High Pressure Range Research Articles

Design and fabrication of ultrathin silicon-based strain gauges for piezoresistive pressure sensor

Ultra-thin (20 μm) silicon strain gauges were fabricated with silicon-on-insulator (SOI) wafer by a newly-conceived wet etching process. Buffered oxide etchant (BOE, NH4F: HF = 6:1) solution with additives of octylamine and octanol was used for wet etching process in which the operating temperature was 50°C. Photoresist as a passivation layer was deposited on the upper side of SOI wafer to minimize strain gauge damage by chemical etchants. Small amount of octylamine and octanol were added to BOE solution to improve surface wettability and SiO2/Si selectivity. The fabricated strain gauges were attached to the pressure diaphragm and the performance of strain gauge was investigated by measuring with the hydraulic pressure system. The resistance changed linearly with tensile and compressive strains. Maximum values of non-linearity, hysteresis, thermal coefficient of resistance (TCR) and sensitivity were -0.341 %, 0.909 %, 4128 ppm/°C and 34.22 mV/V respectively. The fabricated strain gauges might be well applicable to the hydrogen pressure sensor which is detectable for high pressure range (0–900 bar).

3D Network Spacer-Embedded Flexible Iontronic Pressure Sensor Array with High Sensitivity over a Broad Sensing Range.

Microstructure construction is a common strategy for enhancing the sensitivity of flexible pressure sensors, but it typically requires complex manufacturing techniques. In this study, we develop a flexible iontronic pressure sensor (FIPS) by embedding an isolated three-dimensional network spacer (3DNS) between an ionic gel and a flexible Ti3C2Tx MXene electrode, thereby avoiding complex microstructure construction techniques. By leveraging substantial deformation of the 3DNS and the high capacitance density resulting from the electrical double layer effect, the sensor exhibits high sensitivity (87.4 kPa-1) over a broad high-pressure range (400-1000 kPa) while maintaining linearity (R2 = 0.998). Additionally, the FIPS demonstrates a rapid response time of 46 ms, a low limit of detection at 50 Pa, and excellent stability over 10 000 cycles under a high pressure of 600 kPa. As practical demonstrations, the FIPS can effectively monitor human motion such as elbow bending and assist a robotic gripper in accurately sensing gripping tasks. Moreover, a real-time, adaptive 7 × 7 sensing array system is built and can recognize both numeric and alphabetic characters. Our design philosophy can be extended for fabricating pressure sensors with high sensing performance without involving complex techniques, facilitating the applications of flexible sensors in human motion monitoring, robotic tactile sensing, and human-machine interaction.

Flexible and transparent leaf-vein electrodes fabricated by liquid film rupture self-assembly AgNWs for application of heaters and pressure sensors

The leaf veins with hierarchically interconnected network structures have great potential as self-assembly templates for transparent and flexible electrodes. In this paper, a liquid membrane ruptured assisted AgNWs self-assembly method was adopted to obtain conductive veins, which show a low sheet resistance of 3.6Ω/□ and a high transparency of 79 % at a minimal materials waste. The figure of merit of conductive veins was as high as 433Ω-1 and can be further increased by increasing the number of soaking because the light transmittance is nearly immune to the AgNWs layer number. The veins maintained a good electrical conductivity even after bending 10,000 times at a 2 mm radius of curvature and exhibited a good corrosion resistance under harsh conditions. Heaters based on the conductive veins are shown as application examples. A high temperature of 104 °C was achieved at a low voltage of 2 V, which is enough to heat cold water. They still have good heating properties even in the bending state or tensile state. Furthermore, pressure sensors based on the conductive veins were fabricated as examples of wearable devices. The sensor exhibits a high sensitivity of 3.8 kPa−1 in the low-pressure range (0–15 kPa) and 17.4 kPa−1 in the high pressure range (15–50.96 kPa). It can monitor human actions such as finger bending, finger taping, throat swallowing and wrist pulse in real-time, which has promising potential for motion monitoring and information encryption applications.

Numerical evidence for the existence of three different stable liquid water structures as indicated by local order parameter.

Structures of liquid water are controversial not only in supercooled polyamorphism but also in stable bulk liquids in the high temperature and pressure range. Several experimental studies in bulk liquid have assumed the existence of three different liquid water structures. If indeed the three liquid water structures are different, they should be clearly distinguished by some measure other than density that characterizes the difference in structural order. In this study, whether the three different bulk liquid water structures are real or not is numerically verified based on molecular simulations using a reliable water molecular model. Since these liquid water structures have been suggested to be related to three different crystal structures (i.e., ice Ih, III, and V), liquid structures are sampled from the vicinity of the ice Ih-liquid coexistence point, the ice III-V-liquid triple point, and the ice V-VI-liquid triple point, respectively. An attempt is made to introduce local order parameters (LOPs) as an indicator to distinguish these structures. A fast and exhaustive LOP search is performed by the molecular assembly structure learning package for Identifying order parameters. The selected LOP distinguishes the molecular structures of three different stable liquid waters with high accuracy, providing numerical evidence that these structural orders differ from each other. Furthermore, regions of the liquid water structures are drawn on a phase diagram using the LOP, demonstrating their consistency with experimental studies.

Assessment of Solubility Behavior of a Copolymer in Supercritical CO2 and Organic Solvents: Neural Network Prediction and Statistical Analysis.

In the industrial sector, understanding the behavior of block copolymers in supercritical solvents is crucial. While qualitative agreement with polymer solubility curves has been evaluated using complex theoretical models in many cases, quantitative predictions remain challenging. This study aimed to create a rapid and accurate artificial neural network (ANN) model to predict the lower critical solubility and upper critical solubility space of an atypical block copolymer, poly(styrene-co-octafluoropentyl methacrylate) (PSOM), in different supercritical solvent systems over a wide range of temperatures (51.75-182.05 °C) and high pressure (3.28-200.86 MPa). The experimental data set used in this study included one copolymer, five supercritical solvents, one cosolvent, and one initiator. It consisted of seven unique copolymer-solvent combinations (252 cloud point pressures) used to predict the model quantitatively and qualitatively. To predict the PSOM-solvent interactions, the study considered two different input systems: a six-variable system, a five-variable system, and one target output. Initially, we used a three-layer feed-forward neural network to select the best learning algorithm (Levenberg-Marquardt) from 14 different algorithms, considering one sample PSOM-solvent system. Then, the network topology was optimized by varying hidden neuron numbers from 2 to 80 for all seven PSOM-solvent combination systems. The predicted cloud point pressures were in excellent agreement with the experimental cloud point pressures, confirming the model's accuracy. It is clear from the results of a minimum mean square error (≤1.90 × 10-27) and maximum linear regression R 2 (≥0.99) during training, validation, and testing of all the data sets. Further, the ANN model accuracy was tested by statistical analysis, confirming the model's ability to accurately capture the miscibility regions of polymers, enabling efficient processing of various polymer materials. This data-driven approach facilitates the prediction of coexistence curves for other polymers and complex macromolecular systems.

Pressure-dependent bandgap characteristics in photonic crystals with sensing applications

The present study elucidates a photonic crystal (PhC)-based pressure sensor exploiting the change in refractive index with pressure and the corresponding structural deformation of the dielectric material. The stress-sensitive refractive indices of the constituent materials of the PhC have been considered to study the effect of applied pressure on the photonic bandgap (PBG) characteristics of the structure. The designed pressure sensor, proposed using a two-dimensional hexagonal lattice arrangement of air holes in a dielectric slab, operates in the high-pressure range of 1–6 GPa. A comparative study of the PBG characteristics with the application of high pressure has been reported for three semiconducting materials—GaAs, Ge and Si, used for the dielectric slab in the proposed structure. GaAs is found to exhibit the highest sensitivity to pressure variations and shows more pronounced shifting of the midgap wavelength with pressure in comparison to Ge and Si. The largest PBG is seen in the Ge-based structure, closely followed by the GaAs and Si-based structures. The proposed structure is suitable for high-pressure sensing applications.

Compaction behavior of freeze-dried and spray-dried trypsin/lactose particulate systems

Development of oral solid dosage forms containing biologics has attracted intense interests recently due to the high patient convenience and the commercial potential of related products. The aim of this study was to understand how the difference in the particle properties prepared using two different drying principles, i.e. freeze-drying and spray-drying, may influence the compaction behavior of particulate protein systems. Here, trypsin was used as a model protein drug and lactose as a filler. The raw freeze-dried (FD) powder composed mostly of trypsin and lactose was dissolved in Milli-Q water and processed by spray-drying to produce spray-dried (SD) powder. Meanwhile, the raw FD powder was micronized by a ball mill into fine ball-milled (BM) powder with a comparable particle size to that of SD powder. Next, the FD, BM and SD powders were characterized with regard to morphology, residual moisture content (RMC), solid form, and surface chemistry using scanning electron microscope (SEM), thermogravimetric analysis (TGA), X-ray powder diffraction (XRPD), and X-ray photoelectron spectroscopy (XPS), respectively. Subsequently, a compaction simulator was employed to prepare tablets within the compaction pressure range of 25 to 400 MPa. The results showed that FD and BM powders could be compressed into tablets within the investigated compaction pressure range. In contrast, tablets compacted from SD powder displayed capping/lamination tendency under high compaction pressures and thus had poor tabletability. XPS analyses revealed that there were more surface enrichments of trypsin in the SD powder compared to that of FD powder. It implies that there would be more hydrophobic inter-particulate trypsin-trypsin interactions and less hydrophilic lactose-lactose interactions during the compression of SD powder compared to the compaction of FD powder. The weak hydrophobic inter-particulate trypsin-trypsin interactions may not be maintained during the decompression phase especially when compacted at high compaction pressure ranges, resulting in capping/lamination of the SD tablets. This study demonstrates that the two drying principles, i.e. freeze-drying and spray-drying, can result in different particle properties of biologics, which can in turn influence the tabletability of the resulting solid materials.

Preparation of CeO2 particles via ionothermal synthesis and its application to chemical mechanical polishing

CeO2 is a widely used abrasive for the chemical mechanical polishing of silicon during chip manufacturing. CeO2 can be synthesized via traditional coprecipitation, hydrothermal, and solvothermal methods; however, these methods have some issues, including high vapor pressure, flammability, toxicity, volatile solvents, and narrow heating temperature range. To overcome these issues, we developed a new ionothermal synthesis approach for high-quality CeO2 particles using 1-ethyl-3-methylimidazolium tetrafluoroborate as an imidazole ionic liquid without a template. Based on the scanning electron microscopy and particle size distribution, CeO2 particles synthesized at a reaction temperature of 210 °C for 16 h displayed sizes ranging between 0.1 and 0.3 μm. Additionally, the spherical shapes exhibited good crystallinity, regular morphology, and uniform dispersion. The results of CMP experiments indicated that the abrasives could reduce the surface roughness from 1.63 to 0.29 nm (scanning area is 5 μm × 5 μm). The obtained synthesized CeO2 particles demonstrated promising performance in Si polishing, achieving removal rates of up to 255.5 nm/min. It found that the removal rate of the abrasive prepared by ionic thermal synthesis in Si polishing was twice as much as other abrasives. Further, a possible mechanism was put forward to explain the formation of CeO2 structures with various morphologies. The proposed method presents a new approach for synthesizing CeO2 particles with uniform morphology and excellent polishing properties.

A strategy to optimize precompression pressure for tablet manufacturing based on in-die elastic recovery

A precompression pressure optimization strategy using in-die elastic recovery was developed to effectively address tablet lamination caused by air entrapment. This strategy involves exacerbating the air entrapment issue using high tableting speeds and main compaction pressures and collecting in-die elastic recovery data as a function of precompression pressure. The optimized precompression pressure, which corresponds to the minimum elastic recovery, is most effective at eliminating air from the powder bed prior to the main compression. When the optimized precompression pressure was employed, intact tablets of a model blend prone to lamination due to air entrapment could be produced over a wide range of high main compaction pressures, while tablets without precompression laminated immediately after ejection at equivalent main compaction pressures. This optimization strategy is effective for addressing lamination issues due to air entrapment using precompression. An advantage of this strategy is that intact tablets are not required to identify an optimized precompression pressure since elastic recovery measurements occur in-die.

Switching of n- and p-type doping with partial pressure of oxygen gas on few layers MoS2-field effect transistor

We examined the oxygen adsorption effect on the electric property of the field-effect transistor with an atomic layer MoS2 channel, whose experiment was executed in well-defined ultra-high vacuum conditions and with surface treatment. The threshold voltage change of the Id-Vg curve with the oxygen partial pressure shows n-type doping in the low-pressure range and p-type doping in the high-pressure range. In this report, the Vth vs. oxygen partial pressure uptake curve is well modeled with the Langmuir type adsorption/desorption. The deduced adsorption energy indicates that the adsorbed species are oxygen atoms on the pristine MoS2, suggesting a catalytic behavior of MoS2 for the oxygen reduction reaction. The oxygen adsorption at the S vacant site induces the initial n-type doping. DFT calculation illustrates that, despite the electron transfer from the substrate to the oxygen molecule, the electronic structure change causes the n-type doping.

A micro-dome array triboelectric nanogenerator with a nanocomposite dielectric enhancement layer for wearable pressure sensing and gait analysis.

The practical application of a triboelectric nanogenerator (TENG) as a self-powered sensor and an energy harvester is constrained by the need for a wide sensitivity range, significant output power, and structural flexibility. However, most research has focused on physical and chemical surface modifications of the charge-generating layer to enhance the TENG performance. Improving the charge storage ability could otherwise further enhance the overall performance. Here, we propose a flexible TENG design that incorporates a micro-dome array Ecoflex as the tribo-negative layer, coupled with a dielectric enhancement layer composed of a carbon black/Ecoflex composite. The addition of the CB/Eco composite layer to the micro-dome array triboelectric layer enhanced the output voltage performance by forming numerous micro capacitors within the dielectric layer. Furthermore, oxygen-containing fluorocarbon plasma treatment of the micro-dome array increased the surface energy, enhancing the interaction between the triboelectric layers. This leads to an enhancement in the output voltage and energy efficiency, exhibiting a power density of 197.4 mW m-2. The pressure sensitivity of the TENG was systematically investigated, demonstrating 2.57 V kPa-1 in the low-pressure range (0.612 to 8.58 kPa) and 1.70 V kPa-1 in the high-pressure range (8.58 to 20.83 kPa). Additionally, the encapsulated TENG sensor with spacers was integrated into insoles for self-powered gait analysis, providing real-time insights into walking patterns and frequencies. Exploring the TENG's energy harvesting capability revealed a peak-peak voltage of 89.4 V when two TENGs are connected in series. The comprehensive performance characterization of the TENG demonstrates its promising applications in wearable, self-powered sensing, and energy harvesting systems.

Dome-Conformal Electrode Strategy for Enhancing the Sensitivity of BaTiO3-Doped Flexible Self-powered Triboelectric Pressure Sensor.

A microstructured surface has been applied in self-powered triboelectric pressure sensors to increase the charge-carrying sites and enhance the output performance. However, the microstructure increases the distance between the electrode and the triboelectric layer, and its influence on the output performance is unknown. Herein, we proposed a dome-conformal electrode strategy for a self-powered triboelectric nanogenerator (TENG) pressure sensor. With a simple reverse-dome adsorption process, an ultrathin triboelectric layer and Ag electrode can be made conformal to the dome PDMS structure. The TENG sensor is constructed with paper as a positive triboelectric layer. Compared with the device based on nonconformal structure, the conformal design strategy endows the device with a faster charge transfer and enhanced output voltage. By doping with BaTiO3, the outermost triboelectric layer can be easily modified to improve its ability of sustaining charge, and an ultrathin PDMS layer is coated on the triboelectric layer to expand the triboelectric polarity difference between two triboelectric layers so as to enhance the output voltage. The synergistic effects enable the optimized TENG sensor with a sensitivity of 0.75 V/kPa in the low-pressure region (0-26 kPa) and 0.19 V/kPa in the high-pressure range (26-120 kPa). Its application in human motion detection, grabbing water beakers, and noncontact distance testing has been demonstrated. This work provides a route such as a conformal structure design strategy to enhance the output performance of a microstructure-based TENG sensor.

Generation of Runaway Electrons near Micro-Inhomogeneities on the Cathode Surface in Subnanosecond Self-Sustained Discharges in a Wide Range of High Pressures

Generation of Runaway Electrons near Micro-Inhomogeneities on the Cathode Surface in Subnanosecond Self-Sustained Discharges in a Wide Range of High Pressures

Generation of Runaway Electrons near Micro-Inhomogeneities on the Cathode Surface in Subnanosecond Self-Sustained Discharges in a Wide Range of High Pressures

The results of numerical 3D modeling of the development of an electron avalanche initiated by a field emission electron in a small-sized region of an amplified electric field near the microinhomogeneities at the cathode have been presented. The simulation has been carried out for the discharge gaps with an initially homogeneous distribution of the electric field with a reduced intensity significantly lower than that required by the electron runaway criterion. The possibility of the transition of the field emission electrons initiating avalanches and the electrons in these avalanches into runaway regime has been investigated. The microinhomogeneities in the form of a cone, metal droplets, and boundaries between pores or microcraters have been considered. The calculations were carried out for nitrogen in the pressure range from atmospheric to 40 atm. It has been shown that the initial energy obtained near the microinhomogeneity can significantly facilitate the transition of the electron into the runaway mode. And the electron will continue to run away in a discharge gap electric field weak according to the runaway criterion. It has been shown that this effect is especially noticeable at gas pressures above 10 atm. A comparative analysis of the simulation results with the experimental data obtained by us on the switching characteristics of a discharge gap filled with nitrogen when exposed to voltage pulses with subnanosecond fronts of different steepness has been carried out. This made it possible to divide the ranges of experimental conditions into those when only the amplification of the electric field near the microinhomogeneities is sufficient for the runaway of electrons and when the electric field of an avalanche of critical or close to critical size is additionally necessary for the runaway.

Enhanced capacitive pressure sensing performance by charge generation from filler movement in thin and flexible PVDF-GNP composite films

ABSTRACT This study introduces an approach to overcome the limitations of conventional pressure sensors by developing a thin and lightweight composite film specifically tailored for flexible capacitive pressure sensors, with a particular emphasis on the medium and high pressure range. To accomplish this, we have engineered a composite film by combining polyvinylidene fluoride (PVDF) and graphite nanoplatelets (GNP) derived from expanded graphite (Ex-G). A uniform sized GNPs with an average lateral size of 2.55av and an average thickness of 33.74 av with narrow size distribution was obtained with a gas-induced expansion of expandable graphite (EXP-G) combined with tip sonication in solvent. By this precisely controlled GNP within the composite film, a remarkable improvement in sensor sensitivity has been achieved, surpassing 4.18 MPa−1 within the pressure range of 0.1 to 1.6 MPa. This enhancement can be attributed to the generation of electric charge from the movement of GNP in the polymer matrix. Additionally, stability testing has demonstrated the reliable operation of the composite film over 1000 cycles. Notably, the composite film exhibits exceptional continuous pressure sensing capabilities with a rapid response time of approximately 100 milliseconds. Experimental validation using a 3 × 3 sensor array has confirmed the accurate detection of specific contact points, thus highlighting the potential of the composite film in selective pressure sensing. These findings signify an advancement in the field of flexible capacitive pressure sensors that offer enhanced sensitivity, consistent operation, rapid response time, and the unique ability to selectively sense pressure.

Evaluating the accuracy of liquid permeability measurements in shale and tight rocks using transient flow method and comparison with gas permeability

The transient flow method for measuring permeability to liquid is a useful technique for shale and tight rocks; however, it is not as popular as the steady-state method in these rocks. One of the issues is the lack of clarity on a key term of compressibility of the fluid and rock system. Various forms of compressibility have been used in literature, which can lead to inconsistent results of liquid permeability. Using gas for the permeability measurement is more common in shale, and the Klinkenberg corrected permeability is often used to represent liquid permeability; however, how the Klinkenberg permeability is compared to liquid permeability in shale or tight rocks is not adequately addressed. This paper presents a study using the transient flow method for water and oil permeability measurement in three Eagle Ford Shale samples. Gas permeability was also measured for these samples. Different forms of the total compressibility of the fluid-rock system (Ct) are summarized from literature, and a new form of Ct is proposed. The accuracy of the calculations based on different forms of Ct is evaluated through the comparison between water and oil permeabilities and the comparison with gas permeability. The results are also compared with oil permeability obtained from the steady-state method. The new form of Ct provided the most accurate results, whereas the other forms of Ct led to errors. However, for samples with bulk compressibility of less than 1 × 10−7 psi−1, the error using those forms of Ct was negligible. The study also found that the Klinkenberg permeability obtained from the linear extrapolation is larger than the oil permeability for two samples by 12% and 37%, respectively, whereas it is smaller than the oil permeability for the other sample. This comparison suggests that a nonlinear gas slippage effect may exist in the high pressure range (>2000 psi) for shale or tight rock samples.

Experimental Comparison of Hydrogen Refueling with Directly Pressurized vs. Cascade Method

This paper presents a comparative analysis of two hydrogen station configurations during the refueling process: the conventional “directly pressurized refueling process” and the innovative “cascade refueling process.” The objective of the cascade process is to refuel vehicles without the need for booster compressors. The experiments were conducted at the Hydrogen Research and Fueling Facility located at California State University, Los Angeles. In the cascade refueling process, the facility buffer tanks were utilized as high-pressure storage, enabling the refueling operation. Three different scenarios were tested: one involving the cascade refueling process and two involving compressor-driven refueling processes. On average, each refueling event delivered 1.6 kg of hydrogen. Although the cascade refueling process using the high-pressure buffer tanks did not achieve the pressure target, it resulted in a notable improvement in the nozzle outlet temperature trend, reducing it by approximately 8 °C. Moreover, the overall hydrogen chiller load for the two directly pressurized refuelings was 66 Wh/kg and 62 Wh/kg, respectively, whereas the cascading process only required 55 Wh/kg. This represents a 20% and 12% reduction in energy consumption compared to the scenarios involving booster compressors during fueling. The observed refueling range of 150–350 bar showed that the cascade process consistently required 12–20% less energy for hydrogen chilling. Additionally, the nozzle outlet temperature demonstrated an approximate 8 °C improvement within this pressure range. These findings indicate that further improvements can be expected in the high-pressure region, specifically above 350 bar. This research suggests the potential for significant improvements in the high-pressure range, emphasizing the viability of the cascade refueling process as a promising alternative to the direct compression approach.

Application of Ultrasonic Methods for Evaluation of High-Pressure Physicochemical Parameters of Liquids

An emerging ultrasonic technology aims to control high-pressure industrial processes that use liquids at pressures up to 800 MPa. To control these processes it is necessary to know precisely physicochemical properties of the processed liquid (e.g., Camelina sativa oil) in the high-pressure range. In recent years, Camelina sativa oil gained a significant interest in food and biofuel industries. Unfortunately, only a very few data characterizing the high-pressure behavior of Camelina sativa oil is available. The aim of this paper is to investigate high pressure physicochemical properties of liquids on the example of Camelina sativa oil, using efficient ultrasonic techniques, i.e., speed of sound measurements supported by parallel measurements of density. It is worth noting that conventional low-pressure methods of measuring physicochemical properties of liquids fail at high pressures. The time of flight (TOF) between the two selected ultrasonic impulses was evaluated with a cross-correlation method. TOF measurements enabled for determination of the speed of sound with very high precision (of the order of picoseconds). Ultrasonic velocity and density measurements were performed for pressures 0.1–660 MPa, and temperatures 3–30°C. Isotherms of acoustic impedance Z_a, surface tension σ and thermal conductivity k were subsequently evaluated. These physicochemical parameters of Camelina sativa oil are mainly influenced by changes in the pressure p, i.e., they increase about two times when the pressure increases from atmospheric pressure (0.1 MPa) to 660 MPa at 30°C. The results obtained in this study are novel and can be applied in food, and chemical industries.

Design of PDMS/CNT flexible pressure sensor based on double structure with the regulation of electrical properties

Introducing microstructure on the surface or porous structure inside of dielectric layer can improve the sensitivity and monitoring range of the flexible pressure sensor. However, developing pressure sensors with high sensitivity in the high-pressure range is challenging because of the trade-off between sensitivity and linearity of pressure. Here, we report a design approach based on the collaboration of double structure and electrical characteristics that can improve sensor sensitivity at high pressure. The surface microstructural and internal porous structure of the dielectric layer provide a more comprehensive deformation range for the sensor from a mechanical perspective. The effects of the conductive carbon nanotube (CNT) content between two structures on the overall electromechanical characteristics of the sensor were studied. This collaborative (structure and component) design can effectively increase the monitoring range of the sensor and accomplish “gear shifting” of the sensitivity by the non-uniform distribution of CNT in the structure. The optimized capacitive pressure sensor exhibits outstanding sensitivity over a wide monitoring range (1.17 kPa−1 in the 0−100 kPa, 0.49 kPa−1 in the 100−350 kPa, and 0.23 kPa−1 in the 350−1000 kPa), and fast response capability (30 ms). The pressure sensor has excellent integrated sensing performance in rubber wheels' static/dynamic pressure monitoring, demonstrating application potential in high-pressure fields.

Sintering pure polycrystalline boron carbide bulks with enhanced hardness and toughness under high pressure

Boron carbide ceramics possess high hardness, but they generally are subjected to low toughness due to strong covalent bonds. However, the fabrication of dense and pure polycrystalline boron carbide bulks with excellent mechanical properties by conventional methods remains a significant challenge. Here, the fine-grained and pure polycrystalline boron carbide bulks have been successfully fabricated utilizing submicron-sized boron carbide powder as starting materials under the condition of high pressure (5.5 GPa) and low temperature range (1000–1400 °C). The well-sintered boron carbide bulk recovered at 1000 °C exhibits a mean grain size of 205.2 ± 191.2 nm and relative density of up to ∼97%, and the measured Vickers hardness and fracture toughness achieve 35.0 ± 2.8 GPa and 4.6 ± 0.5 MPa m0.5, respectively. The outstanding trade-off between hardness and toughness demonstrated that the synergistic effect between fine grain size and dislocation, and the interplay between amorphous grain-boundary phases and pores via grain-boundary sliding have critical role in contributing to improve hardness and toughness, respectively. This study has essential implications in sintering fine-grained and pure polycrystalline engineering ceramics and superhard materials, which provide a tuning approach to enhance the mechanical properties.