Black Oxidation Research Articles

Effect of electrolyte pH value on microstructure and corrosion resistance of black MAO coating on 6063 aluminum alloy

Black micro-arc oxidation (MAO) coatings were obtained on the surface of 6063 aluminum alloy by using the MAO technique in silicate electrolyte with colorant NH4VO3. The work aimed to study the effect of adjusting the electrolyte pH (pH10, pH11, pH12, and pH13) on the microstructure, mechanical properties, and corrosion resistance of black MAO coatings on 6063 aluminum alloy. The experimental results showed that the electrolyte pH had an important effect on the macroscopic morphology of the MAO coatings. As the electrolyte pH value increased, the process voltage of the sample decreased, the duration of the anodic oxidation stage and the spark discharge stage were shortened, while the duration of the micro arc oxidation stage was prolonged. Reasonable adjustment of the electrolyte pH could reduce the poriness and defects of the coatings, decrease the surface roughness of the coatings, and improve the quality and wear resistance of the coatings. The corrosion resistance of the black MAO coating obtained in the electrolyte with pH12 was superior and the corrosion current density was only 3.207×10−7 A/cm2. The immersion corrosion test further demonstrated the same results of corrosion resistance.

Chemical Origin of in Situ Carbon Dioxide Outgassing from a Cation-Disordered Rock Salt Cathode.

In situ carbon dioxide (CO2) outgassing is a common phenomenon in lithium-ion batteries (LiBs), primarily due to parasitic side reactions at the cathode-electrolyte interface. However, little is known about the chemical origins of the in situ CO2 released from emerging Li-excess cation-disordered rock salt (DRX) cathodes. In this study, we selectively labeled various carbon sources with 13C in cathodes containing a representative DRX material, Li1.2Mn0.4Ti0.4O2 (LMTO), and performed differential electrochemical mass spectrometry (DEMS) during galvanostatic cycling in a carbonate-based electrolyte. When charging LMTO cathodes, electrolyte solvent (EC) decomposition is the dominant source of the CO2 outgassing. The amount of EC-originated CO2 is strongly correlated with the total surface area of carbon black in the electrode, revealing the critical role of electron-conducting carbon additives in the electrolyte degradation mechanisms. In addition, unusual bimodal CO2 evolution during the first cycle is found to originate from carbon black oxidation. Overall, the underlying chemical origin of in situ CO2 release during battery cycling is highly voltage- and cycle-dependent. This work further provides insights into improving the stability of DRX cathodes in LiBs and is envisioned to help guide future relevant material design to mitigate parasitic reactions in DRX-based batteries.

Maize edible-legumes intercropping systems for enhancing agrobiodiversity and belowground ecosystem services

Intensification of staple crops through conventional agricultural practices with chemical synthetic inputs has yielded positive outcomes in food security but with negative environmental impacts. Ecological intensification using cropping systems such as maize edible-legume intercropping (MLI) systems has the potential to enhance soil health, agrobiodiversity and significantly influence crop productivity. However, mechanisms underlying enhancement of biological soil health have not been well studied. This study investigated the shifts in rhizospheric soil and maize-root microbiomes and associated soil physico-chemical parameters in MLI systems of smallholder farms in comparison to maize-monoculture cropping systems (MMC). Maize-root and rhizospheric soil samples were collected from twenty-five farms each conditioned by MLI and MMC systems in eastern Kenya. Soil characteristics were assessed using Black oxidation and Walkley methods. High-throughput amplicon sequencing was employed to analyze fungal and bacterial communities, predicting their functional roles and diversity. The different MLI systems significantly impacted soil and maize-root microbial communities, resulting in distinct microbe sets. Specific fungal and bacterial genera and species were mainly influenced and enriched in the MLI systems (e.g., Bionectria solani, Sarocladium zeae, Fusarium algeriense, and Acremonium persicinum for fungi, and Bradyrhizobium elkanii, Enterobacter roggenkampii, Pantoea dispersa and Mitsuaria chitosanitabida for bacteria), which contribute to nutrient solubilization, decomposition, carbon utilization, plant protection, bio-insecticides/fertilizer production, and nitrogen fixation. Conversely, the MMC systems enriched phytopathogenic microbial species like Sphingomonas leidyi and Alternaria argroxiphii. Each MLI system exhibited a unique composition of fungal and bacterial communities that shape belowground biodiversity, notably affecting soil attributes, plant well-being, disease control, and agroecological services. Indeed, soil physico-chemical properties, including pH, nitrogen, organic carbon, phosphorus, and potassium were enriched in MLI compared to MMC cropping systems. Thus, diversification of agroecosystems with MLI systems enhances soil properties and shifts rhizosphere and maize-root microbiome in favor of ecologically important microbial communities.

Studi perbandingan metode oksidasi enzimatis terhadap aktivitas antioksidan ekstrak air teh kratom (Mitragyna speciosa Korth.)

One of the kratom (Mitragyna speciosa Korth.) products in Kapuas Hulu is fermented kratom tea powder, produced by the enzymatic oxidation process, which is very different from the processing of black tea. Until now, there has been no research on the manufacture of fermented kratom tea powder using the black tea enzymatic oxidation method. This study aimed to determine the differences between the enzymatic oxidation method to the antioxidant activity of water extract kratom tea. The technique used in this study was a comparative method to compare the data obtained from water extract kratom tea. The treatments compared were the manufacture of fermented kratom tea powder with the enzymatic oxidation method of the Kapuas Hulu community and the enzymatic oxidation method of black tea. The parameters tested in this study consisted of phenol content, flavonoid content, alkaloid content, and antioxidant activity. The study showed that the phenol and alkaloid contents were higher in product of black tea methods (199.22 mg GAE/g and 44.73%) than Kapuas Hulu traditional methods (50.45 mg GAE/g and 40.68%). Flavonoid content was higher in Kapuas Hulu traditional methods (169.32 mg QE/g) than black tea methods (48.77 mg QE/g). The difference was found in the antioxidant activity of the water extract kratom tea produced by two different enzymatic oxidation methods. The enzymatic oxidation of the black tea method was found to higher antioxidant activity of water extract kratom tea.

Experimental study of CeO2 after hydrothermal aging on emission characteristics of carbon black oxidation process

The CeO2 catalyst is commonly utilized in diesel particulate filter (DPF) to promote soot regeneration. It is necessary to give a particular attention to the performance of hydrothermal aging and the effect on DPF regeneration characteristics. Based on the fixed-bed test bench, the gas and particle emission characteristics of carbon black (PU) oxidation following hydrothermal aging and sieving treatment of CeO2 are investigated under a 3% water concentration condition. CeO2 is subjected to characterization and analysis combined with X-ray Photoelectron Spectroscopy (XPS), Electron Spin Resonance Spectroscopy (ESR), X-ray Powder Diffraction (XRD), and Scanning Electron Microscopy (SEM). The results indicate that the addition of fresh CeO2 proves beneficial in improving the oxidation efficiency (η) of PU, reducing CO emission and the total average particle number (PN). Meanwhile, CO2 emission rapidly increases. After hydrothermal aging, the average catalyst size and agglomeration degree of CeO2 increase, resulting in an increase in lattice defects and bulk oxygen vacancies (VO-b). The reduction of surface oxygen vacancies (VO-s) plays a dominant role in the catalytic oxidation process of PU, leading to a decrease in η and CO2 emission, while CO increase; And the contact mode between CeO2 and PU, as well as alterations in the microstructure of CeO2, consequently contributing to hindering particle movement and reducing total PN. Furthermore, the sieving treatment of catalyst increases particle emission, but significantly promotes the η and reduces harmful gas CO. This research establishes a theoretical and experimental foundation for enhancing the hydrothermal stability of catalysts and controlling particle emission at the DPF outlet.

Soil legacies in maize-edible legume intercropping alter maize growth and reduce Spodoptera frugiperda larval feeding

Plant-soil feedback can influence aboveground interactions between plants and herbivores by affecting plant chemistry. Such interactions can be utilized in pest management. However, cropping systems such as maize-legume intercropping (MLI) can influence these interactions which is not well understood. In this study, we explored effects of MLI systems on soil physico-chemical properties, maize growth, larval feeding and development of fall armyworm (Spodoptera frugiperda). We used sterile soil and soil conditioned by different MLI and maize-monoculture cropping systems to explore these interactions. Soil samples that included soil conditioned by different MLI and maize-monoculture cropping systems were collected from smallholder farmer fields in eastern Kenya, where different MLI and maize-monoculture cropping systems were being practiced. These soil samples were compared with sterile soils for physico-chemical properties using black oxidation and Walkley methods. Three-weeks-old maize plants grown in the different soil treatments in the greenhouse were used for larval feeding and development assays. Neonate S. frugiperda larvae were allowed to feed on maize leaf discs for 24 hours and another set of plants were inoculated with the neonates for 15 days and the larval survival and development monitored. Soil obtained from different maize-edible legume intercropping systems had a higher pH, electrical conductivity, nitrogen, organic carbon, potassium, phosphorus, calcium, magnesium, exchangeable acidity, copper, clay and silt compared to maize-monoculture and sterile soil. Maize plants grown in MLI soil had better growth parameters compared to those in maize-monoculture and sterile soils. A high correlation was found between pH and plant biomass, while no significant correlation with other physico-chemical properties was noted. There were significant differences in larval feeding by S. frugiperda neonates when exposed to constitutive and induced maize leaf discs with more leaf tissue fed on maize grown in maize-monoculture and sterile soil. When allowed to feed for 15 days, S. frugiperda larval weight and length were significantly lower on maize plants grown in soils conditioned by MLI than those grown in soil conditioned by maize-monoculture and sterile soils. Findings from this study show how conditioning soil by MLI systems improve soil health, maize growth and reduces S. spodoptera larval feeding and development.

Impact of combustion-derived black carbon oxidation states on optical properties and cellular metabolomics in HeLa cells: Insights into soot organics

The 2021 WHO guidelines recommend limits for black carbon (BC) due to its role in oxidative stress and inflammation. BC is highly light-absorbing and quickly undergoes coating by secondary organic aerosols (SOA), enhancing their toxicological and optical properties. Using a miniCAST, this study produced BC at six oxidation states. HPLC-DAD-QTOF-MS and LC-MS/MS technologies were employed to characterize the organic coatings on BC and investigate the associated chromophores and metabolomics effects on Hela cells. The chemical compositions of SOA organics resembled those in ambient air. Interestingly, greater BC maturity did not correlate with increased light absorption. Intermediate maturity showed the strongest absorption, with common chromophores but higher intensities. Aliphatic and polyaromatic compounds were the primary absorbers, with C21H41O6 and C24H50N2O4 as the strongest chromophores in ESI+ mode, and C16H32O2 and C10H7NO3 in ESI- mode. Metabonomics and pathway analysis revealed down-regulation of 13 metabolites involved in lipid synthesis in cells exposed to different SOA organics. Plasmalogen, triacylglycerol, and cardiolipin pathways were significantly influenced. Plasmalogens emerged as potential therapeutic targets for neurodegenerative and cardiometabolic diseases, and cardiolipin, a crucial mitochondrial phospholipid for cellular energy production, indicating that reduced metabolites due to SOA organics disrupt cellular lipid homeostasis and alter normal cellular functions.

Experimental study on gas and particle emission characteristics of carbon black oxidation process in the presence of water and catalysts

The study of oxidation characteristics of carbon black particle is the basis to investigate the regeneration process and characteristics of diesel particulate filter (DPF). Based on the fixed-bed test bench, the gas and particle emission characteristics of carbon black oxidation process in the presence of water are investigated under different temperatures, Printex-U (PU) masses, and catalysts. The experimental results show that the rise of temperature and PU mass increases the emissions of CO, CO2 and the total average particle number (PN). The oxidation efficiency (η) increases with temperature, but decreases with PU mass. The addition of catalysts promotes PU oxidation, and reduces CO emission. Due to the influence of particle diffusion, CeO2 has slightly lower efficiency than Pt/Al2O3 in the same ratio (1:1), but it is beneficial to significantly reduce particle emission, especially as the ratio increases (1:5). Water decreases CO and the η in PU oxidation, and the negative impact is gradually reduced after 3 % water concentration; However, the PN significantly increases, and expands the particle size range, particularly at high temperature and adding Pt/Al2O3 (from about 10 nm to 6– 30 nm, and a large number of particles with 30– 100 nm are produced). Additionally, the CO2/CO ratio of carbon black oxidation gradually increases with water concentration. Controlling DPF regeneration needs to strike a balance between the benefits on increasing oxidation efficiency and the potential negatives on particulate and harmful gas emission.

Chemical identification and optimization of the 4-aminophenol colorimetric test for the differentiation between hemp-type and marijuana-type cannabis plant samples.

The 4- Aminophenol (4-AP) colorimetric test is a fast, easy-to-use, and cost-effective presumptive assay of cannabis plant material producing different chromophores with THC-rich cannabis (blue color) and with CBD-rich cannabis (pink color). The main drawback of the 4-AP test is a brief observation window where the color rapidly changes to black, limiting the utility of the test. We now report for the first time, the identification of the product chromophores between 4-AP and CBD/THC as well as propose an explanation and a solution for the color degradation of the chromophores. The identification of the chromophores is provided by spectroscopic (UV-Vis), chromatography, and mass spectrometry (TLC and LC-QToF-MS). Oxidation of excess 4-AP (Reagent A) in the presence of NaOH (Reagent B) produces the black color observed for the previously reported 4-AP tests and reported in the literature. The adjustment of reactants concentrations and volumes of 4-AP:THC/CBD to a 1:1 ratio significantly reduces the black oxidation by-product and increases the observation window up to 2 h instead of the previously reported 5-10 min. For the first time, mass spectrometry and chromatography confirmed that the reaction of THC and CBD with 4-AP produced chromophores with m/z (M + H) = 420, consistent with proposed indophenol structures. The TLC method developed confirmed the separation between CBD and THC chromophores. The specificity of the test is also reported, showing false positive results for the presence of THC (blue color) for samples of thyme and oregano. LDA and SIMCA models showed that the optimized 4-AP procedure performs better than the previously reported 4-AP color test.

Examining the Fluctuation of Soil Organic Carbon Levels: An Analysis of the Shuklaphanta National Park in Nepal

Soil organic carbon (SOC) is a crucial carbon reservoir that needs to be monitored for deforestation and forest degradation. The top one-meter layer of soil contains around 1500–1600 Pg of carbon. Assessing the SOC pool is essential for understanding the soil system’s carbon sequestration potential (CSP) as a mitigation strategy and determining whether it acts as a source or sink for atmospheric CO2, depending on the level of saturation. However, there are limited studies on SOC in Nepal’s forests. This research aims to assess SOC variation in the Shuklaphanta National Park in Nepal. It focuses on determining SOC according to depth and analyzing the variation of SOC among the core area of the national park, grasslands, and buffer zone community forests (CFs) and identifying the factors that contribute to the variation in soil carbon across different land uses. The study was conducted using a systematic sampling method with a sampling intensity of 6.59% on 180 soil samples taken from permanent plots set up by the Forest Resource Assessment (FRA) Nepal. The analysis was based on SOC estimated up to the depth of 0–10, 11–20, and 21–30 cm using a modified Walkley–Black wet oxidation method. The study also analyzed contributing factors affecting soil carbon such as vegetation, forest fire, rate of forest resource use, and different soil properties like pH and bulk density. The study found that the mean SOC% up to the depths of 0–10 cm, 11–20 cm, and 21–30 cm was 2.08, 0.98, and 0.68, respectively, in forest areas. Mean SOC% in grasslands was found to be 1.7, 1.68, and 1.87 in 0–10, 11–20, and 21–30 cm, respectively, and in community forests, it was found to be 1.3, 0.98, and 0.58 in 0–10, 11–20, and 21–30 cm, respectively. Similarly, the vertical mean SOC in tC⋅ha−1 (0–30 cm) was found to be 41.75 tC·ha−1 in the core area of the national park, 46.64 tC·ha−1 in grassland, and 37.50 tC·ha−1 in CFs. The study also found that there was variation in SOC with depth and that most of the SOC was concentrated in the topsoil in the core area of the national park and buffer zone community forests. Deep layers of SOC were found in grasslands, core area of the national park, and CF in decreasing order. The study implies that the national park has enormous potential to recapture atmospheric CO2 into the soil. Participating in the sustainable management of the national park can enhance the soil quality and help meet strategies to mitigate climate change. Factors such as vegetation cover, fire, bulk density, and vegetation type were found to be promising for SOC concentration.

Methods for determining the organic carbon content in soils (critical review)

The paper presents theoretical basis of the methods for determining the content of soil organic carbon (SOC) both by direct dry combustion using automated analyzers and indirectly – by I.V. Tyurin and Walkley–Black oxidation. Author's and literature experimental data of SOC analyses in various soils by these methods are presented. Comparative analysis of the above data showed that in some cases the content of SOC determined by oxidability is lower than the one obtained by dry combustion (in most cases), while in others, on the contrary, the content of SOC is higher. This conclusion fully complies with the theoretical views of I.V. Tyurin on the chemical nature of soil organic matter (SOM). A schematic description of determining the content of total (organic) carbon in non-carbonate soils by dry combustion method using automated analyzers Leco (USA) and AH-7529 (Gomel, Belarus) is given. It was pointed out that it is difficult to determine SOC content by dry combustion method with automated analyzers in carbonate soils. For these soils it is recommended to determine the content of inorganic carbon by decomposition of carbonates with HClO4 solution using express analyzer AN-7529. The direct method of determining the content of SOC has the best metrological characteristics compared to ones of the indirect method, which convincingly confirms the authoritative opinions of Schollenberg and Tyurin about the inaccuracy of the latter. It is concluded that the indicators determined by the methods of Tyurin and Walkley–Black and dry combustion are chemically independent, characterizing, respectively, the oxidability and organic carbon content of SOM. It is recommended to use dry combustion method with automated analyzers when monitoring the content and stocks of organic carbon in soils.

Preparation of Pt catalysts supported on polyaniline modified carbon black and electrocatalytic methanol oxidation

The supports are of vital importance for supported catalysts. In this work, an excellent anode catalyst support for methanol oxidation reaction is prepared by using polyaniline (PANI) surface modified carbon black (CB), and Pt catalysts are supported on the surface of carbon black modified by polyaniline (Pt/PANI-CB). The characterizations of structure and morphology show that Pt nanoparticles with an average diameter of 2.89 nm are uniformly dispersed on the surface of carbon black modified by polyaniline. Compared with Pt supported on the surface of carbon black (Pt/CB) and commercial Pt/C catalysts, the optimal Pt/PANI-CB has higher electrocatalytic activity, and better stability for methanol oxidation reaction. In 0.5 M H2SO4 solution containing 0.5 M CH3OH, the area specific activity of Pt/PANI-CB is 1.81 mA cm−2Pt, and those of Pt/CB and Pt/C is 1.29 and 0.68 mA cm−2Pt. After 1000 cycles of cyclic voltammetry, the area specific activity retention of Pt/PANI-CB is 74.0%, while those of Pt/CB and Pt/C are 60.4% and 38.2%. Obviously, as a catalyst support, carbon black modified by polyaniline has broad application prospects.

Study on Microstructure and Properties of Black Micro-Arc Oxidation Coating on AZ31 Magnesium Alloy by Orthogonal Experiment.

The effects of CuSO4 concentration, voltage and treating time on the hemisphere emissivity and corrosion resistance of AZ31B magnesium-alloy black micro-arc oxidation coatings were studied by orthogonal experiment. The microstructure, phase composition, corrosion resistance and hemisphere emissivity of the coating were investigated by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, electrochemical test and infrared emissivity spectrometer, respectively. The results showed that the influences of each factor on corrosion current density and the hemisphere emissivity are as follows: voltage > treating time > CuSO4 concentration. The black MAO coatings are mainly composed of WO3, MgAl2O4, CuAl2O4, MgO, CuO and MgF2. The CuO and CuAl2O4 phases are the main reasons for blackness of the coatings. The coating exhibits the best corrosion resistance under the conditions of CuSO4 concentration 1.5 g/L, oxidation voltage 500 V and treating time 10 min. Additionally, the variation trends of hemispherical emissivity and roughness of the black MAO coating are the same when the composition of the coatings is similar. When the concentration of CuSO4 is 1.5 g/L, the oxidation voltage is 450 V and the treatment time is 10 min, the coating with the highest hemispherical emissivity of 0.84 can be obtained.

Performance comparison of black liquor gasification and oxidation in supercritical water from thermodynamic, environmental, and techno-economic perspectives

The black liquor poses a great threat to the environment and it is also a kind of available biomass resources. By the supercritical water gasification (SCWG) and supercritical water oxidation (SCWO) technology, the black liquid with high water content can be converted into hydrogen-rich gas or heat energy. In this study, a pulp mill integrated with black liquor SCWG and SCWO subsystems, which have a processing capacity of 11.2 t/h of black liquor with a concentration of 15.2 wt%, is designed. The thermodynamic analysis, techno-economic analysis (TEA), and life cycle assessment on the system are conducted. The gasification characteristics and thermodynamic performance of the SCWG and SCWO systems under different working conditions are studied. The thermodynamic analysis shows that the highest energy efficiencies of SCWG and SCWO systems are 41.53 % and 19.89 %, respectively. The lowest processing cost of black liquor is 398.68 RMB/t, which is obtained in the SCWO system at 600 °C. At 800 °C, the minimum hydrogen production cost of SCWG system is 23.28 RMB/kg H2. The LCA results show that the environmental benefits of SCW system at high temperatures are significantly better than those of integrated black liquor combustion systems. Finally, a multi-attribute decision making results of the SCWG and SCWO systems show that the optimal reaction temperature is 800 °C.

Long-Term Monitoring of an In Situ Activated Carbon Treatment to Reduce Polychlorinated Biphenyl Availability in an Active Harbor.

Activated carbon-based amendments have been demonstrated as a means of sequestering sediment-associated organic compounds such as polychlorinated biphenyls (PCBs). In a 2012 effort, an activated carbon amendment was placed at a 0.5-acre amendment area adjacent to and underneath Pier 7 at the Puget Sound Naval Shipyard and Intermediate Maintenance Facility, Bremerton, Washington, USA to reduce PCB availability. Multiple postplacement monitoring events over a 3-year period showed an 80%-90% reduction in PCBs, stability of activated carbon, and no significant negative impacts to the benthic community. To further evaluate the long-term performance, a follow-on to the approximately 7-year (82-month) postplacement monitoring event was conducted in 2019. The results of in situ porewater and bioaccumulation evaluations were consistent with previous observations, indicating overall PCB availability reductions of approximately 80%-90% from preamendment conditions. Multiple measurement approaches for quantifying activated carbon and amendment presence indicated that the amendment was present and stable in the amendment area and that the activated carbon content was similar to levels observed previously. As in the previous investigation, benthic invertebrate community metrics indicated that the amendment did not significantly impair benthic health. An application of carbon petrography to quantify activated carbon content in surface sediments was also explored. The results were found to correspond within a factor of 1.3 (on average) with those of data for the black carbon content via a black carbon chemical oxidation method, an approach that quantifies all forms of black carbon (including activated carbon). The results suggest that at sites with low soot-derived black carbon content in sediment (relative to the targeted activated carbon dose), the black carbon chemical oxidation method would be a reasonable method for measurement of activated carbon dosage in sediment at sites amended with activated carbon. Environ Toxicol Chem 2022;41:1568-1574. © 2022 SETAC.

Investigation on gas and particle emission characterization of carbon black oxidation process promoted by catalyst/ash

The study of the gas and particle emission characteristics during the oxidation of carbon black particles is the basis for exploring the particle emission characteristics during diesel particulate filter (DPF/CDPF) regeneration process. The gas and particle emission of Printex U (PU) particles oxidation under different oxidation temperatures and sample masses are investigated based on fixed bed and thermogravimetric analysis, and the oxidation processes are conducted under the cooperative effect of catalyst (CeO2)/ash (ZnO). The experimental results show that, with the increase of oxidation temperature, the CO/CO2 concentration, the extent of oxidation (η) and the total emitted solid particulate number (PN) increase, but the average particulate diameter (Da) range reduces from 60 to 100 nm to 20–40 nm. On the other hand, with the increase of PU mass, the CO/CO2 concentration and the total PN increase together, and the Da rises from about 30 nm to 40–160 nm, while the η decreases markedly. Both the CeO2 and ZnO nanoparticles can promote the PU oxidation process, and then reduce CO emissions, which lead to the rise the CO2 emissions. Beneficially, the η and the Da increase under the effect of CeO2 and ZnO, and the total PN decreases sharply. Adding catalyst (CeO2) and ash (ZnO) can effectively reduce the emission of small particle size (<23 nm) during oxidation process, which provides a research basis for controlling the emission of particles below 23 nm during DPF regeneration process.

Doping and defects: The coloring mechanism of black plasma electrolytic oxidation (PEO) films on aluminum alloys

Plasma electrolytic oxidation (PEO) can be used to fabricate black ceramic films on aluminum alloy by adding transition-metal anions into the electrolyte. Although the coloration was attributed to transition-metal oxides, a thorough explanation of the relationship between oxides and black color was required. In this study, black PEO films were created by incorporating ammonium metavanadate or sodium tungstate into the electrolyte. The research focused on alumina band-gap modification to explain the mechanism of black coloring. The absorption spectrum and X-ray photoelectron spectroscopy (XPS) valence band characterization revealed that the bandgap of alumina after doping was significantly narrowed. The density of state of alumina, including before doping, after doping, and introducing point defect was simulated by first-principles density functional theory calculation. It was discovered that doping transition metals into alumina decrease the conduction band while defects in alumina cause an upper shift of the valence band. The narrowing of the bandgap resulted in the absorption of all visible light and the appearance of black.

Real-time observation and quantification of carbon black oxidation in an environmental transmission electron microscope: Impact of particle size and electron beam

Carbon black oxidation is a post-treatment method to control its properties for different applications, and its outcomes may depend on the particle size. Three different sizes of carbon blacks were oxidized in an environmental transmission electron microscope to study the size effect on their oxidation pathway and rate. The oxidation at the nanoscale has been quantified using the ASTM D3849-14a standard method for the carbon blacks and compared with the theory of solid particle burning, i.e., D2 law. This comparison confirms the validity of the diffusion-controlled burning model for all three samples oxidized at 800°C in the presence of oxygen molecules. Electron microscope images show surface burning is the governing mode under this condition. Oxidation under electron-beam irradiation shows that the oxidation rate reduces by ∼0%, 30%, and 80% for particles with 33, 112, and 356 nm in diameter, respectively. The results suggest that the electron beam is causing the atomic bonds to break and transform to the graphitic structure at relatively high temperatures (e.g., 800°C) that causes oxidation rate reduction in larger particles. Despite the reduction in oxidation rate as the initial size of carbon particles increases, observations show that surface burning is the dominant mode under electron-beam irradiation.

Low-temperature deposition process for black phosphate-selenide coatings

Oxide coatings are widely used as protective and decorative coatings on ferrous metals under non-harsh operating conditions. For protective and decorative oxidation, a chemical oxidation method is widely used using concentrated alkaline solutions (600&ndash;800 g/l NaOH) operating at very high temperatures (130&ndash;150 &deg;C). The obvious disadvantages of the process are the high energy consumption, difficult working conditions, the aggressiveness of the solutions used and low protective ability of the coatings due to their high porosity. In addition, it is known that to harden the surfaces of machine parts in order to increase wear resistance, they are thermally laser treated. The surface hardening is the more effective, the higher the absorption coefficient of the treated surface. For laser heat treatment, high-temperature (95&ndash;98 &deg;C) processes of applying black phosphate coatings with a high absorption coefficient (0.8&ndash;0.9) are used. The disadvantages of these processes are also the instability of solutions and the irreproducibility of the results. This work is about to the study of the process of formation of phosphate-selenide coatings on steel in order to replace high-temperature solutions of black oxidation and phosphating. A low-temperature process has been developed for the deposition of black selenide-containing phosphate coatings on steel, corresponding to a point of 10 on a ten-point color scale, in a solution containing: 4&ndash;8 g/l Na2SeO3; 1&ndash;4 g/l CuSO4&sdot;5H2O; 0.5&ndash;5 g/l NaH2PO4 and 0.25&ndash;2.5 g/l Na2HPO4 ([NaH2PO4]/[Na2HPO4] molar ratio is 2); 5 min at pH = 2&ndash;3, t = 18&ndash;25 &deg;C. Oiling the coatings in I-20A industrial oil for 2 min leads to an increase in the protective ability of the coatings according to Akimov from 1 to 25 min. Corrosion tests of coatings in a salt spray chamber in accordance with ASTM B117 have shown that oiled phosphate-selenide coatings have the greatest protective ability: the first spots of red corrosion appear after 20 hours of testing, while oxidized, oiled samples begin to corrode after 18 hours. After 100 hours of testing, the area of the oxidized sample affected by corrosion is 90 %, and the oiled phosphated sample is 50. The work was carried out with the financial support of&nbsp;the Mendeleev University of Chemical Technology. Project&nbsp;number X-2020-027.

Characterizing the dielectric properties of carbon fiber at different processing stages

The polyacrylonitrile (PAN) fibers go through a series of chemical reactions in various processing temperatures/stages and finally turn into the so-called carbon fibers. Oxidization is the first stage, and it takes the largest proportion of the entire processing time for the tremendous change from a chain texture to a ladder texture. The pre-carbonization of carbon fibers is then achieved using a furnace with a higher processing temperature (typically at 700–900 °C). During the reaction processes, the color of the fibers changes from white (PAN) to light black (oxidation), and eventually to black (pre-carbonization). Characterizing the complex permittivity helps us determine the carbonization status of the fibers. This work employed the enhanced-field method (EFM) and the contour mapping method to determine the fibers’ dielectric properties for the first time. Results show that both the real and imaginary parts of permittivity increase as the processing temperature rises. The dielectric constants change from 2.82 (PAN) to 6.50 (pre-carbonization), and the loss tangents increase from 0.007 (lossless) to 0.089 (lossy). This study provides a simple and effective method for characterizing carbon fibers’ processing status and can be applied to the measurement of other fibrous materials.