Structural Characterization of Nanocrystalline Mo and W Carbide and Nitride Catalysts Produced by Co2 Laser Pyrolysis

1994 ◽  
Vol 368 ◽  
Author(s):  
Xiang-Xin Bi ◽  
K. Das Chowdhury ◽  
R. Ochoa ◽  
W. T. Lee ◽  
S. Bandow ◽  
...  
Keyword(s):  
Crystallite Size ◽  
Hexagonal Phase ◽  
Particle Surface ◽  
Transition Metal Carbide ◽  
Line Broadening ◽  
Small Crystallite Size ◽  
Laser Pyrolysis ◽  
Crystallite Sizes ◽  
Small Crystallite

ABSTRACTUsing both XRD and HRTEM lattice imaging, we have shown that CO2 laser pyrolysis (LP) produces nanoscale transition metal carbide and nitride catalysts, including cubic Mo2C, Mo2N, and W2N, which possess highly crystalline structures in their as-synthesized form In contrast, LP-produced W2C in its hexagonal phase is disordered. Clear lattice expansion, induced by the small crystallite size of the nanoparticles has been observed for LP-produced Mo2C particles, which have a typical crystallite size of 2 nm. No carbon coating was observed in HRTEM for LP-produced Mo2C particles. Furthermore, Mo=N and Mo=C bonding in Mo2N and Mo2C, respectively, were identified by an XPS measurement, which also reveals the presence of a thin oxide layer formed on the particle surface during the passivation process. Finally, the average crystallite sizes determined from HRTEM and XRD are in good agreement, indicating that the line broadening observed in XRD is due to the small crystallite size of the nanoparticles.

X-ray diffraction characterization of the microstructure of close-packed hexagonal nanomaterials

2008 ◽  
Vol 23 (3) ◽  
pp. 213-223 ◽  
Author(s):  
Zhao-hui Pu ◽  
Chuan-zheng Yang ◽  
Pei Qin ◽  
Yu-wan Lou ◽  
Li-fang Cheng
Keyword(s):  
Stacking Faults ◽  
Triple Line ◽  
Stacking Fault ◽  
Line Broadening ◽  
X Ray Diffraction ◽  
Nano Zno ◽  
X Ray ◽  
Crystallite Sizes ◽  
Small Crystallite ◽  
Charge Discharge

A general least-squares technique for X-ray diffraction line broadening analysis has been developed. The technique can be used to determine single, double, and triple line broadening effects caused by small particle sizes, microstrain, stacking faults, or all three presented in a closed-packed hexagonal nanomaterial. The technique was applied to characterize the microstructure of β-Ni(OH)2, a negative electrode material in nickel-metal hydride (NiMH) batteries. Double line broadening effects caused by both small crystallite sizes and stacking faults in β-Ni(OH)2 were detected and analyzed. Triple line broadening effects caused simultaneously by small crystallite sizes, microstrain, and stacking faults were detected in β-Ni(OH)2 after activation and charge-discharge cycle tests. The triple line broadening effects were found to be selective and most pronounced for diffraction lines with h−k=3n±1. The broadening effects were larger when l=even, but smaller when l=odd. The shape and the average size of the crystallites, microstrain, and stacking fault probability in β-Ni(OH)2 changed dramatically after activation and charge-discharge cycles. The method was also applied to characterize and investigate the microstructure of nano ZnO materials. Results indicate that no selective broadening appears in the XRD patterns of the nano ZnO materials. The average crystallite sizes were different slightly, and the stacking fault probabilities differed significantly with different dopants.

Formation and characterization of germanium nanoparticles

2000 ◽  
Vol 15 (11) ◽  
pp. 2400-2407 ◽  
Author(s):  
N. J. Welham
Keyword(s):  
Raman Spectroscopy ◽  
Crystallite Size ◽  
Magnesium Oxide ◽  
Phonon Confinement ◽  
X Ray Diffraction ◽  
Acid Leach ◽  
Crystallite Sizes ◽  
Crystal Core ◽  
Individual Particles

Elemental germanium was mechanically milled with magnesium oxide with the intention of forming disperse nanoparticulate germanium in a soluble matrix. The crystallite size was determined by x-ray diffraction (XRD) and Raman spectroscopy using a phonon confinement model. The crystallite size was found to decrease exponentially with milling time; however, the size determined by XRD was typically five to ten times greater than that by Raman. This was attributed to the presence of two separate crystallite sizes, which were averaged when using the Scherrer equation for the XRD data. Sonication of the powder resulted in the breakup of >20 μm aggregates into individual particles of approximately 40 nm. These particles are thought to compose a single crystal core with a crystallite size of approximately 28 nm surrounded by a layer of smaller crystallites (approximately 5 nm), which showed quantization during Raman spectroscopy. Separation of the germanium from the magnesium oxide was readily achieved using a simple acid leach, although some oxidation of germanium was evident when using an aqueous leach.

A Full-Trace Database for the Analysis of Clay Minerals

1994 ◽  
Vol 38 ◽  
pp. 117-125
Author(s):  
D. K. Smith ◽  
G. G. Johnson ◽  
R. Jenkins
Keyword(s):  
Crystallite Size ◽  
Clay Minerals ◽  
Clay Mineral ◽  
Powder Diffraction ◽  
Powder Diffraction File ◽  
Oriented Sample ◽  
Small Crystallite Size ◽  
Clay Deposits ◽  
Extensive Collection ◽  
Small Crystallite

Abstract A file of digitized diffraction traces for clay minerals has been developed as a test for the usefulness of such traces in the analysis of clays and clay deposits. The kaolin, smectite, mica clay and chlorite groups are represented by patterns of the most common mineral species in the small crystallite size which is typical of their natural occurrences. Patterns are included for the oriented sample and for glycolated and heated samples when appropriate. This database may form a nucleus for an extensive collection of clay mineral traces in the same manner as the early Powder Diffraction File did for the modern PDE.

Thermodynamic stability of tetragonal zirconia nanocrystallites

2001 ◽  
Vol 16 (3) ◽  
pp. 666-669 ◽  
Author(s):  
Nae-Lih Wu ◽  
Ton-Fon Wu ◽  
Irene A. Rusakova
Keyword(s):  
Crystallite Size ◽  
Thermodynamic Stability ◽  
Strong Evidence ◽  
Tetragonal Zirconia ◽  
Thermal Treatments ◽  
Small Crystallite Size ◽  
20 Nm ◽  
Small Crystallite

The thermodynamic stability of tetragonal (t-) ZrO2 nanocrystallites below the bulk stability temperature 1200 °C was studied through specially synthesized crystallites that exhibited an extremely slow coarsening rate. The nanocrystallites were mechanically transformed to the monoclinic (m-) structure, and, because the crystallite size was kept below approximately 20 nm, the t-structure was completely recovered solely by thermal treatments between 900 and 1100 °C. These results gave strong evidence to the notion that, for sufficiently small crystallite size, nanocrystalline t-ZrO2 is not just kinetically metastable but can be truly thermodynamically more stable than the mpolymorph in air below 1200 °C.

X-Ray Investigation of Aerosols from Wires Exploded in Nitrogen

1963 ◽  
Vol 7 ◽  
pp. 240-251 ◽  
Author(s):  
Frank G. Karioris ◽  
Jerome J. Woyci
Keyword(s):  
Crystallite Size ◽  
Capacitor Bank ◽  
Nitrogen Pressure ◽  
Reaction Products ◽  
Line Broadening ◽  
X Ray ◽  
Glass Slides ◽  
Aluminum Iron ◽  
Subsequent Exposure ◽  
Crystallite Sizes

AbstractWires of 18 different metals were exploded in nitrogen by the discharge of a 20-μF capacitor bank charged to 10 kV. The resulting aerosols were collected under nitrogren on membrane e filters, which were mounted on glass slides and used directly in the sample holder of a recording X-ray diffractometer. The X-ray data were analyzed to determine the composition and approximate crystallite size of the particulates produced by the wire explosions in nitrogen and subsequent exposure to air.Nitrides are found as reaction products from the explosion in nitrogen of aluminum, iron, indium, tantalum, thorium, uranium, tungsten, and zirconium. No nitrides were detected in the samples from cadmium, copper, magnesium, molybdenum, lead, and tin explosions, although such nitrides are known to exist; and the aerosols produced in nitrogen by the explosion of silver, gold, molybdenum, platinum, and tin consist almost entirely of metal particles. Oxides are attributed to contamination of the nitrogen or exposure of the samples to air.Most of the crystallites observed are less than 1000 Å as determined from X-ray line broadening find confirmed in some instances by electron microscopy. For the UN2 and ThO2, crystallite sizes of the order of 130 Å and 50 Å, respectively, are observed. In samples comprised of a mixture of phases, the constituents usually have different mean crystallite sizes. The crystallite size is not affected dramatically by the ambient nitrogen pressure or voltage used.

Routine Crystallite-Size Determination by X-Ray Diffraction Line Broadening

1961 ◽  
Vol 5 ◽  
pp. 104-116 ◽  
Author(s):  
R. C. Rau
Keyword(s):  
Crystallite Size ◽  
Ceramic Materials ◽  
Diffraction Line ◽  
Line Broadening ◽  
X Ray Diffraction ◽  
X Ray ◽  
Routine Basis ◽  
Crystallite Sizes ◽  
Standard Set ◽  
Sintering Characteristics

AbstractIncreasing interest in the sintering characteristics of various ceramic materials has resulted in the need for a knowledge of the crystallite sizes of many constituent ceramic powders. Standard X-ray diffraction line-broadening techniques have been utilized to determine these crystallite sizes. This paper presents a general review of the theory of line broadening as a means of measuring crystallite size and gives the methods and modifications used to perform this type of analysis rapidly and on a routine basis.Four modifications have been used in the determination of crystallite size routinely by X-ray line broadening. These methods are (1) a graded set of powder photographs, (2) a computer program to calculate sizes from diffractometer data, (3) a set of crystallite-size curves for a given material for use with diffractometer data, and (4) a standard set of curves to use with diffractometer data for any strain-free materials. The preparation, use, and limitations of each of these methods is presented.

Characterization of Ferroelectric PZT Thin Films - Line Broadening Study (Using Grazing Incidence Geometry)

1991 ◽  
Vol 35 (A) ◽  
pp. 601-605
Author(s):  
Michael O. Eatough ◽  
Raymond P. Goehner ◽  
Thomas J. Headley ◽  
Bruce A. Tuttle
Keyword(s):  
Thin Films ◽  
Crystallite Size ◽  
Incidence Angle ◽  
Incident Angle ◽  
Grazing Incidence ◽  
Processing Parameters ◽  
Phase Changes ◽  
Incidence Geometry ◽  
Line Broadening

AbstractFerroelectric polycrystalline thin films are being pursued as materials for use in the next generation of radiation hardened nonvolatile semiconductor memories, optical switches and optical computers. Of particular interest are PZT films with a composition near the morphotropic phase boundary. In order to fully understand the the difference in electrical properties as a function of processing parameters it is necessary to fully characterize phase composition and crystallographic properties of these films. Since some films are produced by either spinning or dipping successive layers to obtain the desired thickness it was necessary to compare the properties of each layer.X-ray diffraction techniques employing parallel beam optics with grazing incidence angle geometry were used to characterize the films. Experimental procedures using sealed tube xray diffraction systems to determine differences in crystallite size and microstrain as a function of depth into the films are a rather unique application of this technique. Discerning the contribution to line broadening due to phase changes, grazing incident angle geometry, crystallite size and microstrain are key to the success of this technique.This paper discusses the experimental techniques employed and will demonstrate how we were able to successfully determine microstrain as a function of depth into the film. We use transmission electron microscopy (TEM) to aid in the characterization of the films. A brief description of the processing procedures used to produce the films is also provided.

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