scholarly journals Thermodynamic simulation of oxidation process of the Moss-Mo3Si hypoeutectic alloy, doped with yttrium

2019 ◽  
Vol 57 (2) ◽  
pp. 101-110
Author(s):  
Alexey V. Larionov ◽  
◽  
Ludmila Y. Udoeva ◽  
Vladimir M. Chumarev ◽  
◽  
...  
Keyword(s):  
Water Vapor ◽  
Oxidation Process ◽  
Thermodynamic Simulation ◽  
Oxidation Products ◽  
Hypoeutectic Alloy ◽  
Protective Film ◽  
Chemical Transformations ◽  
Moist Air ◽  
Condensed Product ◽  
Hsc Chemistry

In order to study the effect of yttrium additives on the oxidation of molybdenum silicide alloys, thermodynamic modeling of the interaction in the Mo-Mo3Si-Y5Si3 system with dry and moist air was performed in the temperature range 25-2000 °C. To predict the composition of oxidation products and the sequence of the formation of phase components, the dependences on the temperature and consumption of oxidants – water vapor and oxygen of the air – are obtained. The calculations were performed using the HSC Chemistry 6.12 software, into the database of which the calculated missing thermochemical characteristics of Y2Si2O7, Y2SiO5 silicates and yttrium molybdates Y2Mo3O12, Y2MoO6 were entered. It is shown that, under equilibrium conditions, the oxidation process with dry and moist air proceeds almost equally, since the interaction of the components of the alloy with oxygen is thermodynamically preferable than with water vapor. According to the obtained thermodynamic models, the oxidation process of the Mo-5 wt. % Si alloy of the hypoeutectic composition doped with yttrium can be represented as a sequence of the following chemical transformations: firstly Mo and Y silicides oxidize forming Y2O3, SiO2 and metallic Mo, then molybdenum is oxidized to MoO2 and Y2O3 interacts with SiO2 with the formation of silicates Y2SiO5 and Y2Si2O7. As a result of the complete oxidation of the alloy, MoO3 and Y2Mo3O12 are added to the condensed product, and molybdenum oxide (MoO3)n vapor appears in the gas phase. Based on the results of a complete thermodynamic analysis, the possibility of the formation of silicates and yttrium molybdate during the oxidation of the hypoeutectic alloy Mo-5Si-3Y (wt. %) was established. This can increase its oxidation resistance due to the formation of a protective film limiting the diffusion of oxygen into the alloy, which, of course, requires experimental confirmation.

scholarly journals Thermodynamic simulation of oxidation process of the Moss-Mo3Si hypoeutectic alloy, doped with scandium or neodymium

2019 ◽  
Vol 57 (2) ◽  
pp. 90-100
Author(s):  
Alexey V. Larionov ◽  
◽  
Ludmila Y. Udoeva ◽  
Vladimir M. Chumarev ◽  
◽  
...  
Keyword(s):  
Oxidation Process ◽  
Thermodynamic Simulation ◽  
Oxidation Products ◽  
Hypoeutectic Alloy ◽  
Protective Film ◽  
Chemical Transformations ◽  
Reaction Products ◽  
Moist Air ◽  
Condensed Product ◽  
Hsc Chemistry

In order to study the effect of yttrium additives on the oxidation of molybdenum silicide alloys, thermodynamic modeling of the interaction in Mo-Mo3Si-Sc5Si3 и Mo-Mo3Si-NdSi systems with dry and moist air was performed in the temperature range 25-2000 °C. The calculations were performed using the HSC Chemistry 6.12 software, into the database of which the calculated missing thermochemical characteristics silicates, molybdates of scandium and neodymium were entered. Based on the obtained dependences of the composition of phases on temperature and charge of the oxidant (air or vapor-air mixture), the sequence of phase formation was determined and the compositions of oxidation products were estimated. It is shown that, under equilibrium conditions, the oxidation process with dry and moist air proceeds almost equally, since the interaction of the components of the alloy with oxygen is thermodynamically preferable than with water vapor. According to the obtained thermodynamic models, the oxidation process of the Mo-5Si-3(Sc, Nd) (wt.%) alloys involves a sequence of the following chemical transformations: at the beginning Mo and Sc (Nd) silicides oxidize forming Sc2O3 ( Nd2O3), SiO2 and elemental Mo, then molybdenum is oxidized to MoO2 and Sc2O3 or Nd2O3 interacts with SiO2 with the formation of appropriate silicates Sc2Si2O7 или Nd2Si2O7. As a result of the complete oxidation of the alloy, MoO3 and Sc2(MoO4)3 or Nd2Mo4O15 are added to the condensed product, and molybdenum oxide (MoO3)n vapor appears in the gas phase. In addition, the formation of Nd2Mo2O7 and Nd2 (MoO4)3 is possible. During the oxidation of the Mo-5Si-3Nd alloy at T> 1700 oC, Nd(OH)3 can be formed in the condensed reaction products. According to the results of complete thermodynamic analysis, the formation of silicates and molybdates of scandium and neodymium can promote to the formation of a protective film on the surface of the alloys, which limits the diffusion of oxygen in them, and as a result, the oxidation resistance of alloys should increase.

Ultraviolet blocking and antioxidant polyvinyl alcohol films incorporated with baicalin extraction from Scutellaria baicalensis Georgi

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Jinshu Liu ◽  
Xiaoyan Ma ◽  
Wenzhao Shi ◽  
Jianwei Xing ◽  
Chaoqun Ma ◽  
...  
Keyword(s):  
Water Vapor ◽  
Polyvinyl Alcohol ◽  
Radical Scavenging Activity ◽  
Antioxidant Properties ◽  
Radical Scavenging ◽  
Water Vapor Permeability ◽  
Scutellaria Baicalensis ◽  
Vapor Permeability ◽  
Protective Film ◽  
Uv Blocking

Abstract Baicalin, an active flavonoid ingredient of Scutellaria baicalensis Georgi, was extracted by heat reflux extraction and showed the same significance UV absorption property with standard baicalin. Active films were prepared from polyvinyl alcohol (PVA) containing baicalin extract by casting method. The effect of baicalin extracts on the UV-blocking, optical, antioxidant property, water vapor permeability, swelling and mechanical properties of the films were studied. UV–vis transmittance spectra showed that PVA films incorporated with baicalin extract blocked ultraviolet light range from 280–400 nm even with low concentration of baicalin (0.5 wt%) and maintain the high transparency in visible spectrum. The outstanding UV-blocking properties of PVA films incorporated with baicalin extract were also confirmed by Rhodamine B degradation. Baicalin conferred antioxidant properties to PVA films as determined by DPPH radical scavenging activity. Due to the interaction between hydroxy groups of baicalin and PVA molecule, water vapor permeability, swelling and elongation at break of the films were decreased accompanied with the increasing in tensile strength and Young’s modulus. FTIR reveal that the interaction between PVA molecules was significant changed by the introduction of baicalin. These results suggest that PVA film incorporated with baicalin extract can be used for the development of functional protective film.

scholarly journals Water Vapor Sorption Characteristics of Powder Type Organic Sorbent in a Moist Air Fluidized Bed.

2001 ◽  
Vol 67 (660) ◽  
pp. 2105-2112 ◽  
Author(s):  
Hideo INABA ◽  
Takahisa KIDA ◽  
Akihiko HORIBE ◽  
Kiyohiro KAMEDA ◽  
Tamio OKAMOTO ◽  
...  
Keyword(s):  
Water Vapor ◽  
Fluidized Bed ◽  
Water Vapor Sorption ◽  
Vapor Sorption ◽  
Moist Air ◽  
Powder Type ◽  
Sorption Characteristics

scholarly journals The lightness of water vapor helps to stabilize tropical climate

2020 ◽  
Vol 6 (19) ◽  
pp. eaba1951 ◽  
Author(s):  
Seth D. Seidel ◽  
Da Yang
Keyword(s):  
Water Vapor ◽  
Longwave Radiation ◽  
Tropical Climate ◽  
Climate Feedback ◽  
Tropical Atmosphere ◽  
Radiative Effect ◽  
Buoyancy Effect ◽  
Moist Air ◽  
Dry Air ◽  
Earth’S Climate

Moist air is lighter than dry air at the same temperature, pressure, and volume because the molecular weight of water is less than that of dry air. We call this the vapor buoyancy effect. Although this effect is well documented, its impact on Earth’s climate has been overlooked. Here, we show that the lightness of water vapor helps to stabilize tropical climate by increasing the outgoing longwave radiation (OLR). In the tropical atmosphere, buoyancy is horizontally uniform. Then, the vapor buoyancy in the moist regions must be balanced by warmer temperatures in the dry regions of the tropical atmosphere. These higher temperatures increase tropical OLR. This radiative effect increases with warming, leading to a negative climate feedback. At a near present-day surface temperature, vapor buoyancy is responsible for a radiative effect of 1 W/m2 and a negative climate feedback of about 0.15 W/m2 per kelvin.

Investigation of Destruction Mechanisms for Heat-Resistant Coatings in Hypersonic Flows of Air Plasma

2017 ◽  
Vol 269 ◽  
pp. 14-30 ◽  
Author(s):  
Alexey N. Astapov ◽  
Lev N. Rabinskiy
Keyword(s):  
Oxide Film ◽  
Ambient Pressure ◽  
Structural Phase ◽  
Hypersonic Flows ◽  
Oxidation Products ◽  
Protective Film ◽  
Air Plasma ◽  
Main Layer ◽  
Heat Resistant ◽  
Erosion Loss

The authors present the results of investigations of degradation processes that occur in the structure of heat-resistant coating of the Si-TiSi2-MoSi2-B-Y system in hypersonic flows of air plasma. It is found that coating operating capacity at surface temperatures Tw ≤ 1820÷1830°C is provided by the structural-phase state of its microcomposite main layer and formation on the coating surface of a heterogeneous passivating protective film. It is based on borosilicate glass reinforced by rutile microneedles. The mechanism of coating destruction at Tw ≥ 1850÷1860°C is erosion loss of oxide film as well as generation and growth of gas-filled cavities at the "coating main layer–oxide film" interface. As the pressure of saturated vapor of gaseous oxidation products (SiO, CO, MoO3 and B2O3) exceeds that of the ambient, the oxide film integrity is disrupted and oxidation process becomes active. The rates of erosion loss and sublimation grow as operating temperature increases and ambient pressure decreases.

scholarly journals <i>A Tale of Two Dust Storms</i>: analysis of a complex dust event in the Middle East

2019 ◽  
Vol 12 (9) ◽  
pp. 5101-5118 ◽  
Author(s):  
Steven D. Miller ◽  
Louie D. Grasso ◽  
Qijing Bian ◽  
Sonia M. Kreidenweis ◽  
Jack F. Dostalek ◽  
...  
Keyword(s):  
Water Vapor ◽  
Mineral Dust ◽  
Weather Prediction ◽  
Detection Threshold ◽  
Dust Storms ◽  
Moist Air ◽  
Air Mass ◽  
Dry Air ◽  
Environmental Controls ◽  
Dust Detection

Abstract. Lofted mineral dust over data-sparse regions presents considerable challenges to satellite-based remote sensing methods and numerical weather prediction alike. The southwest Asia domain is replete with such examples, with its diverse array of dust sources, dust mineralogy, and meteorologically driven lofting mechanisms on multiple spatial and temporal scales. A microcosm of these challenges occurred over 3–4 August 2016 when two dust plumes, one lofted within an inland dry air mass and another embedded within a moist air mass, met over the southern Arabian Peninsula. Whereas conventional infrared-based techniques readily detected the dry air mass dust plume, they experienced marked difficulties in detecting the moist air mass dust plume, becoming apparent when visible reflectance revealed the plume crossing over an adjacent dark water background. In combining information from numerical modeling, multi-satellite and multi-sensor observations of lofted dust and moisture profiles, and idealized radiative transfer simulations, we develop a better understanding of the environmental controls of this event, characterizing the sensitivity of infrared-based dust detection to column water vapor, dust vertical extent, and dust optical properties. Differences in assumptions of dust complex refractive index translate to variations in the sign and magnitude of the split-window brightness temperature difference commonly used for detecting mineral dust. A multi-sensor technique for mitigating the radiative masking effects of water vapor via modulation of the split-window dust-detection threshold, predicated on idealized simulations tied to these driving factors, is proposed and demonstrated. The new technique, indexed to an independent description of the surface-to-500 hPa atmospheric column moisture, reveals parts of the missing dust plume embedded in the moist air mass, with the best performance realized over land surfaces.

ON THE EDDY TRANSFER OF WATER VAPOR ABOVE AN OUTDOOR SURFACE

1962 ◽  
Vol 40 (9) ◽  
pp. 1182-1190
Author(s):  
D. R. Hay ◽  
E. V. Pemberton
Keyword(s):  
Refractive Index ◽  
Water Vapor ◽  
Moist Air ◽  
Radio Path ◽  
Local Fluctuations ◽  
Standard Deviations ◽  
Extended Path ◽  
Upward Transfer

Fluctuations in the refractive index of the air above an outdoor surface have been examined by a 180-ft microwave interferometer. The observed standard deviations of refractivity are less than 10−6. These deviations are associated with instability of the air at the interferometer path but not with instability of the air immediately above it. Smallest refractivity deviations occur for weak eddy transfer of water vapor downwards through moist air in the radio path; intermediate deviations are associated with strong eddy transfer of vapor upwards through drier air in the path. Largest refractivity deviations are observed for less vigorous upward transfer of water vapor from the surface. It is suggested that the more vigorous eddies disperse the entrained water vapor more rapidly into smaller eddies than do the less vigorous eddies; and hence, lesser local fluctuations in air refractivity appear along an extended path that is highly-unstable than along the same path under conditions of greater stability.

scholarly journals Secondary organic aerosol formation and primary organic aerosol oxidation from biomass-burning smoke in a flow reactor during FLAME-3

2013 ◽  
Vol 13 (22) ◽  
pp. 11551-11571 ◽  
Author(s):  
A. M. Ortega ◽  
D. A. Day ◽  
M. J. Cubison ◽  
W. H. Brune ◽  
D. Bon ◽  
...  
Keyword(s):  
Mass Spectrometer ◽  
Biomass Burning ◽  
Flow Reactor ◽  
Organic Aerosol ◽  
Proton Transfer Reaction ◽  
Oxidation Products ◽  
Chemical Transformations ◽  
Aerosol Formation ◽  
Aerosol Mass ◽  
Smog Chambers

Abstract. We report the physical and chemical effects of photochemically aging dilute biomass-burning smoke. A "potential aerosol mass" (PAM) flow reactor was used with analysis by a high-resolution aerosol mass spectrometer and a proton-transfer-reaction ion-trap mass spectrometer during the FLAME-3 campaign. Hydroxyl (OH) radical concentrations in the reactor reached up to ~1000 times average tropospheric levels, producing effective OH exposures equivalent to up to 5 days of aging in the atmosphere, and allowing for us to extend the investigation of smoke aging beyond the oxidation levels achieved in traditional smog chambers. Volatile organic compound (VOC) observations show aromatics and terpenes decrease with aging, while formic acid and other unidentified oxidation products increase. Unidentified gas-phase oxidation products, previously observed in atmospheric and laboratory measurements, were observed here, including evidence of multiple generations of photochemistry. Substantial new organic aerosol (OA) mass ("net SOA"; secondary OA) was observed from aging biomass-burning smoke, resulting in total OA average of 1.42 ± 0.36 times the initial primary OA (POA) after oxidation. This study confirms that the net-SOA-to-POA ratio of biomass-burning smoke is far lower on average than that observed for urban emissions. Although most fuels were very reproducible, significant differences were observed among the biomasses, with some fuels resulting in a doubling of the OA mass, while for others a very small increase or even a decrease was observed. Net SOA formation in the photochemical reactor increased with OH exposure (OHexp), typically peaking around three days of equivalent atmospheric photochemical age (OHexp~3.9 × 1011 molecules cm−3 s), then leveling off at higher exposures. The amount of additional OA mass added from aging is positively correlated with initial POA concentration, but not with the total VOC concentration or the concentration of known SOA precursors. The mass of SOA formed often exceeded the mass of the known VOC precursors, indicating the likely importance of primary semivolatile/intermediate volatility species, and possibly of unidentified VOCs as SOA precursors in biomass burning smoke. Chemical transformations continued even after mass concentration stabilized. Changes in the biomass-burning tracer f60 ranged from substantially decreasing to remaining constant with increased aging. With increased OHexp, oxidation was always detected (as indicated by f44 and O/C). POA O/C ranged from 0.15 to 0.5, while aged OA O/C reached up to 0.87. The rate of oxidation and maximum O/C achieved differs for each biomass, and appears to increase with the initial O/C of the POA.

A photo-oxidation of croconic acid into oxalic acid

1995 ◽  
Vol 73 (8) ◽  
pp. 1298-1304 ◽  
Author(s):  
Paul-Louis Fabre ◽  
Paule Castan ◽  
Diane Deguenon ◽  
Nicole Paillous
Keyword(s):  
Nmr Spectroscopy ◽  
Oxalic Acid ◽  
Electrochemical Oxidation ◽  
Oxidation Process ◽  
Aqueous Media ◽  
Oxidation Products ◽  
Acid Oxidation ◽  
Experimental Conditions ◽  
Photo Oxidation ◽  
C Nmr

Croconic acid, H2C5O5, is readily oxidized. This may be attested by decolorization of the solutions and by observation of oxalic acid complexes. The oxidation products are identified by 13C NMR spectroscopy as oxalic and mesoxalic acids, and experimental conditions are specified. The oxidation process requires dioxygen and photons. In parallel, the electrochemical oxidation of croconic acid is studied in aqueous media and in acetonitrile. A potential–pH diagram is drawn. Keywords: croconic acid, oxalic acid, oxidation, electrochemistry, photochemistry.

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