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Langmuir 1987, 3, 681-686 681 is deposited upon the larger particles ( Figure 10). CBET values remain unchanged, which show that nitrogen adsorption takes place on the same kind of surface, as similar silanol groups are present in both amorphous silica and unattacked montmorillonite surfaces. A change is shown in N2 adsorption-desorption isotherms, and in the f-plot a peak in the higher pore size region appears. DRX patterns and IR spectra correspond almost exclusively to amorphous free silica.Finally, as the insolubilization of polymeric silica increases, a progressively thicker silica layer is formed on the unaltered or partially altered bentonite particles, thus reducing or impeding the posterior attack. An apparent "passivation" of the samples takes place and losses in the total amount of N2 adsorbed and in the cations abstracted are produced. The amount of adsorbed nitrogen diminishes, but the general appearance of the isotherm remains because silica is always present. In the f-plot a small shift of the peak toward the higher p / p o is produced. DRX and IR show a corresponding reverse in the characteristic peaks.

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The article contains sections titled: 1. Introduction 2. Properties and Raw Materials 2.1. Physical Properties 2.2. Chemical Properties 2.3. Resources, Raw Materials 3. Production 3.1. Boron Monofilament 3.2. Silicon Carbide Fibers 3.3. High Alumina Fibers 3.4. Zirconia Fibers 4. Uses 5. Economic Aspects 6. Toxicology and Occupational Health