Crystallization of Pyrolyzed Polysilazanes

1990 ◽  
Vol 180 ◽  
Author(s):  
Roger L. K. Matsumoto
Keyword(s):  
Ceramic Material ◽  
Amorphous Material ◽  
Amorphous Structure ◽  
Crystalline Material ◽  
Inorganic Polymers ◽  
Processing Conditions ◽  
Polymer Backbone ◽  
Crystalline Materials

ABSTRACTPolysilazanes are inorganic polymers which convert to a ceramic material when pyrolyzed. Initial pyrolysis results in a solid, amorphous material. Further heating transforms the amorphous structure to a crystalline material. In addition to the Si-N linkages in the polymer backbone, polysilazanes generally contain appreciable amounts of carbon in side groups. Consequently, pyrolysis can result in mixed Si3N4 - SiC crystalline materials. It will be shown that either Si3N4 or SiC could be selectively crystallized depending upon processing conditions.

scholarly journals The Interpretation of HRTEM Images of Partially Amorphized Pyrochlore Structure Types.

1990 ◽  
Vol 183 ◽  
Author(s):  
Mark L. Miller ◽  
R. C. Ewing
Keyword(s):  
Limit Of Detection ◽  
Amorphous Material ◽  
Pyrochlore Structure ◽  
Image Contrast ◽  
Crystalline Material ◽  
Total Thickness ◽  
Volume Percent ◽  
Crystalline Materials ◽  
Image Simulations ◽  
Crystalline Matrix

AbstractThe results of image simulations on partially amorphous microlite (Ca2Ta2O7, pyrochlore structure) are presented. Results indicate that HRTEM images are not sensitive to the position of amorphous layers within a crystalline matrix. In addition, it is observed that the limit of detection of amorphous material within a crystalline matrix is dependent upon the total thickness of the sample. In thin crystals (<150 Å), up to 75 volume percent crystalline material can give rise to aperiodic images, yet the addition of a small amount of crystalline material (80 volume percent crystalline) produces a periodic image. Images calculated for isolated spheres of amorphous material distributed within crystalline microlite suggest that isolated domains of amorphization are observable at sample thicknesses less than three times the diameter of the feature. The image contrast of amorphized domains is enhanced by imaging at defocus settings significantly different than Scherzer focus. These results indicate that interpretation of HRTEM images of partially amorphized crystalline materials should be undertaken with caution, and estimates of the volume of damage considered only qualitative.

scholarly journals Impact of Thermal Oxidation on Morphological, Structural and Magnetic Properties of Fe-Ni Wire-Like Nanochains

2021 ◽  
Author(s):  
Marcin Krajewski ◽  
Mateusz Tokarczyk ◽  
Sabina Lewińska ◽  
Kamil Bochenek ◽  
Anna Ślawska-Waniewska
Keyword(s):  
Magnetic Properties ◽  
Thermal Oxidation ◽  
Amorphous Material ◽  
Crystalline Material ◽  
Future Application ◽  
Energy Storage Devices ◽  
Storage Devices ◽  
Structural And Magnetic Properties ◽  
Source Of Information ◽  
The Magnetic Field

AbstractThis work presents the evolution of morphological, structural and magnetic properties of amorphous Fe-Ni wire-like nanochains caused by thermal oxidation. The initial Fe1−xNix samples (x = 0.75; 0.50; 0.25) were prepared through the magnetic-field-induced synthesis, and then they were heated in dry air at 400 °C and 500 °C. These treatments led to two competing simultaneous processes occurring in the investigated samples, i.e., (i) a conversion of amorphous material into crystalline material, and (ii) their oxidation. Both of them strictly affected the morphological and structural properties of the Fe-Ni nanochains which, in turn, were associated with the amount of iron in material. It was found that the Fe0.75Ni0.25 and Fe0.50Ni0.50 nanochains were covered during thermal treatment by the nanoparticle oxides. This coverage did not constitute a good barrier against oxidation, and these samples became more oxidized than the Fe0.25Ni0.75 sample which was covered by oxide nanosheets and contained additional Ni3B phase. The specific morphological evolutions of the Fe-Ni nanochains also influenced their saturation magnetizations, whereas their coercivities did not vary significantly. The obtained results constitute an important source of information for future application of the thermally treated Fe-Ni nanochains which could be applied in the energy storage devices or catalysis.

Geochemical and Petrological Characterization of Ash Samples from Cascade Range Volcanoes

1971 ◽  
Vol 1 (2) ◽  
pp. 261-282 ◽  
Author(s):  
Keith Randle ◽  
Gordon G. Goles ◽  
Laurence R. Kittleman
Keyword(s):  
Pacific Northwest ◽  
Volcanic Ash ◽  
Cascade Range ◽  
Crystalline Material ◽  
Refractive Indices ◽  
Crystalline Materials ◽  
The Pacific ◽  
Volcanic Ashes ◽  
Different Sources

Twenty-nine samples of volcanic ash from the Pacific Northwest were analyzed by instrumental neutron activation techniques, with the aim of distinguishing among ashes from different sources. Preliminary results of petrographic studies of 42 ash or pumice samples are also reported. Geochemical characteristics of Mazama ash are defined, and problems induced by winnowing of crystalline material during transport and by weathering are discussed. Contents of La, Th, and Co, and La/Yb ratios are shown to be good discriminants. Data on refractive indices and on proportions of crystalline materials also aid in distinguishing among the various volcanic ashes studied. Ash and pumice found in archaeological contexts at Fort Rock Cave, Paisley Cave, Wildcat Canyon, and Hobo Cave are all from Mount Mazama, presumably from the culminating cruption of 7000 years ago.

Mechanism of the Crystallization of High Polymers

1954 ◽  
Vol 27 (2) ◽  
pp. 374-384 ◽  
Author(s):  
G. Schuur
Keyword(s):  
Mechanical Properties ◽  
Natural Rubber ◽  
Amorphous Material ◽  
Crystalline Polymer ◽  
Longitudinal Direction ◽  
Crystalline Material ◽  
Current View ◽  
X Ray ◽  
Made In ◽  
High Polymers

Abstract The crystallization of higher polymers is a phenomenon which is not yet fully understood, one of the main difficulties being to explain how the spherulites arise. An attempt will be made in this paper to draw a clearer picture of the mechanism of crystallization and thus to account for the origin of spherulites. It will then be seen how several other phenomena involved in the crystallization of natural rubber can be shown to be logically interrelated. The current view is that a crystalline polymer consists of a continuous amorphous phase containing small crystalline regions, the crystallites. The evidence as to the size of these crystallites, however, is at present inconclusive, because only the lower limit of their size can be measured by means of x-ray examination. The reason is that, owing to the absence of reflections of a higher order, the effect of irregularities in the crystallites and of the heat motion of the molecules cannot be measured separately. Another doubtful question is whether the small angle interference maxima are to be interpreted as a measure of mean distances between the crystallites. To do this, Wallner has to resort to the assumption that the crystallites are unstable, whereas it is presumed, on the evidence of the mechanical properties of the high polymers, that a crystallite is stable and permanent. Hoffmann found 82 ± 7 per cent of crystalline material in polychlorotrifluoroethylene and Buckley, Cross, and Ray found as much as 95 per cent in polymethylene. Such high percentages make it doubtful whether the crystalline phase can be discontinuous at all. In this article any volume of material in which the molecules lie parallel is called a crystallite. The direction in which the molecules are oriented is termed the longitudinal direction of the crystallite. It is immaterial to the argument whether a crystallite consists of several crystallites, aligned in parallel separated by a small amount of amorphous material, or of a single crystallite containing large irregularities.

Synthesis and Useful Reactions of Organosilicon Polymeric Precursors for Ceramics

1991 ◽  
Vol 249 ◽  
Author(s):  
Dietmar Seyferth ◽  
Carsten Strohmann ◽  
Henry J. Tracy ◽  
Jennifer L. Robison
Keyword(s):  
World War Ii ◽  
Repeat Unit ◽  
Organometallic Polymers ◽  
Inorganic Polymers ◽  
World War ◽  
Commercial Development ◽  
Polymer Backbone ◽  
Polymeric Systems ◽  
Macromolecular Systems ◽  
Long Time

Inorganic and organometallic polymers are macromolecular systems in which the polymer backbone contains elements other than the carbon, oxygen and nitrogen usually found in organic polymers [1]. To take as an example silicon-containing polymers, in the silicones the polymer backbone is composed of the Si-O repeat unit; in polysilazanes, of the Si-N unit; in polysilmethylenes, of the Si-C unit. In the polysilanes there are only silicon atoms in the polymer backbone. Many of the other metalloids and metals among the elements in the Periodic Table have been or, in principle, can be incorporated into polymeric systems, so it is clear that the field of inorganic and organometallic polymers is a very large one. Inorganic and organometallic polymers have been of interest to chemists for a long time. It was the commercial development of the silicones in the 1940's that gave this field of research its modem impetus [2]. Once it was appreciated how useful these versatile organosilicon polymers could be, chemists became interested in the possibility of developing other organometallic (and also inorganic) polymers, ones that might complement or even surpass the silicones as far as useful applications were concerned. Research on inorganic and organometallic polymers became very active in the 1950's and 1960's. Work in this area became an international effort, prompted by the need for new materials that would meet the exacting demands of the jet age that had effectively commenced around the end of World War II. Even greater demands, in terms of materials that would still be useful under extreme conditions, came with the space age.

Extended X-ray absorption fine-structure analysis of vacuum-deposited amorphous germanium

1989 ◽  
Vol 67 (4) ◽  
pp. 358-364 ◽  
Author(s):  
G. W. Johnson ◽  
D. E. Brodie ◽  
E. D. Crozier
Keyword(s):  
Fine Structure ◽  
Amorphous Materials ◽  
Amorphous Material ◽  
Amorphous Structure ◽  
Low Energy ◽  
X Ray Diffraction ◽  
Two Phase ◽  
Edge Structure ◽  
X Ray ◽  
Low Energy Electrons

In this study, thin films of germanium have been vacuum deposited in four regimes. Care was taken to prepare reproducible films, which required that the partial pressure of water be below 10−8 Torr during deposition (1 Torr = 133.3 Pa). First, films deposited onto substrates held during deposition at a temperature Ts that is below 473 K are amorphous. Once annealed above 423 K, their electrical conductivity and optical band gap are independent of deposition temperature and rate, and of whether or not low-energy electron irradiation of the substrate is used during deposition. This suggests that a well-defined and reproducible structure is being prepared. Second, a "precrystallization regime" is obtained when Ts is between 473 and 513 K. Extended X-ray adsorption fine-structure and X-ray diffraction confirm that this regime is a two-phase mixture of amorphous material and crystallites. Third, films deposited with Ts near 513 K, while using low-energy electrons to bombard the substrate, are amorphous, but these films have different electrical and optical properties from the films m the first regime. From this, we infer that a second well-defined amorphous structure exists. Fourth, films deposited with Ts above 513 K are polycrystalline. Extended X-ray adsorption fine-structure and X-ray adsorption near-edge structure could not distinguish between the two amorphous materials in the first and third regimes.

Laser Ablation of Crystalline Material With and Without Water on Material Surface

2019 ◽  
Author(s):  
Wenlong Yao ◽  
Li Yan ◽  
Yunshu Qi ◽  
Ning Mei
Keyword(s):  
Statistical Physics ◽  
Morphological Changes ◽  
Phase Variation ◽  
Water Layer ◽  
Density Variation ◽  
Crystalline Material ◽  
Material Surface ◽  
Ablation Process ◽  
Crystalline Materials ◽  
Atomic Image

Abstract The phase and morphological changes of crystalline material during laser internal ablation with and without water on the material surface are studied using molecular dynamics simulations. The atomic image of the material morphology was obtained by recording the velocity and position variation of atoms. Temperature distribution contour of the crystalline material along the ablation process are charted by statistical physics method. Furthermore, density variation and phase variation contour of water are also charted. The results suggest that: First, during the ablation process of crystalline materials, energy transfer occurs between water and crystalline materials. Supercritical water is formed first, which restrains the sputtering of crystalline materials due to phase explosion and puts off the sputtering. Then the physical state of water changes from liquid to gaseous. Second, with water on the surface, the cavity shape is different from that without water, the width of upper part of cavity is decreased. Third, the volume of the cavity is affected by the thickness of the water layer.

Fabrication of polycrystalline thin films of liquid crystalline materials by solution process and its application to OFETs

2008 ◽  
Vol 1091 ◽  
Author(s):  
Hiroaki Iino ◽  
Jun-ichi Hanna
Keyword(s):  
Thin Films ◽  
Crystalline Phase ◽  
Liquid Crystalline ◽  
Solution Process ◽  
Crystalline Material ◽  
Crystalline Materials ◽  
Polycrystalline Thin Films ◽  
Channel Performance ◽  
Liquid Crystalline Materials ◽  
Liquid Crystalline Material

AbstractWe have fabricated polycrystalline OFETs of two different liquid crystalline materials i.e., ω,ω'-dihexylquaterthipohene (6-QTP-6) and N, N'-ditridecylperylenediimide (13-Per-13) by solution process. Liquid crystalline materials help fabricating uniform thin films on the substrate when spin-coated at their temperature range of liquid crystalline phase. The FETs fabricated with 6-QTP-6 exhibited p-channel performance and its mobility was determined to be 0.04 cm2/Vs, which was comparable to that determined by time-of-flight experiments. The FETs fabricated with 13-Per-13 exhibited n-channel performance and its FET mobility was 0.008 cm2/Vs, while the mobility was increased up to 0.11 cm2/Vs after thermal annealing of the film at a liquid crystalline temperature of 220°C for an hour. Judging from these facts, the grain boundaries are controlled not so as to across the conduction channels formed by self-aligned π-conjugated aromatic cores in liquid crystalline molecules. We conclude that liquid crystalline material is a good candidate for quality polycrystalline thin films for OFETs.

MULTISCALE MODELING FOR AMORPHOUS MATERIALS — MAPPING ATOMISTIC DISPLACEMENTS TO MACROSCOPIC DEFORMATION

2012 ◽  
Vol 04 (04) ◽  
pp. 1250037 ◽  
Author(s):  
ZHOU CHENG SU ◽  
TONG-EARN TAY ◽  
YU CHEN ◽  
VINCENT B. C. TAN
Keyword(s):  
Amorphous Materials ◽  
Amorphous Material ◽  
Multiscale Simulations ◽  
Mathematical Form ◽  
Computational Domain ◽  
Crystalline Materials ◽  
Macroscopic Deformation ◽  
T Matrix ◽  
Representative Points ◽  
Good Agreement

A method to relate the displacements of atoms within a representative volume element (RVE) of amorphous material to the deformation of the RVE is presented. The displacement relationship is expressed as a mapping matrix, T, which operates on the displacements of representative points in the RVE to return the atom displacements within it. While the mapping operation has the same mathematical form as an interpolation operation, the T matrix is not an interpolant. It is derived taking into account atom displacements in amorphous materials which cannot be simplified as a continuous, much less homogenous, field. It is shown that the computational domain of a material can be partitioned into nonintersecting sub-domains comprising representative cells — pseudo-amorphous cells (PAC) — and sub-domains of atoms for concurrent multiscale simulations of amorphous materials through the T matrix. Multiscale simulations of nanoindentation on a polymer substrate using the T matrix show good agreement with pure molecular mechanics simulations. When homogenization techniques commonly used for crystalline materials were employed for the same simulations, they gave much less accurate predictions.

Irradiation Defect Structures In YBa2Cu3O7-xand their Correlation with Superconducting Properties

1990 ◽  
Vol 209 ◽  
Author(s):  
Marquis A. Kirk
Keyword(s):  
Critical Temperature ◽  
Critical Current Density ◽  
Critical Current ◽  
Neutron Irradiation ◽  
Current Density ◽  
Amorphous Material ◽  
Amorphous Structure ◽  
Fast Neutrons ◽  
High Fluences ◽  
Defect Microstructures

ABSTRACTWe review our work on irradiation effects in single crystal YBa2Cu3O7-x. Transmission electron microscopy has been employed to study the defect microstructures produced by irradiations with fast neutrons, MeV ions (Kr, Ne and p), and electrons. The atomic structure within defect cascades was investigated using 50 keV Kr and Xe ion irradiations to low doses. Evidence is shown for an amorphous structure with some incoherent recrystallization within individual cascades. Correlation with enhancements in critical current density produced by neutron irradiations suggest that this cascade structure effectively pins magnetic flux lines.At sufficiently high fluences of fast neutrons or MeV Kr and Ne ions, a cellular microstructure is found. This structure consists of cells or microcrystallites of good crystalline and superconducting material (in the case of neutron irradiation), with cell walls of amorphous material. Full amorphization proceeds with the growth of cell wall volume. The formation of this microstructure coincides with a decrease in critical transport current, but is not observed by magnetization measurements.Increases in critical current density under proton irradiation, comparable to those produced by neutron irradiation, have been reported. The defect structure produced by proton irradiations is examined here and found to differ from that of neutron irradiations. The structure is suggested to be consistent with the clustering of mobile defects (at 300 K) produced by the lower energy recoils which dominate in proton irradiations. In both the proton and fast neutron irradiations, to fluences producing the maximum enhancements in critical current densities, the degradations in critical temperature are not severe, <10 K.Our most recent measurements of changes in critical temperature and current density, and defect microstructure following electron irradiations will be described

Sign in / Sign up

Export Citation Format

Share Document