Determination of Friction Sensitivity

During the life cycle of explosives, they are very often subjected to friction either between the explosive particles, or between explosive particles and various types of working surfaces, and this friction is likely to cause initiation of an explosive. 

a common hazard in the handling of explosives is for them to be subjected to the effects of a blow which is, to some extent, at a glancing angle. This corresponds neither to pure impact nor to pure friction. Also, it is difficult to devise a test which delivers only the friction stimulus without impacting the sample and indirectly heating it by contact with a sliding component in the apparatus. 

The determination of friction sensitivity can be carried out using different types of apparatuses discussed at length in the literature which are briefly outlined here. 

Ten trials are conducted from each height and the number of ignitions are recorded. 

The critical heights where minimum 0/10 and at least 1/10 ignition occurs are recorded and reported. 

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Determination of friction sensitivity is applicable to solids, pastes, and gel-type substances. To determine the friction sensitivity, a thin sample is placed under a load between two roughened surfaces, and the surfaces are then rubbed together in a controlled manner. The load can be varied. Results from this action, such as smoke, cracking, or discoloration, are observed. Examples of apparatus of this type are the BAM friction apparatus, shown in Figure 2.30, the rotary friction test, and the ABL friction test. 

Attempts to correlate the data from various types of apparatus have not been successful, and again a paucity of information on the properties of azides and the action of the stimulus has prevented the development of a universal standard test. To progress from the barely qualitative determinations of friction sensitivity... 

One of the recommended test methods for the determination of friction sensitivity was also developed by the German BAM [38]. If the substance to be tested is a solid, drying and sieving is recommended. This increases the sample s sensitivity to an extent, diich most probably exceeds the same under process condition. For the test the sieve fiaction is used which has passed the 0,0005 m mesh. Approximately 10 mm are spread over 0,1 m on a specific part of a porcelain plate. A specially shaped porcelain peg, which is fixed to a loading arm, is once moved forward and back over the sample, thus exerting a mechanical stimulus. 

EPF (Emery Paper Figure), Brit, test for detn of friction sensitiveness of explosives. See under Friction Sensitiveness Determinations in Vol 6 of Encycl... 

The truly unnerving characteristic of HMTD was its sensitivity to friction. Earlier, the test apparatus used to determine friction sensitivity was briefly described. Usually, some form of pressure needs to be exerted on the wheel in order to create enough frictional force to initiate an explosive. In the case of HMTD, a sample could be placed on the plate and the wheel placed over it with no pressure exerted at all. The minute the plate was slid under the wheel, the HMTD detonated. 

Also, di-f-butyl peroxalate (233) can be synthesized according to equation 81 from the analogous reagents. The iodometric determination of 233 can be carried out by letting iodide react for about 30 min. The titration shows only half of the expected equivalents. The mechanism of this reduction involves a slow step leading to an anionic intermediate (234), which decomposes in a fast step before the second reduction can be accomplished, as shown in equation 82 . An explosion has been reported when handling wet crystals of 233, which seem to be extremely friction-sensitive . 

Determination of Detonation Velocity (71-4) Sensitivity to Impact (Sensibilite/ au choc) (74-5) Sensitivity to Friction (75-6) Sensitivity to Initiation (Sensibilite a 1 amorce) (76) Pressure Measurements by Manometric Bomb, by Crusher Test and by Piezoelectric Manometer (79 97) Density Determination (99-100) Chronographs of Schulze and of Le Boulange (101) Tests for Stability by Methods of Abel, Spica, Vieille at 110°C, German at 135° Bergmann-Junk, Su, Hansen-Grotannelli, Silvered Vessel and Taliani (107-09) Explosion Test (109-10)... 

H. Kast (104-07) Determination of Sensitivity to Friction (Medicion de la sensibili-dad al rozamiento) (107) Determination of Sensitivity to Initiation by Detonation (110-12) Determination of Sensitivity to Initiation by Influence (112-13) Determination of Power of Explosives using Trauzl Test (113-17), Small Lead Block Test (117), Quinan Apparatus (118), Guttmann Apparatus (118-19), Ballistic Pendulum (119-20), Mortar (Mortero probeta) (120-21) Determination of Efficiency of Initiating Devices by Lead Plate Test (121-23), Nail Test (123), Sand Test (124) and Acoustic Tests (124) Determination of Characteristics of Flames Produced on Explosion (125-29)... 

Friction Sensitivity, It is a measure of the resistance of an expl to friction, one of the properties required for determining safety in handling and transportation. Several methods for its determination are briefly described in Vol 1, p XIII... 

Friction Sensitivity. The importance of standardizing the method and instrument for determining and comparing the sensitivity to ftiction of expl materials is discussed by Bowden et al (Ref 1) and Kinoshita and Arimura (Ref 2). Bowden points out that, using NG as an example, noexpln occurs until a certain minimal temp is attained from the conversion of mechanical to thermal energy i... 

The impact, friction and spark sensitivities of pyrotechnic formulations are assessed by the methods given in Chapter 3. The outlines of methods for the determination of burning rate, luminous intensity, IR intensity, and total obscuring power of smoke are given in this section. 

Starting with ketones and hydrogen peroxide in the presence of a catalytic amount of acid, mixtures of up to eight components have been identified, i.e.. (1, X = OH. R3 = H), (1, X = OOH, R3 = H), (2, X = Y = OH). (2, X = Y = OOH), (2, Y = OH, Y = OOH), (3). (4), and (5). The ketone structure and reaction conditions, i.e., acid strength, reactant molar ratios, temperature, and time, determine which compounds form and predominate. Mixtures of several peroxide structures usually are present. Individual peroxides have been isolated from several ketones under different conditions (Table 5). The pure peroxides should be handled with extreme caution since most, especially those derived from the low moleculai weight ketones, ate shock- and friction-sensitive and can explode violently. Methyl ethyl ketone peroxide (MEKP) mixtures are produced commercially only as solutions containing <40 wt% MEKPs in solvents, commonly dialkyl phthalates. 

British Tests. See Physical Tests for Determining Explosive and Other Properties Vol 1 and specifically the following British tests a)Ballistic Pendulum Test, p VII b)Exudation(ot sweating) Tests, p XI c)F7 lest(Figure of Insensitiveness Test) p XII Fragment Gun, p XII d)Friction Sensitivity Tests, p XIII e)Hopkinson s Pressure Bar Test, p XVI and i)Silvered Vessel Test or Waltham Abbey Silver Vessel Test, p XXIV... 

The same arguments should hold well for C and H solutes in the case of CHCI3, because their individual masses are considerably different (C = 12 g/ mol and H = 1.008 g/mol), which means that H is more free to move than C and therefore the solvent influence on H is likely to have a dominant role in the determination of the C-H bond friction. Furthermore, C is actually shielded by the presence of three Cl atoms, a factor that has not been considered here. However, this is not expected to be serious because the dephasing is more sensitive to the friction dynamics of the H atom. The time-dependent friction profiles for H and C show similar strong bimodal behavior as in the case of CH3 and I systems. 

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