Nucleation Kinetics of NaF in Photo-Thermo-Refractive Glass

• Grant number: 10/06201-0
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• Start date: November 01, 2010
• End date: April 30, 2012
• Field of knowledge: Engineering - Materials and Metallurgical Engineering - Nonmetallic Materials
• Principal Investigator: Edgar Dutra Zanotto
• Grantee: Itay Dyamant
• Host Institution: Centro de Ciências Exatas e de Tecnologia (CCET). Universidade Federal de São Carlos (UFSCAR). São Carlos , SP, Brazil
• Associated research grant: 07/08179-9 - Kinetic processes in glasses and glass ceramics, AP.TEM

Abstract

The complex crystallization pathways of photo-thermo-refractive (PTR) glass combine several secondary processes such as liquid-liquid phase separation, the nucleation of Ag and/or Br containing nanoparticles, and the spontaneous NaF crystallization, all that in addition to the primary photo-thermo-induced crystallization of NaF nano-crystals. This primary process introduces localized refractive index changes to the glass, which are utilized in fabricating various optical devices. Nevertheless, the detailed crystallization mechanism and kinetics of PTR glass are still largely unknown, and commercial diffractive optical elements based on this glass yet experience unwanted scattering losses. Comprehensive understanding and control of the primary and secondary crystallization processes are therefore of great scientific and technological importance. Thus, investigation of NaF nucleation kinetics is expected to contribute in further understating the crystallization process in PTR glass. Optical microscopy measurements of the NaF crystals number density as a function of nucleation time ,Nv(t), in UV-exposed and thermally treated (i.e. photo-thermo-induced) glass, should result in values for the steady-state nucleation rate (Ist) and the induction period (tind), to be used for constructing the nucleation rate curve, I(T). Similar microscopy measurements from UV-unexposed and thermally treated glass regions, should yield the corresponding Nv(t), Ist, tind and I(T) data for the spontaneous NaF crystallization. From the obtained I(T) curves the temperature of maximum nucleation rate (TMN) of each process can be found. The values of TMN may also be obtained from nucleation rate type curves by methods of thermal analysis (e.g. differential scanning calorimetry), which will be used for comparison. The expected kinetic data of the proposed research may be used for the design of photo-thermo-induced glass crystallization treatments, and hence obtain devices with desired optical characteristics.