Ultra-Low Thermal Conductivity in Nanoscale Layered Oxides

2009 ◽  
Vol 132 (3) ◽  
Author(s):  
J. Alvarez-Quintana ◽  
Ll. Peralba-Garcia ◽  
J. L. Lábár ◽  
J. Rodríguez-Viejo
Keyword(s):  
Thermal Conductivity ◽  
Thermal Barrier Coatings ◽  
Room Temperature ◽  
Thermal Barrier ◽  
Layered Oxides ◽  
Barrier Coatings ◽  
3Ω Method ◽  
Nanometer Thickness ◽  
Intrinsic Thermal Conductivity ◽  
Strong Barrier

The cross-plane thermal conductivity of several nanoscale layered oxides SiO2/Y2O3, SiO2/Cr2O3, and SiO2/Al2O3, synthesized by e-beam evaporation was measured in the range from 30 K to 300 K by the 3ω method. Thermal conductivity attains values around 0.5 W/m K at room temperature in multilayer samples, formed by 20 bilayers of 10 nm SiO2/10 nm Y2O3, and as low as 0.16 W/m K for a single bilayer. The reduction in thermal conductivity is related to the high interface density, which produces a strong barrier to heat transfer rather than to the changes of the intrinsic thermal conductivity due to the nanometer thickness of the layers. We show that the influence of the first few interfaces on the overall thermal resistance is higher than the subsequent ones. Annealing the multilayered samples to 1100°C slightly increases the thermal conductivity due to changes in the microstructure. These results suggest a route to obtain suitable thermal barrier coatings for high temperature applications.

Development of Operating Temperature Prediction Method Using Thermophysical Properties Change of Thermal Barrier Coatings

2004 ◽  
Vol 126 (1) ◽  
pp. 102-106 ◽  
Author(s):  
T. Fujii ◽  
T. Takahashi
Keyword(s):  
Thermal Conductivity ◽  
Thermal Barrier Coatings ◽  
Operating Temperature ◽  
Thermal Barrier ◽  
Conductivity Measurements ◽  
Barrier Coatings ◽  
Barrier Performance ◽  
Very High ◽  
General Method ◽  
Exposure Conditions

Thermal barrier coatings (TBCs) have become an indispensable technology as the temperature of turbine inlet gas has increased. TBCs reduce the temperature of the base metal, but a reduction of internal pores by sintering occurs when using TBCs, and so the thermal barrier performance of TBCs is deteriorated. This in turn increases the temperature of the base metal and could shorten its lifespan. The authors have already clarified by laboratory acceleration tests that the deterioration of the thermal barrier performance of TBCs is caused by a decrease in the noncontact area that exists inside TBCs. This noncontact area is a slit space that exists between thin layers and is formed when TBCs are coated. This paper examines the relations between the decrease of the noncontact area and the exposure conditions, by measuring the thermal conductivity and the porosity of TBCs exposed to the temperatures that exist in an actual gas turbine, and derives the correlation with exposure conditions. As a result, very high correlations were found between the thermal conductivity and exposure conditions of TBCs, and between the porosity and exposure conditions. A very high correlation was also found between the thermal conductivity and porosity of TBCs. In addition, techniques for predicting TBC operating temperature were examined by using these three correlations. The correlation of diameter and exposure conditions of the gamma prime phase, which exists in nickel base super alloys, is used as a general method for predicting the temperature of parts in hot gas paths. This paper proposes two kinds of operating temperature prediction methods, which are similar to this general method. The first predicts the operating temperature from thermal conductivity measurements of TBCs before and after use, and the second predicts the operating temperature from thermal conductivity measurements of TBCs after use and porosity measurements before use. The TBC operating temperatures of a combustor that had been used for 12,000 hours with an actual E-class gas turbine were predicted by these two methods. The advantage of these methods is that the temperature of all parts with TBC can be predicted.

Design, Preparation and Thermal Properties of (La0.4Sm0.5Yb0.1)2Zr2O7 Ceramic for Thermal Barrier Coatings

2012 ◽  
Vol 512-515 ◽  
pp. 469-473 ◽  
Author(s):  
L. Liu ◽  
Z. Ma ◽  
F.C. Wang ◽  
Q. Xu
Keyword(s):  
Thermal Conductivity ◽  
Thermal Expansion ◽  
Thermal Properties ◽  
Rare Earth ◽  
Thermal Expansion Coefficient ◽  
Thermal Barrier Coatings ◽  
Expansion Coefficient ◽  
Phonon Transport ◽  
Thermal Barrier ◽  
Barrier Coatings

According to the theory of phonon transport and thermal expansion, a new complex rare-earth zirconate ceramic (La0.4Sm0.5Yb0.1)2Zr2O7, with low thermal conductivity and high thermal expansion coefficient, has been designed by doping proper ions at A sites. The complex rare-earth zirconate (La0.4Sm0.5Yb0.1)2Zr2O7 powder for thermal barrier coatings (TBCs) was synthesized by coprecipitation-calcination method. The phase, microstructure and thermal properties of the new material were investigated. The results revealed that single phase (La0.4Sm0.5Yb0.1)2Zr2O7 with pyrochlore structure was synthesized. The thermal conductivity and the thermal expansion coefficient of the designed complex rare-earth zirconate ceramic is about 1.3W/m•K and 10.5×10-6/K, respectively. These results imply that (La0.4Sm0.5Yb0.1)2Zr2O7 can be explored as the candidate material for the ceramic layer in TBCs system.

Evaluation of CeSZ Thermal Barrier Coatings for Diesels

2000 ◽  
Author(s):  
P.J. Huang ◽  
J.J. Swab ◽  
P.J. Patel ◽  
W.S. Chu
Keyword(s):  
Thermal Conductivity ◽  
Thermal Expansion ◽  
Thermal Barrier Coatings ◽  
Coefficient Of Thermal Expansion ◽  
Fuel Efficiency ◽  
Atmospheric Plasma ◽  
Thermal Barrier ◽  
Mechanical And Thermal Properties ◽  
Barrier Coatings ◽  
Spray Process

Abstract The development of thermal barrier coatings (TBCs) for diesel engines has been driven by the potential improvements in engine power and fuel efficiency that TBCs represent. TBCs have been employed for many years to reduce corrosion of valves and pistons because of their high temperature durability and thermal insulative properties. There are research programs to improve TBCs wear resistance to allow for its use in tribologically intensive areas of the engine. This paper will present results from tribological tests of ceria stabilized zirconia (CeSZ). The CeSZ was applied by atmospheric plasma spray process. Various mechanical and thermal properties were measured including wear, coefficient of thermal expansion, thermal conductivity, and microhardness. The results show the potential use of CeSZ in wear sensitive applications in diesel applications. Keywords: Thermal Barrier Coating, Diesel Engine, Wear, Thermal Conductivity, and Thermal Expansion

Thermal Cycling Behavior of Lanthanum-Cerium Oxide Thermal Barrier Coatings Prepared by Air Plasma Spraying

2007 ◽  
Vol 336-338 ◽  
pp. 1759-1761 ◽  
Author(s):  
Wen Ma ◽  
Yue Ma ◽  
Sheng Kai Gong ◽  
Hui Bin Xu ◽  
Xue Qiang Cao
Keyword(s):  
Cerium Oxide ◽  
Plasma Spraying ◽  
Thermal Barrier Coatings ◽  
Bond Coat ◽  
Room Temperature ◽  
Thermal Barrier ◽  
Air Plasma ◽  
Air Plasma Spraying ◽  
Cyclic Testing ◽  
Barrier Coatings

Lanthanum-cerium oxide (La2Ce2O7, LC) is considered as a new candidate material for thermal barrier coatings (TBCs) because of its low thermal conductivity and high phase stability between room temperature and 1673K. The LC coatings with different La2O3 contents were prepared by air plasma spraying (APS) and their lifetime was evaluated by thermal cyclic testing from room temperature to 1373 K. The structures of the coatings were characterized by XRD and SEM and the deviation of the composition from the powder was determined by EDS analysis. Long time annealing for the freestanding coating at 1673K reveals that the near stoichiometric LC coating is stable up to 240h, and the stability decreases with increasing the deviation from stoichiometric LC composition. During thermal cyclic testing, spallation was observed within the top coat near the bond coat. It is considered that the effect of intrinsic stress caused by the coefficient of thermal expansion (CTE) mismatch between top coat and bond coat is larger than that of thermally grown oxide (TGO) and the bond adherence of top coat with TGO.

scholarly journals Analysis of the energetic/environmental performances of gas turbine plant: Effect of thermal barrier coatings and mass of cooling air

2009 ◽  
Vol 13 (1) ◽  
pp. 147-164 ◽  
Author(s):  
Ion Ion ◽  
Anibal Portinha ◽  
Jorge Martins ◽  
Vasco Teixeira ◽  
Joaquim Carneiro
Keyword(s):  
Thermal Conductivity ◽  
Gas Turbine ◽  
Thermal Barrier Coatings ◽  
Turbine Blades ◽  
Heat Transfer Analysis ◽  
Thermal Barrier ◽  
Inlet Temperature ◽  
Barrier Coatings ◽  
Cooling Air Flow ◽  
Cooling Air

Zirconia stabilized with 8 wt.% Y2O3 is the most common material to be applied in thermal barrier coatings owing to its excellent properties: low thermal conductivity, high toughness and thermal expansion coefficient as ceramic material. Calculation has been made to evaluate the gains of thermal barrier coatings applied on gas turbine blades. The study considers a top ceramic coating Zirconia stabilized with 8 wt.% Y2O3 on a NiCoCrAlY bond coat and Inconel 738LC as substrate. For different thickness and different cooling air flow rates, a thermodynamic analysis has been performed and pollutants emissions (CO, NOx) have been estimated to analyze the effect of rising the gas inlet temperature. The effect of thickness and thermal conductivity of top coating and the mass flow rate of cooling air have been analyzed. The model for heat transfer analysis gives the temperature reduction through the wall blade for the considered conditions and the results presented in this contribution are restricted to a two considered limits: (1) maximum allowable temperature for top layer (1200?C) and (2) for blade material (1000?C). The model can be used to analyze other materials that support higher temperatures helping in the development of new materials for thermal barrier coatings.

Mechanical Properties of Thermal Barrier Coatings at Room Temperature

2005 ◽  
Vol 290 ◽  
pp. 336-339 ◽  
Author(s):  
G. Guidoni ◽  
Y. Torres Hernández ◽  
Marc Anglada
Keyword(s):  
Mechanical Properties ◽  
Thermal Barrier Coatings ◽  
Room Temperature ◽  
Inconel 625 ◽  
Thermal Barrier ◽  
Barrier Coatings ◽  
Bending Tests ◽  
Four Point Bending ◽  
Barrier Coating ◽  
Plasma Sprayed

Four point bending tests have been carried out on a thermal barrier coating (TBC) system, at room temperature. The TBC system consisted of a plasma sprayed Y-TZP top coat with 8 % in weight of Yttria, a bond coat of NiCrAlY and a Ni-based superalloy Inconel 625 as substrate. The TBC coating was deposited on both sides of the prismatic specimens. Efforts have been done in detecting the damage of the coating by means of Maltzbender et al [1] model.

Two-channel model for ultralow thermal conductivity of crystalline Tl3VSe4

Science ◽  
2018 ◽  
Vol 360 (6396) ◽  
pp. 1455-1458 ◽  
Author(s):  
Saikat Mukhopadhyay ◽  
David S. Parker ◽  
Brian C. Sales ◽  
Alexander A. Puretzky ◽  
Michael A. McGuire ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Random Walk ◽  
Specific Heat ◽  
Thermal Barrier Coatings ◽  
Lattice Thermal Conductivity ◽  
Channel Model ◽  
Disordered Materials ◽  
Thermal Barrier ◽  
Barrier Coatings ◽  
Transport Component

Solids with ultralow thermal conductivity are of great interest as thermal barrier coatings for insulation or thermoelectrics for energy conversion. However, the theoretical limits of lattice thermal conductivity (κ) are unclear. In typical crystals a phonon picture is valid, whereas lowest κ values occur in highly disordered materials where this picture fails and heat is supposedly carried by random walk among uncorrelated oscillators. Here we identify a simple crystal, Tl3VSe4, with a calculated phonon κ [0.16 Watts per meter-Kelvin (W/m-K)] one-half that of our measured κ (0.30 W/m-K) at 300 K, approaching disorder κ values, although Raman spectra, specific heat, and temperature dependence of κ reveal typical phonon characteristics. Adding a transport component based on uncorrelated oscillators explains the measured κ and suggests that a two-channel model is necessary for crystals with ultralow κ.

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