Search2016 Vol. 23, No. 9
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2016, vol. 23, no. 9, pp.
991-1000.
https://doi.org/10.1007/s12613-016-1316-y
Abstract:
Ultrafine barium hexaferrite (BaFe12O19) powders were synthesized from the metallurgical extracts of low-grade Egyptian barite ore via a co-precipitation route. Hydrometallurgical treatment of barite ore was systematically studied to achieve the maximum dissolution efficiency of Fe (~99.7%) under the optimum conditions. The hexaferrite precursors were obtained by the co-precipitation of BaS produced by the reduction of barite ore with carbon at 1273 K and then dissolved in diluted HCl and FeCl3 solution at pH 10 using NaOH as a base; the product was then annealed at 1273 K in an open atmosphere. The effect of Fe3+/Ba2+ molar ratio and the addition of hydrogen peroxide (H2O2) on the phase structure, crystallite size, morphology, and magnetic properties were investigated by X-ray diffraction, scanning electron microscopy, and vibrating sample magnetometry. Single-phase BaFe12O19 powder was obtained at an Fe3+/Ba2+ molar ratio of 8.00. The formed powders exhibited a hexagonal platelet-like structure. Good maximum magnetization (48.3 A·m2·kg–1) was achieved in the material prepared at an Fe3+/Ba2+ molar ratio of 8.0 in the presence of 5% H2O2 as an oxidizer and at 1273 K because of the formation of a uniform, hexagonal-shaped structure.
Ultrafine barium hexaferrite (BaFe12O19) powders were synthesized from the metallurgical extracts of low-grade Egyptian barite ore via a co-precipitation route. Hydrometallurgical treatment of barite ore was systematically studied to achieve the maximum dissolution efficiency of Fe (~99.7%) under the optimum conditions. The hexaferrite precursors were obtained by the co-precipitation of BaS produced by the reduction of barite ore with carbon at 1273 K and then dissolved in diluted HCl and FeCl3 solution at pH 10 using NaOH as a base; the product was then annealed at 1273 K in an open atmosphere. The effect of Fe3+/Ba2+ molar ratio and the addition of hydrogen peroxide (H2O2) on the phase structure, crystallite size, morphology, and magnetic properties were investigated by X-ray diffraction, scanning electron microscopy, and vibrating sample magnetometry. Single-phase BaFe12O19 powder was obtained at an Fe3+/Ba2+ molar ratio of 8.00. The formed powders exhibited a hexagonal platelet-like structure. Good maximum magnetization (48.3 A·m2·kg–1) was achieved in the material prepared at an Fe3+/Ba2+ molar ratio of 8.0 in the presence of 5% H2O2 as an oxidizer and at 1273 K because of the formation of a uniform, hexagonal-shaped structure.
2016, vol. 23, no. 9, pp.
1001-1010.
https://doi.org/10.1007/s12613-016-1317-x
Abstract:
The co-gasification behavior and synergistic effect of petroleum coke, biomass, and their blends were studied by thermogravimetric analysis under CO2 atmosphere at different heating rates. The isoconversional method was used to calculate the activation energy. The results showed that the gasification process occurred in two stages: pyrolysis and char gasification. A synergistic effect was observed in the char gasification stage. This effect was caused by alkali and alkaline earth metals in the biomass ash. Kinetics analysis showed that the activation energy in the pyrolysis stage was less than that in the char gasification stage. In the char gasification stage, the activation energy was 129.1–177.8 kJ/mol for petroleum coke, whereas it was 120.3–150.5 kJ/mol for biomass. We also observed that the activation energy calculated by the Flynn–Wall–Ozawa (FWO) method were larger than those calculated by the Kissinger–Akahira–Sunosen (KAS) method. When the conversion was 1.0, the activation energy was 106.2 kJ/mol when calculated by the KAS method, whereas it was 120.3 kJ/mol when calculated by the FWO method.
The co-gasification behavior and synergistic effect of petroleum coke, biomass, and their blends were studied by thermogravimetric analysis under CO2 atmosphere at different heating rates. The isoconversional method was used to calculate the activation energy. The results showed that the gasification process occurred in two stages: pyrolysis and char gasification. A synergistic effect was observed in the char gasification stage. This effect was caused by alkali and alkaline earth metals in the biomass ash. Kinetics analysis showed that the activation energy in the pyrolysis stage was less than that in the char gasification stage. In the char gasification stage, the activation energy was 129.1–177.8 kJ/mol for petroleum coke, whereas it was 120.3–150.5 kJ/mol for biomass. We also observed that the activation energy calculated by the Flynn–Wall–Ozawa (FWO) method were larger than those calculated by the Kissinger–Akahira–Sunosen (KAS) method. When the conversion was 1.0, the activation energy was 106.2 kJ/mol when calculated by the KAS method, whereas it was 120.3 kJ/mol when calculated by the FWO method.
2016, vol. 23, no. 9, pp.
1011-1018.
https://doi.org/10.1007/s12613-016-1318-9
Abstract:
In this paper, the diffusion behavior between MgO and Fe2O3 (the main iron oxide in pellets) is investigated using a diffusion couple method. In addition, the distribution regulation of MgO in MgO-bearing pellets is analyzed via pelletizing experiments. The results illustrate that MgO is prone to diffuse into Fe2O3 in the form of solid solution; the diffusion rate considered here is 13.64 µm·min-1. Most MgO content distributes in the iron phase instead of the slag phase. The MF phase {(Mg1-x Fex)O·Fe2O3, x ≤ 1} is generated in the MgO-bearing pellets. However, the distribution of MgO in the radial direction of the pellets is inconsistent. The solid solution portion of MgO in the MF phase is larger in the outer layer of the pellets than in the inner layer. In this work, the approximate chemical composition of the MF phase in the outer layer of the pellets is {(Mg0.35-0.77·Fe0.65-0.23) O·Fe2O3} and in the inner layer is {(Mg0.13-0.45·Fe0.87-0.55) O·Fe2O3}.
In this paper, the diffusion behavior between MgO and Fe2O3 (the main iron oxide in pellets) is investigated using a diffusion couple method. In addition, the distribution regulation of MgO in MgO-bearing pellets is analyzed via pelletizing experiments. The results illustrate that MgO is prone to diffuse into Fe2O3 in the form of solid solution; the diffusion rate considered here is 13.64 µm·min-1. Most MgO content distributes in the iron phase instead of the slag phase. The MF phase {(Mg1-x Fex)O·Fe2O3, x ≤ 1} is generated in the MgO-bearing pellets. However, the distribution of MgO in the radial direction of the pellets is inconsistent. The solid solution portion of MgO in the MF phase is larger in the outer layer of the pellets than in the inner layer. In this work, the approximate chemical composition of the MF phase in the outer layer of the pellets is {(Mg0.35-0.77·Fe0.65-0.23) O·Fe2O3} and in the inner layer is {(Mg0.13-0.45·Fe0.87-0.55) O·Fe2O3}.
2016, vol. 23, no. 9, pp.
1019-1028.
https://doi.org/10.1007/s12613-016-1319-8
Abstract:
Experiments on the solid-state reaction between iron ore particles and MgO were performed to investigate the coating mechanism of MgO on the iron ore particles’ surface during fluidized bed reduction. MgO powders and iron ore particles were mixed and compressed into briquettes and, subsequently, roasted at different temperatures and for different time periods. A Mg-containing layer was observed on the outer edge of the iron ore particles when the roasting temperature was greater than 1173 K. The concentration of Fe in the Mg-containing layer was evenly distributed and was approximately 10wt%, regardless of the temperature change. Boundary layers of Mg and Fe were observed outside of the iron ore particles. The change in concentration of Fe in the boundary layers was simulated using a gas–solid diffusion model, and the diffusion coefficients of Fe and Mg in these layers at different temperatures were calculated. The diffusion activation energies of Fe and Mg in the boundary layers in these experiments were evaluated to be approximately 176 and 172 kJ/mol, respectively.
Experiments on the solid-state reaction between iron ore particles and MgO were performed to investigate the coating mechanism of MgO on the iron ore particles’ surface during fluidized bed reduction. MgO powders and iron ore particles were mixed and compressed into briquettes and, subsequently, roasted at different temperatures and for different time periods. A Mg-containing layer was observed on the outer edge of the iron ore particles when the roasting temperature was greater than 1173 K. The concentration of Fe in the Mg-containing layer was evenly distributed and was approximately 10wt%, regardless of the temperature change. Boundary layers of Mg and Fe were observed outside of the iron ore particles. The change in concentration of Fe in the boundary layers was simulated using a gas–solid diffusion model, and the diffusion coefficients of Fe and Mg in these layers at different temperatures were calculated. The diffusion activation energies of Fe and Mg in the boundary layers in these experiments were evaluated to be approximately 176 and 172 kJ/mol, respectively.
2016, vol. 23, no. 9, pp.
1029-1040.
https://doi.org/10.1007/s12613-016-1320-2
Abstract:
The influences of additives on the phase transformation, occurrence state, and the interface of the Ti component in Ti-bearing blast furnace slag were investigated. After oxidation, most of the Ti component in the slag was enriched into the perovskite phase, which served as the Ti-rich phase during the crystallization process. The phase transformation, occurrence state, and the interface of the Ti component were observed to be affected by the addition of different types of agents. During the oxidation process, titanaugite and Ti-rich diopside phases gradually transformed into non-Ti phases (anorthite: CaMgSi2O6 and CaAl2Si2O8) in the form of dendrites or columns, which were observed to be distributed at the surface of the perovskite phase. Several more cracks appeared along the grain boundaries of the perovskite phase after the addition of P2O5, facilitating the liberation of the perovskite phase. Composite additives combining both an acid and a base, such as CaO + CaF2 or P2O5 + CaF2, were used. We observed that the disadvantages of using single additives were successfully overcome.
The influences of additives on the phase transformation, occurrence state, and the interface of the Ti component in Ti-bearing blast furnace slag were investigated. After oxidation, most of the Ti component in the slag was enriched into the perovskite phase, which served as the Ti-rich phase during the crystallization process. The phase transformation, occurrence state, and the interface of the Ti component were observed to be affected by the addition of different types of agents. During the oxidation process, titanaugite and Ti-rich diopside phases gradually transformed into non-Ti phases (anorthite: CaMgSi2O6 and CaAl2Si2O8) in the form of dendrites or columns, which were observed to be distributed at the surface of the perovskite phase. Several more cracks appeared along the grain boundaries of the perovskite phase after the addition of P2O5, facilitating the liberation of the perovskite phase. Composite additives combining both an acid and a base, such as CaO + CaF2 or P2O5 + CaF2, were used. We observed that the disadvantages of using single additives were successfully overcome.
2016, vol. 23, no. 9, pp.
1041-1047.
https://doi.org/10.1007/s12613-016-1321-1
Abstract:
The mechanism of grain fracturing in a zirconia metering nozzle used in the continuous casting process was studied. The phase composition, microstructure, and chemical composition of the residual samples were studied using an X-ray fluorescence analyzer, scanning electron microscope, and electron probe. Results revealed that the composition, structure, and mineral phase of the original layer, transition layer, and affected layer of the metering nozzle differed because of stabilizer precipitation and steel slag permeation. The stabilizer MgO formed low-melting phases with steel slag and impure SiO2 on the boundaries (pores) of zirconia grains; consequently, grain fracturing occurred and accelerated damage to the metering nozzle was observed.
The mechanism of grain fracturing in a zirconia metering nozzle used in the continuous casting process was studied. The phase composition, microstructure, and chemical composition of the residual samples were studied using an X-ray fluorescence analyzer, scanning electron microscope, and electron probe. Results revealed that the composition, structure, and mineral phase of the original layer, transition layer, and affected layer of the metering nozzle differed because of stabilizer precipitation and steel slag permeation. The stabilizer MgO formed low-melting phases with steel slag and impure SiO2 on the boundaries (pores) of zirconia grains; consequently, grain fracturing occurred and accelerated damage to the metering nozzle was observed.
2016, vol. 23, no. 9, pp.
1048-1055.
https://doi.org/10.1007/s12613-016-1322-0
Abstract:
Simultaneous thermal analysis (STA) was used to investigate the effects of silicon content on the oxidation kinetics of silicon- containing steels under an atmosphere and heating procedures similar to those used in industrial reheating furnaces for the production of hot-rolled strips. Our results show that when the heating temperature was greater than the melting point of Fe2SiO4, the oxidation rates of steels with different silicon contents were the same; the total mass gain decreased with increasing silicon content, whereas it increased with increasing oxygen content. The oxidation rates for steels with different silicon contents were constant with respect to time under isothermal conditions. In addition, the starting oxidation temperature, the intense oxidation temperature, and the finishing oxidation temperature increased with increasing silicon content; the intense oxidation temperature had no correlation with the melting of Fe2SiO4. Moreover, the silicon distributed in two forms: as Fe2SiO4 at the interface between the innermost layer of oxide scale and the iron matrix, and as particles containing silicon in grains and grain boundaries in the iron matrix.
Simultaneous thermal analysis (STA) was used to investigate the effects of silicon content on the oxidation kinetics of silicon- containing steels under an atmosphere and heating procedures similar to those used in industrial reheating furnaces for the production of hot-rolled strips. Our results show that when the heating temperature was greater than the melting point of Fe2SiO4, the oxidation rates of steels with different silicon contents were the same; the total mass gain decreased with increasing silicon content, whereas it increased with increasing oxygen content. The oxidation rates for steels with different silicon contents were constant with respect to time under isothermal conditions. In addition, the starting oxidation temperature, the intense oxidation temperature, and the finishing oxidation temperature increased with increasing silicon content; the intense oxidation temperature had no correlation with the melting of Fe2SiO4. Moreover, the silicon distributed in two forms: as Fe2SiO4 at the interface between the innermost layer of oxide scale and the iron matrix, and as particles containing silicon in grains and grain boundaries in the iron matrix.
2016, vol. 23, no. 9, pp.
1056-1064.
https://doi.org/10.1007/s12613-016-1323-z
Abstract:
The effects of heat treatment on the precipitates and strengthening mechanism in AISI H13 steel were investigated. The results showed that the presence of nanoscale precipitates favorably affected grain refinement and improved the yield strength. The volume fraction of precipitates increased from 1.05% to 2.85% during tempering, whereas the average precipitate size first decreased then increased during tempering. Contributions to the yield strength arising from the various mechanisms were calculated quantificationally, and the results demonstrated that grain refinement and dislocation density most strongly influenced the yield strength. In addition, under the interaction of average size and volume fraction, precipitates’ contribution to the yield strength ranged from 247.9 to 378.5 MPa. Finally, a root-mean-square summation law of σ = σg + σs + (σd2 + σp2)1/2, where σg, σs, σd, and σp represent the contributions of fine-grain strengthening, solid-solution strengthening, dislocation strengthening, and precipitation strengthening, respectively, was confirmed as the most applicable for AISI H13 steel, which indicates a strong link between precipitates and dislocations in AISI H13 steel.
The effects of heat treatment on the precipitates and strengthening mechanism in AISI H13 steel were investigated. The results showed that the presence of nanoscale precipitates favorably affected grain refinement and improved the yield strength. The volume fraction of precipitates increased from 1.05% to 2.85% during tempering, whereas the average precipitate size first decreased then increased during tempering. Contributions to the yield strength arising from the various mechanisms were calculated quantificationally, and the results demonstrated that grain refinement and dislocation density most strongly influenced the yield strength. In addition, under the interaction of average size and volume fraction, precipitates’ contribution to the yield strength ranged from 247.9 to 378.5 MPa. Finally, a root-mean-square summation law of σ = σg + σs + (σd2 + σp2)1/2, where σg, σs, σd, and σp represent the contributions of fine-grain strengthening, solid-solution strengthening, dislocation strengthening, and precipitation strengthening, respectively, was confirmed as the most applicable for AISI H13 steel, which indicates a strong link between precipitates and dislocations in AISI H13 steel.
2016, vol. 23, no. 9, pp.
1065-1075.
https://doi.org/10.1007/s12613-016-1324-y
Abstract:
In this study, plasma nitriding was used to fabricate a hard protective layer on AISI P20 steel, at three process temperatures (450°C, 500°C, and 550°C) and over a range of time periods (2.5, 5, 7.5, and 10 h), and at a fixed gas N2:H2 ratio of 75vol%:25vol%. The morphology of samples was studied using optical microscopy and scanning electron microscopy, and the formed phase of each sample was determined by X-ray diffraction. The elemental depth profile was measured by energy dispersive X-ray spectroscopy, wavelength dispersive spectroscopy, and glow dispersive spectroscopy. The hardness profile of the samples was identified, and the microhardness profile from the surface to the sample center was recorded. The results show that ε-nitride is the dominant species after carrying out plasma nitriding in all strategies and that the plasma nitriding process improves the hardness up to more than three times. It is found that as the time and temperature of the process increase, the hardness and hardness depth of the diffusion zone considerably increase. Furthermore, artificial neural networks were used to predict the effects of operational parameters on the mechanical properties of plastic mold steel. The plasma temperature, running time of imposition, and target distance to the sample surface were all used as network inputs; Vickers hardness measurements were given as the output of the model. The model accurately reproduced the experimental outcomes under different operational conditions; therefore, it can be used in the effective simulation of the plasma nitriding process in AISI P20 steel.
In this study, plasma nitriding was used to fabricate a hard protective layer on AISI P20 steel, at three process temperatures (450°C, 500°C, and 550°C) and over a range of time periods (2.5, 5, 7.5, and 10 h), and at a fixed gas N2:H2 ratio of 75vol%:25vol%. The morphology of samples was studied using optical microscopy and scanning electron microscopy, and the formed phase of each sample was determined by X-ray diffraction. The elemental depth profile was measured by energy dispersive X-ray spectroscopy, wavelength dispersive spectroscopy, and glow dispersive spectroscopy. The hardness profile of the samples was identified, and the microhardness profile from the surface to the sample center was recorded. The results show that ε-nitride is the dominant species after carrying out plasma nitriding in all strategies and that the plasma nitriding process improves the hardness up to more than three times. It is found that as the time and temperature of the process increase, the hardness and hardness depth of the diffusion zone considerably increase. Furthermore, artificial neural networks were used to predict the effects of operational parameters on the mechanical properties of plastic mold steel. The plasma temperature, running time of imposition, and target distance to the sample surface were all used as network inputs; Vickers hardness measurements were given as the output of the model. The model accurately reproduced the experimental outcomes under different operational conditions; therefore, it can be used in the effective simulation of the plasma nitriding process in AISI P20 steel.
2016, vol. 23, no. 9, pp.
1076-1086.
https://doi.org/10.1007/s12613-016-1325-x
Abstract:
The corrosion behavior of corrosion resistant steel (CRS) in a simulated wet–dry acid humid environment was investigated and compared with carbon steel (CS) using corrosion loss, polarization curves, X-ray diffraction (XRD), scanning electron microscopy (SEM), electron probe micro-analysis (EPMA), N2 adsorption, and X-ray photoelectron spectroscopy (XPS). The results show that the corrosion kinetics of both steels were closely related to the composition and compactness of the rust, and the electrochemical properties of rusted steel. Small amounts of Cu, Cr, and Ni in CRS increased the amount of amorphous phases and decreased the content of γ-FeOOH in the rust, resulting in higher compactness and electrochemical stability of the CRS rust. The elements Cu, Cr, and Ni were uniformly distributed in the CRS rust and formed CuFeO2, Cu2O, CrOOH, NiFe2O4, and Ni2O3, which enhanced the corrosion resistance of CRS in the wet–dry acid humid environment.
The corrosion behavior of corrosion resistant steel (CRS) in a simulated wet–dry acid humid environment was investigated and compared with carbon steel (CS) using corrosion loss, polarization curves, X-ray diffraction (XRD), scanning electron microscopy (SEM), electron probe micro-analysis (EPMA), N2 adsorption, and X-ray photoelectron spectroscopy (XPS). The results show that the corrosion kinetics of both steels were closely related to the composition and compactness of the rust, and the electrochemical properties of rusted steel. Small amounts of Cu, Cr, and Ni in CRS increased the amount of amorphous phases and decreased the content of γ-FeOOH in the rust, resulting in higher compactness and electrochemical stability of the CRS rust. The elements Cu, Cr, and Ni were uniformly distributed in the CRS rust and formed CuFeO2, Cu2O, CrOOH, NiFe2O4, and Ni2O3, which enhanced the corrosion resistance of CRS in the wet–dry acid humid environment.
2016, vol. 23, no. 9, pp.
1087-1096.
https://doi.org/10.1007/s12613-016-1326-9
Abstract:
The coarsening behaviors of γ″-phase particles in Inconel 718 alloy aged at 750, 800, and 850°C were investigated by scanning electron microscopy (SEM). Detailed observations and quantitative measurements were conducted to characterize the coarsening behavior of the γ″-phase under various aging conditions. The experimental results indicate that the existence of the δ-phase retards the formation and coarsening of the γ″-phase, without influencing its final particle size or amount. Moreover, when cold rolled with a reduction of 50%, the dimensions of the γ″ particles in Inconel 718 alloy decrease with increasing aging time. Furthermore, the coarsening behavior of the γ″-phase in the Inconel 718 alloy after a normal aging treatment (sample A) and that of the primary δ-phase (sample B) follow the Lifshitz–Slyozov–Wagner (LSW) diffusion-controlled growth theory; the thus-obtained activation energies for the γ″-phase are 292 kJ·mol-1 and 302 kJ·mol-1, respectively.
The coarsening behaviors of γ″-phase particles in Inconel 718 alloy aged at 750, 800, and 850°C were investigated by scanning electron microscopy (SEM). Detailed observations and quantitative measurements were conducted to characterize the coarsening behavior of the γ″-phase under various aging conditions. The experimental results indicate that the existence of the δ-phase retards the formation and coarsening of the γ″-phase, without influencing its final particle size or amount. Moreover, when cold rolled with a reduction of 50%, the dimensions of the γ″ particles in Inconel 718 alloy decrease with increasing aging time. Furthermore, the coarsening behavior of the γ″-phase in the Inconel 718 alloy after a normal aging treatment (sample A) and that of the primary δ-phase (sample B) follow the Lifshitz–Slyozov–Wagner (LSW) diffusion-controlled growth theory; the thus-obtained activation energies for the γ″-phase are 292 kJ·mol-1 and 302 kJ·mol-1, respectively.
2016, vol. 23, no. 9, pp.
1097-1103.
https://doi.org/10.1007/s12613-016-1327-8
Abstract:
A low-clad-ratio AA4045/AA3003 cladding billet was fabricated using a semi-continuous casting process and was subsequently extruded indirectly into a cladding pipe. The temperature distribution near the interface was measured. The microstructures, elemental distribution, Vickers hardness around the bonding interface, and the interfacial shear strength were examined. The results showed that the interface temperature rebounded when AA4045 melt contacted the supporting layer. The two alloys bonded well, with few defects, via the diffusion of Si and Mn in the temperature range from 569°C to 632°C. The mean shear strength of the bonding interface was 82.3 MPa, which was greater than that of AA3003 (75.8 MPa), indicating that the two alloys bonded with each other metallurgically via elemental interdiffusion. Moreover, no relative slip occurred between the two alloys during the extrusion process.
A low-clad-ratio AA4045/AA3003 cladding billet was fabricated using a semi-continuous casting process and was subsequently extruded indirectly into a cladding pipe. The temperature distribution near the interface was measured. The microstructures, elemental distribution, Vickers hardness around the bonding interface, and the interfacial shear strength were examined. The results showed that the interface temperature rebounded when AA4045 melt contacted the supporting layer. The two alloys bonded well, with few defects, via the diffusion of Si and Mn in the temperature range from 569°C to 632°C. The mean shear strength of the bonding interface was 82.3 MPa, which was greater than that of AA3003 (75.8 MPa), indicating that the two alloys bonded with each other metallurgically via elemental interdiffusion. Moreover, no relative slip occurred between the two alloys during the extrusion process.
2016, vol. 23, no. 9, pp.
1104-1111.
https://doi.org/10.1007/s12613-016-1328-7
Abstract:
Cobalt ferrite nanoparticles (CFNPs) were prepared via a reverse micelle method. The CFNPs were subsequently coated with carbon shells by means of thermal chemical vapor deposition (TCVD). In this process, acetylene gas (C2H2) was used as a carbon source and the coating was carried out for 1, 2, or 3 h at 750°C. The Ar/C2H2 ratio was 10:1. Heating during the TCVD process resulted in a NP core size that approached 30 nm; the thickness of the shell was less than 10 nm. The composition, structure, and morphology of the fabricated composites were characterized using X-ray diffraction, simultaneous thermal analysis, transmission electron microscopy, high-resolution transmission electron microscopy, and selected-area diffraction. A vibrating sample magnetometer was used to survey the samples’ magnetic properties. The deposited carbon shell substantially affected the growth and magnetic properties of the CFNPs. Micro-Raman spectroscopy was used to study the carbon coating and revealed that the deposited carbon comprised graphite, multiwalled carbon nanotubes, and diamond- like carbon. With an increase in coating time, the intensity ratio between the amorphous and ordered peaks in the Raman spectra decreased, which indicated an increase in crystallite size.
Cobalt ferrite nanoparticles (CFNPs) were prepared via a reverse micelle method. The CFNPs were subsequently coated with carbon shells by means of thermal chemical vapor deposition (TCVD). In this process, acetylene gas (C2H2) was used as a carbon source and the coating was carried out for 1, 2, or 3 h at 750°C. The Ar/C2H2 ratio was 10:1. Heating during the TCVD process resulted in a NP core size that approached 30 nm; the thickness of the shell was less than 10 nm. The composition, structure, and morphology of the fabricated composites were characterized using X-ray diffraction, simultaneous thermal analysis, transmission electron microscopy, high-resolution transmission electron microscopy, and selected-area diffraction. A vibrating sample magnetometer was used to survey the samples’ magnetic properties. The deposited carbon shell substantially affected the growth and magnetic properties of the CFNPs. Micro-Raman spectroscopy was used to study the carbon coating and revealed that the deposited carbon comprised graphite, multiwalled carbon nanotubes, and diamond- like carbon. With an increase in coating time, the intensity ratio between the amorphous and ordered peaks in the Raman spectra decreased, which indicated an increase in crystallite size.
2016, vol. 23, no. 9, pp.
1112-1118.
https://doi.org/10.1007/s12613-016-1329-6
Abstract:
Fe3O4@SiO2 core–shell composite nanoparticles were successfully prepared by a one-pot process. Tetraethyl-orthosilicate was used as a surfactant to synthesize Fe3O4@SiO2 core–shell structures from prepared Fe3O4 nanoparticles. The properties of the Fe3O4 and Fe3O4@SiO2 composite nanoparticles were studied by X-ray diffraction, transmission electron microscopy, energy dispersive spectroscopy, and Fourier transform infrared spectroscopy. The prepared Fe3O4 particles were approximately 12 nm in size, and the thickness of the SiO2 coating was approximately 4 nm. The magnetic properties were studied by vibrating sample magnetometry. The results show that the maximum saturation magnetization of the Fe3O4@SiO2 powder (34.85 A·m2·kg–1) was markedly lower than that of the Fe3O4 powder (79.55 A·m2·kg–1), which demonstrates that Fe3O4 was successfully wrapped by SiO2. The Fe3O4@SiO2 composite nanoparticles have broad prospects in biomedical applications; thus, our next study will apply them in magnetic resonance imaging.
Fe3O4@SiO2 core–shell composite nanoparticles were successfully prepared by a one-pot process. Tetraethyl-orthosilicate was used as a surfactant to synthesize Fe3O4@SiO2 core–shell structures from prepared Fe3O4 nanoparticles. The properties of the Fe3O4 and Fe3O4@SiO2 composite nanoparticles were studied by X-ray diffraction, transmission electron microscopy, energy dispersive spectroscopy, and Fourier transform infrared spectroscopy. The prepared Fe3O4 particles were approximately 12 nm in size, and the thickness of the SiO2 coating was approximately 4 nm. The magnetic properties were studied by vibrating sample magnetometry. The results show that the maximum saturation magnetization of the Fe3O4@SiO2 powder (34.85 A·m2·kg–1) was markedly lower than that of the Fe3O4 powder (79.55 A·m2·kg–1), which demonstrates that Fe3O4 was successfully wrapped by SiO2. The Fe3O4@SiO2 composite nanoparticles have broad prospects in biomedical applications; thus, our next study will apply them in magnetic resonance imaging.
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