Drop height

Contact angle Drop height or volume Spreading velocity... 

When plotted as a function of drop size (Fig. 9), the contact angle was found to decrease with increasing drop height. A different analysis of these data was performed in the original paper. In that case the maximum slope near the drop edge was used, as well as a direct inversion of the droplet shape. The data could be fit to an empirical 1/z function. In the present analysis we use the method of the effective contact angles defined earlier, together with Eq. (18). For the Flamaker constant A, we calculated a value of approximately -2 X 10 ° J. However, the best fit to Eq. (18) is for a pure exponential decay of the form ... 

FIG. 12 Plot of the effective contact angle 0 of the glycerol drops on contaminated mica vs. drop height e. A rapid increase occurs up to 200 A (corresponding to a drop with a base diameter of 2.2 p.m), where it reaches a constant value Gq. Inset Plot of (Go - 0 )/(l + e/8) vs. e. This plot shows that the potential due to the long-range forces depends exponentially on the distance. (From Ref. 9.)... 

More recently, explosives have been tested for impact sensitivity by an impact machine in which 40 mg of explosive on sandpaper are placed between an anvil and a steel cylinder. A 2.5 kg weight is dropped from different heights and the sound produced serves to indicate a go or no go . The result from 25 drops is calculated to give a height at which the probability of explosion is 50%. Results from a compilation104 are presented in Table 12 and show that the relative values of TNT and picric acid are reversed from the previous table. TNT is relatively more sensitive on the Type 12 impact machine than in the FI impact test. TATB is so insensitive that it fails to explode at the maximum drop height of the machine. 

Compound Impact sensitivity Type 12 machine Drop height (cm) Temperature of onset of exotherm ( C)... 

Fig. 9. Alcoa test site details A, tap diameter B, water depth C, drop height D, water vessel.

For most tests, if the drop height were too high (S3 m), no explosions resulted. Also, inhibition was obtained when a steel grid (spacing 2.5 cm) was placed between the crucible and water surface. 

It is difficult to draw many conclusions from this study. Drop masses were far below those considered minimal in the Alcoa tests also the drop height was large and the water deep. Judging from the Alcoa studies, one would not have expected any thermal explosions to result with pure aluminum. The presence of lithium apparently could change even small systems from a nonexplosive to a potentially explosive one if a sufficiently eneiigetic external shock were also imposed. 

The charcoal, or rather the coated charcoal, contributes to the fountain effect as does the gunpowder and aluminium by processes such as those described above. The flitter aluminium has a rather coarser particle structure than does the fine aluminium so that sparks from the former are longer lived and can survive a greater drop-height. Antimony trisulfide is commonly used to enhance the glittering effect in a series of chemical reactions with the gunpowder and aluminium. 

Fig 45 shows a plot of drop height in inches vs cumulative percent explns for 5 common expls [from Dunkle s Syllabus (1957-58), p 150]... 

The Bruceton test (as expected) gives a good value of the mean drop height, ie 50%... 

Two other observations are of interest P does not depend on hammer drop height (or drop velocity)... 

The relationship between contact angle 9 and the maximum drop height... 

Minimize drop height. Drop height serves to aerate the material, induce dust, and increase momentum of the material as it hits the pile, increasing the tendency for each of the three segregation mechanisms described earlier. 

There is a general trend in which logarithm of 50% drop height (log h50%) decreases with increasing oxidant balance (OBi00). 

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