Molecular orbital study on a mechanism of adhesion between carbides and optical glass with high refractive index

A mechanism of adhesion between carbide molds and optical glass species with high refractive index in precision molding was elucidated on the basis of DV-Xα molecular orbital calculations. An interfacial cluster model comprising Nb-P-Na-O glass and glassy carbon (GC) was applied in order to examine the changes in the chemical bonds between atoms at the interface and the effect of the substitution of niobium with other transition metals (denoted with; Md_I) at the interface. The bond overlap population (BOP) between oxygen atoms at the surface of the glass and carbon atoms at the surface of the GC increases when the surface of the glass approaches the GC, while that between Me_I-O correspondingly decreases. When introducing oxygen deficiency at the surface of the glass, the BOP of the Me_I-carbon bonds against the Me_I-oxygen increased in the order of Nb<Ti<W, which mostly coincided with the experimentally obtained order of increased probability of occurrence of adhesion between the glass and the GC mold. This supports the validity of the model where adhesion between the glass and the carbide occurs following the reduction of the transition metal in the glass.