Jean A. Tangeman

Vitreous forsterite (Mg2SiO4): Synthesis, structure, and thermochemistry

Here we report the first synthesis of a forsterite (Mg2SiO4) composition glass as an essentially phase-pure bulk material. Under containerless conditions, with heterogeneous nucleation sites minimized, glass forms by cooling ca. 1 mm liquid Mg2SiO4 droplets in oxygen at 700 K/s. 29Si NMR spectroscopic data indicate that the SiO4 tetrahedra and MgO6 octahedra exist in a corner sharing arrangement in the glass, but upon crystallization the polyhedral units reorganize to form edge-sharing linkages. Transposed temperature drop calorimetry shows that the glass is 61.4±1.3 kJ/mol higher in enthalpy than the crystal.

Novel Synthesis of Calcium Oxide?Aluminum Oxide Glasses

Binary Al2O3:CaO glasses containing 36?50 mole% Al2O3 were synthesized by containerless processing of liquids in nitrogen using aerodynamic and a pressurized electrostatic-aerodynamic levitator. The critical cooling rate for glass formation RC under containerless conditions was ca. 70 K/s. The Vickers hardness of the glasses was 775?785; and the infrared transmission extended to approximately 5500 nm. The work function of the 36 mole% Al2O3 composition was 3.7 eV at 1100 K.

Investigation of Liquid-Liquid Phase Transitions in Molten Aluminates Under Containerless Conditions

Aluminum oxide-yttrium oxide (AY) compositions form liquids that undergo a variety of metastable behaviors including glass formation and liquid-liquid phase transitions. Containerless techniques in combination with the reduced fluid motion achieved in low gravity provide the control needed to study the kinetics of phase transitions in diffusion-limited transport conditions and to obtain accurate measurements of the viscosity of the undercooled liquid. Containerless liquid phase processing experiments have established 1) conditions for phase transitions in AY liquids, 2) that the liquid structure plays an important role in glass formation and increased liquid viscosity, and 3) requirements for microgravity experiments on AY liquids. Results of the research are discussed in the context of developing a microgravity research experiment.

New infrared transparent oxide glasses

Glass materials based on rare earth oxides and aluminum oxide can provide a combination of infrared transparency, strength, hardness, and environmental stability in a formable material. This article describes a new family of rare earth oxide-aluminum oxide glass materials that can be made by casting from melts formed in platinum crucibles. The glasses transmit light in the wavelength range from 0.3 to 5 μm in sections of ~0.3 cm, they have a Vickers hardness of 800-1000, and exhibit excellent environmental stability typical of refractory oxide materials. The composition of the glass can be adjusted to achieve refractive indices in the range 1.7-1.8 and Abbe numbers of 30-60. The materials are promising candidates for passive optical elements or as a host for optically active ions such as Yb or Nd that provide laser action or absorb at laser line wavelengths.

Device materials based on Er-, Ho-, Tm-, and Yb-doped rare earth aluminum oxide (REAl) glass

Glasses based on rare earth oxide-aluminum oxide and containing high concentrations of Er2O3, Tm2O3, Yb2O3, or Ho2O3 were synthesized. The host glass is strong, hard, highly resistant to chemical attack, and stable to temperatures ~1000°C. Addition of up to 20 mole % silica markedly increased glass formability while maintaining infrared transmission to ~ 5000 nm in sections up to a few mm. The fluorescence lifetime of excited states in the dopant ions was measured as a function of dopant concentration, pump power and host composition. The absorption cross section and fluorescence line shape were measured for selected compositions. We present details of the glass synthesis and properties, and results of the optical measurements in the context of developing glass-based optical devices.