Silver fulminate

Silver fulminate
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Names
	IUPAC name Silver oxidoazaniumylidynemethane
	Other names Silver fulminate; Silver(I) fulminate
Identifiers
CAS Number	5610-59-3
PubChem	62585
Properties
Chemical formula	AgCNO
Molar mass	149.885 g/mol
Density	3.938 g/cm3
Explosive data
Shock sensitivity	Extremely high
Friction sensitivity	Extremely high
Vapor pressure	{{{value}}}
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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	Infobox references

Silver fulminate (AgCNO) is the highly explosive silver salt of fulminic acid.

Silver fulminate is a primary explosive but has limited use as such due to its extreme sensitivity to impact, heat, pressure and electricity. The compound becomes progressively sensitive as it is aggregated, even in small amounts; the touch of a falling feather, the impact of a single water droplet or a small static discharge are all capable of explosively detonating an unconfined pile of silver fulminate no larger than a dime and no heavier than a few milligrams. Aggregation of larger quantities is impossible due to the compound's tendency to self-detonate under its own weight.

Silver fulminate was first prepared in 1800 by Edward Charles Howard in his research project to prepare a large variety of fulminates. Along with mercury fulminate, it is the only fulminate stable enough for commercial use. Detonators using silver fulminate were used to initiate picric acid in 1885, but since have only been used by the Italian navy.^[2] The current commercial use has been in producing non-damaging novelty noisemakers as children's toys and tricks.

Structure

File:Silver-fulminate-cyclic-hexamer-from-trigonal-xtal-3D-balls-A.png

Ball-and-stick model of the cyclic hexamer in trigonal silver fulminate

Silver fulminate occurs in two polymorphic forms, an orthorhombic one and a trigonal one with a rhombohedral lattice.^[3] The trigonal polymorph consists of cyclic hexamers, (AgCNO)₆.^[4]

File:The needles of silver fulminate.jpg

The needles of silver fulminate

Properties

Fulminates are very toxic, about the same as cyanides.^[2] Silver fulminate when pure is very chemically stable, not decomposing after years of storage. Like many silver salts it darkens with light exposure. It is only slightly soluble in cold water and can be recrystallized using hot water.^[5]^[2] It can also be recrystallized from a 20% solution of ammonium acetate.^[2] It is not hygroscopic and can explode when moist or under water; it was reported to remain explosive after 37 years under water.^[2] It explodes upon contact with concentrated sulfuric acid or chlorine or bromine, but not when contacting iodine.^[2] It is insoluble in nitric acid but dissolves in ammonia, alkali chlorides, alkali cyanides, aniline, pyridine, and potassium iodide by forming complexes.^[2] Concentrated hydrochloric acid decomposes it non-explosively with a hissing noise; thiosulfate also decomposes it non-explosively, and can be used for disposal.^[2]

Preparation

This compound can be prepared by pouring a solution of silver nitrate in nitric acid into ethanol, under careful control of the reaction conditions, to avoid explosion.^[6] The reaction is usually done at 80-90 deg C; at 30 deg C the precipitate may not form.^[2] Only very tiny amounts of silver fulminate should be prepared at once, as even the weight of the crystals can cause them to self-detonate.

Silver fulminate also forms when nitrogen oxide gas is passed through a solution of silver nitrate in ethanol.^[2]

Silver fulminate can be prepared unintentionally, when an acidic solution of silver nitrate comes in contact with alcohol.^[6] This is a hazard in some formulations of chemically silvering mirrors.

Novelty explosive

Silver fulminate, often in combination with potassium chlorate, is used in trick noise-makers known as "crackers", "snappers", "whippersnappers", "pop-its", or "bang-snaps", a popular type of novelty firework. They contain approximately 200 milligrams of fine gravel coated with a minute quantity (approximately 80 micrograms)^[7] of silver fulminate. When thrown against a hard surface, the impact is sufficient to detonate the tiny quantity of explosive, creating a small report from the supersonic detonation. Snaps are designed to be incapable of producing damage (even when detonated against skin) due to the buffering effect provided by the much greater mass of the gravel medium. It is also the chemical found in Christmas crackers.^[8] The chemical is painted on one of two narrow strips of card, with abrasive on the second. When the cracker is pulled, the abrasive detonates the silver fulminate.

A fulminate mixture with 10-20% potassium chlorate is cheaper and more brisant than the fulminate alone.^[2]