Geopolymerisation: A review and prospects for the minerals industry

X-ray microtomography shows pore structure and tortuosity in alkali-activated binders

Epitaxial thin films of Ba2YCu3O7−x (BYC) were prepared on (001) LaAlO3 single‐crystal substrates by metalorganic deposition of metal trifluoroacetate precursors. This is an ex situ process that requires high‐temperature annealing in a humid atmosphere to produce stoichiometric BYC thin films. The chemically derived superconducting films were found to have high critical temperatures and high current densities when crystallized under low‐oxygen partial pressures. Superconducting films of 70 nm thickness with zero‐field critical current densities greater than 5×106 A/cm2 at 77 K and zero resistance at 92 K were prepared by annealing at 780 and 830 °C in 2.5 × 10−4–1 × 10−3 atm oxygen furnace atmospheres. As the film thickness was increased, the superconducting properties and surface smoothness of the films tended to degrade. This behavior was consistent with a microstructural model in which the films are composed of a dense slab of c‐axis normal BYC near the film/substrate interface with the overlying mater...

Effect of growth conditions on the properties and morphology of chemically derived epitaxial thin films of Ba2YCu3O7−x on (001) LaAlO3

Global time scale and regional stratigraphic reference scales of Central and West Europe, East Europe, Tethys, South China, and North America as used in the Devonian-Carboniferous-Permian Correlation Chart 2003 (DCP 2003)

A comprehensive overview about the influence of different additives on the properties of alkali-activated slag – A guide for Civil Engineer

Steady‐state flow stress of dense (99% of theoretical) polycrystalline YBa2Cu3O7−δ has been measured in direct compression at temperatures between 870 and 980 °C in oxygen partial pressures of 0.03, 0.18, and 1.0×105 Pa for strain rates between 5×10−6 and 4×10−5 s−1. The stress exponent was close to one, indicating that diffusional flow was the dominant deformation mechanism. The flow stress decreased with decreasing oxygen partial pressure, obeying a power law with an exponent of approximately 1/2 . The activation energy was about 800 kJ/mol at an oxygen partial pressure 1×105 Pa, but decreased to 600 kJ/mol at a pressure of 3×103 Pa.

High‐temperature deformation of YBa2Cu3O7−δ

The sintering kinetics of YBa2Cu3O7−x have been studied from 870 to 930 °C in oxygen/argon mixtures ranging from 0.2% to 100% oxygen. For sintering at temperatures below that required for formation of any liquid phase, densification rates increased with decreasing oxygen concentration, and transport critical current densities increased with increasing density. The activation energy for sintering was 190±30 kJ/mol.

Influence of oxygen concentration on processing YBa2Cu3O7−x

Solid-particle erosion of a geopolymer containing fly ash and blast-furnace slag

Dense (Bi, Pb)2Sr2Ca2Cu3Ox bars were fabricated by sinter forging. The bars were highly phase-pure and exhibited strong textures in which the c axes of the platelike grains were preferentially aligned parallel to the pressing direction. Transport critical current densities increased with texture, reaching a maximum of 8*103 A cm-2 at 77 K in a self-field. Optimal processing in air occurred at 845-850 degrees C.

Sinter-forged (Bi, Pb)2Sr2Ca2Cu3Ox superconductors

Thermomechanical properties of fine-grained, 96% dense, polycrystalline BaZrO3 specimens were studied. The average thermal expansion coefficient of BaZrO3 at 25–1000°C was 7.72×10−6°C−1. At 25°C, Young's modulus was 240.5 GPa and the shear modulus was 97.2 GPa. These values decreased by ≈10% with heating to 1015°C. Poisson's ratio was 0.237 and was independent of temperature. The BaZrO3 specimens exhibited a thermal expansion coefficient of about one half, and elastic moduli more than twice, those of polycrystalline high-temperature superconductors. Diffusional creep was observed when BaZrO3 was compressed at 1300–1400°C; the activation energy for steady-state deformation was 460±30 kJ/mole. The mechanism was probably grain-boundary sliding, controlled by diffusion of one of the cations along grain boundaries. Deformation rates below 1000°C were too low to relax thermally generated stresses.

Nan Chen

Papers

High‐temperature deformation of YBa2Cu3O7−δ

Influence of oxygen concentration on processing YBa2Cu3O7−x

Solid-particle erosion of a geopolymer containing fly ash and blast-furnace slag

Sinter-forged (Bi, Pb)2Sr2Ca2Cu3Ox superconductors

Thermomechanical response of polycrystalline BaZrO3