High Pressure Ignition and Combustion of Aluminum Hydride

Abstract

An experimental study was conducted to determine the high pressure ignition characteristics of α-aluminum hydride. Aluminum hydride particles were heated on a platinum filament at heating rates of approximately 1 × 10 5 K/s in a pressure vessel for pressures ranging up to about 7 MPa, in order to quantify the ignition temperature and to observe the ignition process. Experiments were conducted in air, argon, and nitrogen as the pressurizing environment. This study revealed that the dehydrogenation of aluminum hydride is not a function of pressure under the conditions tested. In addition, ignition temperatures were found to be approximately linearly related to pressure until pressures exceeded about 0.4 MPa, at which point they remained constant through the highest pressures tested. High speed imaging of the ignition process showed a dramatic change in the ignition behavior for pressures above 0.4 MPa, corresponding to what we believe is a threshold for H 2 /air autoginition or perhaps even an explosion limit. We find that the combustion behavior of aluminum hydride particles shared many traits similar to what has been previously observed with aluminum particles including a diffusion flame surrounding the particle, spinning, jetting, and explosions/fragmentation. Quenched particles also showed clear evidence of gas phase combustion with parent particles containing nanofeatures, which were condensed from the gas phase. The results of this study provide additional understanding on the ignition and combustion process of aluminum hydride at extreme conditions, which may be useful in modeling efforts or in the development of solid propellants.

Fundamental Study on Mechanisms of Thermal Decomposition and Oxidation of Aluminum Hydride

“…In the oxygen environment, likewise, H2O is preferentially formed relative to H2 at the early stage of the reaction, the significant extent of which can be seen in Figure 6b. However, in a reported experiment [53], H2O was considered as a product of H2/O2 reaction after the H2 release. In addition to the discussion and explanation given in the last paragraph of Section 3.1.1., the high surface-to-volume ratio of nanoparticle also contributes to the great amount of H2O generated.…”

Combustion of HTPB Based Solid Fuels Containing Metals and Metal Hydrides with Nitrous Oxide

“…Table 1 provides a summary of the solid fuels under consideration. The aluminum hydride used in this study was from the same batch as used in previous studies [4][5][6]18] while the aluminum was from the same batch used in reference [5] and was of similar scale. Table 1 also provides the theoretical and measured density of the fuels, which are in reasonable agreement.…”

Reactive Structural Materials: Preparation and Characterization

“…Depending on the filament diameter and the power supply, the heating rates attainable are from 100 to 10 6 K s −1 . This method was used extensively to determine how the ignition temperature changes as a function of the heating rate for a broad range of RMs prepared by mechanical milling, for example, as well as for other types of RMs . In a variant of this experiment, the powder‐coated wire is mounted in a vacuum chamber connected to the inlet of a time of flight mass spectrometer (TOF‐MS) .…”

“…Constant volume explosion experiments are rather common; they can be performed in vessels of different sizes, with different powders initiated using a heated wire, pyrotechnic igniter, or a spark. Pressure is usually measured in real time and the maximum achieved pressure is associated with the total energy release.…”