Amorphous materials formation

The results of the Hg2 reaction experiments using particle-size-mediated synthesized metal sulfides are shown in Table 5. The powder XRD pattern of the resulting solids reveals amorphous material formation. Previous studies using Cu,S revealed the removal of Hg by a process other than dissolved sulfide precipitation [10], Other researchers have shown that MoS2 removes Fig2 from aqueous solutions via an intercalation mechanism [11]. 

Addressing the chemical impurity formation during extrusion is also generally achieved through process modification by altering the mechanical energy input and residence time of the process. However, it may not be possible to adjust these attributes independently of the composition while balancing requirements for amorphous material formation and minimization of impurity formation. Formulations may... 

The properties of elastomeric materials are also greatly iafluenced by the presence of strong interchain, ie, iatermolecular, forces which can result ia the formation of crystalline domains. Thus the elastomeric properties are those of an amorphous material having weak interchain iateractions and hence no crystallisation. At the other extreme of polymer properties are fiber-forming polymers, such as nylon, which when properly oriented lead to the formation of permanent, crystalline fibers. In between these two extremes is a whole range of polymers, from purely amorphous elastomers to partially crystalline plastics, such as polyethylene, polypropylene, polycarbonates, etc. 

In one of the most significant observations, small amounts of recrystallized material were observed in rutile at shock pressure of 16 GPa and 500 °C. Earlier studies in which shock-modified rutile were annealed showed that recovery was preferred to recrystallization. Such recrystallization is characteristic of heavily deformed ceramics. There has been speculation that, as the dislocation density increases, amorphous materials would be produced by shock deformation. Apparently, the behavior actually observed is that of recrystallization there is no evidence in any of the work for the formation of amorphous materials due to shock modification. Similar recrystallization behavior has also been observed in shock-modified zirconia. 

This mechanism is also confirmed by X-ray diffraction measurements [94, 100]. It is also mentioned that the absence of reflexes belonging to Li3NbC>4, in X-ray diffraction patterns obtained for mixtures treated at relatively low temperatures, could be explained by the formation of an amorphous material at the very beginning of the process [103]. 

Fabrication techniques, especially the preparation of thin films of functional materials, have made major progress in recent years. Thin-film solid electrolytes in the range of several nanometers up to several micrometers have been prepared successfully. The most important reason for the development of thin-film electrolytes is the reduction in the ionic resistance, but there is also the advantage of the formation of amorphous materials with stoichiometries which cannot be achieved by conventional techniques of forming crystalline compounds. It has often been observed that thin-film electrolytes produced by vacuum evaporation or sputtering provide a struc-... 

Thermal decomposition of [Cu0Si(0 Bu)3]4 in the solid phase begins at ca. 100 °C under argon (by TGA) and results in formation of an amorphous material until roughly 600 °C, at which temperature Cu metal was detected (by PXRD) [105]. Conversely, decomposition under oxygen led initially to a material with Cu crystalhtes and small amounts of CU2O and CuO, and subsequent heating beyond 800 °C resulted in oxidation of all the copper to CuO. 

A final point needs to be made. Theory has indicated that AB cements should be amorphous. However, a degree of crystallization does sometimes occur, its extent varying from cement to cement, and this often misled early workers in the field who used X-ray diffraction as a principal method of study. Although this technique readily identifies crystalline phases, it cannot by its nature detect amorphous material, which may form the bulk of the matrix. Thus, in early work too much emphasis was given to crystalline structures and too little to amorphous ones. As we shall see, the formation of crystalUtes, far from being evidence of cement formation, is often the reverse, complete crystallinity being associated with a non-cementitious product of an acid-base reaction. 

The solid state stability of indinavir sulfate has been evaluated under a variety of storage conditions and containers. For materials stored in open dishes or in double polyethylene liners within fiber containers, changes in crystallinity i.e., conversion of the crystalline etlranolate to amorphous material or to a hydrate crystal form) have been detected using XRPD or KF methods [7]. Changes in chemical purity i.e., formation of degradation products) have been detected using GC and HPLC methods... 

A variation of the CD process for PbSe involved deposition of a basic lead carbonate followed by selenization of this film with selenosulphate [64]. White films of what was identified by XRD as 6PbC03-3Pb(0H)2-Pb0 (denoted here as Pb—OH—C) were slowly formed over a few days from selenosulphate-free solutions that contained a colloidal phase and that were open to air (they did not form in closed, degassed solutions). CO2 was necessary for film formation—other than sparse deposits, no film formation occurred of hydrated lead oxide under any conditions attempted in this study. Treatment of these films with selenosulphate solution resulted in complete conversion to PbSe at room temperature after 6 min. The selenization process of this film was followed by XRD, and it was seen to proceed by a breakdown of the large Pb—OH—C crystals to an essentially amorphous phase of PbSe with crystallization of this phase to give finally large (ca. 200 nm) PbSe crystals covered with smaller (15-20 nm) ones as well as some amorphous material. 

Through the choice of the appropriate combination of solvent and operating conditions for a particular compound, PGSS can eliminate some of the disadvantages of traditional methods of particle-size redistribution in material processing. Solids formation by PGSS therefore shows potential for the production of crystalline and amorphous powders with a narrow and controllable size-distribution, thin films, and mixtures of amorphous materials. 

The physical form of the salt must be taken into account and several issues must be considered (Serajuddin and Pudipeddi, 2002). Forexample, amorphous material might result. Even if crystalline, the salt form might prove to be polymorphic. On crystallization or recrystallization, formation of a hydrate or a solvate might occur, and the effect of temperature and humidity on this form should be investigated. Both the physical and chemical stability of the different candidate salt forms in the solid state will ultimately deLne the optimal form of the drug. 

The calculation of residual stresses in the polymerization process during the formation of an amorphous material was formulated earlier.12 The theory was based on a model of a linear viscoelastic material with properties dependent on temperature T and the degree of conversion p. In this model the effect of the degree of conversion was treated by a new "polymerization-time" superposition method, which is analogous to the temperature-time superposition discussed earlier. 

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