Index of content:
Volume 23, Issue 3, 01 March 1952
Phenomena Associated with the Flight of Ultra‐Speed Pellets. Part III. General Features of Luminosity23(1952); http://dx.doi.org/10.1063/1.1702196View Description Hide Description
Ultra‐speed pellets of the lighter metals such as aluminum and magnesium generate intensely luminous trails when fired through air. A pronounced characteristic of the luminous trails is the intermittent manner in which the light is emitted. This effect has also been observed in meteors and in studies of conventional shaped charges. Photographs indicate that flashing is caused by yawing of the pellet.
The brilliant flashes of light are associated with the ablation and subsequent burning of material from the pellet. There is evidence that the material is removed from the pellet in the form of small droplets.
The brightness, luminous output, and temperature of the trail generated by an aluminum pellet have been measured. The brightness is approximately 25,000 lamberts, the luminous output is 30,000 lumen‐seconds, and the color temperature is 2900°K.
Mechanisms of Positive and Negative Corona in Hydrogen and Argon between Coaxial Cylindrical Electrodes over an Extended Pressure Range23(1952); http://dx.doi.org/10.1063/1.1702197View Description Hide Description
Mechanisms in the corona discharge from a fine platinum wire at a positive potential along the axis of a hollow nickel cylinder have been investigated by using the oscilloscope to analyze the pulses caused by α‐particles passed through the low field region parallel to the wire. γ p , the secondary coefficient for the photo‐electric effect at the cathode in hydrogen, had values from 70×10−5 at 100 mm to 5×10−5 at 650 mm pressure. γ i for the hydrogen ions at the cathode was less than 10−6. The mobility of the positive ions (presumably H2 +) was 13.4 (±0.4) cm2/volt×sec at 760 mm and 20°C. Adding 0.1 to 1.0 percent of oxygen to hydrogen resulted in the formation of O2 − ions. γ i for the argon positive ions was about 9×10−4 extrapolated to zero pressure and decreased with increasing pressure and γ p was less than . Most of the ions were A2 + with a mobility of 1.94 (±0.08) cm2/volt×sec. Positive wire dc current voltage data were taken in hydrogen and argon at several pressures. Sparks occurred with the positive wire in argon at relatively lower gap voltages than in hydrogen. Current‐voltage data were taken with the wire negative. In hydrogen the discharge started as a small (10−11 amp) self‐supporting current (probably uniformly distributed along the wire) which changed with increasing gap voltage to a larger (microampere) discharge localized in luminous spots on the wire in analogy to Miller's observations in nitrogen. No small self‐supporting currents were observed in argon. The discharge started as a spark above 200 mm and as a glow that spread uniformly over the wire below 100 mm pressure.
23(1952); http://dx.doi.org/10.1063/1.1702198View Description Hide Description
The effects of network formation of non‐Gaussian chains on the stress‐birefringence are calculated. If the birefringence is plotted against the stress, the effects make the curve deviate from a straight line. When it is plotted against the elongation, the curve will rise above that corresponding to independent Gaussian chains in agreement with the experiments.
23(1952); http://dx.doi.org/10.1063/1.1702199View Description Hide Description
Values of the steady‐state dc resistance of copper oxide and selenium rectifiers as a function of temperature from 79°K to 300°K have been obtained. The maximum potentials used were 2.5 volts in the forward direction and 6.0 volts in the backward direction.
It was found that a plot of the logarithm of the resistance against the reciprocal of the temperature was nearly linear for all except the reverse direction of the selenium rectifier. For the latter case at 6.0 volts the resistance went through a minimum below 200°K.
23(1952); http://dx.doi.org/10.1063/1.1702200View Description Hide Description
An investigation has been made of the magnetic domain structure of Perminvar (43 percent Ni, 34 percent Fe, 23 percent Co) ring specimens having rectangular hysteresis loops after heat‐treatment in a magnetic field. Domain patterns obtained with colloidal magnetite showed curved domain boundaries extending completely around the rings, forming circles concentric with them. Changes in magnetization occur when an applied field causes the circular boundaries either to expand or contract so that there is a change in the relative values of clockwise and counter‐clockwise flux. A nucleus of reversed magnetization was formed by making a small notch in a specimen, and this decreased the coercive force and hysteresis loss by a factor of two. It was found that in a 180° domain boundary it was possible to make the change in spin orientations, which occurs in going from one side of the boundary to the other, have either a right‐ or left‐hand screw relation, by the application of a field of appropriate sign perpendicular to the surface. The effect of super‐posing an applied alternating field was also investigated, and an effective permeability of 4,000,000 was obtained.
Study of Imperfections of Crystal Structure in Polycrystalline Materials: Low Carbon Alloy and Silicon Ferrite23(1952); http://dx.doi.org/10.1063/1.1702201View Description Hide Description
The technique of the new x‐ray double spectrometer method as described in a former paper1 is applied to the study of angular misalignment of crystal structure in alloys.
To obtain a better statistical evaluation of the x‐ray intensity data the method is extended to include arrays of spots on the Debye‐Scherrer lines at high elevations. A complete mathematical discussion of the photometric transformation of the crystallite rocking curves is presented.
The specimens investigated include a low carbonalloyannealed at 850°C and three siliconferrite samples annealed at 980°, 1100°, and 1200°C.
The quantitative data obtained disclose a significant dependence of crystal perfection on annealing temperature, and demonstrate clearly that the angular misalignment of the coherently reflecting regions within the grains decreases with annealing temperature provided this temperature is not excessive.
Valuable information regarding the influence of cold rolling on the subsequent annealing process is obtained. Thus, the extent of partial recrystallization of the siliconferrite is deduced from the statistical data, and the differential grain size between the surface layers and the interior of the specimen is revealed through the study of the diffraction effects with radiation of different wavelengths.
A mechanism of grain bending during plastic deformation is suggested and a relationship between magnetic properties, annealing temperature, and crystal perfection of the siliconferrite is pointed out.
Lattice Parameters, Coefficients of Thermal Expansion, and Atomic Weights of Purest Silicon and Germanium23(1952); http://dx.doi.org/10.1063/1.1702202View Description Hide Description
Lattice parameter determinations of 99.97 percent pure silicon (containing 0.03 percent carbon) were carried out using the asymmetric method, a 64‐mm precision camera in a thermostat at constant temperatures (10, 20, 30, 40, and 50°C). The powder mounts, about 0.12‐mm in diameter, were translated and rotated during the exposure. Only the (444)‐CuKα1 line was used for the determinations. The lattice parametera=5.41991±0.00003kX (5.43086A) at 20°C, corrected for refraction, was obtained; the linear lattice expansion coefficient (between 10 and 50°C) was 4.15×10−6, the density at 20°C was 2.32831±0.00031 g/cm3 (determined by the suspension method), and the atomic weight was 28.083±0.013 (in agreement with the new chemical weight 28.09) showing that the silicon crystals used, under certain limitations, were sound although the possibility of interstitial atoms is not excluded.
The lattice parameter of purest germanium (99.99 and 99.999 percent) was measured by the same method using the (422)‐CrKα1 and α2 lines: a 20=5.64607±0.00004kX (5.65748A) for both materials. The expansion coefficients were α=6.65×10−6 and 5.92 ×10−6, respectively. The density was 5.3234±0.0025 g/cm3 at 25°C and the calculated atomic weight 72.593±0.037 in agreement with the present chemical weight 72.60. Thus, germanium crystals are sound; however, interstitial atoms are possible.
The precision of lattice parameter determination was about 1:200,000, but in the case of 99.999 percent germanium the precision was considerably better. This shows again that lattice constant determinations can be performed with highest precision and without use of any extrapolation method. The method of lattice parameter determination applied is an absolute one.
23(1952); http://dx.doi.org/10.1063/1.1702203View Description Hide Description
The temperature diffuse scattering of x‐rays from a single crystal of β‐brass has been measured at room temperature using a Geiger counter spectrometer and crystal monochromated CuKα radiation. Measurements were made throughout a large region in reciprocal space, with special attention given to the hko plane. The results were in excellent qualitative agreement with the theory developed by Laval and James in which temperature vibrations are expressed in terms of elastic waves. From the measurements, dispersion curves are obtained giving the velocity and frequency of the elastic waves, in the , , and  directions, as a function of their wavelengths. An approximate frequency spectrum is then calculated on the basis of these dispersion curves. The velocities at infinite wavelength are shown to agree with those given by elastictheory using the static elastic constants.
Analysis of Certain Errors in the X‐Ray Reflection Method for the Quantitative Determination of Preferred Orientations23(1952); http://dx.doi.org/10.1063/1.1702204View Description Hide Description
The reflection method for quantitative determination of pole figures, proposed by Schulz, proved to be limited with respect to the range of tilting angles in which satisfactory results can be obtained. It is shown that the previously unexplained decrease in the diffracted intensity with increasing tilting angle for specimens with random orientation distribution can be accounted for on the basis of an elementary analysis of defocusing effects. Experimental evidence is presented to show that variation of the receiving slit length and of the main slit width has the effect predicted by the analysis. The importance of accurate specimen alignment is discussed, and a satisfactory alignment check procedure is described.
23(1952); http://dx.doi.org/10.1063/1.1702205View Description Hide Description
This report describes a study of dc and microsecond pulsed emission from oxide coatedcathodes prepared on four different base metals. One of the base metals used was pure electrolyticnickel and the other three had impurities of 0.2 percent silicon, 4 percent silicon, and 4.7 percent tungsten added to the nickel. The flat base metalcathode was coated with equal molar barium‐strontium carbonate. The tubes were placed on life test at a cathode temperature of 1125°K with no emission current drawn. Dc and pulsed emission measurements were taken periodically. Three methods were used to measure the zero field emission current, (1) dc retarding potential, (2) dc Schottky, and (3) pulsed Schottky. These gave essentially the same Richardson plot indicating a positive correlation of dc and pulsed emission. From these Richardson plots obtained using methods (1) and (3), the work function, the emission constant, and J 0, the characteristic emission current density at 650°K, were determined. The results show that the different cathode base metals control the variation in emission with life. The emission from the tungsten‐nickel base metal is stable with life and is of much higher value than the other base metals.
The Allotropic Transformation of Hafnium and a Tentative Equilibrium Diagram of the System Zirconium‐Hafnium23(1952); http://dx.doi.org/10.1063/1.1702206View Description Hide Description
23(1952); http://dx.doi.org/10.1063/1.1702207View Description Hide Description
It is concluded from electron metallographic results that the high coercive force and anisotropy of Alnico 5 are caused by a very finely divided precipitate produced by the permanent magnetheat treatment. This precipitate is a transition structure rich in cobalt and is face‐centered cubic with a 0 = 10A and appears as rods growing along the  directions of the matrix crystal when no magnetic field is applied during heat treatment. The size of the precipitate rods at optimum properties is approximately 75–100A by 400A long. The spacing between rows of rods is about 200A. The rods are not distinctly resolved in the electron images unless they are grown by aging at 800°C. Their orientation and structure is clearly evident in the electron diffraction patterns at all stages of growth. The precipitate responds to a magnetic field applied during heat‐treatment both by suppression of nuclei making an angle greater than about 70° with the field and by the forcing of the rods off the  direction into that of the field. The precipitate rods tend to scatter in direction about the field vector when the field is off the  but are aligned accurately when the field is along .
23(1952); http://dx.doi.org/10.1063/1.1702208View Description Hide Description
As a result of measurements of magnetic anisotropy and coercive force on single crystals of Alnico 5 and the electron metallography of Part I, the following conclusions were obtained. When the crystals are heat treated in a field in the principal crystallographic directions, the easy direction of magnetization is the field direction, and magnetically the crystals have twofold symmetry. However, there is a strong tendency because of crystal forces for the precipitate to grow in 〈100〉 directions; and, therefore, the crystal has the highest anisotropy when the heat‐treating field and a 〈100〉 direction are parallel. The large increase in residual induction of Alnico 5 which results from the magnetic fieldheat treatment is caused by the easy directions of the crystal changing from the 〈111〉 directions to a single easy direction approximately parallel to the field. Domain rotations rather than boundary movements account for the coercive force of the alloy, since the dimensions of the individual particles are approximately 200 angstroms. The present physical picture of the alloy is one of single domains of precipitate material in parallel with single domains of matrix material, the observed coercive force being the resultant of this parallel combination.
23(1952); http://dx.doi.org/10.1063/1.1702209View Description Hide Description
23(1952); http://dx.doi.org/10.1063/1.1702212View Description Hide Description