Degradation mechanism of SiCf/SiC composites after long-time water vapor and oxygen corrosion at 1300 oC

AbstractAmbient air is used as an oxygen source in SOFCs to be commercialized. Various chemical species which can lead to poisoning of SOFC cathodes are included as minor constitutions in air, such as water vapor, SOx, NOx and NaCl etc. However, their effects on the cathode performance have not yet well known, even though they are expected to cause a degradation of the electrode performance and to reduce the long-term durability of SOFCs. Therefore, in this study, we focused on the poisoning caused by water vapor and SOx in the oxygen source to clarify their effects on SOFCs performances and to reveal the degradation mechanism of cathodes. SOFCs with typical electrolyte-supported structure were used in this work, which were composed with ScSZ (10 mol% Sc2O3, 1mol% CeO2, 89 mol% ZrO2) plate with the thickness of 200 µm as electrolyte, NiO-ScSZ (mixture of 56 wt% NiO and 44 wt% ScSZ) porous layer as anode, and two cathode layers of LSM ((La0.8Sr0.2)0.98MnO3) and LSM-ScSZ (mixture of 50 wt% LSM and 50 wt% ScSZ). Power generation characteristics of the cells had been analyzed by measuring cell voltage at a constant current density (200 mA/cm2) and by comparing changes in cell impedance, upon supplying the artificially-contaminated air with water vapor or SOx, to the SOFC cathodes at various operational temperatures. High-resolution FESEM (S-5200, Hitachi) was used to analyze microstructural changes caused by the impurities. Mg Kα radiation from a monochromatized X-ray source was used for XPS measurements (ESCA-3400, KRATOS). AC impedance was measured at various temperatures under the open circuit voltage condition by an impedance analyzer (Solatron 1255B/SI 1287, Solatron), in a frequency range from 0.1 to 105 Hz with an amplitude of 10 mV.

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Origin of the Hydrogen Absorbed by Incoherent TiC Particles in Iron

Materials Science Forum ◽

10.4028/www.scientific.net/msf.475-479.233 ◽

2005 ◽

Vol 475-479 ◽

pp. 233-236 ◽

Cited By ~ 1

Author(s):

Kaneaki Tsuzaki ◽

Fu Gao Wei

Keyword(s):

Heat Treatment ◽

Water Vapor ◽

High Temperatures ◽

Thermal Desorption ◽

Hydrogen Absorption ◽

Room Temperature ◽

Trap Hydrogen ◽

Thermal Desorption Spectrometry ◽

Long Time

Hydrogen absorption of incoherent TiC particles that were once reported to be strong hydrogen traps in iron at room temperature was investigated by means of thermal desorption spectrometry (TDS). The results indicated that incoherent TiC particles in iron do not trap hydrogen at all at room temperature even they are cathodically charged for a long time. Only at high temperatures and in atmosphere containing hydrogen source, incoherent TiC particles can trap hydrogen. The origin of hydrogen trapped by incoherent TiC particles was justified to be water vapor in the atmosphere during heat treatment.

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C/C-ZrB2-ZrC-SiC Composite Derived from Polymeric Precursor Infiltration and Pyrolysis Part 2

Nanotechnology ◽

10.4018/978-1-4666-5125-8.ch018 ◽

2014 ◽

pp. 447-465

Author(s):

Weigang Zhang ◽

Changming Xie ◽

Xi Wei ◽

Min Ge

Keyword(s):

Fracture Toughness ◽

Wind Tunnel ◽

Thermal Shock ◽

Plasma Torch ◽

Volume Fraction ◽

Pyrolytic Carbon ◽

Glass Layer ◽

Polymeric Precursors ◽

Long Time ◽

Sic Composites

Mechanical and ablation properties of the 2D C/C-ZrB2-ZrC-SiC composites with a fiber volume fraction of 17.6%, fabricated by infiltration and co-pyrolysis of blended polymeric precursors, were studied in this Part II. Flexural strength and fracture toughness of the composites were found to be influenced strongly by the thickness of the deposited pyrolytic carbon interphase, a composite with the pyrolytic carbon volume fraction of 22.3% exhibits improved bending strength and fracture toughness of 127.9 MPa and 6.23 MPa·m1/2, respectively. The pseudo-plastic strain to failure of the composite is ascribed to sliding of the interphase and pulling out of carbon fibers from the brittle ceramics matrix. Ablation properties of the composite were investigated with a plasma torch and arc-heated wind tunnel tests at temperatures above 1800~2200°C. The composite exhibits very low ablation rates of 0.18×10-3 mm/s at 1800°C and 0.37×10-3 mm/s at 2000°C in the plasma torch after 1000s testing, as compared to a similar rate of 0.30×10-3 mm/s in the wind tunnel at 1900°C after 600s testing. Ablation rates increase with increasing of temperatures from 1800 to 2200°C. The maximum ablation rate is only 1.67×10-3 mm/s in a plasma torch at 2200°C for 1000s, decreased by 71.0% as compared with the C/C-SiC composite with the same fiber and interphase contents. The 2D C/C-ZrB2-ZrC-SiC composite simultaneously showed excellent thermal shock resistance, on account of no cracks on the surface and breakage of the material being detected after these abrupt temperature increasing and long time ablations. The heating-up rate at the center of the composite specimen was found as high as above 30K/s in the plasma torch tests. Excellent ablation and thermal shock resistances of the composite can be attributed to its architecture of carbon fiber and interphase, as well as its matrix microstructures characterized by nano sized dispersions of ZrB2-Zr-SiC phases inherent formed by co-pyrolysis of three polymeric precursors. These meso- and microstructures make the composites possess very small and steady coefficients of thermal expansion (CTE) around 1.5~2.5×10-6/K and high thermal conductivities around 10~14 W/mK (which increases with increasing of temperature) from room temperature to 1300°C, respectively. Surface products and cross sectional morphologies of the composite after the ablation tests were also investigated using SEM and XRD, it was found that a homogeneous distributed and continuous glass layer composing of ZrO2-SiO2 with zirconia as a skeleton was in-situ formed. These special features of coating benefits from the merits of matrix microstructures, and inhibits the inward diffusion of oxygen and protects the composite from further oxidation and spalled off by strong gas fluid.

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Three Destinies of Solution-Processable Polymer Light-Emitting Diodes under Long-Time Operation

Polymers ◽

10.3390/polym13111853 ◽

2021 ◽

Vol 13 (11) ◽

pp. 1853

Author(s):

Ruslana Udovytska ◽

Pavel Chulkin ◽

Aleksandra Wypych-Puszkarz ◽

Jaroslaw Jung

Keyword(s):

Charge Transport ◽

Indium Tin Oxide ◽

Degradation Mechanism ◽

Protective Layer ◽

Transport Layer ◽

Internal Layers ◽

Carrier Injection ◽

Light Emitting ◽

Time Operation ◽

Long Time

The article describes three different ways of polymer light-emitting diode (PLED) degradation, caused by damage of the protective layer. The electroluminescence and charge-transport properties of a completely encapsulated diode, the diodes with a leaky protective layer and diodes without encapsulation were compared under long-time exploitation. The studied devices incorporated Super Yellow light-emitting poly-(1,4-phenylenevinylene) PPV copolymer as an electroluminescence component, and (poly-(3,4-ethylenedioxythiophene)–poly-(styrene sulfonate) (PEDOT:PSS) as a charge-transport layer between the indium tin oxide (ITO) anode and aluminum–calcium cathode. To analyze the PLED degradation mechanism regarding charge transport, impedance spectroscopy was used. The values of resistance and capacitance of the internal layers revealed an effect of applied voltage on charge carrier injection and recombination. The factors responsible for the device degradation were analyzed on a macromolecular level by comparing the plots of voltage dependence of resistance and capacitance at different operation times elapsed.

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SiC-Coated Carbon Nanotubes with Enhanced Oxidation Resistance and Stable Dielectric Properties

Materials ◽

10.3390/ma14112770 ◽

2021 ◽

Vol 14 (11) ◽

pp. 2770

Author(s):

Rong Li ◽

Yuchang Qing ◽

Juanjuan Zhao ◽

Shiwen Huang

Keyword(s):

Carbon Nanotubes ◽

High Temperature ◽

Dielectric Properties ◽

Oxidation Resistance ◽

Pyrolysis Temperature ◽

X Band ◽

Pristine Cnts ◽

Long Time ◽

Sic Composites ◽

Coated Carbon

Carbon nanotubes (CNTs) coated with SiC coating was successfully prepared by pyrolysis of polycarbosilane (PCS) used as a precursor. The function of pyrolysis temperature on the oxidation resistance and the dielectric properties of CNTs/SiC were studied in X-band. The results demonstrate that the obtained dense SiC film can prevent the oxidation of CNTs when the pyrolysis temperature reaches 600 °C. Correspondingly, after heat treatment is at 400 °C for 200 h, the mass loss of P-600 is less than 1.86%, and the real and imaginary parts of the dielectric constant nearly keep constant (ε′ from 14.2 to 14, and ε″ from 5.7 to 5.5). SiC-coated CNTs have a better oxidation resistance than pristine CNTs. Therefore, this work, with a facile preparation process, enhances the oxidation resistance of CNTs at high temperature for a long time and maintains a stable dielectric property, which means CNTs/SiC composites can be good candidates for applications in the field of high-temperature absorbers.

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Recession of BN Coatings in SiC/SiC Composites through Reaction with Water Vapor

Journal of the American Ceramic Society ◽

10.1111/jace.18052 ◽

2021 ◽

Author(s):

Virginia E. Collier ◽

Wenbo Xu ◽

Robert M. McMeeking ◽

Frank W. Zok ◽

Matthew R. Begley

Keyword(s):

Water Vapor ◽

Sic Composites ◽

Reaction With Water

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An update on the uncertainties of water vapor measurements using Cryogenic Frostpoint Hygrometers

10.5194/amt-2016-44 ◽

2016 ◽

Author(s):

Holger Vömel ◽

Tatjana. Naebert ◽

Ruud Dirksen ◽

Michael Sommer

Keyword(s):

Water Vapor ◽

Data Series ◽

Climate Variables ◽

Stratospheric Water Vapor ◽

Tropospheric Measurements ◽

Long Time ◽

Climate Series ◽

Term Data ◽

Better Than

Abstract. Long time series of observations of essential climate variables in the troposphere and stratosphere are often impacted by inconsistencies in instrumentation and ambiguities in the interpretation of the data. To reduce these problems of long term data series all measurements should include an estimate of their uncertainty and a description of their sources. Here we present an update of the uncertainties for tropospheric and stratospheric water vapor observations using the Cryogenic Frostpoint Hygrometer (CFH). The largest source of measurement uncertainty is the controller stability, which is discussed here in detail. We describe a method to quantify this uncertainty for each profile based on the measurements. We also show the importance of a manufacturer independent ground check, which is an essential tool to continuously monitor the uncertainty introduced by instrument variability. A small bias, which has previously been indicated in lower tropospheric measurements, is described here in detail and has been rectified. Under good conditions the total from all sources of uncertainty of frostpoint or dewpoint measurements using the CFH can be better than 0.2 K. Systematic errors, which are most likely to impact long term climate series are verified to be less than 0.1 K.

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C/C-ZrB2-ZrC-SiC Composite Derived from Polymeric Precursor Infiltration and Pyrolysis

MAX Phases and Ultra-High Temperature Ceramics for Extreme Environments ◽

10.4018/978-1-4666-4066-5.ch014 ◽

2013 ◽

pp. 435-459

Author(s):

Weigang Zhang ◽

Changming Xie ◽

Xi Wei ◽

Min Ge

Keyword(s):

Fracture Toughness ◽

Wind Tunnel ◽

Thermal Shock ◽

Plasma Torch ◽

Volume Fraction ◽

Pyrolytic Carbon ◽

Glass Layer ◽

Polymeric Precursors ◽

Long Time ◽

Sic Composites

Part II. Mechanical and ablation properties of the 2D C/C-ZrB2-ZrC-SiC composites with a fiber volume fraction of 17.6%, fabricated by infiltration and co-pyrolysis of blended polymeric precursors, were studied in this Part II. Flexural strength and fracture toughness of the composites were found to be influenced strongly by the thickness of the deposited pyrolytic carbon interphase, a composite with the pyrolytic carbon volume fraction of 22.3% exhibits improved bending strength and fracture toughness of 127.9 MPa and 6.23 MPa·m1/2, respectively. The pseudo-plastic strain to failure of the composite is ascribed to sliding of the interphase and pulling out of carbon fibers from the brittle ceramics matrix. Ablation properties of the composite were investigated with a plasma torch and arc-heated wind tunnel tests at temperatures above 1800~2200°C. The composite exhibits very low ablation rates of 0.18×10-3 mm/s at 1800°C and 0.37×10-3 mm/s at 2000°C in the plasma torch after 1000s testing, as compared to a similar rate of 0.30×10-3 mm/s in the wind tunnel at 1900°C after 600s testing. Ablation rates increase with increasing of temperatures from 1800 to 2200°C. The maximum ablation rate is only 1.67×10-3 mm/s in a plasma torch at 2200°C for 1000s, decreased by 71.0% as compared with the C/C-SiC composite with the same fiber and interphase contents. The 2D C/C-ZrB2-ZrC-SiC composite simultaneously showed excellent thermal shock resistance, on account of no cracks on the surface and breakage of the material being detected after these abrupt temperature increasing and long time ablations. The heating-up rate at the center of the composite specimen was found as high as above 30K/s in the plasma torch tests. Excellent ablation and thermal shock resistances of the composite can be attributed to its architecture of carbon fiber and interphase, as well as its matrix microstructures characterized by nano sized dispersions of ZrB2-Zr-SiC phases inherent formed by co-pyrolysis of three polymeric precursors. These meso- and microstructures make the composites possess very small and steady coefficients of thermal expansion (CTE) around 1.5~2.5×10-6/K and high thermal conductivities around 10~14 W/mK (which increases with increasing of temperature) from room temperature to 1300°C, respectively. Surface products and cross sectional morphologies of the composite after the ablation tests were also investigated using SEM and XRD, it was found that a homogeneous distributed and continuous glass layer composing of ZrO2-SiO2 with zirconia as a skeleton was in-situ formed. These special features of coating benefits from the merits of matrix microstructures, and inhibits the inward diffusion of oxygen and protects the composite from further oxidation and spalled off by strong gas fluid.

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Degradation of Persistent Organic Pollutants Mechanism Summary

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.356-360.620 ◽

2011 ◽

Vol 356-360 ◽

pp. 620-623 ◽

Cited By ~ 1

Author(s):

Ru Qin Wang

Keyword(s):

Organic Pollutants ◽

Persistent Organic Pollutants ◽

Chemical Structure ◽

Environmental Chemistry ◽

Degradation Mechanism ◽

Structure Stability ◽

Major Health Problem ◽

Major Health ◽

Ecological Problems ◽

Long Time

Persistent organic pollutants (POPs) refers to the chemical structure stability, the toxicity, big,difficult biodegradation , there is a long time in nature,.to concentrate the detention easily in organism kind of organic chemistry pollutant.POPs has become the field of environmental chemistry and toxicology studies of ecological problems affecting human survival, it is the 21st century, a major health problem. Overview of the current domestic and international persistent organic pollutants on the degradation mechanism of the type. Presented on persistent organic pollutants to solve the problem.

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