Recent developments in geopolymer composites and their potential applications

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In situ synchrotron studies of oxide ceramics to 3,000°C

A quadrupole halogen lamp furnace (QLF) capable of heating to 2,000°C in air has been developed in our laboratory, in collaboration with Dr. Julius Schneider at the Ludwig Maximillian University in München, Germany. A conical nozzle levitator (CNL) developed by Dr. Richard Weber at Materials Modification in Chicago, Illinois is capable of in situ XRD measurements of oxides to 3,000°C in air. These two instruments were used at the Advanced Photon Sources (APS) at the Argonne National Laboratory, and the QLF was used at the National Synchrotron Light Source II (NSLSII) at Brookhaven National Laboratory to carry out the following experiments: (i) Thermal expansion measurements in 3-D (ii) Solid state phase transformations (iii) Solid state chemical reactions (iv) In situ determination of phase diagrams A variety of ceramic and mineral examples are provided to illustrate the seven crystal systems (cubic, tetragonal, orthorhombic, rhombohedral, hexagonal, monoclinic and triclinic). Computer software (Program CTEAS) has been developed to visualize the thermal evolution in 3D for individual {hkl} planes, principle strain directions and whether they are increasing or decreasing. When a crystal undergoes a phase transformation upon heating, the 3D crystal structural, lattice correspondence between the parent and product phases can be identified from the continuity of thermal expansion for planes in the parent phase which approximately “become” planes in the product phase. The example is given of a peritectic reaction in the binary HfO2-Ta2O5 system where Hf6Ta2O17 decomposes on heating into liquid HfO2-Ta2O5 solid solution plus HfO2 at 2242 ± 16 °C. A Z = 4, pseudo-subcell is identified which is common to the parent and product phases, which, coupled with vector analysis identifies a lattice correspondence between them, and hence possible orientation relationship. The oxidation of SiC dispersed into ZrB2 was studied as an example of a solid state reaction where the kinetics and chemical mechanisms were elucidated. Intermediate crystalline phases that were formed during oxidation of ZrB2, could be identified and quantified in real time. The oxidation of ZrB2 phase could be followed independently of concurrent phases, whether amorphous or crystalline, or simultaneous reactions. Increasing the SiC content in the ZrB2-SiC composites retarded the oxidation of ZrB2. A novel approach to estimate the thickness of an oxidation layer formed during oxidation of ZrB2 and ZrB2-SiC composites, in-situ at high temperatures was proposed, based on fractional conversion of ZrB2 to ZrO2 A systematic approach to the rapid production of the high temperature, ternary HfO2-Ta2O5-TiO2 phase diagrams is presented. This study highlights the combined use of: (i) in-situ high temperature X-ray diffraction on heating to 2,000°C in the QLF, as well as on cooling of liquidi from 3000 ˚C in air in the CNL, and (ii) extraction of common atomic motifs with associated material symmetry analysis. The HfO2-Ta2O5-TiO2 ternary phase diagram has 4 congruently melting compounds: HfO2, Ta2O5, TiO2 and TiTa2O7 and 2 incongruently melting compounds: Hf6Ta2O17 and HfTiO4. There are no ternary congruently melting compounds. Symmetry relations between Hf6Ta2O17 and HfTiO4 have been identified. Symmetry decomposition shows that these two structures are simply related to each other via polyhedral rotations. Finally, 10 invariant reactions were identified in this phase space. There is sufficient in-situ high temperature X-ray diffraction data to analyze the ternary between the lowest melting point isotherm and the room temperature isotherm

High-temperature behavior in entropy-stabilized oxide (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)O

High entropy oxide (HEO) (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)O has been synthesized by the polymeric steric entrapment method and characterized through high-temperature in-situ synchrotron experiments. HEOs are a new area in ceramics derived from high entropy alloys with disordered cations located in oxygen sites. The polymeric steric entrapment method has advantage over other methods because it can enhance homogeneity during synthesis. In HEO (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)O, only a small amount of secondary copper oxide phase with tenorite structure can be found without quenching. At 2000 degrees Celsius under in-situ synchrotron experiments, material (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)O was partially melted, which indicated that some of the oxides (e.g. cobalt oxide, nickel oxide) separated from the disordered oxide phase and melted at their individual oxide melting temperatures. The dominant material above 2000 degrees Celsius is magnesium oxide, the only oxide in (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)O sample with a melting temperature higher than 2000 degrees Celsius. No secondary phase in (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)O was found from synthesized temperature to melting Please click Additional Files below to see the full abstract

Reactive metal/graphene oxide doping to fabricate porous geopolymers for arsenic removal

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Understanding the relationship between micro and macro-scale properties in sodium silicate activated slag-fly ash binders

Sodium silicate activated slag-fly-ash binders (SFBs) are room temperature hardening binders that have excellent mechanical properties and significantly lower carbon footprint than OPC. The aim of this study is two-fold. One is to understand setting in slag fly ash binders as a function of slag/fly ash ratio by using two complementary methods namely, Ultrasonic Wave Reflectometry (UWR), and modified Procter penetration test (ASTM C403). The other aim is to develop a method to differentiate and quantify all poorly-ordered phases (unreacted slag, unreacted fly ash, C(A)SH and geopolymer) present in slag fly ash binders as a function of curing time, curing temperature and slag/fly ash ratio. This was achieved by using selective chemical extractions and nuclear magnetic resonance (MAS-NMR) spectroscopy of binders and extraction residues. The results from MAS-NMR were used to explain the observed trend in compressive strength, as a function of the same variables listed above. Please click Additional Files below to see the full abstract

In-situ phase diagram determination of the HfO2-Ta2O5 binary up to 3000˚C

Ceramic equilibrium phase diagrams have proven to be difficult to produce for materials above 1500 ˚C. We demonstrate that in-situ X-ray diffraction on laser heated levitated samples can be used to elucidate phase fields. In these experiments, solid spherical samples are suspended and rotated by a gas stream through a conical nozzle levitator, heated by a 400 W CO2 laser at Argonne National Labs beamline 6-ID-D. Please click on the link below for the full content

Directions of zero thermal expansion in anisotropic oxides

Figure 13. – Quadric surface visualizing the coefficients of thermal expansion of HfTiO4 at room temperature. Blue is positive, red is negative and yellow represents directions of zero thermal expansion. Oxide materials often have anisotropic crystal structures, which can result in direction-dependent material properties. While they typically have positive coefficients of thermal expansion, it has been observed that some oxide materials can have directions of negative thermal expansion over certain temperature ranges. Such materials, having both positive and negative coefficients of thermal expansion, must also have particular directions in which the thermal expansion is zero. Using the Quadrupole Lamp Furnace (QLF) developed in the Kriven group at the University of Illinois at Urbana Champaign, high-temperature in-situ x-ray diffraction has been performed at the National Synchrotron Light Source II (NSLS II) X-ray powder diffraction beamline (XPD – 28-ID) to track directions of zero thermal expansion in orthorhombic HfTiO4. These results have important implications for the design of composites for high-temperature applications. Please click Additional Files below to see the full abstract

Metakaolin particle size reduction and geopolymer composite modeling for higher strength

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