TY - JOUR

T1 - Pressure DSC for energetic materials. Part 2. Switching between evaporation and thermal decomposition of 3,5-dinitropyrazole

AU - Gorn, Margarita V.

AU - Monogarov, Konstantin A.

AU - Dalinger, Igor L.

AU - Melnikov, Igor N.

AU - Kiselev, Vitaly G.

AU - Muravyev, Nikita V.

PY - 2020/8/1

Y1 - 2020/8/1

N2 - Differential scanning calorimetry at an elevated external pressure (Pressure DSC) allows for shifting the vaporization of a sample to higher temperatures, thus often facilitating the direct observation of its thermal decomposition. In the present work, the thermolysis of a promising energetic material 3,5-dinitropyrazole was studied under pressures up to 10 MPa. The thermokinetic analysis of the datasets acquired at 2 and 5 MPa exhibited a pronounced kinetic compensation, thus allowing to build the joint formal kinetic model. The final kinetic scheme is comprised of the two parallel reactions, viz., the first-order process (Ea = 198 kJ mol−1) along with a first-order autocatalysis (Ea = 127 kJ mol−1). The experiment was complemented with the highly accurate CCSD(T)-F12 quantum chemical calculations. Theory revealed an unusual primary decomposition channel, viz., a sigmatropic [1,5]H-shift followed by the pyrazole ring opening yielding a molecular nitrogen and a nitro radical as simple primary products. Apart from this, the comparative thermogravimetry at a normal pressure yielded the vapor pressure of 3,5-dinitropyrazole along with the internally consistent set of phase change enthalpies. In general, the pressure DSC is a facile technique to study the true decomposition kinetics of the compounds that vaporize/sublime in conventional DSC experiments.

AB - Differential scanning calorimetry at an elevated external pressure (Pressure DSC) allows for shifting the vaporization of a sample to higher temperatures, thus often facilitating the direct observation of its thermal decomposition. In the present work, the thermolysis of a promising energetic material 3,5-dinitropyrazole was studied under pressures up to 10 MPa. The thermokinetic analysis of the datasets acquired at 2 and 5 MPa exhibited a pronounced kinetic compensation, thus allowing to build the joint formal kinetic model. The final kinetic scheme is comprised of the two parallel reactions, viz., the first-order process (Ea = 198 kJ mol−1) along with a first-order autocatalysis (Ea = 127 kJ mol−1). The experiment was complemented with the highly accurate CCSD(T)-F12 quantum chemical calculations. Theory revealed an unusual primary decomposition channel, viz., a sigmatropic [1,5]H-shift followed by the pyrazole ring opening yielding a molecular nitrogen and a nitro radical as simple primary products. Apart from this, the comparative thermogravimetry at a normal pressure yielded the vapor pressure of 3,5-dinitropyrazole along with the internally consistent set of phase change enthalpies. In general, the pressure DSC is a facile technique to study the true decomposition kinetics of the compounds that vaporize/sublime in conventional DSC experiments.

KW - 3,5-Dinitropyrazole

KW - Energetic materials

KW - Phase change data

KW - Predictive electronic structure theory

KW - Pressure DSC

KW - Thermokinetic analysis

KW - Thermolysis mechanism

KW - Vapor pressure

KW - STABILITY

KW - FOX-7

KW - STATE

KW - MECHANISMS

KW - PYRAZOLE

KW - VAPOR-PRESSURE

KW - TUNNELING CONTROL

KW - KINETICS

UR - http://www.scopus.com/inward/record.url?scp=85087336233&partnerID=8YFLogxK

U2 - 10.1016/j.tca.2020.178697

DO - 10.1016/j.tca.2020.178697

M3 - Article

AN - SCOPUS:85087336233

VL - 690

JO - Thermochimica Acta

JF - Thermochimica Acta

SN - 0040-6031

M1 - 178697

ER -