Phase Transformations in Ceramics: Science and Applications: Experimental Studies on Structure and Control II
Sponsored by: ACerS Basic Science Division, ACerS Electronics Division, ACerS Engineering Ceramics Division
Program Organizers: Scott Mccormack, University Of California, Davis; Pankaj Sarin, Oklahoma State University; Sanjay V. Khare, University of Toledo; Waltraud Kriven, University of Illinois at Urbana-Champaign
Monday 2:00 PM
October 18, 2021
Room: B230
Location: Greater Columbus Convention Center
2:00 PM Invited
Symmetry-mode Analysis of Phase Transitions in Solids: Branton Campbell1; Harold Stokes2; 1Brigham Young University; 2Brigham Young Univ
Group-representation theory is one of the most important layers in the bedrock of modern chemistry and physics. Its reach includes any physical or mathematical system that exhibits any kind of symmetry, and provides a unique parameter set for describing structures that break the parent symmetries of a system. Representation (a.k.a. “symmetry mode”) analysis is an essential tool in the classification of phase transitions. New crystallographic infrastructure within the ISOTROPY Software Suite now enables a broad range of applications, including the compact description of general order-parameter types (displacive, magnetic, rigid-unit-rotational, occupational, lattice-strain, etc.), a common parameter set for the phases of a complicated phase diagram, the solution of large and subtle superstructures, the analysis of local order in disordered crystals, and the characterization of incommensurately modulated crystals. The presentation will introduce basic concepts, highlight recent developments and discoveries, and describe unexplored opportunities.
2:30 PM Invited
High Pressure Phase Transformations of Zircon-type Silicate Materials: Xiaofeng Guo1; Andrew Strzelecki1; Xiaodong Zhao1; Jason Baker2; Stella Chariton3; Vitali Prakapenka3; Hongwu Xu4; 1Washington State University; 2Lawrence Livermore National Laboratory; 3The University of Chicago; 4Los Alamos National Laboratory
Understanding the crystallographic transformations of zircon-type silicate materials under pressure have wide and important implications in their application as nuclear waste forms, as high temperature coating materials, and for geochemical mineralization. The orthosilicate mineral zircon (ZrSiO4) with its tetragonal crystal structure, crystallizing into the I41/amd space group. Ce, Th, U can also crystalize into zircon structure, forming coffinite, thorite, and stetindite, respectively. Although ZrSiO4 and HfSiO4 are known to exhibit a pressure-induced phase transition from the zircon structure (I41/amd) to scheelite structure (I41/a1), the high pressure phase diagrams for other tetravalent 4f/5f metal orthosilicate are more ambiguous and may have alternative routes to P21/n or C2/c phases. Here we reported in situ high pressure synchrotron powder x-ray diffraction and Raman spectroscopy implemented with diamond anvil cells on Ce, Th, U bearing orthosilicate to reveal their transformation under hydrostatic compression. Equations of state of these silicate materials were also reported.
3:00 PM Invited
Initial Stages of Transformation of 2-D Assemblies of Nanosheets to Tunnel Structures: Scott Misture1; 1Alfred University
In the case of exfoliated 2-D oxides, little work has been published concerning the thermal stability and phase transitions that occur upon heating these high surface area solids. The talk will describe the evolution of phases in layered oxides including MnO2 and CoO2 over broad temperature ranges, where porous assemblies of nanosheets yield porous monoliths of thermodynamically stable phases. We focus on measuring nucleation and growth of new phase fragments – to capture the mechanisms of structural phase transitions – using primarily Raman spectroscopy and X-ray total scattering. We demonstrate that it is feasible though not straightforward to track, for example, conversion of assemblies of MnO2 nanosheets into tunnel-structured MnO2. We further show that properties such as the electrochemical capacitance and electrocatalytic activity vary with the structure changes, giving confidence in our ability to track phase transitions from the very early stages of nucleation at the sub-nanometer size scale.
3:30 PM Break
3:50 PM
Crystallographic Studies of the Leucite-pollucite System Synthesized by Geopolymer Crystallization: Andrew Steveson1; Waltraud Kriven1; 1University of Illinois at Urbana-Champaign
Geopolymers are a type of chemically bonded ceramics of chemical formula M2O•Al2O3•4SiO2•11H2O. They are refractory, inorganic polymers formed from both aluminum and silicon sources containing AlO4- and SiO4 tetrahedral units, under highly alkaline conditions (NaOH, KOH, CsOH) at room temperature. They result in an amorphous, nano-particulate, nanoporous, impervious, acid-resistant structure. The strained nature of the 5-coordination aluminum cation polyhedra is identified as the reason why metakaolin-based geopolymer ceramics are made from solution, rather than with high temperature diffusion. Applications of geopolymers in high temperature environments require characterization of the crystalline phases that develop. In this work, we examined the temperature-driven structural evolution of samples belonging to the K[AlSi2O6]-Cs[AlSi2O6] pseudo-binary synthesized by heat treatment of pure geopolymer using in situ high-temperature synchrotron X-ray powder diffraction. The data was analyzed by Rietveld refinement and the mechanisms underlying the thermal expansion and phase transitions were elucidated by statistical methods.
4:10 PM
In-situ Phase Equilibria in the TiO2-HfO2-WO3 System up to 1400˚C: Benjamin Hulbert1; Dylan Blake1; Waltraud Kriven1; 1University of Illinois at Urbana-Champaign
The TiO2-HfO2-WO3-temperature phase diagram was investigated up to 1400℃ in air with in-situ synchrotron powder diffraction. The high melting temperatures of these multi-component Ti-Hf-W-oxides and their applications as refractory structural materials and in high temperature electronics and sensors motivated this study. The temperatures required were reached with a quadrupole lamp furnace with powder samples mounted in fused-silica capillaries in air from 25℃ to 1200℃. Additionally, a 400W CO2 laser, with a conical nozzle levitator, heated solid spherical samples from 700℃ to 1400℃. Synchrotron data at ~50℃ intervals allowed determination of phase-fractions and crystal structures. Equilibrium phases were determined by checking the reversibility of phase transformations in XRD experiments. Temperature-dependent thermal expansions of all phases present were measured. Phase diagram development is vital in the ceramics industry, as engineers refer to them during the material selection process to ensure thermodynamic stability of the materials under the required conditions.