Instantaneous decompression

As far as the external pressure (p ) is concerned, thee are two simple cases (1) instantaneous decompression when is a constant, and (2) linear decompression with constant rate of decompression. The first case might occur in a sudden volcanic explosion or when a magma column is decompressed by sector collapse. The second case is an approximation to pressure evolution during magma ascent. 

Thick shell melt model during instantaneous decompression... 

Linear profiles are the simplest profiles to use for powder compressions. Typically, a sawtooth or v-shaped profile is used where the punch is extended at a constant velocity and retracts at a constant velocity. In theory, during a sawtooth profile, the punch reverses its motion instantaneously between the compression and a decompression strokes. At low speeds (e.g.. <1 mm/sec), the hydraulic response system can easily accommodate this discontinuity. However, at high speeds (>100mm/.sec), the control system may show a small lag in the position-time waveform (<10 milliseconds) as it attempts to rapidly reverse the direction of punch. The sawtooth waveform is commonly used for more fundamental compression studies (e.g.. Heckel analysis), where the desired powder volume reduction is proportional to time. It is also u.seful when evaluating instrument performance during factory acceptance testing. 

Studies conducted by AIM (2009) and AIM and AIM (2014) show the major importance of the rate of DIG pressure drop. Similarly, their studies on MFD showed that the drying rate was substantially faster when achieved by instantaneous pressure drop (between 20 and 200 ms) compared with 2 s decompressions. Indeed, measurements were carried out under the same conditions and it is noteworthy that T- T. In various cases, the magnitude of this difference depends closely on the rate at which the pressure drop occurs. 

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