Crystallization Behavior of ZBLAN Glass Under Combined Thermal and Vibrational Effects: Part II - COMSOL Simulation and Apparatus Redesign

Abstract

In Part I of this study, vibration assisted heat treatments of ZBLAN glass revealed irregular crystallization at higher vibration levels, attributed to intermittent loss of thermal contact between the sample and the inner silica ampoule wall. The present work (Part II) investigates this mechanism through finite element modeling (FEM) and experimental validation.COMSOL Multiphysics simulations incorporating conduction, radiation, and contact resistance confirm that intermittent contact markedly reduces heat transfer efficiency, lowering the sampletemperature. To mitigate this effect, the experimental setup was redesigned with a four-degree inclination to maintain stable contact during vibration. Subsequent experiments at vibration levels H3-H5 demonstrated uniform heating and consistent crystallization behavior.Comprehensive microscopic, Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS), and Atomic Force Microscopy (AFM) analyses revealed that even at subtle vibration levels (~50 Hz), partially crystallized ZBLAN transformed into well-developed crystalline structures near 360C. With increasing vibration amplitude, amorphous ZBLAN began forming incipient crystalline phases around 330C, and at higher frequencies (~100 Hz), partial crystallization initiated at approximately 350C. These results indicate that higher vibration frequencies accelerate nucleation, enhance heat transfer, and reduce the effective fiber-drawing temperature window by about 30C. Prolonged exposure above 330C under vibration promotes unwanted phase transitions, emphasizing the need for precise thermal and vibrational control. This study establishes a predictive framework for vibration-resistant ZBLAN processing applicable to both terrestrial and microgravity environments.