Conduction Channel Research Articles

A new wormhole mechanistic model for radial acid flow geometry using novel 3D flow correlations

In carbonate reservoirs, matrix acidizing is used to improve well performance by creating conductive channels called wormholes. Predicting wormhole propagation rate in radial acid flow geometry up to the real wellbore scale is the main problem regarding designing field operations in previous studies which are still challenging. In this study, a new mechanistic approach is presented to predict the radial flow acidizing up to near wellbore scale by considering the vital effects of porous media size and geometrical parameters of wormhole patterns.Accordingly, wormhole tip velocity and wormhole wall fluid loss rate will be introduced as the scale transferring parameters between different porous media sizes which are correlated in terms of rock diameter and wellbore height, wormhole size and density. These novel correlations are extracted from the large databank of flux distribution between rock matrix and wormhole channel obtained in 60 different 3D FEM flow simulations for various patterns of wormhole propagating and different wellbore sizes. In addition, an HPHT radial acid flooding setup is designed and constructed to perform radial acid coreflood on ultra-low permeable rocks (k«1md) for model validation. During the experiments, the breakthrough pore volume, pressure behavior and CT scan of samples are closely monitored. The results showed that due to the tight window of pore size distribution, faster breakthroughs with 1.23 and 1.45 pore volumes occurred in these tight samples compared to those reported already which are confirmed by developed model prediction. Besides, the model results showed that increasing the rock height (open-hole interval) would increase wormhole tip velocity and decrease acid breakthrough time. In addition, the higher temperature shifted the acid response curve to the right, toward higher acid breakthrough volume and higher acid concentration shifted it toward lower breakthrough volumes. The model is validated using radial acid experiments and previous radial acid models for different rock sizes with good agreement (R2 = 0.9547, MSE = 0.02161 and RMSE = 0.14701). The new radial acidizing model is capable to quickly predict wormhole propagation rate up to wellbore scale without requiring excess up-scaling data due to considering wide ranges of porous rock sizes from (25.4–152.4 cm) diameter and (5–25.4 cm) pay zone height (sufficient size for considering repetitive wormhole patterns). This technique can be utilized for tuning parameters of various radial cases to predict the acid tests results leading to reduce the number of required experiments.

Highly stable and reversible hydrogen sensors using Pd-coated SnO2 nanorods and an electrode–substrate interface as a parallel conduction channel

We demonstrated highly stable and reversible H2 sensors using a dual electron-conduction channel comprising Pd-coated SnO2 nanorods (NRs) and a parallel conduction channel containing Cr/native oxide/p-type Si interface. The dual-channel sensor exhibited highly reversible resistance changes during H2 in-and-out cycles at operating temperatures of 25 °C− 100 °C, while typical single-channel sensors with SnO2 NRs fabricated on SiO2 (300 nm)/Si substrates showed irreversible response because of insufficient recovery from Pd-Hx to Pd-Ox. In particular, the sensor showed significantly high repeatability, long-term stability, and selectivity for H2 sensing at 80 °C. Additionally, the time taken to detect H2 above 1% was less than 2 s and the response to H2 above 500 ppm was unaffected by high humidity. These results indicate that the dual-channel Pd-coated SnO2 NR sensor is suitable for applications such as hydrogen leak detectors that require high speed and precision. Moreover, it was found that the sensor could detect H2 below 0.5 ppm even at low temperatures. This work provides a pathway for improving gas-sensing performance by interface engineering, enabling various practical hydrogen sensor applications.

RF loss reduction by a carbon-regulated Si substrate engineering in GaN-based HEMT buffer stacks

A carbon-regulated Si substrate engineering has been adopted to reduce the RF loss of GaN-based HEMT buffer stacks. By implanting the substrate with high-dose carbon, undersaturation of Si self-interstitials is formed, and the self-interstitial-assisted aluminum diffusion into the Si substrate during the growth can be significantly suppressed. Consequently, the formation of parasitic conductive channel is suppressed, and the RF loss of the buffer stacks can be reduced. By combining the substrate engineering with low-temperature growth, the RF loss of the buffer stacks is reduced to as low as 0.13 dB/mm at 10 GHz. In addition, the crystal quality of the buffer stacks grown on the regulated substrates does not degrade. This work shows a great potential for fabrication of high-quality and low-loss GaN-on-Si RF devices.

Numerical Simulation of Electrical Properties of Carbonate Reservoirs Using Digital Rocks

Rock electrical experiments are essential means of researching the conductive properties of rocks and are fundamental to interpreting resistivity logging. Carbonate rocks have more complex pore structures than sandstone, which results in more complex conductive properties. However, conducting experiments on representative rock samples from carbonate reservoirs is difficult, making it challenging to study the micro factors affecting electrical properties. Therefore, researching the conductive properties of carbonate rocks is difficult. To address this, in this paper, three-dimensional (3D) digital rock models with different porosities are generated, and conductive simulations are carried out on these models using the finite element method (FEM). Firstly, a micro-computed tomography (μ-CT) 3D image of a carbonate rock is obtained. Secondly, mathematical morphology-based methods are used on the μ-CT image to generate cores with varying porosities and fluid distributions. Then, the electrical properties are simulated using the FEM method, and the results are analyzed. The results reveal that the formation factor of the reservoir is mainly influenced by the shape and structure of the pores. The Archie equation is more suitable for carbonate reservoirs with water saturation levels greater than 60%. The wettability of the rock can alter the distribution of fluid in the reservoir space under different water saturation conditions. In pure water-wet rocks, the water phase mainly occupies small pores, while the oil phase occupies larger pores. As a result, compared to pure oil-wet rocks, water-wet rocks have more conductive channels and better conductivity. Therefore, it is important to determine the wettability of the rock when calculating water saturation using the Archie equation. The saturation index value of water-wet carbonate rock is about 2, while that of oil-wet rock is around 3–4. This research lays a foundation for studying the electrical conductivity of carbonate reservoirs using digital rocks.

Ablation behavior and mechanism of SiCnw modified SiC-ZrC coating for graphite under a plasma ablation flame

The intrinsic brittleness and low bonding strength of SiC-ZrC coatings to the graphite severely limit the ablation performance. Herein, SiC nanowires (SiCnw) were introduced between pre-oxidized graphite and coatings. The brittleness of coatings was reduced and the bonding strength was increased from 5.49 ± 0.88 MPa to 8.33 ± 0.65 MPa by SiCnw. Both simulation and experimental results show SiCnw also worked as thermal conduction channels to improve the ablation resistance. After plasma ablation for 120 s, the ablation rates of SiCnw/SiC-ZrC coated graphite were 0.315 mg/s and 0.217 µm/s, respectively, which are much lower than those of pure graphite and SiC-ZrC coated graphite.

Modulation of Exchange Bias in La0.35Sr0.65MnO3/La0.7Sr0.3MnO3 through Volatile Polarization of P(VDF‐TrFE) Gate Dielectric

AbstractElectric‐field regulation of magnetic properties in perovskite manganites has attracted much attention for its potential in spintronics. For antiferromagnetic perovskite manganites, fewer studies are reported due to technological difficulties in probing their magnetic properties. Here, negative exchange bias (EB) is realized in epitaxial antiferromagnetic/ferromagnetic manganite bilayers with atomically flat interfaces. The low‐voltage pulse modulation of EB is demonstrated using the field‐effect device geometry with the ferroelectric copolymer, polyvinylidene fluoride with trifluoroethylene as a dielectric gating layer, antiferromagnetic La0.35Sr0.65MnO3 (AF‐LSMO) as pinning layer, and ferromagnetic La0.7Sr0.3MnO3 (FM‐LSMO) as conduction channel. Instead of using non‐volatile polarizations to control the EB, volatile polarizations in ferroelectric field effect transistors are suggested to be capable of modulating the EB. With high‐resolution electron microscopy and spectroscopy, the non‐volatile regulation of EB is attributed to the creation/annihilation of oxygen vacancies in the AF‐LSMO layer via low‐voltage pulses. This study reveals the effect of volatile electric polarizations in ferroelectric field effect devices and highlights the potential for low‐voltage pulse control of the physical properties in antiferromagnetic perovskite oxide insulators.

In Situ Visualization of the Pinning Effect of Planar Defects on Li Ion Insertion.

Longevity of Li ion batteries strongly depends on the interaction of transporting Li ions in electrode crystals with defects. However, detailed interactions between the Li ion flux and structural defects in the host crystal remain obscure due to the transient nature of such interactions. Here, by in situ transmission electron microscopy and density function theory calculations, we reveal how the diffusion pathways and transport kinetics of a Li ion can be affected by planar defects in a tungsten trioxide lattice. We uncover that changes in charge distribution and lattice spacing along the planar defects disrupt the continuity of ion conduction channels and dramatically increase the energy barrier of Li diffusion, thus, arresting Li ions at the defect sites and twisting the lithiation front. The atomic-scale understanding holds critical implications for rational interface design in solid-state batteries and solid oxide fuel cells.

Ca2+ -activated K+ channels regulate cell volume in human glioblastoma cells.

Glioblastoma (GBM), the most lethal form of brain tumors, bases its malignancy on the strong ability of its cells to migrate and invade the narrow spaces of healthy brain parenchyma. Cell migration and invasion are both critically dependent on changes in cell volume and shape driven by the transmembrane transport of osmotically important ions such as K+ and Cl- . However, while the Cl- channels participating in cell volume regulation have been clearly identified, the precise nature of the K+ channels involved is still uncertain. Using a combination of electrophysiological and imaging approaches in GBM U87-MG cells, we found that hypotonic-induced cell swelling triggered the opening of Ca2+ -activated K+ (KCa ) channels of large and intermediate conductance (BKCa and IKCa , respectively), both highly expressed in GBM cells. The influx of Ca2+ mediated by the hypotonic-induced activation of mechanosensitive channels was found to be a key step for opening both the BKCa and the IKCa channels. Finally, the activation of both KCa channels mediated by mechanosensitive channels was found to be essential for the development of the regulatory volume decrease following hypotonic shock. Taken together, these data indicate that KCa channels are the main K+ channels responsible for the volume regulation in U87-MG cells.

Structure, magnetic and electrical properties of Tb0.5Nd0.5CoO3 perovskite solid solutions with carbon material flakes (CMF)

In this paper, we study the ceramics of cobaltite [Tb0.5Nd0.5CoO3]1−yCy with equiatomic contents of terbium and neodymium and with the addition of a carbon material flakes (СMF) with the content of carbon in the range of weight fraction 0 < y < 0.01. The ceramics were obtained by the method of solid-phase reactions according to the standard ceramic technology in air. Using X-ray diffraction and energy-dispersive analysis, it was established that the initial (undoped) solid solution is single-phase with perovskite structure. It was shown that Co3+ ions in undoped ceramics under study are in a non-magnetic low-spin state over the entire temperature range under consideration (2–320 K), and the entire contribution to the magnetization is due to Tb3+ and Nd3+ ions. An analysis of the temperature dependences of the electrical resistance R(T) shows that the initial solid solution behaves like a dielectric with a reduced activation energy of about 0.3–0.35 eV in the temperature range of 280–320 K, due to hopping conduction with a constant activation energy (constant range hopping) by defects in Tb0.5Nd0.5CoO3 matrix. At lower temperatures (200 – 275 K) in the initial (undoped) Tb0.5Nd0.5CoO3 samples, the Mott-type hopping conductivity mechanism with a variable range hopping and high values of the characteristic temperature To ∼ 109 K was observed. Simultaneously, at 300 K, we observed hopping conductivity on alternating current according to the law σ(ω) ∼ ω-α(ω), where the exponent α, which determines a hopping probability, depends on the frequency. In [Tb0.5Nd0.5CoO3]1−yCy samples, heavily doped with СMF with y = 0.01, carrier transport in the entire studied temperature range of 2–320 K mainly occurs along highly conductive carbon-based channels, formed inside of Tb0.5Nd0.5CoO3 matrix by СMF. At temperatures below 15–20 K, these samples show hopping behavior of R(T) with a variable range hopping over localized states, described by the Mott–Kirkpatrick law. In the temperature range 20–100 K electrical resistance versus temperature R(T) along carbon-based channels obey the law R(T) ∼ Ln T. In this case, the relative magnetoresistance MR(T, B) is characterized by a negative sign at temperatures below 10 K in magnetic fields less than 1 T. This behavior of the R(T, B) dependences were described on the basis of the theory of quantum corrections to the Drude conductivity for two-dimensional samples under conditions of weak localization, which is consistent with the behavior of layered carbon-based materials known from the literature. At T > 150 K curves R(B) follow to Lorentz-like positive magnetoresistive effect in Tb0.5Nd0.5CoO3 matrix in the whole magnetic field range.

Thin Vanadium Dioxide Films for Use in Microwave Keys with Electric Control

Introduction. In view of the ever-tightening bandwidth requirements for wireless communication systems, the use of tunable or switching devices based on microwave keys is becoming increasingly popular. Currently, the development of microwave keys based on nonlinear materials, such as vanadium dioxide, is a relevant research direction. The keys based on this material are distinguished by a planar and simple design, thus being suitable for creating microwave devices using hybrid technology.Aim. To study the properties of thin vanadium dioxide films and to develop a microwave switch with electrical switching on their basis.Materials and methods. Experimental samples of thin vanadium dioxide films were obtained by magnetron sputtering. The phase transition parameters of the samples obtained experimentally were used in computer simulation of a planar two-electrode structure of a microwave key by the finite element method.Results. Experimental samples of vanadium dioxide films were manufactured, and the dependences of their resistivity on temperature were studied. The resistance of the obtained vanadium dioxide films was found to change threefold. A microwave key design based on vanadium dioxide films was developed. The formation of a currentconducting channel in vanadium dioxide films was simulated when a control voltage was applied. The threshold voltage of the element was estimated depending on its design parameters.Conclusion. The use of experimental data as a basis for computer simulation made it possible to determine the threshold values of currents depending on the topology and design of the proposed microwave key. The results of simulating the key structure showed the formed conductive channel to have clearly defined boundaries in terms of distribution of both current density and temperature across the film surface.

Electron and hole injection barriers between silicon substrate and RF magnetron sputtered In2O3 : Er films

In2O3 : Er films have been synthesized on silicon substrates by RF magnetron sputter deposition. The currents through the synthesized metal/oxide/semiconductor (MOS) structures (Si/In2O3 : Er/In-contact) have been measured for n and p type conductivity silicon substrates and described within the model of majority carrier thermoemission through the barrier, with bias voltage correction to the silicon potential drop. The electron and hole injection barriers between the silicon substrate and the film have been found to be 0.14 and 0.3 eV, respectively, by measuring the temperature dependence of the forward current at a low sub-barrier bias. The resulting low hole injection barrier is accounted for by the presence of defect state density spreading from the valence band edge into the In2O3 : Er band gap to form a hole conduction channel. The presence of defect state density in the In2O3 : Er band gap is confirmed by photoluminescence data in the respective energy range 1.55–3.0 eV. The band structure of the Si/In2O3 : Er heterojunction has been analyzed. The energy gap between the In2O3 : Er conduction band electrons and the band gap conduction channel holes has been estimated to be 1.56 eV.

Electron and hole injection barriers between silicon substrate and RF magnetron sputtered In2O3 : Er films

In2O3 : Er films have been synthesized on silicon substrates by RF magnetron sputter deposition. The currents through the synthesized metal/oxide/semiconductor (MOS) structures (Si/In2O3 : Er/In-contact) have been measured for n and p type conductivity silicon substrates and described within the model of majority carrier thermoemission through the barrier, with bias voltage correction to the silicon potential drop. The electron and hole injection barriers between the silicon substrate and the film have been found to be 0.14 and 0.3 eV, respectively, by measuring the temperature dependence of the forward current at a low sub-barrier bias. The resulting low hole injection barrier is accounted for by the presence of defect state density spreading from the valence band edge into the In2O3 : Er band gap to form a hole conduction channel. The presence of defect state density in the In2O3 : Er band gap is confirmed by photoluminescence data in the respective energy range 1.55–3.0 eV. The band structure of the Si/In2O3 : Er heterojunction has been analyzed. The energy gap between the In2O3 : Er conduction band electrons and the band gap conduction channel holes has been estimated to be 1.56 eV.

Anisotropic, ultra-sensitive, self-adhesive, biocompatible, and conductive hydrogels prepared for wearable sensors

Conductive hydrogels (CHs) stand as ideal candidates for flexible electronic devices. However, existing CHs cannot integrate the high sensitivity under low deformation, adhesion capability and biocompatibility into one system, which greatly retard their applications. Inspired by muscle structures, anisotropic conductive hydrogels were fabricated to address this challenge. The hydrogels were obtained through a stretch-induced orientation strategy, that is, freezing − thawing the aqueous mixture of poly(vinyl alcohol) (PVA), carbon nanotubes (CNTs), tannic acid (TA) and deionized water two cycles to obtain the precursor hydrogel; disrupting the H bonds between PVA chains by thermal stretching at 60 °C to induce anisotropic microstructures; and finally reforming them by freezing the pre-stretched gel at −20 °C for 4 h to fix the regular structures. This strategy resulted in anisotropic conductivities and mechanics. For instance, the mechanical anisotropy ratio (defined as the ratio between parallel and orthogonal directions) was 2.83. In addition, the electrical anisotropy ratio was 2.19. Meanwhile, CNTs and regular conductive channels imparted high sensitivity (GF = 8.5 within 50% strain), fast response (0.2 s), and low detect limit (0.2% strain). Additionally, the existence of catechol groups of TA enabled self-adhesion ability (maximum adhesion strength = 72.63 kPa). Due to non-toxicity of raw materials and physical process, the hydrogel was also biocompatible (cell viability = 100%). All of these merits hold great potential in human − machine interactions, medical monitoring, and smart electronic skins.

First-Principles Studies on Spin-Dependent Transport of Magnetic Junctions with Half-Metallic Heusler Compounds

Two types of magnetoresistance (MR), i.e., tunnel magnetoresistance (TMR) and current perpendicular to plane giant magnetoresistance (CPP-GMR), are theoretically discussed for systems with half-metallic (HFM) Co-based full Heusler compounds. In TMR, the non-collinear spin structure at the Co2MnSi(CMS)/MgO(001) interface that results from thermal spin fluctuations significantly reduced the TMR ratio at room temperature (RT). Enhancement of the exchange stiffness of CMS/MgO was essential to suppress the reduction in TMR at RT. Furthermore, it is proposed that inserting of a B2-CoFe layer between CMS and MgO is a promising way to enhance the interface exchange stiffness constant. In CPP-GMR, the interface spin asymmetry γ in the Valet-Fert model was essential to enhance GMR at RT, because the temperature dependence of γ in experiments was much larger than that of the bulk spin asymmetry β. I showed that the experimental CPP-GMR ratio increases with the decrease in the theoretical resistance-area product RPA, which is roughly consistent with the RP dependence of γ. This means that matching of the conductive channel between HMF and a non-magnetic metallic spacer is a key parameter to enhance γ. These findings will be very important for room temperature spintronics devices applied in future artificial intelligence hardware.

Proton Conduction Properties of Intrinsically Sulfonated Covalent Organic Framework Composites

The long–term stability of proton conductors is one of the most important factors in evaluating materials. Guest molecules can act as “bridges” for proton conduction channels and reside in the channels of covalent organic frameworks, but they are prone to leakage. Therefore, it is important to develop proton conductors with intrinsic proton conductivity. In this paper, we synthesized an intrinsically sulfonated covalent organic framework, TpPa–SO3H, which has a more stable proton conducting performance than that of TpPa@H2SO4 by loading guest molecules. Meanwhile, the proton conductivity of TpPa–SO3H was further improved by coating a superabsorbent polymer through an in situ reaction to obtain PANa@TpPa–SO3H (PANa: sodium polyacrylate). As a result, the modified composite exhibits an ultrahigh proton conductivity of 2.33 × 10−1 S cm−1 at 80 °C under 95% relative humidity (RH). The stability of PANa@TpPa–SO3H makes it an efficient proton transport platform with excellent proton conductivity and long–term durability.

Graphitic nanostructure integrated NiO composites for high-performance lithium-ion batteries

So far, various graphite-Nickel Oxide (NiO) composites have been investigated as anodes for Li-ion batteries. However, developing an ideal composite that overcomes NiO's electrical conductivity limitations remains a significant challenge. The current study presents an in-situ one-step hydrothermal technique for integrating NiO into a 3D peony-like graphitic nanostructure (NiO-GNF), resulting in unique thin nanosheet arrays with porous, conductive channels. Notably, the composites endowed controlled aggregation and restacking of NiO, buffered electrode stress and improved electrical conductivity due to the expanded nature of graphite. In addition, the enlarged interlayer spacing of expanded graphite facilitated an improved Li-ion insertion. Overall, in comparison to pure NiO anodes, the NiO-GNF composite achieved an impressive electrochemical improvement exhibiting a highly reversible discharge capacity of 678.2 mAh/g after 370 cycles at a current density of 0.5 A g−1, corresponding to a capacity retention of 60.7 %. The composite also demonstrated a capacity of 752 mAh/g at a high current density of 1.2 A g−1.

Anisotropic mass transport enables distinct synaptic behaviors on 2D material surface

Anisotropy is an intrinsic property in crystals with low structural symmetry, and such well-textured materials usually show distinct electronic transport and optical properties along different lattice orientations, offering wide applications in electronic and photonic devices. As a typical low-symmetry materials, crystalline GeSe with orthorhombic structure shows large electric and optical anisotropies. In this work, we take advantage of the anisotropic mass transport and filamentary growth of Ag ions on the GeSe surface to fabricate planar memristive devices which show directional memory and transient switching phenomena. The anisotropic switching behaviors stem from the distinct morphology of metallic filaments that are directionally dependent on the mobility of ions, e.g., ions diffusing along the low-barrier direction tend to form stark conductive channels while those with low mobility only entail slim and weak dendrites, which have been clearly observed under electronic microscopy. The functionality could be utilized to mimic various synaptic events, such as long-term memory enabled by stable conductive channels and short-term memory by the spontaneous rupture of weak filaments, all implemented in one physical device. Two integration schemes based on the anisotropic devices are designed and demonstrated for different application scenarios, paving the way for its applications in multifunctional brain-inspired computing systems.

Constructing lamellar low temperature anion exchange membranes based on polymerized ionic liquid and graphene oxide nanosheets

Polymerized ionic liquid (PIL) of poly(1-vinyl-3-methylimidazolium) chloride (poly(vmim)Cl) and graphene oxide (GO) nanosheets were respectively deposited on the surface of Kevlar aramid nanofibers (KANFs) substrates to construct anion exchange membranes (AEMs). The multilayered microstructure resulted in orderly distributed components, which thus improved the mechanical properties and dimension stability of the lamellar low-temperature AEMs. The imidazolium cations in PIL and the polar oxygen functional groups in GO nanosheets constituted the interconnected hydroxide ion conduction channels in the prepared Kevlar/(PIL/GO)60 membrane. Relative to the ionic liquid (IL) monomer of 1-vinyl-3-methylimidazolium chloride, the PIL with polymerized molecular chains could be embedded in GO nanosheets with the formation of a stable microstructure. The Kevlar/(PIL/GO)60 membrane exhibited the enhanced alkaline stability relative to the Kevlar/(IL/GO)60 membrane. Furthermore, the hydroxide conduction behavior in the AEMs at subzero temperatures has been researched in consideration of the long-term exposure in colder conditions of the vehicles equipped with fuel cells. As a result, the Kevlar/(PIL/GO)60 membrane exhibited a hydroxide conductivity of 0.94 mS/cm at −25 °C, 5.25 mS/cm at 30 °C, and 64.7 mS/cm at 80 °C. Meanwhile, good alkaline stability was revealed from the ten-cycle hydroxide conductivities and long-time hydroxide conductivities. In addition, the PIL enhanced the mechanical strength of the Kevlar/(PIL/GO)60 membrane, with the tensile stress at break increasing by 31.3% compared with that of the Kevlar/(IL/GO)60 membrane.

Investigation of p-n sensing transition and related highly sensitive NH3 gas sensing behavior of SnPx/rGO composites

Tin phosphides (SnPx) with alternating layers of P and Sn atoms possess abundant acidic P vacancy sites and high electronegativity, which can be potential candidates for gas sensing at room temperatures (RT). Herein, SnPx/rGO composites were fabricated for NH3 gas sensing at RT. Structural characterizations indicated the uniform distribution of SnPx on the rGO surface with small sizes and the existence of abundant acidic P vacancy sites. Gas sensing results showed that the response of SnPx/rGO composites with the phosphating ratio of 1:5 (SG-5) to 40 ppm NH3 at RT can be calculated as 117.5%. Moreover, SG-5 also exhibited a high response to NH3 gas with low concentrations (Response: 3% to 500 ppb NH3) and a LOD of 43.6 ppb. Besides, the NH3-TPD and in situ DRIFTs analysis were conducted to reveal the physical adsorption and complete desorption of NH3 gas on the material surface. More interestingly, due to different adsorption sites and conductive channels, the SnPx/rGO composites exhibited different sensing types upon exposure to reducing and oxidizing gases. Sensing response under different background gas atmospheres indicated that NH3 gases were mainly adsorbed on the heterojunctions to react with the surface oxygen species, exhibiting an n-type sensing behavior. However, NO2 gases were mainly adsorbed on the rGO surface to attract electrons, exhibiting a p-type sensing behavior. Density functional theory calculation results also confirmed the preferred adsorption of NH3 on SnPx and NO2 on rGO surface. This work provides an insight into gas adsorptions and desorptions on the SnPx surface and will promote the applications of metal phosphides in gas sensing.

Optimized ablation resistance behavior and mechanism of C/SiC composites with high thermal conductive channels

AbstractAimed to enhance the high‐temperature service performance of C/SiC composites in high‐speed aircraft thermal protection system, in this article, pitch‐based carbon fibers were used to construct high thermal conductive channels to improve the heat transfer capability of C/SiC composites. The results revealed that the as‐prepared composites equipped with 4.7 times higher thermal conductivity than that of conventional C/SiC composites. The oxyacetylene flame ablation test confirmed that the constructed high thermal conductive channels, which quickly conducted the heat flow from the ablation center area to other areas is the main reason of as‐prepared composites exhibiting a very impressive ablation resistance property. Briefly, the ablation temperature of the as‐prepared composite surfaces considerably dropped by about 300°C compared with conventional C/SiC composites, while the linear ablation rate and mass ablation rate of the composites are 1.27 μm/s and 0.61 mg/s respectively, which is superior to many recent reports, demonstrating that this article provides a simple but highly effective measure to improve the ablation resistance property of C/SiC composites.