Enabling Technologies for Ceramic Hot Section Components

Silicon-based ceramics are attractive materials for use in gas turbine engine hot sections due to their high temperature mechanical and physical properties as well as lower density than metals. The advantages of utilizing ceramic hot section components include weight reduction, and improved efficiency as well as enhanced power output and lower emissions as a result of reducing or eliminating cooling. Potential gas turbine ceramic components for industrial, commercial and/or military high temperature turbine applications include combustor liners, vanes, rotors, and shrouds. These components require materials that can withstand high temperatures and pressures for long duration under steam-rich environments. For Navy applications, ceramic hot section components have the potential to increase the operation range. The amount of weight reduced by utilizing a lighter gas turbine can be used to increase fuel storage capacity while a more efficient gas turbine consumes less fuel. Both improvements enable a longer operation range for Navy ships and aircraft. Ceramic hot section components will also be beneficial to the Navy's Growth Joint Strike Fighter (JSF) and VAATE (Versatile Affordable Advanced Turbine Engines) initiatives in terms of reduced weight, cooling air savings, and capability/cost index (CCI). For DOE applications, ceramic hot section components provide an avenue to achieve low emissions while improving efficiency. Combustors made of ceramic material can withstand higher wall temperatures and require less cooling air. Ability of the ceramics to withstand high temperatures enables novel combustor designs that have reduced NO{sub x}, smoke and CO levels. In the turbine section, ceramic vanes and blades do not require sophisticated cooling schemes currently used for metal components. The saved cooling air could be used to further improve efficiency and power output. The objectives of this contract were to develop technologies critical for ceramic hot section components for gas turbine engines. Significant technical progress has been made towards maturation of the EBC and CMC technologies for incorporation into gas turbine engine hot-section. Promising EBC candidates for longer life and/or higher temperature applications relative to current state of the art BSAS-based EBCs have been identified. These next generation coating systems have been scaled-up from coupons to components and are currently being field tested in Solar Centaur 50S engine. CMC combustor liners were designed, fabricated and tested in a FT8 sector rig to demonstrate the benefits of a high temperature material system. Pretest predictions made through the use of perfectly stirred reactor models showed a 2-3x benefit in CO emissions for CMC versus metallic liners. The sector-rig test validated the pretest predictions with >2x benefit in CO at the same NOx levels at various load conditions. The CMC liners also survived several trip shut downs thereby validating the CMC design methodology. Significant technical progress has been made towards incorporation of ceramic matrix composites (CMC) and environmental barrier coatings (EBC) technologies into gas turbine engine hot-section. The second phase of the program focused on the demonstration of a reverse flow annular CMC combustor. This has included overcoming the challenges of design and fabrication of CMCs into 'complex' shapes; developing processing to apply EBCs to 'engine hardware'; testing of an advanced combustor enabled by CMCs in a PW206 rig; and the validation of performance benefits against a metal baseline. The rig test validated many of the pretest predictions with a 40-50% reduction in pattern factor compared to the baseline and reductions in NOx levels at maximum power conditions. The next steps are to develop an understanding of the life limiting mechanisms in EBC and CMC materials, developing a design system for EBC coated CMCs and durability testing in an engine environment

Thermal resistant environmental barrier coating

A process for preparing a silicon based substrate with a protective coating having improved thermal resistance at temperature up to at least 1500.degree. C., and the resulting article

Consumo de drogas ilegales, apoyo familiar y factores relacionadosen estudiantes universitarios. Un estudio transversal basado en datosdel Proyecto uniHcos

Objective: To assess the prevalence of illegal drug use in college students on any previous occasion, duringthe previous year and the previous month, and to analyze the relationship between illegal drug use andfamily support and other factors.Methods: A cross-sectional study using data from students participating in the uniHcos project (n = 3767)was conducted. The prevalence and age of onset of consumption of cannabis, non-prescription sedatives,stimulants and depressants was evaluated. Polyconsumption was also assessed. The independent vari-ables were: family support, age, residence, and employment status. To determine the factors related todrug use multivariate logistic regression models stratified by gender were fitted.Results: Differences between men and women in prevalence of illegal drug use except non-prescriptionsedatives were observed. In both genders, less family support was associated with higher consumptionof all drugs, except depressants, and with polyconsumption. To be studying and looking for work wasrelated to cannabis and stimulant use and to polyconsumption among women, but only to cannabis useamong men.Conclusions: These results support the notion that the start of university studies is a particularly relevantstage in the onset of illegal drug use and its prevention, and that consumption may be especially associatedwith family support.Objetivo: Evaluar la prevalencia del consumo de drogas ilegales en estudiantes universitarios y analizarla relación entre dicho consumo, el apoyo familiar y otros factores.Método: Se realizó un dise?no transversal basado en datos de participantes en el proyecto uniHcos (n =3767). Se evaluaron la prevalencia y la edad de inicio del consumo de cannabis, tranquilizantes sin receta,estimulantes y depresores, y el policonsumo. Como variables independientes se consideraron el apoyofamiliar, la edad, la residencia y la situación laboral. Para la determinación de los factores asociados alconsumo de drogas se ajustaron modelos de regresión logística estratificados por sexo.Resultados: Se observaron diferencias entre hombres y mujeres en la prevalencia del consumo de todaslas drogas ilegales, excepto tranquilizantes sin receta. En ambos sexos, cuanto peor apoyo familiar, mayorconsumo de todas las drogas, excepto depresores y policonsumo. Encontrarse estudiando y buscandotrabajo se relacionó con el consumo de cannabis, estimulantes y policonsumo en las mujeres, y solo concannabis en los hombres.Conclusiones: Los resultados de este estudio aportan nueva evidencia a favor de que el inicio de la etapauniversitaria es un momento de especial relevancia en el inicio del consumo de drogas ilegales y suprevención, pudiendo este consumo estar especialmente relacionado con el apoyo familiar

Enabling Technologies for Ceramic Hot Section Components

Silicon-based ceramics are attractive materials for use in gas turbine engine hot sections due to their high temperature mechanical and physical properties as well as lower density than metals. The advantages of utilizing ceramic hot section components include weight reduction, and improved efficiency as well as enhanced power output and lower emissions as a result of reducing or eliminating cooling. Potential gas turbine ceramic components for industrial, commercial and/or military high temperature turbine applications include combustor liners, vanes, rotors, and shrouds. These components require materials that can withstand high temperatures and pressures for long duration under steam-rich environments. For Navy applications, ceramic hot section components have the potential to increase the operation range. The amount of weight reduced by utilizing a lighter gas turbine can be used to increase fuel storage capacity while a more efficient gas turbine consumes less fuel. Both improvements enable a longer operation range for Navy ships and aircraft. Ceramic hot section components will also be beneficial to the Navy's Growth Joint Strike Fighter (JSF) and VAATE (Versatile Affordable Advanced Turbine Engines) initiatives in terms of reduced weight, cooling air savings, and capability/cost index (CCI). For DOE applications, ceramic hot section components provide an avenue to achieve low emissions while improving efficiency. Combustors made of ceramic material can withstand higher wall temperatures and require less cooling air. Ability of the ceramics to withstand high temperatures enables novel combustor designs that have reduced NO{sub x}, smoke and CO levels. In the turbine section, ceramic vanes and blades do not require sophisticated cooling schemes currently used for metal components. The saved cooling air could be used to further improve efficiency and power output. The objectives of this contract were to develop technologies critical for ceramic hot section components for gas turbine engines. Significant technical progress has been made towards maturation of the EBC and CMC technologies for incorporation into gas turbine engine hot-section. Promising EBC candidates for longer life and/or higher temperature applications relative to current state of the art BSAS-based EBCs have been identified. These next generation coating systems have been scaled-up from coupons to components and are currently being field tested in Solar Centaur 50S engine. CMC combustor liners were designed, fabricated and tested in a FT8 sector rig to demonstrate the benefits of a high temperature material system. Pretest predictions made through the use of perfectly stirred reactor models showed a 2-3x benefit in CO emissions for CMC versus metallic liners. The sector-rig test validated the pretest predictions with >2x benefit in CO at the same NOx levels at various load conditions. The CMC liners also survived several trip shut downs thereby validating the CMC design methodology. Significant technical progress has been made towards incorporation of ceramic matrix composites (CMC) and environmental barrier coatings (EBC) technologies into gas turbine engine hot-section. The second phase of the program focused on the demonstration of a reverse flow annular CMC combustor. This has included overcoming the challenges of design and fabrication of CMCs into 'complex' shapes; developing processing to apply EBCs to 'engine hardware'; testing of an advanced combustor enabled by CMCs in a PW206 rig; and the validation of performance benefits against a metal baseline. The rig test validated many of the pretest predictions with a 40-50% reduction in pattern factor compared to the baseline and reductions in NOx levels at maximum power conditions. The next steps are to develop an understanding of the life limiting mechanisms in EBC and CMC materials, developing a design system for EBC coated CMCs and durability testing in an engine environment

Effect of liquid precursor pyrolysis on phase selection in the MgO-MgAl2O4 system

Aqueous solutions of Al and Mg nitrates have been spray pyrolysed at 673 K to synthesize powders with compositions varying between MgO and MgAl2O4. This has been carried out with the aim of studying phase selection and phase evolution in this system. The powders have been subsequently heat treated and the sequence of phases characterised by X-ray diffraction and transmission electron microscopy. Metastable extensions of the different phase fields have been calculated based on functions which predict the equilibrium phase diagram accurately. The appearance of phases is closely related to the temperature and to the non-stoichiometry in different compositional ranges of the system. The sequence of phase evolution has been correlated to the thermodynamics of nucleation in the system

Effect of rapid solidification on microstructural evolution in MgO-MgAl<SUB>2</SUB>O<SUB>4</SUB>

The response of the MgO-20 and 30 mol% Al<SUB>2</SUB>O<SUB>3</SUB> compositions to rapid solidification has been studied. The oxides were twin-roller quenched and the resulting flakes were characterized by X-ray diffraction and transmission electron microscopy. The results indicate that metastable extensions of spinel and periclase occurred and the microstructural pathway was determined from the final microstructure. The flakes having MgO-20 mol% Al<SUB>2</SUB>O<SUB>3</SUB> show a dendritic structure consisting of periclase and spinel. In the MgO-30 mol% Al<SUB>2</SUB>O<SUB>3</SUB> composition, the liquid transforms to spinel partitionlessly. The spinel is believed to undergo decomposition by a modulation in composition, and the resulting microstructure consists of spinel and periclase. Kinetic and thermodynamic aspects of phase selection have been rationalized based on the metastable extensions of the different phase fields in the phase diagram. It has been proposed that composition fluctuations in spinel are stabilized because of the formation of disordered phases with a continuous range of order parameter on the tetrahedral sublattice

Effect of Rapid Solidification on Microstructural Evolution in MgO−MgAl2O4MgO-MgAl_2O_4

The response of the MgO–20 and 30 mol% $Al_2O_3$ compositions to rapid solidification has been studied. The oxides were twin-roller quenched and the resulting flakes were characterized by X-ray diffraction and transmission electron microscopy. The results indicate that metastable extensions of spinel and periclase occurred and the microstructural pathway was determined from the final microstructure. The flakes having MgO–20 mol% $Al_2O_3$ show a dendritic structure consisting of periclase and spinel. In the MgO–30 mol% $Al_2O_3$ composition, the liquid transforms to spinel partitionlessly. The spinel is believed to undergo decomposition by a modulation in composition, and the resulting microstructure consists of spinel and periclase. Kinetic and thermodynamic aspects of phase selection have been rationalized based on the metastable extensions of the different phase fields in the phase diagram. It has been proposed that composition fluctuations in spinel are stabilized because of the formation of disordered phases with a continuous range of order parameter on the tetrahedral sublattice

Segregation in the MgO−MgAl2O4MgO-MgAl_{2}O_{4} system processed from nitrate precursors

The occurrence of segregation and its influence on microstructural and phase evolution have been studied in $MgO-MgAl_{2}O_{4}$ powders synthesized by thermal decomposition of aqueous nitrate precursors. When the nitrate solutions of Mg and Al were spray-pyrolyzed on a substrate held at 673 or 573 K, homogeneous mixed oxides were produced. Spraying and drying the nitrate solutions at 473 K resulted in the formation of compositionally inhomogeneous, segregated oxide mixtures. It is suggested that segregation in the dried powders was caused by the difference in solubility of the individual nitrate salts in water which caused Mg-rich and Al-rich salts to precipitate during dehydration of the solutions. The occurrence of segregation in the powders sprayed at 473 K and not 573 or 673 K is ascribed to the sluggish rate at which the early stages of decomposition occurred during which the cations segregated. The phase evolution in segregated and segregation-free $MgO-MgAl_{2}O_{4}$ powders has been compared. The distinguishing feature of the segregated powders was the appearance of stoichiometric periclase grain dimensions in excess of 0.3 \mu m at temperatures as low as 973 K. By comparison, the segregation- free powders displayed broad diffraction peaks corresponding to fine-grained and nonstoichiometric periclase. The grain size was in the range 5-30 nm at temperatures up to 1173 K. The key to obtaining fine-grained periclase was the ability to synthesize (Mg Al)O solid solutions with the rock salt structure. In the temperature range 973-1173 K, spinel grain size varied from 5 to 40 nm irrespective of its composition and did not appear to be influenced by segregation

Segregation in the MgO-MgAl<SUB>2</SUB>O<SUB>4</SUB> system processed from nitrate precursors

The occurrence of segregation and its influence on microstructural and phase evolution have been studied in MgO-MgAl2O4 powders synthesized by thermal decomposition of aqueous nitrate precursors. When the nitrate solutions of Mg and Al were spray-pyrolyzed on a substrate held at 673 or 573 K, homogeneous mixed oxides were produced. Spraying and drying the nitrate solutions at 473 K resulted in the formation of compositionally inhomogeneous, segregated oxide mixtures. It is suggested that segregation in the dried powders was caused by the difference in solubility of the individual nitrate salts in water which caused Mg-rich and Al-rich salts to precipitate during dehydration of the solutions. The occurrence of segregation in the powders sprayed at 473 K and not 573 or 673 K is ascribed to the sluggish rate at which the early stages of decomposition occurred during which the cations segregated. The phase evolution in segregated and segregation-free MgO-MgAl2O4 powders has been compared. The distinguishing feature of the segregated powders was the appearance of stoichiometric periclase grain dimensions in excess of 0.3 μm at temperatures as low as 973 K. By comparison, the segregation-free powders displayed broad diffraction peaks corresponding to fine-grained and nonstoichiometric periclase. The grain size was in the range 5-30 nm at temperatures up to 1173 K. The key to obtaining fine-grained periclase was the ability to synthesize (Mg Al)O solid solutions with the rock salt structure. In the temperature range 973-1173 K, spinel grain size varied from 5 to 40 nm irrespective of its composition and did not appear to be influenced by segregation

Segregation in the MgO–MgAl2O4 system processed from nitrate precursors

The occurrence of segregation and its influence on microstructural and phase evolution have been studied in MgO–MgAl2O4 powders synthesized by thermal decomposition of aqueous nitrate precursors. When the nitrate solutions of Mg and Al were spray-pyrolyzed on a substrate held at 673 or 573 K, homogeneous mixed oxides were produced. Spraying and drying the nitrate solutions at 473 K resulted in the formation of compositionally inhomogeneous, segregated oxide mixtures. It is suggested that segregation in the dried powders was caused by the difference in solubility of the individual nitrate salts in water which caused Mg-rich and Al-rich salts to precipitate during dehydration of the solutions. The occurrence of segregation in the powders sprayed at 473 K and not 573 or 673 K is ascribed to the sluggish rate at which the early stages of decomposition occurred during which the cations segregated. The phase evolution in segregated and segregation-free MgO–MgAl2O4 powders has been compared. The distinguishing feature of the segregated powders was the appearance of stoichiometric periclase grain dimensions in excess of 0.3 μm at temperatures as low as 973 K. By comparison, the segregation-free powders displayed broad diffraction peaks corresponding to fine-grained and nonstoichiometric periclase. The grain size was in the range 5–30 nm at temperatures up to 1173 K. The key to obtaining fine-grained periclase was the ability to synthesize (Mg Al)O solid solutions with the rock salt structure. In the temperature range 973–1173 K, spinel grain size varied from 5 to 40 nm irrespective of its composition and did not appear to be influenced by segregation