Constant-volume Combustion Energies 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.

Synthesis and characterization of the rare-earth complexes with salicylic acid

AbstractSeven rare-earth complexes with salicylic acid RE(HSal)3·nH2O (HSal = C7H5O3; RE = La-Sm, n = 2; RE = Eu, Gd, n = 1) were synthesized and characterized by elemental analysis, the IR spectrum, and cyclic voltammetry. The constant-volume combustion energies of complexes, Δc U, were determined by a precise rotating-bomb calorimeter at 298.15 K. Their standard molar enthalpies of combustion, Δc H mo, and standard molar enthalpies of formation, Δf H mo, were calculated.

Guanidinium-Based Ionic Liquids

Cyclic (subset=N+<, subset = imidazolidine 3 and 4, hexahydro-pyrimidine 7 and 8, tetrahydro-1,3,5-oxadiazine 12, and triazoline 15 and 16) and acyclic [(R2N)2C=N+<, 19] guanidinium-based salts were synthesized via the quaternization of guanidine derivatives with nitric or perchloric acid or with iodomethane followed by metathesis reaction with silver nitrate, silver perchlorate, or ammonium dinitroamide. The structure of 15d was confirmed by single-crystal X-ray analysis. Most of the salts exhibited low melting points and good thermal stabilities. Their densities range between 1.2 and 1.5 g/cm3. Standard molar enthalpies of formation were calculated from experimentally determined constant-volume combustion energies obtained using an oxygen bomb calorimeter.

Determination of combustion energies and the standard enthalpies of formation for the complexes of RE(Et2dtc)3(phen)

Solid complexes, RE(Et2dtc)3(phen) (RE=La, Pr, Nd, Sm—Lu), were synthesized with sodium diethyldithiocarbamate (NaEt2dtc3H2O), 1,10-phenanthroline (o-phen•H2O) and hydrated lanthanide chlorides in absolute ethanol. The constant-volume combustion energies of complexes, Δ C U, were determined by a precise rotating-bomb calorimeter at 298.15 K. The standard enthalpies of combustion, ΔCHm θ, and standard enthalpies of formation, ΔfHm θ, were calculated for these complexes, respectively. The experiment results showed the “tripartite effect” of rare earth.

Energetic Salts from N-Aminoazoles

New energetic salts (2, 3, 5, 6, 13, 14, 21, 22) were synthesized via the quaternization of derivatives of N-aminoazoles with nitric or perchloric acid or with iodomethane followed by metathesis reaction with silver nitrate or silver perchlorate. The structure of 2-amino-4,5-dimethyltetrazolium nitrate (21) was confirmed by single-crystal X-ray analysis. Most of the salts exhibit good thermal stabilities and low melting points. By using experimentally determined constant volume combustion energies, the standard molar enthalpies of formation were derived on the basis of designed Hess thermochemical cycles.

Preparation and Thermochemistry of Complexes of Zinc Nitrate with Threonine

The solubility property of Zn(NO3)2–Thr–H2O system (Thr—threonine) at 25°C in the entire concentration range has been investigated by the phase equilibrium semimicromethod. The corresponding phase diagram and refractive index diagram were constructed. From the phase equilibrium results, the incongruently soluble compounds of Zn(Thr)(NO3)2 · 2H2O, Zn(Thr)2(NO3)2 · H2O, and Zn(Thr)3(NO3)2 · H2O were synthesized and characterized by IR, XRD, TG–DTG, chemical and elemental analyses. The constant-volume combustion energies of the compounds, Δ c E, determined by precision rotating bomb calorimeter at 298.15 K, were –6266.88 ± 3.72, –9263.28 ± 2.23, and –11 423.11 ± 6.81 J/g, respectively. The standard enthalpies of combustion for these compounds, Δ c Hm° (complex, s., 298.15 K), were calculated as –2147.40 ± 1.28, –4120.83 ± 0.99, and –6444.68 ± 3.85 kJ/mol and the standard enthalpies of formation, Δ f Hm° (complex, s., 298.15 K), are –1632.82 ± 1.43, –1885.55 ± 1.50, and –2770.25 ± 4.21 kJ/mol. The enthalpies of dissolution of the complexes in a medium of simulated human gastric juice (37°C, pH 1, in the solution of hydrochloric acid), Δ dis Hm° (complex, s., 310 K), which were also measured by a microcalorimeter to be 13.36 ± 0.06, 15.53 ± 0.06, and 17.04 ± 0.05 kJ/mol, respectively.

Preparation, crystal structure and thermochemistry of Zn(AMP)2Cl2

The complex of zinc chloride and 2-amino-4,6-dimethyloxyl pyrimidine (AMP) was prepared, and the composition of the complex was determined by chemical and elemental analyses. Complex was characterized by IR, XPS, 1H NMR and TG–DTG techniques. In addition X-ray structural analysis was performed. Crystals of [Zn(AMP)2Cl2] revealed the following parameters: Mr=446.59; orthorhombic Pbca; a=13.0208 (10); b=13.8531 (11); c=20.0652 (15)Å; V=3619.3 (5)Å3; Z=8; Dcalc=1.639Mgm−3; Mo Kα λ=0.71073Å; μ=1.683mm−1; T=293K; R=0.0431 for 2510 observed reflections. The constant-volume combustion energies of the ligand and the complex, ΔcE, were determined by a precise rotating-bomb calorimeter at 298.15K. They were −3340.01±1.54 and −6552.76±3.55kJmol−1, respectively. Their standard enthalpy of combustion, ΔcHmθ, and standard enthalpy of formation, ΔfHmθ, were calculated, which were −3339.39±1.54, −6546.56±3.35 and −307.91±1.74, −995.10±3.93kJmol−1.

Thermochemistry of the complexes of chromium nitrate with l-a-amino acids

The solid complexes of Cr(NO3)3 with L-α-amino acids (AA=Val, Leu, Thr, Arg, Phe and Try) have been prepared in 95% alcoholic, the compositions of which were identified as the general formula Cr(AA)2(NO3)3·2H2O by elemental and chemical analyses. The bonding characteristics of the title complexes were characterized by IR, indicating that nitrogen and oxygen atoms in the ligands coordinated to Cr3+ in a bidentate fashion. With the aid of TG-DTG and IR techniques, the complexes were subjected to thermal decomposition in an atmosphere of oxygen, presuming that the decompositions of the complexes consist of two steps and the complexes were decomposed into chromium hemitrioxide after undergoing dehydration and skeleton splitting of the complexes. The constant volume energies of combustion of the complexes were determined by a RBC-P type rotating-bomb calorimeter. According to Hess's law, the standard enthalpies of formation of the complexes were calculated as (-1831.40±4.40), (-2542.03±6.13), (-1723.81±3.99), (-2224.31±3.02), (-2911.61±6.53) and (-659.32±7.42) kJ mol-1, respectively.

Combustion energies and standard molar enthalpies of formation for the complexes of the first-row transitional metal chlorides withL-α-histidine

Seven novel solid complexes of the first-row transitional metal withL-α-histidine were synthesized, and their compositions were determined. The constant-volume combustion energies of the complexes were measured by a precision rotation bomb calorimeter. The standard molar enthalpies of combustion and the standard molar enthalpies of formation were calculated. The results indicated that the plots of the standard enthalpies of formation against the atomic number of the metal show a regularity of zigzag.

Thermochemistry of the complexes of some microelements and histidine

Solid complexes of M(His)2Cl2•nH2 O( M=Mn, Co, Ni, Cu) of MnCl2•6H2O, CoCl2•6H2O, NiCl2•6H2O, CuCl2•2H2O and L-α-histidine (His) have been prepared in 95% ethanol solution and characterized by elemental analyses, chemical analyses, IR and TG-DTG. The constant-volume combustion energies of the complexes have been determined by a rotating-bomb calorimeter. The standard enthalpies of formation of the complexes have been calculated as well.

Thermochemical properties of crown ether compounds

The constant-volume combustion energies have been determined for three kinds of crown ether (CE) using a precision rotating-bomb calorimeter (RBC). The standard enthalpies of combustion, Δ c CE H θ , and standard enthalpies of formation, Δ f CE H θ , have been calculated for these CE. Two empirical formulas have been proposed about the standard combustion enthalpies of aromatic CE.

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.