Spelling suggestions: "subject:"matematerials - bthermal properties"" "subject:"matematerials - 3thermal properties""
41 |
Two-dimensional temperature model for target materials bombarded by ion beamsBostick, Kent C. 04 February 1992 (has links)
The ion implantation process is a very precise, controllable, and
reproducible method used to enhance material properties of finished
components such as ball bearings. Essentially, the target material is
bombarded by accelerated ions to form a thin alloyed layer in the
substrate. As the ions deposit their kinetic energy in the target it
begins to heat up. To prevent thermal distortion in the finished pieces
the ion implantation is performed at dose levels (dependent on the ion
fluence and time duration of implantation) to insure that the target
pieces stay at relatively low temperatures. Consequently, the low
temperature requirement for many applications limits the economic, and
probably, the physical success of ion implantation.
The purpose of this study was to show the applicability of using a
two-dimensional computer code developed to model plasma disruptions and
subsequent energy deposition on a fusion reactor first wall to calculate
surface and bulk temperature information during ion implantation. In
turn the code may assist researchers pursuing development of adequate
cooling for target materials in an attempt to overcome the low
temperature constraint.
All data supported the hypotheses that the two-dimensional code
previously developed for fusion reactor applications was adequate to
model the ion implantation process. / Graduation date: 1992
|
42 |
Exploring the thermal expansion of fluorides and oxyfluorides with ReO₃-type structures: from negative to positive thermal expansionGreve, Benjamin K. 21 December 2011 (has links)
This thesis explores the thermal expansion and high pressure behavior of some materials with the ReO₃ structure type. This structure is simple and has, in principle, all of the features necessary for negative thermal expansion (NTE) arising from the transverse thermal motion of the bridging anions and the coupled rotation of rigid units; however, ReO₃ itself only exhibits mild NTE across a narrow temperature range at low temperatures. ReO₃ is metallic because of a delocalized d-electron, and this may contribute to the lack of NTE in this material. The materials examined in this thesis are all based on d⁰ metal ions so that the observed thermal expansion behavior should arise from vibrational, rather than electronic, effects.
In Chapter 2, the thermal expansion of scandium
fluoride, ScF₃, is examined using a
combination of in situ synchrotron X-ray and neutron variable temperature diffraction. ScF₃ retains the cubic ReO₃ structure across the entire temperature range examined (10-1600 K) and exhibits pronounced negative thermal expansion at low temperatures. The magnitude of NTE in this material is comparable to that of cubic ZrW₂O₈, which is perhaps the most widely studied NTE material, at room temperature and below. This is the first report of NTE in an ReO₃ type structure across a wide temperature range.
Chapter 3 presents a comparison between titanium oxyfluoride, TiOF₂, and a vacancy containing titanium hydroxyoxyfluoride, Tiₓ(O/OH/F)₃. TiOF₂ was originally reported
to adopt the cubic ReO₃ structure type under ambient conditions, therefore the initial
goal for this study was to examine the thermal expansion of this material and determine
if it displayed interesting behavior such as NTE. During the course of the study, it was
discovered that the original synthetic method resulted in Tiₓ(O/OH/F)₃, which does adopt
the cubic ReO₃ structure type. The chemical composition of the hydroxyoxyfluoride is
highly dependent upon synthesis conditions and subsequent heat treatments. This material
readily pyrohydrolyizes at low temperatures (~350 K). It was also observed that TiOF₂ does not adopt the cubic ReO₃ structure; at room temperature it adopts a rhombohedrally
distorted variant of the ReO₃ structure. Positive thermal expansion was observed for TiOF₂
from 120 K through decomposition into TiO₂. At ~400 K, TiOF₂ undergoes a structural
phase transition from rhombohedral to cubic symmetry. High pressure diffraction studies
revealed a cubic to rhombohedral phase transition for Tiₓ(O/OH/F)₃ between 0.5-1 GPa.
No phase transitions were observed for TiOF₂ on compression.
In Chapter 4, an in situ variable pressure{temperature diffraction experiment examining the effects of pressure on the coefficients of thermal expansion (CTE) for ScF₃ and TaO₂F is presented. In the manufacture and use of composites, which is a possible application for low and NTE materials, stresses may be experienced. Pressure was observed to have a negligible effect on cubic ScF₃'s CTE; however, for TaO₂F the application of modest pressures, such as those that might be experienced in the manufacture or use of composites, has a major
effect on its CTE. This effect is associated with a pressure-induced phase transition from
cubic to rhombohedral symmetry upon compression. TaO₂F was prepared from the direct
reaction of Ta₂O₅ with TaF₅ and from the digestion of Ta₂O₅ in hot hydro
uoric acid. The
effects of pressure on the two samples of TaO₂F were qualitatively similar. The slightly
different properties for the samples are likely due to differences in their thermal history
leading to differing arrangements of oxide and
uoride in these disordered materials.
In Chapter 5, the local structures of TiOF₂ and TaO₂F are examined using pair distribution
functions (PDFs) obtained from X-ray total scattering experiments. In these materials,
the anions (O/F) are disordered over the available anion positions. While traditional X-ray
diffraction provides detailed information about the average structures of these materials,
it is not suffcient to fully understand their thermal expansion. Fits of simple structural
models to the low r portions of PDFs for these materials indicate the presence of geometrically
distinct M{X{M (M = Ti, Ta; X = O, F) linkages, and a simple analysis of the TaO₂F variable temperature PDFs indicates that these distinct links respond differently to temperature.
|
43 |
Nanomaterials characterization and bio-chemical sensing using microfabricated devicesYu, Choongho 28 August 2008 (has links)
Not available / text
|
44 |
A volumetric sculpting based approach for modeling multi-scale domainsKarlapalem, Lalit Chandra Sekhar 28 August 2008 (has links)
Not available / text
|
45 |
A measurement of solar reflectivity of building materials, Tucson, ArizonaAcklam, David Mark, 1946- January 1977 (has links)
No description available.
|
46 |
Analytical and experimental analysis of heat transfer from current microelectronics package designsRay, Atris A., III 12 1900 (has links)
No description available.
|
47 |
Reaction synthesis of dynamically-densified Ti-based intermetallic and ceramic forming powdersNamjoshi, Shanatanu Ashok 05 1900 (has links)
No description available.
|
48 |
Structural and high pressure studies of some low and negative thermal expansion materialsÇetinkol, Mehmet 17 November 2008 (has links)
The research presented in this thesis focuses on the structural studies and the high pressure behavior of oxide negative thermal expansion (NTE) materials that can be classified as framework materials. First two chapters were devoted to TaO2F which adopts the ReO3-type cubic structure. Our studies under pressure revealed a rather complicated high pressure behavior for this deceivingly simple compound. The diffraction measurements at variable temperature and high pressure indicated that pressure had a significant effect on the linear coefficient of thermal expansion of TaO2F. In the remainder of the thesis, compounds that belong to the Sc2W3O12 family were examined. High-pressure in-situ powder diffraction studies were conducted on Zr2WO4(PO4)2, Zr2MoO4(PO4)2, Hf2WO4(PO4)2, and Sc2W3O12 in order to investigate the effects of pressure on the coefficients of thermal expansion, existence of phase transitions, phase transition pressures and structural changes occurring upon phase transitions.
|
49 |
Dependence of physical and mechanical properties on polymer architecture for model polymer networksGuo, Ruilan. January 2008 (has links)
Thesis (Ph. D.)--Polymer, Textile and Fiber Engineering, Georgia Institute of Technology, 2008. / Committee Chair: Karl I. Jacob; Committee Member: Anselm C. Griffin; Committee Member: C. P. Wong; Committee Member: Rina Tannenbaum; Committee Member: William J. Koros; Committee Member: Yonathan S. Thio.
|
50 |
An x-ray investigation of the thermal decomposition of unirradiated and irradiated silver permanganate.Woods, Geoffrey Steward January 1963 (has links)
[From Introduction] The first step in the study of the thermal decompositions of solids is an examination of the kinetics, since this casts much light on the mechanism of the reaction. It must be borne in mind, however, that a theoretical expression, derived on the basis of a particular mechanism, even if it fits the observed experimental results, is not conclusive proof of the validity of the mechanism when applied to the decomposition under examination.
|
Page generated in 0.1284 seconds