Showing papers on "Electron backscatter diffraction published in 1973"

Morphology-property studies of amorphous polycarbonate

Abstract: The relationship between morphology and several physical properties (tensile, thermal, dielectric, and dynamic mechanical properties) of amorphous poly-bisphenol-A-carbonate was examined as a function of annealingtime at temperatures below the glass transition temperature (Tg). The change in structure of the amorphous films was studied by means of X-ray diffraction and with electron diffraction using a rotating sector in an electron microscope as well as by electron micrographs of replicas of surfaces prepared by etching with dilute aqueous NaOH solutions. The changes in morphology and physical properties caused by annealing below Tg are, in general, closely related. The relationship cannot be explained only by changes in free volume; it is proposed that changes in the degree and type of order (nodular structure) also play a role. The design and application of the rotating sector is described in an Appendix.

A new approach to the determination of crystallinity of polymers by X-ray diffraction

Abstract: A new X-ray diffraction method for the determination of crystallinity of polymers is reported. A probability function is used to express the intensity distribution of an amorphous halo. The intensity of the halo buried under any crystalline peak can be calculated by this function. An amorphous-standard-addition method was used to determine crystallinity. A linear relationship between intensity and concentration is derived theoretically and applied to polyethylene terephthalate. No previous chemical or structural information about the polymer is necessary for this method. Very good agreement between X-ray data and density measurements were obtained. This method is rapid, practical and suitable for routine analysis.

A brief note on the chemical nature of the precipitate within nerve fibers after the rapid Golgi reaction: selected area diffraction in high voltage electron microscopy.

Abstract: The use of selected area electron diffraction in the high voltage electron microscope permits the identification of the crystalline rapid Golgi precipitate within single nerve fibers in nervous tissue Spot diffraction patterns and ring patterns show the impregnation to be silver chromate,Ag2CrO4 This is confirmed by cobalt Debye-Scherrer X-ray diffraction

X-ray-diffraction approach for studies on fatigue and creep

Abstract: It is well known that X-ray diffraction is one of the most powerful means for investigating the microscopic structure of crystalline materials. X-ray diffraction is advantageous when it is applied to metallic materials; it responds very sensitively to changes in the metal's crystalline structure. Another characteristic advantage of the X-ray-diffraction approach is its nondestructive nature in the measurement of crystalline-material parameters, enabling us to observe the process of mechanical phenomena of metals, such as fatigue and creep.

Electron State of Mn4N Studied by Electron Diffraction

Abstract: Low order electron diffraction intensity is sensitive to the electron state of a crystal. Based on this fact, an electron diffraction study has been made to determine the electron state of the ferrimagnetic interstitial compound Mn 4 N by measuring its low order superstructure reflection intensities from polycrystalline films. The result shows that the electron state can be expressed as Mn 0 (Mn +0.2 ) 3 N -0.6 . X-ray crystal structure factors obtained from the observed electron diffraction crystal structure factors not only coincide well with those determined by X-ray diffraction, but also have an accuracy of about one order higher. Electrons filling the 3d band of Mn 4 N are also investigated according to the above electron state model and the magnetic moment distribution in the crystal. Hund's rule is shown not to hold for Mn 4 N. Some discussions are made about the electron state determined by the diffraction method.

Electron diffraction determination of the molecular structure of 1,6-dicarba-closo-hexaborane(6)

Abstract: The molecular structure of 1,6-dicarba-closo-hexaborane(6), 1,6-C2B4H6, has been determined in the vapour phase by electron diffraction.

Low-energy electron diffraction for surface structure analysis

Abstract: Recent progress in the theory of low-energy electron diffraction is reviewed. It is shown, to what extent the theory can already extract information about the structure of solid surfaces out of the experimental results. The kinematic, the multiple-scattering and the data-averaging approach are discussed.

Morphology and Crystal Structure of Wholly Aromatic All-Para Polyamide-Hydrazide Polymers

Abstract: The morphology of some amide-hydrazide polymers of the type useful for high-modulus X-500 class fibers has been characterized by transmission electron microscopy of thin films crystallized from dilute solution. Selected area electron diffraction was used to characterize the crystallinity and crystal structure of the thin films and precipitated polymer. The films were cast from concentrated solutions and crystallized by heating the films. The results of these studies revealed several unique features relative to the crystal structure of the all-para polymers. Thin films of the crystallized polymer showed a distinctive crystalline texture—the molecular chains were found to be preferentially oriented parallel to the film plane and randomly oriented about an axis normal to the film plane. Electron diffraction measurements showed equatorial reflection maxima at tilt angles of = 30, ±48, and =59 when the films were tilted on an axis parallel to the film plane. From these results a tentative crystal unit...

X-Ray Diffraction Microscopy

Abstract: The individual diffraction spots which are obtained in single crystal transmission or back-reflection x-ray patterns contain a fine structure that can be matched on a point by point basis with the crystal surface appearance and with the internal strain pattern of the underlaying crystal volume. Barrett (1) pointed this out for individual diffraction spots resulting from Laue (transmission) x-ray patterns. Figure 1 indicates the first step which might be taken to further investigate the inner structure of individual diffraction spots, say, as are obtained in a back-reflection photograph of a zinc single crystal. Berg (2) independently demonstrated that detailed structural information could be obtained from an x-ray spot by utilizing a single lattice reflection which satisfied the Bragg equation for characteristic x-radiation under conditions such that very good resolution resulted for the x-ray (back-reflection) picture of the diffracting crystal. This involved placing the crystal at a relatively large distance from the x-ray source so as to achieve a small divergence of x-rays satisfying the Bragg condition and, then, recording the diffracted x-ray intensity at a small distance from the crystal surface so as to minimize the spreading of the x-ray intensity diffracted from any point within the crystal volume. Barrett (3) further demonstrated the potential of this new microscopy in his presentation of the twenty-fourth annual lecture of the Institute of Metals Division of the AIME. For the back reflection geometry, an enhanced x-ray intensity was observed to be diffracted from mildly strained regions of the crystal. Barrett attributed the enhanced intensity to be due both to the greater angular range of x-rays able to be diffracted from a locally strained volume and to the thicker crystal layer able to diffract x-rays if it contains local strains. Near to the time of this latter work by Barrett, quite the reverse x-ray result was found by Borrmann (4) in that an anomalously large x-ray intensity was observed to be transmitted through relatively thick crystals satisfying the (Laue) diffraction condition so long as the crystals were very nearly perfect. Anomalous transmission was said to occur when a transmitted x-ray intensity was detected of magnitude far in excess of that expected from the normal attenuation of the beam due to absorption processes. Thus, anomalous transmission may occur for a transmitted x-ray beam when the product of the crystal absorption coefficient, μ times the crystal thickness, t, is much greater than 1. 0. This property of very nearly perfect crystals being able to anomalously transmit x-rays is explained within the framework of the dynamical theory of x-ray diffraction as given, for example, by von Laue (5).