Strength of Crystals of Small Dimensions and their Triboluminescence

Abstract

Stress-dependence of triboluminescence (TBL) in uranyl nitrate, tartaric acid and other nine crystals has been studied with the help of a new technique of crushing the crystals. As the appearance of TBL needs the creation of new surfaces in a crystal, the minimum stress a t which TBL appears has been taken to be the fracture-strength of the crystal. The value of the fracture-strength and stress coefficient of binding energy determined from TBL measurements are found to be of correct order. It has been found that the rate of rise of TBL intensity with stress is higher for those crystals which have less value of the fracture-strength. The fracture strength (a,) is found to be higher for those crystals which have less value of stress coefficient of binding energy (8) and the product of a , and ,!I is higher for those crystals which have higher melting point. It has been shown that the rate of rise of TBL intensity with stress decreases a t higher values of stress due to strain hardening in the crystals.Die Spannungsabhangigkeit der TBL in Uranylnitrat, Weinskure und weiteren neun Kristallen wurde mit Hilfe einer neuen Bruchtechnik untersucht. Da das Erscheinen der TBL die Entstehung neuer Oberflachen im Kristall erfordert, wurde die unterste Grenze der Spannung, bei der die TBL auftritt, als dessen Bruchfestigkeit gewiihlt. Der Wert der Bruchfestigkeit und des Spannungskoeffizienten der Bindungsenergie, die aus TBL-Messungen ermittelt wurden, sind von der richtigen GroBenordnung. Es wurde gefunden, daB die Geschwindigkeit des Anstiegs der TBL-Intensitat mit der Spannung fiir solche Kristalle hoher liegt, deren Bruchfestigkeit niedriger ist. Die Bruchfestigkeit (a,) lie@ hoher fiir solche Kristalle, deren Spannungskoeffizient der Bindungsenergie (B) geringer ist, und das Produkt von a , und ,!I ist groJ3er fiir Kristalle mit hoherem Schmelzpunkt. Es wird gezeigt, daB die Anstiegsgeschwindigkeit der TBL-Intensitat mit der Spannung abnimmt bei hoheren Werten der Spannung infolge der Kaltverfestigung des Kristalls.

Correlation between deformation bleaching and mechanoluminescence in coloured alkali halide crystals

“…Ueta et al [11] have shown that the decay curve of the electric current produced during plastic deformations of non-irradiated KCl crystals and the decay curve of the ML produced during deformation of the irradiated crystals are of the same form. Chandra and Elyas [12] have reported that the ML is produced in coloured alkali halide crystals during the application of pressure as well as during the release of applied pressure. Guerrero and Alvarez Rivas [13] have studied the dependence of ML and thermoluminescence on the strain of irradiated KCl crystals.…”

Mechanoluminescence response to the plastic flow of coloured alkali halide crystals

“…2 shows the time dependence of the ML intensity and the applied pressure for g-irradiated KCl crystals. It seems that when the pressure is applied using the device reported in our previous investigation [5], then initially the pressure increases with time and very soon it attains a fixed value. However, the ML intensity initially increases with time, attains a peak value, and later on it decreases with time.…”

“…Chandra and Elyas [5] have reported that the coloured alkali halide crystals exhibit ML during the application as well as release of pressure. Chandra et al [6] have studied the pressure and temperature dependence of the ML of g-irradiated alkali halide crystals.…”

Mechanoluminescence induced by elastic deformation of coloured alkali halide crystals using pressure steps

“…(15) and (16). The measurement of ML was done following the technique reported previously [39], in which the ML was induced by placing a load onto the crystal and the ML intensity was measured using a photomultiplier tube connected to an X-Y recorder. Fig.…”