Density polymorphs

However, at some specific pressure the high-density polymorph becomes mechanically unstable. This low-pressure limit is seldom observed, since it often corresponds to negative pressures. When the mechanical stability limit is reached the phase becomes unstable with regard to density fluctuations, and it will either crystallize to the low-pressure polymorph or transform to an amorphous phase with lower density. 

Increasing P increases the stability of high-density polymorphs. 

The physical and chemical properties necessary to characterize fully the drug substance, which includes, but is not limited to, identification of impurities, particle size, solubility, bulk density, polymorphism, hygroscopicity, etc. 

Definition of the API in terms of its critical quality attributes. Among the attributes that should be considered are chemical purity qualitative and quantitative impurity profiles physical characteristics such as particle size, bulk and tap density polymorphic forms moisture and solvent content homogeneity and microbial quality (if the product is susceptible to microbial contamination). 

Figure 14 depicts the density of states for -quartz, stishovite and co-esite. The low energy part of the phonon density of states of stishovite shows pronounced Debye-like behavior This is in contrast to the low density polymorphs of quartz and coesite. The high frequency regions ( 30 THz) for a-quartz and coesite exhibit some strong Einstein-like optic modes. 

HMX, the highest density and highest energy soHd explosive produced on a large scale, primarily for military use, exists in four polymorphic forms. The beta form is the least sensitive, most stable, and the type requited for military use. The mole fraction products of detonation of HMX in a calorimetric bomb are 3.68 N2, 3.18 H2, 1.92 CO2, 1.06 CO, 0.97 C, 0.395 NH3, and 0.30 H2. 

Unlike other synthetic polymers, PVDF has a wealth of polymorphs at least four chain conformations are known and a fifth has been suggested (119). The four known distinct forms or phases are alpha (II), beta (I), gamma (III), and delta (IV). The most common a-phase is the trans-gauche (tgtg ) chain conformation placing hydrogen and fluorine atoms alternately on each side of the chain (120,121). It forms during polymerization and crystallizes from the melt at all temperatures (122,123). The other forms have also been well characterized (124—128). The density of the a polymorph crystals is 1.92 g/cm and that of the P polymorph crystals 1.97 g/cm (129) the density of amorphous PVDF is 1.68 g/cm (130). 

Bismuth Penta.fIuoride, Bismuth(V) fluoride consists of long white needles that have been shown to have the same stmcture as the body-centered, tetragonal a-polymorph of uranium hexafluoride. The density of the soHd is 5.4 g/mL at 25°C. The soHd consists of infinite chains of trans-bridged BiF polyhedra dimers and trimers are present in the vapor phase (22). Bismuth pentafluoride may be prepared by the fluorination of BiF or... 

The determination of precise physical properties for elemental boron is bedevilled by the twin difficulties of complex polymorphism and contamination by irremovable impurities. Boron is an extremely hard refractory solid of high mp, low density and very low electrical conductivity. Crystalline forms are dark red in transmitted light and powdered forms are black. The most stable ()3-rhombohedral) modification has mp 2092°C (exceeded only by C among the non-metals), bp 4000°C, d 2.35 gcm (a-rhombohedral form 2.45gcm ), A77sublimation 570kJ per mol of B, electrical conductivity at room temperature 1.5 x 10 ohm cm- . 

Polymorph Density/gem MP/°C Pressure at triple pt/mmHg A//subi/kJ (mol P40io)- ... 

Many of the high-pressure forms of ice are also based on silica structures (Table 14.9) and in ice II, VIII and IX the protons are ordered, the last 2 being low-temperature forms of ice VII and III respectively in which the protons are disordered. Note also that the high-pressure polymorphs VI and VII can exist at temperatures as high as 80°C and that, as expected, the high-pressure forms have substantially greater densities than that for ice I. A vitreous form of ice can be obtained by condensing water vapour at temperatures of — 160°C or below. 

The ring adopts the chair Ibrm and its dimensions are compared with those of other polymorphs in Table 15.5. Note that cyc/o-S has the smallest bond angle and dihedial angle of all poly-sulfur species for which data are available and this, Uigether with the small hole at the centre of the molecule and the efficient packing within the crystal, lead to the highest density of any known polymorph of sulfur (Table 15.6). 

Calculated valence band (VB) densities of states (DOS) for all six polymorphs studied are presented in Figure 2. These plots correspond to zero pressure geometries. 

Figure 2. Density of electron states (states/eV) for six different polymorphs at P=0.

As yet, no human diseases have been identified as a result of FATPl mutations. However, genetic polymorphisms in the human FATPl gene have been linked to dyslipidemia. An A/G exchange at position +48 in intron 8 of the FATPl gene has been shown to result in increased TG concentrations in female but not in male subjects. In a second study, the same polymorphism was linked to increased postprandial TG concentrations and smaller low density lipoprotein (LDL) particles. To date, it is still unknown if this polymorphism is associated with altered levels of FATPl expression and/or function. 

To achieve the desired cast density for Octol of 1.8g/cc it is necessary that the ratio of HMX TNT be 3 1. However, at this ratio the apparent viscosity, or efflux, is strongly dependent on the polymorphic variety of HMX used and on its particle size distribution. In the initial pilot production of Octol (Ref 3) it was found that for the desired efflux of < 15 sec, 60—70% of the solid HMX must consist of the beta-polymorph having particle diameters in the range of 500—800 microns. Such precise control of particle size was not possible at that time and early Octol casts were made at approximately 50 secs efflux. The economical production of Octol with a satisfactorily short efflux time continues to present a problem in loading shells with this expl (Refs 4, 11 29)... 

A polymorph is a solid crystalline phase of a compound resulting from the possibility of at least two different crystal lattice arrangements of that compound in the solid state [42], Polymorphs of a compound are, however, identical in the liquid and vapor states. They usually melt at different temperatures but give melts of identical composition. Two polymorphs of a compound may be as different in structure and properties as crystals of two different compounds [43,44], Apparent solubility, melting point, density, hardness, crystal shape, optical and electrical properties, vapor pressure, etc. may all vary with the polymorphic form. The polymorphs that are produced depend upon factors such as storage temperature, recrystallization solvent, and rate of cooling. Table 2 suggests the importance of polymorphism in the field of pharmaceutics [45],... 

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