摘要:

A semi‐automated system has been developed for identifying the components of a crystalline mixture according to correlations between the diffraction pattern of the mixture and the Hanawalt index of the Powder Diffraction File. The system is designed for use in the laboratory with modest computing facilities,e.g.a disc or tape‐based 16 K mini‐computer. In the computerized stage of the system those components which cannot contribute to the measured pattern are automatically eliminated. Subsequent manual interpretation of the results of the computer search, preferably with the support of a semi‐quantitative elemental analysis, further reduces the number of poss

ISSN:1600-5767    

DOI:10.1107/S0021889876011849

出版商:International Union of Crystallography    

年代:1976

数据来源: WILEY

摘要:

In the computer indexing of powder diffraction patterns, an advance estimate of the volume of the unit cell is extremely valuable. This paper describes a method for estimating it directly from powder‐pattern data for the case of triclinic materials. The method involves an easily prepared graphical plot, the slope of which is proportional to the unit‐cell volume. First, the diffraction lines are numbered consecutively, starting with the largestdvalue (N= 1). A plot is then made of 1/Nversusd3. Theoretically, the resulting line has a slope of 3/(2πV) = 0.4775/Vfor triclinic compounds, whereVis the unit‐cell volume. Examination of the graphs plotted for a number of triclinic materials where the experimental data are of high quality shows that the slope consistently falls around 0.60/V. Hence, the volume of the unit cell and/or the calculated density can be estimated. In addition, this analysis gives a numerical measure of the fraction of possible diffraction lines actually ob

ISSN:1600-5767    

DOI:10.1107/S0021889876011850

出版商:International Union of Crystallography    

年代:1976

数据来源: WILEY

摘要:

A mathematical model for X‐ray powder‐diffraction phase analysis is formulated and, based on this model, new identification criteria are established and the conditions under which a solution is optimal are discussed. The proposed concept is illustrated with a three‐phase sample pr

ISSN:1600-5767    

DOI:10.1107/S0021889876011862

出版商:International Union of Crystallography    

年代:1976

数据来源: WILEY

摘要:

The total X‐ray intensity as a function ofh(his the radial coordinate in reciprocal space), scattered by an isotropic system of particles of equal shapes but of different sizesR, can, under certain conditions, be expressed as an integral over the particle size distribution functionD(R), multiplied by a common single‐particle function ofhRwhich can be calculated from the assumed particle shape. In the first methodD(R) is calculated from this relation by the method of least squares, in which values ofDat a limited number of particle sizes are the unknowns. To avoid oscillations in theDcurve, constraints are imposed on theDvalues. The proper weight to be assigned to these constraints must be determined by trial and error. The method has been adapted to suit various assumptions and requirements as to the shape of the particles, the type of distribution function to be calculated, and experimental conditions (slit or pinhole focusing). The second method is essentially the one described by Schmidt, Weil&Brill [X‐ray&Electron Methods of Analysis, pp. 86–100. (1968), New York: Plenum], which, however, is adapted to the use of slit‐smeared intensities. Both methods may give rise to artefacts in the calculated distribution functions in the range of the smallest particle sizes, which are sensitive to the setting of the various parameters and to experimental errors. However, the position and shape of the main maxima can usually be determined quite well. The agreement between the results obtained by the two methods is sat

ISSN:1600-5767    

DOI:10.1107/S0021889876011874

出版商:International Union of Crystallography    

年代:1976

数据来源: WILEY

摘要:

A computer program for numerical calculation has been written in Fortran which enables Fourier coefficients of associated generalized Legendre polynomials to be obtained in the general case. Thus the generalized spherical harmonics, involved in the quantitative analysis of the distribution function of the orientations of a texture, can be calculated.

ISSN:1600-5767    

DOI:10.1107/S0021889876011886

出版商:International Union of Crystallography    

年代:1976

数据来源: WILEY

摘要:

A description is given of the computer‐controlled triple‐axis neutron spectrometer system installed at the PLUTO reactor at Harwell. Following the operation of the original system for several years a number of major improvements have been made which have resulted in a highly reliable system which provides the users with very powerful and extensive facilities. Following a general description of the modified spectrometer, details are given of the new computerized control system which utilizes a CAMAC modular interface and the functions of the various programs which are now available to the users are descri

ISSN:1600-5767    

DOI:10.1107/S0021889876011904

出版商:International Union of Crystallography    

年代:1976

数据来源: WILEY

摘要:

A new type of thermal neutron polarizing monochromator, consisting of alternate thin layers of iron and germanium, has been constructed and tested. Bragg reflection from such artificial `crystals' in the fully magnetized state yields a highly polarized beam with high reflecting efficiency (~0.84) for the reflected spin state. These multilayer monochromators have the additional advantage that higher orders in the reflected beam are almost completely suppressed. Since d spacings are typically large (~100 Å), they produce a broader wavelength distribution than conventional single‐crystal polarizing monochromators. Nevertheless, there are many applications where wavelength resolution is of secondary importance and the large gain in intensity (~40‐fold) over conventional polarizing crystals can be a considerable advantage. Multilayers can also be used to advantage in combination with good monochromating crystals such as pyrolytic graphite or beryllium to produce polarized beams of high intensity and good wavelength reso

ISSN:1600-5767    

DOI:10.1107/S0021889876011916

出版商:International Union of Crystallography    

年代:1976

数据来源: WILEY

摘要:

It may be very useful to know a mathematical expression which helps reconstruct the X‐ray diffraction profile. It is in fact easier to work on one relationI(θ) =f(θ) rather than on a series of experimental points. The relation proposed in this paper,gives a good correspondence between experimental values and the values calculated in the case of a monochromatic source. Its use still remains very simple in the case of a doublet,Kα1Kα2, which can be expressed as follows:IKα1(x) is given by the previous expression, Δ represents the angular separation of the doublet. Different forms of profiles are used in order to verify the validity of the relation proposed and the results are compared with those resulting from the Rachinger classical

ISSN:1600-5767    

DOI:10.1107/S0021889876011928

出版商:International Union of Crystallography    

年代:1976

数据来源: WILEY

摘要:

A vertical float zoner combined with thermal imaging is uniquely suited to investigation of high‐temperature noncontaminating melts by X‐ray diffraction. Radiation from a halogen lamp is focused on the sintered‐powder rods by means of the gold‐plated internal surface of an ellipsoidal shell. This image furnace can easily be mounted on a conventional horizontal type of powder diffractometer, provides atmosphere control, and permits rapid heating and cooling. A temperature of 1700°C can readily be reached. The presence of a gap for the passage of X‐rays solves the problem of X‐ray absorption by window materials, and sufficient lateral length of the gap allows X‐ray measurement over a wide dif

ISSN:1600-5767    

DOI:10.1107/S002188987601193X

出版商:International Union of Crystallography    

年代:1976

数据来源: WILEY

摘要:

The fluidized‐bed vapour phase deposition of β‐SiC on nuclear fuel granules can produce polygonal crystals. The examination of these and their etch figures by scanning electron microscopy indicates an internal structure composed of {111} planar sheets. The disposition of these sheets is discussed with the aid of three‐dimensional models. It is concluded that a maximum of four sheet orientations can occur. From these, six families of sheet pairs can be made by appropriate combinations: these are labelled according to the [110] directions of the spines created by their intersections. The sheets produce traces on the external crystal faces, and the various possible juxtapositions of these traces are dis

ISSN:1600-5767    

DOI:10.1107/S0021889876011941

出版商:International Union of Crystallography    

年代:1976

数据来源: WILEY