摘要:

A horizontal diffractometer has been set up for transmission studies of liquid samples. An asymmetric, singly bent LiF monochromator in the primary X‐ray beam focuses the radiation on the receiving slit of the diffractometer. The sample rotates at half the angular speed of that of the X‐ray detector to retain focusing at all angles of diffraction. A high temperature furnace assembly (camera) has been constructed which fits on the diffractometer. Its heating element consists of a thin‐walled, pyrolitic graphite tube 38 mm in diameter. A special sample holder for the liquids is mounted on a boron nitride stool bolted to the bottom plate of the camera. The entire set‐up allows the measurement of the diffracted intensity between 2θ = 2° and 2θ = 90° corresponding toK= 4πsinθ/λ = 0.3 Å−1at 12.4 Å−1when MoKα radiation is used. Correction procedures to obtain the scattered intensity per atom from the raw data are discussed, and a comparison is made between the transmission and reflect

ISSN:1600-5767    

DOI:10.1107/S0021889869006844

出版商:International Union of Crystallography    

年代:1969

数据来源: WILEY

摘要:

The strain induced phase transformations produced in lead monoxide powders by ball milling at temperatures ranging from −196 to 200°C have been studied by X‐ray diffraction methods. It has been found that either of the two polymorphs, litharge and massicot, was partially converted to the other at all the temperatures investigated, and that, whichever polymorph was the starting material, the end product, after a sufficiently long time, was a mixture of the two polymorphs, both highly strained. The percentage of each phase present was found to be dependent on the temperature of deformation. The results have been interpreted by consideration of the production of the microstrain energy required to overcome the energy barrier to the transformation, and of the shear generated in the mill on the pressure‐temperature phase diagram. It is considered that shear stresses can affect the nature of the pressure‐temperature phase diagram, in a manner theoretically postulated by Kumazawa. The commercial importance of the results has been briefly

ISSN:1600-5767    

DOI:10.1107/S0021889869006856

出版商:International Union of Crystallography    

年代:1969

数据来源: WILEY

摘要:

A new study of the structure of vitreous silica has been made under greatly improved conditions. Using RhKα radiation with the method of fluorescence excitation, reliable intensity values were measured to 4π sinθ/λ = 20. The interpretation was in terms of pair functions, thereby eliminating the approximations in earlier work. Each silicon is tetrahedrally surrounded by 4 oxygen atoms, with a Si–O distance which is closely 1.62 Å. Each oxygen atom is bonded to 2 silicon atoms. The Si–O–Si bond angle α shows a distributionV(α) extending all the way from 120° to 180°, with a maximum at α = 144°. This wide variation in α is an important distinction between the vitreous and the crystalline forms of silica, and it furnishes an important criterion for any proposed model of vitreous silica. Good agreement with the measured pair function distribution curve was obtained by assuming a random orientation about the Si–O bond directions. The interpretation leads to the familiar random network model, but with the new results the

ISSN:1600-5767    

DOI:10.1107/S0021889869006868

出版商:International Union of Crystallography    

年代:1969

数据来源: WILEY

摘要:

For the measurement of crystallite orientation in regenerated cellulosic fibers, Hermans and co‐workers defined a parameterKin terms of the intensity distribution in the (10, 021) sickle. Their theory is extended in the present study to mercerized fibers. It is found from the experimental observations thatK is itself dependent on the X‐ray orientation factor, and possible reasons for this are advanced. The dependence ofKon the ratio of the number and diffractive powers of (021) and (10) planes is, however, confirmed. A regression equation based on the correlation ofKwith the readily observed relative peak height of 021 is found to be of practical interest in estimating the crystallite orientat

ISSN:1600-5767    

DOI:10.1107/S002188986900687X

出版商:International Union of Crystallography    

年代:1969

数据来源: WILEY

摘要:

The theory of the direct comparison X‐ray method of phase analysis is extended to correct for preferred orientation effects. Texture parameters are defined to assess the type and intensity of preferred orientation using data from diffractometer patterns. The analysis is illustrated with results obtained on three austenitic stainless steel

ISSN:1600-5767    

DOI:10.1107/S0021889869006881

出版商:International Union of Crystallography    

年代:1969

数据来源: WILEY

摘要:

Apparent particle sizes corresponding to the slope and intercept of the variance‐range curve are interpreted geometrically; the analytical results of Lele&Anantharaman for cylinders and certain prisms are confirmed. The slope apparent particle size is half the harmonic mean ofhsec ϕ andbcsc ϕ, wherehis the height of the cylinder or prism,bis the breadth of a rectangle having an area equal to that of its top face and a width equal to that of its radiation shadow, and ϕ is the angle between its axis and the diffraction vector. For cylinders, but not in general for prisms, the intercept apparent particle size is 1/√2 times the geometric mean of the same quantities. For a hemisphere of diameter d the slope apparent particle size is given byd/(1 + cos ϕ), where ϕ is the angle between the diffraction vector and the normal to the plane face, and the intercept apparent particle size is the square root of

ISSN:1600-5767    

DOI:10.1107/S0021889869006893

出版商:International Union of Crystallography    

年代:1969

数据来源: WILEY

摘要:

A new method of etching diamond is described which produces rapid etching and etch patterns which are decidedly better and more easily interpreted than those produced by the conventional method. It is also shown that the new method produces etch patterns having the same morphology as that of trigons observed on natural (111) faces and quadrons on (100) natural faces of diamond.

ISSN:1600-5767    

DOI:10.1107/S002188986900690X

出版商:International Union of Crystallography    

年代:1969

数据来源: WILEY

摘要:

Slightly twinned and untwinned single crystals of Ba2NaNb5O15have been studied by X‐ray techniques. Oscillation and full rotation X‐ray photographs show thecaxis to be twice the previously reported value; therefore, there are 8 formula units per unit cell. It was also found thatCmm2 (C2v11) is not the correct space group assignment for the crystals studied, and thatCcc2 (C2v13) appears to be lik

ISSN:1600-5767    

DOI:10.1107/S0021889869006911

出版商:International Union of Crystallography    

年代:1969

数据来源: WILEY

ISSN:1600-5767    

DOI:10.1107/S0021889869006935

出版商:International Union of Crystallography    

年代:1969

数据来源: WILEY

ISSN:1600-5767    

DOI:10.1107/S0021889869006959

出版商:International Union of Crystallography    

年代:1969

数据来源: WILEY