کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
208528 | 461256 | 2006 | 10 صفحه PDF | دانلود رایگان |
![عکس صفحه اول مقاله: Evidence for network formation during the carbonization of coal from the combination of rheometry and 1H NMR techniques Evidence for network formation during the carbonization of coal from the combination of rheometry and 1H NMR techniques](/preview/png/208528.png)
High-temperature rheometry and 1H NMR have been combined to assess the microstructural changes taking place during carbonization of a number of different coals. A linear relationship exists between the logarithm of the material's complex viscosity (η*) and the fraction of hydrogen present in rigid structures (ϕrh) for the resolidification region in which the material is liquid-like with small amounts of dispersed solid. The relationship is best characterized by the Arrhenius viscosity equation given by η*=η0*exp([η]ϕrh), where η0* is the complex viscosity of the liquid medium and [η] is the intrinsic viscosity of the resolidified material. Attempts to fit the Krieger–Dougherty suspension equation showed that the solid regions formed do not pack together like a normal suspension. Instead, it is more likely that cross-linking and cyclization reactions within the liquid medium give rise to a network structure of solid material and a characteristic gel point. The ratio of hydrogen present in rigid structures to that still present in liquid form at the gel point is approximately 2:3. The resolidified material was found to have a higher [η] than the components of the coal that remained unsoftened, which suggests that while the unsoftened components have a fairly equant shape, the resolidified components have a much higher hydrodynamic volume. The resolidification process bears similarity with thermosetting polymer networks and the η* measurements taken for a blend of two coals follow a common two-component polymer blending rule.
Journal: Fuel - Volume 85, Issues 12–13, September 2006, Pages 1821–1830