Protective Layer Research Articles

Additive manufactured ODS-FeCrAl steel achieves high corrosion resistance in lead-bismuth eutectic (LBE)

Developing corrosion resistant alloys used in lead-bismuth eutectic (LBE) is essential for lead-cooled fast reactors (LFRs). In this work, additive manufacturing was applied to fabricate oxide dispersion-strengthened FeCrAl steels (ODS and Y-ODS), and the latter contains 1.5 wt.% Y2O3 nanoparticles. After exposure in LBE at 450 °C for 1000 hours, both alloys generate a compact, uniform and stable Cr2O3/Al2O3 protective oxide layer (below 200 nm). Benefits from the quick transient oxidation rate at the initial stage, the oxide layer realizes a slow oxidation kinetics and achieves high corrosion resistance to LBE attack. More importantly, the addition of Y2O3 induce the formation of Y-Al-O-type oxide nanoparticles which provides an additional source of Al3+ at the interface and promotes the growth of an internal oxide layer within Al2O3, and thus subsequently the oxides layer demonstrates remarkable stability. This study highlights the potential application of additive manufacturing in advanced materials for LFRs.

Study on the anti-ablation behavior of (Ti,W)3AlC2 under oxyacetylene flame above 2500 K

To evaluate the reliability of (Ti,W)3AlC2 in aerospace ablation conditions, the ablation behavior of (Ti,W)3AlC2 ceramic is investigated by using oxyacetylene flame above 2550 K. Results show a four-stage process exists with the formation of TiO2-Al2TiO5-Al2O3. Once the central ablation temperature exceeds 2350 K, the innermost Al2O3 layer melts and collapses, exposing the decomposed TiCx-Al matrix directly to the flame with rapid oxidation and a remarkable increase of the linear ablation rate. The melt finally flows out with the flame from the ablation center and solidifies into a stripe-like TiO2-Al2TiO5 eutectic oxide above the protective oxide layer. The refractory W particles detected in the eutectic TiO2-Al2TiO5 may retard the flowing rate of the fluid by increasing its viscosity, resulting in a better ablation resistance performance in the later period of the ablation process, making the linear ablation rate lower from 10.30 μm/s of Ti3AlC2 to 9.01 μm/s of (Ti,W)3AlC2.

Enhancing dry sliding wear resistance of high-Mn austenitic steel by adding N

In this study, the wear resistance of two high-Mn austenitic steels, i.e., Fe−18.5Mn−7Cr−0.6C and Fe−18.5Mn−7Cr−0.6C−0.21N was tested in dry sliding friction on a disc friction and wear testing machine (MMU-5G). The wear behavior and microstructure evolution of the two tested steels were investigated. The results revealed that adding N enhanced the wear resistance of high-Mn austenitic steel due to the synergistic effects of hardness, wear hardening, and oxide layer. Interstitial N atoms increased the matrix hardness and decreased the stacking fault energy (SFE). The lower SFE facilitated wear hardening, and the active mechanical twins along with the higher dislocation density induced the formation of a thicker nanocrystalline layer with finer grains. The nanocrystalline layer with higher surface activity promoted the adsorption of a protective oxide layer. These factors decreased the surface roughness, coefficient of friction (COF), and wear rate of N-alloyed high-Mn austenitic steel. This study provided valuable insights into the application of N-alloyed high-Mn austenitic steels under dry sliding friction conditions.

The Corrosion-Inhibitory Influence of Graphene Oxide on Steel Reinforcement Embedded in Concrete Exposed to a 3.5M NaCl Solution

Steel reinforcement corrosion significantly reduces the durability and service life of concrete structures, particularly in chloride-rich environments such as marine and coastal areas. This study aims to reduce the corrosion rate using graphene oxide (GO) as a corrosion inhibitor. Two GO dosages (0.0005 and 0.005 wt.%) were evaluated for their effectiveness in mitigating corrosion in reinforced concrete exposed to a 3.5M NaCl solution. To assess the corrosion behavior of the steel reinforcement, Open Circuit Potential (OCP), Electrochemical Impedance Spectroscopy (EIS), and Linear Polarization Resistance (LPR) were evaluated to monitor corrosion over one year by of wetting/drying cycles. Oxygen permeability and electrical resistivity tests were also conducted to evaluate the concrete's susceptibility to corrosion. Both GO content demonstrated significant corrosion inhibition, with the 0.005 wt.% dosage providing the most effective protection. This was evidenced by the lowest icorr values recorded during the final cycle (52), larger capacitive loops, and higher impedance in EIS results, indicating enhanced corrosion resistance. Visual inspection of steel bars further confirmed these findings, showing no signs of deterioration or discoloration in GO-modified concrete compared to steel bars extracted from reference concrete. SEM-EDS analysis revealed higher carbon content on the steel surface, suggesting GO adsorption and the formation of a protective passive layer. These results suggest that GO is a promising nanomaterial for inhibiting corrosion in steel-reinforced concrete exposed to aggressive environmental conditions.

Enhancing high-temperature wear resistance of plasma-sprayed NiCrBSi coatings with nanodiamond reinforcement

High-temperature wear causes industrial components to degrade quickly, leading to reduced efficiency, frequent breakdowns, and costly repairs. Thermal spraying is a surface modification technique employed to address these wear issues by shielding the component using protective coatings. In this study, the high-temperature wear behavior of plasma-sprayed NiCrBSi coatings reinforced with Nanodiamond (ND) particles was systematically evaluated. The coatings were reinforced with 1 wt% and 2 wt% ND, and their tribological performance was assessed under varying thermal conditions. Tribological tests were conducted using a ball-on-disk setup at elevated temperatures of 473 K, 673 K, and 873 K for 60 min. The experimental results demonstrated a significant improvement in the wear response and frictional characteristics of the NiCrBSi coatings with the incorporation of ND particles. Specifically, the NiCrBSi coating reinforced with 2 wt% ND exhibited a significantly lower wear volume loss and a reduced coefficient of friction when compared to the pure NiCrBSi coating. At 873 K, the NiCrBSi-2ND coating demonstrated a 64 % reduction in wear volume loss and 85 % decrease in the coefficient of friction, compared to the pure NiCrBSi coating. The incorporation of NDs greatly enhanced the lubrication and hardness of the NiCrBSi-2ND coating as well as improved the adhesion of wear debris to the newly exposed wear track. The high thermal conductivity of NDs enhanced heat transfer to the coatings, facilitating the formation of a protective tribo layer at elevated temperatures, which improved the wear resistance of the NiCrBSi-2ND coating. These findings underscore the potential of ND as a reinforcing agent to significantly enhance the durability and efficiency of NiCrBSi coatings in extreme thermal environments.

Synthesis of polyaniline tannate-modified carbon nanotubes by oxidative copolymerization as highly efficient corrosion inhibitors for mild steel in HCl solution

Corrosion is a prevalent issue in industrial production, directly impacting the production process and causing severe damages. To mitigate this problem, corrosion inhibitors are highly desired. Herein, a novel type of nano corrosion inhibitor, referred to as PTCNT, was synthesized through an oxidative copolymerization method utilizing aniline, ammonium persulfate (APS), and tannic acid (TA)-modified multiwalled carbon nanotubes (MWCNTs). The results demonstrated that the PTCNT effectively inhibited the corrosion of mild steel in 1 M HCl solution, achieving the corrosion inhibition efficiency of 90.6 % at the concentration of 75 mg/L. Characterization results implied that the PTCNT adsorbed onto the surface of the mild steel, forming a protective shielding layer. Potentiodynamic polarization measurements proved that the PTCNT functioned as the hybrid corrosion inhibitor. Furthermore, the adsorption of PTCNT on the mild steel surface was investigated using adsorption isotherm and adsorption kinetic modeling. Quantum chemical calculations were used to elucidate the adsorption mechanism of PTCNT. These findings raise new avenues for the development of highly efficient corrosion inhibitors for the mild steel in HCl solutions.

Three-dimensional PDC-SiBCN network in MA-SiBCN ceramics: Toughening-reinforcing effect and oxidation barrier

A three-dimensional (3D) precursor-derived (PDC) SiBCN network was incorporated into mechanical alloying-derived (MA) SiBCN (MA@PDC-SiBCN) ceramic through a novel hybrid organic-inorganic method, enhancing densification while providing significant reinforcement and toughening effects. The PDC-SiBCN network's submicron continuity and uniformity enable efficient load transfer between under-sintered MA-SiBCN particles, increasing strength by 130%, compared to MA-SiBCN ceramics of the same density. Additionally, as cracks penetrate the PDC-SiBCN network, crack tip deflection and bifurcation result in 57% and 352% increases in fracture toughness respectively, compared to fully sintered and under-sintered MA-SiBCN ceramics of the same density. Besides, due to synergistic oxidation characteristics, the three-dimensional PDC-SiBCN network acts as an oxidation barrier, inhibiting the heterogeneous oxidation of the encapsulated MA-SiBCN component, especially limiting the consumption of BN(C) phase at lower temperatures. The residual PDC-SiBCN network in the oxide layer serves as a rigid framework, preventing bubble growth in the molten oxide layer thereby forming a dense protective oxide layer.

Numerical Analysis on Three-phase Coaxial HTS Cable With Copper Protective Layers

Numerical Analysis on Three-phase Coaxial HTS Cable With Copper Protective Layers

Efficient sodium ion transport enhanced by anionophilic sites in polymer-supported plastic crystal electrolyte for high performance sodium metal anode

The design of sodium metal batteries (SMBs) is seen as an excellent solution to solve the request of next-generation energy storage technologies with high energy density, high safety, low cost, and environmental friendliness. However, the direct use of sodium metal as an anode produces the dendritic sodium, which harms the normal operation of battery. Inspired by solid-state lithium metal batteries, solid-state electrolyte (SSE) designed for SMBs effectively solves this shortcoming. Herein, a novel SSE with mask-based polymer membrane supporting plastic crystal electrolyte with ZIF-67 (MPPZ) is designed. The experimental results and density functional theory (DFT) calculations indicate that the addition of ZIF-67 in MPPZ electrolyte availably fixes TFSI− and achieves high Na+ transference number. Additionally, a protective layer of NaF is formed in situ on the surface of sodium metal to avoid side reactions between Na and MPPZ electrolyte while further guide the uniform deposition of Na. Accordingly, Na||Na symmetric battery with NaF-coated Na metal anode and MPPZ electrolyte has a stable deposition and stripping of Na for 3000 h. The assembled room temperature solid-state sodium-sulfur battery (RTSSSSB) exhibits a good cycle stability. This study provides an innovative thinking for the construction of high performance dendrite-free SMBs.

Tumor microenvironment activated MXene-protected Cu2O heterojunctions induce tumor-specific cuproptosis for enhanced sono-immunotherapy

The utilization of a copper ionophore to induce programmed cell death, known as cuproptosis, shows potential in augmenting the efficacy of traditional anticancer treatments and eliciting robust adaptive immune responses. Nevertheless, the non-tumor-specific release of Cu ions may initiate cuproptosis and cause irreversible damage to normal tissues. Herein, this work reports for the first time the regulation of degradation behaviors of Cu-based nanomaterials using Ti3C2Tx nanosheets as a protection layer to maximize the therapeutic effects of tumor-specific cuproptosis. A Z-scheme heterojunction termed Cu2O/Ti3C2Tx is facilely constructed by coating Ti3C2Tx nanosheets on the surface of Cu2O nanocubes. The fabrication of heterojunctions not only improves the sonodynamic and chemodynamic activities of Cu2O nanocubes owing to the manipulation of electron-hole transfer process, but also avoids the degradation of Cu2O nanocubes under normal physiological conditions. The tumor-specific released Cu ions not only realized the cascade amplification of ROS generation through Cu+-mediated Fenton-like reaction and Cu2+-facilitated GSH depletion, but also triggered cuproptosis through Cu+-induced DLAT oligomerization and mitochondrial dysfunction. More importantly, the immunosuppressive TME could be reversed by the greatly enhanced ROS levels and high-efficiency cuproptosis, ultimately inducing immunogenic cell death that promotes robust systemic immune responses for the eradication of primary tumors and suppression of distant tumors. This work provides a promising perspective for potential cancer treatment based on tumor-specific cuproptosis by controlling the degradation behaviors of Cu-based nanomaterials.

Performance optimization of AlN ultrasonic thin-film sensors deposited by RF magnetron sputtering

The AlN thin-film ultrasonic transducers were deposited by reactive RF magnetron sputtering technique. The effects of deposition parameters: target-substrate distance, argon-nitrogen flow ratio, deposition time, substrate temperature and radial distance from the deposition center on the ultrasonic performance of AlN thin films were studied. A metal electrode layer was deposited on the AlN film transducer to fabricate an ultrasonic temperature sensor, and the effects of the size and thickness of the electrode layer on the performance of the sensor were studied. Piezoelectric response measurements were performed in air over a temperature range of −60 °C–900 °C, and the dependence of ultrasonic response (time-of-flight and pulse echo amplitude) on temperature was analyzed. Long-term heat treatment in air at 750 °C for 128 h showed that the high-entropy alloy oxide protective layer could effectively delay oxidation of the AlN layer and improve the service life of the sensor.

Enhancement of an intumescent fire shield paint from the nanotube rutile mineral for the fire performance of steel structures

Building and construction fire safety is an important issue for the protection of people and property. Research investigates nano-rutile minerals' synergistic role in intumescent fire shield paint (IFSP). A synergistic ingredient was introduced to intumescent fire shield paint to evaluate its impact on char morphology, fire protection test, fire propagation test, and compare it with current market products. A hydrothermal process was used to create a rutile mineral, with various techniques used to describe its structure, size, and composition. Intumescent char was found in a furnace using FESEM and X-ray fluorescence. The results showed that rutile minerals contain a rutile phase and a nanotube structure. The surface of the sample IFSP A's char showed layer and foam structures with homogenous voids during a fire test, indicating a high porosity structure. Large holes and recurring gaps were observed in the char of the IFSP B, C, and D. Sample IFSP A took more time at the structural critical temperature (about 550 o C) than other intumescent fire shield paint samples, making it a barrier layer that effectively shields the metal substrate from heat. The intumescent char residue had the highest C/O ratio of 0.57, indicating the best char yield degree and anti-oxidation abilities. The IFSP A had a phosphorous content of 36.2%, which could combine with phosphorus and TiO2 to form a ceramic barrier. The increased TiO2 in IFSP A suggests that char layers with TiO2 may still contain strong ceramic structures and function as effective thermal protection layers.

NiFe pyrophosphate enables long-term alkaline seawater oxidation at an ampere-level current density

Seawater electrolysis has potential for scalable hydrogen (H₂) production, yet anode corrosion by chloride ions (Cl⁻) remains a critical challenge. Herein, we present an amorphous NiFe pyrophosphate (P2O74−) on Ni foam (NiFe-PPi/NF) for long-term alkaline seawater oxidation (ASO). Ex situ and in situ characterizations demonstrate that the in situ released P2O74− can act as an anion protective layer, effectively repelling Cl⁻ and safeguarding high-valence active metal sites during ASO. Through surface-anticorrosion design, NiFe-PPi/NF demonstrates stable operation at 1000 mA cm⁻2 for over 1000 hours with no loss in activity and requires a low overpotential of just 370 mV to achieve this industrial current density in alkaline seawater. This study offers a valuable strategy for developing corrosion-resistant anodes for ASO.

In-depth investigation of corrosion inhibition mechanism: Computational, electrochemical, and theoretical studies of vanillin meldrum’s acid on mild steel surface in 1 M HCl

Vanillin Meldrum’s acid (VanMA) was successfully synthesized and thoroughly examined using techniques like elemental analysis, FTIR, NMR, UV–Vis spectroscopies, and single crystal X-ray diffraction. It crystallizes in a triclinic crystal system under the P-1 space group. A quantitative analysis of the intermolecular interactions in the crystal structures was performed using Hirshfeld surface analysis, which reveals that H···H contacts are the most significant contributing 43.2 % and the O···H/H···O contacts contributing 36.2 % of the total Hirshfeld surfaces. VanMA proved effective as a corrosion inhibitor in 1 M HCl, demonstrating a 62.19 % inhibition efficiency at an optimal concentration of 0.1 mM. It creates a protective layer on mild steel surfaces, adhering to the Freundlich adsorption isotherm (R2 = 0.9983) and displaying a physical adsorption mechanism (−12.72 kJ/mol). The corrosion inhibition efficacy of VanMA (0.1 mM) decreases in 1 M HCl as the temperature increases from 303 to 383 K. A shift towards physisorption is indicated by the increase in activation energy (Ea) from 12.37 to 16.42 kJ/mol. VanMA’s adsorption efficacy reduces at higher temperatures, increasing surface exposure and corrosion rates, but increasing activation enthalpy (ΔH° = 31.32 kJ/mol) and ΔS° = −113.63 J mol−1 K−1). The diameter of the semicircle rose as the concentration of VanMA increased, indicating that VanMA adsorption is responsible for the mild steel surface’s greater resistance to corrosion with increasing Rct values from 224 to 641 Ω cm2 and decreasing capacitance double layer (Cdl) values from 4.480 × 10−5 to 1.560 × 10−5 μFcm2, confirming VanMA’s efficacy as a corrosion inhibitor at 65.05 %. The SEM-EDX and AFM images show the smoother mild steel surface at 0.1 mM VanMA. VanMA was verified as a mixed-type inhibitor by showing shifts of less than 85 mV with respect to the blank PDP. The inhibition efficiency (IE%) increased up to 77.89 % while the icorr values decreased to 1.1850 × 10−5 A/cm2 as the VanMA concentration rose. In XPS, the presence of VanMA was identified by the presence of FeO (713.60 eV) and CO (287.93 eV), which signifies the adsorption of VanMA onto mild steel by the O atom and the negatively charged O ion via a mixed adsorption. DFT and Mulliken population analysis deduced that the VanMA interacted with the mild steel through mixed adsorption. VanMA adsorbs almost parallel to the Fe (1 1 0) surface, forming a barrier that protects from corrosion, according to the MD modeling. While the significant negative adsorption energy (−309.490 kcal/mol) verifies the stability and spontaneity of the adsorption process.

A hole-selective hybrid TiO2 layer for stable and low-cost photoanodes in solar water oxidation

The use of conductive and corrosion-resistant protective layers represents a key strategy for improving the durability of light absorber materials in photoelectrochemical water splitting. For high performance photoanodes such as Si, GaAs, and GaP, amorphous TiO2 protective overlayers, deposited by atomic layer deposition, are conductive for holes via a defect band in the TiO2. However, when coated on simply prepared, low-cost photoanodes such as metal oxides, no charge transfer is observed through amorphous TiO2. Here, we report a hybrid polyethyleneimine/TiO2 layer that facilitates hole transfer from model oxides BiVO4 and Fe2O3, enabling access to a broader scope of available materials for practical water oxidation. A thin polyethyleneimine layer between the light absorber and the hybrid polyethyleneimine/TiO2 acts as a hole-selective interface, improving the optoelectronic properties of the photoanode devices. These polyethyleneimine/TiO2 modified photoanodes exhibit high photostability for solar water oxidation over 400 h.

Achieving the dendrite-free zinc anode by constructing a Sn-C interfacial layer with zincophilic and conductive network

Under the basic national policy of sustainable green development, high-performance and low-cost energy storage devices are urgently needed for intermittent generation of clean energy and storage of electrical energy. Zn metal with high capacity, abundant reserves and excellent plasticity, but the inevitable side reactions (hydrogen precipitation and corrosion, etc.) of the Zn metal anode itself have severely limited the development of aqueous Zn ion batteries (AZIBs) in the market. In this study, an artificial protective layer of polymer-derived carbon material combined with Sn is prepared to inhibit hydrogen precipitation and corrosion and prolong the lifetime of AZIBs. With these advantages, the Zn@Sn@N doped carbon (Zn@CNS) symmetric cell could achieve a stable cycle life of 1000 h at 2 mA cm-2 and low overpotential. The excellent stripping life of over 400 h is achieved in half-cells assembled with Cu foils. Furthermore, the α-MnO2//Zn@CNS full battery shows superior stability in rate capability and long-term capacity retention compared to the α-MnO2//Zn battery, indicating that the CNS coating provides excellent performance and practical value.

Blast response and protection level of concrete composite wall panels made with recycled tyre fibres in a cement matrix

This paper investigates the blast response and protection level of a new blast-resistance wall panels made of Recycled Tyre Fibres Concrete (RTFC) as an exterior protective layer compositely connected to a concrete wall through experiments and numerical modelling. RTFC is a novel sustainable cement-based versatile composite, made with recycled non-biodegradable material (tyre rubber particles) in the form of composite fibres in a cement matrix, with applications in blast and ballistic protection that features high dynamic properties. Three composite wall panels were constructed and subjected to blast loads generated by Advanced Blast Simulator (ABS). Three different loading scenarios, each with an intensity capable of causing complete structural failure, were applied. The blast wave characteristics, such as the imposed overpressure and impulse, were measured alongside the deflection of the specimens. The wall specimens could withstand the blast loads with minimal damage. No cracks were observed in the RTFC layer, with only minor cracks appearing on the concrete side of the wall. The protection performance of the wall specimens was examined following UFC guidelines, revealing their outstanding resistance to blast loads. Moreover, in line with these guidelines, the composite wall panel is eligible for a High Level of Protection (HLoP) classification. Finally, a Single Degree of Freedom (SDOF) analytical model was developed for the wall panel to determine the Dynamic Increase Factor (DIF) of RTFC. The analysis resulted in a DIF value of 1.5, which was then incorporated into the numerical models of the walls. The accuracy of the DIF was validated by comparing the numerical results with experimental data, confirming its reliability.

Supercritical CO2 assisted bioMOF drug encapsulation and functionalization for delivery with a synergetic therapeutic value

Despite the impressive characteristics of biological metal organic frameworks (bioMOFs) for their use as drug delivery systems (DDs), there are still some parameters related to their structural stability and processing routes that have decelerated their realistic application in this field. Both drawbacks are unraveled in this work for the microporous bioMOF CaSyr-1 by using supercritical CO2 (scCO2) to load the bioMOF with the anti-tubercular isoniazid (INH) drug, and functionalize its external surface with a hydrophobic protective layer of stearate (S). The hydrophobicized CaSyr-1(INH)/S vehicle is further coated with a neutral surfactant (PS60) to enhance the wettability of the system. In vitro tests, related to drug carrier biocompatibility and drug release in body simulated fluids, are performed to demonstrate potential prospective of the designed DDs in pharmacy. The synthetized product displayed total biocompatibility even at high concentrations, and the particle size and dissolution rate showed to be adequate for pulmonary administration.

Molecular engineering of oxadiazole-based small organic-functional molecules as hole transporting materials for dopant-free perovskite solar cells

The present investigation concerns the synthesis and characterization of new hole-transporting materials (HTMs) for dopant free perovskite solar cells (PSCs). In this work, emphasis is placed on three new HTMs, specifically materials P-H, P-OMe, and P-CN, whose center-core is 2,2'-(4,8-bis(octyloxy)benzo[1,2-b:4,5-b']dithiophene (OBDT) and combined with two donor units of substituted triphenylamine as at both ends along with oxadiazole acceptor units in between donor and OBDT. The fabrication of perovskite solar cell devices using new HTMs and compared the power conversion performance with the standard spiro-OMeTAD HTM. Several spectroscopic techniques were utilized to characterize the properties of the new HTMs, such as FESEM analysis of thin-film morphologies, time-dependent photoluminescence (PL) spectra, and mobility measurements. The HTMs P-OMe established a compressed and steady protective layer on the perovskite layer. This layer contributed to the development of open-circuit voltage (VOC) and short-circuit current density (JSC), both of which are crucial for accomplishing high power conversion efficiency (PCE) in PSCs. The PSC device integrating the P-OMe HTM displayed a superior PCE of 21.14 % over an active area of 0.22 cm2. This activity was related to the standard device that utilized the standard Spiro-OMeTAD HTM, which accomplished a PCE of 17.46 %. The improved devices with the P-OMe HTM continued about 90 % of their initial PCE throughout maximum power point tracking (MPPT) for 90 days. Furthermore, these devices engaged in their activity over a further 2160 h under various temperature settings (25 °C and 35 °C), probably because of the hydrophobic property of the HTM.

Unraveling the SCC behavior and enhanced creep strength mechanism of AFA alloy in supercritical CO2

The oxide scale of 20Cr25Ni2.5Al AFA alloy formed under the coupling of stress and supercritical carbon dioxide (sCO2, 650 ℃ / 15MPa) consisted of Fe3O4, Cr2O3, preferential intergranular oxidation zones, but lacked a thin Al2O3 protective layer. The poor oxidation resistance resulted in significant CO2 penetration into the matrix and subsequent formation of Cr2O3, thereby hindering the initiation of Cr - rich σ phase beneath the oxide scale. This competition between oxidation and precipitation effectively reduced crack initiation and delayed the connection between SCC and creep cracks, thus significantly prolonging the creep lifetime in sCO2 compared to that in air.