scholarly journals Oxygen Sensing of Pt/PEO-TiO2 in Humid Atmospheres at Moderate Temperatures

Sensors ◽  
2021 ◽  
Vol 21 (7) ◽  
pp. 2558
Author(s):  
Bernd Engelkamp ◽  
Klaus Schierbaum
Keyword(s):  
Conduction Band ◽  
Elevated Temperatures ◽  
Oxygen Sensing ◽  
Adsorbed Water ◽  
Ambient Air ◽  
Molecular Water ◽  
Processes And Reactions ◽  
Recovery Times ◽  
Adsorption Processes ◽  
Plasma Electrolytic

Here, we show that the presence of adsorbed water improves the oxygen-sensing properties of Pt/TiO2 at moderate temperatures. The studied interface is based on porous plasma electrolytic oxidized titanium (PEO-TiO2) covered with platinum clusters. The electrical resistance across Pt/PEO-TiO2 is explained by an electronic depletion layer. Oxygen adsorbates further increase the depletion by inducing extrinsic interface states, which are occupied by TiO2 conduction band electrons. The high oxygen partial pressure in ambient air substantially limits the electron transport across the interface. Our DC measurements at defined levels of humidity at 30 ∘C show that adsorbed water counteracts this shortcoming, allowing oxygen sensing at room conditions. In addition, response and recovery times from temporal oxygen exposure decrease with humidity. We attribute the effects to competing adsorption processes and reactions of water with adsorbed oxygen species and/or lattice oxygen, which involve electron re-injection to the TiO2 conduction band. Elevated temperatures up to 170 ∘C attenuate the effects, presumably due to the lower binding strength to the surface of molecular water compared with oxygen adsorbates.

High Temperature Oxidation and Corrosion of Silicon-Based Non-Oxide Ceramics

1999 ◽  
Vol 122 (1) ◽  
pp. 13-18 ◽  
Author(s):  
H. Klemm ◽  
M. Herrmann ◽  
C. Schubert
Keyword(s):  
High Temperature ◽  
Elevated Temperatures ◽  
Microstructural Analysis ◽  
Temperature Stability ◽  
Ambient Air ◽  
High Temperature Stability ◽  
Temperature Oxidation ◽  
Sic Ceramics ◽  
Silicon Based

The present study is focussed on the oxidation behavior of nonoxide silicon-based ceramics. Various Si3N4 and SiC ceramics were examined after long term oxidation tests (up to 5000 h) at 1500°C in ambient air. The damage mechanisms were discussed on the basis of a comprehensive chemical and microstructural analysis of the materials after the oxidation tests. The diffusion of oxygen into the material and its further reaction in the bulk of the material were found to be the most critical factors during long term oxidation treatment at elevated temperatures. However, the resulting damage in the microstructure of the materials can be significantly reduced by purposeful microstructural engineering. Using Si3N4/SiC and Si3N4/MoSi2 composite materials provides the possibility to improve the high temperature stability. [S0742-4795(00)00301-X]

Studies on mechanical behavior of LSFT-CGO dual-phase membranes at elevated temperatures in ambient air and slightly reducing environments

2014 ◽  
Vol 40 (6) ◽  
pp. 7783-7790 ◽  
Author(s):  
Thangamani Nithyanantham ◽  
Somnath Biswas ◽  
Nagabhushana Nagendra ◽  
Sukumar Bandopadhyay
Keyword(s):  
Mechanical Behavior ◽  
Elevated Temperatures ◽  
Ambient Air ◽  
Dual Phase

scholarly journals Air Quality Analyses for Photochemical Smog Associated with Atmospheric Aerosol Particles and Ozone Precursors Using CMAQ and CAMx Modeling Systems

2019 ◽  
pp. 224-235
Author(s):  
Muhammad Ibrahim
Keyword(s):  
Air Quality ◽  
Human Health ◽  
Ambient Air ◽  
Well Being ◽  
Scientific Discipline ◽  
Photochemical Smog ◽  
Air Quality Model ◽  
Quality Model ◽  
Processes And Reactions ◽  
Modeling Systems

Pollution due to air quality deterioration is directly or indirectly connected to the phenomenon of biogeochemistry (i.e the scientific discipline that involves the study of the chemical, physical, geological, and biological processes and reactions that influence the composition of the natural environment) which in turn links to the human health. Human health and well-being, along with the well-being of animals, plants, and agricultural products, are solely dependent upon the quality of air we inhale. In response to the emission control threshold levels, prediction of how changes in emission levels could affect ambient air quality has been documented. The use of photochemical air quality models is becoming widely acceptable by various global regulatory agencies for the purpose of regulatory analyses and for the attainment exhibition by evaluating and assessing the effectiveness of control strategies. This review work tries to figure out the two most important and uncommon models namely; Comprehensive Air Quality Model with Extensions (CAMx) and Community Multiscale Air Quality (CMAQ) Modeling System. These modeling systems are used to predict, characterize, determine and simulate the photochemical air quality conditions. This paper gives a substantial detailed information of findings from related multidimensional studies carried out long ago and recently on photochemical smog analyses. Photochemical smog; causes and impacts on both the environment and living-being health were succinctly spelt out. Ozone formation and its different precursors; atmospheric aerosols; emission of biogenics as well as Ozone modeling phases were also discussed. The researcher still talks about the model formulations such as Zhang Model formulation; application and history of CMAQ and CAMx models respectively.

scholarly journals Tribological Performance of Non-halogenated Phosphonium Ionic Liquids as Additives to Polypropylene and Lithium-Complex Greases

2019 ◽  
Vol 68 (1) ◽  
Author(s):  
Moritz Ploss ◽  
Yiyuan Tian ◽  
Sosaku Yoshikawa ◽  
René Westbroek ◽  
Johan Leckner ◽  
...  
Keyword(s):  
Ionic Liquids ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Friction Reduction ◽  
Minor Importance ◽  
Additive Concentration ◽  
Performance Limits ◽  
Lithium Complex ◽  
Adsorption Processes ◽  
Pin On Disk

AbstractFour non-halogenated ionic liquids (ILs) with trihexyl(tetradecyl)phosphonium cation are tested as lubricant additives to polypropylene (PP) and lithium-complex (LiX) greases. In pin-on-disk tests at elevated temperatures, the addition of an IL with bis(oxalato)borate ([BOB]) anion reduces wear by up to 50% when compared to the neat LiX base grease; an IL with bis(mandelato)borate ([BMB]) anion reduces friction by up to 60% for both PP and LiX. Elemental analysis reveals that oxygen-rich tribofilms help to reduce wear in case of [BOB], while the friction reduction observed for [BMB] is likely caused by adsorption processes. We find that temperature has a pronounced effect on additive expression, yet additive concentration is of minor importance under continuous sliding conditions. In contrast, rolling-sliding experiments at 90 °C show that the traction performance of LiX grease is dependent on additive concentration, revealing a reduction in traction by up to 30 and 40% for [BMB]- and [BOB]-containing ILs at concentrations of 10 wt%. Finally, an IL with dicyanamide anion reduces friction and increases wear in pin-on-disk tests at room temperature, while an IL with bis-2,4,4-(trimethylpentyl)phosphinate anion increases wear, showing only limited potential as grease additives. Overall, this work demonstrates the ability of non-halogenated ILs to significantly extend grease performance limits.

Tribological behaviour of low-pressure plasma sprayed WC-Co coatings at elevated temperatures

2019 ◽  
Vol 71 (2) ◽  
pp. 258-266
Author(s):  
Zhe Geng ◽  
Huadong Huang ◽  
Baoshan Lu ◽  
Shaohua Wu ◽  
Gaolian Shi
Keyword(s):  
Wear Resistance ◽  
Elevated Temperatures ◽  
High Hardness ◽  
Cobalt Content ◽  
Ambient Air ◽  
Low Pressure ◽  
Tribological Behaviour ◽  
Content Type ◽  
Pressure Plasma ◽  
Low Pressure Plasma

Purpose This paper aims to investigate the effect of coating microstructure, mechanical and oxidation property on the tribological behaviour of low-pressure plasma spraying (LPPS) tungsten carbide/cobalt (WC-Co) coatings. Design/methodology/approach WC-12Co and WC-17Co coatings were deposited via the LPPS spraying method. Tribological tests on the coatings were performed using a high-temperature ball-on-disc tribometer at temperatures from room temperature (RT, approximately 25 °C) up to 800 °C in ambient air. Findings WC-12Co coating contained brittle phases, pores and microcracks, which led to the low hardness, and finally promoted the splat delamination and the carbide debonding during wear. WC-17Co coating had higher cobalt content which benefited the coating to contain more WC particles, less brittle phases, pores and nearly no microcracks, and resulted in the high hardness and better wear resistance. Higher cobalt content also decelerated the oxidation rate of the coating and promoted the formation of cobalt oxides and CoWO4, which were able to maintain the load-bearing capacity and improve the tribological behaviour of the coating below 650°C. Above 650°C, the increase of oxidation degree and the decrease of mechanical property deteriorated the wear resistance of coatings. Originality/value The LPPS WC-Co coating with higher cobalt content had better tribological properties at different temperatures. The LPPS WC-Co coatings should not be used as wear-resistant coatings above 650 °C.

scholarly journals On the permeability of transparent screens of extreme tenuity by radiant heat

1833 ◽  
Vol 2 ◽  
pp. 310-311
Keyword(s):  
Thin Film ◽  
Elevated Temperatures ◽  
Ambient Air ◽  
Radiant Heat ◽  
The Other ◽  
Small Aperture ◽  
The One

The author states in this paper, that invisible radiant heat, from sources at elevated temperatures, freely permeates thin transparent screens in the same manner as light; but that as this doctine, established by Profesor Prévost and M. de la Roche has been controverted, he thinks it necessary to demonstrate it by fresh experiments: to this end he covered a small aperture with a film of glass almost iridescent, and keeping it constantly cold, by blowing on it, below the temperature of ambient air, he found that afi air-thermometer on one side of it was not affected by a heated iron ball on the other, if the temperature of the ball was low; but that as this temperature was raised, though not to the point of visible ignition, the effect on the thermometer became Sensible and even considerable. In another experiment, two air-thermometers, having their bulbs transparent, and as thin as possible, were placed equidistant from a heated ball just ceasing to be visible in the dark. The one was clear, the other coated inside with a thin film of pounded charcoal. The latter was most affected.

Oxidation behavior of pressureless liquid-phase-sintered α-SiC in ambient air at elevated temperatures

2008 ◽  
Vol 23 (6) ◽  
pp. 1689-1700 ◽  
Author(s):  
F. Rodríguez-Rojas ◽  
O. Borrero-López ◽  
A.L. Ortiz ◽  
F. Guiberteau
Keyword(s):  
Activation Energy ◽  
Liquid Phase ◽  
Oxide Scale ◽  
Oxidation Behavior ◽  
Elevated Temperatures ◽  
Low Cost ◽  
Reaction Diffusion ◽  
Ambient Air ◽  
Outward Diffusion ◽  
Nonoxide Ceramics

The long-duration oxidation behavior of a pressureless liquid-phase-sintered (LPS) α-SiC with 10 vol% Y3Al5O12 additives was studied by furnace oxidation tests in ambient air at 1100 to 1450 °C. The oxidation of this LPS SiC ceramic was found to be passive throughout these temperatures due to the formation of oxide scales, with a change in the oxidation behavior occurring at 1350 °C. It was also found that the oxidation behavior is very complex, exhibiting two distinct stages at all temperatures: (i) initial nonparabolic oxidation, where the rate-limiting mechanism is the outward diffusion of Y3+ and Al3+ cations from the secondary intergranular phase into the oxide scale with the activation energy of the oxidation being 504 ± 32 kJ/mol, followed by (ii) parabolic oxidation below 1350 °C, where the rate-determining mechanism is the inward diffusion of oxygen through the oxide scale with the activation energy being 310 ± 47 kJ/mol, or paralinear oxidation at and above 1350 °C, where oxidation is controlled by some mixed reaction/diffusion process. The existence of two oxidation regimes reflects the progressive crystallization of the oxide scale during the oxidation. Finally, guidelines are provided for the design and fabrication of low-cost, highly oxidation-resistant LPS SiC or other LPS nonoxide ceramics.

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