Low-temperature Oxidation Resistance Research Articles

Enhanced oxidation resistance and thermal shock resistance of low-carbon Al2O3–C refractories with nano-BN: A synergistic of mullitization behavior

The thermal shock stability and oxidation resistance of Al2O3–C refractories are of critical importance for iron and steel making processes. In rapid and repeated thermal shock environments, materials require excellent thermal shock stability and oxidation resistance. In this study, nano-BN synthesized was used to introduce Al2O3–C refractories, as well as in evaluating the oxidation resistance and thermal shock resistance of the materials. The results shows that B2O3 was formed rapidly in the refractory containing nano-BN under low temperature oxidation, hence, it led to the decrease of the formation temperature of the dense insulating layer. As a result, the low temperature oxidation resistance of the material was improved. Simultaneously, at high temperatures, Al18B4O33 enhanced the formation kinetics of Al6Si2O13 by providing epitaxial nucleation sites, forming a synergistic structure of Al18B4O33 and Al6Si2O13. This change promoted the connection of the oxide layer, thereby greatly improving the oxidation resistance of the material. Moreover, the introduction of nano-BN was beneficial for improving the thermal shock stability of Al2O3–C refractories.

Preparation of MoSi2@ZrO2 core-shell powders by hydrothermal-calcination and evaluation of low-temperature oxidation resistance

MoSi2 is a promising candidate for high-temperature, structural materials. However, their oxidation resistance is poor below 600 °C. To prevent MoSi2 from being oxidized at low temperatures, core-shell structured MoSi2@ZrO2 powder were prepared by hydrothermal-calcination approach. First, MoSi2@Zr(OH)4 core-shell composite powder with nano-sized Zr(OH)4 shell particles were synthesised using a hydrothermal method. Subsequently, the MoSi2@ZrO2 core-shell structured powder were obtained by calcination of the MoSi2@Zr(OH)4 powders at 900 °C for 2h. Finally, microstructure and oxidation behaviour of the MoSi2@ZrO2 powder at 400 °C–600 °C in air were investigated systematically. Microstructural analysis revealed that all samples had a distinct core-shell structure, and the ZrO2 shells coated the surface of the MoSi2 core. Oxidation behaviour studies showed that the dense ZrO2 shell layer could isolate the MoSi2 surface from oxygen, improving the low-temperature oxidation resistance and providing better low-temperature antioxidant properties than those of the MoSi2 and MoSi2@Zr(OH)4 core-shell structures.

Spark plasma sintered W, Ti6Al4V, Cu containing Nb-based alloys representing a new generation for high-temperature applications

Novel spark plasma sintering (SPS) of W–Ti–Al–V–Cu containing Nb-based alloys, representing a new generation of refractory materials, are novel candidates for structural applications. Ni superalloys are currently used at temperatures close to their melting point. Therefore, a novel generation of refractory alloys is being applied at even higher temperatures. When compared to other refractory metals for applications in higher temperature environments, Nb-based alloys have shown great prominence owing to higher melting point. However, their applications have not yet been widely implemented. Indeed, there is a lack of research which might improve some restrictive aspects of Nb alloys, such as low temperature oxidation resistance as well as poor fracture toughness and ductility. To fill this gap, novel alloys with composition Nb-xW-15(Ti6Al4V)–1Cu (x = 5, 10 and 15 wt.%) were developed via SPS at 1400 and 1500 °C (with and without pre-compression). The alloys microstructure, density, hardness and oxidation resistance were characterized. X-ray diffraction and energy dispersive spectroscopy microanalysis confirmed the formation of Nb, Ti and W solid phases solution, as well as intermetallic, AlTi3, TiO2 and TiC compounds. The highest densification (97.5%) was obtained in the alloy with the highest content of 15 wt.% W sintered at 1500 °C and pre-compressed. Despite a lower hardness, it exhibited a parabolic oxidation kinetics from the beginning of the oxidation test. This behavior was attributed to the higher amount of Nb2O5, which increased the oxidation resistance of the alloy.

Microstructure and oxidation behavior of Si-MoSi2 coating deposited on Mo substrate at 600 °C and 900 °C in static air

Si-MoSi2 oxidation protective coating was produced on Mo surface by hot dip silicon-plating (HDS) technology. The isothermal oxidation behavior of Si-MoSi2 coating was investigated in air at at 600 °C and 900 °C. The results indicate that the coating consists of Mo5Si3 interface layer, MoSi2 intermediate layer and Si outer layer. The coating surface is smooth and compact, and the average surface roughness (RSa) is only 0.275 μm. The oxidation test results show that the thickness of oxide layer of the coating increases to 17–20 μm, and the weight gain (Δ m/S) of the coating is 3.48 mg/cm2 after exposed at 600 °C for 150 h. After oxidation at 900 °C for 40 h, the Δ m/S and oxide layer thicknesses are only 0.085 mg/cm2 and 6 μm, respectively. The excellent low-temperature oxidation resistance of Si-MoSi2 coating is mainly attributed to its uniform composition, compact structure, high surface silicon content and extremely low surface roughness.

Synthesis of embedded ZrC-SiC-C microspheres via carbothermal reduction for thermal stability and electromagnetic wave absorption

Development of a novel material with electromagnetic wave (EMW) absorbing capability and high-temperature resistance is a definite trend. As an ultra-high temperature ceramic, zirconium carbide (ZrC) can be used in a harsh high-temperature environment. However, ZrC has high electrical conductivity and poor low-temperature oxidation resistance. The introduction of silicon carbide (SiC) and carbon (C) into ZrC to modulate its phase composition and microstructure is a feasible method that can improve the sensitivity of ZrC to oxidizing atmospheres and electromagnetic wave absorption properties. In this study, submicron ZrC-SiC-C microspheres were successfully synthesized by the carbothermal reduction reaction combined with the template method, in which nanoscale ZrC and SiC were uniformly embedded in unreacted C. The results exhibit that nano-sized SiC and ZrC grains nucleate and grow on carbon microspheres successively, forming unique interlocking structures. The minimum reflection coefficient (RCmin) of ZrC-SiC-C microspheres attains −34.8 dB with a thickness of 1.65 mm at 13.8 GHz and the RC is below −10 dB from 12.0 to 16.0 GHz. The structure that nano-sized ZrC, SiC, and unreacted C are embedded into each other leads to dramatic increase in the heterogeneous interface, which is conducive to the loss of EMW. The incipient oxidation temperature of the ZrC-SiC-C microspheres is 411 °C, which is much higher than that of ZrC particles. The unique structure and composition increase the oxygen diffusion path and improve the oxidation resistance of ZrC. The results indicate that ZrC-SiC-C microspheres can be promisingly used as EMW absorbents in ultra-high temperature environments.

Low temperature preservation developed for special foods in East Asia: A review

Low temperature can improve the quality and prolong the shelf life of perishable food effectively. East Asia has some special foods for its individual geography, climate, and culture, which need different low temperature preservation technologies to maintain their unique flavor. In this paper, the differences in food composition or cooking habits are briefly introduced in each section and then the low temperature preservation technologies developed for these special foods are mainly discussed. Also, the recommendations for future research are provided. Very fast chilling and controlled freezing/supercooling point are promising technologies for pre-rigor fresh meat. Low temperature oxidation resistance and its combination with nonthermal sterilization can ensure the color, freshness, and safety of raw aquatic products. Low temperature rapid fermentation can effectively maintain the organoleptic property of pickles. The synergies of physical and biochemistry methods can reduce wrapper cracking and filling oxidation of frozen prepared foods. Novelty impact statement Low temperature is an effective method for the preservation of food. Due to climate and cultural differences, people in different regions have different eating habits. To better meet people's requirements for the special flavor of food, the corresponding low temperature preservation technologies need to be studied and summarized. This review summarizes the low temperature preservation techniques of four representative special foods in East Asia and provides recommendations for future research. These positive results will be helpful to the research and application of food preservation technologies in the future.

Low-temperature oxidation resistance of the silica-coated MoSi2 powders prepared by sol-gel preoxidation method

MoSi2 has been regarded as one of the most promising structural materials, due to its excellent high-temperature oxidation resistance and high emissivity. However, as the most commonly used emittance agent in high emissivity coatings, it can be easily oxidized when the operating temperature is below 600 °C. To address this issue, the silica-coated MoSi2 powders with good low-temperature (400–600 °C) oxidation resistance were fabricated by a sol-gel method followed by a preoxidation process. Here in, by the combination of the non-isothermal and cyclic-isothermal oxidation analysis, we demonstrate that the silica gel film coated on MoSi2 can prevent oxidation to some extent, but the preoxidation treatment plays a more critical role in improving its oxidation resistance at low temperature. Both the sol-gel and preoxidation processes enable the integrated and compact encapsulation of the silica coating. The synthesized silica-coated MoSi2 exhibits excellent oxidation resistance with slightly weight gains (<1 wt%) after cyclic-isothermal oxidation at 400–600 °C for 12 h.

Effect of SiC and ZrO&lt;sub&gt;2&lt;/sub&gt; on Low Temperature Oxidation Resistance of MoSi&lt;sub&gt;2 &lt;/sub&gt;Nanocomposites

The single and synergism effect of SiC and ZrO2 nanoparticles on low temperature oxidation resistance of MoSi2 were investigated by thermo-gravimetric analysis (TGA), phase and micrograph analysis of surface film. The results show that at the oxidation temperature of 600°C, the addition of 10%ZrO2 results in obvious oxidation mass gain of MoSi2, and discontinuous protective film forming on the surfaces, which makes “pesting” phenomenon still occur. The addition of 10%SiC accelerates the oxidation of MoSi2, but compact SiO2 protective film formed on the surface after some time of oxidation, avoiding the occurrence of large scope of “pesting” phenomenon. The synergism of 10%ZrO2 and 10%SiC promotes the formation of compact, even silicate glass film on the surface of MoSi2, as a result, significantly improves the low temperature oxidation resistance of MoSi2.

Influence of hydrothermal treatment temperature on oxidation modification of C/C composites with aluminum phosphates solution by a microwave hydrothermal process

Carbon/carbon (C/C) composites were modified with an aluminum phosphates solution by a novel microwave hydrothermal (MH) process in order to improve their low temperature oxidation resistance. Results show that a H 3PO 4 or HPO 3 continuous molten layer with some regular, white cubic Al(PO 3) 3 crystallites are obtained on the surface of the modified composites. The anti-oxidation property of the composites after modification improves with the increase of the MH temperature from 393 to 473 K. The oxidation rate is almost constant after oxidation at 873 K for 6 h. The formation of annular structure of Al(PO 3) 3 is helpful to improve the oxidation resistance of the composites.

Manufacturing and Oxidation Behavior of Silicide-Based Nanocomposite Coatings on Refractory Metals by Displacement Reaction

The microstructure and oxidation resistance of MSi2-SiC or MSi2-Si3N4 nanocomposite coatings (M = Mo, W, Nb, Ta) on M substrates formed by displacement reactions between M-carbides or M–nitrides and silicon, respectively, was investigated. Present study demonstrated that the crack density formed in the MSi2-base nanocomposite coatings due to mismatch in the coefficient of thermal expansion between nanocomposite coatings and M substrates could be controlled by adjusting the volume fraction of the SiC or Si3N4 reinforcing particles with the low CTE values. The high- and low-temperature oxidation resistance of nanocomposite coatings was superior to that of monolithic MSi2 coatings.

Study on Oxidation Behavior of (W,Mo)Si&lt;sub&gt;2&lt;/sub&gt; Powders in Air at 400, 500 and 600°C

The oxidation of (W,Mo)Si2 powders has been examined at 400, 500 and 600°C for 12.0 hours in air. It was shown that the low temperature oxidation resistance of (W,Mo)Si2 was worse than that of MoSi2, and they showed great changes in mass, volume and colour. At 500°C, the amount of volume expansion of (W,Mo)Si2 was as high as about 7~8 times and color changed from black to yellow after 4.0h with MoO3, WO3, (W,Mo)O3 and amorphous SiO2 as main reaction products. It took about 8.0h to obtain the same results for MoSi2. The mass gain and oxidation rate were relatively slower at 400°C and 600°C than that at 500°C. These were probably due to the lower oxidation rate at 400°C and the protective silica glass on surface of powders formed from the volatilization of MoO3, WO3 and (W,Mo)O3 at 600°C, which would restrain the diffusion of molybdenum from matrix to exterior and oxygen from outside to inside and the further accelerated oxidation.

Si 3N 4 rodlike crystal-reinforced MoSi 2 matrix composites

A MoSi 2-based composite reinforced with 20 vol.% Si 3N 4 rodlike crystals was fabricated by Spark Plasma Sintering (SPS) process. The microstructure and mechanical properties of the composite were investigated. Relative densities of the monolithic material and composite were above 95%. No reactions between Si 3N 4 and MoSi 2 were observed. The composite containing Si 3N 4 rodlike crystal had higher hardness than monolithic MoSi 2. The room-temperature flexural strength increased 60% compared to that of pure MoSi 2. Especially the room-temperature fracture toughness of the composites was higher than that of MoSi 2, from 3.6 MPa m 1/2 for MoSi 2 to 5.1 MPa m 1/2 for composites with 20 vol.% Si 3N 4, respectively. Besides, the yield strength at elevated temperature and the low-temperature oxidation resistance for 20 vol.% Si 3N 4–MoSi 2 composite exhibited considerable improvement over that of monolithic MoSi 2. These results showed that Si 3N 4 rodlike crystal is an effective reinforcement for MoSi 2.

酸化物の複合化によるＭｏＳｉ２材料の低温酸化特性の改善

MoSi2-oxides composites using fine aluminosilicate powder (<0.2, μm) have demonstrated excellent low temperature oxidation resistance and thermal shock resistance. These properties strongly depend on microstructural morphology and are obtained in composites that network-structures of both phases of MoSi2 and oxides are developed, i.e., in composites with oxides of 20-40 vol.%. When one phase is independently dispersed in the other phase, on the other hand, problems of low temperature oxidation and thermal shock occur. The low temperature oxidation problem occurs in the composites with oxides less than 15 vol.% and the thermal shock problem occurs in the composites with oxides more than 50 vol.%. These results will contribute to material design approaches for high temperature structural applications of MoSi2.

Oxidation resistance studies of Ar +- and N 2+-implanted 304 stainless steel

The effects of nitrogen and argon ion implantations on the oxidation resistance of 304 stainless steel were studied. The implantations were carried out at 30 and 160 keV and oxidations were undertaken at 400 and 950 °C. Nitrogen implantation marginally reduces the low-temperature (400 °C) oxidation resistance of 304 stainless steel whereas argon implantation marginally improves it. Transformation to the α-phase arising from implantation does not change the oxidation resistance significantly. Nitrogen implantation does not lead to severe chromium depletion so as to deteriorate significantly the low-temperature oxidation resistance of 304 stainless steel. Both N 2 + and Ar + implantation reduces the high-temperature (950 °C) oxidation resistance of 304 stainless steel.