The distribution of ammonium salts among a size and composition dispersed aerosol

A method to maintain a clean surface of a liquid in a high vacuum is described. Using a very thin and fast liquid jet it is not only possible to prevent freezing of the liquid but also to reduce the number of collisions between evaporating molecules to negligibly small values. Thus many of the standard, vacuum dependent, particle probing techniques for solid surfaces can be used for studies of rapidly vaporizing, high vapor pressure liquids. In a first molecular beam investigation we have used time-of-flight analysis to measure the velocity distribution of H2O molecules vaporizing from thin jets of pure liquid water. The experiments were carried out for liquid jet diameters between 50 and 5 µm. In this range the expanding vapor is observed to undergo the transition to the collision-free molecular flow regime. From the measured velocity distributions the local surface temperature is determined to be less than 210 K. This appears to be the lowest temperature ever reported for supercooled liquid water.

A molecular beam study of the evaporation of water from a liquid jet

The explosive sensitivity of methylammonium perchlorates has been investigated by differential thermal analysis, thermogravimetric analysis, mass spectrometry and explosion delay experiments. The decomposition temperature of these compounds increases in the order CH3NH3ClO4>(CH3)2NH2ClO4>(CH3)3NHClO4. The activation energy shows the reverse order, indicating thereby that the stability increases with increasing substitution. Mass spectrometric investigation, however, suggests an increasing reactivity with increasing substitution. A possible explanation for such behaviour is proposed. It appears that explosion delay is correlated with thermal decomposition and impact sensitivity.

Explosive sensitivity of methylammonium perchlorates

The thermal decomposition of methylammonium perchlorate (MAP) has been studied under isothermal and non-isothermal conditions. Differential thermal analysis of MAP showed, in addition to the exotherm due to decomposition, another exotherm at 408° which was observed for the first time. Chemical analysis and the infrared spectrum of the residue left behind after the decomposition proved it to contain NH4ClO4. The results have been explained on the basis of a methyl group transfer in addition to proton transfer in the decomposition process.

Thermal decomposition of methylammonium perchlorate

Hydrogen Halides on Jupiter and Saturn

: Time-of-flight measurements have been made on the flux of molecules from the surface of ammonium salts vaporizing into vacuum. As expected with ammonium halides and ammonium bi-sulfate the TOF distributions correspond to equimolar fluxes of ammonia and the corresponding acid. In the case of ammonium perchlorate the vapor subliming from a single crystal comprised ammonia and perchloric acid. When the source was compressed powder, the vapor was a mixture of lower molecular weight species. This result seems best explained in terms of subsurface decomposition. (Author)

Steve Tang

Papers

Vacuum Sublimation of Ammonium Perchlorate.