Materials Literature
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Se destaca, tomando como base numerosas determinaciones, la importancia, en el plan industrial, de la estructura granulométrica de las arcillas, como factor principal que determina la actitud de una arcilla para preparar un determinado producto.
A treatment is given of the hysteresis loops of dilute mixtures of various sizes of ferromagnetic particles. Three ranges of particle size are considered: very small particles called ``super-paramagnetic'' which are single domain and equilibrate resulting from thermal vibrations, single domain particles which are larg…
Co mpositional proximity to a morphotropic t ransformation between two ferroelectric solid-s olution phases seems to yie ld ceramic transducers having desirable properties over a wide range of te mperature. Examples of t his phenomenon were observed in the systems PbTi03-PbZr03, PbTi03-PbO:Sn02, PbTi03-PbZr03-PbO:SnO"…
Abstract Previous theoretical work by Stoner & Wohlfarth (1948) on the magnetic properties of single domain ferromagnetic particles is extended to take some account of the interaction between the particles. Earlier theoretical considerations of the interaction problem are critically discussed (§2), and the experim…
Abstract The method described previously for measuring the energy stored in cold-worked metals has now been applied to nickel and arsenical copper as well as to pure copper. Torsion, tension and compression have been used as methods of deformation, and the heating rates were 2, 4 and 6° C/min. For all these materials,…
The theory of the magnetic susceptibility of graphite is presented in terms of a three-dimensional Wallace electron energy band structure. The experimentally observed variation with temperature is explained in a satisfactory manner, provided the interplane resonance integral occurring in the band approximation is give…
The superconducting transition temperatures of alloys between zirconium and VIIIth column elements are substantially higher than those of zirconium. The same is true for zirconium-gold alloys. This observation confirms a rule previously established about the height of transition temperatures.
The neutron diffraction data of Shull et al. on the powder specimens of MnO, FeO, CoO, etc., are re-examined. It is found that except for FeO the observed Debye-Scherrer patterns may be produced by a number of magnetic moment arrangements with the same antiparallel coupling among the moments on the next nearest neighb…
A mechanism is suggested for the nonradiative quenching of excited states of simple impurity centers, namely a crossover to the ground electronic state of the center immediately after excitation and before thermal equilibrium has had time to come about. It is proposed that this mechanism is responsible for the absence…
The symmetry properties of the one-electron energy bands of a crystal of the zinc blende structure are studied by means of group theory. This is done both with and without the inclusion of spin-orbit coupling. The character tables and compatability tables are obtained for the various irreducible representations of the…
The lattice constants of a graphite single crystal, natural graphite powder, and artificial graphite powder have been measured at 297\ifmmode^\circ\else\textdegree\fi{}K, 78\ifmmode^\circ\else\textdegree\fi{}K, and 4.2\ifmmode^\circ\else\textdegree\fi{}K. The $a$-spacing does not change in this temperature range withi…
A study has been made of the magnetic properties of the series of perovskite-type compounds $[(1\ensuremath{-}x)\mathrm{La}, x\mathrm{Ca}]\mathrm{Mn}{\mathrm{O}}_{3}$. The investigations have been made primarily by neutron diffraction methods, but x-ray diffraction measurements of lattice distortions and ferromagnetic…
Zener has suggested a type of interaction between the spins of magnetic ions which he named "double exchange." This occurs indirectly by means of spin coupling to mobile electrons which travel from one ion to the next. We have calculated this interaction for a pair of ions with general spin $S$ and with general transf…
The theory of semicovalent exchange is reviewed and applied to the perovskite-type manganites $[\mathrm{La}, M(\mathrm{II})]\mathrm{Mn}{\mathrm{O}}_{3}$. With the hypothesis of covalent and semicovalent bonding between the oxygen and manganese ions plus the mechanism of double exchange, detailed qualitative prediction…
Abstract Polyisobutylene suffers random main-chain fracture when exposed to high radiation. Identical results are produced by electron and γ-radiation and the average energy absorbed per break amounts to 20 eV at 20° C. The unsaturation produced is proportional to the number of breaks. A new absorption band appears in…
Abstract Durch Hydrolyse von Natriumpalladat(II) entsteht Pd(OH) 2 , das durch Analyse, isobaren Abbau und Röntgenaufnahmen gekennzeichnet wird. Beim Kochen schwach salpetersaurer Palladium(II)‐nitratlösungen bildet sich PdO · xH 2 O, das in einem verzerrten PdO‐Gitter kristallisiert. Die Verzerrung des Gitters wird a…
Polychlorotrifiuo roethylene (I"::el-F) (I ), poly-a,/J,/J-tri[-Iuorostyrene (II), and pol.\'p-xylylene (III) wer e pyrolyzed under con di tions of molccular distillation , and so me of the light volatile fractions analyzed in the mass spectrometer. The volatiles from (I ) consisted of 27.9 ,,"eight percent monome ri…
The thermal insulation of samples of three caribou pelts, six other pelts, and one pile fabric was measured in still air and in winds up to about 26 mph. In still air the values, including ambient air layer, ranged from 2.0 clos for the pile fabric to 5.4 clos for the winter caribou. In a 25-mph wind the insulation af…
Previously described fine-particle magnets have been based upon crystal anisotropy; this paper reports permanent-magnet properties derived from the shape anisotropy of substantially elongated single-domain iron particles. The shape anisotropy of these particles overcomes the limitation imposed on the energy of previou…
Abstract The stress relaxation behavior of peroxide and sulphur vulcanized natural rubber has been investigated using a relaxometer of new design. The peroxide vulcanizates do not degrade significantly in vacuo and degrade by an exponential decrease in stress with time in oxygen. The vulcanizates from the two sulfur r…