Crystalline Deterioration

Both RDX and HMX are stable, crystalline soHds, somewhat less sensitive to impact than PETN. Both may be handled with no physiological effect if appropriate precautions are taken to assure cleanliness of operations. Both RDX and HMX detonate to form mostiy gaseous, low molecular weight products and some intermediate formation of soHd carbons. The calculated molar detonation products of RDX are 3.00 H2O, 3.00 N2, 1.49 CO2, and 0.02 CO. RDX has been stored for as long as 10 months at 85°C without perceptible deterioration. 

Although vitreous silica is nominally a homogeneous isotropic amorphous material, and should normally remain so during its service life, it is in fact in a metastable condition. The tendency to revert to crystalline forms with attendant deterioration in mechanical durability places severe limitations on the range of applications. Figure 18.2 illustrates the polymorphic forms of silica, and the dimensional changes accompanying each transition. 

Dissolution/reprecipitation processes were evaluated for the recycling of poly-epsilon-caprolactam (PA6) and polyhexamethyleneadipamide (PA66). The process involved solution of the polyamide in an appropriate solvent, precipitation by the addition of a non-solvent, and recovery of the polymer by washing and drying. Dimethylsulphoxide was used as the solvent for PA6, and formic acid for PA66, and methylethylketone was used as the non-solvent for both polymers. The recycled polymers were evaluated by determination of molecular weight, crystallinity and grain size. Excellent recoveries were achieved, with no deterioration in the polymer properties. 33 refs. 

The chemical treatment is permanent. Its unique, crystalline growth will not deteriorate under a wide range of conditions. The treated concrete block is structurally strong, and is not affected by a wide range of aggressive chemicals including acids, solvents, chlorides, and caustic materials in the pH range of 3-11. 

It is emphasized that revealing the dynamics as well as the structure (or conformation) based on several types of spin-relaxation times is undoubtedly a unique and indispensable means, only available from NMR techniques at ambient temperature of physiological significance. Usually, the structure data themselves are available also from X-ray diffraction studies in a more refined manner. Indeed, better structural data can be obtained at lower temperature by preventing the unnecessary molecular fluctuations, which are major subjects in this chapter, since structural data can be seriously deteriorated for domains where dynamics are predominant even in the 2D or 3D crystalline state or proteoliposome at ambient temperature. It should be also taken into account that the solubilization of membrane proteins in detergents is an alternative means to study structure in solution NMR. However, it is not always able faithfully to mimick the biomembrane environment, because the interface structure is not always the same between the bilayer and detergent system. This typically occurs in the case of PLC-81(1-140) described in Section 4.2.4 and other types of peptide systems. 

Fig. 21.17. X-ray diffraction pattern of the cream, showing that SnC>2 is present (filled circles). The crystalline fatty acids (open circles) probably formed by deterioration of the animal fat component during burial. Starch is not evident and so must be in a non-crystalline form, consistent with mode of preparation. (Reprinted/redrawn from Nature, 432, 35-36, Copyright 2004, Nature Publishing Group, with permission.)...

It should be realized, however, that when a low molecular weight compound penetrates the crystalline regions certain properties which depend on crystallinity -e.g., tensile strength, and modulus-will deteriorate. With materials where these properties are of prime importance, it may therefore be more advantageous to use only a secondary plasticizer, or softener. 

FeJdmg s Solution consists of two parts. The first, a solution of 69-28 gms. of pure crystalline copper sulphate dissolved in water with the addition of 1 c.c. of pure sulphuric acid, and the whole made up to 1 litre the second, a solution of 350 gms. of Rochelle salt (sodium potassium tartrate) and 120 gms. of sodium hydroxide (purified from alcohol) dissolved in water and made up to 1 litre. Equal volumes of these two parts are mixed just before use. Each c.c. of the resulting solution is equivalent to 0-005 gm. glucose or to 0-00475 gm. cane sugar. The solution deteriorates after a time, and should be standardised frequently against pure glucose or pure cane sugar. 

Kleinert (2 ) observed that ancient linens exhibited low degrees of polymerization, loss of strength, severe fiber deterioration, high overall crystallinity but short crystallites and a high degree of oxidation. Hackney and Hedley (3) examined the aging of linen... 

Anhydrous, having no water is quicker to absorb moisture from the air and must be stored in an airtight container to prevent deterioration. The crystalline form, which tends to lose its water molecules rather rapidly, is rarely seen in current photographic practice. With its single molecule, the monohydrous form is the most stable of the three and for this reason the most desirable. 

Uses Thiram is a dimethyl dithiocarbamate compound and appears as a white to yellow crystalline powder with a characteristic odor. Thiram is used to prevent crop damage in the field and to protect harvested crops from deterioration in storage or transport. Thiram also is used as a seed protectant and to protect fruits, vegetables, ornamentals, and turf crops from a variety of fungal diseases. In addition, it is used as an animal repellent to protect fruit trees and ornamentals from damage by rabbits, rodents, and deer. Thiram is available as dust, flowable, wettable powder, water-dispersible granules, water suspension formulations, and in mixtures with other fungicides. Thiram has been used in the treatment of human scabies, as a sunscreen, and as a bactericide applied directly to the skin or incorporated into soap.17,50,52... 

Sakamoto, D., Hirayama, Y., Kohno, Y., Sakai, T., Shiraishi, Y., and Saijo, S. European Patent 177,248, 1987 (to Taoka Chemical Co., Ltd).. These workers report that crystalline DDM undergoes no decomposition when held at 5°C for lOOhr, but that solutions in CH2CI2 deteriorate faster A 50% solution decomposes 4.9% in 20 days and 30.5% in 40 days at 0°C. 

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