In order to determine the Avogadro constant by the x-ray crystal density method, the molar volume of silicon in a single crystal grown by the float-zone method was determined by absolute measurements of the density and the molar mass of the crystal. The density was directly determined by mass and volume measurements of 1 kg spheres fabricated from the crystal. For the volume determination, a scanning-type optical interferometer was developed to measure the diameters of the spheres. The molar mass measurements were calibrated using synthetic isotope mixtures prepared from enriched silicon isotopes. Two spheres for density measurements, and fourteen samples for molar mass measurements, were systematically prepared from the crystal to evaluate distributions of the density and the isotopic composition of the crystal. The results give a molar volume of 12.058 8646 cm 3 /mol with a standard uncertainty of 0.000 0026 cm 3 /mol, at 22.500 C and 0 Pa after correction for impurities. When this value is combined with the lattice constant of the crystal determined using a combined x-ray/optical interferometer, a value of 6.022 1550 10 23 mol -1 with a standard uncertainty of 0.000 0016 10 23 mol -1 is obtained for the Avogadro constant. Recent data on the absolute measurement of the lattice constant by combined x-ray/optical interferometers have shown a consistent result within the measurement uncertainties [5] when the observed values are corrected for impurity effects. Relative differences
Triboemission is defined as the emission of electrons, ions, photons and neutral particles during tribological surface damage. Triboemission of negatively and positively charged particles and photons by the wearing of solid surfaces of metals, ceramics, glass, anodic aluminium oxide films (Al2O3), polymers and mica were studied using a special triboemission measuring apparatus which permits the simultaneous measurement of negatively and positively charged particles, photons and friction coefficients in a vacuum and in various atmospheres. The emission characteristics of the triboemission depended on the type of solid. Both charged particles and photons were emitted simultaneously in bursts during the scratching of the solid surfaces of semiconductors and insulators. In contrast, no photon emission was observed using conductors. With conductors and semiconductors, the particles emitted were mainly negatively charged particles, while with insulators both negatively and positively charged particles were emitted at the same level but with a slightly higher intensity of negative particles in air. The emission of the charged particles and the photons increased at higher loads and speeds as well as at greater thickness of Al2O3 films. The charge intensity from the insulators decreased with higher Vickers hardnesses. The intensity of the negatively and the positively charged particles was well correlated with that of photons. The mechanism of triboemission is discussed.
It has been hypothesized that plasma is generated at a sliding contact.
However, it has not yet been found.
Here, we report on a discovery of plasma generated in the
microscopic gap around a sliding contact, having an elliptical shape with a
horseshoe pattern and with a size beyond a hundred micrometers. It emits
mostly invisible ultraviolet (UV) photons and, to a lesser extent, infrared
(IR) photons. It must be a main source of the curious tribophysical and
chemical phenomena. The origin, characteristics and the relation to these
curious phenomena are discussed.
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