DIFFERENTIAL THERMAL-ANALYSIS OF HYDROGEN-INDUCED AMORPHIZATION IN C15 LAVES COMPOUNDS RCO2

Structural changes of the C15 Laves compounds RCo2 (R=rare earth metals) during differential thermal analysis (DTA) in a hydrogen atmosphere have been investigated by X-rav diffractometry, transmission electron microscopy and differential scanning calorimetry. The results of TbCo2 and CeCo2 are exemplified. The DTA curves of the RCo2 compounds exhibit three or four exothermic peaks resulting from hydrogen absorption, hydrogen-induced amorphization. crystallization and grain growth. As the atomic number of R increases, the amorphization temperature T(a) increases, but the ratio T(a)/T(m), where T(m) is the melting point of the original compound, is nearly constant at 0.4. The mechanisms of hydrogen-induced amorphization in the RCo2 compounds is discussed.