Explosive and thermic compositions or charges – Structure or arrangement of component or product – Coated component
Patent
1995-02-24
1995-12-05
Walsh, Donald P.
Explosive and thermic compositions or charges
Structure or arrangement of component or product
Coated component
149 46, 423267, 428403, 427215, 71 59, 71 6412, C06B 4530, C06B 3128, A01N 2500, C05G 500
Patent
active
054725305
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method of manufacturing free-flowing ammonium nitrate particles, applying an inorganic coating. The invention also comprises a new type of anticaking coating.
Ammonium nitrate (AN) has high caking tendency, even at very low water content, i.e. the particles stick together and will no longer be free-flowing. Another problem related to ammonium nitrate is its transition from one crystal modification to another. Especially the transition from modification III-IV at about 32.degree. C. might result in dust formation and increased caking problems. This phase transition depends to some degree on the water content of the ammonium nitrate particles.
There are known several methods for dealing with the above problems. Firstly, application of various coatings. However, if the ammonium nitrate is to be used in explosives like ANFO or emulsion explosives, the coating might cause problems for the manufacture and application of the explosive. Conventional anticaking coatings comprising amines or sulphonates with or without inert powder are examples of coatings causing problems when the coated ammonium nitrate is applied in explosives.
The phase transition at 32.degree. C. can be prevented or reduced by adding magnesium nitrate to the AN melt prior to particulation. But this method requires that the melt is evaporated down to a water content of about 0.5 weight % before particulation to attain reasonable caking properties of the particles. Such a superevaporation is not applicable for manufacture of porous AN or crystal AN. Thus AN stabilized against phase transition will in most cases still need an anticaking coating.
In European Patent No. 95814B is described a method for producing non-caking ammonium nitrate granules. This method comprises phase stabilization by a special cooling procedure. The particles are preferably coated with an organic coating and then an inorganic powder prior to storage.
Further, it is in Japanese Patent Publication No. J61291411-A described AN particles having low caking tendency. The ammonium nitrate powder particles are blended with a zinc ammonium sulphate having less than 5 molecules of crystal water per molecule, and a metal oxide micropowder. The amount of sulphate is 0.05-1 weight % of the ammonium nitrate. Though the caking tendency is reduced by this method, the anticaking agent easily results in dust formation. The added sulphate and the metal oxide will also cause problems if the AN should be used in explosives. Especially in emulsion explosives the above applied agent would result in destabilization of the emulsion.
The main object of the present invention was to arrive at a method for producing free-flowing AN particles, especially AN crystals which could be applied in explosives like ANFO- and emulsion explosives.
The second object was to produce free-flowing AN particles without having to lower the water content of the AN solution or melt below 3-4% prior to particulation.
A further object was to attain free-flowing AN particles without using organic anticaking agents and powder like talc, kaoline, SiO.sub.2 etc.
The inventors first investigated various ways of solving the problems related to crystal AN to be used in explosives. The new stabilizing or coating agent should not alter significantly the crystal structure of the AN particles and should also be compatible with the various components of the explosive. In order to avoid problems during crystallization it was decided to look for a new coating and not add chemicals like crystal modifiers to the AN solution prior to crystallization or particulation. In view of the fact that free water present in the AN particles increases the possibility for phase transition and caking, the inventors tried to find a coating agent which would bind free water present and/or prevent the AN particles from absorbing water from the surroundings, i.e. moisture from the air during storage. Known inorganic agents like talc or zinc ammonium sulphate could to some degree reduce the amount of free water present, but
REFERENCES:
patent: 4316736 (1982-02-01), Vanttijfte
Derwent Abstract of EP 95814 (AN 83-840289/50).
Derwent Abstract of JP 61291411-A (AN 87-033913/05).
Helleb.0. Leif G.
Isaksen Jan B.
Juliussen Bj.0.rn
Obrestad Torstein
Chi Anthony R.
Norsk Hydro a.s
Walsh Donald P.
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