title: Premature detonation of an NH₄NO₃ emulsion in reactive ground.
abstract: When NH4NO3 emulsions are used in blast holes containing pyrite, they can exothermally react with pyrite, causing the emulsion to intensively heat and detonate prematurely. Such premature detonations can inflict fatal and very costly damages. The mechanism of heating of the emulsions is not well understood though such an understanding is essential for designing safe blasting. In this study the heating of an emulsion in model blast holes was simulated by solving the heat equation. The physical factors contributing to the heating phenomenon were studied using microscopic and calorimetric methods. Microscopic studies revealed the continuous formation of a large number of gas bubbles as the reaction progressed at the emulsion-pyrite interface, which made the reacting emulsion porous. Calculations show that the increase in porosity causes the thermal conductivity of a reacting region of an emulsion column in a blast hole to decrease exponentially. This large reduction in the thermal conductivity retards heat dissipation from the reacting region causing its temperature to rise. The rise in temperature accelerates the exothermic reaction producing more heat. Simulations predict a migration of the hottest spot of the emulsion column, which could dangerously heat the primers and boosters located in the blast hole.
authors.affiliation: School of Chemistry, University of Sydney, NSW 2006, Australia.
authors.forename: Pramith
authors.initials: P
authors.lastname: Priyananda
authors.affiliation: School of Chemistry, University of Sydney, NSW 2006, Australia.
authors.forename: Alex M
authors.initials: AM
authors.lastname: Djerdjev
authors.affiliation: Dyno Nobel AsiaPacific Pty Ltd, Mt Thorley, NSW 2330, Australia.
authors.forename: Jeff
authors.initials: J
authors.lastname: Gore
authors.affiliation: School of Chemistry, University of Sydney, NSW 2006, Australia.
authors.forename: Chiara
authors.initials: C
authors.lastname: Neto
authors.affiliation: School of Chemistry, University of Sydney, NSW 2006, Australia.
authors.forename: James K
authors.initials: JK
authors.lastname: Beattie
authors.affiliation: School of Chemistry, University of Sydney, NSW 2006, Australia. Electronic address: brian.hawkett@sydney.edu.au.
authors.forename: Brian S
authors.initials: BS
authors.lastname: Hawkett
mesh_terms: D064751:Ammonium Compounds / Q000737:chemistry*; D006358:Hot Temperature; D009566:Nitrates / Q000737:chemistry*; D012987:Soil / Q000737:chemistry; D012989:Soil Pollutants / Q000737:chemistry*
chemical_list: D064751:Ammonium Compounds; D009566:Nitrates; D012987:Soil; D012989:Soil Pollutants
keywords: Emulsion explosives; NH(4)NO(3); Pyrite; Reactive ground; Thermal conductivity