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  • 1
    Electronic Resource
    Electronic Resource
    Small-angle neutron-scattering studies of the template-mediated crystallization of ZSM-5-type zeolite (1992)
    s.l. : American Chemical Society
    Langmuir 8 (1992), S. 1045-1048 
    Details
    ISSN: 1520-5827
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/la00040a005
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  • 2
    Electronic Resource
    Electronic Resource
    Determination of local atomic configurations for binary substitutional alloys (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 351-356 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A method is described whereby the complete distribution of first-nearest-neighbor atomic configurations can be determined from experimental short-range order coefficients for binary substitutional f.c.c. alloys. The process involves the computer simulation of the structure represented by the experimental αi by a Gehlen–Cohen-type procedure, followed by the classification of each atom of a given species in the model as one of the 144 crystallographically distinct nearest-neighbor types. These simulation and searching procedures are then used to demonstrate the consistency of the information one can expect to obtain from a given set of αi by `close fitting' to different numbers of coordination shells. It is shown, for example, that a six-shell close fit to a selected set of αi can yield a solution with a mean relative deviation of about five per cent for the nearest-neighbor configuration concentrations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S002188987901267X
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  • 3
    Electronic Resource
    Electronic Resource
    The short-range-order structure of α-phase Cu–Al alloys (1978)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 34 (1978), S. 667-681 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A three-dimensional X-ray diffuse scattering investigation of the short-range order in a-phase Cu-Al alloys, and its dependence on alloy composition, quenching temperature and isothermal annealing at 250°C, has been carried out. The Cowley-Warren order coefficients were determined after separation of the size effects using a procedure based on the Boric-Sparks quadratic approximation of atomic displacements. These short-range-order coefficients were analyzed in terms of the complete spectrum of nearest-neighbor atomic configurations, without the necessity of invoking a specific model for the characteristic feature(s) of the local-order structure. Although in the composition range investigated the equilibrium condition is a short-range-ordered structure, the nearest-neighbor configurations bear a marked resemblance to the long-period anti-phase-shift structures which have been found in alloys with more Al. Because essentially all of the most highly ordered configurations were found to exist isolated from each other in a 9.13 at.% Al alloy, it is concluded that they represent inherently stable, spatial arrangements of the atoms. In alloys containing 13.56 and 14.76 at.% Al, connected ordered configurations, or small ordered domains, were detected, and this effect increases markedly with increasing Al content. Isothermal annealing at 250°C of a Cu-14.76 at.% Al alloy quenched from 650°C results in a net disordering process; however, superimposed on this, in the early stages of annealing, is an enhancement of the population density of an atomic configuration confined to planes of the { 111 } type. This is interpreted as evidence for occurrence of the Suzuki mechanism. It is argued that the body of published experimental observations on this alloy system is better understood if one recognizes the existence of stacking faults, and their interaction with the matrix, in addition to that of short-range order.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739478001424
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  • 4
    Electronic Resource
    Electronic Resource
    A method for the recovery of local order coefficients from two-dimensional intensity data for binary f.c.c. alloys (1975)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 8 (1975), S. 115-121 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A method is derived which permits the Cowley–Warren order parameters to be recovered from diffuse scattering measurements made in one plane in reciprocal space for systems with only short-range correlations. The procedure is demonstrated first by application to some at-temperature measurements on Cu3Au and then by considering some simulated diffraction profiles, with and without controlled errors. From the simulated scattering without error, an empirical rule is developed which allows one to decide if a given profile is amenable to this recovery method. By simulation of data with varying constant-background contributions, it is shown that such an error can be recognized and corrected.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889875009764
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  • 5
    Electronic Resource
    Electronic Resource
    Comparison of X-ray and neutron small-angle scattering from an Al–Zn alloy (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 581-583 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The normalized integrated small-angle scattered intensity for Al-Zn alloys should be independent of whether the measurements are made with X-rays or neutrons. In order to check this, and thus the correction and standardization processes, the small-angle scattering from an Al-5.05 at.% Zn alloy containing GP zones was measured with these two types of radiation. The data were corrected and converted to absolute units with reference to the commonly accepted secondary standards: vanadium for the neutron data and polyethylene (Lupolen) for the X-ray data. The results are shown to differ by, at best, 6% if reasonable values for the change in atomic volume with alloy composition are taken into account. These findings are compared with those available from the literature, and the consistency is found to be somewhat lacking. Additional careful work is clearly needed to determine if the difficulty is traceable to the data correction or to the conversion to absolute units.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S002188987801393X
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  • 6
    Electronic Resource
    Electronic Resource
    Phase separation in an Ni–12·5 at.% Al alloy at 575 K (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 873-877 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The phase separation in a supersaturated Ni–12.5 at.% Al alloy has been investigated by high-angle diffuse scattering, small-angle scattering, transmission electron microscopy and electrical resistivity methods. High-angle X-ray diffuse scattering measured at room temperature on a bulk single-crystal homogenized and quenched from 1323 K showed well developed short-range atomic ordering. An electrical resistivity isochrone shows a marked peak at about 675 K. Small-angle scattering measurements on samples annealed at 823 K clearly indicate that, at this temperature, phase separation occurs by a nucleation and growth process. It has been argued that a cluster coagulation model well represents the processes occurring at 823 K. It is, however, not required that the same process be operational at lower temperatures, particularly below the break in the resistivity isochrone. Measurements for annealing times up to 840 h at 575 K reveal weak small-angle scattering which has some of the characteristics of a continuous transformation. However, much longer transformation times at the lower temperature will need to be investigated before the possibility that this is only a kinetic effect associated with slow nucleation of the second phase can be ruled out.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889888005333
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  • 7
    Electronic Resource
    Electronic Resource
    On the determination of the metastable miscibility gap in ternary alloys from small-angle measurements. II. Application to the system Al–Zn–Mg (1977)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 10 (1977), S. 28-31 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The method described in the preceding paper [Gerold (1977), J. Appl. Cryst. 10, 25–27] has been applied to the system Al–Zn–Mg where the small-angle scattering has been measured from nine alloys having zinc and magnesium contents up to 5.4 and 2.5 at. %, respectively. The alloys were annealed at room temperature where the metastable equilibrium of GP zone formation is reached after about one month. From combined analysis of the X-ray and neutron results the slopes of the tie-lines have been evaluated in this region of the phase diagram. The further analysis leads to the approximate determination of the miscibility gap limits. The confidence limits of the determination were restricted by it not being possible to make measurements far enough out in the tail of the neutron scattering profile from the small GP zones (diameter less than 30 Å) to allow the background intensity to be separated completely satisfactorily. The ultimate limiting factor for this type of analysis may be the accuracy to which the mean atomic volumes are known.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889877012758
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  • 8
    Electronic Resource
    Electronic Resource
    Characterization of the locally ordered regions in short-range ordered α-phase Cu–Al alloys (1980)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 372-378 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The ordered domain structure present in the α-phase Cu-Al alloys investigated by Epperson, Ffirnrohr & Ortiz [Acta Cryst. (1978), A34, 667-681] is determined by an extension of the computer method developed recently by Epperson [J. Appl. Cryst. (1979), 12, 351-356] for analyzing a Gehlen-Cohen type simulated structure for a binary, f.c.c., locally ordered alloy in terms of nearest-neighbor atomic configurations. The dominant ordered feature of the more concentrated of these alloys is the existence of randomly dispersed Boric-Sparks tetrahedra; that is, four nearest-neighbor Al atoms arranged tetrahedrally about a Cu atom. The majority of these tetrahedra are isolated; however, as many as three or four are occasionally found to be joined in fragments of a Cu3Au-type antiphase-shift structure. This extended ordered structure also incorporates the Cu3Au-type ring configuration, another principal characteristic structural feature of these Cu-Al alloys. As a typical example, a Cu-14.76 at.% Al alloy quenched from 923 K and annealed for 1580 h at 423 K was found to contain 87 such locally ordered regions in an 8000-atom model. Of these 'domains', 74 were isolated tetrahedra and the remainder consisted of pairs of tetrahedra joined such that their central atoms were mutual second-nearest neighbors. For this alloy and heat treatment, the locally ordered regions of this type amount to about 14 volume % of the microstructure and contain 32% of the Al in the alloy. The average (spherical) domain size is only 3.4 Å. Not only are the locally ordered regions very small, but there are also perceptible imperfections in the packing sequence.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739480000848
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  • 9
    Electronic Resource
    Electronic Resource
    The local atomic order of a Ni–12.7 at.% Al alloy quenched from 1323 K (1983)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 740-746 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: High-angle X-ray diffuse scattering has been measured in a volume element in reciprocal space for a Ni-12.7 at.% Al alloy single crystal quenched from 1323 K. The Cowley-Warren order parameters were determined after separation of the first- and second-order size effects, using a procedure based on the Borie-Sparks quadratic approximation of atomic displacements. The experimental order coefficients were used to reconstruct the real-space locally ordered distribution of atoms, from which the spectrum of nearest-neighbor atomic configurations was determined. Some 61% of the Al atoms were found to be in a planar ordered configuration consisting of a nickel atom and four nearest-neighbor aluminum atoms, the basic structural unit of Ni3Al. These planar elementary ordered units were, of course, distributed on the three equivalent {100} planes. While most of the ordered 'domains' consisted of from one to three Ni3Al rings, a few domains were found to contain on the order of a hundred such elementary ordered units. The larger ordered domains may be thought of as embryos of the ordered Ni3Al phase which have formed during quenching of the bulk alloy single crystal. There is evidence that the spatial distribution of ordered domains is not random.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108767383001476
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  • 10
    Electronic Resource
    Electronic Resource
    Small-angle scattering at a pulsed neutron source: comparison with a steady-state reactor (1982)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 15 (1982), S. 443-448 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A time-of-flight small-angle diffractometer employing seven tapered collimator elements and a two-dimensional gas proportional counter was successfully utilized to collect small-angle scattering data from a solution sample of the lipid salt cetylpyridinium chloride, C21H38N+.Cl−, at the Argonne National Laboratory prototype pulsed spallation neutron source, ZING-P′. Comparison of the small-angle scattering observed from the same compound at the University of Missouri Research Reactor corroborated the ZING-P′ results. The results are used to compare the neutron flux available from the ZING-P′ source relative to the well characterized University of Missouri source. Calculations based on experimentally determined parameters indicated the time-averaged rate of detected neutrons at the ZING-P′ pulsed spallation source to have been at least 33% higher than the steady-state count rate from the same sample. Differences between time-of-flight techniques and conventional steady-state techniques are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889882012333
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