Increasing the working temperature range of ZrF4-BaF2-LaF3-AlF3-NaF glass through microgravity processing

Abstract

Fluorozirconate glasses, such as ZBLAN (ZrF 4 -BaF 2 -LaF 3 -AlF 3 -NaF), have the potential for optical transmission from 0.3 μm in the ultraviolet to 7 μm in the infrared regions. However, crystallites formed during the fiber-drawing process prevent this glass from achieving its desired transmission range. The temperature at which the glass can be drawn into a fiber is known as the working range, defined as (Tx-Tg), bounded by the glass transition temperature (Tg) and the crystallization temperature (Tx). In contrast to silica glasses, the working temperature range for ZBLAN glass is extremely narrow. Multiple ZBLAN samples were subjected to a heating and quenching test apparatus on the parabolic aircraft under a controlled μ-g and hyper-g environments and compared with 1-g ground tests. Optical microscopy examination elucidates that crystal growth in ZBLAN is suppressed and initiates at a later temperature when processed in a microgravity environment. Thus, the crystallization temperature, Tx, at which the crystals form has increased. The glass transition temperature, Tg, remains constant, as crystallization does not occur until approximately 360°C for this composition of ZBLAN. Therefore, the working temperature range for ZBLAN has been broadened.

Materials Formed by Combining Inorganic Glasses and Metal‐Organic Frameworks

“…Given these decomposition considerations, the selection of an inorganic glass with a lower T g is essential for MOF‐CIGC formation. Examples of low T g glasses include the glass series (Na 2 O) x (P 2 O 5 ) 100‐x (10≤x≤50) [43] and fluorozirconate glasses, such as ZBLAN (ZrF 4 −BaF 2 −LaF 3 −AlF 3 −NaF), which both have T g s lower than 300 °C [44] . These are potential candidates for the glass matrix and can be paired with MOFs which are stable at temperatures up to 300 °C.…”

Earth and Space 2014

“…This narrow working range, makes ZBLAN a difficult glass to draw into fiber form as microcrystals can begin to form early in the drawing process, resulting in early fracture. It is also documented that ZBLAN is very susceptible to micro-crystallization growth at temperatures above its glass transition temperature (Macfarlane, 1984;Torres, 2014;Torres, 2013;Wilson, 1985). These microcrystals formed during the drawing process create crack initiation locations and cause extreme brittleness of the material.…”