Crystallization of gahnite in CMAS glass forming system. Mechanism and process kinetics

摘要

The crystallisation mechanism of glass-ceramic materials from a CMAS group Al_(0.37)B_(0.34)Fe_(0.01)Mg_(0.02)Zn_(0.29)Ca_(0.05)Si_(0.78)O3 was tested under non-isothermal conditions by the DTA method. Glass-ceramic material of two-phase composition with precipitation of crystallites from islet silicates Zn_2SiO_4 and a crystalline phase from a spinel group, gahnite ZnAl_2O_4 was obtained in the system under investigation. Activation energy of a crystallization process E_a was determined and a crystal growth morphology parameter n was computed. It was revealed that in the test material from a CMAS group one could obtain the crystalline phase in the form of ghanite as a result of a controlled process of crystallization. The occurrence of a spinel phase caused the obtained glass-ceramic material had higher fracture toughness (K_(IC)) than material from a CMAS group, containing pyroxene crystalline phases typical for this system.