Browsing by Author "Hara, Morihisa"

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    lon-exchanged versus as-melted mixed alkali glasses
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1999) Hara, Morihisa
    Assuming that the glass network structure containing Channels for ionic migration is established at the glass transition temperature during cooling and is perfectly rigid below this temperature, the properties of ion-exchanged and as-melted mixed alkali glasses are compared. Alkali ions introduced by ion exchange below the glass transition temperature bring the glass matrix into a State of internal strain by elastic expansion or contraction of ionic sites. In an as-melted mixed alkali glass, an ion-channel mismatch produces a similar strained State, resulting in large internal friction and the so-called thermometer effect. The change in molar volumes due to ion exchange is calculated on the basis of Eshelby's misfitting sphere theory. The molar volumes of ion-exchanged glasses calculated are close to those observed for as-melted mixed alkali glasses. The mixed alkali effect is also expected in ionexchanged mixed alkali glasses from the Standpoint of the ion-channel match model.
  • Thumbnail Image
    Item
    Ritzversuche und Härteprüfung an Glasbruchflächen im Vakuum
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1962) Hara, Morihisa; Kerkhof, Frank
    Verschiedene Silikatglasstäbe wurden im Vakuum, bei Drucken von 10⁻⁴ Torr, zerrissen. Anschließend mit einem Vickers-Diamanten an der frischen Bruchfläche durchgeführte Ritzversuche ergaben die für das mikroplastische Verhalten des Silikatglases charakteristischen Ritzversuchen. Die Form dieser Ritzspuren war auch bei Glasoberflächen, die vor dem Ritzversuch im Vakuum 5 h bei 400 bis 500 °C ausgeheizt worden waren, die gleiche. Außerdem wurde die Mikroeindruckhärte nach Vickers für 16 verschiedene Silikatgläser gemessen, für sieben Gläser auch an im Vakuum erzeugten frischen Bruchflächen. Es ergab sich kein Unterschied für die Mikroeindruckhärte der in Luft und im Vakuum erzeugten Bruchflächen.
  • Thumbnail Image
    Item
    Some aspects of strength characteristics of glass
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1988) Hara, Morihisa
    Strength characteristics of glasses are reviewed with some new aspects, emphasizing their specific features different from those of polycrystalline ceramic materials. The absence of any strength-controlling, structurally inherent defects in glass discriminates between the pristine strength on the GPa order and the practical strength controlled by the presence of surface flaws externally induced. For investigating the nature of the pristine strength, hydrofluoric-acid etching of glass samples having a definite indentation is shown to be quite useful to get consistent experimental results. Some experimental examples clarify the degradation mechanism in glass strength when heated or coated with thin films as well as the fatigue nature of the pristine strength. In evaluating the practical strength of glass, the strength-degrading effect of blisters and strengthening by providing surface compressive stress are discussed. A strength scale of glass and glass ceramics is given.