No abstract

The density, refractive index, molar refractivity, and infrared absorption spectra of soda aluminosilicate glasses containing up to 34.8 wt% alumina have been determined. Changes in these properties with composition can be explained by existing theories which assume that the aluminum ions form only A104 tetrahedra when the Al/Na ratio of the glass is equal to or less than 1. The aluminum ions in glasses having an Al/Na ratio larger than 1 are in both fourfold and sixfold coordination.

The fracture toughnesses of fused SiOt and float glass were measured at high temperatures. In both glasses, low-temperature regions of elastic fracture were identified and correlated with the elastic moduli and their temperature dependence. A viscous flow contribution to the fracture toughness was identified in the fused Si02 at T>800°C. Similar indications of viscous flow were also noted in the float glass, although at much lower temperatures.

Vol. 45, No. 10 differently from the initial additions. The fact that the of the glass is such that its Al/Na ratio equals 1, the main Si-0 absorption band begins to shift to shorter wave-O/Al + Si ratio will equal 2 and the glass network should lengths and that the intensity of the absorption band a t be composed of A104 and SiO, tetrahedra. This network 13 to 1 4 ,~ decreases is interpreted to mean that some of the should resemble that of fused silica. aluminum ions are in different environmental surroundings.The aforementioned property makes these glasses espe-I t seems reasonable to attribute these changes in the becially suitable €or internal friction studies. One of the internal havior of the density and infrared absorption spectra to the friction peaks which has been observed in alkali silicate appearance of aluminum ions in sixfold coordination.glasses has been attributed to the stress-directed movement A rather unique property of the soda aluminosilicate of the nonbridging oxygen ions. If the stress-directed glasses is that the number of nonbridging oxygen ions can movement of the nonbridging oxygen ions is the correct be reduced to a very small number. Initially, the N a @ -explanation, then one would expect this peak t o become 3SiOZ parent glass contains nonbridging oxygen ions as a progressively smaller as the Al/Na ratio varies from 0 to 1. result of the soda content. According to the random net-The predicted behavior of the nonbridging oxygen internal work theory the number of nonbridging oxygen ions is friction peak has been observed and is presented in Part I1 eaual to the number of sodium ions in the glass. Howof this series. e;er, with the addition of alumina to this glass the nonbridging oxygen ions are converted t o bridging oxygen ions, since the aluminum ions must use Some of the nonbridging oxygen ions to form A104 tetrahedra. When the composition Company.Internal friction measurements of soda aluminosilicate glasses, the physical properties of which were reported in Part I of this series, are discussed. The low-and intermediate-temperature internal friction peaks were studied in detail and are shown to be due to the stress-controlled movement of the sodium and nonbridging oxygen ions, respectively. A close correlation was found between the temperature shift of the low-temperature peak and the activation energy for electrical conduction in the soda aluminosilicate glasses. The magnitude of the low-temperature peak was found to depend more on the structural environment of the sodium ions than on the actual soda content. Changes in the intermediate-temperature peak are explained on the basis of the structural model proposed for these glasses.