Amorphous, Self-Healed (ASH-G) geopolymer and (ASH-C) ceramic composites

Basalt is a common volcanic rock found all around the world and on Mars. The abundance of basalt has attracted attention from construction firms and material researchers as an alternative reinforcement source. Potassium geopolymer in the stoichiometric composition K2O • Al2O3 • 4SiO2 • 11H2O was produced from fumed silica, deionized water, potassium hydroxide, (i.e. water glass) and metakaolin. The geopolymer matrix was fabricated in an IKA® high shear mixer. ½” chopped basalt fibers from Kameny Vek in Moscow were added to potassium geopolymer in amounts of 7.5 wt %. The basalt fibers and 7.5 wt % glass frit (900°C) were then dispersed in KGP using a planetary high shear Thinky mixer and the samples were allowed to set under applied pressure at ambient temperatures for 1 day followed by 1 day at 50°C to complete the reaction. A low melting temperature fine glass frit (Tm = 900°C) was added to produce self-sealing/crack filling in a dehydrated but un-crystallized geopolymer composite (900-1000 °C). Sample geometries were 1” x 1” x 6” in dimensions. Six samples from each basalt weight class were heated to 400, 800, 900, 1000, 1100, and 1200 °C. The ramp up and down rates were 7 °C/min with a 1 hour soak time at each set temperature. SEM/EDS data indicated that melting and bonding of the glass phase dispersed into the surrounding KGP matrix, produced a self-sealing effect on the dehydrated and cracked matrix. The chopped basalt fibers melted after the KGP matrix crystallized into leucite, providing a network/glass filling system in a ceramic (1200 °C). At intermediate temperatures the geopolymer was converted to a ceramic, but the basalt fibers remained intact. The amorphous self-healing effect of the glass frit significantly improved to the flexure strength of the geopolymer and ceramic composite

Amorphous, self-healed, geopolymers (ASH-G and ceramics (ASH-C) made by the geopolymer processing route

This work describes the cross fertilization of conventional whiteware production by a low energy, geopolymer processing method. Bone china is conventionally made using natural cow bone ash (calcined) of hydroxyapatite (HA). In this study HA and dicalcium phosphate (DCP) particulate reinforcements were investigated in potassium-based geopolymer composites (KGP). Particulate reinforcements of 5, 10 and 15 wt % each of hydroxyapatite and dicalcium phosphate particulate were added to potassium geopolymer to compare with composites made from BASF® Metamax metakaolin (KGP MT), Mymensingh clay metakaolin, KGP(MW) and synthetic Mymensingh clay metakaolin, KGP(MW-SYN). Microstructural properties using SEM, XRD and mechanical properties using Instron were investigated for the geopolymer samples at both room and high temperature. The XRD of pure and reinforced geopolymer samples at RT confirmed the formation of geopolymer analogues with the characteristic X-ray amorphous hump at 280 in 2θ, along with the crystalline peaks observed in KGP (MW), as well as in potassium geopolymer reinforced with hydroxyapatite and dicalcium phosphate. Thermally treated geopolymer composites at 11500C/1h exhibited crystalline peaks of leucite, kalsilite, monetite and quartz confirming the signature of geopolymer ceramics at elevated temperature. SEM revealed fully reacted and homogenous aluminosilicate matrix in all the geopolymer samples cured at room temperature for 7 days. Geopolymer composites KGP (MT)-15 DCP, KGP(MW)-15DCP and KGP(MW-SYN)-15DCP after thermal exposure at 11500C revealed microstructural integrity with the formation of phosphate glass, while a self-glazed surface was developed in KGP (MW) after being heated at 1125 0C/1h. Their high temperature properties are superior to RT properties due to amorphous self-healed glass formation (ASH) from the DCP phosphate glass. Their high temperature properties were superior to RT properties due to amorphous self-healed glass formation (ASH) from the DCP phosphate glass. The optimum DCP content was 10 wt % which gave flexure strengths of ~32 MPa after heat treatment at 1150 °C/1h

Single-Crystal Elastic Constants of Yttria (Y2O3) Measured to High Temperatures

Yttria, or yttrium sesquioxide (Y2O3), has been considered for use in nuclear applications and has gained interest relatively recently for use in infrared optics. Single crystals of yttria have been grown successfully at the NASA Glenn Research Center using a laser-heated float zone technique in a fiber and rod. Such samples allow measurement of the single-crystal elastic properties, and these measurements provide useful property data for the design of components using single crystals. They also yield information as to what degree the elastic properties of yttria ceramics are a result of the intrinsic properties of the yttria crystal in comparison to characteristics that may depend on processing, such as microstructure and intergranular phases, which are common in sintered yttria. The single-crystal elastic moduli are valuable for designing such optical components. In particular, the temperature derivatives of elastic moduli allow the dimensional changes due to heating under physical constraints, as well as acoustic excitation, to be determined. The single-crystal elastic moduli of yttria were measured by Brillouin spectroscopy up to 1200 C. The room-temperature values obtained were C(sub 11) = 223.6 + 0.6 GPa, C(sub 44) = 74.6 + 0.5 GPa, and C(sub 12) = 112.4 + 1.0 GPa. The resulting bulk and (Voigt-Reuss-Hill) shear moduli were K = 149.5 + 1.0 GPa and G(sub VRH) = 66.3 + 0.8 GPa, respectively. Linear least-squares regressions to the variation of bulk and shear moduli with temperature resulted in derivatives of dK/dT = -17 + 2 MPa/C and dG(sub VRH)/dT = -8 + 2 MPa/ C. Elastic anisotropy was found to remain essentially constant over the temperature range studied

Landau theory applied to phase transitions in calcium orthotungstate and isostructural compounds

The pressure-driven tetragonal-to-monoclinic phase transition in CaWO4 and related scheelite-structured orthotungstates is analysed in terms of spontaneous strains. Based upon our previous high-pressure x-ray diffraction results and the Landau theory, it is suggested that the scheelite-to-fergusonite transition is of second order in nature.Comment: 14 pages, 3 figure