Sensitivity to friction

Dry nitrocellulose, which bums rapidly and furiously, may detonate if present in large quantities or if confined. Nitrocellulose is a dangerous material to handle in the dry state because of sensitivity to friction, static electricity, impact, and heat. Nitrocellulose is always shipped wet with water or alcohol. The higher the nitrogen content the more sensitive it tends to be. Even nitrocellulose having 40% water detonates if confined and sufftcientiy activated. AH large-scale processes use nitric—sulfuric acid mixtures for nitration (127—132). 

Mechanical sensitivity can be divided into two categories—mechanical friction and mechanical shock. Mechanical friction can be defined as mechanical energy imposed by materials being wedged between surfaces and mechanical shock can be defined as mechanical energy imposed by materials undergoing an impact. Several tests for measuring the sensitivity to friction and the impact of materials are detailed in CCPS G-13. 

Organic Peroxides — (R-O-O-R) are very hazardous. Most of the compounds are so sensitive to friction, heat, and shock that they cannot be handled without dilution. As a result, organic peroxides present a serious fire and explosion hazard. Commonly encountered organic peroxides include benzoyl peroxide, peracetic acid, and methyl ethyl ketone peroxide. 

Its suitable sensitivity to friction and impact (comparable to that of MF), its stability and high flame temp, render it very suitable for percussion-fuze use. An additional asset is that LNP functions in a practically smokeless manner, leaving little residue or slag Refs 1) Mellor 8 (1928), 887 2) E.R. von... 

Se4N4 explodes violently on heating or when brought into contact with a drop of coned sulfuric acid. It is very sensitive to friction and impact. Qf —169.2kcal/mole Refs 1) Gmelin, Syst Nr 10 (1949), 108-110 2) R. Espenscheid, Ann 113, 101 (1860) 3) A. 

It is decompd by moisture or on slow heating to about 50°. When heated rapidly to ca 50°, it detonates. It is extremely sensitive to friction, and sometimes detonates on removing the cork from its container. It also detonates on contact with coned sulfuric acid, coned KOH or ammonia Ref L. Gody, Traite des Materieres Explosifs , Namur (1907), 531... 

According to Andreev Belyaev (Ref 32, p 471) PA shows some slight sensitivity to friction in that it produces a weak burning odor under con-... 

In one Instance, a pyrotechnic preparation, which contained aluminium, water traces, potassium chlorate and potassium and barium nitrates detonated violently twenty four hours after teing prepared. A mixture of barium nitrate, aluminium and magnesium proves very sensitive to friction or impact (risk of ignition or spontaneous detonation). 

Pure PETN is too sensitive to friction and impact for direct application for military purposes. It can usefully be mixed with plasticised nitrocellulose, or with synthetic rubbers to obtain plastic or mouldable explosives. The commonest application, however, is in conjunction with TNT in the form of pentolites. Pentolites are usually obtained by incorporating PETN into molten TNT. A small amount of the PETN goes into solution, but the bulk remains suspended in the liquid and the whole mix can suitably be used in preparing cast charges. Pentolites containing 20-50% PETN are the commonest in practice. 

A proportion of finely divided aluminium is often added to TNT explosives in order to increase the power. As aluminium has also a sensitising effect, it is particularly useful in waterproofed compositions. Another power producing additive which is sometimes employed in large diameter charges where its slow reaction is of less disadvantage is calcium silicide. Care must be taken with this material, however, to ensure that it does not lead to sensitiveness to friction and impact. 

Before nitrates and particularly ammonium nitrate were readily available commercially, explosives were developed based on chlorates and perchlorates. These also are still used in some countries. In general perchlorates are considered less dangerous than chlorates and therefore preferred. They are easily sensitised, so that in addition to explosives of this type based on nitroglycerine, others have been based on various organic liquids, particularly nitrobodies. History shows that chlorates and perchlorates must be regarded as temperamental substances, liable in bulk to lead to inexplicable accidents. Particularly when mixtures of chlorates and oxidising materials are allowed to become wet and then dry out, conditions can arise in which there is an appreciable sensitiveness to friction and impact. Explosives of this type have an unfortunate record of accidents. They are used, therefore, to a limited extent only, now that safer compositions are available. 

Lead azide is manufactured by reaction of sodium azide with either lead nitrate or lead acetate. It is a white crystalline solid, insoluble in cold water and stable on storage. It is very sensitive to friction and impact and has a velocity of detonation, when pressed to a density of 3-8, of4500 ms 1. 

Two crystallographic forms of lead azide are important, the ordinary alpha form which is orthorhombic and the beta form which is monoclinic. The densities of these forms are 4-71 and 4-93 respectively. It was for many years believed that the beta form is the more sensitive to friction and impact and accounted for detonations which have occurred in the manufacture and handling of the substance. It is now known that the beta form is in fact no more sensitive than the alpha. Even the alpha form, when present as large crystals, is very sensitive and conditions can arise (particularly when the formation of the lead azide is controlled by diffusion effects) where spontaneous detonation occurs. Although with modern knowledge these hazards can be avoided, pure lead azide is nevertheless a dangerous compound and is now made only for military purposes. 

Lead styphnate is a poor initiating explosive which when dry is very sensitive to friction and impact, to electrostatic discharge, and to flame. Its main use is as an additive to lead azide to improve flame sensitiveness (see p. 101). When pressed to a density of 2-6 g ml-1 it has a velocity of detonation of4900 m s l. 

An intimate mixture of the finely divided components, once widely used as a photoflash composition, is readily ignitable and extremely sensitive to friction or impact. 

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]. 

Readily formed from cyanogen bromide and sodium azide in aqueous solution at 0°C, it is extremely sensitive to friction, heat or pressure. A dry sample under vacuum at 1 mbar will detonate on rapid admission of air. 

It is sensitive to friction and heat, often deflagrating on gentle warming. 

A pyrotechnic mixture containing the powdered ingredients was found dangerously sensitive to frictional initiation and highly explosive. 

An explosion is mentioned consequent upon grinding potasssium chlorate in equipment previously used for thiourea. It is claimed the mixture explodes spontaneously [1], This is an exaggeration, it is very sensitive to friction, shock and heat (ignition <155°C) [2],... 

It ignites at 240°C in air and decomposes explosively, but surprisingly is not sensitive to friction or impact, unlike its nickel analogue. It shows +118% oxygen balance. 

Red Phosphorus smoke mix production. Evaluation of the Sprout Waldron 35 cubic foot Jet Airmix unit for production of Red Phosphorus (RP) M8E1 Smoke Mixtures was conducted (12). Results indicated the mix was stabile and not easily initiated by heat, but sensitive to friction and snark stimuli. The burning time was slow with dense smoke emission. 

Mechanical sensitivity testing is divided into sensitivity to mechanical shock, also called sensitivity to impact, and sensitivity to friction. Equipment is available to investigate these properties [10,22,24,140,155,156]. 

This primary explosive is created by adding lead acetate to a solution of sodium or ammonium azide. Lead azide has a good shelf life in dry conditions but is unstable in the presence of moisture, oxidizing agents, and ammonia. It is less sensitive to impact than mercury fulminate, but more sensitive to friction. Since lead azide is a nonconductor, it may be mixed with flaked graphite to form a conductive mixture for use in low-energy electronic detonators. 

Pentaerythritol tetranitrate (PETN) is a colorless crystalline solid that is very sensitive to initiation by a primary explosive. It is a powerful secondary explosive that 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 usually mixed with plasticized nitrocellulose or with synthetic rubbers to form PBXs. The most common form of explosive composition containing PETN is Pentolite, a mixture of 20 to 50% PETN and TNT. PETN can be incorporated into gelatinous industrial explosives. The military has in most cases replaced PETN with RDX because RDX is more thermally stable and has a longer shelf life. PETN is insoluble in water, sparingly soluble in alcohol, ether, and benzene, and soluble in acetone and methyl acetate. 

Action of alkalies on diazonium solutions, or of acids on alkali diazoates to give a final pH of 5-6, causes these compounds ( diazoanhydrides ) to separate as oils or solids. Many of these are violently explosive (some exceeding nitrogen trichloride in effect), sensitive to friction and heat or contact with aromatic hydrocarbons [1,2], Individually indexed compounds are ... 

This group of compounds is widely used in industry as a radical source for initiation of polymerisation. They are available from several manufacturers in a very wide range of formulations in various diluents to reduce operational hazards. These were classified into 6 hazard levels and of the many materials available, the first list below of 6 compounds (all dry and unformulated except for that suffixed, which is water-wetted) were included in the highest risk category. This specified the material as being sensitive to friction or mechanical shock equivalent to the dissipation of 1 kg m or less of energy within the sample. 

A few diazonium salts are unstable in solution, and many are in the solid state. Of these, the azides, chromates, nitrates, perchlorates (outstandingly), picrates, sulfides, triiodides and xanthates are noted as being explosive, and sensitive to friction, shock, heat and radiation. In view of their technical importance, diazonium salts are often isolated as their zinc chloride (or other) double salts, and although these are considerably more stable, some incidents involving explosive decomposition have been recorded. 

Both 2,4-dinitrosoresorcinol (23) and 2,4-dinitroresorcinol (24) are important in the explosives industry. The lead salt of 2,4-dinitrosoresorcinol has a low ignition temperature and finds use in priming compositions and in electrical igniters. The lead salt of 2,4-dinitroresorcinol is a weak initiator but is found to exhibit high sensitivity to friction and stab action without being highly sensitive to impact, and as such, this compound has found use in primers. 

Polynitropolyphenylene (PNP) (159), which is a polymeric explosive, exhibits high thermal stability and possesses a low sensitivity to friction and impact. This polymeric mixture, synthesized from the reaction of styphnyl chloride (106) with copper powder in nitrobenzene, has found use as a thermally stable binder in pyrotechnic compositions. ... 

Since NG is highly shock-sensitive, other types of nitrate esters can be used to formulate non-NG double-base propellants. DEGDN, TEGDN, and TMETN are typical examples of energetic nitrate esters that can be mixed with NC. These nitrate esters are less energetic than NG, and their sensitivities to friction and mechanical shock are accordingly lower than those of NG. Thus, the mass fraction of desensitizer used in propellant formulation can be lower than when NG is involved. The physicochemical properties of these nitrate esters are shown in Tabs. 2.3 and 2.5-2.7. 

The majority of Sprengel s fuels were energetic hydrocarbons. Chlorate-based composite explosives tend to be very sensitive to friction and shock. When mixed with energetic fuels, the chlorate formulations are even more sensitive. To address this problem, historically two paths were taken. The chlorate was either mixed with a nonenergetic hydrocarbon or the mixture was phlegmatized (lubricated) if an energetic fuel was desired. 

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