Thermal Analysis Studies on Isopropylnitrate

Isopropylnitrate (IPN) is described as a detonable material used in propellants and explosives. While there is considerable information available on its sensitivity and compatibility with other materials, very little is known about its thermochemical properties. This paper will describe the results obtained from some DSC, heat flux calorimetry (HFC) and accelerating rate calorimetry (ARC) measurements. The ASTM DSC method using a hermetic aluminum pan having a lid with a laser-produced pin hole was used to determine the vapour pressure of IPN₁. Results calculated from an Antoine equation are in substantial agreement with those determined from DSC measurements. From the latter measurements, the enthalpy of vaporization was determined to be 35.32±0.62 kJ mol⁻¹. Attempts to determine vapour pressures above about 0.8 MPa resulted in significant decomposition of IPN_g. The enthalpy change for decomposition in sealed glass systems was found to be -3.43±0.09 kJ g⁻¹ and -3.85±0.03 kJ g⁻¹, respectively from DSC and HFC measurements on IPN₁ samples loaded in air. Slightly larger exotherms were observed for the HFC results in air than those in inert gas, suggesting some oxidation occurs. In contrast, no significant difference in the observed onset temperature of about 150°C was observed for both the HFC and ARC results. From DSC measurements, an Arrhenius activation energy for decomposition of 126±4 kJ mol⁻¹ was found. These measurements were also conducted in sealed glass systems and decomposition appeared to proceed primarily from the liquid phase. This revised version was published online in August 2006 with corrections to the Cover Date.     

Sensitive Voltammetric Sensing of the 2,3‐Dimethyl‐2,3‐dinitrobutane (Dmnb) Explosive Taggant

The highly sensitive voltammetric detection of the 2,3‐dimethyl‐2,3‐dinitrobutane (DMNB), a required additive to commercial plastic explosives, is described. The protocol relies on a fast square‐wave voltammetric measurement of the DMNB explosive taggant at an unmodified carbon fiber electrode using a phosphate buffer (pH 7.0) solution. Different solutions and working electrodes were evaluated. Under the optimal conditions, a linear response is observed over the 300–3000 μg/L DMNB concentration range examined, with a detection limit of 60 μg/L. A highly stable response, with a relative standard deviation (RSD) of 2.6%, is observed for 30 repetitive measurements. Such electrochemical approach offers great promise for a simple, rapid, sensitive and inexpensive field screening of plastic explosives. Preliminary data illustrate the utility of electrochemical detection for electrophoretic microchips for the simultaneous measurements of DMNB, cyclotrimethylenetrinitramine (RDX) and pentaerythritoltetranitrate (PETN).     

Fragmentation pathways of 2,3‐dimethyl‐2,3‐dinitrobutane cations in the gas phase

2,3‐Dimethyl‐2,3‐dinitrobutane (DMNB) is an explosive taggant added to plastic explosives during manufacture making them more susceptible to vapour‐phase detection systems. In this study, the formation and detection of gas‐phase [M+H]⁺, [M+Li]⁺, [M+NH₄]⁺ and [M+Na]⁺ adducts of DMNB was achieved using electrospray ionisation on a triple quadrupole mass spectrometer. The [M+H]⁺ ion abundance was found to have a strong dependence on ion source temperature, decreasing markedly at source temperatures above 50°C. In contrast, the [M+Na]⁺ ion demonstrated increasing ion abundance at source temperatures up to 105°C. The relative susceptibility of DMNB adduct ions toward dissociation was investigated by collision‐induced dissociation. Probable structures of product ions and mechanisms for unimolecular dissociation have been inferred based on fragmentation patterns from tandem mass (MS/MS) spectra of source‐formed ions of normal and isotopically labelled DMNB, and quantum chemical calculations. Both thermal and collisional activation studies suggest that the [M+Na]⁺ adduct ions are significantly more stable toward dissociation than their protonated analogues and, as a consequence, the former provide attractive targets for detection by contemporary rapid screening methods such as desorption electrospray ionisation mass spectrometry. Copyright © 2009 Commonwealth of Australia. Published by John Wiley & Sons, Ltd.     

Solid-phase microextraction coupled to gas chromatography for the determination of 2,3-dimethyl-2,3-dinitrobutane as a marking agent for explosives

This paper investigates the detection of 2,3-dimethyl-2,3-dinitrobutane (DMNB), a marking agent in explosives, by gas chromatography (GC) with electron capture detection using solid-phase microextraction (SPME) as a sample preparation technique. The 25,27-dihydroxy-26,28-oxy (2′,7′-dioxo-3′,6′-diazaoctyl) oxy-p-tert-butylcalix[4]arene/hydroxy-terminated silicone oil coated fiber was highly sensitive to trap DMNB from ammonium nitrate matrix. The analysis was performed by extracting 2 g of explosives for 30 s at room temperature and then immediately introducing into the heated GC injector for 1 min of thermal desorption. The method showed good linearity in the range from 0.01 to 1.0 μg/g. The relative standard deviations for these extractions were <8%. The calculated limit of detection for DMNB (S/N = 3) was 4.43 × 10⁻⁴ μg/g, which illustrates that the proposed systems are suitable for explosive detection at trace level. This is the first report of an SPME-GC system shown to extract marking agent in explosives for subsequent detection in a simple, rapid, sensitive, and inexpensive manner.     

Utilization of microcalorimetry for an assessment of the potential for a runaway decomposition of cumene hydroperoxide at low temperatures

The exothermic decomposition of cumene hydroperoxide (CHP) in cumene liquid was characterized by isothermal microcalorimetry, involving the thermal activity monitor (TAM). Unlike the exothermic behaviors previously determined from an adiabatic calorimeter, such as the vent sizing package 2 (VSP2), or differential scanning calorimetry (DSC), thermal curves revealed that CHP undergoes an autocatalytic decomposition detectable between 75 and 90°C. Previous studies have shown that the CHP in a temperature range higher than 100°C conformed to an n ^th order reaction rate model. CHP heat of decomposition and autocatalytic kinetics behavior were measured and compared with previous reports, and the methodology and the advantages of using the TAM to obtain an autocatalytic model by curve fitting are reported. With various autocatalytic models, such as the Prout-Tompkins equation and the Avrami-Erofeev rate law, the best curve fit among models was also investigated and proposed.     

Thermal Decomposition of Strontium and Barium Malonates

The thermal decomposition of strontium and barium malonates has been studied isothermally and non-isothermally employing simultaneous TG-DTG-DTA, DSC, XRD and IR spectroscopic techniques. DSC of these malonates has been recorded both in oxygen and nitrogen atmospheres. The decomposition is a single step process and the end product formed is carbonate. The energy of activation and frequency factor values for the decomposition of strontium malonate are 547 kJ mol⁻¹ and 10⁴¹ s⁻¹ respectively. The activation energy and frequency factor values for isothermal dehydration of barium malonate sester-hydrate are 57–111 kJ mol⁻¹ and 10⁷–10¹² s⁻¹ respectively and the corresponding values for decomposition from DSC are 499.5 kJ mol⁻¹ and 10⁴⁴ s⁻¹ respectively. The higher thermal stability of strontium malonate as compared to that of barium salt is ascribed to its being anhydrous so that decomposition proceeds without restructuring. Their thermal stabilities have also been compared with that of respective oxalate salts. This revised version was published online in July 2006 with corrections to the Cover Date.     

Kinetics of thermal decomposition of a synthetic K–H3O jarosite analog

The thermal decomposition kinetics of a synthetic K–H₃O jarosite analog was determined from thermogravimetric analysis at various heating rates in air. A thermal decomposition mechanism was proposed based on X-ray analysis of partially decomposed material and distinct features observed during thermal decomposition analysis. The decomposition path is complex. The material was treated as a composite of K-jarosite, H₃O-jarosite, and a “vacancy component”. The evolution of (OH)^? and SO₃ from these individual components was modeled. The decomposition is broken into subreactions according to distinct features in the thermoanalytical measurements. The subreactions are arranged sequentially and in parallel according to the evolution of the participating phases. A set of associated apparent activation energies was determined using isoconversion analysis. Kinetic triplets were assigned to each subreaction. A reasonable match with the observed decomposition was achieved by varying pre-exponential factors.     

Kinetic analysis of complex decomposition reactions using evolved gas analysis

For complex decomposition reactions, traditional methods, such as TG and DSC cannot fully resolve all of the steps in the reaction. Evolved gas analysis (EGA) offers another tool to provide more information about the decomposition mechanism. The decomposition of sodium bicarbonate was studied by TG, DSC and EGA using a simultaneous thermal analysis unit coupled to a FTIR. The decomposition of sodium bicarbonate involves two reaction products H₂O and CO₂, which are not evident from either TG or DSC measurements alone. A comparison of the reaction kinetics from TG, DTG and EGA data were compared.     

Thermal investigation of the crystallisation nucleant formed between 2,4,6 trinitrotoluene, (TNT) and 2,2′,4,4′,6,6′ hexanitrostilbene (HNS)

Hexanitrostilbene (HNS), is added to trinitrotoluene (TNT), in order to improve the grain structure of cast munitions. The formation and composition of the nucleant material has been investigated by thermal methods using mixtures of HNS and TNT, with composition in the range 0.5%, the normal casting level, to 50% w/w HNS to TNT. These were cycled between ambient and upper temperatures in the range 160 to 235°C. Endotherms in the DSC traces, due to nucleant decomposition, have been observed in situ without the need for separation and purification. DSC enthalpy measurements, before and after thermal decomposition, were used to determine the composition of separated nucleant. Nucleant regeneration after decomposition, was investigated by thermal methods. Nucleant could not be recrystallised from solvents. Results have been interpreted on the basis of the formation of a, solid solution of TNT in HNS, rather than a complex of formula TNT₂HNS.     

Temperature scanning ultrasonic velocity study of complex thermal transformations in solid lipid nanoparticles

The purpose of this study was to determine whether temperature scanning ultrasonic velocity measurements could be used to monitor the complex thermal transitions that occur during the crystallization and melting of triglyceride solid lipid nanoparticles (SLNs). Ultrasonic velocity ( u) measurements were compared with differential scanning calorimetry (DSC) measurements on tripalmitin emulsions that were cooled (from 75 to 5 degrees C) and then heated (from 5 to 75 degrees C) at 0.3 degrees C min (-1). There was an excellent correspondence between the thermal transitions observed in deltaDelta u/delta T versus temperature curves determined by ultrasound and heat flow versus temperature curves determined by DSC. In particular, both techniques were sensitive to the complex melting behavior of the solidified tripalmitin, which was attributed to the dependence of the melting point of the SLNs on particle size. These studies suggest that temperature scanning ultrasonic velocity measurements may prove to be a useful alternative to conventional DSC techniques for monitoring phase transitions in colloidal systems.     

Thermal decompositions of dialkyl peroxides studied by DSC

Studies on the thermal decompositions of diamyl peroxide (DAPO), dicumyl peroxide (DCPO), and tert-butyl cumyl peroxide (TBCP) were conducted by DSC. Heat of decomposition, exothermic onset point, and chemical kinetics were determined and compared to those data of di-tert-butyl peroxide (DTBP), a model compound for studying thermokinetics of organic peroxide and standardization of a calorimeter. Similarities and differences of decomposition mechanisms between these organic peroxides were proposed and verified. Kinetics on decomposition of uni-molecular reaction via these similar alkoxyl radials accompanying β C–C bond scission were discussed and compared to the results from ab initio calculations. The ranking of thermal stability on dialkyl peroxides is determined to be in the following sequence: DCPO < TBCP < DAPO < DTBP. This rate-determining step in thermal decomposition of dialkyl peroxides possessed an average eigenvalue of log A at about 13.1 ± 1.2. Activation energy on the thermal decomposition of these peroxides was calculated to be 139.5 ± 14.4 kJ mol^?1.     

Simulation approach to decomposition kinetics and thermal hazards of hexamethylenetetramine

The thermal stability of HMT under dynamic, isothermal and adiabatic conditions was investigated using differential scanning calorimeter (DSC) and accelerating rate calorimeter (ARC), respectively. It is found from the dynamic DSC results that the exothermic decomposition reaction appears immediately after endothermic peak, a coupling phenomenon of heat absorption and generation, and the endothermic peak and exothermic peak were indentified at about 277–289 and 279–296 °C (T_peak) with the heating rates 1, 2, 4 and 8 °C min⁻¹. The ARC results reveal that the initial decomposition temperature of HMT is about 236.55 °C, and the total gas production in decomposition process is 6.9 mol kg⁻¹. Based on the isothermal DSC and ARC data, some kinetic parameters have been determined using thermal safety software. The simulation results show that the exothermic decomposition process of HMT can be expressed by an autocatalytic reaction mechanism. There is also a good agreement between the kinetic model and kinetic parameters simulated based on the isothermal DSC and ARC data. Thermal hazards of HMT can be evaluated by carrying out thermal explosion simulations, which were based on kinetic models (Isothermal DSC and ARC) to predict several thermal hazard indicators, such as T_D24, T_D8, TCL, SADT, ET and CT so that we can optimize the conditions of transportation and storage for chemical, also minimizing industrial disasters.

     

Thermal and spectral properties of 2,3-, 2,4- and 3,4- dimethoxybenzoates of light lanthanides

The physico-chemical properties and thermal stability in air of light lanthanide 2,3-, 2,4- and 3,4-dimethoxybenzoates were compared and the influence of -OCH₃ substituent on their thermal stability was investigated. The complexes of these series are crystalline, hydrated or anhydrous salts with colours typical of Ln³⁺ ions. The carboxylate group is a bidentate, chelating (2,4- and 3,4-dimethoxybenzoates) or tridentate chelating and bridging ligand (2,3- dimethoxybenzoates). The thermal stability of 2,4- , 3,4- and 2,3- dimethoxybenzoates of light lanthanides was studied in the temperature range 273-1173 K. The positions of methoxy groups in benzene ring influence the thermal properties of the complexes and their decomposition mechanism. This revised version was published online in July 2006 with corrections to the Cover Date.     

Calorimetric measurements of sodium chloride dihydrate (hydrohalite)

Calorimetric measurements of sodium chloride dihydrate NaCl·2H₂O (mineral name hydrohalite) were carried out with using DSC. Heat capacity from 190 to 250 K was measured and found to increase from 109 to 137 J mol^?1 K^?1. The enthalpy of formation of hydrohalite from solid ice and halite at 273.15 K was derived from the thermal effect of melting/decomposition in DSC measurements and found to be close to ??1.8 kJ mol^?1. The same DSC results show clearly that the upper temperature limit for the existence of hydrohalite is several degrees greater than the current value of 273.15 K accepted for the peritectic decomposition of hydrohalite. The phase diagram of the NaCl–H₂O system needs correction.

     

Thermal Expansion of Liquid Crystalline Polyesters Having Phenanthrene Moieties. Simultaneous DSC-XRD method

Phase transition process of polyester from phenanthrene, poly(oxyheptamethyleneoxy-2,7-phenantrenedicarbonyl), a main chain type liquid crystalline polymer, was investigated by simultaneous DSC-XRD measurements using the synchrotron radiation facility (PF). Three exothermic DSC peaks were observed during cooling from the isotropic liquid state. These DSC peaks were assigned to the transition from the isotropic liquid to the smectic A, that from the smectic A to C, and that from the smectic C to the crystalline state, respectively, as determined by XRD profiles. The rate of transition from the smectic A to C was very slow compared with the liquid crystalline transition and the crystallization. From the DSC-XRD results, the thermal expansion along c-axis in the crystal and smectic phases are 4.1×10⁻⁴ and 1.4×10⁻³ nm K⁻¹ , respectively. This revised version was published online in July 2006 with corrections to the Cover Date.     

Vibrational and thermal characterization of Nafion membranes substituted by alkaline earth cations

The vibrational spectra of Nafion^® membranes with alkaline earth cations as counterions have been obtained by photoacoustic infrared spectroscopy (PAS-IR) and Fourier transform Raman spectroscopy (FT-Raman). The symmetrical stretching band of the sulfonate group (∼1060 cm⁻¹) decreases with increasing atomic mass of the countercation, excepting for Mg²⁺, in both techniques. The thermal behavior of Nafion membranes by means of differential scanning calorimetry (DSC) curves showed a dependence on the water content and a similar profile between Nafion-Mg²⁺ and -Ca²⁺, and between Nafion-Sr²⁺ and -Ba²⁺, for the first scanning curve. An ageing effect was also observed on Nafion by DSC curves. High-resolution thermogravimetry (TG) curves under nitrogen atmosphere showed similar decomposition profiles. It was determined from TG curves that there is a decreasing water content with increasing ionic radius of cation, and the thermal stability increasing from Nafion-Mg²⁺ to -Ba²⁺.     

TG and DSC kinetics of thermal decomposition and crystallization processes

The simplen ^th order model equation combined with the Arrhenius approach of the temperature dependency of the reaction rate constant is widely used in thermal analysis. The new Mettler software package for thermal analysis, GraphWare TA72 allows to access a full model comprising the power law and the crystallization kinetics (AvramiErofe'ev). The kinetics of the following reactions are studied to illustrate some applications:

thermal decomposition of dissolved dibenzoylperoxide, (dynamic and isothermal DSC measurement)

crystallization of polyethylene terephthalate (PET) (isothermal DSC measurements).

The kinetic model applied and the accuracy of the kinetic data obtained are discussed by means of a comparison of a predicted behaviour with the kinetic data measured isothermally.     

Thermal decomposition kinetics of hydrazinium cerium 2,3-Pyrazinedicarboxylate hydrate: a new precursor for CeO2

The thermal decomposition kinetics of N(2)H(5)[Ce(pyrazine-2,3-dicarboxylate)(2)(H(2)O)] (Ce-P) have been studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), for the first time; TGA analysis reveals an oxidative decomposition process yielding CeO(2) as the final product with an activation energy of approximately 160 kJ mol(-1). This complex may be used as a precursor to fine particle cerium oxides due to its low temperature of decomposition.     

Isothermal and rising temperature kinetic studies of doped nonstoichiometric basic nickel carbonate

The techniques of thermal analysis are used to determine the mode of decomposition of nickel carbonates doped by the method of coprecipitation. Nickel carbonate prepared by this method is basic in nature with the stoichiometryxNiCO₃·yNi(OH)₂·zH₂O. Isothermal Thermogravimetry was applied to determine the mechanism of decomposition. Rising temperature Thermogravimetry (TG) and Differential Scanning Calorimetry (DSC) were used to study the effects of doping on the kinetics of the decomposition. Doping was found to strongly influence the kinetics of the decomposition. The kinetics of thermal decomposition of the doped carbonates were compared with conductivity studies. A compensation effect has been observed and is discussed, in the thermal decomposition of the doped nickel carbonates. In celebration of the 60^th birthday of Dr. Andrew K. Galwey     

Synthesis,characterization, and thermal degradation mechanism of fast biodegradable PPSu/PCL copolymers

Poly(propylene succinate)/poly(ε‐caprolactone) (PPSu/PCL) 25/75, 50/50, and 75/25 w/w copolymers were prepared using a combination of polycondensation and ring opening polymerization. The randomness of copolymers was characterized using ¹H NMR and ¹³C NMR spectroscopy. From molecular weights and DSC measurements it was observed that the molecular weight decreased with increasing the wt % content of PPSu, while the copolymers containing 50 and 75 wt % PPSu were completely amorphous. Enzymatic hydrolysis revealed that biodegradation rate was much enhanced compared with that of neat PCL and increased by increasing the PPSu content. From TGA analysis it was also found that the PPSu/PCL copolymers had similar thermal decomposition behaviour with the pure polyesters and exhibited their maximum decomposition rates at temperatures 400–420 °C. Two different mechanisms, which follow each other, were used to adequately describe their decomposition kinetics. The first one corresponded to the first stage taking place at 280–365 °C, where small mass loss was recorded and activation energies ranged between 94 and 156 kJ/mol. The second one took place at 370–460 °C and corresponded to the stage where the main polyester mass was decomposed. The activation energies for this stage ranged between 200 and 240 kJ/mol. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5076–5090, 2007