Pre-oxidation Treatment Research Articles

Effect of preoxidation treatment with H2O2 on ruthenium ion-catalyzed oxidation of Yima long flame coal

Environmental concerns have led researches to investigate carbon neutral and sustainable strategies to satisfy well-being of present and future generations, in which coal oxidation becomes a promising approach to achieve this goal. In this study, Yima long flame coal (YLFC) was subjected to ruthenium-ion-catalyzed oxidation (RICO) after peroxidation with H2O2 (PO). The results indicate that the organic matter in YLFC is mainly oxidized into benzenecarboxylic acids, accounting for 70.36% of all the oxidation products, and the yields of the valuable resulting carboxylic acids are significantly elevated by PO from 12.99 wt% to 35.06 wt%, leading to a higher utilization of carbon and lower CO2 emission. Moreover, PO can enhance remarkably the reactivity of the macromolecular precursors of coals, especially highly condensed aromatic species to produce benzenepentacarboxylic acid and mellitic acid more efficiently with a 20-fold increase and 200-fold increase, which is ascribed to the formation of carboxyl groups from other oxygen-containing groups or bonds in coals via PO. The reactive intermediates OH and OOH generated from H2O2 decomposition can attack the carbon atom of alkyl side chains, ether bonds, C=O bonds, and the bridged linkages to undergo a preliminary degradation of macromolecular networks in coals and produce more active sites for the subsequent RICO, leading to the yield and species number increase of carboxylic acids via PO.

Effect of Al2O3 scales from pre-oxidation on the microstructural evolution and phase transition of NiAlHf coatings at 1200 °C

The pre-oxidation treatment was conducted for NiAlHf coatings in a sealed glass tube with low oxygen atmosphere at 900 °C. The microstructure evolution and oxidation resistance of the NiAlHf coatings with and without pre-oxidation treatment were systematically investigated via isothermal oxidation at 1200 °C for up to 200 h in laboratory air. The results revealed that a dense Al2O3 scale was formed on the NiAlHf coating surface after pre-oxidation treatment, which could effectively reduce oxygen pressure and Al consumption on the NiAlHf coating surface. Furthermore, the NiAlHf coating microstructure evolution was effectively delayed from β-NiAl to the γ′-Ni3Al phase due to Al2O3 scale formation by pre-oxidation treatment. Oxidation resistance of the NiAlHf coating with pre-oxidation treatment was improved after 200 h of oxidation, of which the oxidation rate constant was enhanced by 40% compared to the NiAlHf coating without pre-oxidation treatment. The mechanism of oxygen diffusion inhibition by pre-oxidation was also discussed. This research was beneficial to understand the effect of pre-treatment on the NiAHf coating microstructure evolution and could further guide the improvement of the oxidation resistance of NiAlHf coatings for long-term oxidation.

Pore structure regulation of hierarchical porous carbon derived from coal tar pitch via pre-oxidation strategy for high-performance supercapacitor

Carbon materials with rational pore structure have attracted tremendous attention in high-performance supercapacitor applications. However, designing and constructing such carbon materials with excellent performances via a simple and low-cost route is still a challenge. Herein, the nitrogen self-doped oxygen-rich hierarchical porous carbons (OTSx-PC) derived from coal tar pitch are constructed via a facile strategy of air pre-oxidation-activation. The air pre-oxidation treatment can effectively regulate the small-sized mesopore structure (2–4 nm) of samples. The optimal OTS350-PC sample exhibits a high specific capacitance of 298 F g−1 at 0.5 A g−1, and delivers a high energy density of 14.9 Wh kg−1 at a power density of 0.15 kW kg−1 with remarkable cycling stability in KOH aqueous electrolyte. This excellent electrochemical performance is attributed to its ultrahigh specific surface area (SSA, 2941 m2 g−1), huge total pore volume (Vt, 1.9 cm3 g−1), rational pore structure and reasonable heteroatom configuration, which ensure sufficient charge storage, rapid electrolyte ions diffusion, as well as the contributed pseudocapacitance. This research not only offers a facile route for high-value utilization of coal tar pitch but also provides the cost-effective and excellent porous carbons for supercapacitor with high performance.

Simultaneous recovery of vivianite and produce short-chain fatty acids from waste activated sludge using potassium ferrate as pre-oxidation treatment

Recovery resources from waste active sludge (WAS) is an effective way to alleviate the predicament of WAS disposal, and it is also conducive to the carbon neutralization of wastewater treatment systems. This study discussed the strategy of WAS anaerobic fermentation after pre-oxidation with potassium ferrate (K2FeO4, PF), which can simultaneously recover vivianite and enhance SCFAs production. The results showed that PF pre-oxidation considerably shortened the fermentation time of SCFAs to 2 days, and the main Fe–P mineral was vivianite. The optimal PF dosage of 0.06 g Fe (VI)/g TSS for pre-oxidation WAS resulted in the maximum SCFAs production and vivianite recovery rate of 3698.2 ± 118.98 mg COD/g VSS and 32.39%, respectively. The mechanism analysis showed that the oxidizing properties of PF significantly accelerated the disintegration of tight EPS, release of protein and sludge acidification efficiency. Moreover, the PF strengthened the transfer of P to the solid phase, forming the Fe–P mineral and unsaturated coordination state of phosphate group. Then the key microorganism Geobacter reduced the Fe3+ in Fe–P state to Fe2+ and combined unsaturated phosphate to form vivianite. This study provides an alternative method for resource recovery and environmentally friendly disposal of WAS and contributes to the carbon neutrality of urban water systems.

Improving corrosion resistance of Cu−Al-based anodes in KF−AlF3−Al2O3 melts

The anodic behaviour of pre-oxidised and non-oxidised Cu−Al-based anodes (Cu−10Al and Cu−9.8Al−2Mn) in KF−AlF3−Al2O3 melts was studied through galvanostatic and potentiodynamic polarization techniques. The alloy compositions were oxidised for a short-term (8 h) at 700 °C, followed by galvanostatic polarization for 1 h at 800 °C with an applied current density of 0.4 A/cm2. The potentiodynamic curves were recorded with a sweep rate of 0.01 V/s. XRD analysis was conducted on frozen melt samples collected on the surface of the anode, and SEM observation was performed on the anode after the experiment to study the phases of the scales formed on the alloys. All the anode materials had a steady potential between 2.30 and 2.50 V(vs Al/AlF3). The corrosion rates of the anodes were calculated from the data acquired through potentiodynamic polarization. It was seen that pre-oxidised anodes possess a low corrosion rate compared to those without pre-oxidation treatment.

High-Temperature Corrosion Behaviour of Pt-Modified Aluminide Coating Under the Effect of Nacl Plus Water Vapour and the Influence of Pre-Oxidation Treatment

High-Temperature Corrosion Behaviour of Pt-Modified Aluminide Coating Under the Effect of Nacl Plus Water Vapour and the Influence of Pre-Oxidation Treatment

Corrosion-resistant materials for liquid LiPb fusion blanket in elevated temperature operation

The corrosion tests of CVD-SiC, FeCrAl alloy (APMT, Fe-22Cr-5Al) and ODS FeCrAlZr alloy (NF12, Fe-11.6Cr-6.2Al) were performed in liquid LiPb up to 1173 K for 250 h. High-purity LiPb was synthesized by melting and mixing of Pb and Li granules at 623 K under vacuum condition. CVD-SiC revealed corrosion resistance, though SiC chemically reacted with impurities dissolved in liquid LiPb and formed complex oxides. The α-Al2O3 layer which was formed on the surfaces of the FeCrAl alloys by the pre-oxidation treatment chemically reacted with liquid LiPb at 1023 K and 1173 K, and the layer chemically transformed into γ-LiAlO2.

Comparative Analyses between Raw and Preoxidized Pulverized Coals: Combustion Behaviors and Thermokinetic and Microcharacteristics.

Investigating the difference in the combustion performance and microcharacteristics of oxidized and raw pulverized coal (PC) can contribute to effectively prevent and control the spontaneous combustion of deposited coal dust in high-temperature environment and further help guarantee the safe operation of coal-fired boiler. In this study, the combustion performance and thermokinetic and microcharacteristics of three raw coal samples and their preoxidized forms were explored by a thermogravimetric analyzer (TGA) and Fourier transform infrared spectroscopy (FTIR). According to the characteristic temperatures and variations of the mass loss rate during heating, the entire combustion process of PC was divided into four periods. For each type of coal, the preoxidized PC had relatively lower characteristic temperatures than the corresponding raw PC. The preoxidized samples had larger values of ignition index (Cig) and comprehensive combustibility index (S), but lower values of burnout index (Cb) than raw samples. The values of apparent activation energy (E) for the preoxidized PC were below that of the corresponding raw PC at the same conversion rate (α), which suggested the preoxidized PC required relatively less energy to react and was more prone to spontaneous combustion. In addition, although parts of −OH, C=O, and aliphatic hydrocarbon groups were consumed after the preoxidation treatment, the increase in C–O and −COO– bonds compensated for the adverse effect of the reduction of the aforementioned groups on coal combustion.

Corrosion behaviour of alumina-forming heat resistant alloy with Ti in high temperature steam

The corrosion behaviour of an alumina-forming heat resistant alloy with high Ti (Fe-35Ni-16Cr-4.5Al-3Ti, wt%) was evaluated in high temperature steam. The alloy developed interfacial α-Al2O3 layer during the pre-oxidation treatment in air at 750 °C. However, it formed external Cr2O3 and internal γ-Al2O3 oxides on the austenite matrix during the steam corrosion at 750 °C for 1000 h. This behaviour is attributed to the increased oxygen permeability into the austenite matrix from the synergistic effect of steam and Ti. Meanwhile, the pre-oxidized alloy with interfacial α-Al2O3 layer showed improved corrosion protection with reduced weight gain in steam environment.

Hydrophilic nanoporous copper surface prepared by modified formic acid vapor treatment

Hydrophilic copper surface with average water contact angle down to 18° can be developed through pre-oxidation and low-temperature reduction treatment using Pt-catalyzed formic acid vapor at 200 °C. The high aspect ratio capillary nanoporous structures of reduced pure copper effectively enhance the hydrophilicity, which is almost the same as hydrophilic oxidized surface with a mixture of CuO and Cu2O. Real-time Fourier transform infrared spectroscopy was employed to monitor the reduction kinetics of the oxidized copper surface. The effect of formic acid vapor concentration was studied and the comparison with N2-5%H2 gas was also done. The porosity of reduced copper can be ascribed to CO2 outgassing from formate dissociation. The great potential in industrial applications such as flat-plate heat pipes with narrow slots was also demonstrated.

Microcrystalline regulation of bituminous coal derived hard carbon by pre-oxidation strategy for improved sodium-ion storage

Middle metamorphic coal has the advantages of high earth abundance and easily-adjusted aromatic units and thus is a feasible raw material for the development of functional carbon materials. For the preparation of high-performance Na+ storage hard carbon, the key is to inhibit the long-range graphitization of internal microcrystalline in coal structure during thermal conversion process. Herein, we introduce a simple gas/liquid-phase pre-oxidation procedure to graft oxygen-containing cross bonds into bituminous coal, by which the growth of long-range graphitization process during high-temperature carbonization can be suppressed and thereby enable the preparation of hard carbon with short-range microcrystalline distribution and enlarged interlayer distance of 0.38 ∼ 0.385 nm. Benefiting the regulated microcrystalline environment, the fabricated hard carbon anode delivers a high reversible capacity of 274.2 mAh g−1, which is 24 % higher than the carbon anode prepared without pre-oxidation treatment. Electrochemical kinetics analyses further reveal that the improved Na+ storage capacity mainly stems from the enhanced Na+ diffusion and intercalation into microcrystalline interlayers at the low voltage region, which is of significance for the construction of high energy–density full cell for practical applications.

Study on the formability of self-bonded bulk porous activated carbon

In this paper, self-bonded bulk porous activated carbon is produced from waste cotton fibers by pre-oxidation and high temperatures activation treatment method use ZnCl2 and K2CO3 as activation agents. The technological conditions of forming activated carbon, such as the fibers and ZnCl2 ratio, activation temperature and forming pressure and adsorption property were investigated. The structural morphology, surface chemical properties and pore structure properties of the activated carbon were also analyzed. The QMB of Cotton-CZn is better, but the maximum falling strength is only 59%, and the yield is 40.5%. The Cotton-CKZn has the highest QMB, 450 mg/g when the addition amount increased to 1:1.2. The QMB of cotton-CKZnC is lower, but the falling strength reaches 100% and the yield reaches 45%.

Influence of pre-oxidization on the characterizations of coal gasification fine slag-derived activated carbons for CO2 capture

Coal gasification fine slag (FS)-based activated carbons (ACs) for CO2 capture provided a new method to realize the value-added utilization of FS. Furthermore, pre-oxidation treatment of carbonaceous materials is one of the most efficient possibilities to obtain developed pore structure of activated carbons to enhance the CO2 adsorption capacity. In this study, four types of oxidizing agents (HNO3, NaClO, H2O2, and air) carefully modified the coal gasification fine slag residual carbon (RC) to fix the oxygen content at about 12 wt%, 15 wt%, and 18 wt%. The samples were characterized by XPS, volumetric sorption analyzer, SEM, Raman spectroscopy, TEM, TG, and TGMS. Results suggested that the specific surface area and total pore volume of the ACs were observed to increase after oxidation. The types of oxygen-containing groups also affected the pore structure of the ACs. The results showed that the content of OCO groups were the most predominant factors for high surface area, and the CO group could hinder the development of pore structure. The ACs facilitated by RC oxidation by HNO3 had a high CO2 storage capacity of 12.4 % at 30 °C and a fast adsorption rate, around 86 % of CO2 uptake occurring in a span of 1 min.

Pre-oxidation induced in situ interface strengthening in biodegradable Zn/nano-SiC composites prepared by selective laser melting

IntroductionNano-SiC has attracted great attention as ceramic reinforcement in metal matrix composites, but the weak interface bonding between them remains a bottleneck for efficient strengthening. ObjectiveIn this study, pre-oxidation treatments and selective laser melting (SLM) were employed to prepare Zn/nano-SiC biocomposites with strengthened interface bonding via in situ reaction. MethodsNano-SiC and Zn powders were pre-oxidized respectively, and then used to prepare Zn/nano-SiC biocomposites via SLM. The powder microstructure, and the interface characteristics and mechanical properties of the biocomposites were investigated. The degradation properties and cell response were analyzed to evaluate their feasibility for orthopedic applications. ResultsThe results indicated that the pre-oxidation treatments generated a uniform oxide layer on the surface of both nano-SiC and Zn particles and the thickness of the oxide layer increased with pre-oxidation temperature. During the SLM process, the oxide layers not only improved the metal-ceramic wettability by reducing interface energy, but also induced in situ reaction to form chemical bonding between the Zn matrix and nano-SiC, thereby improving the interface bonding. Consequently, the Zn biocomposite reinforced by nano-SiC with a pre-oxidation temperature of 1000 °C (ZS1000 biocomposite) exhibited more transgranular fracture and significantly enhanced compressive yield strength of 171.5 MPa, which was 31.6% higher than that of the Zn biocomposite reinforced by nano-SiC without pre-oxidation. Moreover, the ZS1000 biocomposite presented slightly accelerated degradation which might be ascribed to the facilitated electron transfer by the interface product (Zn2SiO4). In addition, the ZS1000 biocomposite also showed appropriate biocompatibility for MG-63 cell adhesion, growth, and proliferation. ConclusionThis study shows the potential practical applicability for the preparation of Zn-based biocomposites with strong interface bonding and mechanical properties for orthopedic applications.

Effect of operating parameters on high-temperature selective enrichment and precipitation of titanium component in Ti-bearing blast furnace slag and the precipitation mechanism of perovskite

Ti-bearing blast furnace slag is an important reproducible Ti resource. The effective recovery of the Ti component from this slag can not only alleviate the resultant environmental problems but also overcome the shortage of Ti resources. In this study, the mineral and element of Ti-bearing blast furnace slag were analyzed and adjusted according to the gravity center rule of CaO–SiO2–TiO2 ternary phase diagram. The Ti component in the Ti-bearing blast furnace slag was enriched into the perovskite phase by preoxidation treatment and high-temperature selective enrichment & precipitation. The results indicate that, the preoxidized slag was obtained with adding 2.54% of CaO to the original slag at 1025 °C for 30 min. Subsequently, the preoxidized slag with 1.0% of Fe2O3 was melted at 1470 °C for 40 min, and the temperature was thereupon reduced to 1320 °C at 0.5 °C/min and kept constant for 90 min. The modified slag exhibited obvious enrichment and precipitation of perovskite, which had a crystal size of 63.17 μm and a crystallization volume of 30.62%. The perovskite phase was observed to exhibit mainly an orderly cross-shaped, granular, and beaded arrangement. During the selective enrichment and precipitation process, the fine-grain perovskite crystals fused together, and the concentrations of Ca2+ and TiO32− surrounding the perovskite crystals decreased, which restricted the crystal growth and led to necking. Changes in the surface tension caused the melting point to drop, thereby facilitating remelting and resulting in narrower necking.

Comparison of electroplating and sputtering Ni for Ni/NiFe2 dual layer coating on ferritic stainless steel interconnect

Ni/NiFe2 dual layer coating is fabricated to improve the performance of SUS 430 steel as solid oxide fuel cells (SOFCs) interconnects by a combined approach. Ni layer is deposited by electroplating or magnetron sputtering, and subsequently the NiFe2 layer is sputtered on it. The coated steels are evaluated at 800 °C in air corresponding to SOFC cathode environment. It is found that the coating with electroplated Ni and sputtered NiFe2 results in breakaway oxidation after 5 weeks. Preoxidation treatment in 900 °C air for electroplated Ni steel prior to depositing NiFe2 layer improves oxidation resistance. The sputtered Ni and NiFe2 sample exhibits superior oxidation resistance and inhibition against Cr outward migration while maintaining a low area-specific resistance (ASR) of surface scale. Comparative analyses of the coating preparation and resultant oxidation behavior with possible mechanisms and implications are discussed.

High temperature oxidation behavior of Ni-based superalloy Nimonic95 and the effect of pre-oxidation treatment

The high-temperature oxidation behaviors of Nimonic95 alloy at 800 °C, 900 °C and 1000 °C were studied. The diffusion process of alloying elements in different stages of oxidation was studied and analyzed, and the pre-oxidation process was established. The results showed that multilayer oxide films formed in the air at 800 °C, 900 °C and 1000 °C, the outer layer was mainly Cr2O3 with a small amount of Al2O3, TiO2 and composite oxides such as CrTi spinel. The inner layer was mainly Al2O3. Nimonic95 alloy has excellent oxidation resistance at 800 °C and 900 °C, but poor oxidation resistance at 1000 °C and the oxide film peeled off in a short time. The oxidation resistance of Nimonic95 alloy at 1000 °C can be improved significantly by pre-oxidation at 800 °C for 140 h.

Alloy Design of MARBN for Boiler and Turbine Applications at 650 oC

ABSTRACT Soluble boron stabilises fine distributions of M23C6 carbides near grain boundaries (GBs) in 9Cr steel during creep, enhancing GB precipitation hardening, and suppresses the Type IV fracture in welded joints at 650oC. Excess addition of boron and nitrogen produces BN inclusions at high temperature, degrading creep strength and rupture ductility. A 9Cr-3W-3Co-0.2V-0.05Nb steel with 130 ppm boron and 80 ppm nitrogen, designated martensitic 9Cr steel strengthened by boron and nitrides (MARBN), exhibits not only the much higher creep rupture strength of base metal than Gr.92 but also no Type IV fracture in welded joints at 650oC. The boron and nitrogen concentrations in MARBN are located just inside the phase boundary for BN at normalising heat treatment temperature in the phase diagram, where we can obtain enough soluble boron and soluble nitrogen but no BN inclusion. The oxidation resistance is improved by the pre-oxidation treatment in argon gas.

Wetting and joining of surface-oxidized SiC ceramic with calcium lithium aluminosilicate glass filler

A novel strategy was developed to join SiC ceramics via a two-step method (i.e., SiC surface was modified by pre-oxidation treatment before bonding) using CaO-Li2O-Al2O3-SiO2 (CLAS) glass as the joining material. The wetting behavior, joint microstructure, bonding strength, fracture characteristics, and joining mechanism were investigated. Due to the formation of the SiO2 layer on the SiC surface by the pre-oxidation, the wettability of CLAS glass solder on the SiC matrix was significantly improved and the interfacial bonding was also enhanced. The microstructure of the joint revealed that the nanoscale eutectic structure composed of wollastonite and spodumene and the rod-shaped anorthite with micron-size were the main products in the joint seam. Besides, the content and size of anorthite in the joints increased with the increase of the joining temperature. Compared with one-step joining, the two-step method can obtain more reliable SiC/SiC joints due to the strong interfacial bonding. As a result, the optimal shear strength of 127 MPa was achieved at a joining temperature of 1240 °C, which was 119% higher than that obtained by the one-step joining method.

Surface characteristic and sinking behavior modifications of microplastics during potassium permanganate pre-oxidation

Microplastics (MPs) occur in the source water of worldwide drinking water treatment plants (DWTPs). Pre-oxidation treatments become the initial stage for MPs treatment in DWTPs. Investigating the modifications of MPs after pre-oxidations is important to understand their fate in DWTPs. In this study, potassium permanganate oxidation (PPO) was applied to treat four high abundant MPs in DWTPs, including polyethylene (PE), polyethylene terephthalate (PET), polyvinylchloride (PVC) and polystyrene (PS). Influences of polymer types, sizes and pH were considered. After 10 mg L−1 PPO, only slight corrosions were observed on all MPs. Whereas, the appearances of O-Mn spectrum and the observation of nano-scale particles indicated the generation of nascent state Mn-oxides (MnO2) on MPs surface. This adhesion of MnO2 contributed to increasing density and hydrophilicity. As a result, the sinking performance of MPs was enhanced, e.g. the sinking ratio of 6.5 µm MPs increased 30% (PET), 20% (PVC) and 30% (PS) compared with pristine ones upon pH 7 PPO. These results implied that the practical PPO can enhance the sinking behavior of MPs. Of note, PE seems to be persistent and requires special concern.