Low/high temperature relationships in dinitramide salts by DEA/DSC and study of oxidation of aluminum powders by DSC/TG

Abstract

The dinitramide salts of ammonia (ADN), hexamethylenetetramine (HDN), potassium (KDN), and sodium (NaDN) showed a linear relationship between the DSC rate of decomposition at the peak maximum and the DEA tan5 value at the low temperature transition peak. As the cation basicity increased in the series ADN < HDN < KDN<NaDN, there was an increase in the low temperature transition peak, the energy barrier for relaxation, and the decomposition peak temperature, and a decrease in the tan5 value at the low temperature transition peak, specific heat capacity, and the rate and enthalpy of decomposition. The more basic salts were more thermally stable (i.e., higher decomposition temperature) and less energetic (i.e., lower enthalpy of decomposition). The more internal free volume (disorder) present in these salts, the higher the rates of relaxation and decomposition. Five aluminum powders of different surface areas were analyzed by DSC in platinum sample pans, and it was found that the enthalpy and rate of oxidation increased as the particle size of A! decreased while the enthalpy of the AI melt decreased. TG showed a two-step weight gain in the oxidation of Al with plateaus in the 650 and 1130"C regions and the percent weight gain increased as the particle size of AI decreased. Variable DSC and TG heating rate studies showed that the activation energies for the first step in the oxidation process increased as the particle size of A1 increased.

Thermal Decomposition and Combustion of Ammonium Dinitramide (Review)

“…A less pronounced decrease in E a with increasing reaction extent at a high flow rate of the carrier gas was believed to be evidence for the catalytic action of NO 2 [36]. A DSC investigation by Tompa et al [39] showed that ADN decomposition in a sealed pan had a lower E a than that in an unsealed pan with a pin-hole. A lower value (E a = 29.5 kcal/mole) was observed under pressurized conditions (air or He) than at one atmosphere (N 2 or He).…”

“…In comparison with KDN, sodium dinitramide (NaDN), and hexamethylenetetramine dinitramide (HMDN), ADN has the lowest decomposition temperature and the highest decomposition rate and heat release [39]. ADN is less stable thermally than KDN, but much more stable than NH 4 NO 2 and alkyl dinitramide (alkyl-N(NO 2 ) 2 ) [2].…”

“…The overall characteristics of ADN thermal decomposition can be obtained from the DSC spectra reported in [35,36,28,39,42,2,26]. As is listed in Table 1, depending on ADN samples and experimental conditions, the onset of thermal decomposition is at T decomp = 150-155 • C and the exothermic peak is observed around T exo ≈ 180-198 • C. The decomposition temperature range of 150-155 • C based on DSC coincides with that obtained from MS, FTIR, and TGA [15,25,36,37,50].…”

Oxidation of Mechanically Alloyed Al-rich Al–Ti Powders

“…18,19 The oxidation of aluminum is limited by the diffusion of species through the protective alumina film, and different steps are observed when the diffusion resistance of the film changes as a result of polymorphic transformations in alumina. A similar scenario is expected for the oxidation of Al-Ti mechanical alloys, however, the sequence of the polymorphic phase changes could be altered.…”

“…This sequence of aluminum oxidation was observed in several earlier studies. 18,19 Recently, a mechanism has been proposed connecting the stepwise oxidation of aluminum with polymorphic phase changes occurring in the growing layer of Al 2 O 3 . 20 Oxidation of titanium powder produces a broad exothermic event starting at about 600°C and continuing until about 1050°C.…”