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.
Preparation and size determination of monodisperse silica microspheres for particle size certified reference materials
Abstract Five samples of monodisperse SiO2 microspheres used for certified reference materials for particle size were synthesized by the seed-growth method, that is, through hydrolysis and condensation of tetroethylorthosilicate in a mixture of ethanol and water, using amoniua as catalyst. Their nominal diameters were 0.15 μm, 0.3 μm, 0.5 μm, 1 μm, and 2 μm. The average diameters of these microspheres were accurately determinated by SEM array-sizing method, and the microspheres with 1 μm and 2 μm nominal diameters were determined by both SEM array-sizing method and optical array-sizing method, while the particle size distribution of these spheres was determined by SEM. The measurement errors for each sample were quantitatively assessed. The SEM magnification was calibrated with a SEM calibration standard traceable to CNIM (China National Institute of metrology), while the optical microscopy magnification was calibrated with a NIST stage micrometer (SRM 2800). The average diameters determined by SEM and optical microscopy were identical to each other. For comparison, the average diameter of these microspheres was also measured by other independent techniques -light scattering and photo-correlation methods, and the obtained data agreed well with that obtained by the array sizing method.
Creativity profile of university and conservatory dance students.
What are dance students' creative potential, Special personality characteristics and preferences for high energy activities? Using standardized and original paper and pencil instruments, comparisons were made among dance students in university and conservatory settings, college students and art students. The results demonstrated that dance students are creative, show strong preference for dynamic figures, and have distinct personality characteristics. The university dance students differed from the conservatory students in several important ways.