Opposed flow oxy-flame synthesis of carbon and oxide nanostructures on molybdenum probes

The formation of carbon and metal-oxide nanostructures on molybdenum probes inserted in a counter-flow oxy-fuel flame is studied experimentally. Flame position and probe diameter were varied to achieve a controlled growth of carbon and metal-oxide nanostructures at fuel and oxygen-rich flame zones. Mo probes of 1-mm diameter were introduced in the flame at various heights, starting from the upper hydrocarbon-rich zone on the fuel side of the flame to the oxygen-rich zone on the oxidizer side. High density layers of carbon nanocoils (CNCs) and filamentous structures containing ribbon shapes and straight nanofibers were formed in the upper hydrocarbon-rich flame zone. The formation of carbon micro-trees was observed on the fuel side closer to the flame front. The structures formed in the oxidizer part of the flame were composed of molybdenum-oxides. MoO2 micron-sized channel structures were formed on the oxidizer side in the vicinity of the flame front. The micro-channels had rectangular and square-framed shapes; they were completely hollow, closed, and semi-open with a small circular cavity at their tips. The application of probes with diameters of 0.75 and 0.25 mm resulted in the formation of spectacular 3-D structures with unique and distinct morphologies.