3.

July-August 1966

Elastic constants of synthetic single crystal corundum, W. E. Tefft, J. Res. NBS 70A4-03, pp. 277-280 (July-Aug. 1966).

Key words: Aluminum oxide; corundum; elastic constants; shear modulus; Young's modulus.

The elastic constants of synthetic single crystal corundum (aluminum oxide) were calculated from 0 to 900 °K from data obtained by a resonance technique from 80 to 900 °K.

Phase equilibria as related to crystal structure in the system niobium pentoxide-tungsten trioxide, R. S. Roth and J. L. Waring, J. Res. NBS 70A4-404, pp. 281-303 (July-Aug. 1966).

Key words: Crystal structure; niobium pentoxide; phase equilibria; system; tungsten trioxide.

The phase equilibrium diagram for the binary system niobium pentoxide-tungsten trioxide has been constructed from results of x-ray diffraction studies on both single crystals and powders and from fusion characteristics. Twelve stable compounds have been found in the system. The exact composition of eight of these compounds has been established by single crystal analyses at the Nb2O3:WO, ratios of 6:1, 13:4, 7:3, 8:5, 9:8, 1:1, 4:9, and 2:7. The approximate compositions of the remaining four other phases are 30:1, 6:11, 1:11, and 1:15. The 6:1, "6:11", 4:9, and 2:7 phases melt congruently at 1476, 1378, 1380, and 1357 °C, respectively. The "30:1", 7:3, 8:5, 9:8, "1:11", and "1:15" phases melt incongruently at 1470, 1440, 1385, 1375, 1356, and 1358 °C, respectively; and the 13:4 and 1:1 phases decompose before melting at 1435 and 1115 °C, respectively. The 8:5, 9:8, "6:11", 2:7, "1:11", and "1:15" compounds are shown on the phase diagram as having minimum temperatures of stability. One metastable phase having a narrow range of composition near the 3:8 ratio was also encountered. Although Nb2Os apparently exhibits no solid solution, WO, was found to accept a maximum of three mole percent niobia in solid solution enabling all the reported polymorphs of WO, to be obtained at room temperature.

Properties of aqueous mixtures of pure salts. Thermodynamics of the ternary system: Water-calcium chloride-magnesium chloride at 25 °C, R. A. Robinson and V. E. Bower, J. Res. NBS 70A4405, pp. 305-311 (July-Aug. 1966).

Key words: Isopiestic measurements; vapor pressure; calcium chloride; mixed solutions; activity coefficients. Isopiestic vapor pressure measurements have been made on the system water-calcium chloride-magnesium chloride at 25 °C. Activity coefficients have been evaluated for each salt in the presence of the other in systems of constant total ionic strength. The excess free energy of mixing has been calculated and compared with the values for analogous systems.

Properties of aqueous mixtures of pure salts. Thermodynamics of the ternary system: Water-sodium chloride-calcium chloride at 25 °C, R. A. Robinson and V. E. Bower, J. Res. NBS 70A4406, pp. 313-318 (July-Aug. 1966).

Key words: Calcium chloride; isopiestic measurements; mixed salt solutions; sodium chloride; vapor pressure of aqueous solutions.

Isopiestic vapor pressure measurements have been made to determine some thermodynamic properties of the system: watersodium chloride-calcium chloride at 25 °C. Equations are derived for the activity coefficient of each salt in the presence of the other when the total ionic strength is kept constant. The limiting conditions in very dilute solutions are considered and "trace" activity coefficients calculated. A comparison with previous work is made. The excess free energy of mixing is calculated.

Use of the consistency check in the vector verification method, A. D. Mighell and R. A. Jacobson, J. Res. NBS 70A4-407, pp. 319-321 (July-Aug. 1966).

Key words: Crystal; structure; Patterson; vector; symmetry; consistency; frequency; superposition.

The consistency check is a type of frequency check in which full use is made of the space group symmetry. It is designed for application to a symmetry map, to a tentative atom map, to the results of superpositions, or to any pseudoelectron-density map. Like the frequency check, its purpose is to aid in the analysis of one of the above maps by assigning a relative weight (relative weight equals the number of other peaks that the given peak is consistent with) to the peaks in these maps. To determine the relative weight, each peak in the map is compared with each of the others to see if it is consistent. Two peaks are considered consistent with each other, if and only if, the set of unique vectors between the two is present in the Patterson map. The method is equivalent to doing a full set of symmetry superpositions at each peak in a symmetry map or a tentative atom map; counting the number of points in the resulting map; and outputting this number at the initial peak position. No assumptions other than that for space group symmetry are required to apply the consistency check to a symmetry map. The resulting map, which has been calculated in a routine fashion directly from the Patterson map, may then be conveniently used as the starting point for the structure analysis of an unknown compound.

Self-reversal in the spectral lines of uranium, D. D. Laun, J. Res. NBS 70A4-408, pp. 323-324 (July-Aug. 1966).

Key words: Uranium, spectrum; spectrum, uranium; selfreversal; uranium spectrum.

In 1946, spectrum analysis indicated that the outer-electron configuration of normal uranium atoms was 5f6d17s2, with an energy level designated L representing the normal state. Now that conclusion is experimentally verified by the observation of self-reversed lines in uranium spectra emitted by a high-current pulsed arc between metallic electrodes. Fifty-four reversed lines were observed; thirty-eight involve the normal state and sixteen are distributed among four low metastable states of the same configuration.

Oscillator strengths for ultraviolet lines of Fe 1, C. H. Corliss and B. Warner, J. Res. NBS 70A4-409, pp. 325-371 (July-Aug. 1966).

Key words: Atomic spectra; iron; oscillator strengths; transition probability; ultraviolet lines of Fe I.

Relative intensities and oscillator strengths for 2000 ultraviolet lines of Fe I from several investigations between 2080 and 4150 Å have been critically discussed and adjusted to a uniform absolute scale. New values for many lines not measured heretofore are reported.

September-October 1966

Orientation of calcium molybdate (CaMoO,) and other single crystals having the scheelite structure, E. N. Farabaugh, H. S. Peiser, and J. B. Wachtman, Jr., J. Res. NBS 70A5-410, pp. 379-384 (Sept.-Oct. 1966).

Key words: Calcium molybdate; crystal orientation; crystallographic groups; interplanar angles; physical properties; scheelite structure; single crystal; x-ray backreflection.

Values of interplanar angles useful in distinguishing the [100] from the [110] direction in CaMoO, are given to facilitate orientation by analysis of back-reflection Laue patterns. The distinction between the [001] and [001] directions in the scheelite structure is discussed and examples of physical properties dependent upon this distinction are given. The [001] direction is defined in terms of the crystal structure and a procedure for identifying (001) using Laue patterns is described. The same distinction applies to certain nonpolar directions of all crystals belonging to the following nonenantiomorphous point groups. I, m, 2/m, mmm, 3, 3m, 3m, 4, 4/m, 4/mmm, 6, 6/m, 6/mmm, m3, and m3m.

Crystal structure of BaGe[Ge3O9] and its relation to benitoite, C. Robbins, A. Perloff, and S. Block, J. Res. NBS 70A5-411, pp. 385-391 (Sept.-Oct. 1966).

Key words: Barium tetragermanate; structure; benitoite; crystal; x-ray.

BaGe[Ge3O9] is trigonal space group P3 with lattice constants a = 11.61, c=4.74 Å, and Z=3. The structure was established by three-dimensional Patterson and electron density syntheses. Three-dimensional least-squares refinement resulted in a final R value of 6.8 percent (observed data only).

The previously proposed structural relationship of this compound with benitoite, BaTiSi3O9, has been confirmed. The structure can be considered as composed of GeзO, rings, in which the Ge is tetrahedrally coordinated, linked through octahedrally coordinated Ge atoms to form a three-dimensional Ge-O network. All Ge polyhedra are linked by corner sharing. The Ba ions occupy positions in channels of the network.

A rotating cylinder method for measuring normal spectral emittance of ceramic oxide specimens from 1200 to 1600 °K, H. E. Clark and D. G. Moore, J. Res. NBS 70A5-412, pp. 393415 (Sept.-Oct. 1966).

Key words: Alumina; ceramic oxides; emittance; error sources; magnesia; measurement uncertainties; spectral emittance; thermal radiation; thoria; zirconia.

Equipment was designed and constructed for measuring the spectral emittance of polycrystalline ceramic oxide specimens in the wavelength region 1 to 15 μ and at temperatures of 1200, 1400, and 1600 °K. Specimens consisted of small hollow cylinders that were rotated at 100 rpm in a furnace cavity equipped with a water-cooled viewing port. Emittances were determined by comparing the radiance of the specimen to that of a blackbody at the same temperature.

A series of six measurements (two measurements each on three specimens) was made on commercially pure specimens of alumina, thoria, magnesia, and zirconia. All four materials showed similar behavior in that the emittances were low in the

shorter wavelength regions and high at the longer wavelengths. The temperature coefficients of spectral emittance were positive for all four materials, but varied with the material; those for thoria were appreciably higher than the other three. In all cases coefficients were greater at short wavelengths than at long.

Error sources were investigated, and the measurement uncertainties associated with each source were evaluated. It was concluded that at 1200 °K the true values of emittance at 2 μ for the particular specimens measured might be as much as 0.032 lower or 0.012 higher than the reported values. The data were in good agreement with reflectance measurements of the same material and with recently reported absorption coefficients.

Electron absorption spectrum of cobalt(11)-doped trisphenanthrolinezinc nitrate dihydrate, C.W. Reimann, J. Res. NBS 70A5-413, pp. 417-419 (Sept.-Oct. 1966).

Key words: Trisphenanthroline cobalt(II) nitrate dihydrate; trisphenanthrolinezinc nitrate dihydrate; electron absorption spectrum.

The electron absorption spectrum of cobalt(11)-doped trisphenanthrolinezinc nitrate dihydrate has been observed at room temperature and at 77 °K. Broad bands appear at 10,750 and 22,000 cm-1 which are assigned to the 'T19(F) ←→1T2g(F) and the T19(F) ←→1T19(P) transitions respectively. A broad weak band occurs near 19,000 cm-1 but at 77 °K this band is resolved into a series of narrower bands. These bands are assigned to 2G transitions. The relationship between the spectrum of cobalt(11) trisphenanthrolinezinc nitrate dihydrate and the solution spectra of cobalt(11) in ammonia and ethylenediamine is discussed.

Procedures for homogeneous anionic polymerization, L. J. Fetters, J. Res. NBS 70A5-414, pp. 421-433 (Sept.-Oct. 1966). Key words: Homogeneous anionic polymerization; monodisperse, polystyrene, poly-a-methylstyrene; polyisoprene; and polybutadiene.

This report is a review of the procedures and equipment used in the preparation of polymers of predictable molecular weights and narrow molecular weight distributions. The monomers considered in detail are sytrene, a-methylstyrene, isoprene, and butadiene.

The configurations 4d"+4d1 5s in doubly-ionized atoms of the palladium group, Y. Shadmi, J. Res. NBS 70A5-415, pp. 435445 (Sept.-Oct. 1966).

Key words: Configurations 4d"+4d-1 5s, energy levels; interaction parameters; palladium group; theoretical; third spectra.

Four hundred and eighty-three energy levels belonging to the low even configurations of the third spectra of the palladium group are predicted by the use of interpolation formulas for the interaction parameters.

November-December 1966

Absolute isotopic abundance ratios and atomic weight of magnesium, E. J. Catanzaro, T. J. Murphy, E. L. Garner, and W. R. Shields, J. Res. NBS 70A6-416, pp. 453-458 (Nov.Dec. 1966).

Key words: Absolute ratios; atomic weight; isotopic abundances; magnesium.

Absolute values have been obtained for the isotopic abundance ratios of magnesium, using surface emission mass spectrometry. Samples of known isotopic composition, prepared from nearly pure separated magnesium isotopes, were used to calibrate the mass spectrometers. The resulting absolute values