Charge Transportation and Chirality in Liquid Crystalline Helical Network Phases of Achiral BTBT-Derived Polycatenar Molecules

First examples of multichain (polycatenar) compounds, based on the π-conjugated [1]benzothieno[3,2-b]benzothiophene unit are designed, synthesized, and their soft self-assembly and charge carrier mobility are investigated. These compounds, terminated by the new fan-shaped 2-brominated 3,4,5-trialkoxybenzoate moiety, form bicontinuous cubic liquid crystalline (LC) phases with helical network structure over extremely wide temperature ranges (>200 K), including ambient temperature. Compounds with short chains show an achiral cubic phase with the double network, which upon increasing the chain length, is at first replaced by a tetragonal 3D phase and then by a mirror symmetry is broken triple network cubic phase. In the networks, the capability of bypassing defects provides enhanced charge carrier mobility compared to imperfectly aligned columnar phases, and the charge transportation is non-dispersive, as only rarely observed for LC materials. At the transition to a semicrystalline helical network phase, the conductivity is further enhanced by almost one order of magnitude. In addition, a mirror symmetry broken isotropic liquid phase is formed beside the 3D phases, which upon chain elongation is removed and replaced by a hexagonal columnar LC phase.     

Lithiation MXene Derivative Skeletons for Wide-Temperature Lithium Metal Anodes

Lithium (Li) metal, as an appealing candidate for the next-generation of high-energy-density batteries, is plagued by its safety issue mainly caused by uncontrolled dendrite growth and infinite volume expansion. Developing new materials that can improve the performance of Li-metal anode is one of the urgent tasks. Herein, a new MXene derivative containing pure rutile TiO₂ and N-doped carbon prepared by heat-treating MXene under a mixing gas, exhibiting high chemical activity in molten Li, is reported. The lithiation MXene derivative with a hybrid of LiTiO₂-Li₃N-C and Li offers outstanding electrochemical properties. The symmetrical cell assembling lithiation MXene derivative hybrid anode exhibits an ultra-long cycle lifespan of 2000 h with an overpotential of ≈30 mV at 1 mA cm⁻², which overwhelms Li-based anodes reported so far. Additionally, long-term operations of 34, 350, and 500 h at 10 mA cm⁻² can be achieved in symmetrical cells at temperatures of −10, 25, and 50 °C, respectively. Both experimental tests and density functional theory calculations confirm that the LiTiO₂-Li₃N-C skeleton serves as a promising host for Li infusion by alleviating volume variation. Simultaneously, the superlithiophilic interphase of Li₃N guides Li deposition along the LiTiO₂-Li₃N-C skeleton to avoid dendrite growth.     

热处理对挤压态Mg-6Gd-5Y-1Zn合金组织与性能的影响

通过对Mg-6Gd-5Y-1Zn(质量分数,%)合金在固溶和时效处理状态下显微组织和力学性能的研究发现,α-Mg基体、沿挤压方向分布的条状18R-LPSO相、少量的Mg₂₄(GdYZn)₅ 相以及细层片状的14H-LPSO相构成了挤压态合金的组成相。挤压态合金经固溶(T4)处理后,一部分18R-LPSO相溶入基体,并且基体中的14H-LPSO相伸长同时粗化。挤压态合金经过固溶加时效(T6)处理后,大量β′相从α-Mg基体中析出。T6态合金的室温力学性能最好,其屈服强度、抗拉强度及伸长率分别为272 MPa、406 MPa和6.1%。β′相沉淀也发生在挤压态合金的直接人工时效(T5)处理过程,但相比于T6处理,14H-LPSO相和β′相在基体中的体积分数均偏低。     

Formation mechanism of Ti(C,N) solid solution in Al-brown fused alumina refractory at 1973 K in flowing N2

Brown fused alumina is a cost-effective alumina material, and the state of Ti in alumina has a great influence on its high-temperature performance. In this paper, the Ti-containing phases in brown fused alumina particles and Al-brown fused alumina refractory were successfully transformed into Ti(C,N) at 1973 K in flowing N₂. The evolution of the Ti-containing phases in brown fused alumina under high temperature and nitrogen conditions was investigated by XRD, SEM and EDS. The results show that the Ti-containing phases in brown fused alumina include Ti₂O₃, Ti(C,N,O), TiFeSi₂, Ca_0·95Mg_0·9Al_10·1(Ti)O₁₇ and a low-melting point Ca₃Al₂Si₃(Mg,Ti)O₁₂ phase. Under high temperature and nitrogen conditions, the TiO_2[liquid], MgO_[liquid] and SiO_2[liquid] in the low-melting point phase are transformed into Ti(C,N), Mg(g) and SiO(g), while they are supplemented from Ti₂O₃, Ti(C,N,O) and Ca_0·95Mg_0·9Al_10·1(Ti)O₁₇. After heat treatment at 1973 K for 3 h, Ti₂O₃ and Ti(C,N,O) disappear, Ca_0·95Mg_0·9Al_10·1(Ti)O₁₇ is transformed into plate-like Ca_0·55Al₁₁O_17.05, and Ti(C,N) is formed on the surface of the corundum particles. The formation of Ti(C,N) reduces the porosity of the brown fused alumina particles and increases their strength.     

Hydrogen storage in Zr0.9Ti0.1(Ni0.5Cr0.5-xVx)2 Laves phase,with x = 0, 0.125, 0.25, 0.375, 0.5. A theoretical approach

Density functional calculations were performed on Zr_0.9Ti_0.1(Ni_0.5Cr_0.5-xV_x)₂ Laves Phase, with x = 0, 0.125, 0.25, 0.375 and 0.5, in order to study its H absorption capacity. Binding energy, electronic structure and bonding were analyzed for the intermetallic compound with different V content and increasing amounts of hydrogen.The optimized geometry was found in good agreement with experimental data of the C14 Laves phase. Hydrogen locates preferentially in A₂B₂ tetrahedral sites in the AB₂ matrix (A = Zr, Ti; B = Ni, Cr, V) but AB₃ and B₄sites are also stable. The volume of the intermetallic and the H binding energy increases with vanadium content. Theoretically H absorption is possible up to 4.5 H/F.U. but the strongest binding energy is achieved with 3 H/F. U.The main contribution to density of states is due to d states of all components of the structure and an H-metal bonding is observed in the range ?10 to ?4 eV.     

退火温度对新型锆合金薄板带材析出相和织构的影响

采用扫描电镜和超高分辨透射电镜,对具有良好冲制性能的新型锆合金薄板成品带材进行含晶粒、第二相粒子等在内的显微组织研究,并探索真空退火处理条件下温度对带材显微组织的影响。结果显示:新型锆合金薄板成品带材晶粒平均尺寸2.17 μm,存在{0001}<1010>和{0001}<1120>两种织构,大部分晶粒<1120>平行带材RD方向,较少晶粒<1010>平行带材RD方向;第二相粒子分布在晶粒内部及晶界,平均尺寸114 nm,尺寸较大的为不规则椭圆形的Zr-Nb-Fe相,尺寸较小的为圆形的β-Nb相;热处理退火温度降低,带材晶粒尺寸减小,第二相粒子细小弥散分布;新型锆合金薄板成品带材良好冲制性能主要源于轧制积累应变诱发再结晶过程进行充分,导致晶粒细小及孪晶发生破碎;相对轧制变形,退火对带材冲制性能影响不显著。     

Oxidation mechanisms in bulk Ti2AlC: Influence of the grain size

In this work, oxidation mechanisms were studied in fine-grained (FG) and coarse-grained (CG) Ti₂AlC bulk samples. Results showed that the oxidation kinetics are controlled by the grain size of Ti₂AlC. Bigger are the grains, faster is the oxidation. A dense and protective Al₂O₃ layer forms at the surface of FG-Ti₂AlC samples while for the CG-Ti₂AlC samples, a thick TiO₂ layer forms on top of a discontinuous Al₂O₃. CG-Ti₂AlC was observed to simultaneously transform into Ti₃AlC₂ and TiC instead of being directly transformed into TiC. This transformation result in the following crystallographically sandwich-like structure: (0001) Ti₂AlC // (0001) Ti₃AlC₂ // (111) TiC. The volume shrinkage associated to this transformation produces elongated holes that are partially filled by α-Al₂O₃. The stress caused by the volume shrinkage generates cracks at the surface, which makes the oxygen inwards diffusion easier and thus worsens the oxidation resistance the CG-Ti₂AlC bulk.     

P91钢管道异常低硬度部位的组织和性能

对电厂运行过程中发现的P91钢主蒸汽管道的低硬度部位进行了微观组织观察、短时力学性能试验和高温持久强度试验,分析了其硬度偏低的原因。结果表明,低硬度区域P91钢组织为铁素体+析出物,位错密度较低,M₂₃C₆相在晶界处粗化聚集,同时析出新相Laves相,使得P91钢的短时力学性能和高温持久强度下降严重。