A study of experimental techniques for the determination of
diffusion coefficients for binary mixtures and a study of the existing
relationships for these coefficients were carried out.
A new three-compartment diffusion cell was developed capable
of measuring diffusion coefficients at temperatures up to the normal
boiling point (24). By means of this cell, diffusion coefficients were
measured for the systems ethanol-water, acetone-water and acetone-
chloroform for a range of temperatures up to the normal boiling points.
Thus diffusion coefficients for the above mixtures including those at
boiling points and at infinite dilution are presented.
A relationship was developed to relate diffusion coefficients
with temperature and concentration (equation 3-1.21) in binary systems. It agrees better with the experimental data for the associated systems
than some literature correlations.
By application of parachors a new equation (3-2.4) was
developed for the prediction of diffusion coefficients at infinite dilution
(201). This equation, because of the ease of calculating parachors,
is more convenient to use than other equations based on the Stokes-Einstein equation.
An additive method for the prediction of self-diffusion coefficients
was introduced and a correlating equation (3-3.4) was developed. The
bond and structural contributions to the constant of the equation
were calculated on the basis of a limited amount of experimental data.
Despite this the correlation gives reasonable predictions for the temperature range between melting point and boiling point.
Another correlation for the prediction of self-diffusion coefficients
was developed (203) (equation 3-3.6) by modifying an existing equation.
This was possible by applying the relationship between the molal volume
at the boiling point and the critical molal volume developed in this
work (202). The new equation is more convenient to use.
The correlating property of the critical temperature was used to
devise a relationship between diffusion coefficients, critical temperature
and the working temperature. The two correlating equations (3-4.6)
and (3-4.7) can predict diffusion coefficients at various temperatures
if one value of the diffusion coefficient at a single temperature is known.
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.