Methods using a series expansion as an approximation for the exponential integral

3 Methods using a series expansion as an approximation for the exponential integral 

Series expansions for P(t/) have been extensively used, various limited ranges of terms being used by different investigators, but that most frequently employed is [532,533] 

The process of calculation becomes more complicated on adding further terms. Coats and Redfem [555] effectively put (U-2)/U equal to a constant value and the relationship is equivalent to that already given for In g i/T2 from the single term expansion. They assumed that f(q) = (1 — q) and determined n by testing values which have significance in solid state decomposition reactions (i.e. n = 0, 0.5, 0.67 and 1.00). Sharp [75,556] has shown that the approach may be applied to other functions of g(q). If it is assumed that the zero-order equation applied at low a, as q - 0, then g(q) == a. 

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