ABSTRACT
Geopolymers are inorganic crosslinked polymers with much less carbon footprint than ordinary Portland cement. Geopolymers and geopolymer-based materials have superior mechanical and durability properties with extreme thermal and chemical resistance. Carbon nano- or microfibers-reinforced geopolymers show potential properties such as electric conductivity, enhanced mechanical and thermal stability, and multi-functionality. This study evaluated the effect of incorporating carbon nanofibers in natural zeolite-based geopolymers and their impact on the mechanical, thermal, and electric conductivity of yielded geopolymer composites. Additionally, a life cycle assessment for 1 m3 geopolymer and its carbon fiber reinforced geopolymers' production has been conducted to evaluate the environmental impact of the processes.
ABSTRACT
The rapid formation of tungsten oxide nanorods through electron beam (EB) irradiation on the surface of micron-sized flame formed tungsten-oxide fragments is reported. The micro-sized fragments (precursor material) were formed in a counter-flow methane diffusion flame on the surface of a tungsten wire. Nanorods of various lengths and aspect ratios were rapidly formed in the surrounding area of a transmission electron microscope copper grid as the micro-sized fragments were exposed to a concentrated electron beam. The EB was produced using a 200 keV transmission electron microscope. The length of the formed nanorods is inversely proportional to the distance of the precursor material. We show that the most significant growth or conversion of nanorods from a flame formed fragment occurs within the first second of the EB irradiation; principally owing to the considerable amount of residual stresses attained in the material as they are formed in a high flame temperature environment. It was found that the produced nanorods are composed of a lower oxygen state of tungsten oxide than the precursor material. A growth mechanism is proposed and discussed.
ABSTRACT
Well-defined faceted inorganic Mo oxide nanocrystals are synthesized in the gas phase using a solid-fed-precursor flame synthesis method. The solid crystals have rectangular cross-section with characteristic size of 10-20 nm and with lengths ranging from 50 nm to a few hundred nanometres. A 1 mm diameter high purity Mo probe introduced in the oxygen-rich part of the flame serves as the material source. A combination of the strong temperature gradient and varying chemical species concentrations within the flame volume provides the ideal conditions for the rapid and direct formation of these unique nanocrystals. Oxidation and evaporation of MoO3 in the oxygen-rich zone are followed by reduction to MoO2 in the lower temperature, more fuel-rich zone. The MoO3 vapours formed are pushed in the direction of the gas flow and transformed into mature well-defined convex polyhedron nanocrystals bounded with six faces resembling rectangular parallelepipeds.
ABSTRACT
The growth and morphological evolution of molybdenum-oxide microstructures formed in the high temperature environment of a counter-flow oxy-fuel flame using molybdenum probes is studied. Experiments conducted using various probe retention times show the sequence of the morphological changes. The morphological row begins with micron size objects exhibiting polygonal cubic shape, develops into elongated channels, changes to large structures with leaf-like shape, and ends in dendritic structures. Time of probe-flame interaction is found to be a governing parameter controlling the wide variety of morphological patterns; a molecular level growth mechanism is attributed to their development. This study reveals that the structures are grown in several consecutive stages: material "evaporation and transportation", "transformation", "nucleation", "initial growth", "intermediate growth", and "final growth". XRD analysis shows that the chemical compositions of all structures correspond to MoO(2).
