Increasing Oxidation Time Research Articles

Mechanical and high-temperature steam oxidation properties of Cr coatings deposited via high-power impulse magnetron sputtering

Applying protective coatings to Zr alloy cladding surfaces is one of the better methods to design fuel tolerant materials. In this study, the surface of a Zr-4 alloy was coated with Cr using high-power impulse magnetron sputtering. Furthermore, the mechanisms by which bias voltages affect the mechanical characteristics, resistance to high-temperature steam oxidation, and coating structure were elucidated. The coating exhibits a strong (200) weave structure with coarse grains at a bias voltage of -100 V. With increasing bias, the energy of deposited particles increases, grains continue to grow, (200) preferential growth orientation disappears, and the coating exhibits a (110) crystal orientation. The growth structure of the coating first shows a tendency to be dense and then loose. For the Cr coating with a (200) crystal orientation, a dense oxide layer is preferentially formed after oxidation, which can effectively block the internal diffusion of O. With increasing oxidation time, coarse Cr grains can effectively block the external diffusion of Zr. Furthermore, the Cr coating exhibiting a (110) crystal orientation was severely oxidized after oxidation, resulting in the formation of cracks at the film base; this accelerated the outward diffusion of Zr.

Effect of voltage and time on microstructure and corrosion resistance of anodic oxidation film on Al-5.5Zn-0.03In-1Mg-0.03Ti-0.08Sn alloy

Anodic aluminum oxide (AAO) films were prepared on the surface of Al-5.5Zn-0.03In-1Mg-0.03Ti-0.08Sn alloy in a 160 g/L H2SO4 electrolyte. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), immersion weight loss, and electrochemical testing were used to analyze the element and phase composition, surface and cross-section morphology and corrosion resistance of AAO films in NaCl solution. The effects of anodic oxidation voltage and time on the microstructure and corrosion resistance of AAO films were discussed. The results show that the AAO film on the surface of Al-5.5Zn-0.03In-1Mg-0.03Ti-0.08Sn alloy was mainly composed of Al2O3, with a dense barrier layer near the aluminum matrix and a porous layer on the outer layer. With the increase of anodic oxidation voltage and oxidation time, the thickness and pore diameter of AAO film increases gradually, and the corrosion resistance increases gradually. After anodizing for 15V-60min, the thickness of AAO film on the surface of Al-5.5Zn-0.03In-1Mg-0.03Ti-0.08Sn alloy reached 45.51μm, the corrosion current density decreased to 0.79 µA/cm2, and the weight loss decreased to 0.19 µg·cm−2·h−1, showing the best corrosion resistance. This study provides a new method to improve the corrosion resistance of Al-5.5Zn-0.03In-1Mg-0.03Ti-0.08Sn alloy used in the Marine environment and discusses the corrosion behavior of Al-5.5Zn-0.03In-1Mg-0.03Ti-0.08Sn alloy with AAO films in the Marine environment.

Effect of oxidation times on Gas sensitivity and characterization for (In2O3) thin films produced by thermal evaporated

Abstract thin films were prepared by the thermal evaporated method of Indium metal on a glass substrate, then conventional oxides in the presence of O2 at 400° C. The indium thin films have a thickness of 400nm and different oxidation times (60, 90, and 120) min. The findings from X-ray diffraction (XRD) pertain to the polycrystalline phase. The films (In2O3) had a polycrystalline cubic structure The films have prominent peaks that match (112), (222), and (004) planes at 21.448°, 30.515, 35.38 in the order mentioned. Change with increasing oxidation time each of The amounts The text refers to the number of crystallites, the dimensions of the crystallites, the density of dislocations inside the crystallites, and the level of microstrain present in the crystallites. The UV-vis spectra were used to investigate the optical characteristics such as(The transmittance and absorbance spectra, the absorption coefficient (α) and from there, the energy gap was computed. with different times are 3.1,3.3 and 3.05 eV, respectively. The film’s gas sensing performance approaches CO2 Gas measurements were made at many oxidation times. The performance of the gas detecting system was found to have significantly improved.

Influence of phospholipid structures on volatile organic compounds generation in model systems

To investigate the regularities and differences in oxidation products of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) by gas chromatography-mass spectrometry (GC–MS), and examine the influence of variations in fatty acid compositions and head groups on the kinds and contents of volatile organic compounds (VOCs) generated. A total of 42 VOCs were identified from PE (16:0–18:2), PC (16:0–18:2), and PC (16:0–18:1), with aldehydes and ketones being the main VOCs in three phospholipids (PLs). The content of most VOCs produced by PE (16:0–18:2), PC (16:0–18:2), and PC (16:0–18:1) increases with the increase of oxidation temperature and time. Reached peak at 175 °C for 60 min. The total VOCs contents generated by PE (16:0–18:2) and PC (16:0–18:2) were higher than those produced by PC (16:0–18:1), with PC (16:0–18:2) showing the highest total VOCs contents. PLs exhibited three mass loss processes with increasing temperature, namely stability, reduction, and stabilization. PC (16:0–18:2) experienced the highest mass loss, followed by PE (16:0–18:2), while PC (16:0–18:1) showed the least mass loss. These findings showed that polyunsaturated fatty acids were more susceptible to oxidation and degradation during oxidation, and the presence of choline groups in the form of PE may enhance the oxidative stability of fatty acyl groups compared to PC.

Accurately Measuring the Infrared Spectral Emissivity of Inconel 601, Inconel 625, and Inconel 718 Alloys during the Oxidation Process.

Accurate measurement of the infrared spectral emissivity of nickel-based alloys is significant for applications in aerospace. The low thermal conductivity of these alloys limits the accuracy of direct emissivity measurement, especially during the oxidation process. To improve measurement accuracy, a surface temperature correction method based on two thermocouples was proposed to eliminate the effect of thermal conductivity changes on emissivity measurement. By using this method, the infrared spectral emissivity of Inconel 601, Inconel 625, and Inconel 718 alloys was accurately measured during the oxidation process, with a temperature range of 673-873 K, a wavelength range of 3-20 μm, and a zenith angle range of 0-80°. The results show that the emissivity of the three alloys is similar in value and variation law; the emissivity of Inconel 718 is slightly less than that of Inconel 601 and Inconel 625; and the spectral emissivity of the three alloys strongly increases in the first hour, whereafter it grows gradually with the increase in oxidation time. Finally, Inconel 601 has a lower emissivity growth rate, which illustrates that it possesses stronger oxidation resistance and thermal stability. The maximum relative uncertainty of the emissivity measurement of the three alloys does not exceed 2.6%, except for the atmospheric absorption wavebands.

Structure and Properties of Thermally Stabilized and Ecologically Friendly Organic Cotton Fibers as a New Activated Carbon Fiber Precursor

Organic cotton precursor yarn was impregnated in an aqueous solution consisting of diammonium hydrogen phosphate (DAP), boric acid (BA), and urea (U) mixtures before the thermal stabilization stage and then subjected to heat treatments in an air environment at 245 °C. The effect of chemical pretreatment on organic cotton yarn was examined using methods such as X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and infrared (IR) spectroscopy. The XRD analysis revealed a gradual decrease in the crystalline structure, attributed to the disruption of intermolecular hydrogen bonds. DSC and TGA measurements showed an improved thermal stability due to the formation of pre-graphitic structures with aromatic entities at higher temperatures. For samples chemically impregnated and then stabilized, the char yield values increased from 25% to 68% at 500 °C and 23% to 53% at 1000 °C. Analysis of IR spectra indicated a gradual reduction in both intermolecular and intramolecular hydrogen bonds associated with dehydration and dehydrogenation reactions. The IR spectra also confirmed a decrease in crystallinity with increasing oxidation time, which is consistent with the findings from X-ray diffraction. In addition, the IR spectra showed the presence of C = C bonds, indicating the formation of a crosslinked ladder-like structure. The results showed that DAP-BA-U integration increased the thermal stability of organic cotton fibers and the obtained samples were ready for the next stage, carbonization.Graphical

High-temperature oxidation and gas thermal shock studies of IC10 simulated specimens with thermal barrier coatings

PurposeThe purpose of this study is to investigate the effects of high-temperature oxidation tests and gas thermal shock tests on IC10 simulated components with thermal barrier coatings under different temperatures and oxidation times.Design/methodology/approachIn the high-temperature oxidation test, specimens were oxidized at three different temperatures of 850, 980, and 1,100 °C for durations of 10, 20, 50, 100, 200, and 300 h, respectively. In the gas thermal shock test, specimens were pre-oxidized for 10, 20, 50, and 100 h, followed by a high-temperature gas thermal shock test at 1,100 °C.FindingsIn the high-temperature oxidation tests, with increasing oxidation time, the oxidation layer thickened, and the air-film holes diameter decreased. The microstructure of the bond coat transitioned from strip-like to block-like, and internal cracks transformed from numerous and short to larger and deeper. Below the bond coat, a noticeable disappearance layer of strengthening phase appeared, with increasing thickness. The strengthening phase in the substrate transitioned from regular square shapes to circles as temperature increased. In gas thermal shock tests at 1,100 °C, the oxidation weight gain ratio increased with longer pre-oxidation times, whereas the erosion weight loss ratio gradually decreased.Originality/valueThe originality and significance of this study lie in its departure from the typical subjects of high-temperature oxidation and thermal shock tests. Unlike common research targets, this study focuses on IC10 simulative specimens with thermal barrier coatings and air-film holes. Furthermore, it investigates the effects of varying temperatures and oxidation durations.

Oxide Scale Microstructure and Scale Growth Kinetics of the Hot-Pressed SiBCN-Ti Ceramics Oxidized at 1500 °C.

In this study, the SiBCN-Ti series ceramics with different Ti contents were fabricated, and the oxidation resistance and microstructural evolution of the ceramics at 1500 °C for different times were explored. The results show that with the increase in oxidation time, pores and bubbles are gradually formed in the oxide layer. When the oxidation time is less than or more than 4 h, the Ti(C, N) in the ceramics will maintain its initial structure or mostly transform to TiN. The introduction of Ti content can promote the formation of rutile silicate glass, thus healing the cracks and improving the oxidation resistance of the ceramics effectively.

Inhibition effect of biodiesel on the formation of oxidized insoluble matter in diesel: characteristics and mechanism

ABSTRACT To address the problem that oxidized insoluble matter in diesel is easily generated in the process of using, we proposed the idea of blending biodiesel into diesel to inhibit the formation of oxidized insoluble matter. We also studied the effect of the biodiesel blending ratio on the generation of oxidized insoluble matter and revealed the mechanism of biodiesel inhibiting the formation of diesel oxidized insoluble matter. According to the results, the color of the blended fuel became darker with the increase in oxidation time for B0–B100 blended fuel. The generation of oxidized insoluble matter during the oxidation of B0–B30 was obvious since the amount increased with the enhancement of biodiesel ratio. The formation phenomenon of oxidizing insoluble matter in diesel disappeared, however,when the addition ratio of biodiesel increased from 0%–30% to 40%–100%. Based on the results from Fourier transform infrared spectroscopy and gas chromatography-mass spectroscopy, the main component of oxidizing insoluble matter was tetralone. At low blending ratios, small molecule compounds such as alcohols, aldehydes, and ketones, were rapidly generated with the oxidation process of biodiesel, which maybe acted as precursors for formation of oxidation insoluble matter, thereby increasing the amount of oxidized insoluble matter. For high blending ratios, oxidized insoluble matter was gradually dissolved in biodiesel, because the polarity between biodiesel and oxidized insoluble matter was similar. The dielectric constant of biodiesel was 3.35, which indicated that biodiesel was a weak polar liquid. Meanwhile the oxidized insoluble matter was a polar substance, and its dielectric constant was 6.28–13.59. The results showed that the blending of biodiesel was expected to slow down the appearance of oxidized insoluble matter in diesel, thereby optimizing the performance of diesel and reducing the carbon emissions of diesel.

Effect of anodizing pretreatment on laser joining stainless steel to CFRTP

Metal-carbon fiber reinforced thermoplastic (CFRTP) hybrid joints have demonstrated its effectiveness in achieving lightweight design concept in engineering application. However, it is difficult to produce high-reliability joint due to differences in physical as well as chemical properties between metal and CFRTP. In this study, porous oxide film was prepared by anodizing treatments with various anodic oxidation times on steel surface to enhance joint performance of laser-welded steel/CFRTP. The maximum steel/CFRTP joint fracture load of 1960 N was reached, which was three times as much as that obtained with pretreated steel. The results indicated that porous structure was introduced into steel surface by anodization process, which resulted in better wettability of molten CFRTP and higher surface roughness, thus contributing to the enhancement of joint area as well as mechanical interlocking at the interface, further improving joint performance. Meanwhile, more Cr-O-C chemical bonds were produced because Cr-rich oxide film formed after anodizing contributed to interfacial chemical reaction. The chemical bond between oxide film and CFRTP was proved through density functional theory (DFT) calculation. Additionally, with the increase of anodic oxidation time, chemical bond content and surface roughness first enhanced and then reduced, which suggested that the porous structure prepared with 20 min anodizing time could best improve the interfacial mechanical interlocking, and promote the chemical bonding as well as steel/CFRTP joint interfacial bonding.

High-temperature oxidation behavior of AlCoCrFeNi2.1 eutectic high-entropy alloy: Microstructure evolution and microhardness

In this work, the high-temperature oxidation behavior at 820 °C of an AlCoCrFeNi2.1 eutectic high-entropy alloy (EHEA) prepared by vacuum induction melting was studied, while the evolution of microstructure and microhardness at different oxidation times (1 h, 3 h, 5 h, 10 h, 20 h, 30 h, and 50 h) were also investigated. The prepared AlCoCrFeNi2.1 EHEA shows a typical FCC/BCC bi-phase microstructure with Cr-rich precipitation phase. Compared to 304 stainless steels, the AlCrCoFeNi2.1 EHEA exhibits a better oxidation resistance, which is due to the continuous and dense Al2O3 generated during high-temperature oxidation process. The AlCoCrFeNi2.1 EHEA also has an excellent high-temperature structure stability, proved by that the phase composition and elemental composition of each phase remain almost unchanged with the increase in oxidation time. After high-temperature oxidation, the microhardness of AlCoCrFeNi2.1 EHEA decreases as expected, however, with the increase in oxidation time, the microhardness shows a noticeable increasing trend due to the solid solution strengthening of the σ phase and formation of the α-Cr phase.

Effects of OCF content and oxidation treatment on thermal conductivity and corrosion resistance of CF/BN/EPN coating

The effects of oxidation time and content of oxidized carbon fiber (OCF) on the thermal conductivity (TC) and corrosion resistance of the OCF/BN/EPN coating are investigated. The results show that the oxidation treatment does not change the chemical organization of OCF, while the amount of carboxyl group grafting and the roughness of OCF surface increase with the increase in the oxidation time. Moreover, SEM results show that the higher content OCF fillers causes the more severe contact in the coatings. As the oxidation time increases, the TC gradually enhances, whereas the EIS results increase firstly and then decrease. This can be attributed to the dual effect of the oxidation treatment and content of OCF. The positive effect of oxidation treatment is that it enhances the interfacial compatibility between the coating and the OCF, improving the thermal conductivity and corrosion resistance of the coating. The downside is that the increase in the amount of carboxyl groups on the surface of the OCF with the oxidation time increases the hydrophilicity of the coating, which reduces the corrosion resistance. In terms of content, it significantly shortens the transmission distance of phonons between fillers and improves phonon transmission efficiency but leads to the increase in the number of defects between the filler and resin interfaces, thus enhancing the thermal conductivity of the coating and reducing the corrosion resistance. As a result, when the oxidation time of the OCF is 1.5 h and 15 wt% OCF is added, the best comprehensive performance can be obtained, i.e., and the TC of the coating reaches 1.4 W/m·K while the impedance modulus at 0.1 Hz is 4.6 × 109 Ω·cm2. This work provides an important guidance for the design of heat exchanger coatings with excellent TC and corrosion resistance.

The Effect of Water Content on Engine Oil Monitoring Based on Physical and Chemical Indicators.

Engine oil oxidation is one of the major reasons for oil aging which can result in variations in the physical and chemical properties of oil. Organic acids generated by oil oxidation can react with water to form inorganic acids and acidic substances (including organic and inorganic acids) that corrode engine parts, resulting in the generation of rust or damage to engine parts. This is one of the important reasons why oil should be regularly changed. One of the most commonly applied methods for judging the aging degree of engine oil is monitoring its acid number (AN). However, generally, the effect of oil water content on acid value measurement is not considered. When oils are used in engines, they are often contaminated by water due to condensation, which accelerates engine oil aging. Therefore, it is crucial to explore the water content effect on AN in the process of engine oil aging. In this research, a water content sensor was applied to characterize moisture content in oxidized oil samples. The sensor could also obtain oil sample electrical conductivity which corresponded to its dielectric constant. Using a mid-infrared spectrometer to measure oil sample AN at this point to obtain the variation in AN with oxidation time, oil sample AN was connected in series with the water content, dielectric constant and electrical conductivity. These parameters were monitored through sensors, and the effect of water content on AN was studied. Experimental results revealed that with the increase in oxidation time, the water content, electrical conductivity, dielectric constant increase and AN of oil were increased. At the same time, since the temperature had a greater effect on electrical conductivity, the application of an air-conditioned constant-temperature environment removed the effect of temperature change on electrical conductivity.

High-temperature oxidation behavior of a 9Cr oxide dispersion strengthened alloy under limited oxygen condition

Hot compression bonding is a promising process to fabricate large-scale oxide dispersion strengthened alloys. Inevitable interface oxidation could affect the effectiveness of the joint. The high-temperature oxidation behavior of a 9Cr ODS alloy under limited oxygen condition was investigated. The oxidized surface consisted of inner Fe2O3 scale and outer Cr2O3 particles at 800 °C. Reoxidation at 1000 °C, Cr2O3 particles were decomposed and converted into Cr(Ti)O2. With increasing oxidation time, Fe2O3 and Cr(Ti)O2 were decomposed and Y2O3 pegs formed. Furthermore, TiO2, Y2O3 and Y-Ti-O nanoparticles formed along grain boundaries. In conclusion, the oxide evolution could be summarized as Fe2O3→Cr2O3→Cr(Ti)O2→TiO2→Y2O3→Y-Ti-O nanoparticles. The evolution from initial coarse Cr-rich and Fe-rich oxides to fine Y-Ti-O nanoparticles is expected to be critical for hot compression bonding processes.

Study of the structure of graphene oxide obtained by oxidation of intercalated graphite compound by Raman light scattering method

This work shows the strategy of GO synthesis from intercalated graphite compound, rotation of the synthesis conditions was carried out, and the starting material and synthesis products were characterized in detail by a complex of physical and chemical methods: scanning electron microscopy, transmission electron microscopy, atomic force microscopy, Raman spectroscopy, and high-temperature catalytic oxidation. It was found by Raman spectroscopy that the initial IGC sample is a graphite structure with a low content of defects in graphene layers. Oxidation of this sample leads to a gradual increase in the measure of disordered carbon framework. One of the reasons for this is a decrease in the size of graphite-like crystallites with subsequent reorientation in the space of graphene layers. It has been established by a complex of physicochemical methods of research that the oxidation of IGC graphite with increasing oxidation time leads to an increase in the defectivity of the initial carbon framework due to a decrease in the linear size of carbon crystallites. When a certain reaction time is reached, the initial structure of the sample changes, and there is a partial reorientation of the crushed graphite-like fragments with a simultaneous increase in the number of defects.

Study on oxidation behaviors of Zr–Sn–Nb alloy in water steam at 1250 °C

To investigate the effect of different oxidation times on the oxidation behavior of Zr–Sn–Nb alloy in a high-temperature steam environment at 1250 °C, steam oxidation tests were conducted on the Zr–Sn–Nb alloy at 1250 °C for durations ranging from 100 to 5000 s. Microstructural and elemental composition analyses of the Zr–Sn–Nb alloy were carried out using scanning electron microscopy, energy-dispersive x-ray spectroscopy, and optical microscopy. The results showed that in the initial stages of oxidation (0–1000 s), the weight gain per unit area followed a parabolic trend. After 2500 s of oxidation, the weight gain rate significantly increased. In the later stages of oxidation (after 4000 s), the weight gain curve transitioned from a parabolic shape to a linear law. With increasing oxidation time, the thickness of the oxide layer gradually increased. In the early stages (0–2500 s), the growth rate of the oxide layer thickness was relatively slow, but the appearance of micro-pores and cracks was observed. However, after 2500 s, the steam oxidation rate of the Zr–Sn–Nb alloy significantly accelerated, leading to fracture and failure of the alloy specimens. The change in oxide layer thickness over time followed a parabolic law before 2500 s and a linear law after 2500 s. The growth curve of the α-Zr(O) layer within 5000 s also followed a parabolic law.

Effect of oxidation time on fracture behavior of C/SiC composites at 800 °C in air

The fracture behavior of C/SiC composites after oxidation treatment for different time at 800 °C in air was studied by in-situ test technology combining DIC, AE and X-CT. From results of fracture toughness tests, it can be found that with the increase of oxidation time, the stress intensity factor and the work of fracture show different trends, and the fracture mode after oxidation changes from quasi-brittle to ductile. Combined with AE clustering analysis and X-CT images obtained through in-situ load tests, the mechanism of the coupling effect of oxidation time, toughening behavior and C-phase consumption on energy dissipation is explained. In addition, long-term oxidation causes the crack initiation point to deviate from the prefabricated notch tip and the delamination damage, which may lead to the change of failure position and unexpected damage mode in the engineering structures.

Adsorption properties of cellulose beads prepared by emulsion-gelation method and subsequent oxidation

Cellulose beads with diameters in the micro- to millimeter scale are used in various fields. The search for a novel and straightforward method for producing cellulose beads has attracted significant research attention. In this study, we successfully manufactured cellulose beads using a simple cellulose/LiBr solution-in-oil emulsion-gelation method. Subsequently, we evaluated the dye adsorption capacity of the resultant cellulose beads. The effects of the ratio of the cellulose solution to oil, surfactant concentration, stirring speed, cellulose concentration, and type of surfactant on the size of the beads were investigated. The cellulose beads exhibited a highly porous structure, with a high specific surface area and high adsorption performance for the anionic dye Congo red. In addition, carboxyl groups were introduced into the cellulose beads by oxidation, while retaining their highly porous structure. The adsorption capacity of the cationic dye methylene blue on the oxidized cellulose beads significantly increased with increasing oxidation time and carboxyl group content. In contrast, the adsorption of the anionic dye, Congo red, was inhibited. Cellulose beads with a high carboxyl group content maintained a high adsorption capacity even after repeated adsorption-desorption cycles, demonstrating their potential as reusable adsorbent materials.

High temperature oxidation behavior and oxide film properties of IN718 alloy after heat treatment by hot pressing sintering

The IN718 superalloy was prepared by hot pressing sintering method, and the IN718 alloy blocks under different sintering pressures were obtained. The hot-pressed IN718 superalloy(HPS IN718) prepared by the optimum sintering pressure was treated by solid solution and aging. The high temperature oxidation behavior and the properties of oxide film of HPS IN718 at 850 °C in air were studied. The microstructure of HPS IN718 was characterized by optical microscope(OM), X-ray diffractometer(XRD), scanning electron microscope(SEM), and energy dispersive spectrometer(EDS). The morphology and microstructure of the oxide film of HPS IN718 at 850 °C for different oxidation times were analyzed. The adhesion and wear resistance of the oxide film was tested by an automatic scratch tester and a pin-on-disc friction and wear tester. The results show that the IN718 alloy prepared by sintering pressure 30 MPa has good density, and more uniform structure. The results of the oxidation test show that with the increase in oxidation time, the weight of the sample increases parabolically. The oxidation rate was 3.84 × 10−3 mg/(cm2·h1), which belongs to the complete oxidation resistance level. The oxides gradually aggregate and grow from small particles and clusters in the early stage of oxidation. After 125 h oxidation, the thickness of the oxide layer is 3–4 µm. The outermost layer of the oxide film is composed of TiO2, Fe2Cr2O4, and Fe0.7Cr1.3O3, the subsurface layer is dense Cr2O3, and the inner oxide is Al2O3. As the oxidation time increases, the adhesion between the oxide film and the substrate increases. The surface friction coefficient of the sample is reduced. It is found that after oxidation for 125 h, the adhesion between the oxide film and the substrate is 15 N, the surface friction coefficient is 0.08, the friction coefficient is reduced by 0.37 compared with the substrate, and the wear resistance is the better.

High-performance Fe–Si soft magnetic composites with controllable silicate/nano-Fe composite coating

The design of magnetic insulation coating structure has always been a challenge for high-performance soft magnetic composites (SMCs). In this work, we prepared Fe–Si SMCs with silicate/nano-Fe composite coating successfully by in-situ oxidation method combined with spark plasma sintering (SPS). The formation mechanism of the composite coating and its effect on the electro-magnetic properties of Fe–Si SMCs were investigated. The results showed that a uniform Fe2O3 coating can be obtained by reactions between Fe and H2O/O2 during in-situ oxidation process, and became thicker with the increased oxidation time. After sintering, the oxide coating was transformed into a composite coating composed of Fe2SiO4 with excellent insulation and nano-Fe with high ferromagnetism, which resulted from the interfacial reaction between Fe2O3 coating and Fe–Si core. The increased oxidation time led to the gradually thicker composite coating, and resulted in a linear decrease in saturation magnetization, indicating good controllability of the coating. However, excessive oxidation time led to the increased eddy current loss as well as the core loss due to the weakened resistivity. Thus, the Fe–Si SMCs exhibited high saturation magnetic induction (1.66T) and very low core loss (643.9 kW/m3 at 0.1 T/50 kHz) especially when the oxidation time was 1 h.