Multiphase Oxidation Research Articles

Reactive chlorine-, sulfur-, and nitrogen-containing volatile organic compounds impact atmospheric chemistry in the megacity of Delhi during both clean and extremely polluted seasons

Abstract. Volatile organic compounds (VOCs) significantly impact the atmospheric chemistry of polluted megacities. Delhi is a dynamically changing megacity, and yet our knowledge of its ambient VOC composition and chemistry is limited to few studies conducted mainly in winter before 2020 (all pre-COVID-19). Here, using a new extended volatility range high-mass-resolution (10 000–15 000) proton transfer reaction time-of-flight mass spectrometer, we measured and analysed ambient VOC mass spectra acquired continuously over a 4-month period, covering “clean” monsoon (July–September) and “polluted” post-monsoon seasons, for the year 2022. Out of 1126 peaks, 111 VOC species were identified unambiguously. Averaged total mass concentrations reached ∼ 260 µg m−3 and were > 4 times in the polluted season relative to the cleaner season, as driven by enhanced emissions from biomass burning and reduced atmospheric ventilation (∼ 2). Among 111, 56 were oxygenated, 10 contained nitrogen, 2 chlorine, 1 sulfur, and 42 were pure hydrocarbons. VOC levels during polluted periods were significantly higher than most developed world megacities. Methanethiol, dichlorobenzenes, C6 amides, and C9 organic acids/esters, which have previously never been reported in India, were detected in both the clean and polluted periods. The sources were industrial for methanethiol and dichlorobenzenes, purely photochemical for the C6 amides, and multiphase oxidation and partitioning for C9 organic acids. Aromatic VOC / CO emission ratio analyses indicated additional biomass combustion/industrial sources in the post-monsoon season, along with year-round traffic sources in both seasons. Overall, the unprecedented new information concerning ambient VOC speciation, abundance, variability, and emission characteristics during contrasting seasons significantly advances current atmospheric composition understanding of highly polluted urban atmospheric environments like Delhi.

Investigating the Kinetics of Heterogeneous Lipid Ozonolysis by an Online Photoionization High-Resolution Mass Spectrometry Technique.

Lipid oxidation-induced imbalance in the redox system is one of the key causative factors leading to accelerated aging in living organisms and related diseases. Online sampling and analysis of the heterogeneous ozonolysis kinetics of lipid aerosols are highly important in revealing the oxidation-driven aging process of lipids. In this paper, an online detection method based on atmospheric pressure photoionization combined with ultrahigh resolution mass spectrometry (APPI-HRMS) is developed for real-time analysis of the heterogeneous reactions between lipid particles (oleic acid and squalene) and ozone. The online APPI-HRMS technique serves as an ideal platform for analyzing the heterogeneous oxidation of particles, exhibiting remarkable stability, sensitivity, and responsiveness across a wide range of particle concentrations. Owing to the distinctive characteristics of soft ionization, the heterogeneous effective oxidation rate of lipid aerosols was quantitatively measured. This has facilitated the detection of a series of fingerprint particle-phase products, including aldehydes, secondary ozonides, and hydroperoxides. Additionally, the kinetics evolution of these products with the ozone concentration was captured. Consequently, the ability of this online APPI-HRMS technique in assessing the multiphase oxidation of organic particles has been demonstrated, positioning it as a promising and feasible tool for revealing the heterogeneous reactions of particles.

Hydroxyl radical oxidation of chemical contaminants on indoor surfaces and dust

Humans are widely exposed to semivolatile organic contaminants in indoor environments. Many contaminants have long lifetimes following partitioning to the large surface reservoirs present indoors, which leads to long exposure times to gas-phase oxidants and multiphase chemistry. Studies have shown selective multiphase oxidation of organics on indoor surfaces, but the presence of hydroxyl radicals with nonselective reactivity and evidence of multiphase OH radical reactivity toward common indoor contaminants indicates that there may be additional unknown transformation chemistry indoors. We screened genuine indoor samples for 60 OH radical oxidation products of the common plasticizer and endocrine-disrupting contaminant bis(2-ethylhexyl) phthalate (DEHP) identified in laboratory experiments using nontargeted high-resolution mass spectrometry. At least 30 and 10 of these products are observed in indoor dust and DEHP films exposed to ambient indoor conditions, respectively, indicating that multiphase OH reactions occur indoors. Using the PROTEX model and a multimedia indoor chemical fate model, we demonstrate that these products have long indoor lifetimes and cause a higher potential for human exposure than DEHP. Some of these products are more active endocrine disruptors than DEHP itself, but most have unknown toxicities. Coexposure to all oxidation products will likely have an additive effect, leading to higher human health risks from indoor organic contaminants than previously thought. Due to the nonselective reactivity of OH radicals, it is likely that most indoor contaminants follow similar chemistry, and further study is needed to understand the prevalence and human health implications of such multiphase chemistry.

Direct observation of the complex S(IV) equilibria at the liquid-vapor interface

The multi-phase oxidation of S(IV) plays a crucial role in the atmosphere, leading to the formation of haze and severe pollution episodes. We here contribute to its understanding on a molecular level by reporting experimentally determined pKa values of the various S(IV) tautomers and reaction barriers for SO2 formation pathways. Complementary state-of-the-art molecular-dynamics simulations reveal a depletion of bisulfite at low pH at the liquid-vapor interface, resulting in a different tautomer ratio at the interface compared to the bulk. On a molecular-scale level, we explain this with the formation of a stable contact ion pair between sulfonate and hydronium ions, and with the higher energetic barrier for the dehydration of sulfonic acid at the liquid-vapor interface. Our findings highlight the contrasting physicochemical behavior of interfacial versus bulk environments, where the pH dependence of the tautomer ratio reported here has a significant impact on both SO2 uptake kinetics and reactions involving NOx and H2O2 at aqueous aerosol interfaces.

Spontaneous Molecular Bromine Production in Sea-Salt Aerosols.

Bromine chemistry is responsible for the catalytic ozone destruction in the atmosphere. The heterogeneous reactions of sea-salt aerosols are the main abiotic sources of reactive bromine in the atmosphere. Here, we present a novel mechanism for the activation of bromide ions (Br-) by O2 and H2O in the absence of additional oxidants. The laboratory and theoretical calculation results demonstrated that under dark conditions, Br-, O2 and H3O+ could spontaneously generate Br and HO2 radicals through a proton-electron transfer process at the air-water interface and in the liquid phase. Our results also showed that light and acidity could significantly promote the activation of Br- and the production of Br2. The estimated gaseous Br2 production rate was up to 1.55×1010 molecules cm-2 ⋅ s-1 under light and acidic conditions; these results showed a significant contribution to the atmospheric reactive bromine budget. The reactive oxygen species (ROS) generated during Br- activation could promote the multiphase oxidation of SO2 to produce sulfuric acid, while the increase in acidity had a positive feedback effect on Br- activation. Our findings highlight the crucial role of the proton-electron transfer process in Br2 production; here, H3O+ facilitates the activation of Br- by O2, serves as a significant source of atmospheric reactive bromine and exerts a profound impact on the atmospheric oxidation capacity.

The interface interaction within multi-phase oxides on the ablation behavior of the (Hf0.25Zr0.25Ti0.5)C-coated C/C composites

To investigate the effect of the multi-phase Ti-containing oxides on the ablation behavior of (Hf-Zr-Ti)C coating, the (Hf0.25Zr0.25Ti0.5)C coating was prepared on the SiC-coated C/C composites, and their ablation resistance was investigated. After ablation, Ti-poor and Ti-rich areas appeared on the coating surface, corresponding to the Ti-doped m-(Hf, Zr)O2 and o-(Hf, Zr)TiO4, respectively. Their interface interaction on the ablation resistance, microstructural evolution and defect initiation of the coating during ablation was discussed. The combination of the experimental results (SEM/TEM), first-principle calculation (VASP) and finite element simulation (ABAQUS) indicated the latter had poor plastic deformation to resist crack initiation and propagation compared to the former. The mechanical denudation produced the stress concentration, which resulted in some damaged areas appearing at the phase interface between Ti-doped m-(Hf, Zr)O2 and o-(Hf, Zr)TiO4, as well as the grain boundaries of different o-(Hf, Zr)TiO4 grains, in the forms of phase interface cracks and intergranular pores/cracks, respectively. Although these ablative defects accelerated the damage to the coating, without exposed carbon fibers and broken SiC coating after ablation for 120 s, the intact interface between SiC and C/C composites indicated that (Hf0.25Zr0.25Ti0.5)C coating had good ablation protection for C/C composites.

Spontaneous Molecular Bromine Production in Sea‐Salt Aerosols

AbstractBromine chemistry is responsible for the catalytic ozone destruction in the atmosphere. The heterogeneous reactions of sea‐salt aerosols are the main abiotic sources of reactive bromine in the atmosphere. Here, we present a novel mechanism for the activation of bromide ions (Br−) by O2 and H2O in the absence of additional oxidants. The laboratory and theoretical calculation results demonstrated that under dark conditions, Br−, O2 and H3O+ could spontaneously generate Br and HO2 radicals through a proton–electron transfer process at the air–water interface and in the liquid phase. Our results also showed that light and acidity could significantly promote the activation of Br− and the production of Br2. The estimated gaseous Br2 production rate was up to 1.55×1010 molecules cm−2 ⋅ s−1 under light and acidic conditions; these results showed a significant contribution to the atmospheric reactive bromine budget. The reactive oxygen species (ROS) generated during Br− activation could promote the multiphase oxidation of SO2 to produce sulfuric acid, while the increase in acidity had a positive feedback effect on Br− activation. Our findings highlight the crucial role of the proton‐electron transfer process in Br2 production; here, H3O+ facilitates the activation of Br− by O2, serves as a significant source of atmospheric reactive bromine and exerts a profound impact on the atmospheric oxidation capacity.

Enhanced Organic Nitrate Formation from Peroxy Radicals in the Condensed Phase.

Organic alkoxy (RO) and peroxy (RO2) radicals are key intermediates in multiphase atmospheric oxidation chemistry, though most of the study of their chemistry has focused on the gas phase. To better understand how radical chemistry may vary across different phases, we examine the chemistry of a model system, the 1-pentoxy radical, in three phases: the aqueous phase, the condensed organic phase, and the gas phase. In each phase, we generate the 1-pentoxy radical from the photolysis of n-pentyl nitrite, run the chemistry under conditions in which RO2 radicals react with NO, and detect the products in real time using an ammonium chemical ionization mass spectrometer (NH4 + CIMS). The condensed-phase chemistry shows an increase in formation of organic nitrate (RONO2) from the downstream RO2+NO reaction, which is attributed to potential collisional and solvent-cage stabilization of the RO2-NO complex. We further observe an enhancement in the yield of carbonyl relative to hydroxy carbonyl products in the condensed phase, indicating changes to RO radical kinetics. The different branching ratios in the condensed phase impact the product volatility distribution as well as HO x -NO x chemistry, and may have implications for nitrate formation, aqueous aerosol formation, and radical cycling within atmospheric particles and droplets.

Evaluating Possible Formation Mechanisms of Criegee Intermediates during the Heterogeneous Autoxidation of Squalene.

Organic molecules in the environment oxidatively degrade by a variety of free radical, microbial, and biogeochemical pathways. A significant pathway is heterogeneous autoxidation, in which degradation occurs via a network of carbon and oxygen centered free radicals. Recently, we found evidence for a new heterogeneous autoxidation mechanism of squalene that is initiated by hydroxyl (OH) radical addition to a carbon-carbon double bond and apparently propagated through pathways involving Criegee Intermediates (CI) produced from β-hydroxy peroxy radicals (β-OH-RO2•). It remains unclear, however, exactly how CI are formed from β-OH-RO2•, which could occur by a unimolecular or bimolecular pathway. Combining kinetic models and multiphase OH oxidation measurements of squalene, we evaluate the kinetic viability of three mechanistic scenarios. Scenario 1 assumes that CI are formed by the unimolecular bond scission of β-OH-RO2•, whereas Scenarios 2 and 3 test bimolecular pathways of β-OH-RO2• to yield CI. Scenario 1 best replicates the entire experimental data set, which includes effective uptake coefficients vs [OH] as well as the formation kinetics of the major products (i.e., aldehydes and secondary ozonides). Although the unimolecular pathway appears to be kinetically viable, future high-level theory is needed to fully explain the mechanistic relationship between CI and β-OH-RO2• in the condensed phase.

Multiphase manganese-based layered oxide for sodium-ion batteries: structural change and phase transition

Sodium-ion batteries (SIBs) are recognized as a leading option for energy storage systems, attributed to their environmental friendliness, natural abundance of sodium, and uncomplicated design. Cathode materials are crucial in defining the structural integrity and functional efficacy of SIBs. Recent studies have extensively focused on manganese (Mn)-based layered oxides, primarily due to their substantial specific capacity, cost-effectiveness, non-toxic nature, and ecological compatibility. Additionally, these materials offer a versatile voltage range and diverse configurational possibilities. However, the complex phase transition during a circular process affects its electrochemical performance. Herein, we set the multiphase Mn-based layered oxides as the research target and take the relationship between the structure and phase transition of these materials as the starting point, aiming to clarify the mechanism between the microstructure and phase transition of multiphase layered oxides. Meanwhile, the structure-activity relationship between structural changes and electrochemical performance of Mn-based layered oxides is revealed. Various modification methods for multiphase Mn-based layered oxides are summarized. As a result, a reasonable structural design is proposed for producing high-performance SIBs based on these oxides.

Microstructure evolution and phase interface characterization in anti-ablation (Hf1/4Zr1/4Ta1/4Ti1/4)C-coated C/C composites

Ta and Ti elements are often used as modified components to densify the loose oxide film for HfC/ZrC coatings after long-term ablation, while the synergistic effect among their multi-phase oxides on the ablation resistance of the coatings for C/C composites is still being explored. In this work, a (Hf1/4Zr1/4Ta1/4Ti1/4)C high-entropy carbide ceramic was proposed as an advanced anti-ablation coating for C/C composites and the multicomponent synergistic effect on the ablative behavior was investigated. At the initial ablation, the O atoms first reacted with Hf and Zr elements to form m-(Hf, Zr)O2. The TiO2 was prone to decompose into TiO and then evaporated from the coating during ablation, slowing down the volatilization of Ta2O5. The remaining TiO2 and Ta2O5 diffused to m-(Hf, Zr)O2 and produced a phase transition from Ta/Ti-doped m-(Hf, Zr)O2 to o-(Hf, Zr)6Ta2O17/o-(Hf, Zr)TiO4. The formation of nanotwin between (Hf, Zr)6Ta2O17 and (Hf, Zr)TiO4 enhanced the toughness of the oxide film. Although excessive Ta2O5 broke the stability of the oxide film, the Hf-Zr-rich oxide skeleton (Ta/Ti-doped (Hf, Zr)O2, (Hf, Zr)6Ta2O17 and (Hf, Zr)TiO4)) ensured that C/C substrates were intact after ablation for 180 s, showing superior ablation resistance.

Preparation and ablation behavior analysis of non-equimolar Cf/(Hf1/2Zr1/3Ti1/6)C composites under oxyacetylene flame with different heat fluxes

In this study, the synthesis of Cf/(Hf1/2Zr1/3Ti1/6)C non-equimolar middle-entropy composites was reported through precursor infiltration and pyrolysis processing for the first time. The pyrolysis process of the (Hf1/2Zr1/3Ti1/6)C precursor was examined by XRD, while the resultant ceramic was characterized by SEM, EDS, and TEM. The results showed that precursor-derived (Hf1/2Zr1/3Ti1/6)C powders were characterized by single-phase and uniformly distributed elements from microscale to nanoscale. The Cf/(Hf1/2Zr1/3Ti1/6)C composites exhibited a density of 2.741 g/cm3 and a porosity of 11.49 vol%. The various elements were uniformly distributed throughout the material. It also demonstrated outstanding mechanical properties, with a flexural strength of 219.34 MPa and a modulus of 24.82 GPa. At the heat flux of 3 MW/m2, the oxides after ablation were inadequate to fully envelop the substrate. When the heat flux increased to 4 MW/m2, a dense Hf-Zr-Ti-O multiphase oxide layer was formed on the surface of the sample, providing the internal Cf/(Hf1/2Zr1/3Ti1/6)C composites against further ablation. At the heat flux of 5 MW/m2, (Hf, Zr)TiO4 was severely consumed. Our research expands the application scope of non-equimolar middle-entropy composites in the domain of ultra-high temperature ablation resistance.

Microstructure and anti-ablation of laser cladding Ti-Zr-B-C coating on TC11 titanium alloy

To enhance the service life and application range of titanium alloys in the aerospace sector, Ti-Zr-B-C coatings with varying B4C contents (0–30 wt%) on TC11 titanium alloy was fabricated by laser cladding. The microstructure and anti-ablation were investigated in the present work. The results show that the whisker-like TiB phases and granular TiC and ZrC phases were observed in the coatings due to the in-situ reactions. With increasing the content of B4C, the number of reinforcing phases in the coating increased and distributed uniformly, resulting in the improvement of the microhardness up to 803.8HV. Furthermore, due to the formation of TiO2-ZrO2-B2O3 dense multiphase oxide layer on the surface during the ablation process, the coating with 20 wt% B4C exhibited the best anti-ablation at 1400ºC, the mass ablation rate (MAR) and linear ablation rate (LAR) were −2.62 mg/s and 3.67μm/s, respectively, which were just 62.8 % and 50.07 % in comparison with the substrate. This is mainly attributed to the formation of TiO2-ZrO2-B2O3 layer is beneficial to reduce the infiltration of O2 and the evaporation of liquid B2O3, leading to the excellent anti-ablation.

Relative Humidity Modulates the Physicochemical Processing of Secondary Brown Carbon Formation from Nighttime Oxidation of Furan and Pyrrole.

Light-absorbing secondary organic aerosols (SOAs), also known as secondary brown carbon (BrC), are major components of wildfire smoke that can have a significant impact on the climate system; however, how environmental factors such as relative humidity (RH) influence their formation is not fully understood, especially for heterocyclic precursors. We conducted chamber experiments to investigate secondary BrC formation from the nighttime oxidation of furan and pyrrole, two primary heterocyclic precursors in wildfires, in the presence of pre-existing particles at RH < 20% and ∼ 50%. Our findings revealed that increasing RH significantly affected the size distribution dynamics of both SOAs, with pyrrole SOA showing a stronger potential to generate ultrafine particles via intensive nucleation processes. Higher RH led to increased mass fractions of oxygenated compounds in both SOAs, suggesting enhanced gas-phase and/or multiphase oxidation under humid conditions. Moreover, higher RH reduced the mass absorption coefficients of both BrC, contrasting with those from homocyclic precursors, due to the formation of non-absorbing high-molecular-weight oxygenated compounds and the decreasing mass fractions of molecular chromophores. Overall, our findings demonstrate the unique RH dependence of secondary BrC formation from heterocyclic precursors, which may critically modulate the radiative effects of wildfire smoke on climate change.

Significantly Accelerated Photosensitized Formation of Atmospheric Sulfate at the Air-Water Interface of Microdroplets.

The multiphase oxidation of sulfur dioxide (SO2) to form sulfate is a complex and important process in the atmosphere. While the conventional photosensitized reaction mainly explored in the bulk medium is reported to be one of the drivers to trigger atmospheric sulfate production, how this scheme functionalizes at the air-water interface (AWI) of aerosol remains an open question. Herein, employing an advanced size-controllable microdroplet-printing device, surface-enhanced Raman scattering (SERS) analysis, nanosecond transient adsorption spectrometer, and molecular level theoretical calculations, we revealed the previously overlooked interfacial role in photosensitized oxidation of SO2 in humic-like substance (HULIS) aerosol, where a 3-4 orders of magnitude increase in sulfate formation rate was speculated in cloud and aerosol relevant-sized particles relative to the conventional bulk-phase medium. The rapid formation of a battery of reactive oxygen species (ROS) comes from the accelerated electron transfer process at the AWI, where the excited triplet state of HULIS (3HULIS*) of the incomplete solvent cage can readily capture electrons from HSO3- in a way that is more efficient than that in the bulk medium fully blocked by water molecules. This phenomenon could be explained by the significantly reduced desolvation energy barrier required for reagents residing in the AWI region with an open solvent shell.

Important Role of Low Cloud and Fog in Sulfate Aerosol Formation During Winter Haze Over the North China Plain

AbstractSulfate aerosol greatly contributes to wintertime haze pollution in emission‐intensive regions like the North China Plain (NCP) in China. Fast sulfate increase and accumulation are usually recorded during winter haze; however, the multiphase oxidation of sulfur dioxide (SO2) and the physical processes affecting near‐surface sulfate are not fully understood. By combining in situ observations and numerical simulations, we found that high sulfur oxidation ratios (&gt;0.6) under heavily polluted conditions are associated with low clouds and fog over NCP, induced by the moist southerly airflow. Thick low clouds and high SO2 levels in NCP provide a reaction environment for sulfate production. The sulfate production rate in cloud water can reach 0.5–1.3 μg m−3 h−1. The results demonstrate that the vertical mixing of sulfate generated within the cloud water to the surface plays a significant role in rapid sulfate production, highlighting the importance of understanding cloud‐water processes in haze pollution.

Self-Assembly Dual Active Site Nanocomposite Anode Ce0.6Mn0.3Fe0.1O2-δ/NiFe/MnOx for Electrooxidative Dehydrogenation of Ethane to Ethylene.

As the demand for ethylene grows continuously in industry, conversion of ethane to ethylene has become more and more important; however, it still faces fundamental challenges of low ethane conversion, low ethylene selectivity, overoxidation, and instability of catalysts. Electrooxidative dehydrogenation of ethane (EODHE) in a solid oxide electrolysis cell (SOEC) is an alternative process. Here, a multiphase oxide Ce0.6Mn0.3Fe0.1O2-δ-NiFe-MnOx has been fabricated by a self-assembly process and utilized as the SOEC anode material for EODHE. The highest ethane conversions reached 52.23% with 94.11% ethylene selectivity at the anode side and CO with 10.9 mL min-1 cm-2 at the cathode side, at 1.8 V at 700 °C. The remarkable electrooxidative performance of CMF-NiFe-MnOx is ascribed to the NiFe alloy and MnOx nanoparticles and improvement of the concentration of oxygen vacancies within the fluorite substrate, generating dual active sites for C2H6 adsorption, dehydrogenation, and selective transformation of hydrogen without overoxidizing the ethylene generated. Such a tailored strategy achieves no significant degradation observed after 120 h of operation and constitutes a promising basis for EODHE.

The synergistic effect of multi-phase oxides on the ablation resistance of TaC-modified HfC-ZrC coatings for C/C composites

Traditional HfC- and ZrC-based coatings for C/C composites had loose oxide films after long-term ablation, limiting their application above 2000 ℃. In this work, through adjusting the TaC content, the formation of stable and dense Hf-Zr-Ta-O compound films composed of Ta-doped (Hf, Zr)O2 and (Hf, Zr)6Ta2O17 prolonged the service life of HfC-ZrC coating. Additionally, the first-principle calculation based on the VASP software helped to understand the solid solution process among multi-component oxides (HfO2, ZrO2 and Ta2O5) of TaC-modified HfC-ZrC coatings during ablation. As for HfC-ZrC coating, the formed (Hf, Zr)O2 skeleton was loose and hard to resist long-term ablation (less than 180 s). A small amount of Ta2O5 diffused to (Hf, Zr)O2 and produced the stable and dense Ta-doped (Hf, Zr)O2 and (Hf, Zr)6Ta2O17 oxide films, increasing the ablation resistance of the HfC-ZrC-TaC coating (5:5:1, more than 180 s). Excessive Ta2O5 was damaged by mechanical denudation during ablation, failing HfC-ZrC-TaC coatings (3:3:1 less than 180 s and 1:1:1 less than 120 s).

Kinetics of the Reaction MSI− + O3 in Deliquesced Aerosol Particles: Implications for Sulfur Chemistry in the Marine Boundary Layer

AbstractMultiphase oxidation of methane sulfinic acid (MSIA) by ozone (O3) in deliquesced aerosol particles is an important but poorly constrained reaction in the marine boundary layer, hindering the accurate prediction of radiative forcing of natural aerosols. Large uncertainties arise from the unmeasured reaction rate constant for the aerosol multiphase reaction between O3 and methanesulfinate (MSI−), the dominant MSIA species in sea salt aerosols. Here, we directly measured by performing flow cell experiments coupled with a Raman spectroscopy to investigate the kinetics of multiphase oxidation of MSI− by O3 in pH‐buffered deliquesced aerosol particles relevant to marine atmospheric conditions. for aerosol particles was determined to be (2.2 ± 0.5) × 107 M−1 s−1, 10 times the value in dilute solutions. This higher rate constant would increase the yield of methane sulfonic acid from multiphase oxidation of MSIA and has important implications for accurate modeling of sulfur species.

High-temperature self-healing behavior of reaction-bonded silicon carbide porous ceramic membrane supports

Reaction-bonded silicon carbide porous ceramics (SCPCs) are increasingly employed as membrane supports for the high-temperature filtration. However, the inevitable expansion of cracks limits their application. Herein, we studied the crack propagation behavior of SCPCs and discovered the commendable self-healing properties at high temperatures. Results show that the optimal healing conditions are 1200 °C for 2 h, which can recover the strength from 41.9% to 88.4%, and maintain the initial pore structure and permeance. This is mainly attributed to the infiltration of the multi-phase oxide melt that healed the cracks rather than the oxidation of SiC. Neck cracks are more prone to healing than surface cracks on SiC particles due to the residual compressive stress and a high proportion of melt volume. Nonetheless, the recovery of residual compressive stress and the crack width constrain the upper limit of strength recovery. These insights lay the groundwork for the high-temperature industrial application of SCPCs.