Powder X-ray diffraction (XRD) has been exploited to establish the structural properties of a porous interpenetrated mixed-ligand metal-organic framework material prepared by solid-state grinding, recognizing that product phases from mechanochemical synthesis are typically microcrystalline powders. The importance of subjecting the powder XRD data to rigorous scrutiny in such applications is emphasized.
The limitations of the various X-ray diffraction methods which have been used to study the structure of aged alloys are discussed. A method which employs a stationary single crystal and characteristic radiation is described. The method is applied to the structures in aged A1-Ag and A1-Mg-Si alloys. Evidence for one-and two-dimensional diffraction is reported for both alloys. Limitation of particle dimensions is proposed as a ~eneral explanation of the diffraction effects; this is the most suitable explanation for patterns of A1-Mg-Si alloys. Reciprocal-lattice points for thick particles of the precipitate structure evolve from rods for thin platelets, and evolve earlier from planar areas in the reciprocal lattice corresponding to particles that have only one resolvable dimension. A change in structure to that of the precipitate has occurred at the earliest detectable stage. Indefinite periodicities in the matrix structure cannot account for the data for either this alloy or for a previously studied A1-Mg alloy. The interpretation based on particle size is also adequate for other alloy systems, such as A1-Cu and A1-Ag, in which the diffraction effects of the precipitate are more intimately related to those of the matrix. The existence of predominantly one-dimensional particles prior to the platelike particles in the sequence of growth is identified. This is a new concept in the theory of the precipitation process.
A new method for preparing divergent beam x-ray photographs of crystals is presented. This employs the usual Laue transmission camera and a collimated primary beam of x-rays. Fluorescent radiation originating either in the crystal sample or at a radiator in front of the crystal is used as the source of divergent x-rays. Some applications of the technique to determinations of orientation, lattice parameters, and crystal perfection are illustrated.
The integration was performed graphically from Blackett's energy-distribution curve (I vs. E) for the ionizing component at sea level, 5 using Bethe's theory for the values of s{E). Since the form of Bethe's curve is not dependent on the substance of the absorber, there is real meaning to the comparison of the theoretical value of s c /s e for hydrogen with the experimental value for the helium-butane mixture.It is clear that the results given here are essentially in agreement with theory. Cosyns' method, which employs only one counter, seems to be subject to scattering effects to a greater extent than he indicates.Hazen's value of s e was obtained from the cloud-chamber tracks of twenty-one beta-particles in the 0.4-7.0-Mev range, which may account somewhat for the discrepancy in this case, since the primary ionization rises quite sharply for energies less than 1 Mev.The construction of a beta-ray spectrometer is now in process, which should make possible an accurate determination of s(E) for various gases. This measurement for hydrogen is being made at the present time by the method herein described.The author wishes to express his sincere appreciation of the frequent advice and suggestions of Mr.
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