scholarly journals EFFECT OF VARIOUS PRETREATMENTS ON X-RAY DIFFRACTION PATTERNS OF CLAY FRACTIONS OF PODZOLIC B HORIZONS

1981 ◽  
Vol 61 (2) ◽  
pp. 311-316 ◽  
Author(s):  
C. WANG ◽  
H. KODAMA ◽  
N. M. MILES

The objective of this study was to compare the effects of various pretreatments on the X-ray identification and quantification of clay-sized minerals from some podzolic B horizons. After soil samples were treated with H2O2 to remove organic matter, clay fractions were dispersed, separated, and freeze-dried. A portion of each clay sample was subjected to the following pretreatments: ultrasonic bath, extraction by citrate-dithionite, extraction by 0.5 N NaOH, and extraction by Tiron. Oriented slides were used for identification and quantification of clay minerals after each pretreatment. The X-ray patterns for ultrasonically dispersed samples were used as a basis for evaluating the effectiveness of the three chemical pretreatments. Tiron pretreatment was found to be the most suitable method for removal of amorphous material from clay separates of podzolic B horizons. The traditional citrate-dithionite method was not effective in removing amorphous Si from clays. The 0.5 N NaOH method is not recommended because it resulted in significant destruction of phyllosilicates and it was not effective in removing amorphous Fe.

The presence on X-ray diffraction patterns of anomalous reflexions, that is to say, reflexions which cannot be accounted for by the simple theory of diffraction, is almost a commonplace. Many of these effects are no doubt to be ascribed to imperfections in the specimen, strains, etc., but even after these have been taken into account there remain streaks and spots for which there is no satisfactory explanation. The observation of effects of the type considered here is by no means novel; Friedrich (1913) recorded them as radial streaks running through the Laue spots in a photograph of KCl. The extra spots are generally very weak compared with the normal Laue reflexions and indeed may not be observed at all unless the photographs are somewhat over-exposed. They are most easily observed on Laue photographs taken with a tube emitting a characteristic radiation such as the K radiation of Cu or Ag, and their study will be greatly facilitated by the use of powerful sources of monochromatic radiation.


Author(s):  
Racquel Z. LeGeros ◽  
John P. LeGeros ◽  
Otto R. Trautz ◽  
W. Paul Shirra

The inorganic phase of calcified tissues of vertebrates he an apatite structure [Ca10(PO4)6(OH)2] while the inorganic phase of the invertebrates such as crustaceans is well crystallized calcium carbonate [CaCO3] in the form of either calcite, aragonite, and sometimes, vaterite. In rare cases, “amorphous” deposits are found such as in the concretions of tapeworm (Saginata Marginata), in the tendon of lobster claw, and in the statoconia of the human ear.Considerable differences in the “crystallinity” of human enamel, bone or dentine, and tapeworm concretions are demonstrated in the size and/or strain broadening of their x-ray diffraction patterns (Fig.1). The pattern of human enamel (1A) demonstrates that it is very well crystallized apatite; whereas the pattern of bone or dentine suggest that it is poorly crystallized (1B); and the pattern of tapeworm concretions (no discernible peaks) indicate an amorphous material (1C).


2013 ◽  
Vol 28 (3) ◽  
pp. 212-221 ◽  
Author(s):  
W. Wong-Ng ◽  
G. Liu ◽  
Y.G. Yan ◽  
J.A. Kaduk

The structure and X-ray patterns of two series of barium lanthanide cobaltates, namely, Ba4Sr2R2Co4O15 (R = La, Nd, Sm, Eu, Gd, and Dy), and Ba5SrR2Co4O15 (R = La, Nd, Sm, Eu, and Gd) have been determined. These compounds crystallize in the space group P63mc; the unit-cell parameters of Ba4Sr2R2Co4O15 (R from La to Dy) decrease from a = 11.6128(2) Å to 11. 5266(9) Å, c = 6.869 03(11) to 6. 7630(5) Å, and V = 802.23(3) Å3 to 778.17(15) Å3, respectively. In the Ba5SrR2Co4O15 series (R = La to Gd), the unit-cell parameters decrease from a = 11.735 44(14) Å to 11.619 79(12) Å, c = 6.942 89 (14) Å to 6.836 52(8) Å, and V = 828.08(3) Å3 to 799.40(2) Å3. In the general structure of (Ba6−xSrx)R2Co4O15, there are four Co ions per formula unit occupying one CoO6 octahedral and three CoO4 tetrahedral units. Through corner-sharing of these polyhedra, a larger Co4O15 unit is formed. Sr2+ ions adopt both octahedral and 8-fold coordination environment. R3+ ions adopt 8-fold coordination (mixed site with Sr), while the larger Ba2+ ions assume both 10- and 11-fold coordination environments. The samples were found to be insulators. X-ray diffraction patterns of these samples have been determined and submitted to the Powder Diffraction File (PDF).


The X-ray diffraction patterns from specimens of bacterial flagella taken by Astbury, Weibull and others consist essentially of three sets of reflexions, two sets on the meridian and one set on the equator. The equatorial set gives information on the packing arrange-merit of the polypeptide chains within a single flagellum. This paper is concerned with the interpretation in terms of a physical model of the equatorial diffraction from flagella from Proteus vulgaris for which the published diffraction data are most detailed. The polypeptide chains are all assumed to be in the α -helical form though the meridional diffraction gives some indication that a smaller ‘cross- β ’ component may also be present. The separation (121 Å) between the flagella in the X-ray specimens is inferred from the spacings of the equatorial reflexions and two alternative models (model I and model II) for the detailed structure of a flagellum are inferred from the intensity data. The structures proposed are similar in outline but differ in detail and postulate that a flagellum is composed of a number of identical interwoven filaments which themselves comprise a limited number of α -helices in a centred hexagonal or pseudo-hexagonal array. In model I the flagella are assumed to be in contact in the X-ray specimens and the structure comprises three filaments of diameter 56 Å each containing 19 single α -helices. In model II the flagella are not in contact and each of the seven filaments of diameter 33 Å contains seven α -helices; the diameter of the flagellum on this model is about 100 Å. The equatorial X-ray patterns from the two models are calculated in detail including effects due to the packing of the flagella within an X-ray specimen, for comparison with the observed diffraction. Both calculated patterns give a satisfactory explanation of the spacings of the observed reflexions and show reasonable agreement with the experimental intensities. The relative merits of the two models are discussed from the diffraction point of view and in conjunction with available data from electron microscopy. The diffraction pattern from model II is in better agreement with the experimental results than the pattern from model I but the latter agreement may be improved if the hexagonal packing of the α -helices within a filament is slightly modified; a cylindrical lattice is considered from this point of view. It is concluded that, at the present time, there is insufficient evidence to differentiate between the two models of a flagellum presented.


1972 ◽  
Vol 52 (3) ◽  
pp. 465-475 ◽  
Author(s):  
J. E. BRYDON ◽  
S. SHIMODA

The major portion of the clay fraction of the B horizons of the Bayswater soil, a podzol from Nova Scotia, consisted of an amorphous component that had the properties of allophane. The X-ray diffraction patterns, the infrared (IR) spectra, the Differential Thermal Analysis (DTA) curve, the Thermogravimetric Analysis (TGA) curve and loss in weight data, and the chemical analysis were similar to the data obtained from allophane of volcanic ash origin. The C horizon clay fraction consists of mica, vermiculite, quartz, and feldspar plus a substantial amount of amorphous material. As previously found, the montmorillonite in the Ae horizon showed beidellite-vermiculite-mica characteristics. The B horizon clays contained a small amount of a vermiculite material and an Fe, Al-organic matter complex in addition to the allophane. The data provided evidence that the compositional-depth relations were genetic and that the allophane in the B horizons arose through chemical weathering, physical weathering, and coprecipitation as previously suggested by other workers.


1993 ◽  
Vol 333 ◽  
Author(s):  
T.J. White ◽  
H. Mitamura

ABSTRACTPowder X-ray diffraction patterns were collected from three titanate waste forms - a calcine powder, a prototype ceramic without waste, and a ceramic containing 10 wt% JW-A simulated waste - and interpreted quantitatively using the Rietveld method. The calcine consisted of fluorite, pyrochlore, rutile, and amorphous material. The prototype waste form contained rutile, hollandite, zirconolite and perovskite. The phase constitution of the JW-A ceramic was freudenbergite, loveringite, hollandite, zirconolite, perovskite and baddeleyite. Procedures for the collection of X-ray data are described, as are assumptions inherent in the Rietveld approach. A selection of refined crystal data are presented.


2009 ◽  
Vol 23 (1) ◽  
pp. 51-58 ◽  
Author(s):  
I. Bratu ◽  
Irina Kacso ◽  
Gh. Borodi ◽  
Daniela E. Constantinescu ◽  
Felicia Dragan

Solid state interactions of bioactive substance (4-cyclohexyl-1-[2-[(2-methyl-1-propanoyloxy-propoxy)-(4-phenylbutyl)phosphoryl]acetyl]-pyrrolidine-2-carboxylic acid, called Fosinopril), withβ-cyclodextrin (β-CD), the so-called inclusion compounds of a bioactive (cardiovascular) drug is obtained by different preparation methods: kneading, co-precipitation and freeze-drying. The so obtained compounds were investigated by FTIR spectroscopy, X-ray diffraction method, and differential scanning calorimetric measurements (DSC) to evidence their formation. X-ray diffraction patterns show that the inclusion compound was obtained for kneaded, co-precipitation and freeze-dried products. The crystalline/amorphous degree for these compounds was also investigated. Molecular modeling (MM+ molecular mechanics) shows the spatial architecture of the inclusion compound in good agreement with FTIR experimental data: the drug is included with the propanoyloxy-propoxy group insideβ-cyclodextrin cavity. These findings may constitute a direct contribution to the molecular encapsulation of Fosinopril intoβ-cyclodextrin, improving Fosinopril stability and bioavailability of the drug, also.


Author(s):  
T. Gulik-Krzywicki ◽  
M.J. Costello

Freeze-etching electron microscopy is currently one of the best methods for studying molecular organization of biological materials. Its application, however, is still limited by our imprecise knowledge about the perturbations of the original organization which may occur during quenching and fracturing of the samples and during the replication of fractured surfaces. Although it is well known that the preservation of the molecular organization of biological materials is critically dependent on the rate of freezing of the samples, little information is presently available concerning the nature and the extent of freezing-rate dependent perturbations of the original organizations. In order to obtain this information, we have developed a method based on the comparison of x-ray diffraction patterns of samples before and after freezing, prior to fracturing and replication.Our experimental set-up is shown in Fig. 1. The sample to be quenched is placed on its holder which is then mounted on a small metal holder (O) fixed on a glass capillary (p), whose position is controlled by a micromanipulator.


Author(s):  
J. P. Robinson ◽  
P. G. Lenhert

Crystallographic studies of rabbit Fc using X-ray diffraction patterns were recently reported. The unit cell constants were reported to be a = 69. 2 A°, b = 73. 1 A°, c = 60. 6 A°, B = 104° 30', space group P21, monoclinic, volume of asymmetric unit V = 148, 000 A°3. The molecular weight of the fragment was determined to be 55, 000 ± 2000 which is in agreement with earlier determinations by other methods.Fc crystals were formed in water or dilute phosphate buffer at neutral pH. The resulting crystal was a flat plate as previously described. Preparations of small crystals were negatively stained by mixing the suspension with equal volumes of 2% silicotungstate at neutral pH. A drop of the mixture was placed on a carbon coated grid and allowed to stand for a few minutes. The excess liquid was removed and the grid was immediately put in the microscope.


2020 ◽  
Vol 86 (6) ◽  
pp. 29-35
Author(s):  
V. P. Sirotinkin ◽  
O. V. Baranov ◽  
A. Yu. Fedotov ◽  
S. M. Barinov

The results of studying the phase composition of advanced calcium phosphates Ca10(PO4)6(OH)2, β-Ca3(PO4)2, α-Ca3(PO4)2, CaHPO4 · 2H2O, Ca8(HPO4)2(PO4)4 · 5H2O using an x-ray diffractometer with a curved position-sensitive detector are presented. Optimal experimental conditions (angular positions of the x-ray tube and detector, size of the slits, exposure time) were determined with allowance for possible formation of the impurity phases during synthesis. The construction features of diffractometers with a position-sensitive detector affecting the profile characteristics of x-ray diffraction peaks are considered. The composition for calibration of the diffractometer (a mixture of sodium acetate and yttrium oxide) was determined. Theoretical x-ray diffraction patterns for corresponding calcium phosphates are constructed on the basis of the literature data. These x-ray diffraction patterns were used to determine the phase composition of the advanced calcium phosphates. The features of advanced calcium phosphates, which should be taken into account during the phase analysis, are indicated. The powder of high-temperature form of tricalcium phosphate strongly adsorbs water from the environment. A strong texture is observed on the x-ray diffraction spectra of dicalcium phosphate dihydrate. A rather specific x-ray diffraction pattern of octacalcium phosphate pentahydrate revealed the only one strong peak at small angles. In all cases, significant deviations are observed for the recorded angular positions and relative intensity of the diffraction peaks. The results of the study of experimentally obtained mixtures of calcium phosphate are presented. It is shown that the graphic comparison of experimental x-ray diffraction spectra and pre-recorded spectra of the reference calcium phosphates and possible impurity phases is the most effective method. In this case, there is no need for calibration. When using this method, the total time for analysis of one sample is no more than 10 min.


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