In this paper, a selection of the results obtained on the crystallization of the energetic materials RDX, HMX, and CL-20 will be briefly reported. Furthermore, the shock sensitivity of these explosives, when incorporated in a so-called plastic bonded explosive (PBX), will be discussed in more detail. One of the most important results is a direct correlation between the mean density of the energetic material and the shock sensitivity of the PBX containing this explosive. This implies that, similar to many other solid materials, the ability to control the product quality is also one of the major key factors playing a role during the crystallization of these energetic materials.

A method is described for determining the solubility of multicomponent crystalline compounds from clear points upon sample dilution at a constant temperature. Clear points are established by continuously adding a solvent mixture to a suspension of known composition until a clear solution appears. For validation, this solvent addition method is compared to the traditional equilibrium concentration method at constant temperature and the more recent temperature variation method with which clear point temperatures are determined upon increasing the sample temperature. Solubility data of binary systems (1 solute, 1 solvent) measured using the solvent addition method are obtained relatively quickly compared to the equilibrium concentration method. These solubility data are consistent with those of the temperature variation and the equilibrium concentration method. For the temperature variation method, the results are dependent on the heating rate. Likewise, for the solvent addition method, they are dependent on the addition rate. Additionally, for ternary systems involving antisolvent or cocrystals, solubilities are determined at a constant temperature using the solvent addition method. The use of the solvent addition method is especially valuable in the case of solvent mixtures and other complex multicomponent systems, in which the temperature variation method cannot be applied easily. ■ INTRODUCTIONIn production often a crystallization step is required for purification and final crystalline particulate product formation. 1,2 The solubility or phase diagram of such compounds is essential information for efficient and reliable crystallization process design and operation. 3−6 The phase diagram indicates the most stable phases at specific compositional and temperature conditions, 1,4−6 determines the achievable yield, 7 and enables the monitoring of the supersaturation during the crystallization process. 7,8 Traditionally the solubility is measured through equilibration of a suspension. 1 The solubility is then equal to the concentration in the equilibrated solution, which can be sampled and determined by, for example, a gravimetric method or HPLC (Figure 1 (left)). Although the Equilibrium Concentration (EqC) method is widely accepted and considered accurate, 1 it is laborious and time-consuming. Currently, commercial equipment from various suppliers is available that streamlines measurements through a temperature variation (TV) method in which clear points are measured. 9−11 In the TV method the solubility is changed by changing the temperature, until it matches the concentration. A clear point is then the temperature at which, upon increasing the temperature, a suspension turns into a clear solution. Figure 1 (center) shows the principle of a clear point measurement using the TV method. If the heating rate is sufficiently small, the crystal dissolution rate is fast and the clear point can be assumed to be equal to the saturation temperature. 10 This TV method is much less labor intensive, is much faster, and allows f...

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Nano-and submicron-sized crystals are too small to contain inclusions and are, therefore, expected to have a higher internal quality compared to conventionally sized particles (several tens to hundreds of microns). Using electrospray crystallization, nano-and submicron-sized crystals can be easily produced. With the aid of electrospray crystallization, a mist of ultrafine solution droplets is generated and subsequent solvent evaporation leads to crystallization of submicron-sized crystals. Using cyclotrimethylene trinitramine (RDX) solutions in acetone, the conditions for a stable and continuous jet were established. At relatively small nozzle diameters and relatively low potential differences, hollow spheres of RDX crystals were observed. At a higher nozzle diameter and potential difference and in the region of a continuous jet, RDX crystals with an average size of around 400 nm could be produced. In order to test the quality of the submicron-sized energetic material, impact and friction sensitivity tests were carried out. The test results indicate that the submicron-sized product had reduced friction sensitivity, indicating a higher internal quality of the crystalline product.