Insight into the vacancy effects on mechanical and electronic properties of Tantalum Silicide

The effects of the vacancies on the structural stability, elastic constants, elastic moduli, brittle-to-ductile transition and electronic properties of Tantalum Silicide (TaSi₂) are investigated in detail by first-principles calculations. The values of vacancy formation energy confirm that the perfect TaSi₂ and TaSi₂ with different atomic vacancies can exhibit the structural stability at ground state. It is found that Ta atom vacancies are more stable than Si atom vacancies in TaSi₂ with vacancies. The elastic constants and elastic moduli describe the mechanical behavior for TaSi₂ and TaSi₂ with vacancies. The different atomic vacancies weaken the elastic stiffness for TaSi₂. But the values of B/G confirm that the brittle-to-ductile transition occurs with different atomic vacancies for TaSi₂. Although these vacancies make the shear and volume deformation resistance of TaSi₂ weaker, they obviously improve the brittle behavior of TaSi₂. The difference charge density and electronic structures are calculated to discuss and analyze the structural stability and mechanical properties for the perfect TaSi₂ and TaSi₂ with vacancies.     

Growth of nano-textured graphene coatings across highly porous stainless steel supports towards corrosion resistant coatings

In this paper, we demonstrated for the first time the growth of 3D networks of graphene nano-flakes across porous stainless steel substrates of micron sized metal fibres, and its anti-corrosion properties. The controlled formation of graphene-grade coatings in the form of single sheets to complex and homogeneously distributed 2–4 μm long nano-pillars is demonstrated by Scanning Electron Microscopy. The morphology and stability of these structures are shown to be particularly related to the temperature and feed gas flow rate during the growth. The number of layers across the graphene materials was calculated from the Raman spectra and is shown to range between 3 and more than 15 depending on the growth conditions and to be particularly related to the time and flow rate of the experiment. The presence of the graphene was shown to massively enhance the specific surface area of the material and to contribute to the increased corrosion resistance and electrical conductivity of the material without compromising the properties or structure of the native stainless steel materials. This new approach opens up a new route to the facile fabrication of advanced surface coatings with potential applications in developing new thermal exchangers, separation and bio-compatible materials.     

Improved catalytic stability and anti-coking ability of Ni/La2O3–Al2O3 catalyst by doping alkaline earth metals for n-decane reforming

In this paper, a series of alkaline earth metals oxides doped Ni/La₂O₃–Al₂O₃ catalysts were synthesized by the coprecipitation method combined with two step impregnation methods. n-decane reforming was used to investigate these catalysts, in order to develop an excellent catalyst with better hydrogen selectivity, activity, stability, as well as lower carbon deposition. Deactivation by carbon deposition, the catalyst regenerability and stability tests were also used to weigh the selected catalyst. These catalysts are characterized by N₂ adsorption-desorption, XRD, NH₃-TPD, Raman, and TEM. The introduction of alkaline earth metals modifiers enhances the activity, stability and anti-coking ability, meanwhile the SrO modified Ni/La₂O₃–Al₂O₃ shows the best catalytic activity. Moreover, the hydrogen selectivity and conversion over regenerative Ni/La₂O₃–Al₂O₃/SrO catalysts were quite close to the results of fresh ones. The enhancements of M oxides doped catalysts (especially Sr) can be due to the improved textural properties, basicity, metal-support interaction and anti-coking ability. As a consequence, loading different metals in different ways helps to gradually improve the stability, activity and coking inhibition of catalysts is an effective approach to obtain a multi-function catalyst.     

Transition metal atom doped C2N as catalyst for the oxygen reduction reaction: A density functional theory study

The catalytic mechanism and activity of transition metal atom doped C₂N (M-C₂N, M = Fe, Co, Ni, and Cu) for the oxygen reduction reaction (ORR) are investigated in detail by density functional theory method. All the screened M-C₂N are thermodynamically stable based on the binding energy calculations. The adsorption energy results indicate that the adsorption strength of O₂ and ORR intermediates are decreased in the order of Fe-C₂N ˃ Co-C₂N ˃ Ni-C₂N ˃ Cu-C₂N, in which the adsorption energy values on Cu-C₂N are most close to those on the Pt(111). Based on the relative energy diagram of ORR, the energetically favorable pathway on Fe-C₂N and Co-C₂N is direct 4e⁻ mechanism, in which the O–O bond is directly dissociated after the second electron transfer. While for Ni-C₂N and Cu-C₂N, the most favorable pathway is indirect 4e⁻ mechanism, in which the H₂O₂ is formed as the intermediate product. For all studied M-C₂N, the Ni-C₂N and Cu-C₂N hold better catalytic activity, which could attribute to the contribution of metal atom and part of its activated nitrogen atoms.     

Sn substitution endows NaTi2(PO4)3/C with remarkable sodium storage performances

The further development of clean energy requires the use of more stable and reliable energy storage system. In addition to lithium ion battery power supplies, sodium ion batteries also have prospects for application and development thanks to the low cost and abundant resource. NaTi₂(PO₄)₃ has attracted much attention due to its three-dimensional channels for sodium ion transfer. In order to meliorate sodium storage properties of NaTi₂(PO₄)₃ electrode, a facile strategy of Sn substitution at Ti sites was employed, and a series of electrodes were successfully synthesized through sol-gel route. The electrochemical performances of Sn substituted composites are significantly improved compared with bare NaTi₂(PO₄)₃/C. And it was found that NaSn_0.2Ti_1.8(PO₄)₃ (NTP/C-Sn-2) delivers the largest capacity, and it also demonstrates the outstanding cycling performances. NTP/C-Sn-2 has discharge capacity of 131.1 mAh g⁻¹ at 4 A g⁻¹ in rate test and 121.4 mAh g⁻¹ at 1 A g⁻¹ after 1000 cycles in cycling test. The experimental results show that NaTi₂(PO₄)₃/C with Sn substitution with proper content exhibits the great potential in anode for sodium ion batteries, and can further provide reference for next generation electrode materials and battery systems.     

An optimization method to find the thermodynamic limit on enhancement of solar thermal decomposition of methane

An optimization approach to enhancing the solar thermal decomposition of methane (TDM) reaction process based on the fluid flow pattern reconstruction is proposed. The sum of entropy generations due to TDM reaction and heat convection in the process is shown to tend to its maximum when the performance of the reaction is enhanced, and thus, is used as the criterial to optimize the velocity field of the fluid. This optimization problem is solved by the calculus of variations method. The obtained flow pattern is shown to be able to give the conditions to achieve the optimally enhanced TDM process. As the sum of the entropy generations tends to its extremum, the solution found by the optimization can be known as the thermodynamic limit for the TDM process enhancement. The obtained flow pattern can then be used to inspire the design of internal structures of the solar TDM reactor.     

Effect of introducing a steam pipe to n-dodecane decomposition by in-liquid plasma for hydrogen production

A method has been developed to improve the hydrogen production efficiency (HPE) by in-liquid plasma n-dodecane decomposition. A thin steam pipe is placed over the plasma electrode to recover the thermal energy emitted from the plasma to its surroundings. The steam generated by this energy is supplied to the vaporized n-dodecane around the edge of the plasma to cause a steam reforming reaction (SRR). Water pyrolysis is suppressed by not supplying the steam directly to the plasma. A large amount of CO and a small amount of CO₂ were detected in the produced gas. This indicates that a strong SRR has occurred. The HPE obtained by this method is 0.28 Nm³/kWh, which is two times greater than those obtained by previous methods, and similar to or greater than the yield of water electrolysis. This result is a major advance in the field of plasma heavy hydrocarbon decomposition aimed at hydrogen production. HPE is expected to be further improved by simply increasing the input power, due to synergy between the heat recovery effect of the steam pipe and the bubble stabilization effect. This indicates that this method has a high potential.     

纳米TiO2对D16T铝合金微弧氧化膜耐磨性的影响及机理

目的 提高D16T铝合金的耐磨损性能。方法 通过向硅酸盐和磷酸盐混合电解液体系中添加2 g/L纳米TiO2添加剂,利用微弧氧化技术在其表面制备微弧氧化陶瓷膜。采用X射线衍射仪（XRD）、扫描电镜（SEM）、能谱分析仪（EDS）、显微硬度计、厚度测试仪、摩擦磨损试验机等,研究了纳米TiO2添加剂对D16T铝合金微弧氧化膜的结构和耐磨损性能的影响及机理。结果 纳米TiO2的添加使得微弧氧化膜层的表面变得更加平整、致密,具有更少的微孔和裂纹,大大改善了膜层结构。相比于未添加纳米TiO2的电解液中制得的微弧氧化膜,在含纳米TiO2的电解液中所制得的微弧氧化膜中有新相TiO2生成,并且促使更多的α-Al2O3相和γ-Al2O3相生成,使膜层厚度得到明显增加,膜厚达31.2 μm,显微硬度也得到显著提高,达510HV。纳米TiO2的添加,降低了D16T微弧氧化膜层试样的摩擦系数,平均摩擦系数为0.45,明显低于不含纳米TiO2的D16T微弧氧化膜层试样的摩擦系数（0.75）。结论 加入到电解液中的纳米TiO2在微弧氧化反应过程中已进入到所形成的氧化膜层,并且填充了膜层中的微孔和裂纹,改善了膜层结构,增加了膜层厚度,显著提高了微弧氧化膜层的显微硬度和耐磨损性能。     

Experimental study the collapse failure mechanism of cemented casing under non-uniform load

Under non-uniform in-situ stress, the casing collapse failure often happens easily, and especially in soft rock the problem is more serious. In addition, only the few scholars do some studies about failure mechanism of cemented casing under non-uniform in-situ stress which has a strong effect on collapse properties of cemented casing, especially testing investigation. Hence, the collapsing test was performed for cemented casing under non-uniform load (NFL) by adopting self-developed testing equipment, by which the radial deformation of cemented casing and damage rules of cement sheath have been measured and the stress-strain laws of cemented casing are obtained during the testing process by the electrical method. The initial yield load and plastic limit load of cemented casing as well as the subsequent yield load have been obtained. By analyzing testing data, the stress-hardening rate and strain-hardening rate after hardening have been determined. The effects of cement sheath on collapse properties of P110SS casing and strain and deformation laws of P110SS casing after hardening have been obtained. The hardening character and failure mechanism of cemented casing have been figured out under NFL.     

Erosion resistance of CO2 corrosion scales formed on API P110 carbon steel

The erosion resistance of CO₂ corrosion scales formed on carbon steel was investigated in water–sand two-phase flow utilizing weight loss test, scanning electron microscopy, and X-ray diffraction. The effects of CO₂ partial pressure, stirring speed, test time, and grain size on the erosion resistance of the scales were analysed. Results show that several characteristics of CO₂ corrosion scales are key factors affecting erosion resistance. Cubic polynomials are used to fit the erosion rate data, and effectively evaluate the ability of CO₂ corrosion scales to resist erosion. An erosion mechanism, based on fluid dynamics and CO₂ corrosion scales characteristics, is discussed.