Structure Study of Si Nanocrystals Formed by Electron-Induced Reduction of SiO2at High Temperature

ABSTRACTThe effects of high temperature annealing on the microstructure and optical properties of luminescent SiOx:H films have been investigated. Micro-Raman scattering and IR absorption, in combination with atomic force microscopy (AFM), provide evidence for the existence of both a-Si clusters in the as-grown a-SiOx:H and Si nanocrystals in the 1170°C annealed films. The dependence of optical coefficients (μ) on photon energy (hv) near the absorption edge (Eg) is found to follow the square root law: (μhv)½ μ (Eg – hv), indicating that nano-Si embedded in Si02 is still an indirect material. A comparison of the deduced absorption edge with the PL spectra shows an obvious Stokes shift, suggesting that phonons should be involved in the optical transition process.

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The Effect of a Discontinuous Welding Technique on Stress Levels of a Hot Tap Tee

2004 International Pipeline Conference, Volumes 1, 2, and 3 ◽

10.1115/ipc2004-0226 ◽

2004 ◽

Cited By ~ 1

Author(s):

X. L. Xue ◽

Z. F. Sang ◽

W. Z. Jiang

Keyword(s):

High Temperature ◽

Internal Pressure ◽

Stress Level ◽

Heat Treating ◽

Structure Study ◽

Economic Losses ◽

Radial Deformation ◽

Test Model ◽

Operating Pressure ◽

Metallurgical Structure

With the development of petrochemical industry, the hot tapping technology has been widely used. A hot tapping is a technique that allows establishing a branch connection to a live pipeline. As it is a technology without halting transportation, it can avoid large economic losses and serious air pollution. When an operation of hot tapping is performed, a technology of discontinuous welding is sometimes used to reduce the localized high temperature that may cause burn-through of pipe. The purpose of this paper is to investigate whether the structure fabricated by discontinuous welding can work safely. Simulation of discontinuous welding was conducted to compare the temperature and stress distribution between continuous and discontinuous welding. It can be concluded that the temporary high temperature can be reduced effectively by discontinuous welding. However, due to frequent arc starting, a larger residual stress is resulted in. The stress level under internal pressure was studied by experiment using stress-gauging method. And the internal pressure was imposed by a high-lift pump. The failure load of the test model was 24.0MPa. Finite element simulation was also conducted to study the stress level under internal pressure. Then a comparison between experimental and FEA results was made. The experimental and FEA results indicate that the maximal stress occurs at the intersection area of the branch and run pipe. And it also can be seen that the results of radial deformation in the cross section are in good agreement. The metallurgical structure study shows that the welding and heat-treating procedures were proper. It can be concluded from this study that although the stress level is high under operating pressure, the structure can undergo the operating pressure safely.

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Spatially correlated erbium and Si nanocrystals in coimplanted SiO2 after a single high temperature anneal

Journal of Applied Physics ◽

10.1063/1.3294645 ◽

2010 ◽

Vol 107 (4) ◽

pp. 044316 ◽

Cited By ~ 11

Author(s):

Iain F. Crowe ◽

Reza J. Kashtiban ◽

Ben Sherliker ◽

Ursel Bangert ◽

Matthew P. Halsall ◽

...

Keyword(s):

High Temperature ◽

Spatially Correlated ◽

Si Nanocrystals ◽

High Temperature Anneal

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Influence of Ru, Mo and Ir on the Behavior of Ni-Based MCrAlY Coatings in High Temperature Oxidation

Volume 6: Ceramics; Controls, Diagnostics and Instrumentation; Education; Manufacturing Materials and Metallurgy ◽

10.1115/gt2014-26391 ◽

2014 ◽

Author(s):

Kang Yuan ◽

Ru Lin Peng ◽

Xin-Hai Li ◽

Sten Johansson ◽

Yan-Dong Wang

Keyword(s):

High Temperature ◽

Microstructural Evolution ◽

Structure Study ◽

Micro Structure ◽

Temperature Oxidation ◽

Coating Surface ◽

Mcraly Coating ◽

Mcraly Coatings ◽

Oxidation Performance ◽

Temperature Exposure

To improve the oxidation/corrosion resistance of MCrAlY coatings (M for Ni and/or Co), elements like Y, Si and Ta have been added into the coatings in past decades. In this study the oxidation performance of a Ni-based MCrAlY coating with small proportion of Ru, Mo and/or Ir were investigated after high-temperature exposure. The oxidation tests were carried out at 900°C, 1000°C or 1100°C. The micro structure study showed that the addition of Ru, Mo and/or Ir had significant influence on the oxidation behavior at the coating surface and the microstructural evolution in the material. The microstructural evolution was quantitatively evaluated by measuring the phase degradation of β-NiAl in the coating and γ′-Ni3Al in the substrate of superalloy. Since no oxides of Ru, Mo and Ir were found on the coating surface, it was believed that the effects by those elements were mainly due to their dissolution in the metallic phases in the coatings.

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