Inhomogeneous composites preparation

In order to prove that the high composition inhomogeneity was the only reason for microphase separation both (ST + HA) and (ST + MA) copolymers, some of their samples with the same compositions prepared, however, at low conversions (p < 0.10) of monomers with their subsequent distillation were studied [310,210]. All these copolymers whose dispersion is by one or two orders of magnitude less than that of the products of complete conversion (p = 1), turn out to be dear. 

On calcination of this prepared powder, particles having the composition ZrY(, k03.2 were obtained. The electrokinetic measurements with aqueous dispersions of the latter showed an isoelectric point at pH 6.8, characteristic of Y203. This example further substantiates the inhomogeneity within the particles, but also indicates that heating, as carried out in this case, did not produce internal uniformity. 

Acidic properties of heteropoly compounds in the solid state are sensitive to countercations, constituent elements of polyanions, and tertiary structure. Partial hydrolysis and inhomogeneity of composition brought about during preparation are also important in governing the acidic properties. There are several possible types of origins of acidity (5) ... 

Figure 4. Inhomogeneity of silica-aluminas prepared by various methods. A series of 17 commercial samples of silica-aluminas from seven different producers was submitted to microanalysis. All of them showed considerable fluctuations of composition at the scale of several tens of nanometers to several micrometers. These samples were prepared by coprecipitation or by the sol-gel method. It is not known whether some of these samples were prepared from alkoxides. Smaller but significant fluctuations at the micrometer scale were also observed for two laboratory samples prepared from alkoxides. The samples were dispersed in water with an ultrasonic vibrator. A drop of the resulting suspension was deposited on a thin carbon film supported on a standard copper grid. After drying, the samples were observed and analyzed by transmission electron microscopy (TEM) on a JEOL-JEM 100C TEMSCAN equiped with a KEVEX energy dispersive spectrometer for electron probe microanalysis (EPM A). The accelerating potential used was 100 kV.

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