrami-Erofeev equation was applied for the first decomposition stage along with the extended Prout-Tompkins equation for the second and third processes, respectively. The formal exponent in the former equation turned out to be close to a second order, thus suggesting a two-dimensional nuclei-growth model for the first stage. We rationalized this fact with the aid of optical microscopy experiments tracking the changes in the morphology of a solid DDF sample. Then, we complemented the formal macroscopic kinetics with some mechanistic patterns of the primary decomposition channels from quantum chemical calculations. The three reactions involving all important moieties of the DDF molecule turned out to compete very closely: viz., the nitro-nitrite isomerization, radical C(heterocycle)-N(bridge) bond scission and molecular decomposition comprised of the consequent N-O and C-C bond scissions in a furoxane ring. The DLPNO-CCSD(T) activation barriers of all these reactions were close to ∼230 kJ mol-1. Most importantly, the calculations provide some mechanistic details missing in thermoanalytical experiment and formal kinetic models. Apart from this, we also determined a mutually consistent set of thermochemical and phase change data for DDF.

Kinetics of Thermolysis of a Low-Temperature Tar in the Presence of a Catalyzer Agent with Deposited Metals

The thermal decomposition of low-temperature coal tar (LTCT) obtained from the coals of Shubarkol Komir JSC of the Republic of Qazaqstan in the presence of nanocatalysts with metal oxides (iron, cobalt and nickel) supported on microsilicate was studied for the first time. Microsilicate acts as a carrier and catalyst. Microsil-icate is a product of the Karaganda silicon plant of “Tau-Ken.temir” LLP. The main chemical component of the original microsilicate is silicon oxide. The individual and chemical phase composition of the microsilicate was determined using X-ray spectral analysis. The particle size of the initial microsilicate and the mixture of microsilicate with metal oxide catalysts (nickel, cobalt, and iron) was determined using a nanosizer. Stages of thermal decomposition of LTCT and a mixture of LTCT with catalysts under conditions of programmed heat-ing up to 640 °С in a nitrogen atmosphere have been established. On the basis of thermogravimetric analysis, the kinetic parameters (activation energy, mass loss rate, and pre-exponential factor) of LTCT pyrolysis and mixture with added catalysts were determined. The modeless integral isoconversion Ozawa–Flynn–Wall method was used to determine the kinetic parameters. The values of the activation energy for the thermal de-struction of the LTCT in the absence and presence of the nanocatalyst ranged from 54.04 to 297.5 kJ/mol. A kinetic compensation effect was revealed, probably due to the multicomponent composition of the LTCT and the influence of added catalysts to the LTCT. The thermogravimetry method showed a high effect of the sup-ported catalysts on the thermal degradation of LTCT. This method was used to determine the values of the ac-tivation energy and the pre-exponential degradation factor for the LTCT and the mixture with catalysts at dif-ferent heating rates, which allows a detailed interpretation of the thermal analysis data. The obtained results of the kinetics of decomposition of LTCT can be used to create a database for mathematical modeling of the process of processing this type of raw material.

Upcycling Postconsumer High-Density Polyethylene (PC-HDPE): Thermal Stability and Kinetics Study of the Filaments Extruded from PC-HDPE

Thermal stability and kinetics of thermolysis of postconsumer milk containers made of high-density polyethylene (PC-HDPE) and filament rods extruded from them (HDPE-F) were examined by thermogravimetric analysis (TGA) with six linear temperature programs under a stream of nitrogen. The total weightloss of each sample took place in a one-step decomposition to volatiles at the heating rates, β = 1, 10, 25, 50, 70, and 100 Kmin-1. The values of initial decomposition temperature, the temperature at the maximum thermal degradation rate, and the maximum rate of decomposition were increased by increasing the heating rate as was the expectation. The isoconversional method was used to evaluate the fundamental kinetic parameters, the activation energy barrier (Ea ), the Arrhenius pre-exponential factor (A), and the mechanism of the reaction, f(α). The values of Ea were independent of the model and heating rate, as was expected. However, the values of A depended on the model and the extent of reaction (α). The values of the Ea of PC-HDPE initiated at 171 kJ/mol at α = 0.05 and it increased to 207 kJ/mole at α = 0.95. The values of Ea of the HDPE-F rod were relatively constant for all α values, being 227 ± 3 kJ/mol. It was justified by the absence of easily volatilized substances in the HDPE-F. Knowledge of the thermal stability and decomposition kinetics of the starting materials (PC-HDPE) and the product (HDPE-F) is important in the context of thermochemical conversion processes aimed at the use of PC-HDPE as raw materials for recycling, upcycling, and down-cycling for objects used under room conditions.

Synthesis, crystal structure and thermolysis kinetics of [Co(H2O)6](ClO4)2.(HMTA)2.2H2O (HMTA = hexamethylenetetramine)

A new compound, [Co(H 2 O) 6 ](ClO 4 ) 2 .(HMTA) 2 .2H 2 O; HMTA = hexamethylenetetramine) has been synthesized and characterized with the assistance of X-ray crystallography, elemental analysis, FT-IR spectroscopy, TG-DTA and DSC (N 2 atmosphere). Both TG data model-fitting method as well as method of model free isoconversional have been employed to observe the kinetics of thermolysis of the compound. In order to understand the effect of sudden high heat, measurements of explosion delay are undertaken at regular five unique temperatures and the kinetics of explosion has also been explored using Arrhenius equation.

The power of model-fitting kinetic analysis applied to complex thermal decomposition of explosives: reconciling the kinetics of bicyclo-HMX thermolysis in solid state and solution

Thermal decomposition of cis-1,3,4,6-tetranitrooctahydroimidazo-[4,5-d]imidazole (Bicyclo-HMX) both in solid state and in solution has been studied with a set of thermal analysis methods. Differential scanning calorimetry data obtained at several heating rates were analyzed using the model-fitting kinetic technique using the free open-source THINKS thermokinetic software. The kinetic parameters for a noncatalytic stage of thermolysis in solution are found to be Ea = 168.7 ± 1.4 kJ mol−1, log (A, s−1) = 15.7 ± 0.2, to prove the activation energy agrees with the theoretical prediction of the barrier for N–NO2 bond rupture in BC-HMX molecule. Thermal decomposition of solid BC-HMX is a complex process, typical for explosives. A formal three-step kinetic scheme is proposed, which explains the numerous experimental findings (thermal behavior at various confinement degree, morphology changes under heating) and the previous literature results as well. The first step of the process obeys a third-order nucleation-growth model with the Ea = 186.6 ± 1.2 kJ mol−1 and log (A, s−1) = 16.7 ± 0.3. Overall, the power of the model-fitting kinetic analysis is demonstrated and the extension of the proposed methodology to other energetic materials with complex decomposition patterns is suggested.

Copper–iron mixed oxide catalyst precursors prepared by glycine-nitrate combustion method for ammonia borane dehydrogenation processes

The influence of the properties of copper ferrite, prepared by the combustion method from glycine-nitrate precursor, on the kinetics of NH3BH3 hydrolysis, thermolysis and hydrothermolysis are presented. As-prepared and annealed samples were studied by X-ray diffraction, scanning electron microscopy, differential dissolution, and attenuated total reflection infrared spectroscopy. It has been shown that in the hydrolysis and hydrothermolysis of NH3BH3, the as-prepared combustion product, which mainly consisted of a cubic spinel Cu0.67Fe2.33O4 with Fe2+ higher content, had the highest activity, as compared with oxides of copper and iron and the annealed samples. According to transmission electron microscopy and X-ray diffraction, in the reaction medium copper ferrite is reduced to nanosized Cu0 and Fe0. This allowed the average rate of H2 evolution per 1 g of the composition to be increased from 30 to 76 ml⋅min−1, as compared with non-catalytic process. The high gravimetric hydrogen capacity (7.3 wt%) was observed at 90 °C.

Metal chelate monomers based on nickel(II) cinnamate and chelating N-heterocycles as precursors of nanostructured materials

Metal chelate monomers (MCMs) have been widely used as precursors for the production of advanced functional polymers and nanomaterials. In this articel, new metal chelate monomers based on nickel(II) cinnamate (cinn) and various chelating N-heterocycles, [Ni(cinn)2(bpy)(C2H5OH)] and [Ni(cinn)2(phen)(C2H5OH)2] (bpy = 2,2′-bipyridine and phen = 1,10-phenanthroline), were first synthesized and characterized. A detailed analysis of the main stages and features of the kinetics of thermolysis of MCMs was carried out. Metal-polymer nanocomposites with a core-shell structure containing metal nanoparticles evenly distributed in a stabilizing nitrogen-containing polymer matrix were obtained by thermolysis at 300 °C. Thermolysis at 450 °C resulted in pure nickel oxide nanoparticles. The nature of the ligand has been shown to affect the structure and size of the product obtained. The tribological characteristics of nanoparticles as additives to lubricating oils were studied using the pin-on-disc tribometer. At the optimum concentration of nanoparticles, the coefficient of friction is the smallest, and an increase in the concentration above the optimum level leads to an increase in the coefficient of friction.

Effect of Irradiation on the Dynamics of Gas Evolution in Thermal Oxidation of Diamide Extractants in F-3 Diluent

The dynamics of gas evolution in thermal oxidation of solutions of 2,2'-bipyridine-6,6'-dicarboxylic acid di(N-ethyl-4-hexylanilide) (DYP-7), 2,6-pyridinedicarboxylic acid di(N-ethyl-4-fluoroanilide) [Et(pFPh)· DPA], and 2,2'-bipyridine-6,6'-dicarboxylic acid di(N-ethyl-4-ethylanilide) (DYP-9) in m-nitrobenzotrifluoride (F-3) diluent with 14 M HNO3 in open and closed vessels was studied. The effect of preliminary irradiation of the organic phase on the kinetics of thermolysis of the two-phase system was determined. Heating of the irradiated samples in a closed vessel (autoclave) leads to the pressure buildup, with the pressure reached increasing from 18 to 23 atm as the absorbed dose is increased from 0 to 1 MGy. The exothermic processes occurring in the systems caused a 4 to 10°С increase in the sample temperature. The thermal stability of all the irradiated diamide–F-3 diluent extraction systems studied is acceptable for practical use.

Pursuing reliable thermal analysis techniques for energetic materials: decomposition kinetics and thermal stability of dihydroxylammonium 5,5'-bistetrazole-1,1'-diolate (TKX-50).

Thermal decomposition of a novel promising high-performance explosive dihydroxylammonium 5,5'-bistetrazole-1,1'-diolate (TKX-50) was studied using a number of thermal analysis techniques (thermogravimetry, differential scanning calorimetry, and accelerating rate calorimetry, ARC). To obtain more comprehensive insight into the kinetics and mechanism of TKX-50 decomposition, a variety of complementary thermoanalytical experiments were performed under various conditions. Non-isothermal and isothermal kinetics were obtained at both atmospheric and low (up to 0.3 Torr) pressures. The gas products of thermolysis were detected in situ using IR spectroscopy, and the structure of solid-state decomposition products was determined by X-ray diffraction and scanning electron microscopy. Diammonium 5,5'-bistetrazole-1,1'-diolate (ABTOX) was directly identified to be the most important intermediate of the decomposition process. The important role of bistetrazole diol (BTO) in the mechanism of TKX-50 decomposition was also rationalized by thermolysis experiments with mixtures of TKX-50 and BTO. Several widely used thermoanalytical data processing techniques (Kissinger, isoconversional, formal kinetic approaches, etc.) were independently benchmarked against the ARC data, which are more germane to the real storage and application conditions of energetic materials. Our study revealed that none of the Arrhenius parameters reported before can properly describe the complex two-stage decomposition process of TKX-50. In contrast, we showed the superior performance of the isoconversional methods combined with isothermal measurements, which yielded the most reliable kinetic parameters of TKX-50 thermolysis. In contrast with the existing reports, the thermal stability of TKX-50 was determined in the ARC experiments to be lower than that of hexogen, but close to that of hexanitrohexaazaisowurtzitane (CL-20).

Study of thermal and radiation stability of the extractant based on CMPO in fluorinated sulfones

ABSTRACTThe two-phase systems of pure diluent FS-13 – aqueous solution of 14 mol/L nitric acid and 0.02 mol/L solution of CMPO in diluent FS-13 – aqueous solution of 14 mol/L HNO3 were studied at autoclave temperatures 170 °C and 200 °C. The effect of pre-irradiation on the kinetics of thermolysis was determined. All samples were irradiated using an electron accelerator at a dose rate of 10 kGy/h up to absorbed doses of 0.1, 0.5 and 1 MGy. The parameters of heat and gas emissions were determined during thermolysis of the studied extraction system in a closed apparatus. It has been shown that the conditions required for the growth of autocatalytic oxidation are not created during heating of the two-phase systems in closed vessels even for the extraction systems contacted with 14 mol/l HNO3 for two weeks.

Kinetics of thermolysis of vacuum tower bottoms mixed with pine sawdust

Basic features of thermal degradation of mixtures of vacuum tower bottoms with pine sawdust have been studied by dynamic thermogravimetry. The kinetic parameters of the process have been determined using the integral model-free Ozawa–Flynn–Wall method. The enthalpies and ethropies of activation of the thermal degradation of the vacuum residue, the sawdust, and their mixtures have been calculated on the basis of the transition state theory. It has been shown that pine sawdust and its degradation products have an activity to enhance the kinetic parameters and the rate of thermal degradation of vacuum tower bottoms. It has been found that the E value of thermolysis of the heavy petroleum residue substantially decreases with an increase in the proportion of sawdust in the vacuuum resid to 225.0 kJ/mol for the mixture containing 18.0 wt % pine sawdust at a degree of conversion of the mixture of 0.8.

In English

Gelatin-based films with silica-to-gelatin weight ratio 1:5 or 8:5, containing either hydrophilic or hydrophilic-hydrophobic silica, have been prepared and studied by means of thermogravimetric analysis and temperature-programmed desorption mass spectrometry. It has been shown that silica presence has no effect on the mechanism of thermal decomposition of gelatin; however, it affects the kinetics of gelatin thermolysis both in vacuum and in air, including an increase in the activation energy of the volatile products formation at hydrophilic silica content about 17 wt. %. Hydrophobization of silica surface as well as an increase in hydrophilic silica concentration in the film from 17 to 62 wt. % decreases the activation energy of the volatile products formation during gelatin thermolysis. This effect is explained by reduced binding of gelatin with silica owing to either substitution of some surface silanol groups upon partial hydrophobization of silica, or their involving into interparticle rather than in silica-gelatin interactions at higher silica content.

A uranium (VI) complex: Synthesis, structural and thermal kinetic analysis

A new complex [UO2(2,6–DNP)2phen] (1) (2,6–DNP = 2,6–dinitrophenol, phen = 1,10–phenanthroline) was synthesized, and identified by elemental analysis, IR, Powder XRD and single crystal X-ray crystallography. Crystal structure provides the abundant information's about the bonding and geometry around the U(VI) metal center. The thermal decomposition was studied by TG–DSC, and the kinetics of thermolysis was investigated by applying model fitting as well as isoconversional methods. Explosion delay measurement (De) was also evaluated to determine the response of this complex under the condition of rapid heating.

Study the kinetics of thermolysis of textile materials modified by polyorganosiloxanes

Analysis of the parameters of thermal oxidative degradation of textile materials, modified commercial polyorganosiloxanes (DowCorning 3605, Silastic 9252/250 P) is performed. The influence of encapsulated adjuvants-refrigerant 23 (CHF3) and ultrafine carbon-on the kinetic characteristics of thermolysis of cellulose fabrics is studied.

Structurally based constitutive model of epoxy adhesives incorporating the influence of post-curing and thermolysis

Performance of the adhesively joined composite structures frequently depends on their stiffness since excessive deformation can alter their functionality. In this article, we present the structurally based constitutive model which takes into account the influence of the post-curing as well as thermolysis process on stiffness of epoxy adhesives. We propose the chemomechanical model considering the autocatalytic post-curing process and thermolysis, which dominates in the first phase of the degradation process at elevated temperatures. The proposed model employs reaction kinetics of curing and thermolysis of epoxy, statistical mechanics as well as non-linear large strain constitutive material model which incorporates influence of chemical reactions. Presented model is calibrated to the results of experimental investigations probing the influence of the aging cycles according to the SAE/USCAR standard on stiffness of the epoxy adhesives. The material model is validated by comparison with results of single lap shear tests after Humidity–Temperature aging in class I and V. We achieve 98.3% compliance for investigated aging cycles. Proposed model takes into account not only aging effects but elevated temperatures as well. Thus it can be used for prediction of the mechanical behavior of heavy loaded epoxy adhesive joints working in engine compartment. The consistency of the experimental results with model predictions, proves that our chemomechanical model constitutes a useful tool for the prediction of the durability and lifetime of adhesively joined structures.

Role of Metal Surface Catalysis in the Thermolysis of Morpholine and Ethanolamine under Superheater Conditions

Amines like ethanolamine and morpholine have great potential for protecting steam–water cycles against corrosion, but their thermal stability is limited and acidic decomposition products are a concern because of increased corrosion risk. In this study, metal catalysis of amine thermolysis caused by oxides on the inner surface of superheater tubes has been investigated by using a flow reactor and metal tubes of varying sizes and elemental composition. The kinetics of morpholine and ethanolamine thermolysis decreased as the tube size increased. The relationship between the S:V ratio and the degradation rate constant k was linear. Heterogeneous thermolysis accounted for 82–92% of the value of the degradation rate constant k at an S:V ratio of 4.65 mm–1. This decreased to only 6–17% at an S:V ratio of 0.4 mm–1. Although the results varied between the two applied materials, there is no consistent trend that can link thermolysis kinetics to the tube wall composition. Organic acid anion production was weakly rel...

Kinetics of thermolysis of lanthanum nitrate with hexamethylenetetramine: Crystal structure, TG–DSC, impact and friction sensitivity studies, Part-96

The development of high energetic materials includes process ability and the ability to attain insensitive munitions (IM). This paper investigates the preparation of lanthanum metal nitrate complex of hexamethylenetetramine in water at room temperature. This complex of molecular formulae [La (NO3)2(H2O)6] (2HMTA) (NO3−) (H2O) was characterized by X-ray crystallography. Thermal decomposition was investigated using TG, TG–DSC and ignition delay measurements. Kinetic analysis of isothermal TG data has been investigated using model fitting methods as well as model free isoconversional methods. The sensitivity measurements towards mechanical destructive stimuli such as impact and friction were carried out and the complex was found to be insensitive. In order to identify the end product of thermolysis, X-ray diffraction patterns of end product was carried out which proves the formation of La2O3.

Thermal decomposition and kinetics studies on poly(BDFAO/THF), poly(DFAMO/THF), and poly(BDFAO/DFAMO/THF)

Poly(3,3-bis(difluoroaminomethyl)oxetane/tetrahydrofuran), poly(3-difluoroaminomethyl-3-methyloxetane/tetrahydrofuran), and poly(3,3-bis(difluoroaminomethyl)oxetane/3-difluoroaminomethyl-3-methyloxetane/tetrahydrofuran) were synthesized via cationic bulk polymerization using boron trifluoride etherate/polyol mixture as catalyst system. Thermal decomposition behaviors of these polymers were investigated by thermogravimetric analysis/differential scanning calorimetry. Kinetics of thermolysis was studied by a model-free method. All of these polymers exhibited a two-stage mass-loss process. The elimination of HF with the activation energy at 95–110 kJ mol−1 dominated the first stage, while the second stage contained the thermolysis of the remaining polymer chain with monofluoroimino and cyano groups. Fourier transform infra red spectra of the degradation residues showed that the difluoroamino groups decomposed in a two-step HF loss at different temperatures. The existence of monofluoroimino groups was responsible for the two-stage thermolysis process.

Thermal Decomposition, Kinetics and Compatibility Studies of Poly(3‐difluoroaminomethyl‐3‐methyloxetane) (PDFAMO)

AbstractThe thermal decomposition of poly(3‐difluoroaminomethyl‐3‐methyloxetane) (PDFAMO) with an average molecular weight of about 6000 was investigated using thermogravimetric analysis (TG) and differential scanning calorimetry (DSC). The kinetics of thermolysis were studied by a model‐free method. The thermal decomposition of PDFAMO occurred in a two‐stage process. The first stage was mainly due to elimination of HF and had an activation energy of 110–120 kJ mol−1. The second stage was due to degradation of the polymer chain. The Fourier transform infrared (FTIR) spectra of the degradation residues showed that the difluoroamino groups decomposed in a two‐step HF loss at different temperatures. The remaining monofluoroimino groups produced by the incomplete elimination of HF were responsible for the two‐stage thermolysis process. The compatibility of PDFAMO with some energetic components and inert materials used in polymer‐bonded explosives (PBXs) and solid propellants was studied by DSC. It was concluded that the binary systems of PDFAMO with cyclotrimethylenetrinitramine (RDX), 2,4,6‐trinitrotoluene (TNT), 2,4‐dinitroanisole (DNAN), pentaerythritol tetranitrate (PETN), ammonium perchlorate (AP), aluminum powder (Al), aluminum oxide (Al2O3) and 1,3‐diethyl‐1,3‐diphenyl urea (C1) were compatible, whereas the systems of PDFAMO with lead carbonate (PbCO3) and 2‐nitrodiphenylamine (NDPA) were slightly sensitized. The systems with cyclotetramethylenetetranitroamine (HMX), hexanitrohexaazaisowurtzitane (CL‐20), 3‐nitro‐1,2,4‐triazol‐5‐one (NTO), ammonium nitrate (AN), magnesium powder (Mg), boron powder (B), carbon black (C. B.), diphenylamine (DPA), and p‐nitro‐N‐methylamine (PNMA) were incompatible. The results of compatibility studies fully supported the suggested thermal decomposition mechanism of PDFAMO.

Kinetics of Thermolysis of Nickel(II) Perchlorate Complex with n-Propylamine

Complex of nickel perchlorate with n-propylamine has been synthesised with molecular formula [Ni(n-pa)3(ClO4)(H2O)]ClO4. It has been characterised by elemental analysis, thermogravimetry, UV-VIS, and IR spectroscopic data. Thermal properties have been investigated by thermogravimetry (TG) in static air and by simultaneous thermogravimetry-derivative thermogravimetry-differential thermal analysis (TG-DTG-DTA) in flowing nitrogen atmosphere. Kinetics of thermolysis has been analysed applying model-fitting and model-free isoconversional method on isothermal TG data recorded at five different temperatures. To observe the response of complex towards fast heating, explosion delay time has been recorded at various temperatures and kinetics of explosion has been studied using these data.