| Due to the depletion of fossil energy and environmental pollution,we eager to find new green energy alternatives to fossil energy.Nuclear energy is the best choice for solving the energy crisis in the future.The main methods of nuclear energy utilization mainly include nuclear fission and unclear fusion.The fission reactor has limited nuclear fuel,and the release of radionuclides from nuclear fission can cause nuclear radioactive contamination in the atmosphere.Compared to nuclear fission,fusion reactors rarely cause problems such as radioactive contamination of the environment and fuel is almost inexhaustible.At present,a series of researches on fusion reactors have been carried out in major countries and regions including Europe,China,Japan and South Korea.The complex working conditions in nuclear fusion reactors have placed unprecedented demands on materials.Hydrogen and its isotopes readily penetrate into the first wall material to initiate hydrogen embrittlement,so the hydrogen permeation barrier is required on the structural components.Ceramic materials have high thermal stability and low hydrogen isotope permeation reduction factor,and are the most promising hydrogen permeation barriers in fusion reactors.Therefore,Cr2O3-Y2O3 and CrxCy@Cr2O3/Al2O3 composite coatings were prepared and their hydrogen resistance properties were analyzed.(1)Hydrogen permeation properties of CrxCy@Cr2O3/Al2O3 coatingA compact and uniform Cr-C alloy coating was deposited on a stainless steel substrate by pulsed electrochemical methods.A CrxCy@Cr2O3 coating was formed by subsequent chemical conversion in a weak oxidation environment.Furthermore,an Al2O3 coating was deposited on the CrxCy@Cr2O3 coating by ALD to reduce surface defects.The surface potential and leakage current indicate that chrome carbide and amorphous carbon embedding in the chromic oxide.The phase and chemical state of the films were analyzed and compared both before and after hydrogen exposure at 300℃.The results show that this new kind composite coating,based on the principles of grain boundary pinning of chromic oxide with carbide and defect healing of alumina,can remarkably improve the hydrogen permeation barrier performance.(2)Hydrogen interaction characteristics of a Cr2O3-Y2O3 coatingBy adding YCl3 to the conventional chrome plating bath,the dense Cr-Y alloy coating was successfully deposited on the stainless steel substrate using pulse electroplating technique.The sample was placed in an ultra-low oxygen partial environment to synthesize a novel Cr2O3-Y2O3 coating with a thickness of about 100 nm.The interactions between the coating and hydrogen plasma were comprehensively analyzed and compared via surface analysis techniques,including TEM,XPS and electrochemical impedance spectroscopy(EIS).The carrier concentration of Cr2O3 and Cr2O3-Y2O3 coatings were calculated by M-S curves,which indicated that the diffusion of Cr3+was suppressed in Y-doped chromium coating.The mechanical properties of the coating before and after hydrogen permeation were studied by tensile testing.It was found that this ceramic coating effectively reduced the defect concentration and retained a high protective performance upon hydrogen exposure.Therefore,this new Cr2O3-Y2O3 coating has potential as a promising hydrogen permeation barrier.(3)α-Al2O3 formed at low temperatureCr/Al coating was prepared by pulse plating and AlCl3-EMIC ionic liquid on stainless steel substrates.Subsequently,the coating was oxidized at the ultra-low pressure and a part of Al successfully formed α-Al2O3 at 600℃.When the temperature rises to 700℃,the XRD spectrum shows that Al2O3 is converted to α-Al2O3.The results show that the conversion mode of the aluminum chromium compound is Al13Cr2→Al8Cr5→AlCr2 due to the increase of temperature.The condition of ultra-low oxygen pressure limits the growth of Al,and it is difficult to reach the critical phase change size.Oxygen enters the composite coating and reacts with Al.At this time,Cr2O3 regards as the nucleation center and Al directly forms α-Al2O3. |
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