Harkins-Jura constant

The term K in equation (7.9) is the Harkins-Jura (HJ) constant and is assumed to be independent of the adsorbent and dependent only on the adsorbate. 

Equation 17.26, derived by Harkins and Jura(15) may be plotted as In (P/To) against I / V2 to give a straight line. The slope is proportional to A2. The constant of proportionality may be found by using the same adsorbate on a solid of known surface area. Since the equation was derived for mobile layers and makes no provision for capillary condensation, it is most likely to fit data in the intermediate range of relative pressures. 

Method of Jura and Harkins—This adsorption method was discussed in Chapter 11 (Eqs 11-23 and 11-24). The method involves use of the same procedure as the Brunauer technique—that is, the determination of the isotherm. Thereafter,. the linear plot of data in accordance with Eq (11-23) yields the constant necessary to determine the surface of a mass of particles. This method is comparable to that of Brunauer and his associates just described, and may be used as a check. 

It is due to Harkins and Jura and was derived on the basis of an empirical two-dimensional equation of state. Here, A and B are constants. 

Jura and Harkins claimed that this is the simplest equation found so far for describing adsorption from sub-monolayer to multilayer regions, and it is valid over more than twice the pressure range of any two-constant adsorption isotherms (More about multilayer adsorption will be presented in Chapter 3). They showed that for Ti02 in the form of anatase, their isotherm agrees with the data at both lower and higher values of pressure than the commonly used BET equation (Section 3.3). 

Harkins and Jura (1943) have shown that a plot of ln(P/Po) versus 1/v would yield a straight line with a slope of - C. The square root of this constant is proportional to the surface area of the solid. They gave the following formula ... 

Equation (2.65) involves only the quantities P and V which are measured directly in the experimental determination of adsorption. Harkins and Jura reported that this simple equation was valid over more than twice the pressure range of any other two-constant adsorption isotherm equation. 

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