Low surface area measurements

As a result of the positive and negative nature of the signal, accurate 

When the same sample was analyzed using a micro cell, Fig. 15.10b, the results obtained were considerably improved, as shown in Table 15.2. 

The onset of thermal diffusion depends on the gas concentrations, the sample surface area, the rate at which the sample cools to bath temperature, and the packing efficiency of the powder. In many instances, using a conventional sample cell, surface areas less than 0.1 m can be accurately measured on well-packed samples that exhibit small interparticle void volume. The use of the micro cell (Fig. 15.10b) is predicated on the latter of these observations. Presumably, by decreasing the available volume into which the lighter gas can settle, the effects of thermal diffusion can be minimized. Although small sample quantities are used with a micro cell, thermal conductivity detectors are sufficiently sensitive to give ample signal. 

Another cell design that aids to minimize the effects of thermal diffusion is the capillary cell. Fig. 15.10c. By using capillary tubing on the vent side of the cell, a sufficiently high linear flow velocity is maintained to prevent 

Lowell has published a method to circumvent the problem of thermal diffusion by using an adsorbate with a low vapor pressure, such as 

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The low surface area measured for calcined mesocaged AMS-8,[86] 408m2/g, in... 

When fitted with the krypton option the ASAP can reach a vacuum level of less than 0.00001 mm Hg which leads to accurate micropore and low surface area measurements. 

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