Effect of Addition of Hydrophobic Hydrocarbons on the Hygroscopic Tendency of Ammonium Nitrate Crystals

Abstract

The present study is aimed towards the use of selected hydrophobic hydrocarbons to attain a waterproof coating on Ammonium Nitrate crystals. High hygroscopic nature of Ammonium Nitrate makes it impractical for its use as oxidizer in composite solid propellant formulations as absorption of water molecules by Ammonium Nitrate from moisture in the atmosphere negatively affects the structural integrity, energetics and ballistic performance of the Ammonium Nitrate based propellant grains. Hydrocarbons, generally waxes and oils, are hydrophobic in nature and may thus be utilized to repel water molecules resulting in a reduced water absorption by Ammonium Nitrate crystals. In the present study, the effect of addition of Paraffin Wax, Micro-crystalline Wax & Bees Wax along with pure Ammonium Nitrate is observed and compared. Samples were prepared by adding varying and significantly small weight percentages of waxes with Untreated Ammonium Nitrate and were kept under normal laboratory conditions. A weight increment rate study of all the prepared samples were conducted on a daily basis for a period of 20 days. All prepared samples, under same atmospheric conditions, exhibited different water absorption rates which were then compared to reveal the waterproofing capabilities of specific additives.