In the case of coatings, the Ni-P/TiO2 coating effectively inhibits corrosion by galvanic coupling compared to Ni-P. Schematic diagram of the E-C mitigation concept through the development of resistive coatings and alloys. Effects of water chemistry on the E-C behavior of alloys: (a) temperature, (b) DO concentration, (c) pH, and (d) pH control agents.
EIS fitting parameters ti CS, Ni-P ken Ni-P/TiO2 iti nangato ti temperaturana a danum nga addaan iti nadumaduma a temperatura.
Introduction
- Materials Degradation in Secondary System of PWRs
- Types of E-C and Related Accidents
- Failures in NPPs due to E-C
- Key Parameters on the E-C Behavior
- Mitigation of E-C by Employing New Materials
FAC is the continuous dissolution of Fe3O4 due to the destructive chemical reaction of Fe oxidation and dissolution of Fe3O4, and mass transport in flowing water (Figure 1.4(b)). While FAC is the dissolution of the oxide layer by chemical reaction, LDIE is the destruction of the metal substrate due to mechanical damage. Where Δ𝑃 is the pressure difference across a component, 𝜌 is the fluid density, v2 and v1 is the flow rate.
The key to mitigating or preventing E-C is the obstruction of electrochemical interaction at metal/oxide/water interface.
PROBLEM DEFINITION
- Monitoring and Predicting of E-C in NPPs
- Mitigation of E-C by Water Chemistry Modification
- Mitigation of E-C by Materials Modification
- Experiments on E-C
When the Cr content in the material increases from 0.03 to 0.5 wt. %, the FAC level of the alloy is reduced to one tenth. The results show that Mo acts to reduce the dissolution rate of the salt layer. One promising corrosion-resistant coating that can be used for secondary water chemistry is ENP, as it has excellent corrosion and wear resistance when incorporated into noble nanoparticles.
The superior erosion-corrosion resistance of HVAF AMC compared to that of the HVOF AMC may be related to the mechanical properties due to its more compact structure.
APPROACH AND GOAL
Development of E-C Resistive Coatings
- Requirements for E-C Resistive Coatings
- Candidate Materials
Development of E-C Resistive Alloys
- Strategy to Develop E-C Resistive Alloys
- Candidate Materials
Enhancement in Nuclear Safety and Materials Integrity of NPPs
Thus, HVOF sprayed Fe-based AMC are expected to be effective against E-C as they have excellent corrosion and wear resistance in corrosive environments. Schematic diagram of the concept of mitigation of E-C by deposition of nanostructured coatings on CS surface. Schematic diagrams of CX of (a) Ni-P/TiO2 and (b) Fe-based AMC coatings for E-C resistance.
Relative amounts of E-C resist alloys based on degree of single-phase FAC, crack susceptibility, and cost.
MATERIALS AND METHODS
- Preparation of the E-C Resistive Coatings
- Electroless Ni-P/TiO 2 Coatings
- Fe-based Amorphous Metallic Coatings
- Preparation of the E-C Resistive Alloys
- Design of Alloy Contents
- Manufacturing Process
- Microstructure and Chemical Analysis
- Optical, Electron Microscopy and X-ray Photoelectric Spectroscopy
- Synchrotron STXM and XAS
- Mechanical Properties
- Corrosion and Erosion Experiments
- Electrochemical Experiments in Seawater
- Water Chemistry Control System
- Electrochemical Experiments in High-temperature and Pressure Water
- FAC Simulation Experiments
- FAC Experiments
Prior to the process, phase diagrams of bonds were calculated using ThermoCalc as shown in Figure 4.4. Microstructure characterizations of the materials were performed using OM, SEM (Quanta 200, FEI, US) and TEM (JEM-2100F, JEOL, Japan). For hardness measurements, 10 points were in the central region of the specimens based on Vickers hardness.
The corrosion behavior of the material in seawater was investigated by LSV and EIS using PAR 273A potentiostat (Princeton Applied Research, USA) and Solartron 1260A impedance analyzer (Solartron Analytical, USA). The loop consists of the reservoir water tanks, the feedwater system and high-pressure pumps, the water chemistry sensors (DO, pH and inlet and outlet conductivity), the autoclave, the condensers and the ion exchanger. The corrosion behavior of the materials in high-temperature water was also investigated at LSV and EIS.
The samples were mounted on a rotating cage coaxially attached to the shaft of the magnetic drive. Located at FNC Technology Co., Ltd., the system consists of two sets of high-pressure pumps, a feed pump, tank water tanks and water chemistry sensors. The temperature of the test sections was set to 150 oC, and the water chemistry in the system was: pH25 = 9.3, DO concentration < 1 ppb.
The thickness of the samples was measured by UT (PT-878, General Electric, USA) with attached dual element transducer. Schematic diagram of the water chemistry control system, test chambers and specification for FAC simulation and LDIE simulation tests.
RESULTS AND DISCUSSION
Performance of the E-C Resistive Coatings
- Microstructure and Chemical Analysis
- Electrochemical Properties in Seawater
- Electrochemical Properties in High-temperature and Pressure Water
- Performance in FAC Simulation Condition
- Performance in FAC Condition
The XPS spectra of the as-sprayed coatings are shown in Figure 5.4 with Fe, Cr and Mo alloying elements. The AC responses of the coatings are shown in Figure 5.7 and the fitting parameters are listed in Table 5.2. The rate of loss or corrosion of CS and coating metals is shown in Figure 5.13.
In the Bode plots (Figure 5.14 (b)), it can be seen that the bulk resistance of Ni-P is higher than that of CS and Ni-P/TiO2. The corrosion rate of CS, Ni-P and Ni-P/TiO2 with temperature variation is compared in Figure 5.21. However, severe peeling of the top surface is evident when the coating is exposed to 150 oC (Figure 5.22(e)).
As previously discussed in Figure 5.21(b), Ni-P shows serious weight loss compared to Ni-P/TiO2 coating at 150 oC. While Ni-P shows the release of the oxide film at 150 oC, the release of NiO from the surface is not observable in Figure 5.22(h). Compared to corrosion in static conditions, corrosion in flowing water is shown in Figure 5.25(b) and (c).
In Figure 5.26(a) neither oxide scales nor polyhedral oxide crystals can be observed on the surface. TEM images of the CX morphologies of the samples immersed at 150 °C and 200 °C are displayed in Figure 5.29 and Figure 5.30, respectively.
Performance of the E-C Resistive Alloys
- Microstructure and Chemical Analysis
- Mechanical Properties
- Electrochemical Properties in Seawater
- Performance in FAC Simulation Condition
In Nyquist plots (Figure 5.42(a)), the circuit model was Randle's circuit model so there is single oxide at the metal/water interface. After the FAC simulation experiments, the corrosion rate of the samples was calculated based on the weight loss, surface area and immersion time as shown in Figure 42 In Figure 5.43(a), the corrosion rate of CS, P22, FRA 1, FRA 2, and MFRA is plotted with calculated result of Ducreux's model. The surface morphology of P22 (Figure 5.44(a)) shows some oxide scale but the number of the oxide scale decreases in that of FRA 1 (Figure 5.44(b)).
From Figure 5.45 to Figure 5.48, they illustrate the CX images of P22, FRA 1, FRA 2 and MFRA, and the yellow dotted lines indicate the region of the EDS line profile for the corresponding chemical analysis result. In the case of P22, three oxide layers are observable in Figure 5.45(a): the oxide scale at the highest site, the thin compact oxide that can be clearly seen in Figure 5.45(b), and the bulk oxide region. The chemical composition of the oxide layers appears to be Fe3O4 and there is enrichment of Cr in the uppermost oxide (Figure 5.47(b)).
As Cr increases in metal (Figure 5.49(c)), both the enrichment in the outer oxide and the inner oxide is observable. To investigate the detailed chemistry and crystal structure of the oxide layers, electron DPs were analyzed based on HRTEM measurement as shown in Figure 5.50 and Figure 5.51. As shown in Figure 5.52(a), the composition of Cr in the outer oxide is the highest for FRA 2, followed by MFRA, FRA 1 and P22.
To evaluate the correlation between the corrosion rate and the Cr content, that of the oxides is divided by that of the metal as shown in Figure 5.51(b). This causes enrichment of Cr in the outer layer, so the higher Cr content strengthens the passivity of the steel [36].
Performance Evaluation of the Developed Materials
Because the continuous layer hinders the exposure of the inner layer to H2O in the solution, Cr3+. Because it cannot locate Ni-P/TiO2 coating and Fe-based AMC due to weight gain, the position of Ni-P is localized. SEM morphologies of Fe-based AMC: (a) raw material powder, (b) surface, (c, d) CX with indication of porosity by white and yellow arrows, and (e) EDS line profiles indicated in (c).
Schematic diagram of the corrosion process of ENP coatings with and without nanoparticles: (a) Ni-P coating, (b) Ni-P/TiO2 coating. EIS results of CS and Fe-based AMC in seawater condition: (a) equivalent circuit model, (b) Nyquist plot. Fitting parameters of CS- and Fe-based AMC after EIS test in seawater: (a) Rct, (b) Cdl and (c) ndl.
TEM CX morphologies of Ni-P and Ni-P/TiO2 after the immersion at 150 oC. a) STEM morphologies on NiO/Ni-P interfaces corresponding to chemical element mappings. XPS depth profiling results of Fe-based AMC after the FAC simulation experiments at 150 oC: (a) Fe, (b) Cr and (c) Mo. XPS depth profiling results of Fe-based AMC after the FAC simulation experiments at 200 oC: (a) Fe, (b) Cr and (c) Mo.
SEM of surface and CX morphology of Ni-P/TiO2 on (a, b) intrados and (c, d) extrados at position 3. SEM of surface and CX morphology of Fe-based AMC on (a, b) intrados and (c), d ) extrado at position 3. Results of Vicker hardness measurement of alloys - black scatters are the measured points, and red are the average of the region.
Corrosion rate of commercial alloys, E-C resist coatings and alloys in the FAC preferred condition.
CONCLUSION
The UT results from the CS, LAS and coated 90 oC experiments show that strong corrosion is particularly noticeable in CS and Ni-P/TiO2 intradoses.
SUMMARY
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또한 리뷰어는 아니었지만 지난 몇 년간 아르곤국립연구소에서 많은 지도를 해 주신 박창용 박사님께도 감사의 말씀을 전하고 싶습니다. 하지만 그것이 계속해서 내 침대 자리를 잠식하지 않기를 바랍니다. 믿음직한 처남 서익이가 계획한 대로 앞으로의 행보가 잘 되길 바랍니다.
훌륭한 선배님들 덕분에 제가 핵물질 연구의 수렁에 빠질 수 있었습니다. 또한 내 인생에서 잊지 못할 시간을 함께해준 친구들에게도 감사의 말씀을 전하고 싶습니다. 다들 각자의 방식으로 잘 지내길 바랍니다.
어려운 시기를 이겨내고 앞으로도 힘을 낼 수 있는 우리가 되기를 바랍니다. 또한 많은 분들이 저의 롤모델이자 영감이 되어 주셨습니다.
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