Impact/shock sensitivities

Explosion often occurs as a result of a blow or shock. Impact sensitivity is shown by the tendency of a substance to explode from a blow, and the shock sensitivity is shown by the tendency to explode from a shock. It is important to distinguish between both kinds of sensitivity. 

Looking first at nitroaromatics, we have extended our earlier work correlating Vmid and shock/impact sensitivity [10] to include a larger number of molecules. Vmid die electrostatic potential at the midpoint of the C-NO2 bond, is approximated by equation (2),... 

Chlorine heptoxide is more stable than either chlorine monoxide or chlorine dioxide however, the CX C) detonates when heated or subjected to shock. It melts at —91.5°C, bods at 80°C, has a molecular weight of 182.914, a heat of vapori2ation of 34.7 kj/mol (8.29 kcal/mol), and, at 0°C, a vapor pressure of 3.2 kPa (23.7 mm Hg) and a density of 1.86 g/mL (14,15). The infrared spectmm is consistent with the stmcture O CIOCIO (16). Cl O decomposes to chlorine and oxygen at low (0.2—10.7 kPa (1.5—80 mm Hg)) pressures and in a temperature range of 100—120°C (17). It is soluble in ben2ene, slowly attacking the solvent with water to form perchloric acid it also reacts with iodine to form iodine pentoxide and explodes on contact with a flame or by percussion. Reaction with olefins yields the impact-sensitive alkyl perchlorates (18). 

The material is impact-sensitive when dry and is supplied and stored damp with ethanol. It is used as a saturated solution and it is important to prevent total evaporation, or the slow growth of large crystals which may become dried and shock-sensitive. Lead drains must not be used, to avoid formation of the detonator, lead azide. Exposure to acid conditions may generate explosive hydrazoic acid [1], It has been stated that barium azide is relatively insensitive to impact but highly sensitive to friction [2], Strontium, and particularly calcium azides show much more marked explosive properties than barium azide. The explosive properties appear to be closely associated with the method of formation of the azide [3], Factors which affect the sensitivity of the azide include surface area, solvent used and ageing. Presence of barium metal, sodium or iron ions as impurities increases the sensitivity [4], Though not an endothermic compound (AH°f —22.17 kJ/mol, 0.1 kj/g), it may thermally decompose to barium nitride, rather than to the elements, when a considerable exotherm is produced (98.74 kJ/mol, 0.45 kJ/g of azide) [5]. 

Extremely explosive, heat- and shock-sensitive as liquid or vapour [1], During determination of the impact-sensitivity of the confined material, rough handling of the container caused ignition. The material should only be handled in small quantity and with great care [2]. 

The determination of the mechanical shock sensitivity or impact sensitivity is applicable to both solids and liquids. The principle involved is that a drop weight falls from a specified height onto the confined test sample. The load can be varied by changing the height of the drop and by changing the drop weight. 

The dry solid is sensitive to shock, impact and friction. It decomposes explosively when heated to 275°C. Contact with acid can produce the explo-... 

Critical Energy of Impact (or Shock) in Detonation (or Explosion). This term signifies the minimum available energy of the falling hammer to produce explosions in impact sensitivity tests. It is designated as Ac and expressed... 

Drop Tests. See IMPACT SENSITIVITY OR SHOCK SENSITIVITY TESTS... 

IMPACT SENSITIVITY OR SHOCK SENSITIVITY TESTS (Drop Weight or Falling Weight Tests). A list of various tests with refs is given in Vol 1, p XVII. Brief descriptions of US Bureau of Mines (BM) Apparatus and of Picatinny Arsenal (PA) Apparatus are also given on p XVII. British test called Figure of Insensitiveness (FI) is described on p XII (See also Refs 36, 38d, 41, 42, 53, 55b,... 

Dunkle s Syllabus (1957-1958) Shock Tube Studies in Detonation (pp 123-25) Determination of Pressure Effect (144-45) Geometrical and Mechanical Influences (145-48) Statistical Effects of Sensitivity Discussion on Impact Sensitivity Evaluation (148-49) Pressure in the Detonation Head (175) Temperature of Detonation (176) Charge Density, Porosity, and Granulation (Factors Affecting the Detonation Process) (212-16) Heats of Explosion and Detonation (243-46) Pressures of Detonation (262-63) A brief description of Trauzl Block Test, Sand Test, Plate Dent Test, Fragmentation Test, Hess Test (Lead Block Crushing Test), Kast Test (Copper Cylinder Compression Test), Quinan. Test and Hop-kinson Pressure Bar Test (264-67) Detonation Calorimeters (277-78) Measurements... 

We have thus far avoided distinguishing between impact sensitivity, projectile (or bullet) sensitivity and shock sensitivity which also involve impact loading of the test explosive. Shock sensitivity, as the name implies, is the response of an explosive to an externally generated shock. Measurements of shock sensitivity are very reproducible, although many existing measure-... 

Bullet (or Rifle Bullet) Impact Sensitiveness, See Vol 1, p IX and under impact (or Shock) Sensitiveness. Also " Rifle Bullet, Impact Test" in AMCP 706-177 (1971), p 2... 

Sensibility au choc du petit mouton (Sensitivity to Shock with Small Ram, which means Impact Sensitivity With Small Weight). See Ref 24, p E139-L... 

This represents the ease with which an explosive can be set off by a blow shock from another explosive charge. This is also termed gap sensitivity or initiability which is less defined than the impact sensitivity and cannot be expressed in absolute units. The sensitivity of high explosives (HE) to initiation is usually determined... 

Drop Weight (or Impact) Tests. See Impact Sensitivity or Shock Sensitivity Test in Vol 1 of Encycl, p XVII also in Vol 4, pp D321-R... 

Recent developments of novel explosive materials have concentrated on reducing the sensitivity of the explosive materials to accidental initiation by shock, impact and thermal effects. The explosive materials, which have this reduced sensitivity, are call Insensitive Munitions, (IM). Although these explosive materials are insensitive to accidental initiation they still perform very well when suitably initiated. Examples of some explosive molecules under development are presented in Table 1.5. A summary of the significant discoveries in the history of explosives throughout the world is presented in Table 1.6. 

J. Eadie reported in Ref 71 that the shock sensitivity of HMX/wax compacts is found to decrease as the amount of the HMX surface coated with wax increased. This thus indicates that the shock sensitivity depends on the surface area of the reactive expl exposed to reaction products. Similar results were observed 20 years earlier and reported in Ref 26. The following is a quote from this Ref, It was noted in the course of this work that the quantity of inert material per se was not the important factor in the phenomenon of desensitization. As a matter of fact, it was the thoroughness with which the explosive crystals (PETN) were coated that appeared to be an important factor in desensitization. Table 6 contains the results of the impact sensitivity tests conducted on PETN-wax mixts where both the quantity of wax in the mix and the degree of coating on the expl crystal are taken into account... 

Fallhammerprobe (Ger) see Impact sensitivity or shock sensitivity test 1 XVII and F11 XII 4D304... 

---