Tham khảo tài liệu 'thermal analysis - fundamentals and applications to polymer science part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Page 82 reaction interval iii the heat evolved is proportional to the number of moles reacting during a given time interval and iv the volume of the sample does not change appreciably during the reaction. Under these assumptions the heat evolved by the reaction is given by SỈỈ AT 5-16 where K is the heat transfer coefficient of the sample and p is the total area under the DTA curve. The expression for the reaction rate constant of an wth-order reaction is written as where V is the sample volume and X the number of moles of reactant. If the correct value of n is chosen a plot of In k against 1 will yield a straight line from which A and E can be estimated. This method is insensitive to errors because both the heat capacity and DTA cell constant cancel out in the derivation. A similar method 11 uses the area of the DSC curve to calculate E. This method is based on the relationship where p is the total area of the DSC curve a is the area of the curve up to time t V is the volume of the sample and Nq the number of moles of reactant. The functional form y oc l - a is assumed and from a plot of In k against 1 T E can be estimated. Integral Methods Doyle 12 introduced a procedure for deriving kinetic data from a TG curve based on the assumption that a single non-isothermal TG curve is equivalent to a large number of comparable isothermal curves. Realizing the arbitrary nature of this assumption the author treats the Arrhenius equation as empirical and recognizes the potential triviality of kinetic parameters derived using this relation. In the derivation equation is rewritten in an approximate fonn At a constant heating rate Ộ substituting the Arrhenius equation for k and integrating equation becomes di The function Page 83 is introduced and values ofp E RT are calculated for the normal range of experimental values 10 E RT 30. When E RT 20 a linear approximation is made This method was further simplified by Ozawa 13 and applied to the random
