Rare Earth Oxide Pigmented Thermal Control Coatings PDF Download
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Author: Daniel E. Prince
Publisher:
ISBN:
Category :
Languages : en
Pages : 51
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Book Description
The purpose of the program was to develop improved pigmented polymeric and inorganic coatings having low solar absorptance and high emittance and improved stability to 'space' radiation effects (vacuum, ultraviolet, and particulate radiation) for use in the passive thermal control of spacecraft. Efforts were undertaken to investigate the radiation stability of selected rare earth oxide pigments and pigmented silicone and silicate coatings to a laboratory simulated space environment. Environmental tests of silicone and silicate formulations included exposure to vacuum-ultraviolet, vacuum-electrons, and vacuum-ultraviolet-electrons with both in situ and non-in situ optical reflectance measurements being taken. (Author).
Author: Daniel E. Prince
Publisher:
ISBN:
Category :
Languages : en
Pages : 51
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Book Description
The purpose of the program was to develop improved pigmented polymeric and inorganic coatings having low solar absorptance and high emittance and improved stability to 'space' radiation effects (vacuum, ultraviolet, and particulate radiation) for use in the passive thermal control of spacecraft. Efforts were undertaken to investigate the radiation stability of selected rare earth oxide pigments and pigmented silicone and silicate coatings to a laboratory simulated space environment. Environmental tests of silicone and silicate formulations included exposure to vacuum-ultraviolet, vacuum-electrons, and vacuum-ultraviolet-electrons with both in situ and non-in situ optical reflectance measurements being taken. (Author).
Author: Michael C. Shai
Publisher:
ISBN:
Category : Coatings
Languages : en
Pages : 30
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Book Description
Author: Virendra Singh
Publisher:
ISBN:
Category : Cerium oxides
Languages : en
Pages : 182
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Book Description
Cerium oxide (Ceria) at nano scale has gained significant attention due to its numerous technological applications. Ceria in both doped and undoped forms are being explored as oxygen sensor, catalysis, protective coating against UV and corrosion, solid oxide fuel cell (SOFC) electrolyte and newly discovered antioxidant for biomedical applications. Therefore, there is an imminent need of a technology which can provide a cost effective, large scale manufacturing of nanoceria and its subsequent consolidation, specially using thermal spray. This dissertation aims to develop a scientific understanding towards the development of pure and doped ceria- based coating for a variety of technological applications, from SOFC applications to corrosion resistant coating. Atmospheric plasma spray (APS) and solution precursor plasma spray (SPPS) techniques for the fabrication of nano ceria coating were investigated. For feedstock powder preparation, a spray drying technique was used for the agglomeration of cerium oxide nano particles to achieve high density coating. Deposition efficiencies and coating porosity as a function of processing parameters were analyzed and optimized using a statistical design of experiment model. The coating deposition efficiency was dependent on the plasma temperature and vaporization pressure of the ceria nanoparticles. However, low standoff distance and high carrier gas flow rate were responsible for the improved density upto 86±3%. An alternative novel SPPS technique was studied for a thin film of cerium oxide deposition from various cerium salt precursors in doped and undoped conditions. The SPPS process allows controlling the chemistry of coating at a molecular level. The deposition mechanism by single scan experiments and the effect of various factors on coating microstructure evolution were studied in terms of splats formation. It was found that the precursor salt (nitrate of cerium) with lower thermal decomposition temperatures was suitable for a high density coating. The high concentration and low spray distance significantly improve the splat morphology and reduced porosity (upto 20%). The feasibility of the trivalent cations (Sm3 and Gd3) doping into cerium oxide lattice in high temperature plasma was discussed and experimentally studied. XRD analysis revealed the nano crystalline characteristic of the coating and lattice expansion due to doping. The extensive transmission electron microscopy, Scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and thermo gravimetric were conducted to evaluate the precursors, and coating microstructure. Due to facial switching between Ce4+ and Ce3+ oxidation state, the cerium oxide surface becomes catalytically active. Thus, the APS ceria coatings were investigated for their applicability under extreme environmental conditions (high pressure and temperature). The air plasma sprayed coated 17-4PH steel was subjected to high pressure (10 Kpsi) and temperature (300 °F) corrosive environment. The coated steel showed continuous improvement in the corrosion resistance at 3.5 wt% NaCl at ambient temperature for three months study whereas, high pressure did not reveal a significant role in the corrosion process, and however, one needs to do further research. The ceria coated steel also revealed the improvement in corrosion protection (by 4 times) compared to the bare steel at low pH, 300 °F and 4000 Psi environment. This study projects the importance of cerium oxide coatings, their fabrication, optimization and applications.
Author:
Publisher:
ISBN:
Category : Aeronautics
Languages : en
Pages : 970
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Book Description
Lists citations with abstracts for aerospace related reports obtained from world wide sources and announces documents that have recently been entered into the NASA Scientific and Technical Information Database.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 13
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Book Description
Thermal control coatings play a critical role in the thermal management of space assets through reflection of incident solar energy and emittance of infrared heat. An investigation into the potential minimization of required film thickness through optimization of zinc oxide pigment particle size was performed. The utilization of a 1.5-micron average particle size pigment in the coating formulation resulted in a slightly improved solar absorbance/emittance value of 0.132 in comparison with the currently used 5.0 micron average particle size pigment. Furthermore, this improved value was obtained at a dry film thickness 18% thinner (4.9 mils) than the current state of the art, which translates to weight savings without a sacrifice in thermal management properties. Use of the smaller particle size pigment also resulted in an improvement in the measured emittance (0.94), likely due to a more uniform surface roughness and fewer large pores present in the film.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 178
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Book Description
Author: United States. National Aeronautics and Space Administration Scientific and Technical Information Division
Publisher:
ISBN:
Category : Aeronautics
Languages : en
Pages : 1440
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Author: Ludvig Landälv
Publisher: Linköping University Electronic Press
ISBN: 9176850889
Category :
Languages : en
Pages : 42
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Book Description
The state-of-the-art tools for machining metals are primarily based on a metal-ceramic composite (WC-Co) coated with different combinations of carbide, nitride, and oxide coatings. Combinations of these coating materials are optimized to withstand specific wear conditions. Oxide coatings, mainly α-Al2O3, are especially desired because of their high hot-hardness, chemical inertness with respect to the workpiece, and their low friction. The search for possible alloy elements, which may facilitate the deposition of such oxides by means of physical vapor deposition (PVD) techniques, has been the goal of this thesis. The sought alloy should form thermodynamically stable or metastable compounds, compatible with the temperature of use in metal cutting application. This thesis deals with process development and coating characterization of such new oxide alloy thin films, focusing on the Al-V-O, Al-Cr-Si-O, and Cr-Zr-O systems. Alloying aluminum oxide with iso-valent vanadium is a candidate for forming the desired alloys. Therefore, coatings of (Al1-xVx)2O3, with x ranging from 0 to 1, were deposited with reactive sputter deposition. X-ray diffraction showed three different crystal structures depending on V-metal fraction in the coating: α-V2O3 rhombohedral structure for 100 at.% V, a defect spinel structure for the intermediate region, (63 - 42 at.% V), and a gamma-alumina-like solid solution at lower V-content, (18 and 7 at.%), were observed, the later was shifted to larger d-spacing compared to the pure γ-Al2O3 sample obtained if deposited with only Al-target. Annealing the Al-rich coatings in air resulted in formation of V2O5 crystals on the surface of the coating after annealing to 500 °C for 42 at.% V and 700 °C for 18 at.% V metal fraction respectively. The highest thermal stability was shown for pure γ-Al2O3-coating which transformed to α-Al2O3 after annealing to 1100° C. Highest hardness was observed for the Al-rich oxides, ~24 GPa. The hardness then decreases with increasing V-content, larger than 7 at.% V metal fraction. Doping the Al2O3 coating with 7 at.% V resulted in a significant surface smoothening compared to the binary oxide. The measured hardness after annealing in air decreased in conjunction with the onset of further oxidation of the coatings. This work increases the understanding of this complicated material system with respect to possible phases formed with pulsed DC magnetron sputtering deposition as well as their response to annealing in air. The inherent difficulties of depositing insulating oxide films with PVD, requiring a closed electrical circuit, makes the investigation of process stability an important part of this research. In this context, I investigated the influence of adding small amount of Si in Al-Cr cathode on the coating properties in a pulsed DC industrial cathodic arc system and the plasma characteristics, process parameters, and coating properties in a lab DC cathodic arc system. Si was chosen here due to a previous study showing improved erosion behavior of Al-Cr-Si over pure Al-Cr cathode without Si incorporation in the coating. The effect of Si in the Al-Cr cathode in the industrial cathodic arc system showed slight improvements on the cathode erosion but Si was found in all coatings where Si was added in the cathode. The Si addition promoted the formation of the B1-like metastable cubic oxide phase and the incorporation led to reduced or equal hardness values compared to the corresponding Si-free processes. The DC-arc plasma study on the same material system showed only small improvements in the cathode erosion and process stability (lower pressure and cathode voltage) when introducing 5 at.% Si in the Al70Cr30-cathode. The presence of volatile SiO species could be confirmed through plasma analysis, but the loss of Si through these species was negligible, since the coating composition matched the cathode composition also under these conditions. The positive effect of added Si on the process stability at the cathode surface, should be weighed against Si incorporation in the coating. This incorporation seems to lead to a reduction in mechanical properties in the as-deposited coatings and promote the formation of a B1-like cubic metastable oxide structure for the (Al,Cr)2O3 oxide. This formation may or may not be beneficial for the final application since literature indicates a slight stabilization of the metastable phase upon Si-incorporation, contrary to the effect of Cr, which stabilizes the α-phase. The thermal stability of alloys for metal cutting application is crucial for their use. Previous studies on another alloy system, Cr-Zr-O, had shown solid solution, for Cr-rich compositions in that material system, in the sought corundum structure. The thermal stability of α-Cr0.28Zr0.10O0.61 coating deposited by reactive radio frequency (RF)-magnetron sputtering at 500 °C was therefore investigated here after annealing in vacuum up to 870 °C. The annealed samples showed transformation of α-(Cr,Zr)2O3 and amorphous ZrOx-rich areas into tetragonal ZrO2 and bcc-Cr. The instability of the α-(Cr,Zr)2O3 is surprising and possibly related to the annealing being done under vacuum, facilitating the loss of oxygen. Further in situ synchrotron XRD annealing studies on the α-Cr0.28Zr0.10O0.61 coating in air and in vacuum showed increased stability for the air annealed sample up to at least 975 °C, accompanied with a slight increase in ex-situ measured nanohardness. The onset temperature for formation of tetragonal ZrO2 was similar to that for isothermally vacuum annealing. The synchrotron-vacuum annealed coating again decomposed into bcc-Cr and t-ZrO2, with an addition of monoclinic–ZrO2 due to grain growth. The stabilization of the room temperature metastable tetragonal ZrO2 phase, due to surface energy effects present with small grains sizes, may prove to be useful for metal cutting applications. The observed phase segregation of α-(Cr,Zr)2O3 and formation of tetragonal ZrO2 with corresponding increase in hardness for this pseudobinary oxide system also opens up design routes for pseudobinary oxides with tunable microstructural and mechanical properties.
Author: United States. National Aeronautics and Space Administration. Scientific and Technical Information Division
Publisher:
ISBN:
Category : Aeronautics
Languages : en
Pages : 1680
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Book Description
Author: Leroy Eyring
Publisher: Elsevier
ISBN: 1483185877
Category : Science
Languages : en
Pages : 373
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Book Description
Progress in the Science and Technology of the Rare Earths, Volume 2 is a collection of papers that details the advancement in various areas of rare earth technology. The coverage of the text includes the practical applications and methods of preparation of rare earth materials. The selection also covers topics about the various properties of rare earths, such as the molecular field model of exchange coupling in rare earth materials; thermodynamic and magnetic properties of the rare earth chalcogenides and pnictides; and structural and solid state chemistry of pure rare earth oxides. The book will be of great use to individuals involved in the research and development of technologies that utilize rare earth materials.
