Compression Crystal forms

Polymorphs are different crystal forms of the same compound [55], They are usually prepared by crystallization of the drug from different solvents under diverse conditions. However, exposure to changes in temperature, pressure, relative humidity, and comminution which are encountered in processes such as drying, granulation, milling, and compression may also lead to polymorphic transformations. 

In addition to silica (silicon dioxide SiO ), the crystal form of silicon is found in several semiprecious gemstones, including amethyst, opal, agate, and jasper, as well as quartz of varying colors. A characteristic of quartz is its piezoelectric effect. This effect occurs when the quartz crystal is compressed, producing a weak electrical charge. Just the opposite occurs when electric vibrations are fed to the crystal. These vibrations are then duphcated in the crystal. Quartz crystals are excellent timekeeping devices because of this particular characteristic. 

The shape of moving boundary of crystals was different if the composition of melt mixture was changed. When pure benzene was compressed, the shape of moving boundcu y of crystal was roundish. The fringe shape made 1 90.0 mole percent benzene was slightly sharp, and the crystals formed from the melt 80.0 and 70.0 mole percent benzene had sharper moving boundary. But the details of these difference are not clear and future studies are expected. 

The sulfuric and nitric acids and calcium carbonate fed to the reactor are completely consumed. The carbon dioxide leaving the reactor is compressed to 30 atm absolute and 40 C and sent elsewhere in the plant. The remaining reactor effluents are sent to a crystallizer operating at 30 C, at which temperature the solubility of calcium sulfate is 2.0 g CaS04/1000 g H2O. Calcium sulfate crystals form in the crystallizer and all other species remain in solution. 

Polymorphism refers to the arrangement of a drug in various crystal forms (polymorphs). Polymorphs have the same chemical structure but different physical properties, such as solubility, density, hardness, and compression characteristics. Some polymorphic crystals may have much lower aqueous solubility than the amorphous forms, causing a product to be incompletely absorbed. Chloramphenicol, for example, has several crystal forms, and when given orally as a suspension, the drug concentration in the body depended on the percentage of p-polymorph in the suspension. The p-form is more soluble and better absorbed (Fig. 7). In general, the crystal form that has the lowest... 

Effects due to compression can be further divided two categories. One of these concerns the phase transformations that accompany the compaction and consolidation steps of tablet manufacture. The other relates to the effect on tablet properties that arise from the use of different crystal forms in a direct compression tablet formulation. Case studies pertaining to each of these categories will be discussed in turn. 

Change in dissolution rate of disintegrated tablets of phenylbutazone as a function of particle size, compression pressure, and crystal form. Shown are the profiles for tablets prepared from Form A of 6 pm particle size (O), tablets prepared from Form B of 6 pm particle size (D), tablets prepared from Form A of 137 pm particle size ( ), and tablets prepared from Form B of 146 pm particle size ( ). (The figure is adapted from data presented in Ref 53.)... 

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