Gradient hot stage

The purpose of the present study was to examine the coal-to-coke transformation away from the heating stage of the electron microscope. We carbonized samples at various heat-treatment temperatures in a plastometer. The plastometer has the advantage over the electron microscope hot stage not only in that it is the apparatus we used in the fluidity test but also in that it minimizes thermal gradients across the sample. Semicokes thus... 

FIGURE 3.4 Hot stage A linear temperature gradient from 50 to 250 °C is oreated by resistanoe heaters along the metal bar. The sample (as finely divided as possible) is plaoed direotly on the metal bar. The temperature at the border between solid powder and molten material oan be determined direotly from a soale on the hot stage. 

Li et al. 48) studied how 1.0 pm particles of polystyrene and poly(methyl methacrylate) interacted when they were melt processed at 180 °C. They observed by confocal microscopy on a hot stage that there was a preferential motion for particles, which they attributed to a buoyancy-driven flow because of the 10% density difference between the polymers. Jang et al. had made a similar observation 49), Li et al. did not consider possible surface-tension induced convection or that droplets could migrate in a temperature gradient, as has been observed by Balasubramaniam et al. for the thermocapillary migration of bubbles 50),... 

The photographs presented here were taken on a temperature gradient microscope stage ( ) shown schematically in Fig. 2. The sample contained in a thin glass cell can be moved at a controlled rate across the gap between a hot and a cold plate. The temperatures of the two plates can be adjusted to give the desired temperature gradient, with the transformation occurring between the two temperatures. 

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