Measurement of adsorbed weight

Measurement of weight changes is a very direct method of obtaining adsorption kinetics, and is also used to follow the course of other heterogeneous reactions (see Section 3). It is particularly suitable for adsorption measurements with small surface areas at relatively high pressures, where the volumetric method is insensitive. Several comprehensive reviews are available which discuss the theory, 

The simplest method of beam microbalance operation is to measure the deflection of the ends of the beam by optical magnification. This method has the disadvantage that the maximum weight change that can be observed is limited and the vacuum system must usuaUy be opened to reset the zero point. However, a beam microbalance can be readily converted to a null point instrument by electromagnetic adjustment. A commercially available instrument which features electromagnetic compensation and automatic recording is shown schematicaUy in Fig. 10. 

Microbalances have been used to measure adsorption kinetics under a wide variety of conditions. Several authorshave studied adsorption on single crystal surfaces of semiconductors under ultra high vacuum conditions and utilising ion bombardment to obtain a clean surface. Gulbransen et al and Walker et have made a special study of microbalance operation at high temper- 

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