Journal of research of the National Bureau of Standards (1977)最新文献

The densities of four silicon artifacts were measured in SI units to 1 × 10^-6 by NML (Australia) and NBS (U.S.). Agreement is within the experimental uncertainty of each laboratory. Two of the artifacts had been used in the determination of the Avogadro constant at NBS. The remaining two objects had been used at NBS to establish silicon density artifacts available as a Standard Reference Material (SRM).

This paper describes a high precision electronic mass comparator with a range from 250 kg to 5,000 kg. It is suggested that it would be useful to transport the comparator to the test weights rather than to transport the weights to the comparator, the usual method, thus economizing time and monies.

While it is generally assumed that the use of microcomputers helps to improve productivity in an office environment, quantitative measures in this area are lacking. This paper addresses the measurement of the effect on productivity in an end user, office environment as a result of the introduction of micromputer-based technology. It is concerned with defining how productivity can be measured in such an environment and with current efforts to measure changes in productivity. It identifies and assesses the various techniques and measures used to describe the magnitude of productivity improvements that result from the use of microcomputers in the workplace, and makes recommendations for ways in which changes in productivity, may be measured.

The U.S. national prototype kilogram, K20, and its check standard, K4, were recalibrated at the Bureau International des Poids et Mesures (BIPM). Both these kilograms are made of platinum-iridium alloy. Two additional kilograms, made of different alloys of stainless steel, were also included in the calibrations. The mass of K20 in 1889 was certified as being 1 kg-0.039 mg. Prior to the work reported below, K20 was most recently recalibrated at the BIPM in 1948 and certified as having a mass of 1 kg-0.019 mg. K4 had never been recalibrated. Its initial certification in 1889 stated its mass as 1 kg-0.075 mg. The work reported below establishes the new mass value of K20 as 1 kg-0.022 mg and that of K4 as 1 kg-0.106 mg. The new results are discussed in detail and an attempt is made to assess the long-term stability of the standards involved with a view toward assigning a realistic uncertainty to the measurements.

To obtain reliable thermodynamic data on substituted triazines, it is necessary to use a calorimeter that is capable of high precision with small quantities of sample and in which a homogeneous solution of the corrosive combustion products can be maintained. The enthalpies of combustion of six substituted triazines have been determined in a platinum-lined adiabatic rotating bomb calorimeter. These are the first determinations of enthalpies of combustion or formation to have been reported for these compounds. The values derived for the enthalpies of formation in kJ/mol at 25 °C are as Follows: 2,4,6-trimethoxy-l,3,5-triazine, - 478.60± 0.87; 2,4,6-triethozy- 1,3,5-triazine, - 584.99± 1.50; 2,4,6-tris(2-fluoro-2,2-dinitroethoxy)-l,3,5-triazine, -1109.80±l.53; 2,4-dimethoxy-6-(2-fluoro-2,2-dimtroethoxy)-l,3,5-triazine, -697.08± 1,15; 2-methoxy- 4,6-bis(2-fluoro-2,2-dinitroethoxy)-l,3,5-triazine, -907.71± 2.40; 2-amino-4,6-bis(2-fluoro-2,2-dinitroethoxy)-l,3,5-triazine, - 773-12±1.50.

This short note describes an apparatus that has been designed and constructed to allow assessment of the extent of chemical decomposition of fluids and fluid mixtures under high temperature, high pressure conditions. The apparatus is used to screen fluid systems prior to PVT (pressure-volume-temperature) or VLE (vapor-liquid equilibrium) experiments under severe conditions. For a predetermined residence time, the fluids are maintained at the temperature and pressure at which the PVT or VLE experiment will be conducted. The residence time in the reactor is comparable to the expected residence time in the PVT or VLE apparatus. Samples of fluid are withdrawn directly at regular intervals for analysis by gas chromatography, or collected In a sampling vessel for more extensive analysis.

The most abundant, long-lived stable gaseous species generated by corona discharges in SF₆ gas containing trace levels of O₂ and H₂O are the oxyfluorides SOF₂, SO₂F₂, and SOF₄. Absolute energy and charge rates-of-production of these and the minor products SO₂, OCS, and CO₂ have been measured at different total gas pressures from 100 kPa to 300 kPa and for discharges of different current, power, and polarity. Oxyfluoride yields for SF₆/O₂ mixtures containing up to 10% O₂ have also been measured. The results indicate that oxyfluoride production is not controlled by the concentrations of either O₂ or H₂O at levels below about 1%, and the rate controlling factor is the dissociation rate of SF₆ in the discharge. The discharge current and time dependence of the production rates are discussed in terms of gas-phase mechanisms that have been proposed to explain previous observations of electrical, thermal, and laser-induced decomposition of SF₆ and SF₆/O₂ mixtures. Upper limits on the total SF₆ decomposition rate in low-current discharges have been estimated. Details of the chemical analysis procedures are given, and application of the results to the design of chemical diagnostics for SF₆-insulated, high-voltage apparatus is discussed.