Papers by Keyword: Oxidation

Abstract: This article summarized depositing craft of the superficial coatings (Ni-Co-Cr-Al-Y-Si) on the Ti60 alloy (Ti-6.5Al-4.2Sn-4Zr-0.6Si) with arc ion plating technology and the oxidation behavior under 600~750 . The X-ray diffraction (XRD) and the scanning electronic microscope (SEM) were used to analyze the surface appearance, the structure and the ingredient conducts of non-coating Ti60 alloy. The contrast shows that the coatings have good protection to Ti60 alloy. The result indicated that the coating has the good oxidation resistance performance under 600°C , 650°C and 750°C . Coated Ti60 alloy oxidation resistance is markly improved. The circulation oxidation dynamics curve basically conforms to the parabola rule.

Abstract: Ni coatings with different grain sizes and preferred orientations were produced by the control of current density during a direct current electrodepositing process. The effects of grain size reduction and preferred orientation on the oxidation behavior in air at 600°C and 960°C of Ni coatings were investigated respectively. An important and interesting result is that after oxidation at 600°C, the Ni coating obtained at lower current density has a better oxidation resistance, whereas after oxidation at 960°C, the Ni coating obtained at higher current density has a more compact scale and a better oxidation resistance. For the Ni coatings oxidation at 600°C, the oxidation behavior was mainly influenced by grain size, whereas in the case of the Ni coatings oxidation at 960°C, the oxidation behavior was only slightly influenced by grain size. The changes in oxidation behavior of Ni coatings at 960°C can be attributed to the different preferred orientation and the corresponding oxidation mechanism.

Abstract: A catalyst comprising SO₄²–/ZrO₂ superacid was prepared by impregnation and characterized by FT-IR, XRD, and BET. A novel procedure for oxidative desulfurization of simulated light fuel oil using K₂FeO₄ over the SO₄²–/ZrO₂ solid superacid was developed. The effects of the oxidantion and extraction conditions on desulfurization were investigated. At temperature of 30 °C, SZ of 0.2 g, K₂FeO₄ of 0.2 g, reaction time of 1 h, 20 mL of oil is oxidized, followed by methanol extraction at 15 °C for 10 min with the volume ratio of solvent/oil of 1, the results display desulfurization rate for simulated light fuel oil and straight-run gasoline were 88.2% and 89.2%, respectively.

Abstract: The long term oxidation test of FeCrAl substrate treated by ultrasonic and electroplating methods was performed at 9000C in air environment for 100 hours. The purpose of this paper is to show the nickel layer evolution of that substrate. Oxide scale and layer evolution were assessed on specimens using scanning electron microscope (SEM) coupled with energy dispersive X-ray spectroscopy (EDX). The nickel layer disappeared and fully converted to be nickel oxide on FeCrAl treated using ultrasonic and nickel electroplating after oxidation exposure at 9000 C in air for 100 hours. In this condition, the nickel oxide still existed. Not only nickel oxide and Al2O3 were occurred when oxidation exposure at this condition but also Cr2O3 and Fe2O3. The lowest parabolic rate constant was obtained from FeCrAl ultrasonic treatment with SiC for 50 minutes at 1.21 x 10-4 mg2mm4h-1, and FeCrAl ultrasonic treatment with Al2O3 for 30 minutes at 1.15 x 10-4 mg2mm4h-1. The lower parabolic rate constant indicated the higher long time to failure of the FeCrAl substrate.

Abstract: The chief aim of the present work is to investigate the preparation for silver nanoparticles antimicrobial agent and its antibacterial activity on cotton fabric. In this study, antimicrobial agent was fabricated by a reaction between an amino-terminated hyperbranched polymer (HBP-NH2) and silver nitrate solution of certain concentration. Meanwhile, cotton fabric was oxygenated to afford aldehyde groups which could connect with the amino groups of the HBP-NH2 to provide cotton fabric with durable antimicrobial properties. The effects of different biocides made of various molecular structures of synthetic material (HBP-NH2) on antimicrobial properties of nano-silver colloid solution were discussed, and three different agents generated then were characterized in following aspects as silver nanoparticles size and distribution by using DLS, TEM and UV-vis. Furthermore, the fabric structure, mechanical properties and antimicrobial property of treated cotton fabric were also tested. Included in this part of experiment were transverse micro morphology of cotton fibre by SEM, fabric strength retention after finishing, silver nanoparticles molecular conformation on fabric and content analysis via ICP-AES. The results showed that stable silver nanoparticles collide solution with 20-30 nano, applied on oxidized cotton fabric under certain condition, could produce ideal antibacterial rate over 94% of bacterial reduction to both Staphylococcus aureus (S.aureus) and Escherichia coli (E.coli) after 50 consecutive washings.

Abstract: Solvent-water suspension free-radical polymerization method was used to synthesize acrylonitrile(AN)-acrylamide(AM) copolymers in this paper. The copolymerization was carried out with azobisisobutyronitrile (AIBN) as an initiator and dimethysulfoxide (DMSO)/ water solution as solvents at a constant monomer ratio (AN:AM(wt)=85:15). The ratio(wt) AN:AM=100:0 was also be used for a comparison. The structure and properties of the copolymers was studied by fourier transform infrared (FT-IR), X-ray diffraction (XRD) and thermogravimetry(TG). The nanofibers were obtained by electrospinning AN-AM copolymer solution with N,N-Dimethyl acetamide(DMAc) as a solvent. Then, the fibers were pre-oxidized in relaxation state and in air by using an oven. The structure of pre-oxidized nanofibers was investigated by scanning electron microscopy (SEM) and FT-IR. The results showed that the ratio of dimethysulfoxide (DMSO)/water 50/50(v) was optimum for the copolymer properties and nanofiber spinnability as a carbon nanofiber precursor. The copolymer fibers only needed lower preoxidation temperature and shorter preoxidation time to reach the same degree of cyclization due to the introduction of AM.

Abstract: The modern jet engines used in commercial and military aircrafts are characterized by operating temperature in turbine section above 1000oC. The Ni-base superalloy turbine blades and vanes working in high temperature in very aggressive environment require using of protective coatings. The aluminide coatings are widely used to protect this engine parts. The pack cementation, out of pack and chemical vapour deposition (CVD) technologies are usually used to produce this type of coating. The aluminide coatings can be modified by platinum or other elements. The Pt-modified aluminide coatings are characterized by better oxidation and corrosion resistance in comparison with conventional aluminide coatings and can be used as a bond coat for Thermal Barrier Coatings deposited by EB-PVD technology. In present study the influence of deposition technology and their’s parameters on structure and chemical composition of Pt-aluminide coatings are presented. The base material for coatings was a Inconel 738 Ni-base superalloy. The first step of coatings production were Pt electroplating with different thickness of platinum layer. The second step of coating production was aluminising process. The aluminide coatings were produced by pack cementation and out of pack technologies. Additional the influence of heat treatment of base alloy with coatings was investigated. The structure of all deposited coatings was observed by scanning electron microscopy and the chemical and phase composition of coatings were investigated by EDS and XRD methods. The observed coatings were characterized by two types of structure: first based on NiAlPt phase obtained on thin Pt layer and the second with additional presence of PtAl2 phase on the thick Pt layer.

Abstract: Ti-Al based intermetallics are prospective high-temperature materials showing low weight combined with a relatively high strength, high creep resistance and good oxidation resistance at high temperatures. Beside Ti and Al, these materials commonly contain other additives modifying their properties. In the present work, structure and oxidation resistance of two Ti-Al-Nb and Ti-Al-Ta alloys are studied. The alloys are prepared by vacuum arc melting and oxidation is conducted in air at 800-1000°C. It is found that there are significant differences in the structure depending on the ternary additive. There are also differences in oxidation behavior and these differences are discussed in relation to oxidation mechanism.

Abstract: In a world increasingly concerned with environmental factors and efficient use of resources, increasing operating temperatures of high temperature machinery can play an important role in meeting these goals. In addition, the cost of failure of such devices is rapidly becoming prohibitive. For example, in an airline crash airframe and engine manufacturers are, on average, held liable for 1,000,000 euros per fatality excluding the loss of property. Thus there is considerable pressure to make machinery that can operate much more safely at high temperatures. This means that the old ways of guarding against high temperature fatigue failure (e.g. factor of safety, S/N curves, creep life) are no longer acceptable; more reliable, accurate, and efficient means are needed to manage life, durability and risk. In this paper, high temperature fatigue is considered in terms of past successes and current challenges. Particular emphasis is placed on understanding damage mechanisms and their interactions both in terms of scientific interest and technological importance. Materials used in nuclear reactors (e.g. selected steels and solid solution Ni-base alloys) and in hot sections of jet engines (e.g. superalloys) are used as vehicles to illustrate damage evolution and interaction. Phenomenological life prediction models are presented and compared with physics-based damage evolution/interaction models which are based on observed physical processes such as creep/fatigue/environment interactions. It is shown that in many cases, in spite of the emphasis on creep-fatigue interactions, the most damaging forms of damage that occur under thermo-mechanical fatigue (TMF) loading result from the interaction of slip bands with oxidized boundaries.

Abstract: Nd--sialons with the stoichiometric composition and extra 2wt.% addition of Nd2O3 in Nd0.333Si10Al-2ON15 were synthesized by hot-press sintering. The longtime oxidation resistance of the two ceramics at high temperature was investigated. The oxidation process is very similar, i.e. the weight gain increases linearly at primary stage, and then tends to be constant with prolonging the oxidation time. The oxidation kinetic obeys the parabolic rate law. Inward diffusion of oxygen into ceramics and outward diffusion of metal cations is the main oxidation mechanism. Due to the variation of the content of the added rare earth oxide, the oxidation performance of the two Nd--sialon ceramics are also different.