Standard X-ray Diffraction Research Articles

Mineral Reaction Pathways and Mass Transfer in Sandstone-Shale Sequences, Brazil: ABSTRACT

The major purpose of this study is to describe and quantify mineral reactions, reaction pathways, and mass transfer accompanying burial of passive margin sandstone-shale sequences, offshore Brazil. Four basins were investigated, encompassing a range of sandstone-shale compositions. Because these basins have similar geologic histories, the effect of original detrital mineralogy on diagenetic products could be ascertained. Standard light microscopy, X-ray diffraction, EM, SEM, and isotopic and chemical analyses provided the basis for interpretation of mineralogy, texture, and diagenetic reactions. The initial mineral composition of the sediments was a major control of diagenetic products. Arkose and lithic arkose are the dominant sandstone types in these basins. Dioctahedral clay minerals, chlorite, and quartz characterize arkoses, whereas trioctahedral clays (saponite and corrensite) and zeolites are found in lithic sandstones. Dioctahedral smectite-rich shales exhibit the classical smectite/illite to illite burial pattern. However, mafic, trioctahedral clay-rich shales show a burial sequence of saponite to chlorite/saponite mixed-layer, a progressive increase of chlorite-rich phases with increasing burial depth. The structural change of disordered to ordered interstratification of mixed-layer chlorite/saponite occurs in the temperature range of 60 to 80°C, and at vitrinite reflectance values around 0.7. Increasing substitution of silicon by aluminum in tetrahedral sites is the major chemical change accompanying transformation of saponite to chlorite via corrensite. Material balance calculations indicate that sandstones lose less than 2% K+, which probably enters interstratified shales, and gain less than 3% H2O, H+, and CO2 during burial diagenesis. Therefore, the burial pathway of Brazilian sandstone End_Page 558------------------------------ diagenesis is nearly isochemical. End_of_Article - Last_Page 559------------

Powder-Pattern: A System of Programs for Processing and Interpreting Powder Diffraction Data

The production of standard x-ray diffraction patterns at NBS imposes special requirements in the data processing of powder patterns. The patterns should be complete and have an overall accuracy of better than 0.01 degree two theta. To ensure completeness all the observable peaks should be indexed. To make certain that the sample is a pure phase, weak peaks have to be identified as well.The indexing of all the peaks implies that the cell constants must be known and there should be a good agreement between all the calculated and observed peak positions. In practice this is achieved by a least-squares refinement of the unit cell parameters. This serves as a test of the assumed unit cell and also as an interpretation of the observed peaks. Finally, an attempt is made to identify the space group. This step also requires the identification of weak peaks. The agreement of a known space group with the observed reflections further confirms the purity of the sample.

X-Ray Diffraction Study of the Ge(001) Reconstructed Surface

Standard x-ray diffraction in which a reflection goemetry is used is shown to have a simple interpretation and adequate sensitivity for determining the structure of monolayers. It has been utilized to verify that subsurface strain occurs in Ge(001)-(2\ifmmode\times\else\texttimes\fi{}1) reconstruction.

Local lattice rotations at second phase particles in deformed metals

An experimental investigation of local lattice rotations at non-deformable second phase particles in the size range 0.02 to 5 μm in aluminium and copper single crystals deformed to tensile strains of up to 0.5 is reported. A TEM method in which the misoriented regions are imaged in dark field as the specimen is accurately tilted has been used, and the results have been confirmed by standard X-ray and electron diffraction techniques. The region of maximum misorientation, close to the particle, is rotated about the roller axis [1 2 1] with respect to the matrix. For particles larger than ~ 2 μm, the misorientation increases linearly with shear strain, and values of up to ~ 45° have been measured. The misorientation for a given strain decreases with decreasing particle size, being very small for particles of diameter less than ~ 0.1 μm. These results, together with previous work, are used to assess the importance of the various deformation mechanisms at particles, over a wide range of strains and particle sizes.

The Electron Microscope in Earth Sciences

Over the last ten years the electron microscope has become well-established in mineralogical research and what used to be an exotic instrument has found its way into several geology departments. The rapidly growing literature on electron microscopy in mineralogy has recently been summarized (Wenk et al., 1976) and there is not much point in systematically reviewing progress of the last two years. Philosophy and techniques remained largely the same except that there is more emphasis on high resolution, and energy dispersive X-ray detectors have become standard attachments of electron microscopes. Instead I would like to use some examples studied at the Geology Department at Berkeley during the last few months to illustrate a variety of applications in materials which could not be investigated with conventional techniques such as light microscopy, standard chemical analyses and X-ray diffraction. Geology is a broad science which ranges from the study of crystal structures on the atomic scale to processes taking place during mountain building on the scale of the size of continents. The transmission electron microscope has been used in such diverse fields as crystallography, petrology, rock deformation, stratigraphy and environmental geology.

Clay-Mineral Stratigraphy of Pre-Illinoian Lake Clays from the Cincinnati Region

The pre-Illinoian lake clays of the Cincinnati region represent remnant stream-valley fills formed when the northward-flowing, preglacial Teays-age drainage was blocked and ponded by the first glacier to enter the region. The age of the clays is not definitely known, but the depositional history and origin of the clays can be inferred to a large extent with the aid of clay-mineral stratigraphy. The two most complete lake-clay deposits in the region were analyzed for clay-mineral composition using standard x-ray diffraction techniques. The vertical succession of clay-mineral compositions is very similar for the two localities analyzed, indicating nearly identical depositional histories. This similar succession of clay-mineral compositions enabled division of each clay deposit into zones, or vertical sequences of lake-clay strata characterized by a distinctive clay-mineral composition and an inferred depositional history. The depositional history of the two clay deposits as interpreted from clay-mineral stratigraphy includes three phases of deposition, each with a different source: (1) initiation of ponding accompanied by reworking of underlying stream alluvium (zone of alluvial contribution), (2) a longer period of ponding in which the northward-flowing drainage was the major source of clay (zone of southern fluvial contribution), and (3) diversion of the northward-flowing drainage and a stage of ponding in which the advancing ice sheet became the major source of clay (zone of till contribution). Eventually, the lakes were breached and overridden by the advancing ice sheet reflected by the presence of till overlying lake clays.

A Diffractometer Based Energy Dispersive Elemental Analyser

Instrumentation has been developed which employs standard x-ray diffraction equipment and an energy dispersive analyzer for elemental and phase analysis. A General Electric XRD-6 diffractometer, a sample chamber, a Nuclear Semiconductor energy dispersive analyzer (EDA) with 155 eV resolution, and a Tracor Northern multichannel analyzer are its main components.

Isothermal compression and bcc→hcp phase transition of iron-cobalt alloys up to 300 kbar at room temperature

Iron-cobalt alloys with 10, 20, and 40 wt% cobalt have been studied at room temperature under high pressure by means of x-ray diffraction techniques, employing the diamond-anvil pressure cell. The crystallographic x-ray data for the three alloys at zero pressure were obtained using the standard Debye-Scherrer x-ray diffraction technique. The volume-pressure relationship was established and, using the Birch-Murnaghan equation of state, the compressibility β for the above alloys was found to remain constant or increase slightly with increasing cobalt content. This is consistent with the electron dilution theory. The bcc→hcp phase transformation in each alloy was seen visually under the microscope in reflected light and it was found to take place when the pressure increased to 163±5, 195±6, and 290±10 kbar respectively, for the 10, 20, and 40 wt% Fe-Co alloys. The volume change at the transition was found to decrease slightly with increasing cobalt content and the crystallographic axis ratio c/a of the hcp phase of the alloys was found to increase with increasing cobalt content.

X-ray Intensities from Copper-Target Diffraction Tubes

The relative intensities of the Kα characteristic radiation obtained from copper-target X-ray diffraction tubes have been calculated for a range of tube accelerating voltages and take-off angles. The calculations employ an over-voltage function, and absorption and atomic number corrections similar to those used in electron microprobe analysis. They apply only to constant potential X-ray generators. Measurements of actual intensities obtained on a Picker diffractometer using a sodium chloride monochromator gave relative intensities in close agreement with those calculated. The calculations and measurements show that there is an optimum tube voltage, with respect to intensity, for each take-off angle. This voltage increases with increasing take-off angle. The application of these results to the consideration of the relative intensities obtainable from broad, standard and fine focus copper-target X-ray diffraction tubes is discussed.

Chemical weathering and Rb-Sr whole rock ages

Weathered whole rock samples of five lithic units from Maine, Virginia, North Carolina and South Carolina were analyzed to evaluate the effect of chemical weathering on the Rb-Sr ages of the original rocks. Major element and turbidity analyses, as well as standard X-ray diffraction and petrographic studies were made on selected samples. All weathered granitic rocks are friable; several are almost saprolites. Volcanic rocks are powdery or are pitted as a result of the weathering of plagioclase phenocrysts. The weathering profiles studied all are young relative to the age of the unaltered rock. Considering the extent of weathering, however, ages of the weathered samples are remarkably close to the published ages for unaltered samples of the same units. Weathered samples have ages ranging from essentially the same as fresh samples to no more than 20% younger than the age obtained from the fresh samples. In one profile, we have attempted to quantify the extent of weathering: there is a positive correlation between our measure of the degree of weathering and per cent ‘lowering’ of the age. Weathering of plagioclase apparently has little effect on whole rock ages; ages are lowered significantly only where biotite and K-feldspar have undergone considerable alteration.

Standard X-ray diffraction powder patterns : 70 substances are analysed, 52 represent experimental data and 18 are calculated US. Nat. Bur. Stand. Monograph. Sect. 11, N25, 1974, 134P Swanson H.E., McMurdie H.F., Morris M.C.

Standard X-ray diffraction powder patterns : 70 substances are analysed, 52 represent experimental data and 18 are calculated US. Nat. Bur. Stand. Monograph. Sect. 11, N25, 1974, 134P Swanson H.E., McMurdie H.F., Morris M.C.

Standard X-ray diffraction powder patterns. Section 11by H. E. Swanson, H. F. McMurdie, M. C. Morris, E. H. Evans and B. Paretzkin

<i>Standard X-ray diffraction powder patterns. Section 11</i>by H. E. Swanson, H. F. McMurdie, M. C. Morris, E. H. Evans and B. Paretzkin

X-ray topographic studies of NaClO 3 crystals grown from aqueous solution

NaClO 3 crystals grown from a spontaneous nucleus in an aqueous solution were studied by standard X-ray diffraction topography. As in the case of NaCl [Ikeno, Maruyama and Kato, J. Crystal Growth 3/4 (1968) 683], dislocations starting from the nucleus were observed. They are always perpendicular to the growth surfaces. Except for these dislocations, the crystal is nearly perfect within a growth sector. Pendellösung fringes are clearly observed in all cases. The growth sectors, however, are mutually misorientated with an angle of the order of 10 -6 radian. Characteristic fringes due to this misorientation were observed.

Crystal and molecular structure of the five-co-ordinate complex diisothiocyanato-[NN-bis-(2-diethylaminoethyl)-2-diphenylarsinoethyl-amine-NNN]-nickel(II)

The structure of di-isothiocyanato-[NN-bis-(2-diethylaminoethyl)-2-diphenylarsinoethylamine-NNN]-nickel(II) has been determined by standard X-ray diffraction methods from 2171 observations measured by a densitometer. The unit-cell dimensions are: a= 15·550 ± 0·013, b= 14·552 ± 0·016, c= 18·114 ± 0·015 A, β= 127° 39′± 4′; space group P21/c. The nickel atom is surrounded by a set of five nitrogen atoms, with approximate square-pyramidal geometry. The average of the two Ni–N(NCS) bond distances is 1·95(1)A. The central Ni–N bond [2·08(1)A] formed by the ligand molecule is shorter than the other two Ni–N bonds [2·20(2)A, average]. The arsenic atom of the ligand does not co-ordinate.

Mössbauer-Effect Studies of Iron-Tin Alloys

Solid solutions $\mathrm{Fe}\mathrm{Sn}$ and the compounds ${\mathrm{Fe}}_{3}$Sn, ${\mathrm{Fe}}_{5}$${\mathrm{Sn}}_{3}$, ${\mathrm{Fe}}_{3}$${\mathrm{Sn}}_{2}$, FeSn, and Fe${\mathrm{Sn}}_{2}$ have been studied by the M\ossabauer effect in both Fe and Sn nuclei. Also, standard x-ray diffraction and magnetization studies were performed. The magnetic hyperfine (hf) fields in the Fe and Sn components are not, in general, proportional to the magnetic moments. It is found that two simple relations containing the coordination numbers can be used within a wide range to describe the variations of these fields as a function of composition. The collected results indicate that the magnetic hf field at the iron nucleus is rather insensitive to the conduction-electron polarization in these alloys. The isomer shifts are linearly related to the number of Fe-Sn bonds in such a way that bonding reduces the electron densities at both nuclei. The bonding is covalentlike and predominantly unpolarized.

Standard x-ray diffraction powder patterns

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Measurement of Whisker Orientation in Composites by X-Ray Diffraction*

Standard x-ray diffraction techniques have been shown to give a quantitative measure of orientation of α-SiC whiskers in polymeric matrices. The pole distributions of the (1120) planes of SiC have been fitted to a normal bivariate distribution where the standard deviation is taken as a measure of the degree of orientation and the volume under the surface as the volume fraction of whiskers oriented within a given set of limits. A semiquantitative trans mission photographic method was also used and the half-arc lengths are shown to give results comparable with those of the quantitative methods. The specimens were whisker filled strands of cellulose triacetate and cupra-ammonium rayon (Cupram), made by a wet spinning process, and an epoxy composite made from the Cupram strand. The strands are shown to exhibit rotational symmetry about the long axis whereas the composite does not.

An automatic balanced filter device for X-ray diffraction experiments

An automatic balanced filter box which may be used on most standard X-ray diffraction tubes is described. It is designed to be used in conjunction with a wide variety of automated X-ray diffraction experiments to change Ross filters and insert attenuators into the incident X-ray beam on receipt of appropriate commands from the control system. The positions of the filters and attenuators may be displayed at all times by using feedback signals generated by a combination of light sources and photocells.

The Martensitic Transformation in Cobalt

The properties of the fcc to hcp transformation in cobalt single-crystal whiskers have been determined. Studies of the crystallographic properties and dislocation structure using optical, standard x-ray diffraction, and high-resolution x-ray diffraction topographic techniques are herein reported. It is shown that the atomic movements associated with the transformation in cobalt initiate at the most highly strained regions in the crystal. The strain configuration and the crystal boundaries act as a combined mechanism restricting the transformation to a particular set of {111} planes. When the strain distribution is nonuniform throughout the crystal, localized regions within the crystal utilize different sets of {111} transformation planes. The transformation from the fcc to hcp phase is accomplished by the glide of Shockley partial dislocations through the lattice. Frank partial dislocations remain pinned in the lattice. These partials are formed from the extension of total dislocations. Martensitic platelets result from either the glide of Shockley partial dislocations which have different slip vectors in parallel and adjacent sections of the crystal or the pinning of Frank partial dislocations which form the boundary of faulted regions. The platelets intersecting the crystal surfaces produce observable slip bands.

A Rapid Method for Determining Compound Composition of Cement Clinker: Application to Closed Loop Kiln Control

A procedure for determination of phase composition of commercial cement clinker using quantitative x-ray powder diffraction analysis is described. An external standard and comparison of peak heights rather than the peak areas are used for rapid analysis. Several standard curves were prepared using diffraction patterns from known mixtures of previously prepared pure components which exist in cement clinker. For purposes of comparison, both the suggested external standard method and the internal standard method which is generally accepted for quantitative X-ray diffraction analysis were used. It was found that the faster external standard method gives analysis of important clinker constituents with accuracy adequate for quality control in a cement plant. With the use of suggested grinding procedure and an automatic sample changer attachment to standard X-ray diffraction equipment, it is possible to obtain an on-line analysis of clinker in one half hour. This analysis can then be deployed in performing closed loop control of a cement kiln with a proposed algorithm.