Ultra-high molecular weight polyethylene (UHMWPE) is a polyethylene with a very long chain, which provides excellent features, however it makes the processing difficult due to high melt viscosity. Many studies intend to found out means to make its processing easier. Recently, the high-energy mechanical milling has been used for polymeric materials and it was detected that physical and chemical changes occur during milling. In such case, powder of UHMWPE was milled in three types of mills: SPEX, attritor e planetary, in different times of milling. The polymer was characterized by SEM and XRD. Thus, it was observed that the material processed in attritor mill showed larger phase transformation from orthorhombic to monoclinic. This is most likely due to the smaller milling temperature of attritor mill when compared with the other two mills and the high shear force generated during milling.
The present paper presents the results of a thermoanalytical investigation on the kinetics of the aluminothermic reduction of Cr 2 O 3 under non-isothermal conditions. Simultaneous differential thermal analysis (DTA) and thermogravimetry (TG) technique were used. It was determined the minimum molar ratio Cr 2 O 3 : Al for the completion of the reaction and the value of the change of enthalpy associated to the reduction. X-ray diffraction was used in order to identify the products of reduction. Since the oxidation of aluminium and the reduction of Cr 2 O 3 occur simultaneously, it was possible to study the kinetics by analysing the rate of generation of the peak area for the Cr 2 O 3 reduction (DTA) and the mass gain due to the oxidation of some of the excess of aluminium (TG). The reduction was controlled by first order chemical reaction and the reduction was isokinetic within the experimental conditions of the present work.
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