The influence of the certain specific vacuum pre-oxidation process on the phase transformation of thermally-grown oxides（TGO） was studied.The CoCrAlY high temperature corrosion resistance coatings were produced onto...The influence of the certain specific vacuum pre-oxidation process on the phase transformation of thermally-grown oxides（TGO） was studied.The CoCrAlY high temperature corrosion resistance coatings were produced onto the nickel-based superalloy substrate by high velocity oxygen fuel（HVOF）.It suggests that the TGO usually consists of a great number of chromium oxides,cobalt oxides and spinel oxides besides alumina during the initial period of the high temperature oxidation if the specimens are not subjected to the appropriate vacuum pre-oxidation process.Furthermore,the amount of alumina is strongly dependent on the partial pressure of oxygen;while the CoCr2O4 spinel oxides are usually formed under the conditions of higher partial pressure of oxygen during the initial period and the lower partial pressure of oxygen during the subsequent period of the isothermal oxidation.After the appropriate vacuum pre-oxidation process,the TGO is mainly composed of alumina that contains lower Y element,while alumina that contains higher Y element sporadically distributes,and the spinel oxides cannot be found.After a longer period of the isothermal oxidation,a small amount of porous CoCr2O4 and the chrome oxide sporadically distribute near the continuous alumina.Additionally,after the appropriate vacuum pre-oxidation process,the TGO growth rate is relatively slow.展开更多
Oxidation behaviors of Ni(Cr)-TiB2 coating deposited by HVOF technique were studied at 800,900 and 1 000℃in air. The microstructures of as-sprayed and oxidized coatings were characterized by X-ray diffractometry(XRD)...Oxidation behaviors of Ni(Cr)-TiB2 coating deposited by HVOF technique were studied at 800,900 and 1 000℃in air. The microstructures of as-sprayed and oxidized coatings were characterized by X-ray diffractometry(XRD)and scanning electron microscopy(SEM).After oxidation at 800℃,a thin and adherent oxide layer was formed on the surface of the coating.With increasing exposure temperature,the thickness of the oxide layer increased;and at 1 000℃the oxide layer separated from the coating.Investigation of the kinetics of oxidation by using the thermogravimetric analysis(TGA)technique shows a parabolic oxidation rate.展开更多
Al_(0.2) CrFeNiCo and Al_(0.2) CrFeNiCu high entropy alloys were deposited with high velocity oxygen fuel(HVOF)on 316 L substrate.Later,a laser re-melting(LR)process was applied to enhancing the coating microstructure...Al_(0.2) CrFeNiCo and Al_(0.2) CrFeNiCu high entropy alloys were deposited with high velocity oxygen fuel(HVOF)on 316 L substrate.Later,a laser re-melting(LR)process was applied to enhancing the coating microstructure.LR process effects on dry sliding wear and oxidation behaviors were investigated.The mixture of powders with free elements led to the formation of inner oxides in HVOF coatings.The oxide and porosity were eliminated using LR.After LR,FCC was the dominant phase in both alloys,while BCC,sigma and Cr2 O3 phases were observed in Al_(0.2) CrFeNiCo alloy.The hardnesses of the Al_(0.2) CrFeNiCo and Al_(0.2) CrFeNiCu coatings after HVOF were HV 591 and HV 361,respectively.After LR,the hardnesses decreased to HV 259 and HV 270,respectively.Although HVOF coatings were most affected by increased load,they showed the highest wear resistance compared to other samples.The lowest wear resistance could be seen in the substrate.After the oxidation tests,HVOF coating layer was completely oxidized and also,the coating layer was delaminated from the substrate after 50 h oxidation due to its porous structure.LR coatings exhibited better oxidation performance.Al_(0.2) CrFeNiCo was dominantly composed of Cr2 O3,exhibiting a slower-growing tendency at the end of the oxidation tests,while Al_(0.2) CrFeNiCu was composed of spinel phases.展开更多
Water samples, sediments from three stations in Euphrates River, lraq were analyzed quantitatively for some physical and chemical characters and six heavy metals （Co, Cu, Fe, Mn, Ni and Pb） using flam atomic absorpt...Water samples, sediments from three stations in Euphrates River, lraq were analyzed quantitatively for some physical and chemical characters and six heavy metals （Co, Cu, Fe, Mn, Ni and Pb） using flam atomic absorption spectrophotpmeter in period Sept. 2009-Oct. 2010. The physical and chemical characters included temperature, pH, water flow, salinity, dissolved oxygen, BOD5, alkalinity total hardness, calcium and nutrients （nitrite, nitrate reactive phosphate and silicate）. The results showed variation in water flow 0.05-0.40 m/sec., according to the values of salinity 0.40%-0.60% values of the BOD5 were ranged between 0.2-4.3 mg/L. The mean concentration of the heavy metals （Pb, Ni, Mn, Co, Cu and Fe） of the dissolved phase in water were 0.13 μg/L, 0.021 μg/L, 0.31 μg/L, 4.29 μg/L, 7.78 μg/L, 6.46 μg/L and 79.04 μg/L, respectively, while their concentration in the particulate phase were 0.59 μg/g, 0.06 μg/g, 0.42 μg/g, 50.06 μg/g, 6.61 μg/g, 7.17 vg/g and 149.42 μg/g dry weight, respectively. Also the mean concentrations of heavy metals in sediment （exchangeable phase） were 0.51 vg/g,0.18 vg/g, 0.08 μg/g, 61.39 μg/g, 5.40 μg/g, 14.06 vg/g and 130.05 μg/g dry weight respectively, and 0.40 μg/g, 0.17 μg/g, 0.10 μg/g, 63.01 μg/g, 4.64 μg/g, 18.44 μg/g and 126.26 μg/g D.W. respectively in residual phase of sediment.展开更多
Previous studies have been shown that synthesis of titania （TiO2） crystalline phase purity could be effectively controlled by the oxygen concentration through titanium tetra-isopropoxide （TTIP） via premixed flame ...Previous studies have been shown that synthesis of titania （TiO2） crystalline phase purity could be effectively controlled by the oxygen concentration through titanium tetra-isopropoxide （TTIP） via premixed flame from a Bunsen burner. In this study, a modified Hencken burner was used to synthesize smaller TiO2 nanoparticles via short diffusion flames. The frequency of collisions among particles would decrease and reduce TiO2 nanoparticle size in a short diffusion flame height. The crystalline structure of the synthesized nanoparticles was characterized by X-ray diffraction （XRD）, transmission electron microscope （TEM）, Barrett-Joyner- Halenda （BJH） and Brnnauer-Emmett-Teller （BET） measurements. The characteristic properties of TiO2 nanoparticles synthesized from a modified Hencken burner were compared with the results from a Bunsen burner and commercial TiO2 （Degussa P25）. The results showed that the average particle size of 6.63 nm from BET method was produced by a modified Hencken burner which was smaller than the TiO2 in a Bunsen burner and commercial TiO2. Moreover, the ruffle content of TiO2 nanoparticles increased as the particle collecting height increased. Also, the size of TiO2 nanoparticles was highly dependent on the TTIP loading and the collecting height in the flame.展开更多
基金Project supported the by State Key Laboratory of Internal Combustion Engines of Tianjin University,ChinaProject(51507077)supported by the National Natural Science Foundation of China+1 种基金Project(15KJB470005)supported by the Natural Science Research of Higher Education Institutions of Jiangsu Province,ChinaProjects(YKJ201308,QKJB201401)supported by Nanjing Institute of Technology,China
文摘The influence of the certain specific vacuum pre-oxidation process on the phase transformation of thermally-grown oxides（TGO） was studied.The CoCrAlY high temperature corrosion resistance coatings were produced onto the nickel-based superalloy substrate by high velocity oxygen fuel（HVOF）.It suggests that the TGO usually consists of a great number of chromium oxides,cobalt oxides and spinel oxides besides alumina during the initial period of the high temperature oxidation if the specimens are not subjected to the appropriate vacuum pre-oxidation process.Furthermore,the amount of alumina is strongly dependent on the partial pressure of oxygen;while the CoCr2O4 spinel oxides are usually formed under the conditions of higher partial pressure of oxygen during the initial period and the lower partial pressure of oxygen during the subsequent period of the isothermal oxidation.After the appropriate vacuum pre-oxidation process,the TGO is mainly composed of alumina that contains lower Y element,while alumina that contains higher Y element sporadically distributes,and the spinel oxides cannot be found.After a longer period of the isothermal oxidation,a small amount of porous CoCr2O4 and the chrome oxide sporadically distribute near the continuous alumina.Additionally,after the appropriate vacuum pre-oxidation process,the TGO growth rate is relatively slow.
文摘Oxidation behaviors of Ni(Cr)-TiB2 coating deposited by HVOF technique were studied at 800,900 and 1 000℃in air. The microstructures of as-sprayed and oxidized coatings were characterized by X-ray diffractometry(XRD)and scanning electron microscopy(SEM).After oxidation at 800℃,a thin and adherent oxide layer was formed on the surface of the coating.With increasing exposure temperature,the thickness of the oxide layer increased;and at 1 000℃the oxide layer separated from the coating.Investigation of the kinetics of oxidation by using the thermogravimetric analysis(TGA)technique shows a parabolic oxidation rate.
基金financially supported by Scientific Research Funds of Bart?n University(No.2019-FEN-A-012,2019-FEN-A-013)。
文摘Al_(0.2) CrFeNiCo and Al_(0.2) CrFeNiCu high entropy alloys were deposited with high velocity oxygen fuel(HVOF)on 316 L substrate.Later,a laser re-melting(LR)process was applied to enhancing the coating microstructure.LR process effects on dry sliding wear and oxidation behaviors were investigated.The mixture of powders with free elements led to the formation of inner oxides in HVOF coatings.The oxide and porosity were eliminated using LR.After LR,FCC was the dominant phase in both alloys,while BCC,sigma and Cr2 O3 phases were observed in Al_(0.2) CrFeNiCo alloy.The hardnesses of the Al_(0.2) CrFeNiCo and Al_(0.2) CrFeNiCu coatings after HVOF were HV 591 and HV 361,respectively.After LR,the hardnesses decreased to HV 259 and HV 270,respectively.Although HVOF coatings were most affected by increased load,they showed the highest wear resistance compared to other samples.The lowest wear resistance could be seen in the substrate.After the oxidation tests,HVOF coating layer was completely oxidized and also,the coating layer was delaminated from the substrate after 50 h oxidation due to its porous structure.LR coatings exhibited better oxidation performance.Al_(0.2) CrFeNiCo was dominantly composed of Cr2 O3,exhibiting a slower-growing tendency at the end of the oxidation tests,while Al_(0.2) CrFeNiCu was composed of spinel phases.
文摘Water samples, sediments from three stations in Euphrates River, lraq were analyzed quantitatively for some physical and chemical characters and six heavy metals （Co, Cu, Fe, Mn, Ni and Pb） using flam atomic absorption spectrophotpmeter in period Sept. 2009-Oct. 2010. The physical and chemical characters included temperature, pH, water flow, salinity, dissolved oxygen, BOD5, alkalinity total hardness, calcium and nutrients （nitrite, nitrate reactive phosphate and silicate）. The results showed variation in water flow 0.05-0.40 m/sec., according to the values of salinity 0.40%-0.60% values of the BOD5 were ranged between 0.2-4.3 mg/L. The mean concentration of the heavy metals （Pb, Ni, Mn, Co, Cu and Fe） of the dissolved phase in water were 0.13 μg/L, 0.021 μg/L, 0.31 μg/L, 4.29 μg/L, 7.78 μg/L, 6.46 μg/L and 79.04 μg/L, respectively, while their concentration in the particulate phase were 0.59 μg/g, 0.06 μg/g, 0.42 μg/g, 50.06 μg/g, 6.61 μg/g, 7.17 vg/g and 149.42 μg/g dry weight, respectively. Also the mean concentrations of heavy metals in sediment （exchangeable phase） were 0.51 vg/g,0.18 vg/g, 0.08 μg/g, 61.39 μg/g, 5.40 μg/g, 14.06 vg/g and 130.05 μg/g dry weight respectively, and 0.40 μg/g, 0.17 μg/g, 0.10 μg/g, 63.01 μg/g, 4.64 μg/g, 18.44 μg/g and 126.26 μg/g D.W. respectively in residual phase of sediment.
基金supported by the National Science Council under grant NSC 98-2621-M-002-037-MY2
文摘Previous studies have been shown that synthesis of titania （TiO2） crystalline phase purity could be effectively controlled by the oxygen concentration through titanium tetra-isopropoxide （TTIP） via premixed flame from a Bunsen burner. In this study, a modified Hencken burner was used to synthesize smaller TiO2 nanoparticles via short diffusion flames. The frequency of collisions among particles would decrease and reduce TiO2 nanoparticle size in a short diffusion flame height. The crystalline structure of the synthesized nanoparticles was characterized by X-ray diffraction （XRD）, transmission electron microscope （TEM）, Barrett-Joyner- Halenda （BJH） and Brnnauer-Emmett-Teller （BET） measurements. The characteristic properties of TiO2 nanoparticles synthesized from a modified Hencken burner were compared with the results from a Bunsen burner and commercial TiO2 （Degussa P25）. The results showed that the average particle size of 6.63 nm from BET method was produced by a modified Hencken burner which was smaller than the TiO2 in a Bunsen burner and commercial TiO2. Moreover, the ruffle content of TiO2 nanoparticles increased as the particle collecting height increased. Also, the size of TiO2 nanoparticles was highly dependent on the TTIP loading and the collecting height in the flame.
