Showing papers in "Journal of Research of the National Bureau of Standards Section A: Physics and Chemistry in 1974"

PVT Relationships for Liquid and Glassy Poly(vinyl acetate).

Abstract: PVT measurements were made on liquid and glassy poly(vinyl acetate) over ranges of -30 to 100 °C and 0 to 800 bar (gage pressure). The data were obtained by three different thermodynamic histories: (a) variable formation pressure, (b) constant formation pressure at one atmosphere, and (c) constant formation pressure at 800 bar. In all of these the glass was formed by isobaric cooling at 5 °C/h. The salient characteristics resulting from the different histories are the following. History (a) produces a glass of structure varying with formation pressure and, hence, does not necessarily give the proper thermodynamic properties of a "single physical substance." However, the liquid-glass intersection temperature, Tg (P), is an important kinetic, or relaxational, property which approximates an isoviscous state. Accordingly, the values of dTg /dP are in close agreement with those obtained from dynamic mechanical and dielectric time-temperature-pressure superposition. Constant formation histories (b) and (c) give proper thermodynamic properties of the glasses, but very little information with respect to kinetics. Increasing the pressure at which the glass is formed increases the density of the glass (at the given cooling rate) considerably in contrast to the entropy (from other work), which appears to be essentially independent of formation pressure. A considerable part of the paper is definitional. The results are related to other PVT, dynamic mechanical, dielectric, and thermodynamic measurements. Interpretations are given in terms of both phenomenological and molecular models.

Correction and Extension of van der Poel's Method for Calculating the Shear Modulus of a Particulate Composite.

Abstract: Van der Poel's method (Rheol. Acta 1, 198 (1958)) for calculating the shear modulus of a particulate composite agrees well with experimental data, but its validity has been questioned, and it was applicable only to composites in which the matrix material is incompressible. These limitations are removed in this paper in which an error in the original derivation is corrected, and the method generalized to apply to any matrix material. Calculations using the corrected theory show that despite the error, a table of shear modulus values published with the original theory is sufficiently correct for most practical purposes. Applicability of the generalized method to the large class of composites having compressible matrices is discussed. Shear moduli calculated by the corrected and extended method are compared with corresponding values calculated by other methods currently used.

A Heat-Loss-Compensated Calorimeter: Theory, Design, and Performance.

Abstract: A new type of 3-body calorimeter for measuring absorbed dose produced by ionizing radiation is described in detail. All three bodies rise in temperature during irradiation, and the heat absorbed by the central core is measured by standard means. Only the central core is heated during electrical calibration, but the increased heat losses are compensated by measuring most of the heat lost to the surrounding jacket and automatically adding it to the heat retained by the core. The third body is a massive, thermally-floating shield, whose presence reduces the heat losses during irradiation, with a consequent increase in sensitivity and stability. A mathematical description of the calorimeter behavior is presented, along with a discussion of control and operation technique. In particular, it is shown how this 3-body calorimeter can be calibrated as a 1-body calorimeter, with large heat losses, or as a 2-body calorimeter, in the quasi-adiabatic mode. This calorimeter design decreases the effects of thermal gradients and at the same time provides the means to test for these effects. The results of these tests show that for this particular model, systematic errors caused by thermal gradients, during electrical measurements, are no larger than 0.1 percent. Errors in comparing an electrical run with an irradiation may be somewhat larger because of different temperature gradients within the system. It is also pointed out that the general design of this calorimeter is not restricted to measuring absorbed dose but can be applied to calorimetry in general.

A Density Scale Based on Solid Objects.

Abstract: We have determined the density of four pieces of single crystal silicon in terms of universally accepted standards of mass and length. These four objects will be used as a working density standard to which all future density work in the United States will be referred. Using these crystals as standards, NBS can calibrate other objects as density standards for associated laboratories. The work was accomplished with the assistance of an interferometer, developed especially for the task, which measures the diameter of commercially available steel balls. From measured diameters ball volumes are calculated. The volumetric information contained in the balls is transferred to the silicon crystals in a newly designed hydrostatic weighing experiment. We have made three independent density determinations on each of the four crystals, and the presently accepted values of the density of each crystal is the average of the three determinations. The random component of uncertainty (3 standard deviations) of these four averages is 0.7 ppm. The systematic error is estimated to be about 0.7 ppm.

Standardization of 60Co and 137Cs Gamma-Ray Beams in Terms of Exposure.

Abstract: At the National Bureau of Standards (NBS), the exposure-rate standards for 60Co and 137Cs gamma rays were based for a number of years on a weighted average of measurements using a cylindrical ionization chamber and a group of small spherical chambers. Complex setup conditions for the cylindrical chamber, differences between the cylindrical and spherical chamber data, and recognition that the institution of this weighted average exposure-rate standard increased the difference between free-air-chamber and cavily-chamber measurements, led to the development of new spherical chambers. All correction factors for exposure-rate measurements were investigated and updated. Excellent agreement was achieved between independent exposure-rate measurements for six spherical chambers and, as of May 1, 1972, the exposure standards were reduced 0.7 percent for 60Co and 0.6 percent for 137Cs gamma rays. Recalculation of correction factors since that time indicates that the standard 137Cs should be further reduced by 0.2 percent, and this adjustment was made on July 1, 1974. The uncertainties associated with each of the quantities entering into the determination of exposure rate were tabulated and the overall uncertainty of the exposure rates used for instrument calibrations at NBS was found to be about 0.7 percent for addition in quadrature.

A Method of Measuring the Solubilities of Hydrocarbons in Aqueous Solutions.

Abstract: An apparatus is described which measures the equilibrium distribution of a hydrocarbon between a gas phase and a liquid water phase. The method involves a multiple equilibration procedure which requires the analysis of only the gas phase. Gas-liquid chromatography was used for the hydrocarbon analysis because of its high sensitivity and selectivity. Supplemented by vapor pressure data, the observed distribution can be used to calculate the solubility of the hydrocarbon in the liquid phase. This was done for benzene, toluene, and ethylbenzene in distilled water over the temperature range 5 to 20 °C and in an artificial seawater over the temperature range 0 to 20 °C. The various factors affecting the accuracy of the results are discussed in detail.

Geometrical Considerations in the Measurement of the Volume of an Approximate Sphere.

Abstract: Expressions are derived for the volume of an approximate sphere in terms of measured breadth, the distance between parallel planes tangent to opposite sides. The difference in volume of a ball and a true sphere of the same average breadth is shown to be of second order, and much smaller than the random and systematic errors in the measurements of the dimension. Thus, a ball commercially available at moderate cost can be used for absolute density measurements of high accuracy. Similar expressions are given for the area of an approximate circle.

Solubility of CaHPO4 · 2H2O in the Quaternary System Ca(OH)2 - H3PO4 - NaCl - H2O at 25 °C.

Abstract: Solubility of CaHPO4 · 2H2O was determined in the quaternary system Ca(OH)2 - H3PO4 - NaCl - H2O at 25 °C in the pH range 4.39-6.38; ionic strengths of the saturated solutions varied from 0.00485 to 0.545, Satisfactory constancy in the solubility product, ( Ksp=[Ca2+]⋅[HPO42-]⋅γCa2+⋅γHPO42-=2.49±0.05×10-7 mol2×1-2 ) was obtained when (i) the ion activity coefficients, γi , were calculated with the Debye-Huckel equation, log γi=-AZi2I/(1+BαiI)+0.0626 I ; the value 0.0626 for the coefficient in the linear term was derived from the solubility data by utilizing a statistical procedure, and (ii) formation of an ion pair NaHPO4- was taken into account; a statistically derived value for the stability constant of this ion pair is 7.0 ± 2.4 1 × mol-1. The ion pair NaHPO4- appears to have significant concentrations in physiological fluids.

Solid-Phase Behavior of Several Long-Chain n-Paraffins, Esters, and a Ketone.

Abstract: The long-spacings of the compounds methyl stearate, ethyl stearate, n-butyl stearate, 2-non-adecanone, n-eicosane, n-hexatriacontane and n-tetratetracontane have been examined as a function of temperature by means of low-angle x-ray diffraction. The intensity of the long-spacing was also determined versus temperature. The effect of annealing temperature and time was examined by means of the DSC. Dielectric loss was studied in two crystalline phases of n-butyl stearate.

The specific heats, Cs, and Cv, of compressed and liquefied methane

Abstract: The specific heats, Cσ , of saturated liquid methane have been measured at 66 temperatures in the temperature range 95-187 K. The specific heats at constant volume, CV , have been measured at 20 densities ranging from 0.8 to 2.8 times the critical density, at temperatures between 91 and 300 K, and at pressures to 330 bar (at 280 PVT states in all). The uncertainty of most of the measurements is estimated to be less than 0.5 percent, except near the critical point. These measurements were performed primarily to provide input data for accurate thermodynamic properties data calculations for liquid methane. They are believed to be the most comprehensive specific heat measurements available for pure compressed gaseous and liquid methane.

Heat Capacities of Polyethylene from 2 to 360 K. II. Two High Density Linear Polyethylene Samples and Thermodynamic Properties of Crystalline Linear Polyethylene.

Abstract: Heat capacities of two high density linear polyethylene samples were measured from 2 to 360 K. By incorporating the results from the previous work of this series, thermodynamic properties of completely crystalline linear polyethylene may be estimated. Cp , H - H0, S and - (G - H0) at 298.15 K for crystalline linear polyethylene are estimated to be 22.60 J K-1 mol-1, 3544 J mol-1, 23.02 J K-1 mol-1 and 3319 J mol-1, respectively. Spontaneous adiabatic temperature drifts were observed in both samples near 240 K. These drifts may be attributed to the enthalpy relaxation phenomena occurring in the glass transformation region.

Theoretical Analysis of Miscibility Gaps in the Alkali-Borates

Abstract: A thermodynamic approach based on the regular solution concept is applied to the description of miscibility gap boundaries in the alkali-borate systems. It is suggested that in each system the structural units which control the entropy of mixing are the stoichiometric compounds at the apparent limit of the alkali-rich edge of the gap, and a complex boron trioxide structure. (The former is inferred by the shape of the gap, and the latter is chosen to fit the regular mixing equation.) The same boron trioxide complex is used for all the systems analyzed. The physical implications of this analysis are discussed.

Analysis of Low Temperature Viscosity Data for Three NBS Standard Glasses.

Abstract: The low temperature viscosities of three glasses established as viscosity standards at the National Bureau of Standards are reported. The data overlap results which appear on the published certificates between 109 and 1012 poise and present extensive measurements up to 1016 poise. The measurements were made using both the fiber-elongation and beam-bending methods. No evidence of an Arrhenius behavior was found for any of the three glasses, even though the measurements covered a narrow range of temperatures. An analysis of the inherent measurement uncertainty associated with each method indicates that the fiber-elongation measurements are more precise than the beam-bending measurements. Analysis of the data and its uncertainty by the Fulcher Equation supports the conclusions of the error analysis.

The Formation of Curved Polymer Crystals: Polyoxymethylene.

Abstract: An optical and electron microscopical study is presented of the habits exhibited by chain-folded polyoxymethylene crystals grown from hot 0.02 percent solutions of the polymer in orthodichlorobenzene when these solutions are cooled to temperatures (Tc ) between 140 and 80 °C inclusive. In contrast with the lamellar crystals formed in the Tc = 140 and 120 °C preparations, which crystals were six-sectored and nearly planar, the crystals formed below Tc = 120 °C exhibited multisectored dendritic habits and were all the more pronouncedly curved the lower the temperature at which they grew. The most pronouncedly curved crystals which were observed were hollow bowl shaped dendrites having a radius of curvature of ~ 2 μm which were formed in the 80 °C preparations. The possible origins of why the lamellar crystals of polyoxymethylene were all the more pronouncedly curved the lower the crystallization temperature are considered in the light of conjectures which have been previously advanced concerning the formation of curved crystals of poly(4-methylpentene-1). Among the features which are discussed is the role played by the bulkiness of the chain folds.

High Pressure Measurements of Density, Velocity of Sound, and Bulk Moduli of Pentane and 2-Methylbutane and Their Mixtures.

Abstract: Dilatometric and ultrasonic measurements were made on mixtures of pentane and 2-methylbutane to give density, relative volume, isothermal bulk modulus, velocity of sound, and adiabatic bulk modulus to pressure of 24 kilobars (2.4 ×109 N/m2).

Prediction of the Viscosities of "Soda-Lime" Silica Glasses.

Abstract: Published data are used to develop factors for predicting the viscosity-temperature relationship from the compositions of "soda-lime" type silicate glasses at specific temperatures in the range of 600 to 1300 °C. The effects of Na2O, K2O, CaO, MgO, Al2O3 and their interactions are evaluated. The influence of minor amounts of BaO, B2O3, Li2O, and F2, in the temperature range of 700 to 1300 °C, is estimated.

Thermophysical Measurements on Iron Above 1500 K Using a Transient (Subsecond) Technique.

Abstract: Simultaneous measurements of heat capacity, electrical resistivity and hemispherical total emittance of iron (99.9% pure) in the temperature range 1500 to 1800 K, and the melting point of iron by a subsecond duration, transient technique are described. The measurements indicate increases in heat capacity and electrical resistivity as the result of the solid-solid phase transformation (γ → δ) in iron. The measured value of the hemispherical total emittance at 1720 K is 0.33. The average of the results of two experiments yield a value of 1808 K for the melting point of iron. Estimated inaccuracies of measured properties are: 3 percent for heat capacity and emittance, 1 percent for electrical resistivity, and 5 K for the melting point.

Energy Levels and Classified Lines in the Second Spectrum of Thorium (Th II).

Abstract: The analysis of Th II has been extended with improved observations of the spectrum between 2000 and 25 000 A. About 6500 lines are classified as transitions between 199 odd levels and 271 even levels. Of the 192 levels expected from the six odd configurations 5f(6d + 7s)2 and (6d + 7s)27p, 188 are now known. In the even level system, all but one of the 37 levels of the three (6d + 7s)3 configurations are known. Of the 268 levels predicted for the configurations 5f27s + 5f7s7p + 5f6d7p + 5f26d, 235 are now known. The identifications are based on the theoretical calculations by N. Minsky. New Zeeman effect observations have increased the number of levels with known g-values to 406 out of 470 known levels. The classifications will be useful in establishing secondary standards of wavelength.

Simultaneous Measurements of Heat Capacity, Electrical Resistivity and Hemispherical Total Emittance by a Pulse Heating Technique: Zirconium, 1500 to 2100 K.

Abstract: Simultaneous measurements of heat capacity, electrical resistivity and hemispherical total emittance of zirconium in the temperature range 1500 to 2100 K by a subsecond duration, pulse heating technique are described. The results are expressed by the relations: C p = 36.65 - 1.435 × 10 - 2 T + 6.624 × 10 - 6 T 2 ρ = 87.95 + 1.946 × 10 - 2 T ϵ = 0.2031 + 6.362 × 10 - 5 T where C p is in J · mol-1 · K-1, ρ is in 10-8 Ω · m, and T is in K. Estimated inaccuracies of the measured properties are: 3 percent for heat capacity, 2 percent for electrical resistivity and 5 percent for hemispherical total emittance.

The Glass Transition Temperature of Monodispersed Polystyrenes and Their Binary Mixtures.

Abstract: Glass transition measurements on monodispersed polystyrenes of different molecular weight and their binary mixtures result in the following conclusions: (a) the effect of molecular weight on the glass transitions of monodispersed samples satisfies the Fox and Flory equation written as Tg = Tg∞ - A/Mn , with constant A = 0.84 × 10-5; (b) polymers of the same number average molecular weight with a broad distribution show lower glass transitions than the monodispersed; (c) the binary mixtures follow the Gordon-Taylor equation derived for copolymers, with constant k (experimental) 0.5.

The System NaCl-AlCl3.

Abstract: The system NaCl-AlCl3 has been restudied by DTA, visual observation, and x-ray diffraction powder techniques for identification of crystalline phases. It was confirmed that the system contains one intermediate compound NaAlCl4 with an incongruent mp of 153 ± 0.5 °C and a region of liquid immiseibility extending from 80.25 to 99.6 mol percent AlCl3 at 191.3 °C, the monotectic temperature.

Proposed secondary wavelength standards and line classifications in thorium spectra between 0.9 and 3 m

Abstract: The spectrum of thorium as emitted by an electrodeless lamp has been recorded by Connes and collaborators by means of Fourier Transform Spectroscopy in the region 0.9 to 3 μm. Of the 3100 lines observed, about 1900 are classified as transitions in the energy level system of Th i and 412 in Th ii. Since the average deviation between the observed and calculated wave numbers is less than 0.002 cm-1, the observed wavelengths are suitable for use as standard wavelengths.

The Formation of Curved Polymer Crystals: Polychlorotrifluoroethylene.

Abstract: The habits and fine structure of crystals of polychlorotrifluoroethylene (PCTFE) grown from dilute solution were studied as functions of crystallization temperature. The solvent used was a low molecular weight PCTFE oil. The simplest crystals found were monolayered chain folded lamellae formed at 110 °C. These lamellae are planar and possess an unusual texture characterized by the presence of fine channel-like voids in the interior of the crystals. These lamellae do not exhibit well-formed crystal faces but are disc-like in overall shape. At lower crystallization temperatures the crystals take the form of complex arrays of curved lamellae which are aggregated into, among others, watchglass-shaped or hollow spherical objects. The variation of the curvature of the crystals with crystallization temperature is discussed in the light of previous studies of the formation of curved crystals of poly(4-methylpentene-1) and polyoxymethylene.

Photoionization of CO2 -CO-O2 Mixtures. Formation and Reactions of Ion Clusters.

Abstract: Various mixtures containing combinations of CO2, O2, or CO have been photoionized at 16.7 and 21.2 eV at pressures up to 1.5 torr in the NBS high pressure photoionization mass spectrometer. In CO2-CO mixtures the interactions of CO2+ ions eventually lead to the formation of (CO)2+ and [(CO)2-CO2]+ cluster ions, while photoionization of CO2-CO-O2 mixtures yields mainly oxygen-containing clusters at higher pressures. The investigation of O2-CO mixtures also revealed reactions between O4+ and CO. The role of impurity reactions involving H2O is considered in some detail, and the implications of all of these data to the vapor phase radiolysis of CO2 is discussed.

Spectrum of Doubly Ionized Praseodymium from 2107 Å to 10716 Å.

Abstract: Wavelengths, relative intensity estimates, and classifications of the spectral lines of doubly ionized praseodymium (Pr iii) in the range of 2107 to 10716 A are given. About 4400 lines are included of which some 2500 are classified.

An Improved Procedure for Synthesis of DL-4-Hydroxy-3-methoxymandelic Acid (DL-"Vanillyl"-mandelic Acid, VMA).

Abstract: An improved procedure for synthesis of DL-4-Hydroxy-3-methoxymandelic Acid (DL-Vanillyl-mandelic Acid, VMA) entails slow addition of an ice-cold, aqueous solution of glyoxylic acid to an ice-cold alkaline solution of guaiacol, with efficient mechanical stirring. This one-step condensation procedure provides VMA in 68-75 percent yield.

Single Particle Motions in Liquids: Qualitative Features of Memory Functions.

Abstract: Memory functions, which enter into the equations of motion for time correlation functions, are constructed from neutron scattering, infrared absorption and light scattering data involving single particle motions in liquids. The qualitative features of these memory functions are related to the shape of the corresponding time correlation functions. It is found that a negative portion to the memory function is indicative of a rapid loss of correlation in time while strong temporal correlations imply a memory function which does not go negative. The mathematical structure of a memory function is examined for the case of the ideal gas by expanding and evaluating the projection operator representation of the function. The resulting expression has a rich mathematical structure and can be expressed in a closed form only for its Laplace transform.

The Infrared Spectra of Matrix Isolated Uranium Oxide Species.

Abstract: : The infrared spectra of matrix isolated products of the interaction of uranium and oxygen have been investigated at high temperatures. By use of collateral, available data on the various uranium oxide species, plus employment of oxygen 16 and 18 isotopes, peak assignments were verified for many of the neutral metal oxide species. (Author)

The enthalpies of combustion and formation of mono-chlorobenzoic acids

Abstract: The enthalpies of combustion of o-, m-, and p-chlorobenzoic acid have been determined in an adiabatic rotating-bomb calorimeter. The enthalpies of formation have been obtained by combination of the experimental data with the accepted values for the enthalpies of formation of water, carbon dioxide, and aqueous hydrochloric acid. The results of other investigators are discussed briefly. The resulting values and their estimated 95 percent confidence limits are as follows: o-Chlorobenzoic acidm-Chlorobenzoic acidp-Chlorobenzoic acid ΔHc° (25 °C)-3087.91 ± 0.69 kJ/mol-3068.05 ± 1.53 kJ/mol-3064.40 ± 0.66 kJ/molΔHf° (25 °C)-404.83 ± 0.74 kJ/mol-424.59 ± 1.55 kJ/mol-428.16 ± 0.72 kJ/mol. Where ΔHc° corresponds to the process: -404.61-424.37-429.94C7H5O2Cl(c) + 7 O2(g) + 198 H2O(liq) → 7 CO2(g) + [HC1 + 200 H2O](liq).

Investigation of Freezing Temperatures of National Bureau of Standards Aluminum Standards.

Abstract: The design of a high-precision furnace for investigating the freezing points of metals up to 700 °C or higher is described. The freezing points of aluminum samples of nominally 99.999 percent purity from two batches were compared in terms of the ratio R(Al)/R(TP), the ratio of the resistance of the platinum resistance thermometer at the aluminum freezing point to that at the triple point of water. The average standard deviation of measurements of the ratio R(Al)/R(TP) obtained on six specimens corresponds to ±0.40 mK, while the average standard deviations of R(Al) and R(TP) correspond to ±0.17 mK and ±0.14 mK, respectively. (The variations in the measurements of R(TP) are amplified by 3.4 in the ratio R(Al)/R(TP).) The spread of the mean R(Al)/R(TP) obtained for five out of the six specimens corresponds to 0.51 mK; the deviation of the mean R(Al)/R(TP) of the sixth specimen from the mean R(Al)/R(TP) of the five specimens corresponds to -1.31 mK. (The sixth specimen may have been contaminated during the assembly of the freezing-point cell or the original sample bar was inhomogeneous.) The results show that aluminum can provide a freezing point (near 660 °C) that is at least as reproducible as the freezing point of antimony (near 631 °C).