Certification of SRM1960: Nominal 10 μm Diameter Polystyrene Spheres (“Space Beads”)
Experimental, theoretical, and calculational details are presented for the three independent micrometrology techniques used to certify the mean diameter of Standard Reference Materisd 1960, nominal 10 μm diameter polystyrene spheres (“space beads”). The mean diameters determined by the three techniques agreed remarkably well, with all measurements within 0.1% of each other, an unprecedented achievement in the dimensional metrology of microspheres. Center distance finding (CDF), a method based on optical microscopy, gave a value of 9.89 ± 0.04 μm, which was chosen to be the certified mean diameter. The supporting measurements were done using metrology electron microscopy (MEM) and resonance light scattering (RLS). The MEM technique, based on scanning electron microscopy, yielded 9.89±0.06 μm for the mean diameter of the microspheres in vacuum, while the RLS value was 9.90 ±0.03 μm for the microspheres in liquid suspension. The main peak of the diameter distribution for SRM 1960 is nearly Gaussian with a certified standard deviation of 0.09 μm, as determined by CDF. Off the main peak, there are about 1% oversized particles and a negligible amount of undersized particles. The report gives a detailed description of the apparatus, the experimental methods, the data-reduction techniques, and an error analysis for each of the micro-metrology techniques. A distinctive characteristic of this SRM is that it was manufactured in microgravity aboard the NASA space shuttle Challenger and is the first commercial product to be made in space.
Oxidative desulfurization of fuel oils-catalytic oxidation and adsorptive removal of organosulfur compounds
Abstract The syntheses and evaluation of oxidovanadium(IV) complexes as catalysts for the oxidation of refractory organosulfur compounds in fuels is presented. The sulfones produced from the oxidation reaction were removed from fuel oils by employing molecularly imprinted polymers (MIPs). The oxidovanadium(IV) homogeneous catalyst, [V IV O(sal-HBPD)], as well as its heterogeneous polymer supported derivatives, poly[V IV O(sal-AHBPD)] and poly[V IV O(allylSB-co-EGDMA)], were synthesized and fully characterized by elemental analysis, FTIR, UV-Vis, XPS, AFM, SEM, BET and single crystal XRD for [V IV O(salHBPD)]. The MIPs were also characterized by elemental analysis, FTIR, SEM, EDX and BET. The catalyzed oxidation of fuel oil model sulfur compounds, thiophene (TH), benzothiophene (BT), dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT), was conducted under batch and continuous flow processes at 40°C by using tert-butylhydroperoxide (t-BuOOH) as oxidant. The continuous flow oxidation process presented the highest overall conversions and very high selectivity for sulfones. Maximum oxidation conversions of 71%, 89%, 99% and 88% was achieved for TH, BT, DBT and 4,6-DMDBT respectively when poly[V IV O(allylSB-co-EGDMA)] was employed at a flow-rate of 1 mL/h with over 90% sulfone selectivity. The process was further applied to the oxidation of hydro-treated diesel containing 385 ± 4.6 ppm of sulfur (mainly dibenzothiophene and dibenzothiophene derivatives), and this resulted to a high sulfur oxidation yield ( 99%), thus producing polar sulfones which are extractible by polar solid phase extractants. Adsorption of the polar sulfone compounds was carried-out by employing MIPs which were fabricated through the formation of recognition sites complementary to oxidized sulfur-containing compounds (sulfones) on electrospun polybenzimidazole (PBI) nanofibers, cross-linked chitosan microspheres and electrospun chitosan nanofibers. Adsorption of benzothiophene sulfone (BTO2), dibenzothiophene sulfone (DBTO2) and 4,6-dimethyldibenzothiophene sulfone (4,6-DMDBTO2) on the various molecularly imprinted adsorbents presented a Freundlich (multi-layered) adsorption isotherm which indicated interaction of adsorbed organosulfur compounds. Maximum adsorption observed for BTO2, DBTO2 and 4,6-DMDBTO2 respectively was 8.5 ± 0.6 mg/g, 7.0 ± 0.5 mg/g and 6.6 ± 0.7 mg/g when imprinted chitosan nanofibers were employed, 4.9 ± 0.5 mg/g, 4.2 ± 0.7 mg/g and 3.9 ± 0.6 mg/g on molecularly
The First Products Made in Space: Monodisperse Latex Particles
Twenty monodisperse polystyrene latexes were made by seeded emulsion polymerization in the MLR-SEP flight hardware on theSTS-3 and STS-4 flights of the Columbia and the STS-6, STS-7, and STS-11 flights of the Challenger. Two polymerizations were small-particle-size controls; the other eighteen were of large particle size. Of these, six failed: four on STS-4 owing to malfunction of the flight hardware; one on STS-6 owing to a broken wire; one on STS-11 owing to a broken stirrer shearpin. Nine monodisperse latexes of 4–30 μm size had narrower particle size distributions than the ground-based controls. The 10 μm STS-6 latex and the 30 μm STS-11 latexes were accepted by the National Bureau of Standards as Standard Reference Materials, the first products made in space for sale on earth. The polymerization rates in space were the same as on earth within experimental error. The flight polymerizations produced only negligible amounts of coagulum; the ground-based control polymerizations produced increasing amounts with increasing particle size, so that these controls were discontinued after the STS-7 experiments. These results confirmed the original rationale of the experiments that polymerization in space would give more uniform large-particlesize monodisperse latexes with less coagulum by: 1. the better uniformity of all 5 μm or larger flight latexes; 2. the more perfect sphericity of the 10 and 30 μm particles; 3. the smaller number of offsize larger particles; 3. the negligible amounts of coagulum; 4. the broadening of the particle size distribution and the formation of more larger offsize particles during the completion on earth of the polymerization of the partially converted STS-4 flight latexes.