Submicron Fibers Research Articles

Formation of Poly(1,1,2,2-tetrahydroperfluorodecyl acrylate) Submicron Fibers and Particles from Supercritical Carbon Dioxide Solutions

Rapid expansion from supercritical solution (RESS) of a crystalline fluoropolymer, poly(1,1,2,2-tetrahydroperfluorodecyl acrylate) or poly(TA-N), in carbon dioxide produces submicron to several micron sized particles and fibers. The understanding of the RESS mechanism has been clarified by careful design of experimental variables and procedures. The concentration of the poly(TA-N)/CO 2 solution was held constant (at 0.5 and 2.0 wt %), the solution cloud point curves were obtained, the pre-expansion temperature was varied above and below the cloud point, and the length to diameter (L/D) ratio of the nozzle was varied from 8.5 to 508. The morphology is explained in terms of the location of phase separation within the expansion nozzle. The L/D is the most influential variable for achieving a transition from particles or fibers. In most cases, manipulation of the solution concentration and the pre-expansion temperature did not produce this transition but did have a large effect on the sizes of the particles and fibers. These results are an important step in demonstrating CO 2 -based spray processes which do not require any volatile organic solvents

Improving the performance of porous radiant burners through use of sub-micron size fibers

An analysis has been carried out to determine the performance of porous radiant burners (PRB) as a function of fiber size. PRB made with silica or alumina fibers are considered. The radiative properties of the fibers are determined using the electromagnetic wave scattering theory for two different characteristics temperatures— 1000 and 1500°C. The properties are used in a combined-mode heat transfer model to calculate the amount of energy radiated by the PRB. It is found that fibers smaller than the order of 1 μm in diameter produce significantly higher radiant output. For a characteristic temperature of 1000°C, in some cases, the increase in output is as high as 63 and 109% for silica and alumina fibers, respectively. For a characteristic temperature of 1500°C, the corresponding increases are 72 and 150%, respectively.

Submicron multifilamentary high performance Nb3Sn produced by powder metallurgy processing of large powders

Powder metallurgy processed submicron multifilamentary Nb3Sn superconducting wires were fabricated starting with 250–500-μm-diam powders. A multiple strand bundling procedure was used to simulate large scale production with actual areal reductions greater than 106 to achieve submicron fibers. Both external tin and tin core processing were successful. Typical Cu-36 wt.% Nb-Sn materials gave overall critical current densities of 8×104 A/cm2 at 12 T, 3×104 A/cm2 at 14 T, and 6×103 A/cm2 at 16 T. These results demonstrate that particle size and billet size can be scaled from earlier laboratory scale to large scale fabrication to produce high performance materials.