The Structure of Amorphous and Deeply Supercooled Liquid Alumina

Abstract

Liquid Al 2 O 3 has been supercooled more than 500 K below its melting point (T m = 2,327 K) using aerodynamic levitation and laser heating techniques. High energy synchrotron x-ray measurements were performed over a temperature range of 1,817 ≤ T (K) ≤ 2,700 and stroboscopic neutron diffraction at 1,984 and 2,587 K. The diffraction patterns have been fitted with Empirical Potential Structure Refinement (EPSR) models and compared to classical Molecular Dynamics (MD) simulation results. Both sets of models show similar trends, indicating the presence of high populations of AlO 4 and AlO 5 polyhedral units predominantly linked by triply shared oxygen atoms. EPSR reveals that the mean Al-O coordination number changes linearly with temperature with n AlO = 4.41-[1.25 × 10 −4 ] (T-T m), with a 2.5 Å cutoff. Both EPSR and MD simulations reveal a direction of the temperature dependence of the aluminate network structure which moves further away from the glass forming ideal (n AlO = 3) during supercooling. Furthermore, we provide new experimental data and models for amorphous alumina grown by sequential infiltration synthesis of a polymer template. The amorphous solid form likely has a larger Al-O coordination number than the liquid, consistent with expectations for the hypothetical glass.

Evaluation of the electrochemical performance of Ag containing AAO layers after extended exposure to a model corrosive medium

“…The absence of CPEdiff in the case of AAO layers suggests that the barrier layer underneath the AAO pores is sparse, due to its amorphous structure. Indeed, the XRD analysis has revealed amorphous alumina, which has a density of between 2.66 and 3.40 g cm -3 [78,79], lower than this of the crystalline corundum. Hence, the barrier layer does not completely prevent the access of corrosive species like Clions towards the metallic surface.…”

Effect of Polymer Removal on the Morphology and Phase of the Nanoparticles in All-Inorganic Heterostructures Synthesized via Two-Step Polymer Infiltration

“…The samples were exposed to 5 cycles of trimethylaluminum (TMA) and water vapors at 90 °C [ 21 , 38 ]: 10 mTorr of the TMA precursor was introduced with 20 sccm nitrogen flow into the reactor for 400 s; the excess of the reactant was evacuated for 10 s followed by introducing of 10 mTorr of H 2 O for 120 s; the chamber was then purged with 100 sccm of nitrogen to remove not-infiltrated byproducts. The process allows the synthesis of amorphous alumina matrix [ 5 , 26 ] that is used here to provide the support for iron oxide NPs.…”

“…In turn, UV ozone treatment is slower and more gentle for substrates but may lead to the trapping of residual carbon [ 16 , 24 , 25 ]. Previous studies on alumina synthesized by SIS and based on the infiltration of polymer block copolymers (BCPs) with trimethylaluminum (TMA) did not reveal a difference in alumina structures obtained by UV ozone treatment and thermal annealing polymer removal [ 26 ]. However, our recent study on the synthesis of porous all-inorganic PdO x /alumina nanoheterostructures indicated that the technique used for polymer template removal drastically affects the size of the PdO x nanoparticles (NPs) uniformly distributed in the alumina matrix [ 16 ].…”

Redox-structure dependence of molten iron oxides

“…The x-ray total structure factor S(Q) and the corresponding differential pair-distribution function D (r) = 4πρr[G(r) -1] as a function of temperature and p(O 2 ) were extracted. Details of the high-energy X-ray analysis used have previously been described by Shi et al 37 from samples prepared in a laser hearth melter 38 . Three-dimensional models describing the atomic structure were obtained using EPSR 39 .…”