Effect of in impurity on crystallization kinetics of (Se.7Te.3)100−xInx system

The effect of In impurity on the crystallization kinetics and the changes taking place in the structure of (Se₇Te₃) have been studied by DTA measurements at different heating rates (α=5 deg·min^?1, 10 deg·min^?1, 15 deg·min^?1 and 20 deg·min^?1). From the heating rate dependence of the values ofT _g,T _c andT _p, the glass transition activation energy (E _t) and the crystallization activation energy (E _c) have been obtained for different compositions of (Se₇Te₃)_100?xIn_x (0≤×≤20). The variation of viscosity as a function of temperature has been evaluated using Vogel-Tamman-Fulcher equation. The crystallization data are analysed using Kissinger's and Matusita's approach for nonisothermic crystallization. It has been found that for samples containing In=0, 10, 15, 20 at%, three dimensional nucleation is predominant whereas for samples containing In=5 at%, two dimensional nucleation is the dominant mechanism. The compositional dependence ofT _g and crystallization kinetics are discussed in terms of the modification of the structure of the Se?Te system.     

Studies on the thermal properties of caprolactam/long chain lactam copolymer

The thermal properties of caprolactam/long chain lactam copolymer were studied with a Perkin-Elmer DSC 7. The melting point (T _m), heat of fusion (δH _m), crystalline degree (X _c), crystallization temperature (T _c) and glass transition temperature (T _g) of the copolymers increase with decrease of the content of the log chain lactam. From the changes in the mechanical properties with corresponding changes in the thermal properties, it is clear that the copolymers are thermal plastic and elastic. In addition, it is found that the results at a heating rate of 10 deg·min^?1 are almost the same as that at 20 deg·min^?1 after thermal history is erased.     

A study of the effect of purity on the use of nickel as a temperature standard for thermomagnetometry

Samples of nickel, varying by four orders of magnitude in their purity, were studied by thermomagnetometry (TM), to determine if the extrapolated end point (T _C ) changes.T _C is virtually identical for the 99.99 and 99.999% samples. Samples of less purity did show changes. Simultaneous DTA/TM can accurately defineT _C by comparing with the melting points of pure metals determined simultaneously. The melting points of lead and zinc bracket theT _C for nickel. They were added to the sample pan prior to TM of nickel. Experiments were performed at heating rates in the range from 1 to 20 deg·min^?1. It serves as a pilot study for the ICTAC Committee for Standardization to more accurately define the recommended values ofT _C .     

Thermal Decomposition Kinetics of Triethylene Glycol Dinitrate

Introduction Triethylene glycol dinitrate (TEGDN) is a novel en-ergetic material containing two groups of NO2, which can be used as an energetic plasticizer ingredient in propellants because of its excellent proformance.1 It exhibits lower impact sensitivity, better thermostability, weaker poisonousness and volatility, and stronger effec-tiveness of plasticizing cellulose nitrate than nitroglyc-erine (NG). As a new plasticizer TEGDN has good ap-plication prospects in the near future. The…     

Chlorine nuclear quadrupole resonance study on 1,3-dichloroacetone: dimorphism and temperature dependence of the 35Cl-NQR

Solid 1,3-dichloroacetone, CH₂ClCOCH₂Cl, is dimorphic. The ³⁵Cl-NQR spectra and the X-ray powder patterns are given for both modifications. Phase I shows a single chlorine resonance, whereas phase II (considered to be metastable) gives a four line spectrum. The implications from the NQR spectra with respect to the crystal structures of the two modifications are discussed. The temperature dependence of the ³⁵Cl-NQR frequencies is described by the relationships v^I = 35.9989 ? 16.02 · 10^?1 · T ? 7.350 · 10^?6 · T² + 8.57 · T^?1 (v in MHz, T in K) (Phase I in the range 77 K ? T ? 318 K), and by v₁^II = 36.2968 + 8.19 · 10^?4 · T ? 11.409 · 10^?6 · T² + 13.39 · T^?1, v₂^II = 36.1459 + 5.93 · 10^?4 · T ? 10.447 · 10^?6 · T² + 12.27 · T^?1, v₃^II = 36.0691 + 1.55 · 10^?4 · T ? 9.537 · 10^?6 · T² + 11.72 · T^?1, v₄^II = 35.8244 + 4.42 · 10^?4 · T ? 13.502 · 10^?6 · T² + 17.22 · T^?1, (Phase II in the range 77 K ? T ? 308 K).     

Non-isothermal Decomposition Kinetics, Specific Heat Capac-ity and Adiabatic Time-to-explosion of a High Energy Material: 4,6-Bis(5-amino-3-nitro-1,2,4-triazol-1-yl)-5-nitropyrimidine

The thermal behavior of 4,6‐bis‐(5‐amino‐3‐nitro‐1,2,4‐triazol‐1‐yl)‐5‐nitropyrimidine (BANTNP) was studied under a non‐isothermal condition by DSC, PDSC and TG/DTG methods. The kinetic parameters (E_a and A) of the exothermic decomposition reaction are 304.52 kJ·mol^?1 and 10^24.47 s^?1 at 0.1 MPa, 272.52 kJ·mol^?1 and 10^21.76 s^?1 at 5.0 MPa, respectively. The kinetic equation at 0.1 MPa can be expressed as: dα/dT=10^25.3(1?α)^3/4exp(?3.8044×10⁴/T)/β The critical temperature of thermal explosion is 588.28 K. The specific heat capacity of BANTNP was determined with a Micro‐DSC method, and the standard molar specific heat capacity is 397.54 J·mol^?1·K^?1 at 298.15 K. The adiabatic time‐to‐explosion of BANTNP was calculated to be 11.75 s.     

Electrochemical Responses and Sensitivities of Films Based on Multi-Walled Carbon Nanotubes in Aqueous Solutions

Novel films consisting of multi-walled carbon nanotubes (MWCNTs) were fabricated by means of chemical vapor deposition with decomposition of either acetonitrile (ACN) or benzene (BZ) using ferrocene as catalyst. The electrochemical responses of MWCNT-based films towards the ferrocyanide/ferricyanide, [Fe(CN)₆]^3?/4? redox couple were probed by means of cyclic voltammetry and electrochemical impedance spectroscopy at 25.0?±?0.5?°C. Both MWCNT-based films exhibit Nernstian response towards [Fe(CN)₆]^3?/4? with some slight kinetic differences. Namely, heterogeneous electron transfer rate constants lying in ranges of 2.69?×?10^?2?C1.7?×?10^?3 and 9.0?×?10^?3?C2.6?×?10^?3?cm·s^?1 were obtained at v?=?0.05?V·s^?1 for MWCNT_ACN and MWCNT_BZ, respectively. The detection limit of MWCNT_ACN, estimated to be about 4.70?×?10^?7?mol·L^?1 at v?=?0.05?V·s^?1, tends to become slightly poorer with the increase of the scan rate, namely at v?=?0.10?V·s^?1 the detection limit of 1.70?×?10^?6?mol·L^?1 was determined. Slightly poorer response ability was exhibited by MWCNT_BZ; specifically the detection limits of 1.57?×?10^?6 and 4.35?×?10^?6?mol·L^?1 were determined at v?=?0.05 and v?=?0.10?V·s^?1, respectively. The sensitivities of MWCNT_ACN and MWCNT_BZ towards [Fe(CN)₆]^3?/4? were determined as 1.60?×?10^?7 and 1.51?×?10^?7?A·L·mol^?1·cm^?2, respectively. The excellent electrochemical performance of MWCNT_ACN is attributed to the presence of incorporated nitrogen in the nanotube??s structure.     

General remarks on the thermal decomposition of some drugs

The thermal decomposition of antituberculous, local anaesthetic and calcium salts of organic acids used as the drugs has been studied by differential thermal and thermogravimetric techniques. General characteristics of their thermal decomposition has been made. The effect of sample size over the range 20–200 mg and heating rate over the range 3–15 deg·min^?1 on the thermal degradation has been investigated. The values of the kinetic parameters has been also determined.     

Characteristics of the thermal decomposition of antituberculous drugs

The thermal decomposition of antituberculous drugs-ethambutol (base and dihydrochloride), isoniazid, ethionamid and pyrazinamid has been studied by DTA, TG and DTG techniques. General remarks have been made on their thermal destruction. The effect of sample size over the range 20–200 mg and heating rate over the range 3–15 deg·min^?1 on the thermal degradation has also been investigated. Moreover, based on the Kissinger’s equation, the values of the kinetic parameters were determined.     

Dehydration Kinetics of Zinc Phosphate Tetrahydrate α-Zn3（PO4）2·4H2O Nanoparticle

TG-DTG technique and Harcourt-Esson integrated equation were used to study the dehydration process of zinc phosphate tetrahydrate α-Zn3（PO4）2·4H2O nanoparticle and its thermal decomposition kinetics. The results show that there are three stages of dehydration between 300 and 800 K during the thermal decomposition of α-Zn3（PO4）2·4H2O nanoparticle. The first stage is controlled by chemical reaction with an activation energy of 69.48 kJ·mol^-1 and a pre-exponential factor of 1.77×10^6 s^-1. The second is controlled by nucleation and growth with an activation energy of 78.74 kJ·mol^-1 and a pre-exponential factor of 5.86×10^9 s^-1. The third is controlled by nucleation and growth with an activation energy of 141.5 kJ·mol^-1 and a pre-exponential factor of 1.01×10^12 s^-1. The kinetic compensative effects not only exist in Arrhenius equation but also in Harcourt-Esson equation. Activation energy E is dependent on both the decomposition fraction α and temperature T.     

Thermal hazard evaluation of tert-butyl peroxide using non-isothermal and adiabatic calorimetric approaches

Tert-butyl peroxide (TBPO), is a typical organic peroxides (OPs),which is widely applied as initiator in poly-glycidyl methacrylate (PGMA) reaction, and is employed to provide a free-radical in frontal polymerization, and which has also caused many thermal runaway reactions and explosions worldwide. To find an unknown and insufficient hazard information for an energetic material, differential scanning calorimetry (DSC) and vent sizing package 2 (VSP2) were employed to detect the fundamental thermokinetic parameters involving the exothermic onset temperature (T ₀), heat of decomposition (??H _d), temperature rise rate (dT · dt ^?1), time to maximum rate under adiabatic situation (TMR_ad), pressure rise rate (dP · dt ^?1), and maximum pressure (P _max), etc. The T ₀ was calculated to be 130?°C using DSC and VSP2. Activation energy (E _a) of TBPO was evaluated to be 136?kJ?mol^?1 by VSP2. In view of the loss prevention, calorimetric applications and model evaluation to integrate thermal hazard development are adequate means for inherently safer design.     

Kinetic Study of 1-β-Cyanoethyl Aziridine for Ring-Opening Polymerization Initiated with Alkyl Sulfate

The kinetics of the cationic polymerization of 1-β-cyanoethyl aziridine initiated 3-hydroxy- 1-propane sulfonic acid sultone and methyl tosylate have been studied. The course of polymerization involved the propagation stage and termination reaction due to the reaction between the growing chain and imino groups in the polymer chain. The propagation constants and termination constants were obtained. The enthalpies of activation for the propagation and termination reactions are ΔH_p? = 12.9 kcal/mol and ΔH_t? = 12.4 kcal/mol, and the entropies of activation are ΔS_p? = -31 cal/deg·mol and ΔS_t? = -39 cal/deg·mol. Otherwise, the polymerization initiated with methyl tosylate involved an early stage which was initiated very quickly.     

The thermal decomposition of (NH4)4V2O11 in a nitrogen atmosphere and the kinetics of the first decomposition step

Although the reaction products are unstable at the reaction temperatures, at a heating rate of 2 deg·min^?1 ammonium peroxo vanadate, (NH₄)₄V₂O₁₁, decomposes to (NH₄)[VO (O₂)₂ (NH₃)] (above 93°C); this in turn decomposes to (NH₄) [VO₃ (NH₃)] (above 106°C) and then to ammonium metavanadate (above 145°C). On further heating vanadium pentoxide is formed above 320°C. The first decomposition reaction occurs in a single step and the Avrami-Erofeev equation withn=2 fits the decomposition data best. An activation energy of 148.8 kJ·mol^?1 and a ln(A) value of 42.2 are calculated for this reaction by the isothermal analysis method. An average value of 144 kJ·mol^?1 is calculated for the first decomposition reaction using the dynamic heating data and the transformation-degree dependence of temperature at different heating rates.     

Transfer reaction of the polystyrene radical with electron-acceptor molecules of tetrachlorophthalanhydride

The transfer constants (C_s) of the polystyrene radical with some derivatives of phthalic acid have been determined. Among the agents used, tetrachlorophthalanhydride (TCPA) differs distinctly from other compounds by its value of C_s 3·1 × 10^?3 for thermal and 3·4 × 10^?3 for initiated polymerization of styrene. The values of C_s for phthalanhydride, dimethyl phthalate, and tetrachlorodimethyl phthalate are lower by two decimal orders. The considerable decrease in the degree of polymerization of styrene prepared in the presence of TCPA is mainly attributed to the increased reactivity of chlorine atoms in TCPA induced by the acceptor effect of anhydride ring. Participation of a TCPA-styrene complex in transfer reaction has been assumed but not proved.     

Picosecond spectroscopic measurement of very fast intersystem crossing for 9,10-dioxa-anti-bimanes

Picosecond spectroscopy, following the buildup of T₁ → T_n absorption (maximum at 420 nm), shows that the T₁ state of 1,5-diazabicyclo[3,3,0]octa-3,7-diene-2,6-diones(9,10-dioxa-anti-bimanes) is formed within about 10 ps. The nature of the T₁ state was confirmed by decay rates of T₁ → T_n absorption in acetonitrile (n = 0.375 cP, k_nr = 4.5 × 10⁵ s^?1), 1,2-ethanediol (n = 26 cP, k_nr = 1.5 × 10⁴ s^?1 and glycerol (n = 1400 cP, k_nr = 1.3 × 10³ s^?1). The very fast intersystem crossing is ascribed to the proximity of a ³nπ* state to the ππ* (S₁ state produced by light absorption (El-Sayed rule).     

Thermal studies and spectral characterization of the chelate of bis-(η5-cyclopentadienyl titanium(IV) with salicylidene-4-methylaniline

A new chelate (η⁵-C₅H₅)₂Ti(SB)₂, whereSB=O, N donor Schiff base salicylidene-4-methylaniline, was synthesized. The course of thermal degradation of the chelate was studied by thermogravimetric (TG) and differential thermal analysis (DTA) under dynamic conditions of temperature. The order of the thermal decomposition reaction and energy of activation was calculated from TG curve while from DTA curve the change in enthalpy was calculated. Evaluation of the kinetic parameters was performed by Coats-Redfern as well as Piloyan-Novikova methods which gaven=1, ΔH=1.114 kJ·mol^?1, ΔE=27.01 kJ·mol^?1, ΔS=?340.12 kJ·mol^?1·K^?1 andn=1, ΔH=1.114 kJ·mol^?1, ΔE=20.01 kJ·mol^?1, ΔS=?342.60 kJ·mol^?1·K^?1, respectively. The chelate was also characterized on the basis of different spectral studies viz. conductance, molecular weight, IR, UV-visible and¹H NMR, which enabled to propose an octahedral structure to the chelate.     

Thermally induced incomplete high-spin (5T2) ⇌ low-spin (1A1) transition in solid bis[2-(2-pyridylamino)-4-(2-pyridyl) thiazolato]iron (II)

The ⁵⁷Fe Mössbauer effect in two samples (A and B) of [Fe(papt)₂] and in its solvates with CHCl₃ and C₆H₆ has been studied between 4.2 and 343 K and clearly indicates a temperature induced high-spin (⁵T₂) ? low-spin (¹A₁) transition in these compounds [paptH = 2-(2-pyridylamino)-4-(2-pyridyl) thiazole]. At 343 K, sample B shows a doublet with ΔE_Q = 2.03 mm s^?1 and δIS = +0.87 mm s^?1, characteristic of a ⁵T₂ ground state. At 257 K, a second doublet, typical for a ¹A₁ ground state, is observed and its intensity increases as the transition progresses but levels off below ～ 100 K. At 4.2 K, 83% of the intensity is due to the ¹A₁ state, and ΔE_Q(¹A₁) = 1.56 mm s^?1 and δ^IS(¹A₁ = +0.32 mm s^?1. In an applied magnetic field, V_zz(¹A₁) < 0 and η ≈ 0.7 have been determined, whereas for the ^sT₂ ground state, V_zz(^sT₂) > 0, η ≈ 0.75, and an internal hyperfine field H_n ≈ ?13 kG have been observed. Similar results have been obtained with the other samples.Debye-Waller factors f5_T2 and f1_A1 were determined from the saturation corrected areas in the Mössbauer spectra, assuming Curie-Weiss dependence of the magnetic susceptibility for the ⁵T₂ and constant υ_cff for the ¹A₁ ground state. The temperature dependence of ?In f1_A1 closely follows the Debye model with Θ1_A1 = 165 K, whereas the same applies to ?ln f5_T2 only above ～ 210 K and Θ5_T2 = 134 K. The nature of the observed transition is discussed and the data presented are shown to be incompatible with a model based on a Boltzmann distribution between the two states.     

Collisional de-excitation of the metastableD-states of Ba+ by He,Ne, N2 and H2

The rate constants 〈σ · υ〉 for collisional de-excitation of the metastable 5D states of Ba⁺ ions have been determined in an ion trap experiment. TheD-states are selectively populated by pulsed laser excitation of the 6P _1/2 or 6P _3/2 state and the decay at different background pressures is monitored by the change in fluorescence intensity of the excited ions. From the pressure dependence of the decay constants we calculate the de-excitation rate constants for different collision partners, averaged over the velocity distribution of the trapped ion cloud. For He, Ne, H₂ and N₂ we obtain in the c.m. energy range of 0.1–0.5 eV: 〈σ·υ〉 (He)=3.0±0.2·10^?13cm³/s, 〈σ·υ〉 (Ne)=5.1±0.4·10^?13cm³/s, 〈σ·υ〉 (H₂)=3.7±0.3·10^?11cm³/s, 〈σ·υ〉 (N₂)=4.4±0.3·10^?11cm³/s. The results can be understood qualitatively by a consideration of the ion-atom and ion-molecules interaction potential.     

Secondary reactions in controlled potential coulometry: Part V. Reversal coulometric study of the reduction of cis- and trans-thioindigo in the presence of carbon dioxide,cinnamonitrile and acrylonitrile

Controlled potential reversal coulometry was applied to the following systems: (I) C+neR; R+C → RC; RC+ne → products. (II) as in (I) except RC not electroactive. (III) C+neR; R+X → RX; RX+ne → products. Equations for these e.c.e. and e.c. mechanisms were obtained and solved numerically. Working curves are presented for the calculation of the rate constants of the homogeneous reactions. This treatment was applied to studies of the reduction of thioindigo (TI) alone and in the presence of several reactants. For TI alone the reaction mechanism involves reaction of the radical anion (TI^?_·) with parent molecule followed by a second electron transfer. In the presence of excess dissolved CO₂, acrylonitrile (AN), or cinnamonitrile (CN), reaction of TI^?_· with these followed by a second electron transfer was proposed. Rate constants for the TI?TI^?_· coupling reaction were 82 (cis-thioindigo), and 323 (trans-thioindigo) l mol^?1 s^?1; pseudo-first-order reactions of TI^?_· were 0.016 (trans-) and 0.047 (cis-) s^?1 with CO₂; 0.023 (trans-) and 0.033 (cis-) s^?1 with CN; 0.022 (trans-) and 0.032 (cis-) s^?1 with AN.     

Compensation effect in heterogeneous non-isothermal kinetics

A number of 1145 sets of kinetic parameters derived in our earlier papers from TG curves have been worked up. The apparent activation energy and pre-exponential factor values have been found to obey a linear compensation law (isokinetic relation) if the thermal decomposition begins in the same temperature interval, irrespective of the nature of the chemical reaction. The isokinetic temperatureT _i has been found to be very close to the mean value of the temperaturesT _0.1 at which the conversion becomes equal to 0.1 and atT _i the rate constant has been found to be approximately equal to 10^?3s^?1 in allT _0.1 intervals investigated. It is concluded that the kinetic compensation effect observed in heterogeneous non isothermal TG kinetics is not a true one.