Simulated Working Conditions Research Articles

Investigation of Friction and Erosion Wear Properties of Titanium and Titanium Alloy Pipes.

Titanium alloys are applied in oil and gas development and transportation to improve conditions because of their high specific strength and corrosion resistance. However, the disadvantage of poor wear resistance has become an obstacle to developing titanium alloys. The friction and wear properties of pure titanium TA3 and titanium alloy TA10 were tested under different loads and different friction forms using a reciprocating friction and wear tester. Moreover, the erosion resistance of pure titanium TA3 and titanium alloy TA10 was studied using a gas-solid erosion tester. The results show that the wear rate of TA3 and titanium alloy TA10 increases with increasing friction load. Under a load of 50 N, the mass losses of TA3 under dry friction and wet friction were 0.0013 g and 0.0045 g, respectively, while the mass losses of TA10 were 0.0033 g and 0.0046 g, respectively. While the load increased to 70 N, the mass loss of TA3 was even greater, reaching 0.0065 g, and the mass loss of TA10 was 0.0058 g. The wear forms of TA3 and TA10 include abrasive wear, adhesive wear and oxidation wear. The joint action of various friction forms leads to the loss of materials. Under the simulated working conditions, the erosion rates of TA3 and TA10 were 1.01 × 10-3 g/s and 0.94 × 10-3 g/s. The erosion mechanism is the same, including plowing, indentation and cracking.

Synergistic regulation of microstructure, properties, and abrasive wear mechanism of a medium carbon dual phase steel for plowshares

In this study, a new medium carbon dual phase (DP) steel for plowshares is prepared. The quenching and partitioning process of the medium carbon steel is designed and optimised using the constrained carbon equilibrium model. The optimised process parameters are quenching temperature of 880 °C, quenching bath temperature of 190 °C and partitioning temperature of 350 °C. The microstructure of the acicular martensite matrix with 13% retained austenite was prepared, so that the good mechanical properties of tensile strength of 2007 MPa, yield strength of 1689 MPa, elongation of 11% and impact energy of 12 J are obtained. The multi-scale characterisation and abrasive wear experiments are carried out to investigate its microstructural evolution and wear mechanism under simulated working conditions. The results show that the coordinated deformation of retained austenite and martensite, as well as the trip effect, endows it with ultra-high strength and good plasticity. The recurring process of formation and spalling of the hardened layer is the main wear pattern of this medium carbon DP steel. The synergism of twinning formation and (Ti, Mo)C precipitation enhances wear resistance of this medium carbon DP steel.

The unique influence of 1000 °C high-speed rotation simulated turbine blade working conditions on microstructural degradation of single-crystal superalloy NiAlReRu

Turbine blades are mainly subjected to thermal stress and gradient centrifugal stress in operational conditions. The effects of centrifugal stress on the microstructural degradation of single crystal superalloys under a multiaxial stress state remain unclear. Here, the NiAlReRu component was exposed to high-speed rotation at 20,000 rpm and a high temperature of 1000 °C for 100 h. The analysis indicates that the centrifugal stress causes the distortion of dendrite stems and the aggregation of micropores. The centrifugal stress promotes the formation of interfacial dislocation networks, accompanied by more severe rafting of γ′ phases. These findings provide a comprehensive experimental understanding of the microstructural evolution under simulated turbine blade working conditions, which provides a reference for the subsequent tests under near-service conditions.

Underground coal gangue recognition based on composite fusion of feature and decision

Abstract The underground coal gangue separation and in-situ filling can reduce environmental pollution, promote the recycling of resources, and ensure the safe operation of mining. However, the harsh environment and abnormal working conditions are a significant challenge to the separation technology. Therefore, it is essential to develop a coal gangue classification method that is highly accurate, robust, and can handle abnormal working conditions. To address the above problems, this paper innovatively combines spectral modalities with image modalities to establish a multimodal fusion idea of composite fusion. Firstly, the feasibility of spectral-image fusion and effective fusion criterion are explored under the concat fusion strategy through various feature combinations and classification algorithms under ideal conditions to improve the performance of the model; Secondly, feature fusion is introduced into the single-layer perceptron and its potential in deep learning is explored to improve the performance of the model; Then the quantitative criteria of the judgment matrix are improved based on the analytical hierarchy method (AHP) to improve the scientificity and objectivity of decision making; Finally, the effectiveness of our method is verified by testing the bimodal dataset of simulated working conditions. The results show that the accuracy of the composite fusion of spectral and image features reaches 91.43%, and our AHP can be applied to all basic model scenarios, which makes the method highly applicable and feasible. The fusion of deep neural networks shows the strong potential of modal fusion in deep learning. This method can provide a new idea for intelligent separation of underground coal gangue.

Enhanced Catalytic Oxidation Reactivity over Atomically Dispersed Pt/CeO2 Catalysts by CO Activation.

The elevation of the low-temperature oxidation activity for Pt/CeO2 catalysts is challenging to meet the increasingly stringent requirements for effectively eliminating carbon monoxide (CO) from automobile exhaust. Although reducing activation is a facile strategy for boosting reactivity, past research has mainly concentrated on applying H2 as the reductant, ignoring the reduction capabilities of CO itself, a prevalent component of automobile exhaust. Herein, atomically dispersed Pt/CeO2 was fabricated and activated by CO, which could lower the 90% conversion temperature (T90) by 256 °C and achieve a 20-fold higher CO consumption rate at 200 °C. The activated Pt/CeO2 catalysts showed exceptional catalytic oxidation activity and robust hydrothermal stability under the simulated working conditions for gasoline or diesel exhausts. Characterization results illustrated that the CO activation triggered the formation of a large portion of Pt0 terrace sites, acting as inherent active sites for CO oxidation. Besides, CO activation weakened the Pt-O-Ce bond strength to generate a surface oxygen vacancy (Vo). It served as the oxygen reservoir to store the dissociated oxygen and convert it into active dioxygen intermediates. Conversely, H2 activation failed to stimulate Vo, but triggered a deactivating transformation of the Pt nanocluster into inactive PtxOy in the presence of oxygen. The present work offers coherent insight into the upsurging effect of CO activation on Pt/CeO2, aiming to set up a valuable avenue in elevating the efficiency of eliminating CO, C3H6, and NH3 from automobile exhaust.

A circadian-informed lighting intervention accelerates circadian adjustment to a night work schedule in a submarine lighting environment.

Night work has detrimental impacts on sleep and performance, primarily due to misalignment between sleep-wake schedules and underlying circadian rhythms. This study tested whether circadian-informed lighting accelerated circadian phase delay, and thus adjustment to night work, compared to blue-depleted standard lighting under simulated submariner work conditions. Nineteen healthy sleepers (12 males; mean±SD aged 29 ±10 y) participated in two separate 8-day visits approximately one month apart to receive, in random order, circadian-informed lighting (blue-enriched and dim, blue-depleted lighting at specific times) and standard lighting (dim, blue-depleted lighting). After an adaptation night (day 1), salivary dim light melatonin onset (DLMO) assessment was undertaken from 18:00-02:00 on days 2-3. During days 3-7, participants completed simulated night work from 00:00-08:00 and a sleep period from 10:00-19:00. Post-condition DLMO assessment occurred from 21:00-13:00 on days 7-8. Ingestible capsules continuously sampled temperature to estimate daily core body temperature minimum (Tmin) time. Tmin and DLMO circadian delays were compared between conditions using mixed effects models. There were significant condition-by-day interactions in Tmin and DLMO delays (both p<0.001). After four simulated night shifts, circadian-informed lighting produced a mean [95%CI] 4.3 [3.3 to 5.4] h greater delay in Tmin timing and a 4.2 [3 to 5.6] h greater delay in DLMO timing compared to standard lighting. Circadian-informed lighting accelerates adjustment to shiftwork in a simulated submariner work environment. Circadian lighting interventions warrant consideration in any dimly lit and blue-depleted work environments where circadian adjustment is relevant to help enhance human performance, safety, and health.

Dynamic breakthrough performance of low concentration CO2 adsorption in fixed-bed column with porous amino acid ionic liquid composites

Low concentration carbon dioxide (CO2) capture from air or confined spaces currently faces significant challenges, such as relatively poor dynamic adsorption breakthrough performance and cyclic stability. In our previous work, functionalized ionic liquid (IL) tetraethylammonium glycine ([N2222][Gly]) and porous molecular sieve (SBA-15) were combined to synthesize porous amino acid IL composite 60 wt% [N2222][Gly]@SBA-15 with microporous and ultra-microporous structures, which provide a new pathway for low concentration CO2 capture. In order to further obtain the dynamic CO2 adsorption breakthrough performance of this material under simulated actual working conditions, the effects of temperatures, relative humidity (RH) and CO2 concentrations on CO2 adsorption and desorption breakthrough performance of 60 wt% [N2222][Gly]@SBA-15 in a fixed-bed column were systematically studied in this work. The results indicated that CO2 adsorption capacity is up to 1.81 mmolCO2/g-adsorbent at 298.15 K, 1 bar and 0 % RH under 1 vol% CO2-containing gas mixture balanced with N2 and reaches 2.44 mmolCO2/g-adsorbent at 15 % RH due to the mechanism change of CO2 reaction with primary amine from 2: 1 under dry gas to 1: 1 stoichiometry in the presence of moisture. Moreover, the adsorbent maintains good cyclic adsorption-desorption performance. Further, CO2 adsorption breakthrough behaviors were well fitted by Avrami kinetic model, and the CO2 adsorption rate of 60 wt% [N2222][Gly]@SBA-15 was controlled by intra-particle diffusion. This work implied that IL-modified adsorbents have great potentials for low concentration CO2 capture applications.

An intelligent body frame structure modeling and optimization system based on conceptual design

The conceptual design stage is an indispensable and important stage in the development of the modern body. However, due to the lack of sufficient body structure parameter support, the design defects generated at this time are difficult to make up for in the subsequent design stage. Therefore, it is of great significance to develop a conceptual design software for body structure that integrates design, analysis, and optimization. This paper proposes an intelligent body frame structure modeling and optimization system based on conceptual design, S-iVCD (Intelligent System for Conceptual Design of Vehicle Body Structure). Based on deep learning methods and body design sketches, a conceptual model of body structure is quickly established. Based on the data parameters stored in the Excel table, the system is seamlessly connected to the domestic independent finite element software SIPESC to calculate the simulated working conditions. The body structure optimization module is driven by the MMA (method of moving asymptotes), and takes the body structure performance and total mass as the optimization goals or constraints of the mathematical model to achieve body structure performance improvement and lightweight design.

Effect and performance analysis of different surface treatments on polymer-metal friction pairs

The reliability of machinery can be directly impacted by severe wear and failure of joint bearings, particularly under harsh operating conditions or after prolonged use. The study aimed to investigate the impact of various surface treatments on the properties of materials using a disc-disc contact friction machine to simulate working conditions similar to those experienced by joint bearings. The application of chrome plating resulted in a significant enhancement in performance, leading to a 20% reduction in the coefficient of friction and an 80% decrease in the wear rate to 0.071 and 1 × 10−5 mm3/(N·m), respectively, at 30 MPa and 42 mm/s. Additionally, it increased the bonding of the transfer film base by 20% compared to untreated specimens, as indicated by nano-scratch tests. On the one hand, the elevated hardness of the chrome-plated coating facilitates uniform load distribution, while on the other hand, the presence of microcracks on the surface aids in retaining a greater amount of abrasive debris and in the formation of a more effective transfer film. Consequently, this diminishes the wear of the polymer material. This discovery has the potential to influence the improvement of surface treatment procedures and the selection of materials for the advancement of engineering practices.

Circadian-based lighting substantially improves vigilance in simulated night shift work conditions compared to standard lighting

Circadian-based lighting substantially improves vigilance in simulated night shift work conditions compared to standard lighting

Testing surveillance thermal imagers under simulated real work conditions

Testing surveillance thermal imagers under simulated real work conditions

拖拉机轮胎在松软土壤上的牵引特性评价：仿真与试验研究

In this study, a tire-soil rolling contact model based on the finite element method was established to determine the traction characteristics of the tire on the loose soil. Considering the soil parameters and tire parameters (loads, slip, inflation pressure and tread pattern), the influence of traction characteristics of the tire was obtained, taking tire sinkage and gross traction as evaluation indexes. The correctness of the tire-soil rolling contact model was verified by carrying out the soil bin-single wheel experiments. The results of the simulation and test showed that with the increase of load and sinkage of the tire, the gross traction tended to increase, thus enhancing the tire traction characteristics. With the increase of slip, the tire sinkage and gross traction increased, and the best tire traction characteristics were exhibited at a slip of 20%. Within the rated inflation pressure, as the inflation pressure increased, the tire sinkage decreased, the tire gross traction decreased and the traction characteristics of the tire were weakened. Under simulated working conditions, the traction characteristics of the tire first increased and then decreased with the increase of the number of tire lug pairs, and 15 tire lug pairs performed best. This paper presents a further study on the interaction between tires and soil under different influencing factors, and its findings provide an effective reference for predicting the traction performance assessment of tractor tires on working roads.

Corrosion Performance Analysis of Tubing Materials with Different Cr Contents in the CO2 Flooding Injection–Production Environment

In order to clarify the difference in corrosion performance between low Cr-containing (3Cr, 5Cr, and 9Cr) tubing material and carbon steel N80 in the Carbon dioxide (CO2) flooding injection and production environment and the range of adaptation, corrosion tests and analysis were carried out in simulated working conditions. In this paper, the electrochemical potentiodynamic testing technology and the weight loss method were used to comparatively analyze the corrosion performance and variation law of three types of tubing materials with different Cr contents in a simulated CO2 flooding-produced water environment under different partial pressure conditions. Additionally, scanning electron microscopy and Energy Dispersive Spectrometer (EDS) analysis were conducted to examine the surface corrosion morphology characteristics and elemental composition of material films under various conditions. The results indicate that the open circuit potentials of 3Cr, 5Cr, and carbon steel N80 were similar under the same experimental conditions. However, the open circuit potentials of 9Cr were relatively high and there was an obvious passivation zone in anodic polarization. Nevertheless, compared to that of 13Cr, the passivation state was unstable, and pitting corrosion continued to expand once it formed. This demonstrates that the corrosion resistance of the material can be effectively enhanced and a stable passivation state can be achieved in the anodic polarization region when the Cr content of the material reaches at least 13%. The service life of materials can be predicted based on their corrosion rate under high temperature and pressure simulation environments. We found that 9Cr materials exhibited good adaptability while 3Cr and 5Cr materials showed poor adaptability. Therefore, it was not recommended to use 3Cr and 5Cr materials. Therefore, 3Cr, 5Cr, and N80 materials will be used at lower partial pressure levels of CO2 (&lt;0.2 MPa).

The fitness and corrosion mechanisms of high‐strength steel in corrosive oil–water environment at high temperature

AbstractThis work investigated the mechanical decay mechanism and high‐temperature corrosion mechanism of high‐strength steel via high‐temperature mechanical experiments, and corrosion and stress corrosion cracking tests were performed in simulated working conditions where water, oil, H2S, and CO2 coexist. The results show that the tensile strength and yield strength of high‐strength steel decrease with increasing temperature; the tensile strength and yield strength at 350°C reduce 11.91% and 19.08%, respectively, compared with 25°C. Moreover, the corrosion rate of high‐strength steel gradually increased from 0.0914 mm/a at 150°C to 1.2288 mm/a at 350°C. In addition, the influence of high temperature on the corrosion mechanism was inferred through thermodynamic calculations, and the reason for the presence of Fe3O4 in the corrosion products at 350°C was analyzed. At 350°C, stress corrosion cracking was observed in high‐strength steels when the applied stress reached 90% of the yield strength. Based on the aforementioned studies, the relevant mechanisms related to the decay of mechanical properties, corrosion, and stress corrosion cracking are also proposed.

CFD analysis of hydrodynamic force on a horizontal axis tidal turbine

Horizontal axis tidal turbines are similar to wind turbines in both geometry and principle of operation, yet they need to withstand much heavier loadings and extreme conditions in a harsh operating environment. Consequently, the loadings on tidal turbine blades need to be accurately evaluated within the design stage to ensure they can withstand loadings with little need for repair. With the advancement of computational capabilities, computational fluid dynamics offers a relatively inexpensive method of simulating working conditions and estimating loadings, compared to traditional physical testing, while maintaining accuracy and applicability under a range of operating conditions. In this research, a computational fluid dynamics model of a tidal turbine rotor has been developed using commercial code ANSYS CFX, where the three-dimensional blade geometry is developed from the prototype tidal turbine used in the Round Robin Tests in the framework of the H2020 MaRINET2 Infrastructures Network project. The outputs from the numerical model are validated against the experimental results, where it is revealed that with an increasing rotating speed of the tidal turbine, the thrust force that turbine experienced increases, while the torque force experiences a rise firstly, reaching a maximum value and then decreases gradually. In addition, the experimental results show that during the operation of ocean tidal turbines, the turbine blades experience frequent and large-scale fluctuation of hydrodynamic loads, including thrust and torque, which may lead to tidal turbine blade damage due to fatigue. Therefore, the next stage of development with this numerical model is fatigue loading evaluation, in order to improve the present fatigue design and testing of tidal turbine blades, while gaining a greater understanding of the damage mechanisms.

Pore engineering in cost-effective and stable Al-MOFs for efficient capture of the greenhouse gas SF6

The capture and separation of the greenhouse gas sulfur hexafluoride (SF6) from nitrogen (N2) holds significant potential for mitigating the greenhouse effect and yielding economic advantages for the semiconductor industry. In this study, a pair of isoreticular cost-effective and stable metal–organic frameworks (MOFs) with slightly different pore environments (CAU-10-H and CAU-10-Py) were prepared at >10 g scale for SF6/N2 separation. CAU-10-Py exhibited a remarkable improvement in SF6 uptake capacity at both low pressure (1.13 mmol/g at 0.1 bar and 298 K, compared to 0.68 mmol/g) and elevated pressure (2.11 mmol/g at 1 bar and 278 K, compared to 1.07 mmol/g). The ideal adsorbed solution theory (IAST) selectivity of SF6/N2 (10/90) was found to be 204 for CAU-10-Py and 123 for CAU-10-H. These enhanced capacities and selectivity endow CAU-10-Py a highly promising candidate for SF6 capture. Single crystal structural analysis, 77 K N2 adsorption data and theoretical calculations indicated that the substitution of benzene by pyridine slightly expand the pore diameter, facilitating more efficient accommodation of SF6 within the channel pores. The SF6 molecule is adsorbed around four benzene rings in CAU-10-H but trapped by two pyridine rings in CAU-10-py, resulting in one fold increase in adsorption capacity. Intriguingly, time-dependant adsorption experiments revealed that CAU-10-Py exhibited a higher SF6 adsorption rate and a lower N2 adsorption rate compared to CAU-10-H, further highlighting the benefit of CAU-10-Py for SF6/N2 separation. Dynamic breakthrough experiments conducted under simulated working conditions further confirmed the outstanding SF6/N2 separation performance of CAU-10-Py. Considering its excellent regeneration ability and cycling performance, this cost-effective and easily scalable MOF demonstrates great promise for SF6/N2 separation.

An Improved Gaussian Process Regression Based Aging Prediction Method for Lithium-Ion Battery

A reliable aging-prediction method is significant for lithium-ion batteries (LIBs) to prolong the service life and increase the efficiency of operation. In this paper, an improved Gaussian-process regression (GPR) is proposed to predict the degradation rate of LIBs under coupled aging stress to simulate working conditions. The complicated degradation processes at different ranges of the state of charge (SOC) under different discharge rates were analyzed. A composed kernel function was conducted to optimize the hyperparameter. The inputs for the kernel function of GPR were improved by coupling the constant and variant characteristics. Moreover, previous aging information was employed as a characteristic to improve the reliability of the prediction. Experiments were conducted on a lithium–cobalt battery at three different SOC ranges under three discharge rates to verify the performance of the proposed method. Some tips to slow the aging process based on the coupled stress were discovered. Results show that the proposed method accurately estimated the degradation rate with a maximum estimation root-mean-square error of 0.14% and regression coefficient of 0.9851. Because of the proposed method’s superiority to the exponential equation and GPR by fitting all cells under a different operating mode, it is better for reflecting the true degradation in actual EV.

Performance analysis of sCO2 tube with high non-uniform heat flux: Thermal-fluid-structural evaluation and optimization

A supercritical carbon dioxide (sCO2) tube is an important component in a sCO2 power system for a wide range of heat sources. The sCO2 tubes experience high temperature and pressure with high non-uniform heat flux when fossil fuel and solar energy are used as heat sources. Herein, a novel tube structure is proposed to match the circumferential thermal resistance with the non-uniform heat flux by changing the Eccentricity. A three-dimensional multi-physical coupling model was constructed to compare the proposed structure with a conventional tube. The fluid dynamics, thermal stress, and coupled heat transfer characteristics were analyzed, and the key working parameters were explored. The maximum temperature of the proposed structure was effectively reduced by 13–36 K and the maximum thermal stress was significantly reduced by approximately 25–33% under all the simulated working conditions when the Eccentricity changed from 0 to 0.4. The proposed novel structure will facilitate the safety and conserve tube material, and the results can serve as a reference for the development of sCO2 power systems for industrial applications.

Effect of Mineral Admixtures on the Mechanical and Shrinkage Performance of MgO Concrete.

Shrinkage deformation of concrete has been one of the difficulties in the process of concrete performance research. Cracking of concrete caused by self-shrinkage and temperature-drop shrinkage has become a common problem in the concrete world, and cracking leads to a decrease in the durability of concrete and even a safety hazard. Mineral admixtures, such as fly ash and mineral powder, are widely used to improve the temperature drop shrinkage of mass concrete; fly ash can reduce the temperature rise of concrete while also reducing the self-shrinkage of concrete, there are different results on the effect of mineral powder on the self-shrinkage of concrete, but the admixture of fly ash will reduce the strength of concrete, and mineral admixtures have an inhibitory effect on the shrinkage compensation effect of MgO expander(MEA). The paper investigates the effect of mineral admixtures on the mechanical and deformation properties of C50 mass concrete with a MgO expander(MEA), aiming to determine the proportion of C50 mass concrete with good anti-cracking properties under working conditions. The experiments investigated the effect of fly ash admixture, mineral powder admixture and MgO expander admixture on the compressive strength and deformation of concrete under simulated working conditions of variable temperature and analyzed the effect of hydration of magnesite in MgO expander and pore structure of cement paste on deformation. The following main conclusions were obtained: 1. When the concrete compounded with mineral admixture was cured under variable temperature conditions, the compounded 30% fly ash and mineral powder decreased by 4.3%, 6.0% and 8.4% at 7d age, and the compounded 40% fly ash and mineral powder decreased by 3.4%, 2.8% and 2.3% at 7d age, respectively. The incorporation of MEA reduced the early compressive strength of concrete; when the total amount of compounding remained unchanged, the early compressive strength of concrete was gradually smaller as the proportion of compounding decreased. 2. The results of concrete deformation showed that when the temperature rose, the concrete expanded rapidly, and when the temperature dropped, the concrete also showed a certain shrinkage, and the deformation of concrete basically reached stability at 18d. 3. The compounding of 30% fly ash and mineral powder As the compounding ratio decreases, the deformation of concrete increases, and the 28d deformation of concrete with a compounding ratio of 2:1 is 280 × 10-6, while the final stable deformation of concrete with a compounding ratio of 2:1 in compounding 40% fly ash and mineral powder is the largest, with a maximum value of 230 × 10-6, respectively. Overall, the concrete with a total compounding of 30% and a compounding ratio of 2:1 has the best shrinkage resistance performance.

Methyl-functionalized microporous metal-organic framework for efficient SF6/N2 separation

The capture and separation of sulfur hexafluoride (SF6) from nitrogen (N2) has the potential to reduce greenhouse gas emissions and provide economic benefits to the semiconductor industry. Herein, a series of metal–organic frameworks (MOFs) with different pore environments (Ni(pba)2 (pba = 4-(4-pyridyl)benzoate), Ni(3-mpba)2 (3-mpba = 3-methyl-4-(4-pyridyl)benzoate), and Co(3-mpba)2) were designed and synthesized for SF6/N2 separation. The most promising candidate is Ni(3-mpba)2, which exhibits excellent SF6 uptake capacity (63.4 cm3 g−1 at 298 K and 100 kPa) and the highest SF6/N2 selectivity (221 at 298 K and 100 kPa). X-ray diffraction analysis and theoretical calculations indicate that introducing the methyl group into Ni(3-mpba)2 alters the microchemical environment of the pores. Ni(3-mpba)2 has a smaller pore structure and more binding sites than Ni(pba)2; its structure and binding sites enhance the affinity between sulfur hexafluoride and the adsorbent. Dynamic breakthrough experiments further verify the remarkable separation performance of Ni(3-mpba)2 under simulated actual working conditions. In combination with its excellent regeneration ability and cycling performance, this porous coordination network shows great promise for SF6/N2 separation.