SECONDARY EXPLOSIVES

Secondary Explosives

• Secondary explosives (also known as high explosives) differ from primary explosives in that they cannot be detonated readily by heat or shock and are generally more powerful than primary explosives.

• Secondary explosives are less sensitive than primary explosives and can only be initiated to detonation by the shock produced by the explosion of a primary explosive.

Secondary explosives

• Some secondary explosives are so stable they can be set on fire without detonating.

• The more stable explosives which detonate at very high velocities exert a much greater force during their detonation than the explosive materials used to initiate them.

• Values of their detonation velocities are in the range of 5500-9000 m

Secondary Explosives• TNT• Picric acid • Nitrocellulose• Nitroglycerine• RDX• HMX• PETN• Examples of commercial secondary explosives are

blasting gelatin, guhr dynamite and 60% gelatine dynamite.

PETN

• PETN also known as pentaerythritol tetra nitrate

• Its chemical formula is

PETN

• It is insoluble in water, sparingly soluble in alcohol, ether and benzene, and soluble in acetone and methyl acetate.

• It shows no trace of decomposition when stored for a long time at 100°C.

• It is relatively insensitive to friction but is very sensitive to initiation by a primary explosive.

Properties of PETN

Characteristics Explosive materialColour Color less crystalline solid

Molecular weight 316.1

Melting temperature/ 141.3

Thermal ignition temperature 202

Crystal density at 20 /g cm -3 1.76

Energy of formation/kJ kg-1 -1509

Enthalpy of formation/kJ kg -1 -1683

Properties of PETN

• PETN is a powerful secondary explosive and has a great shattering effect.

• It is used in commercial blasting caps, detonation cords and boosters.

• PETN is not used in its pure form because it is too sensitive to friction and impact.

• It is therefore usually mixed with plasticized nitro cellulose, or with synthetic rubbers to form polymer bonded explosives (PBXs).

PETN

• In military application PETN is largely replaced by RDX

RDX

• RDX also known as Hexogen, Cyclonite and cyclotrimethylenetrinitramine

• RDX was first prepared in 1899 by Henning for medicinal use and used as an explosive in 1920 by Herz. The properties and preparation of RDX were fully developed during World War 11.

RDX

• It attained military importance during World War I1 since it is more chemically and thermally stable than PETN and has a lower sensitiveness.

• Pure RDX is very sensitive to initiation by impact and friction and is desensitized by coating the crystals with wax, oils or grease.

• It can also be compounded with mineral jelly and similar materials to give plastic explosives.

• Have greater explosive power than TNT and Picric acid

Properties of RDX

Characteristics Explosive materialColour White crystalline solid

Molecular weight 222.1

Melting temperature/ 202-204

Thermal ignition temperature 260

Crystal density at 20 /g cm -3 1.82

Energy of formation/kJ kg-1 +417

Enthalpy of formation/kJ kg -1

+318

HMX

• HMX also known as Octogen and cyclotetramethylenetetranitramine

• HMX is a white, crystalline substance which appears in four different crystalline forms differing from one another in their density and sensitiveness to impact.

• The -form, which is least sensitive to impact, is employed in secondary explosives.

Properties of HMXCharacteristics Explosive materialColour White crystalline solid

Molecular weight 296.2

Melting temperature/ 275

Thermal ignition temperature 335

Crystal density at 20 /g cm -31.871.961.821.78

Energy of formation/kJ kg-1 +353.8

Enthalpy of formation/kJ kg -1 +252.8