Initial crystallinity

An absorbent material is one which changes either chemically, physically, or both during the sorption process. Certain chemicals, in absorbing moisture during this process, will dissolve into the water from the initial crystalline structure. Further added water results in a phase change from solid to liquid. An adsorbent is another material in which there are no chemical, phase, or physical changes during the sorption process. 

Two papers have appeared on the reactions of halogenophosphines with tervalent phosphorus compounds. In a detailed study of the reactions at 20 °C of a range of tertiary phosphines with phosphorus trichloride, dichlorophenylphosphine, and chlorodiphenylphosphine, it has been shown that, in general, 1 1 adducts are formed, provided that the tertiary phosphine is a good nucleophile. With diphenylchlorophosphine, for example, an adduct (18) is formed with dimethylphenylphosphine, but not with diphenylmethylphosphine, although the relative importance of steric and electronic factors remains to be established. The related reactions of phosphorus trichloride and of dichlorophenylphosphine are much more complex, and the initial crystalline products are not amenable to analysis. The reactions at 280 °C of a similar system have been shown to lead to halogen exchange, e.g. the conversion of (19) to (20). 

Reaction with chelating agents. Such reactions have been used primarily for partial dealumination of Y zeolites. In 1968, Kerr (8,21) reported the preparation of aluminum-deficient Y zeolites by extraction of aluminum from the framework with EDTA. Using this method, up to about 50 percent of the aluminum atoms was removed from the zeolite in the form of a water soluble chelate, without any appreciable loss in zeolite crystallinity. Later work (22) has shown that about 80 percent of framework aluminum can be removed with EDTA, while the zeolite maintains about 60 to 70 percent of its initial crystallinity. Beaumont and Barthomeuf (23-25) used acetylacetone and several amino-acid-derived chelating agents for the extraction of aluminum from Y zeolites. Dealumination of Y zeolites with tartaric acid has also been reported (26). A mechanism for the removal of framework aluminum by EDTA has been proposed by Kerr (8). It involves the hydrolysis of Si-O-Al bonds, similar to the scheme in Figure 1A, followed by formation of a soluble chelate between cationic, non-framework aluminum and EDTA. 

T. Aoba, H. Komatsu, Y. Shimazu, H. Yagishita, Y. Taya, Enamel mineralisation and an initial crystalline phase. Connect. Tissue Res. 38 (1998) 129-137. 

A quantity of tetrabutylammonium hydrogen sulfate 28.7 g (Aldrich), that has been recrystallized from acetone, is added to 300 mL of warm methanol in a 500-mL beaker. To this is added a solution of aqueous perrhenic acid (28.0 g, 80 to 85%, titrated 75.7%) (Alfa) with stirring. The total volume is then reduced by boiling to 125 mL, and the solution is then cooled slowly to 0 °C yielding white needles of [CH3(CH2)3]4NRe04. The supernatant liquid is further condensed to 50 mL and the resulting needles are combined with the initial crystalline product and twice recrystallized from methanol to give 30.8 g (74% yield) of product (mp 236-237 °C). 

Irradiation of polytetrafluoroethylene produced acid end groups and the scission occurs in both the crystalline and amorphous regions. When a sample of polytetrafluoroethylene is used with a high initial crystallinity, irradiation decreases the crystallinity 23S). 

Fig. 11. Luminescence spectra from initially crystalline Eu(OH)3 at different pressures (from Chen et al. (1994a)). Amorphization is observed at 5.5 GPa. The transition is reversible as shown by the spectrum quenched from 11 GPa.

Hydrolytic degradation of poly(e-CL)/PLLA block copolyester at pH 7.4 and 37 °C over a 5-week period is controlled by the initial crystallinity of the poly(e-CL) and its overall composition. The rate of degradation increased with increasing PLLA content [203 ]. Microorganisms, such as Fusarium solani and Fusarium moniliforme, that secrete poly(e-CL) depolymerase (cutinase), were more effective with those polymers that had longer poly(e-CL) sequence lengths [218]. The... 

Measurement of initial crystallinity Ability to study previous thermal history Ability to distinguish between reversible and nonreversible transitions... 

Figure 2.8 PXRD traces of bicalutamide (a) the initial crystalline sample (b) the initial amorphous sample and (c) bicalutamide post-24 h agitation in phosphate buffer from the amorphous sample.

I iR. 2.7. X-ray diffraction patterns of an initially crystalline Zr,Rh sample (asquenchcd), which was hydrided during a 4f> h period. The data show the transformation into the amorphous phase... 

The extent of oxidative bond scissions in the insoluble R fractions (in analogy to polyethylene data (12)) may be concentrated in the noncrystalline isotactic PP chain segments (total initial crystallinity is about 50%, but increases presumably owing to secondary crystallization, particularly during thermooxidative degradation at 150°C). 

In those cases when the initial materials are mixtures of alkaline solutions and crystalline aluminosilicates, the dissolution of crystalline material accompanied by the formation of amorphous aluminosilicate phase apparently precedes the beginning of crystallization (6). The induction period in such cases can be associated with the duration of dissolution of the initial crystalline material in the alkaline liquid phase. At a considerable degree of supersaturation of the solution, the formation of aluminosilica gels as an intermediate product appears to be necessary. 

---