Molten barium titanate: a high-pressure liquid silicate analogue.

The structure of molten BaTiO3 has been measured using laser heating, aerodynamic levitation and a combination of neutron diffraction with Ti isotope substitution, x-ray diffraction and spectroscopy. All measurements indicate a Ti-O coordination of n TiO = 4.4(2), far lower than the perovskite or hexagonal crystalline forms. However, n TiO > 4 suggests structural analogy with molten silicates at high pressures. We introduce methodology for ascertaining such analogies and demonstrate similarity with molten CaSiO3 at upper mantle pressures circa 5 GPa. Although some topological differences exist, we propose that planetary melt analogues provide rich insight into important processes relevant to hot exoplanets and Earth's early history.

Corium lavas: structure and properties of molten UO2-ZrO2 under meltdown conditions.

In the exceedingly rare event of nuclear reactor core meltdown, uranium dioxide fuel reacts with Zircaloy cladding to produce eutectic melts which can subsequently be oxidized by coolant/moderator water. Oxidized corium liquids in the xUO2·(100 - x)ZrO2 system were produced via laser melting of UO2-ZrO2 mixtures to temperatures in excess of 3000 K. Contamination was avoided by floating the droplets on a gas stream within an aerodynamic levitator and in-situ high-energy x-ray diffraction experiments allowed structural details to be elucidated. Molecular dynamics simulations well reproduced diffraction and density data, and show less compositional variation in thermal expansion and viscosity than suggested by existing measurements. As such, corium liquids maintain their highly penetrating nature irrespective of the amount of oxidized cladding dissolved in the molten fuel. Metal-oxygen coordination numbers vary with both composition and temperature. The former is due to mismatch in native values, nUO(x = 100) ≈ 7 and nZrO(x = 0) ≈ 6, and the requirement for oxygen site stabilization. The latter provides a thermal expansion mechanism.

Using containerless methods to develop amorphous pharmaceuticals.

BACKGROUND: Many pipeline drugs have low solubility in their crystalline state and require compounding in special dosage forms to increase bioavailability for oral administration. The use of amorphous formulations increases solubility and uptake of active pharmaceutical ingredients. These forms are rapidly gaining commercial importance for both pre-clinical and clinical use. METHODS: Synthesis of amorphous drugs was performed using an acoustic levitation containerless processing method and spray drying. The structure of the products was investigated using in-situ high energy X-ray diffraction. Selected solvents for processing drugs were investigated using acoustic levitation. The stability of amorphous samples was measured using X-ray diffraction. Samples processed using both spray drying and containerless synthesis were compared. RESULTS: We review methods for making amorphous pharmaceuticals and present data on materials made by containerless processing and spray drying. It was shown that containerless processing using acoustic levitation can be used to make phase-pure forms of drugs that are known to be difficult to amorphize. The stability and structure of the materials was investigated in the context of developing and making clinically useful formulations. CONCLUSIONS: Amorphous compounds are emerging as an important component of drug development and for the oral delivery of drugs with low solubility. Containerless techniques can be used to efficiently synthesize small quantities of pure amorphous forms that are potentially useful in pre-clinical trials and for use in the optimization of clinical products. GENERAL SIGNIFICANCE: Developing new pharmaceutical products is an essential enterprise to improve patient outcomes. The development and application of amorphous pharmaceuticals to increase absorption is rapidly gaining importance and it provides opportunities for breakthrough research on new drugs. There is an urgent need to solve problems associated with making formulations that are both stable and that provide high bioavailability. This article is part of a Special Issue entitled "Science for Life" Guest Editor: Dr. Austen Angell, Dr. Salvatore Magazù and Dr. Federica Migliardo.

Aerodynamic levitator for in situ x-ray structure measurements on high temperature and molten nuclear fuel materials.

An aerodynamic levitator with carbon dioxide laser beam heating was integrated with a hermetically sealed controlled atmosphere chamber and sample handling mechanism. The system enabled containment of radioactive samples and control of the process atmosphere chemistry. The chamber was typically operated at a pressure of approximately 0.9 bars to ensure containment of the materials being processed. Samples 2.5-3 mm in diameter were levitated in flowing gas to achieve containerless conditions. Levitated samples were heated to temperatures of up to 3500 °C with a partially focused carbon dioxide laser beam. Sample temperature was measured using an optical pyrometer. The sample environment was integrated with a high energy (100 keV) x-ray synchrotron beamline to enable in situ structure measurements to be made on levitated samples as they were heated, melted, and supercooled. The system was controlled from outside the x-ray beamline hutch by using a LabVIEW program. Measurements have been made on hot solid and molten uranium dioxide and binary uranium dioxide-zirconium dioxide compositions.

Liquid B2O3 up to 1700 K: x-ray diffraction and boroxol ring dissolution.

Using high energy x-ray diffraction, the structure factors of glassy and molten B2O3 were measured with high signal-to-noise, up to a temperature of T = 1710(20) K. The observed systematic changes with T are shown to be consistent with the dissolution of hexagonal [B3O6] boroxol rings, which are abundant in the glass, whilst the high-T (>~1500 K) liquid can be more closely described as a random network structure based on [BO3] triangular building blocks. We therefore argue that diffraction data are in fact qualitatively sensitive to the presence of small rings, and support the existence of a continuous structural transition in molten B2O3, for which the temperature evolution of the 808 cm−1 Raman scattering band (boroxol breathing mode) has long stood as the most emphatic evidence. Our conclusions are supported by both first-principles and polarizable ion model molecular dynamics simulations which are capable of giving good account of the experimental data, so long as steps are taken to ensure a ring fraction similar to that expected from Raman spectroscopy. The mean thermal expansion of the B-O bond has been measured directly to be αBO = 3.7(2) × 10−6 K−1, which accounts for a few percent of the bulk expansion just above the glass transition temperature, but accounts for greater than one third of the bulk expansion at temperatures in excess of 1673 K.

Note: Detector collimators for the nanoscale ordered materials diffractometer instrument at the Spallation Neutron Source.

Five neutron collimator designs were constructed and tested at the nanoscale ordered materials diffractometer (NOMAD) instrument. Collimators were made from High Density PolyEthylene (HDPE) or 5% borated HDPE. In all cases, collimators improved the signal to background ratio and reduced detection of secondary scattering. In the Q-range 10-20 Å(-1), signal to background ratio improved by factors of approximately 1.6 and 2.0 for 50 and 100 mm deep collimators, respectively. In the Q-range 40-50 Å(-1), the improvement factors were 1.8 and 2.7. Secondary scattering as measured at Q ∼ 9.5 Å(-1) was significantly decreased when the collimators were installed.

Molten uranium dioxide structure and dynamics.

Uranium dioxide (UO2) is the major nuclear fuel component of fission power reactors. A key concern during severe accidents is the melting and leakage of radioactive UO2 as it corrodes through its zirconium cladding and steel containment. Yet, the very high temperatures (>3140 kelvin) and chemical reactivity of molten UO2 have prevented structural studies. In this work, we combine laser heating, sample levitation, and synchrotron x-rays to obtain pair distribution function measurements of hot solid and molten UO2. The hot solid shows a substantial increase in oxygen disorder around the lambda transition (2670 K) but negligible U-O coordination change. On melting, the average U-O coordination drops from 8 to 6.7 ± 0.5. Molecular dynamics models refined to this structure predict higher U-U mobility than 8-coordinated melts.