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.

High temperature creep of SiC densified using a transient liquid phase

1991 ◽  
Vol 6 (9) ◽  
pp. 1945-1949 ◽  
Author(s):  
Zuei C. Jou ◽  
Anil V. Virkar ◽  
Raymond A. Cutler
Keyword(s):  
Activation Energy ◽  
Silicon Carbide ◽  
Liquid Phase ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Transient Liquid Phase ◽  
High Strength ◽  
High Temperature Creep ◽  
Fine Grained ◽  
Thermally Activated

Silicon carbide-based ceramics can be rapidly densified above approximately 1850 °C due to a transient liquid phase resulting from the reaction between alumina and aluminum oxycarbides. The resulting ceramics are fine-grained, dense, and exhibit high strength at room temperature. SiC hot pressed at 1875 °C for 10 min in Ar was subjected to creep deformation in bending at elevated temperatures between 1500 and 1650 °C in Ar. Creep was thermally activated with an activation energy of 743 kJ/mol. Creep rates at 1575 °C were between 10−9/s and 10−7/s at an applied stress between 38 and 200 MPa, respectively, resulting in a stress exponent of ≍1.7.

scholarly journals High Temperature Oxidation and Corrosion of Silicon-Based Nonoxide Ceramics

1998 ◽  
Author(s):  
Hagen Klemm ◽  
Mathias Herrmann ◽  
Christian Schubert
Keyword(s):  
High Temperature ◽  
Elevated Temperatures ◽  
Microstructural Analysis ◽  
Temperature Stability ◽  
Ambient Air ◽  
High Temperature Stability ◽  
Temperature Oxidation ◽  
Nonoxide 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.

Effect of nickel on formation of transition layer during liquid-phase aluminizing of titanium

2020 ◽  
pp. 313-317
Author(s):  
A.I. Kovtunov ◽  
Yu.Yu. Khokhlov ◽  
S.V. Myamin
Keyword(s):  
Mechanical Properties ◽  
Liquid Phase ◽  
Intermetallic Layer ◽  
Reaction Diffusion ◽  
Strength Properties ◽  
Effect Of Temperature ◽  
Nickel Concentration ◽  
Aluminum Melt ◽  
Titanium Aluminum ◽  
Titanium Foam

Titanium—aluminum, titanium—foam aluminum composites and bimetals obtained by liquid-phase methods, are increasingly used in industry. At the liquid-phase methods as result of the reaction diffusion of titanium and aluminum is formed transitional intermetallic layer at the phase boundary of the composite, which reduces the mechanical properties of titanium and composite. To reduce the growth rate of the intermetallic layer between the layers of the composite and increase its mechanical properties, it is proposed to alloy aluminum melt with nickel. The studies of the interaction of titanium and molten aluminum alloyed with nickel made it possible to establish the effect of temperature and aluminizing time on the thickness, chemical and phase compositions of the transition intermetallic layer. The tests showed the effect of the temperature of the aluminum melt, the nickel concentration on the strength properties of titanium—aluminum bimetal.

Application of Disk Aerators to Recarbonation of Alkaline Wastewater from Wet Gasification of Carbide

1991 ◽  
Vol 24 (7) ◽  
pp. 277-284 ◽  
Author(s):  
E. Gomólka ◽  
B. Gomólka
Keyword(s):  
Carbon Dioxide ◽  
Liquid Phase ◽  
Gas Phase ◽  
Flue Gas ◽  
Carbonic Acid ◽  
Low Cost ◽  
Flue Gases ◽  
Carbon Dioxide Content ◽  
Patent Claim ◽  
Phase Dispersion

Whenever possible, neutralization of alkaline wastewater should involve low-cost acid. It is conventional to make use of carbonic acid produced via the reaction of carbon dioxide (contained in flue gases) with water according to the following equation: Carbon dioxide content in the flue gas stream varies from 10% to 15%. The flue gas stream may either be passed to the wastewater contained in the recarbonizers, or. enter the scrubbers (which are continually sprayed with wastewater) from the bottom in oountercurrent. The reactors, in which recarbonation occurs, have the ability to expand the contact surface between gaseous and liquid phase. This can be achieved by gas phase dispersion in the liquid phase (bubbling), by liquid phase dispersion in the gas phase (spraying), or by bubbling and spraying, and mixing. These concurrent operations are carried out during motion of the disk aerator (which is a patent claim). The authors describe the functioning of the disk aerator, the composition of the wastewater produced during wet gasification of carbide, the chemistry of recarbonation and decarbonation, and the concept of applying the disk aerator so as to make the wastewater fit for reuse (after suitable neutralization) as feeding water in acetylene generators.

Effect of ionizing radiation on the kinetics of hydrogenation on the Ni-MgO mixed catalyst

1982 ◽  
Vol 47 (7) ◽  
pp. 1780-1786 ◽  
Author(s):  
Rostislav Kudláček ◽  
Jan Lokoč
Keyword(s):  
Experimental Data ◽  
Activation Energy ◽  
Liquid Phase ◽  
Ionizing Radiation ◽  
Oxide Catalyst ◽  
Absorbed Dose ◽  
Hydrogenation Rate ◽  
Solution Composition ◽  
Mixed Catalyst ◽  
Kinetics Of

The effect of gamma pre-irradiation of the mixed nickel-magnesium oxide catalyst on the kinetics of hydrogenation of maleic acid in the liquid phase has been studied. The changes of the hydrogenation rate are compared with the changes of the adsorbed amount of the acid and with the changes of the solution composition, activation energy, and absorbed dose of the ionizing radiation. From this comparison and from the interpretation of the experimental data it can be deduced that two types of centers can be distinguished on the surface of the catalyst under study, namely the sorption centres for the acid and hydrogen and the reaction centres.

scholarly journals Deployment, Calibration, and Cross-Validation of Low-Cost Electrochemical Sensors for Carbon Monoxide, Nitrogen Oxides, and Ozone for an Epidemiological Study

Sensors ◽  
2021 ◽  
Vol 21 (12) ◽  
pp. 4214
Author(s):  
Christopher Zuidema ◽  
Cooper S. Schumacher ◽  
Elena Austin ◽  
Graeme Carvlin ◽  
Timothy V. Larson ◽  
...  
Keyword(s):  
Carbon Monoxide ◽  
Exposure Assessment ◽  
Epidemiological Study ◽  
Electrochemical Sensors ◽  
Low Cost ◽  
Puget Sound ◽  
Ambient Air ◽  
Ambient Air Pollution ◽  
Calibration Models ◽  
Study Participants

We designed and built a network of monitors for ambient air pollution equipped with low-cost gas sensors to be used to supplement regulatory agency monitoring for exposure assessment within a large epidemiological study. This paper describes the development of a series of hourly and daily field calibration models for Alphasense sensors for carbon monoxide (CO; CO-B4), nitric oxide (NO; NO-B4), nitrogen dioxide (NO2; NO2-B43F), and oxidizing gases (OX-B431)—which refers to ozone (O3) and NO2. The monitor network was deployed in the Puget Sound region of Washington, USA, from May 2017 to March 2019. Monitors were rotated throughout the region, including at two Puget Sound Clean Air Agency monitoring sites for calibration purposes, and over 100 residences, including the homes of epidemiological study participants, with the goal of improving long-term pollutant exposure predictions at participant locations. Calibration models improved when accounting for individual sensor performance, ambient temperature and humidity, and concentrations of co-pollutants as measured by other low-cost sensors in the monitors. Predictions from the final daily models for CO and NO performed the best considering agreement with regulatory monitors in cross-validated root-mean-square error (RMSE) and R2 measures (CO: RMSE = 18 ppb, R2 = 0.97; NO: RMSE = 2 ppb, R2 = 0.97). Performance measures for NO2 and O3 were somewhat lower (NO2: RMSE = 3 ppb, R2 = 0.79; O3: RMSE = 4 ppb, R2 = 0.81). These high levels of calibration performance add confidence that low-cost sensor measurements collected at the homes of epidemiological study participants can be integrated into spatiotemporal models of pollutant concentrations, improving exposure assessment for epidemiological inference.

On the use of Ozawa/Flynn/Wall method to determine aging activation energy for elastomers

2021 ◽  
pp. 009524432110203
Author(s):  
Sudhir Bafna
Keyword(s):  
Mechanical Properties ◽  
Activation Energy ◽  
Weight Loss ◽  
Oxygen Consumption ◽  
Dwell Time ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Degradation Mechanism ◽  
Kinetics Of ◽  
Wall Method

It is often necessary to assess the effect of aging at room temperature over years/decades for hardware containing elastomeric components such as oring seals or shock isolators. In order to determine this effect, accelerated oven aging at elevated temperatures is pursued. When doing so, it is vital that the degradation mechanism still be representative of that prevalent at room temperature. This places an upper limit on the elevated oven temperature, which in turn, increases the dwell time in the oven. As a result, the oven dwell time can run into months, if not years, something that is not realistically feasible due to resource/schedule constraints in industry. Measuring activation energy (Ea) of elastomer aging by test methods such as tensile strength or elongation, compression set, modulus, oxygen consumption, etc. is expensive and time consuming. Use of kinetics of weight loss by ThermoGravimetric Analysis (TGA) using the Ozawa/Flynn/Wall method per ASTM E1641 is an attractive option (especially due to the availability of commercial instrumentation with software to make the required measurements and calculations) and is widely used. There is no fundamental scientific reason why the kinetics of weight loss at elevated temperatures should correlate to the kinetics of loss of mechanical properties over years/decades at room temperature. Ea obtained by high temperature weight loss is almost always significantly higher than that obtained by measurements of mechanical properties or oxygen consumption over extended periods at much lower temperatures. In this paper, data on five different elastomer types (butyl, nitrile, EPDM, polychloroprene and fluorocarbon) are presented to prove that point. Thus, use of Ea determined by weight loss by TGA tends to give unrealistically high values, which in turn, will lead to incorrectly high predictions of storage life at room temperature.

scholarly journals Room-Temperature Solution-Processed 0D/1D Bilayer Electrodes for Translucent CsPbBr3 Perovskite Photovoltaics

Nanomaterials ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 1489
Author(s):  
Bhaskar Parida ◽  
Saemon Yoon ◽  
Dong-Won Kang
Keyword(s):  
Solar Cells ◽  
Indium Tin Oxide ◽  
High Performance ◽  
Room Temperature ◽  
Low Cost ◽  
Perovskite Solar Cells ◽  
Ambient Air ◽  
Plasma Damage ◽  
Temperature Solution ◽  
Ito Nanoparticles

Materials and processing of transparent electrodes (TEs) are key factors to creating high-performance translucent perovskite solar cells. To date, sputtered indium tin oxide (ITO) has been a general option for a rear TE of translucent solar cells. However, it requires a rather high cost due to vacuum process and also typically causes plasma damage to the underlying layer. Therefore, we introduced TE based on ITO nanoparticles (ITO-NPs) by solution processing in ambient air without any heat treatment. As it reveals insufficient conductivity, Ag nanowires (Ag-NWs) are additionally coated. The ITO-NPs/Ag-NW (0D/1D) bilayer TE exhibits a better figure of merit than sputtered ITO. After constructing CsPbBr3 perovskite solar cells, the device with 0D/1D TE offers similar average visible transmission with the cells with sputtered ITO. More interestingly, the power conversion efficiency of 0D/1D TE device was 5.64%, which outperforms the cell (4.14%) made with sputtered-ITO. These impressive findings could open up a new pathway for the development of low-cost, translucent solar cells with quick processing under ambient air at room temperature.

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