Shock Gel Process

The most common process to manufacture MTV is the so-called shock gel process also called coacervation process. According to Douda, it had been first used in 1959 [3]. It is an adaptation of the well-known coagulation process of nitrocellulose binder practiced since the 1920s to vinylidenefluoride-hexafiuoropropene-copolymer (70 30mol%) binder (marketed as either Viton or Fluorel ) [4]. 

The binder is dissolved in acetone to give a viscous solution with 8-20wt%. Therefore, Viton or Fluorel slabs are chopped down to pieces 1 x 1 x 1 cm and stirred with acetone overnight in a Cowles-type blender at ambient temperature. 

Dry magnesium and polytetrafluoroethylene (PTFE) powder are then added to the solution to yield a slurry. The slurry volume can be increased by adding a little n-hexane. However, the hexane acetone ratio at this point must not exceed 1 5 as premature precipitation of Viton will occur [5]. After homogenization, a twofold volume of n-hexane is then added to the blender, causing immediate precipitation of the Viton to coacervate both Mg and PTFE particles. A typical composition manufactured by this process is given below  

The dried granules are transferred either manually or automatically to the pressing section. 

According to Diewald and Bickel [8], magnesium powder and PTFE powder and an equal mass of acetone are mixed and worked up in a coUoid mill [9] filled with acetone. The homogenized dispersion is then pressure filtered at 50kPa to leave a solvent-moist Mg/PTFE filter cake. The filter cake is then transferred to a planetary mixer. To this is then added a solution of the necessary amount of Viton binder in acetone. After mixing and forced evaporation of a part of the solvent, the mixer is switched off and about 15 wt96 of the dry weight composition of n-heptane are 

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An experimental shock gel process using supercritical CO2 was explored in the late 1990s by Nauflett and Farncomb in an effort to reduce solvent use, concomitant emissions of VOC and danger of fire [10]. 

Figure 18.8 Supercritical shock gel process. (Adapted from Ref [10].)...

The solvent level in the composition leaving the extruder is 8 wt%. The overall solvent amount per kilogram MTV needed is only 0.225 lkg, which is only 6% the amount needed (3.5 1/kg) for the classical shock gel process [7]. 

Apart from its use in decoy flares, MTV is also used in propellant igniters, and therefore, MTV crumb obtained from shock gel process is extruded in small round or cruciform strands of 2.3-2.4mm diameter. The extrusion is carried out at 121 °C, 4 MPa for round and 8.3 MPa for cruciform strands. Finally, the strand is cut with guillotine type cutter or band saw into length of 3.8-5.8 mm [29, 30]. 

Renner, R.H., Farncomb, R.E., Nauflett, G.W. and Deiter, S.J. (1995) Characterization of MTV made by the shock-gel process. International Symposium on Energetic Materials Technology, Phoenix, Arizona, September 24-27, 1995. 

Experiments with MTV (61.1/33.9/5) obtained with the shock-gel process indicate that fast heating under heavy confinement (Figure 19.14) yields a benign reaction with full consumption of the material (Table 19.9). 

Certain binders such as polyacrylates may not be processed by the shock gel technique. Thus the binder is dissolved in acetone, and successively, both Mg and PTFE powder are added to the mix. Blender equipped with a heating jacket as the one shown in Figure 18.7 is then used to drive off the solvent. The putty-like material obtained is spread on stainless steel trays and dried in way similar to the one described above. However, this material may form larger agglomerates that have to be either separated and/or comminuted in a granulator before further use. Material obtained after deagglomeration is depicted in Figure 18.5. 

Fig. 4. Schematic of cavitation bubbles interacting with a slurry of precipitated gel particles. The configuration shows typical two orifice processing as afforded in the CaviPro 300 processor. Cavitating bubbles initially form, expand in the recovery zone, and collapse with the formation of a microjet and shock wave.

Gel-type ion exchangers are much less resistant to osmotic shock than macroporous ones. For example, after the application of 70 cycles of osmotic shock (by treating sulfonic acid resins alternatively with 76% HNOg and wastewater from an ammonium nitrate processing plant), the number of cracked beads in the case of a gel-type resin (Wofatit KPS) was 78.3%, but for macroporous resins the number varied from only 1.2% (Amberlite 200) to 7.6% (Duolite C26) [24]. Similar results have been obtained for anion exchangers. Thus, the number of the... 

Cloning of cDNA from pea and differential colony hybridization yielded about 70 heat-shock-specific clones which were further characterized by means of hybrid-release translation. Out of these the clones coding for proteins of 26 and 30 kDa,respectively, were further characterized as putative candidates for precursors of plastid heat-shock proteins. To establish a precursor-product relationship the products obtained by hybrid-release translation were studied in a transport assay with isolated chloroplasts from pea. The results are shown in fig. 1. Both products were transported into chloroplasts and processed into proteins indistinguishable in onedimensional polyacrylamide gel. These two clones, furtheron described as P 30-22 and P 26-22, were sequenced. The sequence of P 30-22 turned out to be identical with that from Vierling et al. (5) except for amino acid 225 which is changed from Thr to Arg (not shown). Clone P 26-22 codes for a new plastid protein (Fig. 2). Sequence comparison... 

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