Estimation of the critical rate of temperature rise for thermal explosion of nitrocellulose using non-isothermal DSC

The expressions to calculate the critical rate of temperature rise of thermal explosion $ ({\text{d}}T / {\text{d}}t)_{{\text{T}_{\text{b}} }} $ for energetic materials (EMs) were derived from the Semenov’s thermal explosion theory and autocatalytic reaction rate equation of nth order, C_nB, B_na, first-order, apparent empiric-order, simple first-order, A_u, apparent empiric-order of m = 0, n = 0, p = 1 and m = 0, n = 1, p = 1, using reasonable hypotheses. A method to determine the kinetic parameters in the autocatalytic-decomposing reaction rate equations and the $ ({\text{d}}T / {\text{d}}t)_{{\text{T}_{\text{b}} }} $ in EMs when autocatalytic decomposition converts into thermal explosion from data of DSC curves at different heating rate was presented. Results show that (1) under non-isothermal DSC conditions, the autocatalytic-decomposing reaction of NC (12.97 % N) can be described by the first-order autocatalytic reaction rate equation dα/dt = 10^16.00exp(?174520/RT)(1 ? α) + 10^16.00exp(?163510/RT)α(1 ? α); (2) the value of $ ({\text{d}}T / {\text{d}}t)_{{\text{T}_{\text{b}} }} $ for NC (12.97 % N) when autocatalytic decomposition converts into thermal explosion is 0.354 K s^?1.     

Kinetics of exothermal decomposition of 2-nitrophenylhydrazine and 4-nitrophenylhydrazine using DSC non-isothermal data

Kinetics of exothermal decomposition of 2-nitrophenylhydrazine (2-NPH) and 4-nitrophenylhydrazine (4-NPH) was investigated by differential scanning calorimetry. The isoconversional methods, Friedman and Flynn-Wall-Ozawa, were applied to determine the activation parameters from the common analysis of multiple curves measured at different heating rates. For the processes involving two-step reactions the multivariate non-linear regression was used. A good agreement between the experimental and the fitted data was found.     

Melting and thermal history of poly(hydroxybutyrate-co-hydroxyvalerate) using step-scan DSC

Melting behaviour and crystal morphology of poly(3-hydroxybutyrate) (PHB) and its copolymer of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) with various hydroxyvalerate (HV) contents [5 wt.% (PHB5HV), 8 wt.% (PHB8HV) and 12 wt.% (PHB12HV)] have been investigated by conventional DSC, step-scan differential scanning calorimetry (SDSC) and hot-stage polarised optical microscopy (HSPOM). Crystallisation behaviour of PHB and its copolymers were investigated by SDSC. Thermal properties were investigated after different crystallisation treatments, fast, medium and slow cooling. Multiple melting peak behaviour was observed for all polymers. SDSC data revealed that PHB and its copolymers undergo melting–recrystallisation–remelting during heating, as evidenced by exothermic peaks in the IsoK baseline (non-reversing signal). An increase in degree of crystallinity due to significant melt–recrystallisation was observed for slow-cooled copolymers. PHB5HV showed different crystal morphologies for various crystallisation conditions. SDSC proved a convenient and precise method for measurement of the apparent thermodynamic specific heat (reversing signal) HSPOM results showed that the crystallisation rates and sizes of spherulites were significantly reduced as crystallisation rate increased.     

Approximate critical conditions in thermal explosion theory for a two-step kinetic model

Approximate critical conditions for a thermal explosion problem is developed for a two-step reactions based on theories of Semenov and Frank-Kamenetskii. The aim is to examine the contributions of the radical termination step and the temperature dependent pre-exponential factor on the critical parameters within the framework of classical stationary and non-stationary theories. In the non-stationary case, a more general expression for the critical Semenov parameter (Ψ _cr ) and critical temperature (θ _cr ) were obtained by asymptotic procedure. In the stationary case, numerical estimates for the critical Frank-Kamenetskii parameter (δ _cr ) and the critical temperature (θ _cr ) were obtained by variational method technique. It was observed that the Semenov and Frank-Kamenetskii parameters are greatly influenced by the termination step and the variable pre-exponential factor. Apart from elucidating hitherto unknown features in the theory of thermal explosion, the results are more general as some known results are easily recovered.     

A study on the thermal stability of uranyl phosphates (UO2)3(PO4)2, (UO2)2P2O7, and UO2(PO3)2 using a static non-isothermal method

A static, non iso-thermal method is used to investigate the stability of uranyl phosphates. The resulting oxygen partial pressures can be expressed as: (UO₂)₃(PO₄)₂, (1089–1280°K) log pO₂/atm = (−18480±400)/T+(13.11±0.33)(UO₂)₂P₂O₇, (979–1130°K) log pO₂/atm = (−27460±540)/T+(24.26±0.51)UO₂(PO₃)₂, (963–1118°K) log pO₂/atm = (−25320±680)/T+(22.58±0.66).Using these results, a part of the phase diagram UO_x (x = 2 to 3) − P₂O₅ is calculated.     

Estimation of the storage life of dimethylol urea using non-isothermal accelerated testing

The mechanism and stability of dimethylol urea (DMU) to polycondensation were investigated using thermogravimetric analysis coupled with mass spectroscopy (TG-MS) for evolved gas analysis and a non-isothermal model-free induction period kinetic analysis using three temperature functions; the Arrhenius function and two non-Arrhenian functions. The polycondensation was observed to occur through a two-step process of condensation followed by elimination of formaldehyde during structural rearrangement as has been reported in the literature. The rate equations for each temperature function were evaluated and extrapolated to room (23 °C) and refrigerator (4 °C) temperature to estimate the length of the induction period for the onset of polycondensation for storage life prediction. Based on experience, estimates of the length of the induction periods and, hence, storage life, were most realistically predicted by the non-Arrhenian temperature functions.     

Prediction of thermal hazard of liquid organic peroxides by non-isothermal and isothermal kinetic model of DSC tests

Liquid organic peroxides (LOPs) have been widely used as initiators of polymerization, hardening, or cross-linking agents. We evaluated a beneficial kinetic model to acquire accurate thermokinetic parameters to help preventing runaway reactions, fires or explosions in the process environment. Differential scanning calorimetry was used to assess the kinetic parameters, such as kinetic model, reaction order, heat of reaction (??H _d), activation energy (E _a), frequency factor (lnk ₀), etc. The non-isothermal and isothermal kinetic models were compared to determine the validity of the kinetic model, and then applied to the thermal hazard assessment of commercial package contaminated with LOPs. Simulations of a 0.5-L Dewar vessel and 25-kg commercial package were performed. We focused on the thermal stability of different liquid system properties for LOPs. From the results, the optimal conditions were determined for avoiding violent heat effects that can cause a runaway reaction in storage, transportation, and manufacturing.     

Evaluation of thermal hazards based on thermokinetic parameters of 2-(1-cyano-1-methylethyl)azocarboxamide by ARC and DSC

Journal of Thermal Analysis and Calorimetry - Azo compounds (azos) are widely used as radical initiators in the polymerization industry. Nonetheless, due to the azo group molecular structure, azos...     

Kinetic study of the thermal dehydration of syngenite K2Ca(SO4)2·H2O under non-isothermal conditions

Different calculation methods applied to TG, DTG and DTA curves obtained with a Mettler Thermoanalyzer at one or several heating rates have been tested. It has been shown that the dehydration of syngenite can best be described by the Avrami equation I [–1n(1–)]^1/2=3.46·10²¹exp (–2.73·10⁴/T)·t where is the degree of decomposition,T the absolute temperature, andt the time.The mean value of the activation energy is 54 kcal·mole^–1. This is in good agreement with the results obtained under isothermal conditions. The method of atava and kvára, supplemented by the numerical tables of Zsakó, is most useful in obtaining the kinetic equations describing the thermal decomposition of solids.

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Zusammenfassung Mit verschiedenen Berechnungsmethoden wurde anhand der TG, DTG und DTA-Kurven, die bei einer und mehreren Aufheizgeschwindigkeiten der Probe im Thermoanalysator der Firma Mettler erhalten wurden bewiesen, daß die kinetische Gleichung zur Beschreibung des Dhydratisierungsprozesses des Syngenits folgende Gestalt hat: [–1n(1–)]^1/2=3.46·10²¹ exp (–2.73·10⁴/T)·t (-Zersetzungsgrad,T absolute Temperatur,t-Zeit) Der Mittelwert der Aktivierungsenergie beträgt: 54 kcal·mol^–1. Die Gleichung und die Werte der kinetischen Parameter stimmen gut mit den Ergebnissen der isothermen Experimente überein. Bei den Untersuchungen thermischer Reaktionen der Zersetzung von Festkörpern hat sich die Methode von atava und kvára, ergänzt durch die numerische Tabelle von Zsakó als besonders geeignet erwiesen.

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Résumé Divers procédés de calcul appliqués aux courbes TG, TGD et ATD obtenues à l'aide d'un thermoanalyseur Mettler, avec une ou plusieurs vitesses de chauffage, conduisent à l'équation cinétique suivante pour exprimer le processus de déshydratation de la syngénite: [–1n (1–)]^1/2=3.46·10²¹exp (–2.73·10⁴/T)·t où =degré de décomposition,T=température absolute,t=temps. La valeur moyenne de l'énergie d'activation est 54 kcal·mol^–1, en bon accord avec les résultats des études en conditions isothermes. La méthode de atava et kvára, combinée avec les tables numériques de Zsakó, s'est révélée la plus efficace pour l'obtention de l'équations décrivant la cinétique de la décomposition thermique des corps solides.

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« » -, , . , , : [–1n(1–)]^1/2=3.46·10²¹ exp (–2.73·10⁴/T)·t - ,— ,t — . , 54 . ^–1. , . , , -log() III III.

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The authors would like to thank Dr. E. M. Bulewicz of this Department for valuable discussions, and Dr. M. Szakowicz and Mr. B. Gawliczek for carrying out the measurements on the Mettler instrument at the Institute of Metallurgy at the School of Mining and Metallurgy in Cracow.     

Synthesis and non-isothermal kinetic study of the thermal decomposition of gadolinium(III) complexes

Summary Pyrrolidinedithiocarbamate (Pyr), piperidinedithiocarbamate (Pip), morpholinedithiocarbamate (Mor) and diethanolaminedithiocarbamate (DEDC) ammonium salts; pyrrolidinedithiocarbamic acid-pyrrolidineammonium salt (HPyrPyr), piperidinedithiocarbamic acid-piperidineammonium salt (HPipPip), morpholinedithiocarbamic acid-morpholineammonium salt (HMorMor), hexamethylenedithiocarbamic acid-hexamethyleneammonium salt (HHexHex), diethanolaminedithiocarbamic acid-diethanolamineammonium salt (HDEADEDC) were synthesized, characterized by IR and elemental analysis and their thermal behaviours were investigated using thermogravimetry (TG) and differential scanning calorimetry (DSC).     

Validation of the estimation of oxidation induction time from non-isothermal DSC measurements

In this paper, correctness of the method for estimation of the oxidation induction time (OIT) from a set of non-isothermal DSC measurements is verified for two samples of sunflower oil in the temperature range of 110–160 °C. It can be concluded on the basis of root-mean-square deviations between the experimental and predicted values of OIT in the high-temperature region (above 110 °C) that both the Arrhenius and non-Arrhenian models lead to a very good agreement of the calculated values of OIT with the experimental ones without any statistically significant bias. Moreover, the uncertainties in the predicted values of OIT are practically identical for all three models applied.     

Study of gelation using differential scanning calorimetry (DSC)

A new method for determining the degree of conversion of gelation (_gel) and gel time (t _gel) at gel point using a single technology, DSC, is discussed in this work. Four kinds of thermoset resins are evaluated. It is found that the mutation points of reduced reaction rate (V _r ) vs. reaction conversion () curves, corresponding with the changes of reaction mechanism, represents the gelation of the reaction. The at the mutation point is defined as _gel. From isothermal DSC curves, the point at _gel is defined ast _gel. Traditional techniques (ASTM D3532 and DSC method) are also used to determine _gel andt _gel in order to demonstrate this new method. We have found that the results obtained from this new method are very consistent with the results obtained from traditional methods.     

Tin(II)-EDTA complex: kinetic of thermal decomposition by non-isothermal procedures

Tin on the oxide form, alone or doped with others metals, has been extensively used as gas sensor, thus, this work reports on the preparation and kinetic parameters regarding the thermal decomposition of Sn(II)-ethylenediaminetetraacetate as precursor to SnO₂. Thus, the acquaintance with the kinetic model regarding the thermal decomposition of the tin complex may leave the door open to foresee, whether it is possible to get thin film of SnO₂ using Sn(II)-EDTA as precursor besides the influence of dopants added.The Sn(II)-EDTA soluble complex was prepared in aqueous medium by adding of tin(II) chloride acid solution to equimolar amount of ammonium salt from EDTA under N₂ atmosphere and temperature of 50 °C arising the pH∼4. The compound was crystallized in ethanol at low-temperature and filtered to eliminate the chloride ions, obtaining the heptacoordinated chelate with the composition H₂SnH₂O(CH₂N(CH₂COO)₂)₂·0.5H₂O.Results from TG, DTG and DSC curves under inert and oxidizing atmospheres indicate the presence of water coordinated to the metal and that the ethylenediamine fraction is thermally more stable than carboxylate groups. The final residue from thermal decomposition was the SnO₂ characterized by X-ray as a tetragonal rutile phase.Applying the isoconversional Wall-Flynn-Ozawa method on the DSC curves, average activation energy: E_a=183.7±2.7 and 218.9±2.1 kJ mol⁻¹, and pre-exponential factor: and 19.10±0.27 min⁻¹, at 95% confidence level, could be obtained, regarding the loss of coordinated water and thermal decomposition of the carboxylate groups, respectively. The E_a and log A also could be obtained applying isoconventional Wall-Flynn method on the TG curves.From E_a and log A values, Dollimore and Malék procedures could be applied suggesting R3 (contracting volume) and SB (two-parameter model) as the kinetic model to the loss of coordinated water (177-244 °C) and thermal decomposition of the carboxylate groups (283-315 °C), respectively. Simulated and experimental normalized DTG and DSC curves besides analysis of residuals check these kinetic models.