|Molecular formula||Pb (N 3 ) 2|
colorless, needle-shaped crystals
|External identifiers / databases|
|Molar mass||291.23 g mol −1|
Decomposition from 190 ° C
bad in water (230 mg l −1 )
|Authorization procedure under REACH|
|As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .|
Lead azide was first presented by Theodor Curtius in 1891, as was silver azide and mercury azide . The importance of the connection was recognized early on by the Military Research Office in Berlin , and as early as 1907, an initial igniter based on this salt was patented by Lothar Wöhler . Due to the high tendency towards spontaneous explosions, several decades passed before general international application.
Presentation and extraction
Production takes place in discontinuous or continuous processes by reacting aqueous solutions of sodium azide and lead nitrate . Here it is important to avoid the formation of large crystals, since even small mechanical loads such as the breaking of crystal needles can trigger an explosion. For this reason, dextrin , polyvinyl alcohol or other substances that interfere with crystal growth are added, so that a technical product with a lead azide content of 92-96% results.
In the laboratory, there is only a reduced application of the technical description of the precipitation of a sodium azide solution with a lead nitrate solution with vigorous stirring to avoid the formation of larger crystals:
In order to obtain a purer product for laboratory use, the addition of additives is often dispensed with.
Lead azide forms colorless crystals that are relatively resistant to heat and moisture or are not very hygroscopic. It is practically insoluble in water. Lead azide occurs in four polymorphic modifications. These are an orthorhombic α-form, a monoclinic β-form, a monoclinic γ-form and a triclinic δ-form. The connection has explosive properties, the mechanical sensitivity to shock, impact and friction being particularly relevant. It is relatively temperature-stable and only disintegrates above 315 ° C. The decay products are finely divided lead and nitrogen . Important explosion indicators are:
- Heat of explosion : 1639 kJ kg −1 .
- Detonation velocity : 4630 m · s −1 at a density of 3.0 g · cm −3 or 5180 m · s −1 at a density of 4.0 g · cm −3
- Normal gas volume : 308 l kg −1 .
- Specific energy : 380 kJ kg −1
- Deflagration point : 315 - 360 ° C
- Lead block bulge : 11 cm 3 g −1
- Impact sensitivity : 2.5 - 4 Nm (pure) or 3 - 6.5 Nm (technical)
- Friction sensitivity : 0.1 N
Pure lead azide is also very sensitive to electrostatic charges and ignites easily through field breakdown . The data refer to the common α-form. The β form is much more sensitive. Lead azide can be destroyed in an aqueous solution with 8% sodium nitrite and 15% nitric acid or in a 10% sodium hydroxide solution .
Since it was first used as an initial explosive (Wöhler-Martin), lead azide has become the most important initial explosive, almost completely displacing the mercury that was previously common . Despite its lower energy content and lower density , it has greater initial strength, is less sensitive to impact than fumed mercury and is also significantly more stable at higher temperatures and against moisture. The introduction of aluminum for the manufacture of detonators and thus a significant reduction in price was only possible through the use of lead azide, since mercury fulminate forms an amalgam with aluminum .
- Entry on lead azide. In: Römpp Online . Georg Thieme Verlag, accessed on June 14, 2014.
- Entry on Lead diazide in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on February 1, 2016. Manufacturers or distributors can expand the harmonized classification and labeling .
- Entry in the SVHC list of the European Chemicals Agency , accessed on July 16, 2014.
- Patent DE196824 : initial fuse. Registered on March 2, 1907 , published March 27, 1908 , inventor: L. Wöhler.
- J. Köhler, R. Meyer, A. Homburg: Explosivstoffe. 10., completely revised. Edition. Wiley-VCH, Weinheim 2008, ISBN 978-3-527-32009-7 .
- Georg Brauer: Lead azide . In: Handbook of Preparative Inorganic Chemistry . Ferdinand Enke Verlag Stuttgart, 1954, p. 363 .
- ABC chemistry. FA Brockhausverlag, Leipzig 1971, p. 187.