Vacuum microbalance capacity

One of the classical applications of the vacuum microbalance for adsorption studies was that of Barrett, Birnie, and Cohen (32) in 1940. They measured the physical adsorption of water vapor on silica surfaces at 30°C. by direct weighing. They employed a quartz beam balance using a cemented-on tungsten wire (0.001 in. diameter) and enclosed in a high vacuum housing. The capacity of the balance was relatively high (0.5 g.)... 

H2O, n-hexane and cyclohexane sorption capacities of SAPO-31 were determined gravimetrically using a vacuum microbalance (Cahn Instruments, USA). The size and the morphology of the crystals of SAPO-31 were examined using a JEOL (JSM-840 A) scanning electron microscope. The BET surface area was determined using a volumetric adsorption apparatus ( Model Omnisorb lOOCX, Coulter, USA). 

The pore size of Cs2.2 and Cs2.1 cannot be determined by the N2 adsorption, so that their pore sizes were estimated from the adsorption of molecules having different molecular size. Table 3 compares the adsorption capacities of Csx for various molecules measured by a microbalance connected directly to an ultrahigh vacuum system [18]. As for the adsorption of benzene (kinetic diameter = 5.9 A [25]) and neopentane (kinetic diameter = 6.2 A [25]), the ratios of the adsorption capacity between Cs2.2 and Cs2.5 were similar to the ratio for N2 adsorption. Of interest are the results of 1,3,5-trimethylbenzene (kinetic diameter = 7.5 A [25]) and triisopropylbenzene (kinetic diameter = 8.5 A [25]). Both adsorbed significantly on Cs2.5, but httle on Cs2.2, indicating that the pore size of Cs2.2 is in the range of 6.2 -7.5 A and that of Cs2.5 is larger than 8.5 A in diameter. In the case of Cs2.1, both benzene and neopentane adsorbed only a little. Hence the pore size of Cs2.1 is less than 5.9 A. These results demonstrate that the pore structure can be controlled by the substitution for H+ by Cs+. 

---