Crystallineγ-AlO(OH)was synthesized by the precipitation of sodium aluminate and oxalic acids in aqueous solution. And thenγ-AlO(OH)was successfully transferred toγ-Al2O3 after subsequent high temperature heat trea...Crystallineγ-AlO(OH)was synthesized by the precipitation of sodium aluminate and oxalic acids in aqueous solution. And thenγ-AlO(OH)was successfully transferred toγ-Al2O3 after subsequent high temperature heat treatment.The effects of reaction conditions on formation ofγ-AlO(OH)andγ-Al2O3 were further investigated in detail.The XRD analysis shows that the complete formation of crystallineγ-Al2O3 is at pH 8-9,reaction temperature of 93-96℃and calcination temperature of higher than 400℃.The product ofγ-Al2O3 contains impurity,including iron,calcium and silicon ion with a low content of about 0.01%and has large specific surface area and high pore volume of 269.9 m2/g and 0.57 mL/g,which can be applied in catalysts and catalyst supports.展开更多
The nanometer Al2O3 dispersion strengthened NiCoCrAlY high-temperature protective coatings by crosscurrent CO2 laser on Ni-based superalloy GH4033 were produced. Microscopic morphologies, phase constitutions of claddi...The nanometer Al2O3 dispersion strengthened NiCoCrAlY high-temperature protective coatings by crosscurrent CO2 laser on Ni-based superalloy GH4033 were produced. Microscopic morphologies, phase constitutions of cladding coatings and distribution of nano-Al2O3 particles were examined using SEM and XRD. The results show that the interface grains, after adding proper nano-Al2O3, grow from epitaxial to non-epitaxial shape gradually, and the columnar dendrites become thinner and denser with cellular shape. Cracks in the substrate close to the interface are eliminated. Moreover, dispersive nano-Al2O3 particles mainly distribute around cellular substructure and on grain-boundaries, which prevents the diffusion of alloying elements and restrains the formation of new phase. There is a critical value of nano-Al2O3 addition, and the most suitable content of nano-Al2O3 is 1% (mass fraction) in this experimental conditions. The "nanometer effect" of nano-Al2O3 particles plays an important role in the improvement of coating microstructure.展开更多
The alloy performance to resist high-temperature oxidation is mainly determined either by the formation of oxide scales or by the deposition of oxide coatings on the surface of alloys.In the former case,a protective o...The alloy performance to resist high-temperature oxidation is mainly determined either by the formation of oxide scales or by the deposition of oxide coatings on the surface of alloys.In the former case,a protective oxide scale,such as Al_2O_3,Cr_2O_3 and SiO_2,can be selectively formed by adjusting the composition of alloys.Even if the oxide scale on the surface of alloys is spalled,new oxide can grow continuously,so the oxidation of alloys can be inhibited effectively.In the latter case,theoretically, depositing oxygen diffusion barrier oxide coatings,such as Al_2O_3,Cr_2O_3 and SiO_2,can prevent alloys from oxidation as well.However,the integrity of these oxide coatings can not maintain for a long time,owing to the thermal stress produced by the difference of the expansion coefficients between the oxide coatings and alloy substrates.Consequently,the ability to resist high-temperature oxidation by depositing such oxide coatings should be disappeared.Therefore,an oxide coating possessed both properties to act as an excellent oxygen diffusion barrier and match a suitable expansion coefficient with alloy substrate,is the basic conditions for the coating to maintain the ability to resist high-temperature oxidation of alloys. Based on above-mentioned idea,a novel composite oxide coating has been developed to obtain two kinds of functions,to act as an oxygen diffusion barrier and to adjust the expansion coefficient of coating as required.Figure 1 shows the schematic diagram of such novel oxide coating.This coating is composed of ZrO_2-8%Y_2O_3(YSZ) particles packaged by nano-Al_2O_3 film.The nano-Al_2O_3 film has a bubble-like structure,each YSZ particle is packaged in an Al_2O_3 bubble.Owing to YSZ is a good conductor for oxygen ions,so oxygen diffusion in this composite coating is determined by the walls of Al_2O_3 bubbles or the nano-Al_2O_3 film.If the thickness of all walls of Al_2O_3 bubbles in the direction perpendicular to the surface of alloy is over a critical value,the Al_2O_3 bubbles can act as an excellent oxygen diffusion barrier. Owing to YSZ has a high thermal expansion coefficient,so the thermal expansion coefficient of coatings can be easily increased by enhancing the ratio of YSZ to Al_2O_3 in these coatings. These composite coatings have been prepared by an improved sol-gel method.Firstly, YSZ particles packaged Al_2O_3 gel film were painted or deposited by electrophoresis on the alloy surface. Then,the specimens were treated by thermal pressure filtration to get primary coatings without cracks.Finally,the primary coatings were sintered in microwave furnace to obtain compact coatings. It is demonstrated from the result of cycling oxidation experiment that both of the hightemperature oxidation resistance and oxide spallation resistance are increased obviously with the ratio of YSZ to Al_2O_3 in the coatings,which are much superior to that of MCrAlY coatings.Therefore, these novel coatings can be used to protect various kinds of alloys from high-temperature oxidation,and can be also served as the interlayer in the thermal barrier coating system.展开更多
基金Project(N 20031012)supported by Youth Science Foundation of Shanxi Province,ChinaProject(20080320ZX)supported by the University’s Science and Technology Exploiture of Shanxi Province,China
文摘Crystallineγ-AlO(OH)was synthesized by the precipitation of sodium aluminate and oxalic acids in aqueous solution. And thenγ-AlO(OH)was successfully transferred toγ-Al2O3 after subsequent high temperature heat treatment.The effects of reaction conditions on formation ofγ-AlO(OH)andγ-Al2O3 were further investigated in detail.The XRD analysis shows that the complete formation of crystallineγ-Al2O3 is at pH 8-9,reaction temperature of 93-96℃and calcination temperature of higher than 400℃.The product ofγ-Al2O3 contains impurity,including iron,calcium and silicon ion with a low content of about 0.01%and has large specific surface area and high pore volume of 269.9 m2/g and 0.57 mL/g,which can be applied in catalysts and catalyst supports.
基金Project(20060287019) supported by the Research Fund for Doctoral Program of Higher Education of ChinaProject(kjsmcx07001) supported by the Opening Research Fund of Jiangsu Key Laboratory of Tribology, ChinaProject(CX08B-039Z) supported by the Graduate Innovation Foundation of Jiangsu Province, China
文摘The nanometer Al2O3 dispersion strengthened NiCoCrAlY high-temperature protective coatings by crosscurrent CO2 laser on Ni-based superalloy GH4033 were produced. Microscopic morphologies, phase constitutions of cladding coatings and distribution of nano-Al2O3 particles were examined using SEM and XRD. The results show that the interface grains, after adding proper nano-Al2O3, grow from epitaxial to non-epitaxial shape gradually, and the columnar dendrites become thinner and denser with cellular shape. Cracks in the substrate close to the interface are eliminated. Moreover, dispersive nano-Al2O3 particles mainly distribute around cellular substructure and on grain-boundaries, which prevents the diffusion of alloying elements and restrains the formation of new phase. There is a critical value of nano-Al2O3 addition, and the most suitable content of nano-Al2O3 is 1% (mass fraction) in this experimental conditions. The "nanometer effect" of nano-Al2O3 particles plays an important role in the improvement of coating microstructure.
基金the Chinese National Natural Science Foundation(Grant.50771021)for financial support
文摘The alloy performance to resist high-temperature oxidation is mainly determined either by the formation of oxide scales or by the deposition of oxide coatings on the surface of alloys.In the former case,a protective oxide scale,such as Al_2O_3,Cr_2O_3 and SiO_2,can be selectively formed by adjusting the composition of alloys.Even if the oxide scale on the surface of alloys is spalled,new oxide can grow continuously,so the oxidation of alloys can be inhibited effectively.In the latter case,theoretically, depositing oxygen diffusion barrier oxide coatings,such as Al_2O_3,Cr_2O_3 and SiO_2,can prevent alloys from oxidation as well.However,the integrity of these oxide coatings can not maintain for a long time,owing to the thermal stress produced by the difference of the expansion coefficients between the oxide coatings and alloy substrates.Consequently,the ability to resist high-temperature oxidation by depositing such oxide coatings should be disappeared.Therefore,an oxide coating possessed both properties to act as an excellent oxygen diffusion barrier and match a suitable expansion coefficient with alloy substrate,is the basic conditions for the coating to maintain the ability to resist high-temperature oxidation of alloys. Based on above-mentioned idea,a novel composite oxide coating has been developed to obtain two kinds of functions,to act as an oxygen diffusion barrier and to adjust the expansion coefficient of coating as required.Figure 1 shows the schematic diagram of such novel oxide coating.This coating is composed of ZrO_2-8%Y_2O_3(YSZ) particles packaged by nano-Al_2O_3 film.The nano-Al_2O_3 film has a bubble-like structure,each YSZ particle is packaged in an Al_2O_3 bubble.Owing to YSZ is a good conductor for oxygen ions,so oxygen diffusion in this composite coating is determined by the walls of Al_2O_3 bubbles or the nano-Al_2O_3 film.If the thickness of all walls of Al_2O_3 bubbles in the direction perpendicular to the surface of alloy is over a critical value,the Al_2O_3 bubbles can act as an excellent oxygen diffusion barrier. Owing to YSZ has a high thermal expansion coefficient,so the thermal expansion coefficient of coatings can be easily increased by enhancing the ratio of YSZ to Al_2O_3 in these coatings. These composite coatings have been prepared by an improved sol-gel method.Firstly, YSZ particles packaged Al_2O_3 gel film were painted or deposited by electrophoresis on the alloy surface. Then,the specimens were treated by thermal pressure filtration to get primary coatings without cracks.Finally,the primary coatings were sintered in microwave furnace to obtain compact coatings. It is demonstrated from the result of cycling oxidation experiment that both of the hightemperature oxidation resistance and oxide spallation resistance are increased obviously with the ratio of YSZ to Al_2O_3 in the coatings,which are much superior to that of MCrAlY coatings.Therefore, these novel coatings can be used to protect various kinds of alloys from high-temperature oxidation,and can be also served as the interlayer in the thermal barrier coating system.
