Thermal Barrier Ceramic Coatings — A Review

Thermal barrier coatings (TBCs) provide effective thermal barrier to the components of gas turbine engines by allowing higher operating temperatures and reduced cooling requirements. Plasma spraying, electron-beam physical vapor deposition, and solution precursor plasma spray techniques are generally used to apply the TBCs on the metallic substrates. The present article addresses the TBCs formed by different processing techniques, as well as the possibility of new ceramic, glass-ceramic, and composite materials as TBCs. Promising bond coat materials for a TBC system have been also stated

Time Evolution of Density Parameters for Matter and Dark Energy and their Interaction Term in Brans-Dicke Gravity

In the framework of Brans-Dicke (BD) theory, the first part of the present study determines the time dependence of BD parameter, energy density and equation of state (EoS) parameter of the cosmic fluid in a universe expanding with acceleration, preceded by a phase of deceleration. For this purpose, a scale factor has been chosen such that the deceleration parameter, obtained from it, shows a signature flip with time. Considering the dark energy to be responsible for the entire pressure, the time evolution of energy parameters for matter and dark energy and the EoS parameter for dark energy have been determined. An effective interaction term, between matter and dark energy, has been proposed and calculated. Its negative value at the present time indicates conversion of matter into dark energy. Using this term, the time dependence of the rates of change of matter and dark energy has been determined. It is found that the nature of dependence of the scalar field upon the scale factor plays a very important role in governing the time evolution of the cosmological quantities studied here. The present study provides us with a simple way to determine the time evolution of dark energy for a homogeneous and isotropic universe of zero spatial curvature, without involving any self-interaction potential or cosmological constant in the formulation.Comment: 22 pages, 16 figures, 2 tables. In the present version we have two models of density parameter calculation. Calculations of time derivatives of densities have been added to the previous version. Four new graphs have been added to the older version. Changes have been made to different sections of this articl

Effect of alumina impurity on microstructure and properties of alumina based conventionally brazed joints

96-103Mo-Mn metallization of alumina ceramics of different purity has been performed at 1400 °C for 10 min in moist hydrogen and nitrogen atmosphere. Nickel coating has been applied onto the metallized alumina ceramics at 1000 °C for 1 h in a reducing hydrogen atmosphere. Finally, metallized and nickel coated alumina ceramics has been brazed with another metallized and nickel coated alumina ceramics using CuAg filler alloy at 900 °C for 10 min in a vacuum furnace at 1×10-6 Torr pressure. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis has been carried out for phase analysis, microstructural investigation and elemental composition analysis. The adhesive strength of the metallizing layer and brazing strength of the joint have been measured by pull down breaking strength method. SEM study has shown that the width of the interfacial reaction region between the metallizing layer and substrate enhances with increasing the impurity content in the alumina ceramics. It has been observed that the adhesive strength of the metallizing layer depends on the interfacial reaction layer thickness. The adhesive strength of the metallizing layer has been increased with increasing the thickness of interfacial reaction layer. High adhesive strength of the metallizing layer as well as brazing strength has beenachieved for alumina ceramics with high impurity content

Effect of alumina impurity on microstructure and properties of alumina based conventionally brazed joints

Mo-Mn metallization of alumina ceramics of different purity has been performed at 1400 °C for 10 min in moisthydrogen and nitrogen atmosphere. Nickel coating has been applied onto the metallized alumina ceramics at 1000 °C for 1 hin a reducing hydrogen atmosphere. Finally, metallized and nickel coated alumina ceramics has been brazed with anothermetallized and nickel coated alumina ceramics using CuAg filler alloy at 900 °C for 10 min in a vacuum furnace at 1×10-6Torr pressure. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysishas been carried out for phase analysis, microstructural investigation and elemental composition analysis. The adhesivestrength of the metallizing layer and brazing strength of the joint have been measured by pull down breaking strengthmethod. SEM study has shown that the width of the interfacial reaction region between the metallizing layer and substrateenhances with increasing the impurity content in the alumina ceramics. It has been observed that the adhesive strength of themetallizing layer depends on the interfacial reaction layer thickness. The adhesive strength of the metallizing layer has beenincreased with increasing the thickness of interfacial reaction layer. High adhesive strength of the metallizing layer as wellas brazing strength has beenachieved for alumina ceramics with high impurity content

Effect of alumina impurity on microstructure and properties of alumina based conventionally brazed joints

Mo-Mn metallization of alumina ceramics of different purity has been performed at 1400 degrees C for 10 min in moist hydrogen and nitrogen atmosphere. Nickel coating has been applied onto the metallized alumina ceramics at 1000 degrees C for 1 h in a reducing hydrogen atmosphere. Finally, metallized and nickel coated alumina ceramics has been brazed with another metallized and nickel coated alumina ceramics using CuAg filler alloy at 900 degrees C for 10 min in a vacuum furnace at 1 x 10(-6) Ton pressure. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis has been carried out for phase analysis, microstructural investigation and elemental composition analysis. The adhesive strength of the metallizing layer and brazing strength of the joint have been measured by pull down breaking strength method. SEM study has shown that the width of the interfacial reaction region between the metallizing layer and substrate enhances with increasing the impurity content in the alumina ceramics. It has been observed that the adhesive strength of the metallizing layer depends on the interfacial reaction layer thickness. The adhesive strength of the metallizing layer has been increased with increasing the thickness of interfacial reaction layer. High adhesive strength of the metallizing layer as well as brazing strength has been achieved for alumina ceramics with high impurity content

A Study to Correlate Endometrial Hyperplasia with Ovarian Stromal Change

Background: Endometrial hyperplasia in peri-menopausal age group is frequently encountered as a result of unopposed excess estrogen action, exact source of which is still debatable. Possible source is ovarian stroma. There must be some subtle changes in ovarian stroma to produce excess estrogen in such states. This study was performed to provide new insights into the various patterns of subtle ovarian stromal changes and its relation to morphological alteration of endometrial glands and stroma.Methods: 62 women in peri-menopausal age group, diagnosed as endometrial hyperplasia on uterine curettage and unresponsive to conventional therapy, treated by total hysterectomy with unilateral/bilateral salpingo-oophorectomy, were chosen randomly. Serial step sections of endometrial biopsies were examined by routine microscopy. Endometrial hyperplasia was classified following the current WHO classification. The sections from the ovary were examined for changes in the ovarian stroma.Results: Out of the 62 total cases having endometrial hyperplasia, 53 cases (83.5%) had one or more subtle ovarian stromal changes and 9 cases (14.5%) lacked the ovarian stromal changes. Out of the 50 cases without endometrial hyperplasia, only eight had subtle ovarian changes. In the 53 cases, which showed ovarian stromal changes, the changes were found in combination and variable proportions.Conclusion: Ovarian stromal changes were significantly associated with endometrial hyperplasia

Time Evolution of Density Parameters for Matter and Dark Energy and their Interaction Term in Brans-Dicke Gravity

In the framework of Brans-Dicke (BD) theory, the present study determines the time dependence of BD parameter, energy density and equation of state (EoS) parameter of the cosmic fluid in a universe expanding with acceleration, preceded by a phase of deceleration. For this purpose, a scale factor has been so chosen for the present model that the deceleration parameter, obtained from it, shows a signature flip with time. Considering the dark energy to be responsible for the entire pressure, the time evolution of energy parameters for matter and dark energy and the EoS parameter for dark energy have been determined. A term, representing interaction between matter and dark energy, has been calculated. Its negative value at the present time indicates conversion of matter into dark energy. It is evident from the present study that the nature of dependence of the scalar field upon the scale factor plays a very important role in governing the time evolution of the cosmological quantities studied here. This model has an inherent simplicity in the sense that it allows one to determine the time evolution of dark energy for a homogeneous and isotropic universe, without involving any self-interaction potential or cosmological constant in the formulation

Time Evolution of Density Parameters for Matter and Dark Energy and their Interaction Term in Brans-Dicke Gravity

In the framework of Brans-Dicke (BD) theory, the first part of the present study determines the time dependence of BD parameter, energy density and equation of state (EoS) parameter of the cosmic fluid in a universe expanding with acceleration, preceded by a phase of deceleration. For this purpose, a scale factor has been chosen such that the deceleration parameter, obtained from it, shows a signature flip with time. Considering the dark energy to be responsible for the entire pressure, the time evolution of energy parameters for matter and dark energy and the EoS parameter for dark energy have been determined. An effective interaction term, between matter and dark energy, has been proposed and calculated. Its negative value at the present time indicates conversion of matter into dark energy. Using this term, the time dependence of the rates of change of matter and dark energy has been determined. It is found that the nature of dependence of the scalar field upon the scale factor plays a very important role in governing the time evolution of the cosmological quantities studied here. The present study provides us with a simple way to determine the time evolution of dark energy for a homogeneous and isotropic universe of zero spatial curvature, without involving any self-interaction potential or cosmological constant in the formulation

Time Evolution of Density Parameters for Matter and Dark Energy and their Interaction Term in Brans-Dicke Gravity

In the framework of Brans-Dicke (BD) theory, the present study determines the time dependence of BD parameter, energy density and equation of state (EoS) parameter of the cosmic fluid in a universe expanding with acceleration, preceded by a phase of deceleration. For this purpose, a scale factor has been so chosen for the present model that the deceleration parameter, obtained from it, shows a signature flip with time. Considering the dark energy to be responsible for the entire pressure, the time evolution of energy parameters for matter and dark energy and the EoS parameter for dark energy have been determined. A term, representing interaction between matter and dark energy, has been calculated. Its negative value at the present time indicates conversion of matter into dark energy. It is evident from the present study that the nature of dependence of the scalar field upon the scale factor plays a very important role in governing the time evolution of the cosmological quantities studied here. This model has an inherent simplicity in the sense that it allows one to determine the time evolution of dark energy for a homogeneous and isotropic universe, without involving any self-interaction potential or cosmological constant in the formulation