Aluminum effective interaction between ions

The effective interaction between ions in aluminum. Also shown is the distribution of neighbors as a function of distance in the face-centered cubic structure. [After Harrison, 1964.]... 

Color." The most obvious effect produced in silica gel by radiation is a grayish-purple color (64), which can be almost surely attributed to the same type of center as that responsible for the similar color in irradiated quartz, namely, a positive hole trapped at an oxygen ion adjacent to a substitutional Al + impurity ion (65-67). The attribution rests on the similarity in optical absorption between irradiated gel and irradiated quartz (66), on the dependence of the intensity of the color on the aluminum content (69), and on the observation of a hyperfine interaction characteristic of the spin of the 2 a1 nucleus (I = 5/2) in the ESR spectrum of the irradiated gel (70). Furthermore, the ESR sextet and the color are annealed at comparable rates above 200° (70) and are both destroyed by adsorption of H2 at room temperature (64, 70). Their intensities increase in parallel as the aluminum content, the severity of preirradiation heat treatment, or the length of irradiation is increased (70). The concentration of the center does not increase indefinitely. After some lO i ev/gm, it approaches a limiting value which depends on the impurity content, for typical gels around lO H2/gm (69). 

As discussed in other chapters relating to the effect of aluminum ions, there is a peculiar affinity between the oxides of aluminum and silicon. At this point only a few observations regarding the interaction with monomeric Si(OH)< are noted. 

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