Infinite Dilution Binary Diffusion Coefficients of Benzene in Carbon Dioxide by the Taylor Dispersion Technique at Temperatures from 308.15 to 328.15 K and Pressures from 6 to 30 MPa

Infinite dilution binary diffusion coefficients, D ₁₂, of benzene in carbon dioxide were measured by the Taylor dispersion technique at temperatures from 308.15 to 328.15 K and pressures from 6 to 30 MPa. The diffusion coefficients were obtained by the method of fitting in the time domain from the response curves measured with a UV–vis multidetector by scanning from 220 to 280 nm at increments of 1 or 4 nm. The wavelength dependences on the binary diffusion coefficient and the uncertainty were examined. The detector linearity, in terms of the relationship between the absorbance intensity and the product of the peak area of the response curve and CO₂ velocity, was found to fail at some characteristic absorption wavelengths such as 243, 248, 253, and 259 nm, even when the maximum absorbance intensities of the response curves were less than 0.5 and the fits were good. Although the D ₁₂ values obtained from the response curves measured at 253 nm were almost consistent with some literature data, the D ₁₂ values measured at wavelengths showing the detector linearity to be satisfactory, i.e., at 239 nm, were higher than those at 253 nm. The present D ₁₂ data at 239 nm were well represented by the Schmidt number correlation, except for those showing the anomalous decrease in a plot of D ₁₂ vs density in the density range from 250 to 500 kg·m^–3.     

High-Precision Determination of the Neutron Coherent Scattering Length

The neutron coherent scattering length b_c has been determined interferometrically to an uncertainty of about 5 × 10⁻⁵ by measuring the nondispersive phase. We propose improving the uncertainty to about 10⁻⁶ by optimizing various parameters of the interferometric experiment. Any uncertainty in the b_c determination arising from possible variations in the constitution of the ambient air can be eliminated by performing the experiment in vacuum. When such uncertainty is attained, it becomes necessary to account for the neutron beam refraction at the sample-ambient interfaces, to infer the correct b_c from the observed phase. The formula for the phase used hitherto is approximate and would significantly overestimate b_c. The refractive index for neutrons can thus be determined to a phenomenal uncertainty of about 10⁻¹².     

Development of a Laser Interferometric Dilatometer for Measurements of Thermal Expansion of Solids in the Temperature Range 300 to 1300 K

A laser interferometric dilatometer has been developed for measuring linear thermal expansion coefficients of reference materials for thermal expansion in the temperature range 300 to 1300 K. The dilatometer is based on an optical heterodyne interferometer capable of measuring length change with an uncertainty of 0.6 nm. Linear thermal expansion coefficients of silicon were measured in the temperature range 700 to 1100 K. The performance of the present dilatometer was tested by a comparison between the present data and the data measured with the previous version of the present dilatometer and the data recommended by the Committee on Data for Science and Technology (CODATA). The present data agree well with the recommended values over all the temperature range measured. On the other hand, the present values at lower temperatures are in poor agreement with the previous experimental data. The combined standard uncertainty in the present value at 900 K is estimated to be 1.1×10^–8 K^–1.     

Design and Uncertainty Analysis for a PVTt Gas Flow Standard

A new pressure, volume, temperature, and, time (PVTt) primary gas flow standard at the National Institute of Standards and Technology has an expanded uncertainty (k = 2) of between 0.02 % and 0.05 %. The standard spans the flow range of 1 L/min to 2000 L/min using two collection tanks and two diverter valve systems. The standard measures flow by collecting gas in a tank of known volume during a measured time interval. We describe the significant and novel features of the standard and analyze its uncertainty. The gas collection tanks have a small diameter and are immersed in a uniform, stable, thermostatted water bath. The collected gas achieves thermal equilibrium rapidly and the uncertainty of the average gas temperature is only 7 mK (22 × 10⁻⁶ T). A novel operating method leads to essentially zero mass change in and very low uncertainty contributions from the inventory volume. Gravimetric and volume expansion techniques were used to determine the tank and the inventory volumes. Gravimetric determinations of collection tank volume made with nitrogen and argon agree with a standard deviation of 16 × 10⁻⁶ V_T. The largest source of uncertainty in the flow measurement is drift of the pressure sensor over time, which contributes relative standard uncertainty of 60 × 10⁻⁶ to the determinations of the volumes of the collection tanks and to the flow measurements. Throughout the range 3 L/min to 110 L/min, flows were measured independently using the 34 L and the 677 L collection systems, and the two systems agreed within a relative difference of 150 × 10⁻⁶. Double diversions were used to evaluate the 677 L system over a range of 300 L/min to 1600 L/min, and the relative differences between single and double diversions were less than 75 × 10⁻⁶.     

Isochoric Heat Capacity Measurements for Light and Heavy Water Near the Critical Point

The isochoric heat capacity was measured for D₂O at a fixed density of 356.075 kg·m^–3 and for H₂O at 309.905 kg·m^–3. The measurements cover the range of temperatures from 623 to 661 K. The measurements were made with a high-temperature, high-pressure, adiabatic calorimeter with a nearly constant inner volume. The uncertainty of the temperature is 10 mK, while the uncertainty of the heat capacity is estimated to be 2 to 3%. Measurements were made in both the two-phase and the one-phase regions. The calorimeter instrumentation also enables measurements of PVT and the temperature derivative (P/T)_V along each measured isochore. A detailed discussion is presented on the experimental temperature behavior of C_V in the one- and two-phase regions, including the coexistence curve near the critical point. A quasi-static thermogram method was applied to determine values of temperature at saturation T_S() on measured isochores. The uncertainty of the phase-transition temperature measurements is about ±0.02 K. The measured C_V data for D₂O and H₂O are compared with values predicted from a recent developed parametric crossover equation of state and IAPWS-95 formulation.     

Refractometer for tracking changes in the refractive index of air near 780 nm

A new system, consisting of a double-channel Fabry-Perot etalon and laser diodes emitting around 780 nm, is described and proposed for use for measuring air-refractive index. The principle of this refractometer is based on frequency measurements between optical laser sources. It permits quasi-instantaneous measurement with a resolution of better than 10(-9) and uncertainty in the 10(-8) range. Some preliminary results on the stability of this system and the measurements of the refractive index of air with this apparatus are presented. The first measurements of the index of air at 780 nm are, within an experimental uncertainty of the order of 2 x 10(-8), in agreement with the predicted values by the so-called revised Edlén equations. This result is, to the best of our knowledge, the first to extend to the near IR the validity of the revised Edlén equation derived for the wavelength range of 350-650 nm.     

Photosensitivity in GeO2–SiO2 glasses and optical waveguides

Permanent refractive index changes caused by a KrF excimer laser operating at 248 nm in GeO₂–SiO₂ glasses deposited on Si (100) substrates using flame hydrolysis deposition (FHD) are presented. The sample was amorphouslike investigated by X-ray diffraction (XRD), and the ratio of Ge:Si is 14:86 from X-ray photoelectron spectroscopy (XPS) analysis. The 10-min irradiation with a KrF excimer laser (10 Hz, 187 mJ/cm²) induced a positive refractive index change of 0.341% at 1550 nm, which has achieved an international level of this field. An innovative photomask with a Cr-loaded structure coated on a UV quartz glass, was used to fabricate a 50 μm gap with a period of 100 μm waveguide grating under 1460 mJ/cm²/pulse at 6 Hz, and the diffraction patterns were observed clearly. The extinction coefficients of the samples are also measured over the range 250–1600 nm.     

4He Thermophysical Properties: New Ab Initio Calculations

Since 2000, atomic physicists have reduced the uncertainty of the helium-helium “ab initio” potential; for example, from approximately 0.6 % to 0.1 % at 4 bohr, and from 0.8 % to 0.1 % at 5.6 bohr. These results led us to: (1) construct a new inter-atomic potential ϕ₀₇, (2) recalculate values of the second virial coefficient, the viscosity, and the thermal conductivity of ⁴He from 1 K to 10,000 K, and (3), analyze the uncertainties of the thermophysical properties that propagate from the uncertainty of ϕ₀₇ and from the Born-Oppenheimer approximation of the electron-nucleon quantum mechanical system. We correct minor errors in a previous publication [J. J. Hurly and M. R. Moldover, J. Res. Nat. Inst. Standards Technol. 105, 667 (2000)] and compare our results with selected data published after 2000. The ab initio results tabulated here can serve as standards for the measurement of thermophysical properties.     

Thermal-Conductivity Apparatus for Steady-State,Comparative Measurement of Ceramic Coatings

An apparatus has been developed to measure the thermal conductivity of ceramic coatings. Since the method uses an infrared microscope for temperature measurement, coatings as thin as 20 μm can, in principle, be measured using this technique. This steady-state, comparative measurement method uses the known thermal conductivity of the substrate material as the reference material for heat-flow measurement. The experimental method is validated by measuring a plasma-sprayed coating that has been previously measured using an absolute, steady-state measurement method. The new measurement method has a relative standard uncertainty of about 10 %. The measurement of the plasma-sprayed coating gives 0.58 W·m⁻¹·K^−l which compares well with the 0.62 W·m⁻¹·K^−l measured using the absolute method.     

Laser direct writing of tin oxide patterns

Tin oxide pattern generation by laser deposition from SnCl₄ · 5H₂O in isopropanol is reported. Smooth, even stripes of thicknesses ranging from 20 to 120 nm with sharp, well defined edges and cross-section are deposited by scanning Ar⁺ laser beam (λ = 514.5 nm) focused onto the substrate—solution interface with a constant speed of 1 mm s⁻¹. The linewidth linearly increases from 26 to 42 μm with increasing the power from 40 to 120 mW. The reproducibility of pattern generation is extremely good as revealed by SEM-EDXI and μRBS. The minimum DC resistivity of 1.7×10⁻² Ωcm, measured without any process optimization, favourably compares with those reported for films prepared by other techniques. The chemical composition of the film material is SnO_x with 1.1 < x < 1.5 as determined by an XPS-XAES study.     

Investigation of Doped Inert Gas Solids for Cryogenic Lasers

Inert gas polycrystalline samples containing about 0.05–0.5% of dopants such as neutral excimers XeF, KrF, NeF, and ionic excimers Rb²⁺F^–, Cs²⁺F^–, Cs²⁺Cl^–, and also molecules CO-Hg, NO, N₂O and ¹³CO₂ are considered as active media for cryogenic lasers emitting in a broad wavelength range from VUV through VIS into far IR. A correlation between the values of the oscillator strength f in the range of 0.4–10^–6, the cross section for stimulated emission between 10^–15–10^–17 cm² and the pump energy density at laser threshold (10^–3–10^–2 J/cm³) confirms the lasing potential of the systems XeF/Ar (B-X, 411 nm) and of those emitting in IR in agreement with experiment. For the deep UV and VUV transitions B-X of alkalihalides in solid Ne (196.5 nm, 220.1 nm, 136 nm) high pumping thresholds are derived despite of high f values because of large line width.     

Antireflecting coating from Ta<Subscript>2</Subscript>O<Subscript>5</Subscript> and SiO<Subscript>2</Subscript> multilayer films

Sol-gel method is important for depositing antireflective coating that allows control over thickness as well as the index of refraction. Antireflective coatings which are produced from Ta₂O₅ and SiO₂ multi-layer thin films using sol-gel spin coating method are presented. The refractive index and the thickness are controlled by the composition and the concentration of the solution respectively. The thickness, refractive index and extinction coefficient of the films were calculated through transmission and reflection measurement by an NKD analyser. Mechanical properties of the films were checked by the cross tape test and dry sun test at 760 W/m². The result shows that the sample heat treated at 450^∘C for 15 min approaches a reflectance with less than 0.5% at around 840 nm.     

Fluorescence and nonlinear optical properties of non-aggregating hexadeca-substituted phthalocyanine

Highly non-aggregating hexadeca-substituted phthalocyanine (Pc) complexes were prepared and their fluorescence and nonlinear optical properties were studied. Three visible fluorescence bands were observed when the Pc complexes were excited at 355 nm and found to be concentration dependent. They are attributed to the optical transitions S₂ → S₀ at 415 nm, T₂ → T₁ at 630 nm, and S₂ → S₁ at 755 nm. Nonlinear absorptive and refractive effects were measured with the help of Z-scan technique. Saturation absorption was observed at 632.8 nm where the nonlinear absorption coefficient is found to be very large (β = −2.8 × 10⁻² cm/W) and the refractive nonlinear coefficient γ = −9.5 × 10⁻¹¹ cm²/W. In the transparency domain at 532 nm, reverse absorption saturation is observed and β and γ are found to be 17.5 and 15.5 times smaller, respectively. Optical limiting performances are measured in the absorption and transparency domains. Purely refractive-based optical limiting at 632.8 nm is found to have a threshold of 0.16 kW/cm², lower than the reverse absorption saturation and refractive-based optical limiting of 0.90 kW/cm² at 532 nm.     

Can a Pressure Standard be Based on Capacitance Measurements?

We consider the feasibility of basing a pressure standard on measurements of the dielectric constant ϵ and the thermodynamic temperature T of helium near 0 °C. The pressure p of the helium would be calculated from fundamental constants, quantum mechanics, and statistical mechanics. At present, the relative standard uncertainty of the pressure u_r(p) would exceed 20 × 10⁻⁶, the relative uncertainty of the value of the molar polarizability of helium A_ϵ calculated ab initio. If the relativistic corrections to A_ϵ were calculated as accurately as the classical value is now known, a capacitance-based pressure standard might attain u_r(p) < 6 × 10⁻⁶ for pressures near 1 MPa, a result of considerable interest for pressure metrology. One obtains p by eliminating the density from the virial expansions for p and ϵ − 1. If ϵ − 1 were measured with a very stable, 0.5 pF toroidal cross capacitor, the small capacitance and the small values of ϵ − 1 would require state-of-the-art capacitance measurements to achieve a useful pressure standard.     

Spectral analysis of RE (RE = Sm, Dy, and Tm): P2O5–Al2O3–Na2O glasses

Phosphate glasses in the compositions of 70P₂O₅–15Al₂O₃–14Na₂O–1RE³⁺ (RE = Sm, Dy, and Tm) (mol%) were prepared by melt-quenching technique and characterized optically. The differential thermal analysis (DTA) profile of the host glass was carried out to confirm its thermal stability. For all the glasses absorption, photoluminescence and decay measurements have also been carried out. These glasses have shown strong emission and absorption bands in visible and near-infrared (NIR) region. From the measured absorption spectra, Judd–Ofelt (J–O) intensity parameters (Ω₂, Ω₄ and Ω₆) have been calculated for all the studied ions. For Sm³⁺ doped glass, four emission bands centered at 562 nm (⁴G_5/2 → ⁶H_5/2), 598 nm (⁴G_5/2 → ⁶H_7/2), 644 nm (⁴G_5/2 → ⁶H_9/2), and 704 nm (⁴G_5/2 → ⁶H_11/2) have been observed with 402 nm (⁶H_5/2 → ⁴F_7/2) excitation wavelength. Of them, 598 nm (⁴G_5/2 → ⁶H_7/2) has shown a bright orange emission. With regard to Dy³⁺ doped glass, a blue emission band centered at 486 nm (⁴F_9/2 → ⁶H_15/2) and a bright yellow emission at 575 nm (⁴F_9/2 → ⁶H_13/2) have been observed, apart from 662 nm (⁴F_9/2 → ⁶H_11/2) emission transition with an excitation at 388 nm (⁶H_15/2 → ⁴I_13/2,⁴F_7/2) wavelength. Emission bands of 650 nm (¹G₄ → ³F₄) and 785 nm (¹G₄ → ³H₅) transitions for the Tm³⁺ doped glass, with an excitation wavelength at 466 nm (³H₆ → ¹G₄), have also been observed. The stimulated emission cross-sections of all the emission bands of RE³⁺ glasses (RE = Sm, Dy, and Tm) have been computed based on their measured full-width at half maximum (FWHM, Δλ) and measured lifetimes (τ_m).     

Extraction of water from alkali germanosilicate glasses for optical fibres

A study is reported on the extraction of water from alkali germanosilicate glasses, used for making graded index optical fibres. It is shown that the extraction rate is largely determined by the gas-glass melt interface created during the bubbling of dried O₂ through the melt. Both increased gas stream rates and the use of O₂, containing D₂O, resulted in a significant decrease in water concentration in the glass, thereby reducing the loss of the optical fibres produced from these glasses, e.g. a decrease at 850 nm from 15 to 10 dB km^–1, at 1100 nm from 28 to 10 dB km^–1.     

Related surface and heat of immersion characterization of some alumina samples

MnCl₂- and CuCl₂-loaded aluminas were thermally treatedin vacuo in the temperature range 20–500 °C. The water loss, specific surface area from nitrogen adsorption measurements and the integral heat of immersion in water were determined for all the samples. The high-pressure hysteresis loop displayed in the adsorption isotherms, together with the limited increase in adsorption values near saturation indicate the dominance of mesopores in the tested samples, as also detected by theV _a -t method of isotherm analysis. Changes in the slope ofV _a -t plots suggests that the mesopores rather belong to narrow-ranged mesopore sizes, which are thus considered responsible for adsorption in thet-ranges of 0.5–0.7 and above 0.7 nm. The constancy ofV _a(mlg^–1) values abovet=1.2 nm points out the absence of effective capillary condensation in the high relative pressure region. Variations of BET-surface area and the reciprocal of average pore radius, ¯r^–1 (nm^–1), as functions of the heat-treatment temperature indicate that MnCl₂-loaded samples display a higher thermal stability than CuCl₂-loaded samples; the latter exhibit some aggregation cementation behaviour. At temperatures below 300 °C, the heat of immersion data are not as predicted from changes in water loss and surface-area parameters. Thus, MnCl₂-loaded samples display lower heat of immersion values than the respective CuCl₂-loaded samples, despite the higher BET areas of the former samples; an effect which may be tentatively interpreted in terms of the capability of the smaller sized Mn²⁺ ions to preserve more water molecules via such processes as complex formation, ion hydration and crystallization, which contribute to lowering the integral heat measured. This apparent discrepancy in the behaviour of integral heat of immersion (Jg^–1) data with water loss (gg^–1) at temperatures below 300°C is clarified by considering the change in the heat of immersion per unit area,h _i (J m^–2) with the temperature of treatment.     

High-Pressure Measurements of the Viscosity and Density of Two Polyethers and Two Dialkyl Carbonates

The viscosity and density of four pure liquid compounds (dimethyl carbonate, diethyl carbonate, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether) were measured at several temperatures between 283.15 and 353.15 K. The density measurements were performed up to 60 MPa with an uncertainty of 1×10^–4g·cm^–3. The viscosity at atmospheric pressure was measured with an Ubbelohde-type glass capillary tube viscometer with an uncertainty of ±1%. At pressures up to 100 MPa the viscosity was determined with a falling ball viscometer with an uncertainty of ±2%. The density (410 experimental values) and viscosity data (184 experimental values) were fitted to several correlation equations.     

Dew Point, Liquid Volume, and Dielectric Constant Measurements in a Vapor Mixture of Methane + Propane Using a Microwave Apparatus

An apparatus based on a microwave resonant cavity has been used to measure dew points and liquid volume fractions in a zC₃H₈+(1–z)CH₄ mixture with z=0.250±0.001 mole fraction. The microwave cavity is optimized for the measurement of small liquid volume fractions in lean natural gases. Argon and carbon dioxide were used to calibrate the resonator for dielectric constant and liquid volume measurements in mixtures. Estimated uncertainties are 1×10^–4 for dielectric constants and (0.05 K, 0.05 MPa) for dew points. The novel use of multiple cavity modes, each sensitive to different liquid volume regimes, substantially improves the reliability of liquid volume measurements. Liquid volume fractions can be resolved to better than 0.01%. Densities inferred from (P,T,) measurements agree within 0.6% of equation of state (EOS) densities with an estimated uncertainty of 0.1%. Liquid volume fractions measured with the microwave apparatus compare well with values determined using a conventional PVT cell. Fourteen dew points were measured at ten different temperatures. From these data, the mixture cricondentherm is estimated to be (293.45±0.05) K, which is 0.15 K higher than the value predicted using the Peng–Robinson equation of state.