Sensitivity friction

Friction sensitivity studies have shown a relationship to ignition temperature and heat of reaction, but the critical factor in friction sensitivity appears to be the presence in a composition of a significant amount of a gritty or hard granular component. Such a material, when exposed to frictional action, will generate hot spots that can lead 

Effect of Titanium Powder Black Powder on Sensitivity of 

The Mechanical/Sensitiveness of Titanium/Black Powder Pyrotechnics Composition, Propellants, Explosives, Pyrotechnics, 18, 25, 1993. 

Low values indicate greater sensitivity to ignition in these tests. 

Rotary Friction Sensitivities for Some Pyrotechnic Compositions 

Despite decades of friction testing, the phenomenon is still relatively poorly understood. The quantitative interpretation of the results is problematic due to numerous factors affecting the mechanism of fi iction initiation. In practice, the test is done by placing the tested explosive between two inert surfaces, applying a defined load on the sample and then sHding one or both of the surfaces in a direction normal to the direction of the applied force. Ceramic plates are often the material of choice. 

Some primary explosives are reported to have extreme sensitivity. SF and SA are two such substances. Extreme sensitivity of SF is reported in [33], very high sensitivity (approximately 2-3 times higher than that of LA depending on the testing surface) is reported for SA [55]. Such statements must be carefully considered and evaluation based on solid data. Extreme sensitivity of SA is, for example, commonly found in older sources and could be the result of the method of preparation. In the early days, SA was prepared by direct precipitation of aqueous solutions of sodium azide and the silver salt and such a method of preparation could have led to a more sensitive product. Today s industrial SA (product of BAE Systems) is reported to have sensitivity lower than that of LA (determined by emery Motion test) [56]. 

Comparing Mction sensitivity of LA and MF based on published results can be quite complicated. Some authors report LA to be more sensitive [23, 33, 36] than MF while others refer to it being less sensitive [45, 57]. The reason for such 

Sensitivity to friction is highly dependent on the method of measurement. The most important factors influencing the final results include the material of the plate surface and the peg, speed of the peg sliding, and humidity. These factors are very difficult if not impossible to compare making results of various authors hardly ever directly comparable. 

Figme 2.20 demmistrates another issue regarding sensitivity of primary explosives. Each point on the graph represents the probabiUty of initiation from 15 trials at particular friction force. The curves were obtained by probit analysis [27] for two samples—pure crystalline LA and dextrinated LA. The x-axis shows the used friction force and the y-axis the probabdity of initiation. Interestingly, the 

The classical laws of friction were noted in the works of da Vinci [69, 70], Amontons [71], Coulomb [72], and Euler [73]. In simplest terms friction is the resistance to motion which occurs whenever an object slides across another surface. The laws of sliding friction may be summarized as  

Frictional force is directly proportional to the load or to the total force acting normal to the sliding surface. 

Frictional force for a constant load is independent of the contact area. 

Friction between unlubricated surfaces is due to a combination of adhesion 

Plastic deformation is caused by the ploughing, grooving, or cracking of surface asperities. If this is designed as P, and there is negligible interaction between the two, friction can be considered the sum 

Ehiring their life cycle, explosives are very often subjected to friction either between explosive particles or between explosive particles and various types of working surfaces. Under appropriate conditions, friction can cause the initiation of an explosive. 

Between the surface of two materials in relative motion, sliding frictional force F y) exists. It is proportional to the normal force (F) pressing the two materials together  

The energy used to overcome the frictional force is spent either in the form of mechanical work or as heat. As a result of the heat, two bodies in relative motion become warmed. As the contact areas of two bodies in relative motion are not smooth on a microscopic scale, the dissipation of mechanical energy in the form of heat will mainly be localised. The points of local heating, called hot spots, are initiators of explosive chemical reactions. The temperature of the hot spots depends upon 

When the friction sensitivity is determined, the relative velocity of the bodies in motion, the friction coefficient, and the thermal conductivity coefficient are kept constant, whereas the normal force between contacting areas is 

The testing procedure using the BAM Friction Apparatus is described below. 

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Explds violently on contact with Cu oxide and is friction sensitive. Its Hg salt is also an expl Refs 1) Beil 25, 114 2) D.D. Phillips ... 

Pagowski (Ref 6) proposes an effective OB (again undefined in CA) and claims a linear correlation of effective OB and detonation velocity Mustafa Zahran (Ref 8) prepared a series of substituted Tetryls, Pentyls, Hexyls Nonyls. For each series they claim a correlation between the Martin Yallop corrected OB, and impact or friction sensitivity, and Trauzl Block "power . 

Their impact and friction sensitivity data appear to be monotonic functions of corrected OB, but the relation between corrected OB and Trauzl Block data appears to be complex... 

Pendulum, Friction, Apparatus. See under Friction Sensitivity Tests in Vol 6, F204-L to F206-L... 

As discussed in Vol 7, it is rather futile to assign numerical values to the impact or friction sensitivity of PETN (or any other expl), although the average critical stress of VSkbar for PETN impact initiation (Ref 85a) may be significant. 

Friction Sensitivity. By friction pendulum, it snaps when tested with a steel shoe (Ref 11). With an ABL-designed sliding friction machine, AP required a sliding dist of 16cm for 50% explns (NO 15cm) (Ref 24, p 20)... 

It is an expl, having a ballistic strength of 114% (TNT=100) impact sensitivity-less sensitive than TNT friction sensitivity—no detonations ignition temp—270° practically non-hygroscopic and of satisfactory thermal stability Refs 1) Beil—not found 2) L.F. Fieser et... 

Friction Sensitivity. Comparable to CycIonite Hygroscopicity. Practically non-hygroscopic Impact Sensitivity. Slightly less sensitive than PETN... 

Friction Sensitivity. With BuMines Friction Pend app, unaffected... 

N 42.74% OB to C02 —30.51% cryst (meso), liq (racemic) mp 70—71° (cryst) bp 150° (decompn). Sol in acet and ethanol. Prepn is by nitration of 2,3-diazido-l, 4-butanediol with mixed acid. The procedure involves dropwise addn of 2.58g of the diol to a cooled (0—5°) mixt (1/1) of acetic anhydride/100% nitric acid. The reaction is held to 5—15° and stirred for 30 mins. Several recrysts from ethanol give a (approx) 40% yield. The compd is friction sensitive Qc 682.8 and 671.8kcal/mole Qf 98.8 kcal/mole impact sensy at 50% pt is 6.3cm using a 2kg wt in an Aberdeen Impact App and No 12 tools (PETN=26.7cm) impact sensy of proplnt films (85.15% NC/14.85% diazido compd) is 29—36cm (M2 film=34—36cm) at the 50% pt... 

The importance of frictional heating in the initiation of expls is a subject of considerable importance. The frictional sensitivity is directly involved in the handling hazards of all high-energy materials and considerable attention has been directed toward gathering of frictional sensitivity data on almost all mil expls, in addi- tion to an entire host of pyrotechnic mixts and certain propints (Refs 6 17)... 

Friction sensitivity. Crackles with steel shoes Hygroscopicity. Wt gain after 15 days at 90% RH nU... 

It is a combustible and explosive salt which is very friction-sensitive [1], and may explode spontaneously [2]. 

A bearing assembly from a sodium bromate crusher had been degreased at 120°C, and while still hot the sleeve was hammered to free it. The assembly exploded violently, probably because of the presence of a hot mixture of sodium bromate and a grease component (possibly a sulfurised derivative). It is known that mixtures of bromates and organic or sulfurous matter are heat- and friction-sensitive [1]. The energy of decomposition of the likely components has been calculated as 1.93 kJ/g, with an explosion temperature above 2000°C [2],... 

Watts, C. E., Chem. Eng. News, 1952, 30, 2344 The isolated salt is a friction-sensitive explosive. 

Highly explosive and very friction-sensitive. Higher homologues are more stable. 

The acetylide, produced as an unexpected major product, is a shock- and friction-sensitive explosive. A few mg exploded when touched with a spatula, and the remaining 2 g sample detonated violently when destroyed by a controlled explosion. See Other HALOACETYLENE DERIVATIVES, METAL ACETYLIDES... 

Houben-Weyl, 1975, Vol. 13.3, 288 Friction-sensitive, it decomposes explosively. 

Three beakers containing lead styphnate were being heated in a laboratory oven to dry the explosive salt. When one of the beakers was moved, all 3 detonated. Other heavy metal salts of polynitrophenols are dangerously explosive when dry [1], The desensitising effect of presence of water upon the friction sensitivity of this priming explosive was studied. There is no effect up to 2% content and little at 5%. Even... 

It polymerises slowly at — 20°C, but rapidly at ambient temperature in air to give a friction-sensitive explosive solid, probably a peroxide [1]. Although stable under vacuum at —5°C for a limited period, exposure at 0°C to air led to violent explosions soon afterwards [2], Explosive hazards have again been stressed [3],... 

Picric acid, in common with several other polynitrophenols, is an explosive material in its own right and is usually stored as a water-wet paste. Several dust explosions of dry material have been reported [1]. It forms salts with many metals, some of which (lead, mercury, copper or zinc) are rather sensitive to heat, friction or impact. The salts with ammonia and amines, and the molecular complexes with aromatic hydrocarbons, etc. are, in general, not so sensitive [2], Contact of picric acid with concrete floors may form the friction-sensitive calcium salt [3], Contact of molten picric acid with metallic zinc or lead forms the metal picrates which can detonate the acid. Picrates of lead, iron, zinc, nickel, copper, etc. should be considered dangerously sensitive. Dry picric acid has little effect on these metals at ambient temperature. Picric acid of sufficient purity is of the same order of stability as TNT, and is not considered unduly hazardous in regard to sensitivity [4], Details of handling and disposal procedures have been collected and summarised [5],... 

Negyesi, G., Process Safety Progress, 1996,15(1), 42 This compound shows signs of impact and friction sensitivity. 

Nast, R. et al., J. Organomet. Chem., 1966, 6, 461 Extremely explosive, heat- and friction-sensitive. 

Highly friction sensitive, with considerable explosion hazard [1], Repeating a published method ([2], where explosion at the m.p., 180°C is noted), the product was dried in a desiccator. When the lid (ground glass flange) was slid olf, the friction initiated explosion of a little of the compound deposited on the flange, and a severe explosion resulted [3],... 

It is an explosive of lower power, but of greater impact- or friction-sensitivity than picric acid, so should not be stored in bottles with ground-in stoppers. 

Hafner, K. etal., Org. Synth., 1964, 44, 102 The crystalline solid is an impact- and friction-sensitive explosive and must be handled with precautions. These include use of solvent-moist material and storage in a corked rather than glass-stoppered vessel. 

While the commercial material damped with 30% water is not shock- or friction-sensitive, if it dries out it may become a high-hazard material. As a typical low-melting diacyl peroxide, it may be expected to decompose vigorously or explosively on slight heating or on mechanical initiation [1], It is shock sensitive (presumably when dry) [2]. 

This trimeric propylidene peroxide , formed from propanal and hydrogen peroxide, is an extremely explosive and friction-sensitive oil. 

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