scholarly journals HIGH TEMPERATURE AND ELECTROCHEMICAL CORROSION OF Zn0.5Al ALLOY DOPED WITH CALCIUM IN VARIOUS MEDIA

2020 ◽  
Vol 63 (11) ◽  
pp. 21-26
Author(s):  
Ziyodullo R. Obidov ◽  
Jamshed Kh. Dzhailoev ◽  
Izatullo N. Ganiev ◽  
Odiljon N. Nazarov ◽  
Rakhmatjon Usmanov ◽  
...  
Keyword(s):  
Aluminum Alloy ◽  
High Temperature ◽  
Oxidation Rate ◽  
High Temperature Oxidation ◽  
Atmospheric Oxygen ◽  
Electrochemical Corrosion ◽  
Oxidation Products ◽  
Alkaline Media ◽  
Potential Sweep ◽  
Temperature Oxidation

The article presents the results of a study of high-temperature and electrochemical corrosion of Zn0.5Al alloy doped with calcium in the various media. The thermogravimetric method was used to study the interaction of the Zn0.5Al alloy doped with calcium with atmospheric oxygen in the temperature range 523–623 K in the solid state. The kinetic and energy parameters of the process of high-temperature oxidation of alloys are determined. The process of high-temperature oxidation of Zn-Al-Ca alloys system is characterized by a monotonic decrease in the true oxidation rate and an increase in the effective activation energy when the alloying component in the initial Zn0.5Al alloy is up to 1.0 wt% doping with zinc-aluminum alloy 0.5 and 1.0 wt%. Calcium shows a slight increase in the oxidation rate of alloys. It was revealed that the oxidation process of the studied alloys with oxygen of the gas phase obeys the hyperbolic law. It was found that calcium supplements in the range of 0.01 - 0.1 wt%. The oxidizability of the initial Zn0.5Al alloy is reduced significantly, and the oxidation products of the alloys were ZnO, Al2O3, Al2O3 ∙ ZnO, CaO, Al2O3 ∙ CaO. By potentiostatic methods in the potentiodynamic mode with a potential sweep speed of 2 mV/s, it has been shown that for all samples of the Zn0.5Al-Ca alloys system in the acidic, neutral, and alkaline media, electrochemical potentials of corrosion, pitting formation, and repassivation are shifted to the region of negative values. It was revealed that zinc-aluminum alloys doped with calcium are most resistant to pitting corrosion in all studied media, respectively, in acidic (0.01n.), neutral (0.03-, 0.3-, 3.0 wt%) and alkaline (0.01n.) electrolytes of HCl, NaCl and NaOH. It has been established that calcium additions in the range of 0.01 - 0.1 wt.% reduce the corrosion rate of zinc-aluminum alloy Zn0.5Al by a factor of 2–3. Calcium alloys are recommended as anodic coatings and protectors for corrosion protection of steel products and structures operating at high temperatures.

scholarly journals Additively Manufactured NiTi and NiTiHf Alloys: Estimating Service Life in High-Temperature Oxidation

Materials ◽  
2020 ◽  
Vol 13 (9) ◽  
pp. 2104 ◽  
Author(s):  
Hediyeh Dabbaghi ◽  
Keyvan Safaei ◽  
Mohammadreza Nematollahi ◽  
Parisa Bayati ◽  
Mohammad Elahinia
Keyword(s):  
High Temperature ◽  
Oxidation Rate ◽  
High Temperature Oxidation ◽  
Oxidation Behavior ◽  
Early Stage ◽  
Niti Alloy ◽  
Temperature Oxidation ◽  
X Ray ◽  
Rate Law ◽  
Parabolic Rate

In this study, the effect of the addition of Hf on the oxidation behavior of NiTi alloy, which was processed using additive manufacturing and casting, is studied. Thermogravimetric analyses (TGA) were performed at the temperature of 500, 800, and 900 °C to assess the isothermal and dynamic oxidation behavior of the Ni50.4Ti29.6Hf20 at.% alloys for 75 h in dry air. After oxidation, X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy were used to analyze the oxide scale formed on the surface of the samples during the high-temperature oxidation. Two stages of oxidation were observed for the NiTiHf samples, an increasing oxidation rate during the early stage of oxidation followed by a lower oxidation rate after approximately 10 h. The isothermal oxidation curves were well matched with a logarithmic rate law in the initial stage and then by parabolic rate law for the next stage. The formation of multi-layered oxide was observed for NiTiHf, which consists of Ti oxide, Hf oxide, and NiTiO3. For the binary alloys, results show that by increasing the temperature, the oxidation rate increased significantly and fitted with parabolic rate law. Activation energy of 175.25 kJ/mol for additively manufactured (AM) NiTi and 60.634 kJ/mol for AM NiTiHf was obtained.

Microstructure and High-Temperature Oxidation of Ni-Si3N4 Composite Coatings by Pulse Electrodeposition

2015 ◽  
Vol 817 ◽  
pp. 421-425
Author(s):  
Kun Zhao ◽  
Wan Chang Sun ◽  
Chun Yu Miao ◽  
Hui Cai ◽  
Ju Mei Zhang ◽  
...  
Keyword(s):  
Aluminum Alloy ◽  
High Temperature ◽  
Oxidation Resistance ◽  
High Temperature Oxidation ◽  
Composite Coatings ◽  
X Ray Diffraction ◽  
Temperature Oxidation ◽  
Electro Deposition ◽  
X Ray ◽  
Crystallite Structure

Nickel matrix and Si3N4 micron particles were co-deposited on the aluminum alloy by pulse electro-deposition for high temperature performance. Meanwhile, the oxidation resistance was evaluated through the high temperature oxidation test. The phase structure, micrographs and components of the composite coatings were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) together with energy dispersive spectroscopy (EDS) respectively. The results indicated that Si3N4 particles were uniformly distributed across the coating and there were no pores and cracks or other defects at the coating/substrate interface. Ni-Si3N4 composite coatings are characterized by pyramidal micro-crystallite structure. The thickness of Ni-Si3N4 composite coatings were up to 80 μm for 2h. The results also revealed that the Ni-Si3N4 composite coatings presented better oxidation resistance than the pure Ni coating and aluminum alloy at high temperature. After oxidation at 673 K for 8h, the oxidation resistance of Ni-Si3N4 composite coatings presented the improved oxidation resistance behavior compared to pure Ni and the aluminum alloy, respectively.

scholarly journals Oxidation and Characterization of Low Concentration Gas in High-Temperature Reactor

2020 ◽  
Author(s):  
Jinhua Chen ◽  
Guangcai Wen ◽  
Song Yan ◽  
Xiangyun Lan ◽  
Lu Xiao
Keyword(s):  
High Temperature ◽  
High Temperature Oxidation ◽  
Air Pressure ◽  
Oxidation Products ◽  
Heating Process ◽  
Temperature Oxidation ◽  
Low Concentration ◽  
Temperature Environment ◽  
Explosion Limit ◽  
High Temperature Environment

To achieve efficient utilization of low-concentration mine gas, reduce resource waste, and alleviate environmental pollution, high-temperature oxidation of low-concentration gas at a concentration range of 1.00% to 1.50% that is directly discharged into the atmosphere during coal mine production was oxidized to recover heat for reuse. The gas oxidation equipment was improved for the heating process, and the safety of low-concentration gas oxidation under high-temperature environment was evaluated. Experimental results showed that the reactor could provide a 1000 ℃ high-temperature oxidation environment for gas oxidation after installing high-temperature resistant ceramics. The pressure variation curves of the reactor with air and different concentrations of gas were similar. Due to the thermal expansion, the air pressure slightly increased and then returned to normal pressure. In contrast, the low-concentration gas exhibited a stable pressure response in the high-temperature environment of 1000 ℃. The outlet pressure was significantly greater than the inlet pressure, and the pressure difference between the inlet and outlet exhibited a trend to increase with the gas concentration. The explosion limit varied with the temperature and the blend with oxidation products. The ratio of measured gas pressure to air pressure after oxidation was below the explosion criterion, indicating that the measured concentration gas is still safe after the shift of explosion limit, which provides a safe concentration range for efficient use of low-concentration gas in the future.

High Temperature Oxidation Behaviour of Detonation-Gun-Sprayed Cr3C2-NiCr-CeO2 Coatings on Inconel-718 at 900°C

2014 ◽  
Author(s):  
Sekar Saladi ◽  
Jyoti V. Menghani ◽  
Satya Prakash
Keyword(s):  
High Temperature ◽  
Inconel 718 ◽  
High Temperature Oxidation ◽  
Parabolic Rate Constant ◽  
Coated Specimen ◽  
Oxidation Products ◽  
Temperature Oxidation ◽  
X Ray ◽  
Heating And Cooling ◽  
Detonation Gun

The high temperature oxidation behavior of detonation-gun sprayed Cr3C2-NiCr coatings with and without 0.4 wt. % CeO2 additive on Ni-based superalloy inconel-718 is comparatively discussed in the present study. Oxidation studies were carried out at 900°C for 100 cycles in air under cyclic heating and cooling conditions on bare and coated superalloys. The thermo-gravimetric technique was used to establish kinetics of oxidation. X-ray diffraction, SEM/EDAX and X-ray mapping techniques were used to analyze the oxidation products of bare and coated samples. The results indicate that Cr3C2-NiCr-CeO2 coated specimen showed better oxidation resistance. The overall weight gain and parabolic rate constant of Cr3C2-NiCr-CeO2 coated specimen was found to be lowest in the present study signifying that the addition of CeO2 in Cr3C2-NiCr powder has contributed to the development of adherent and dense oxide scale on the coating at elevated temperature.

Effect of Yttrium Addition on High Temperature Oxidation Resistance of Co-10Cr-5Al Alloys

2011 ◽  
Vol 391-392 ◽  
pp. 606-610 ◽  
Author(s):  
Huai Shu Zhang ◽  
Hong Hua Zhang ◽  
Jun Huai Xiang ◽  
Shan Wang ◽  
Di Wu
Keyword(s):  
High Temperature ◽  
Oxidation Resistance ◽  
Oxidation Rate ◽  
High Temperature Oxidation ◽  
Oxidation Behavior ◽  
Temperature Oxidation ◽  
Linear Rate ◽  
Rate Law ◽  
Yttrium Addition ◽  
Parabolic Rate

The oxidation behavior of Co-10Cr-5Al-0.3Y alloy in 1 atm of pure O2 at 700°C was investigated. The addition of 0.3 at.%Y significantly increased the oxidation rate of the alloy and changed the oxidation behavior from the approximate parabolic rate law to linear rate law. The scale grown on the surface at 700°C was porous with many small voids and cracks, and was composed of an outer CoO layer and an inner complex layer rich in Al2O3 and Cr2O3 which were intermingled with yttric oxide and spinel Co(Cr, Al)2O4.

The Effect of Yttrium Ion Implantation on the High Temperature Oxidation Properties of NiAl

1990 ◽  
Vol 213 ◽  
Author(s):  
B.A. Pint ◽  
A. Jain ◽  
L.W. Hobbs
Keyword(s):  
High Temperature ◽  
Oxidation Rate ◽  
High Temperature Oxidation ◽  
Aluminum Content ◽  
Cyclic Testing ◽  
Cation Diffusion ◽  
Temperature Oxidation ◽  
Oxidation Properties ◽  
Yttrium Ion ◽  
Very High

ABSTRACTNiAl was ion implanted with yttrium (2×1016 cm−2) in order to study its effect on the very high temperature (1000–1500°C) oxidation properties. At 1000°C, implanted Y stabilizes the faster growing θ-Al2O3 phase, thus slightly increasing the oxidation rate. At 1200°C, where predominantly α-Al2 O3 is formed with and without Y, there is a factor of 4 reduction in the oxidation rate. However at higher than 1200°C, there is little effect by Y on the oxidation rate. Cyclic testing showed that the Y implant had an imperfect and short-lived improvement on adherence relative to other Y-containing alloys. Variations in aluminum content from 23.5 to 36.0wt%(40–55at%) had little effect on the oxidation properties. Initial experiments at 1500°C with a novel Rh marker indicate that alumina grows at least partially by outward cation diffusion both with and without Y.

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