Crystallization and high-temperature structural stability of titanium oxide nanotube arrays

2003 ◽  
Vol 18 (1) ◽  
pp. 156-165 ◽  
Author(s):  
Oomman K. Varghese ◽  
Dawei Gong ◽  
Maggie Paulose ◽  
Craig A. Grimes ◽  
Elizabeth C. Dickey
Keyword(s):  
Heat Treatment ◽  
High Temperature ◽  
Titanium Oxide ◽  
Elevated Temperatures ◽  
Anatase Phase ◽  
Argon Atmosphere ◽  
Nanotube Arrays ◽  
Nanotube Array ◽  
Inner Diameter ◽  
The Stability

The stability of titanium oxide nanotube arrays at elevated temperatures was studied in dry oxygen as well as dry and humid argon environments. The tubes crystallized in the anatase phase at a temperature of about 280 °C irrespective of the ambient. Anatase crystallites formed inside the tube walls and transformed completely to rutile at about 620 °C in dry environments and 570 °C in humid argon. No discernible changes in the dimensions of the tubes were found when the heat treatment was performed in oxygen. However, variations of 10% and 20% in average inner diameter and wall thickness, respectively, were observed when annealing in a dry argon atmosphere at 580 °C for 3 h. Pore shrinkage was even more pronounced in humid argon environments. In all cases the nanotube architecture was found to be stable up to approximately 580 °C, above which oxidation and grain growth in the titanium support disrupted the overlying nanotube array.

The Effect of Electrolyte Composition on the Fabrication of Self-Organized Titanium Oxide Nanotube Arrays by Anodic Oxidation

2005 ◽  
Vol 20 (1) ◽  
pp. 230-236 ◽  
Author(s):  
Qingyun Cai ◽  
Maggie Paulose ◽  
Oomman K. Varghese ◽  
Craig A. Grimes
Keyword(s):  
Titanium Oxide ◽  
Anodic Oxidation ◽  
Anatase Phase ◽  
Pure Titanium ◽  
Electrolyte Solutions ◽  
Electrolyte Composition ◽  
Nanotube Arrays ◽  
Solution Ph ◽  
Nanotube Array ◽  
Self Organized

We report on the fabrication of self-organized titanium oxide nanotube arrays of enhanced surface area prepared by anodic oxidation of a pure titanium sheet in electrolyte solutions containing potassium fluoride (KF) or sodium fluoride (NaF). The effects of electrolyte composition and concentration, solution pH, and the anodic potential on the formation of nanotubes and dimensions of the resulting nanotubes are detailed. Although nanotube arrays of length greater than 500 nm are not possible with hydrofluoric acid containing electrolytes [G.K. Mor, O.K. Varghese, M. Paulose,N. Mukherjee, C.A. Grimes, J. Mater. Res. 18, 2588 (2003)], by adjusting the pH of a KF containing electrolyte to 4.5 using additives such as sulfuric acid, sodium hydroxide, sodium hydrogen sulfate, and/or citric acid, we could increase the length of the nanotube-array to approximately 4.4 μm, an order of magnitude increase in length. The as-prepared nanotubes are composed of amorphous titanium oxide. Independent of the electrolyte composition, crystallization of the nanotubes to anatase phase occurred at temperatures ⩾280 °C. Rutile formation occurred at the nanotube-Ti substrate interface at temperatures near 480 °C. It appears geometry constraints imposed by the nanotube walls inhibit anatase to rutile transformation. No disintegration of the nanotube array structure is observed at temperatures as high as 580 °C. The excellent structural and crystal phase stability of these nanotubes make them promising for both low- and high-temperature applications.

High-Temperature Instability of A Cr2Nb-Nb(Cr) Microlaminate Composite

1996 ◽  
Vol 54 ◽  
pp. 374-375
Author(s):  
M. Larsen ◽  
R.G. Rowe ◽  
D.W. Skelly
Keyword(s):  
Heat Treatment ◽  
Solid Solution ◽  
High Temperature ◽  
Elevated Temperatures ◽  
Aircraft Engine ◽  
Lattice Parameter ◽  
Microstructural Stability ◽  
Elevated Temperature Strength ◽  
Cross Sectional ◽  
Bcc Structure

Microlaminate composites consisting of alternating layers of a high temperature intermetallic compound for elevated temperature strength and a ductile refractory metal for toughening may have uses in aircraft engine turbines. Microstructural stability at elevated temperatures is a crucial requirement for these composites. A microlaminate composite consisting of alternating layers of Cr2Nb and Nb(Cr) was produced by vapor phase deposition. The stability of the layers at elevated temperatures was investigated by cross-sectional TEM.The as-deposited composite consists of layers of a Nb(Cr) solid solution with a composition in atomic percent of 91% Nb and 9% Cr. It has a bcc structure with highly elongated grains. Alternating with this Nb(Cr) layer is the Cr2Nb layer. However, this layer has deposited as a fine grain Cr(Nb) solid solution with a metastable bcc structure and a lattice parameter about half way between that of pure Nb and pure Cr. The atomic composition of this layer is 60% Cr and 40% Nb. The interface between the layers in the as-deposited condition appears very flat (figure 1). After a two hour, 1200 °C heat treatment, the metastable Cr(Nb) layer transforms to the Cr2Nb phase with the C15 cubic structure. Grain coarsening occurs in the Nb(Cr) layer and the interface between the layers roughen. The roughening of the interface is a prelude to an instability of the interface at higher heat treatment temperatures with perturbations of the Cr2Nb grains penetrating into the Nb(Cr) layer.

Stability of Nanometer-Thick Layers in Hard Coatings

MRS Bulletin ◽  
2003 ◽  
Vol 28 (3) ◽  
pp. 169-172 ◽  
Author(s):  
Scott A. Barnett ◽  
Anita Madan ◽  
Ilwon Kim ◽  
Keith Martin
Keyword(s):  
High Temperature ◽  
Elevated Temperatures ◽  
Temperature Stability ◽  
Hexagonal Wurtzite Structure ◽  
Thin Layers ◽  
Hard Coatings ◽  
High Temperature Stability ◽  
The Stability ◽  
Hardness Values ◽  
Thick Layers

AbstractThis article reviews two topics related to the stability of hard coatings composed of nanometer-thick layers: epitaxial stabilization and high-temperature stability. Early work on nanolayered hard coatings demonstrated large hardness increases as compared with monolithic coatings, but it was subsequently found that the layers interdiffused at elevated temperatures. More recently, it has been shown that nanolayers exhibit good stability at elevated temperatures if the layer materials are thermodynamically stable with respect to each other and are able to form low-energy coherent interfaces. This article discusses metal/nitride, nitride/nitride, and nitride/boride nanolayers that exhibit good high-temperature stability and hardness values that are maintained (or even increase) after high-temperature annealing. Epitaxial stabilization of nonequilibrium structuresin thin layers is a well-known phenomenon that has been applied to hard nitride materials. In particular, AlN, which crystallizes in the hexagonal wurtzite structure in bulk form, was stabilized in the rock-salt cubic structure in nitride/nitride nanolayers (e.g., AlN/TiN). These results and the current understanding of epitaxial stabilization in hard nanolayers are discussed.

scholarly journals Electrochemical Anodization and Characterization of Titanium Oxide Nanotubes for Photo Electrochemical Cells

2021 ◽  
Vol 2070 (1) ◽  
pp. 012073
Author(s):  
C U Bhadra ◽  
D Henry Raja ◽  
D Jonas Davidson
Keyword(s):  
Titanium Oxide ◽  
Oxygen Vacancies ◽  
Ammonium Fluoride ◽  
Band Gap Energy ◽  
Electrochemical Anodization ◽  
Nanotube Arrays ◽  
Photoluminescence Intensity ◽  
Titania Nanotube Arrays ◽  
Titanium Oxide Nanotubes ◽  
Inner Diameter

Abstract Due to its multitude of applications, titanium oxide is one of the most coveted and most sought-after materials. The above experiment demonstrated that TiO2 nanotube arrays might be formed by electrochemical anodization of titanium foil. The 0.25 wt% ammonium fluoride (NH4F) was added to a solution of 99% ethylene glycol. Anodization is carried out at a constant DC voltage of 12V for 1 hour. Then, the annealing process is carried out for 1 hour at 4800C, which is known as an annealing. FE-SEM were utilized to evaluate the surface morphology of the nanotube arrays that were made. At the wavelength of 405 nm, sharply peaked photoluminescence intensity was observed, which corresponded tothe band gap energy (3.2 eV) of the anatase TiO2 phase. Since free excitations appear at 391 and 496 nm, and since oxygen vacancies are developed on the surface of titania nanotube arrays, it is reasonable to conclude that free excitations and oxygen vacancies are the causes of humps at 391 and 496 nm, and that they may also be present at 412 and 450 nm. FESEM results showed uniformly aligned TiO2 nanotube arrays with an inner diameter of 100 nm and a wall thickness of 50 nm

The effect of thermal exposure on precipitation of Ti3Al(C,N) in Ti-48Al-IV-0.2C

1992 ◽  
Vol 50 (1) ◽  
pp. 22-23
Author(s):  
W.T. Donlon ◽  
W.E. Dowling ◽  
C.E. Cambell ◽  
J.E. Allison
Keyword(s):  
Heat Treatment ◽  
High Temperature ◽  
Titanium Aluminides ◽  
Elevated Temperatures ◽  
Volume Fraction ◽  
Weight Ratio ◽  
Thermal Exposure ◽  
Treatment Temperature ◽  
Field Samples ◽  
Structural Applications

Titanium aluminides are attractive candidates for high temperature structural applications because of their high strength to weight ratio at elevated temperatures. The microstructure of these alloys consists of γ-TiAl (distorted L10 structure) , plus α2-Ti3Al (ordered DO19 structure). Varying the heat treatment temperature and cooling rate of these alloys alters the volume fraction and distribution of the γ and α2 phases. This has significant effects on the room temperature ductility. In addition, precipitation of carbides has been observed during high temperature exposure. The effect of these precipitates on the mechanical properties has yet to be determined.Figure 1 shows the general microstructure that was used for this investigation. TEM foils were prepared by electropolishing using 5% perchloric, 35% 1-butanol, 60% methanol at -40°C. No precipitates were found following heat treatment in the γ+α phase field. Samples approximately 20 mm square were thermally exposed to temperatures between 625° and 1000°C for times between 1 and 2000 hours.

HPM X-750

Alloy Digest ◽  
2006 ◽  
Vol 55 (6) ◽  
Keyword(s):  
Heat Treatment ◽  
High Temperature ◽  
Physical Properties ◽  
Elevated Temperatures ◽  
Alloy Composition ◽  
Heat Treating ◽  
Chromium Alloy ◽  
Nickel Chromium ◽  
Temperature Performance ◽  
Wide Range

Abstract HPM X-750 is a precipitation-hardenable nickel-chromium alloy that is well suited for a wide range of corrosive and oxidizing environments where strength must be maintained to elevated temperatures. The alloy composition provides a product that performs well at elevated temperatures up to 700 deg C (1300 deg F). The strength can be increased by heat treatment. This datasheet provides information on composition, physical properties, elasticity, and tensile properties. It also includes information on high temperature performance as well as forming, heat treating, and joining. Filing Code: Ni-638. Producer or source: Hamilton Precision Metals.

ARMCO PH 15-7Mo STAINLESS STEEL

Alloy Digest ◽  
1997 ◽  
Vol 46 (8) ◽  
Keyword(s):  
Heat Treatment ◽  
Stainless Steel ◽  
Corrosion Resistance ◽  
High Temperature ◽  
Elevated Temperatures ◽  
High Strength ◽  
Heat Treating ◽  
Good Corrosion Resistance ◽  
Temperature Performance ◽  
Minimal Distortion

Abstract Armco PH 15-7 Mo stainless steel is a Cr-Ni-Mo-Al semi-austenitic stainless steel. It is heat treatable to high strength and hardness, maintains good corrosion resistance, and undergoes minimal distortion from heat treatment. The alloy has applications in the aerospace and other industries where high strength at elevated temperatures is required. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties. It also includes information on high temperature performance and corrosion resistance as well as forming, heat treating, and joining. Filing Code: SS-693. Producer or source: Armco Inc., Specialty Steels Division.

Processing Methods for Ultra High Temperature Ceramics

2013 ◽  
pp. 180-202 ◽  
Author(s):  
J.K. Sonber ◽  
T.S.R. Ch. Murthy ◽  
C. Subramanian ◽  
R.C. Hubli ◽  
A.K. Suri
Keyword(s):  
High Temperature ◽  
Elevated Temperatures ◽  
Thermal Protection ◽  
Leading Edge ◽  
Powder Synthesis ◽  
Ultra High Temperature Ceramics ◽  
Sharp Edges ◽  
The Stability ◽  
Intense Heat ◽  
Ultra High Temperature

Ultra-high-temperature ceramics (UHTCs) are a group of materials that can withstand ultra high temperatures (1600-3000 oC) which will be encountered by future hypersonic re-entry vehicles. Future re-entry vehicles will have sharp edges to improve flight performance. The sharp leading edges result in higher surface temperature than that of the actual blunt edged vehicles that could not be withstood by the conventional thermal protection system materials. To withstand the intense heat generated when these vehicles dip in and out of the upper atmosphere, UHTC materials are needed. UHTC materials are composed of borides of early transition metals. From the larger list of borides, ZrB2 and HfB2 have received the most attention as potential candidates for leading edge materials because their oxidation resistance is superior to that of other borides due to the stability of the ZrO2 and HfO2 scales that form on these materials at elevated temperatures in oxidizing environments. Processing of these materials is very difficult as these materials are very refractory in nature. In this chapter, processes available for powder synthesis, fabrication of dense bodies, and coating processes is discussed.

scholarly journals Martensite aging in 〈001〉 oriented Co49Ni21Ga30 single crystals in tension

2018 ◽  
Vol 11 (02) ◽  
pp. 1850024 ◽  
Author(s):  
C. Lauhoff ◽  
P. Krooß ◽  
D. Langenkämper ◽  
C. Somsen ◽  
G. Eggeler ◽  
...  
Keyword(s):  
Heat Treatment ◽  
High Temperature ◽  
Neutron Diffraction ◽  
Single Crystals ◽  
Elevated Temperatures ◽  
Transformation Temperatures ◽  
Chemical Order ◽  
Compressive Loads ◽  
The Impact ◽  
Tension Compression Asymmetry

Co–Ni–Ga high-temperature shape memory alloys (HT-SMAs) are well-known candidate materials for damping applications at elevated temperatures. Recent studies showed that upon heat treatment in stress-induced martensite under compressive loads transformation temperatures can be increased significantly, qualifying Co–Ni–Ga for HT-actuation. The increase in transformation temperatures is related to a change in chemical order recently validated via neutron diffraction experiments. Since SMAs show distinct tension–compression asymmetry in terms of theoretical transformation strains and bearable stresses, understanding the impact of martensite aging in tension is crucial for future applications. The current results indicate that martensite aging in tension provides for a further improvement in functional properties.

Critical Load Analysis of Double-Hinged Circular Steel Arch In-Plane under High Temperature of Fire

2011 ◽  
Vol 243-249 ◽  
pp. 3-6 ◽  
Author(s):  
Yu Lai Han ◽  
Bai Tao Sun ◽  
Zhu Ju ◽  
Yong Gang Wang
Keyword(s):  
High Temperature ◽  
Elevated Temperature ◽  
Critical Load ◽  
Thermal Loading ◽  
Elevated Temperatures ◽  
Structural Response ◽  
Steel Material ◽  
The Stability ◽  
Variation Trends ◽  
Significant Factors

This paper addresses the stability behaviour in-plane and the critical load of the double-hinged circular steel arch when subjected to elevated temperature caused by fire, the study is restricted to the thermoelastic structural response of the steel material and therefore the high-temperature effects of yielding are not considered. In order to model structural response of the steel arch under thermal loading, some significant factors such as the degradation of the stiffness of the steel arch prior to yielding at elevated temperatures is taken into account, the formulation of critical load is proposed and their variation trends with temperatures is analysed. The proposed method has significant potential for use in the analysis of steel arches subjected to uniformly distributed load at elevated temperature and can provide a foundation for codified procedures in design.

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