X-ray diffractometry studies and lattice parameter calculation on KNO3–NH4NO3 solid solutions

Abstract

The solid-state phase transitions of the KNO3-NH4NO3 solid solutions have been determined by high temperature X-ray diffractometry, and lattice parameter calculation has also been performed. Ammonium nitrate (AN) is of great use for gas generators of automobile air bag systems. The X-ray diffraction results showed the single (AN) phase III from 5% to 20% KNO3 in NH4NO3 and up to 373 K, which is the important temperature range for the air bag gas generator applications. The X-ray diffraction patterns of the low temperature KNO3 phase (KN II) are from 92%-100% KNO3 composition range and up to 393 K temperature. The high temperature KNO3 phase (KN I) showed very broad composition range from 20% up to 100% KNO3 at various temperature ranges. The lattice parameters of the NH4NO3-rich (AN III) and KNO3-rich (KN II and KN I) solid solutions have been calculated at different temperature range. The volumes of AN III phase decrease from 0.3201(4) to 0.3166(1) nm 3 at the room temperature and from 0.3250(6) to 0.3215(3) nm 3 at 373 K as the compositions increase from 5% to 20%KNO3. The lattice constants of the hexagonal KN I phase show that there is no significant change in a-direction when the temperature increases. Details of X-ray results, lattice expansions and equations during heating are presented.