Constant-volume Combustion Energy Research Articles

Constant-volume combustion energy of the lead salts of 2HDNPPb and 4HDNPPb and their effect on combustion characteristics of RDX–CMDB propellant

The constant-volume combustion energies of the lead salts of 2-hydroxy-3,5-dinitropyridine (2HDNPPb) and 4-hydroxy-3,5-dinitropyridine (4HDNPPb), ΔUc (2HDNPPb(s) and 4HDNPP(s)), were determined as –4441.92±2.43 and –4515.74±1.92 kJ mol–1 , respectively, at 298.15 K. Their standard enthalpies of combustion, Δcm H θ(2HDNPPb(s) and 4HDNPPb(s), 298.15 K), and standard enthalpies of formation, Δrm H θ(2HDNPPb(s) and 4HDNPPb(s), 298.15 K) were as –4425.81±2.43, –4499.63±1.92 kJ mol–1 and –870.43±2.76, –796.65±2.32 kJ mol–1 , respectively. As two combustion catalysts, 2HDNPPb and 4HDNPPb can enhance the burning rate and reduce the pressure exponent of RDX–CMDB propellant.

The standard molar enthalpy of formation, molar heat capacities, and thermal stability of anhydrous caffeine

The constant-volume energy of combustion of crystalline anhydrous caffeine (C 8H 10N 4O 2) in α (lower temperature steady) crystal form was measured by a bomb combustion calorimeter, the standard molar enthalpy of combustion of caffeine at T = 298.15 K was determined to be −(4255.08 ± 4.30) kJ · mol −1, and the standard molar enthalpy of formation was derived as −(322.15 ± 4.80) kJ · mol −1. The heat capacity of caffeine in the same crystal form was measured in the temperature range from (80 to 387) K by an adiabatic calorimeter. No phase transition or thermal anomaly was observed in the above temperature range. The thermal behavior of the compound was further examined by thermogravimetry (TG), differential thermal analysis (DTA) over the range from (300 to 700) K and by differential scanning calorimetry (DSC) over the range from (300 to 540) K, respectively. From the above thermal analysis a (solid–solid) and a (solid–liquid) phase transition of the compound were found at T = (413.39 and 509.00) K, respectively; and the corresponding molar enthalpies of these transitions were determined to be (3.43 ± 0.02) kJ · mol −1for the (solid–solid) transition, and (19.86 ± 0.03) kJ · mol −1 for the (solid–liquid) transition, respectively.

Synthesis, crystal structure and thermochemical behaviour of a barium complex [Ba(5-OH–BDC)(H 2O) 3] [5-OH–H 2BDC = 5-hydroxyisophtalic acid

A novel complex [Ba(5-OH–BDC)(H 2O) 3] [5-OH–H 2BDC = 5-hydroxyisophtalic acid] was synthesized and characterized by X-ray crystallography. The complex is Monoclinic P2 1/ c, a = 11.1069(4), b = 14.8192(6), c = 6.5005(2) Å, β = 103.465(3)° and Z = 4, which exhibits a three-dimensional framework formed by linkage of adjacent two-dimensional (6, 3) layers via intermolecular hydrogen bonds. The title complex has been studied by IR spectrum and TG–DTG. The constant-volume combustion energy of the complex, Δ c U, was determined as being (−3210.45 ± 1.41) kJ mol −1 by a precise rotating-bomb calorimeter at 298.15 K. The standard enthalpy of combustion, Δ c H m θ , and the standard enthalpy of formation, Δ H m θ f , were calculated as being (−3207.97 ± 1.41) and (−1922.80 ± 1.76) kJ mol −1, respectively. A calculation model for determining the specific heat capacity of the complex with an improved RD496-III microcalorimeter is also derived. The specific heat capacity of the complex was (6158.387 ± 0.187) J mol −1 K −1.

Thermochemical study of the solid complex Ho(PDC)3 (o-phen)

A novel solid complex, formulated as Ho(PDC)3 (o-phen), has been obtained from the reaction of hydrate holmium chloride, ammonium pyrrolidinedithiocarbamate (APDC) and 1,10-phenanthroline (o-phen·H2O) in absolute ethanol, which was characterized by elemental analysis, TG-DTG and IR spectrum. The enthalpy change of the reaction of complex formation from a solution of the reagents, ΔrHmθ (sol), and the molar heat capacity of the complex, cm, were determined as being –19.161±0.051 kJ mol–1 and 79.264±1.218 J mol–1 K–1 at 298.15 K by using an RD-496 III heat conduction microcalorimeter. The enthalpy change of complex formation from the reaction of the reagents in the solid phase, ΔrHmθ(s), was calculated as being (23.981±0.339) kJ mol–1 on the basis of an appropriate thermochemical cycle and other auxiliary thermodynamic data. The thermodynamics of reaction of formation of the complex was investigated by the reaction in solution at the temperature range of 292.15–301.15 K. The constant-volume combustion energy of the complex, ΔcU, was determined as being –16788.46±7.74 kJ mol–1 by an RBC-II type rotating-bomb calorimeter at 298.15 K. Its standard enthalpy of combustion, ΔcHmθ, and standard enthalpy of formation, ΔfHmθ, were calculated to be –16803.95±7.74 and –1115.42±8.94 kJ mol–1, respectively.

Low-temperature heat-capacity and standard molar enthalpy of formation of copper l-threonate hydrate Cu(C 4H 6O 5)·0.5H 2O(s)

The solid copper l-threonate hydrate, Cu(C 4H 6O 5)·0.5H 2O, was synthesized by the reaction of l-threonic acid with copper dihydrocarbonate and characterized by means of chemical and elemental analyses, IR and TG-DTG. Low-temperature heat-capacity of the title compound has been precisely measured with a small sample precise automated adiabatic calorimeter over the temperature range from 77 to 390 K. An obvious process of the dehydration occurred in the temperature range between 353 and 370 K. The peak temperature of the dehydration of the compound has been observed to be 369.304 ± 0.208 K by means of the heat-capacity measurements. The molar enthalpy, Δ d H m, of the dehydration of the resulting compound was of 16.490 ± 0.063 kJ mol −1. The experimental molar heat capacities of the solid from 77 to 353 K and the solid from 370 to 390 K have been, respectively, fitted to tow polynomial equations with the reduced temperatures by least square method. The constant-volume energy of combustion of the compound, Δ c U m, has been determined as being −1616.15 ± 0.72 kJ mol −1 by an RBC-II precision rotating-bomb combustion calorimeter at 298.15 K. The standard molar enthalpy of formation of the compound, Δ f H m ° , has been calculated to be −1114.76 ± 0.81 kJ mol −1 from the combination of the data of standard molar enthalpy of combustion of the compound with other auxiliary thermodynamic quantities.

Measurements of Enthalpy Change of Reaction of Formation, Molar Heat Capacity and Constant-Volume Combustion Energy of Solid Complex Yb(Et 2dtc) 3 (phen)

A ternary solid complex Yb(Et 2dtc) 3(phen) was obtained from the reaction of hydrous ytterbium chloride with sodium diethyldithiocarbamate (NaEt 2dtc), and 1, 10-phenanthroline (o-phen·H 2O) in absolute ethanol. The bonding characteristics of the complex were characterized by IR. The result shows Yb 3+ bands with two sulfur atoms in the Na(Et 2dtc) 3 and two nitrogen atoms in the o-phen. The enthalpy change of liquid-phase reaction of formation of the complex Δ r H θ m(1), was determined as being (-24.838±0.114) kJ·mol −1 at 298.15 K, by an RD-496 III type heat conduction microcalormeter. The enthalpy change of the solid-phase reaction of formation of the complex Δ r H θ m(s), was calculated as being (108.015±0.479) kJ·mol −1 on the basis of an appropriate thermochemistry cycle. The thermodynamics of liquid-phase reaction of formation of the complex was investigated by changing the temperature during the liquid-phase reaction. Fundamental parameters, the activation enthalpy, Δ H θ ≠, the activation entropy, Δ S θ ≠, the activation free energy, Δ G θ ≠, the apparent reaction rate constant k, the apparent activation energy E, the pre-exponential constant A, and the reaction order n, were obtained by a combination of the reaction thermodynamic and kinetic equations with the data from the thermokinetic experiments. At the same time, the molar heat capacity of the complex c m, p , was determined to be (86.34±1.74) J·mol −1·K −1 by the same microcalormeter. The constant-volume combustion energy of the complex, Δ c U, was determined to be (− 17954.08±8.11) kJ·mol −1 by an RBC-II type rotating-bomb calorimeter at 298.15 K. Its standard enthalpy of combustion, Δ c H θ m, and standard enthalpy of formation, Δ f H θ m were calculated to be (-17973.29±8.11) kJ·mol −1 and (-770.36±9.02) kJ·mol −1 respectively.

Thermochemistry of the solid complex Gd(Et2dtc)3(phen)

A ternary solid complex Gd(Et2dtc)3(phen) has been obtained from reactions of sodium diethyldithiocarbamate (NaEt2dtc), 1,10-phenanthroline (phen) and hydrated gadolinium chloride in absolute ethanol. The title complex was described by chemical and elemental analyses, TG-DTG and IR spectrum. The enthalpy change of liquid-phase reaction of formation of the complex, ΔrHΘm(l), was determined as (-11.628±0.0204) kJ mol-1 at 298.15 K by a RD-496 III heat conduction microcalorimeter. The enthalpy change of the solid-phase reaction of formation of the complex, ΔrHΘm(s), was calculated as (145.306±0.519) kJ mol-1 on the basis of a designed thermochemical cycle. The thermodynamics of reaction of formation of the complex was investigated by changing the temperature of liquid-phase reaction. Fundamental parameters, the apparent reaction rate constant (k), the apparent activation energy (E), the pre-exponential constant (A), the reaction order (n), the activation enthalpy (ΔrHΘ≠), the activation entropy (ΔrSΘ≠), the activation free energy (ΔrGΘ≠) and the enthalpy (ΔrHΘ≠), were obtained by combination of the thermodynamic and kinetic equations for the reaction with the data of thermokinetic experiments. The constant-volume combustion energy of the complex, ΔcU, was determined as (-18673.71±8.15) kJ mol-1 by a RBC-II rotating-bomb calorimeter at 298.15 K. Its standard enthalpy of combustion, ΔcHΘm, and standard enthalpy of formation, ΔfHΘm, were calculated to be (-18692.92±8.15) kJ mol-1 and (-51.28±9.17) kJ mol-1, respectively.

Thermochemistry of the ternary complex Eu(Et 2dtc) 3(phen)

A ternary solid complex Eu(Et 2dtc) 3(phen) has been obtained the from reaction of sodium diethyldithiocarbamate (NaEt 2dtc), 1,10-phenanthroline (phen) and hydrated europium chloride in absolute ethanol. The title complex was described by chemical and elemental analyses, TG-GTG and IR spectrum. The enthalpy change of liquid-phase reaction of formation of the complex, Δ r H m θ (l), was determined as−(13.481 ± 0.0314) kJ · mol −1 at T = 298.15 K by a RD-496 III heat conduction microcalorimeter. The enthalpy change of the solid-phase reaction of formation of the complex, Δ r H m θ (s), was calculated as (152.317 ± 0.542) kJ · mol −1 on the basis of a designed thermochemical cycle and other auxiliary thermodynamic qualities. The thermodynamics of reaction of formation of the complex was investigated by changing the temperature of liquid-phase reaction. Fundamental parameters, the apparent reaction rate constant ( k), the apparent activation energy ( E), the pre-exponential constant ( A), the reaction order ( n), the activation enthalpy ( Δ H ≠ θ ), the activation entropy ( Δ S ≠ θ ), the activation free energy ( Δ G ≠ θ ) and the enthalpy ( Δ r H ≠ θ ), were obtained combination the reaction thermodynamic and kinetic equations with the data of thermokinetic experiments. The constant-volume combustion energy of the complex, Δ c U, was determined as −(17410.63 ± 8.95) kJ · mol −1by a RBC-Π rotating-bomb calorimeter at T = 298.15 K. Its standard enthalpy of combustion, Δ c H m θ , and standard enthalpy of formation, Δ f H m θ , were calculated to be −(17429.84 ± 8.95) kJ · mol −1 and −(1231.76 ± 9.92) kJ · mol −1, respectively.

Thermochemical properties and non-isothermal decomposition reaction kinetics of 3,4-dinitrofurazanfuroxan (DNTF)

The constant-volume combustion energy, Δ c U (DNTF, s, 298.15 K) and kinetic behavior of the exothermic decomposition reaction of the title compound (DNTF) are determined by a precise rotating bomb calorimeter and DSC, respectively. Its standard enthalpy of combustion, Δ c H m θ (DNTF, s, 298.15 K), standard enthalpy of formation, Δ c H m θ (DNTF, s, 298.15 K) and kinetic parameters of the major exothermic decomposition reaction in a temperature-programmed mode [the apparent activation energy ( E a) and pre-exponential factor ( A)] are calculated. The values of Δ c U (DNTF, s, 298.15 K), Δ c H m θ (DNTF, s, 298.15 K), and Δ c H m θ (DNTF, s, 298.15 K) of DNTF are −9733.96 ± 8.59 J g −1, −3018.29 ± 2.68 kJ mol −1, and 657.23 ± 2.70 kJ mol −1, respectively. The kinetic model function in integral form and the value of E a and A of the major exothermic decomposition reaction of DNTF are 1 − ( 1 − α ) 1 / 3 , 177.03 kJ mol −1 and 10 13.68 s −1, respectively. The critical temperature of thermal explosion of DNTF is 240.6 °C.

Low-temperature heat capacity and standard molar enthalpy of formation of 9-fluorenemethanol (C 14H 12O)

Low-temperature heat capacities of the 9-fluorenemethanol (C 14H 12O) have been precisely measured with a small sample automatic adiabatic calorimeter over the temperature range between T=78 K and T=390 K. The solid–liquid phase transition of the compound has been observed to be T fus=(376.567±0.012) K from the heat-capacity measurements. The molar enthalpy and entropy of the melting of the substance were determined to be Δ fus H m=(26.273±0.013) kJ · mol −1 and Δ fus S m=(69.770±0.035) J · K −1 · mol −1. The experimental values of molar heat capacities in solid and liquid regions have been fitted to two polynomial equations by the least squares method. The constant-volume energy and standard molar enthalpy of combustion of the compound have been determined, Δ c U(C 14H 12O, s)=−(7125.56 ± 4.62) kJ · mol −1 and Δ c H m ∘(C 14H 12O, s)=−(7131.76 ± 4.62) kJ · mol −1, by means of a homemade precision oxygen-bomb combustion calorimeter at T=(298.15±0.001) K. The standard molar enthalpy of formation of the compound has been derived, Δ f H m ∘(C 14H 12O,s)=−(92.36 ± 0.97) kJ · mol −1, from the standard molar enthalpy of combustion of the compound in combination with other auxiliary thermodynamic quantities through a Hess thermochemical cycle.

Standard enthalpy of formation and heat capacities of 3,5-di- tert-butylsalicylic acid

The constant volume energy of combustion of crystalline 3,5-di- tert-butylsalicylic acid ( t-BSA) in oxygen at 298.15 K was determined using combustion calorimeter to be −8292.57±2.51 kJ mol −1. The standard molar enthalpies of combustion and formation of 3,5-di- tert-butylsalicylic acid were derived, at T=298.15 K, Δ c H m Θ =−8302.48±2.51 kJ mol −1 and Δ f H m Θ=−744.30±3.21 kJ mol −1, respectively. The heat capacities of the compound were measured with an adiabatic calorimeter over the temperature range from 79 to 351 K. No indication of any phase transition or thermal anomaly was observed in this temperature range. The fusion and evaporation behavior of the compound were examined by thermogravimetry (TG), differential thermal analysis (DTA) and differential scanning calorimetry (DSC). The molar enthalpy and entropy of fusion, Δ fus H m Θ and Δ fus S m Θ, at T=437.5 K, were determined to be 22.92±0.55 kJ mol −1 and 139.4±3.3 J mol −1 K −1, respectively; and the molar enthalpy and entropy of evaporation, Δ vap H m Θ and Δ vap S m Θ, at T=477.5 K, were obtained as 83.88±2.1 kJ mol −1 and 341.7±8.4 J mol −1 K −1, respectively.

Determination of constant-volume combustion energy for the complexes of zinc amino acids

The eight solid complexes of zinc with l-α-methionine or l-α-histidine were prepared. The constant-volume combustion energies of the complexes, Δ c,coor E, at 298.15 K have been determined by using a precision rotating-bomb calorimeter. The standard enthalpies of combustion, Δ c,coor H θ , and standard enthalpies of formation, Δ f,coor H θ , have been calculated for these complexes.