Theoretical study of the structural, elastic, electronic and thermal properties of the MAX phase Nb2SiC

Structural, elastic, electronic and thermal properties of the MAX phase Nb₂SiC are studied by means of a pseudo-potential plane-wave method based on the density functional theory. The optimized zero pressure geometrical parameters are in good agreement with the available theoretical data. The effect of high pressure, up to 40 GPa, on the lattice constants shows that the contractions along the c-axis were higher than those along the a-axis. The elastic constants C_ij and elastic wave velocities are calculated for monocrystal Nb₂SiC. Numerical estimations of the bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio, average sound velocity and Debye temperature for ideal polycrystalline Nb₂SiC aggregates are performed in the framework of the Voigt-Reuss-Hill approximation. The band structure shows that Nb₂SiC is an electrical conductor. The analysis of the atomic site projected densities and the charge density distribution shows that the bonding is of covalent-ionic nature with the presence of metallic character. The density of states at Fermi level is dictated by the niobium d states; Si element has a little effect. Thermal effects on some macroscopic properties of Nb₂SiC are predicted using the quasi-harmonic Debye model, in which the lattice vibrations are taken into account. The variations of the primitive cell volume, volume expansion coefficient, bulk modulus, heat capacity and Debye temperature with pressure and temperature in the ranges of 0-40 GPa and 0-2000 K are obtained successfully.     

Densities and mixing volumes of mixtures of fluorobenzene, α,α,α-trifluorotoluene, tert-butylmethyl ether, and ethanol at temperature 298.15 K and pressure 0.1 MPa

The volumetric properties were evaluated from density data for the binary mixtures of (fluorobenzene + tert-butylmethyl ether), (α,α,α-trifluorotoluene + tert-butylmethyl ether), (tert-butylmethyl ether + ethanol), and the ternary mixtures of (fluorobenzene + tert-butylmethyl ether + ethanol) and (α,α,α-trifluorotoluene + tert-butylmethyl ether + ethanol). The observed densities were obtained by means of a vibrating-tube densimeter at the temperature 298.15 K and the pressure 101 kPa.The excess molar volumes of the ternary mixtures were estimated from binary solution data using several empirical equations with mean standard deviation less than 0.03 cm³·mol^-1. Stable chemical cross-associations among the molecules forming the mixtures were revealed.     

On the ferromagnetism of AlFe2B2

Based on extensive Mossbauer effect (ME) and magnetization measurements, the orthorhombic AlFe₂B₂ was characterized as a ferromagnet (FM) because this character is evident as an onset of a FM transition at T_c=320 K and characteristic magnetizations isotherms below T_c. At liquid helium temperatures, the magnetization saturates to μ_sat≈1μ_B per Fe atom; a value which is half the one reported for the iron metal indicating a relatively more filled 3d band. The ME analysis revealed a hyperfine field H(0) of 88(2) kOe, an isomer shift (relative to Fe) of 0.50(2) mm/s, and a quadrupole parameter of 0.02 mm/s: all parameters extrapolated to zero Kelvin. The itinerant character of the magnetic moment will be discussed.     

基于图形方法的冗余函数与自反函数检测

冗余函数和自反函数是特殊的布尔函数，本文阐述了冗余函数和自反函数的定义，提出了冗余函数和自反函数的性质，讨论了冗余函数和自反函数的图形检测方法．并用实例说明之．通过计算机编程操作．可以得到用于多变量冗余函数和自反函数检测的快速算法．     

Room temperature thermoelectric performance of Methyl Ammonium Lead Iodide Perovskite and their MWCNT-PANI composites

The excellent properties of Methyl Ammonium Lead Iodide (MAPI) have already created an extensive research interest in photovoltaic applications. However, their utility in thermoelectric application is still not realized thoroughly by researchers. By continuing this interest, we have explored the formation of low dimensional CH₃NH₃PbI₃ (MAPI) perovskite in presence of Polyaniline (PANI) and Multi-Walled Carbon Nanotubes (MWCNT) and its thermoelectric performance. For this purpose, a two stage, in-situ synthesis method was developed to prepare various composites such as MAPI-PANI, MWCNT-MAPI and MWCNT-PANI-MAPI. The as-formed MWCNT-PANI-MAPI composite revealed p-type conductivity with enhanced ZT (up to ~20,000 times) and power factor (3000 times) at room temperature as compared to pristine MAPI sample. Finally, we have demonstrated a proto-type thermoelectric power generator (TE device) fabricated using the best performing composite sample and measured its power output and efficiency at varied δT.     

Excess molar enthalpies of the ternary mixtures: (diisopropyl ether or 2-methyltetrahydrofuran) + cyclohexane + n-heptane at 298.15 K

Microcalorimetric measurements of excess molar enthalpies, at 298.15 K, are reported for the two ternary systems formed by mixing either diisopropyl ether or 2-methyltetrahydrofuran with binary mixtures of cyclohexane and n-heptane. Smooth representations of the results are presented and used to construct constant excess molar enthalpy contours on Roozeboom diagrams. It is shown that useful estimates of the ternary enthalpies can be obtained from the Liebermann and Fried model, using only the physical properties of the components and their binary mixtures.     

弱碱性和强碱性阴离子交换树脂的离子交换平衡的比较SO_4~(2-)-Cl~--NO_3~-体系

本文详细地比较了在弱碱性和强碱性阴离子交换树脂上,SO_4~(2-)-Cl~-、NO_3~--Cl~-及NO_3~--SO_4~(2-)二元交换的等温线和修正选择系数。实验测定及理论计算了上述三种二元交换反应的标准自由能的改变量。测得了在弱碱性树脂上的SO_4~(2-)-Cl~--NO_3~-三元交换的等温线。适用于强酸性和强碱性树脂的从二元交换平衡数据推算三元交换平衡数据的方法推广应用于弱碱性树脂。     

Phase behavior and interfacial properties of diblock copolymer-homopolymer ternary mixtures: Influence of volume fraction of copolymers and interaction energy

We use a Monte Carlo method to study the phase and interfacial behaviors of A-b-B diblocks in a blend of homopolymers, A and B, which are confined between two asymmetric hard and impenetrable walls. Our results show that, when the interaction strength is weak, the block copolymersare uniformly distributed in the ternary mixtures under considered concentrations. Under strong interaction strength, distribution region of the block copolymers changes from a single smooth interface to a curved interface or multi-layer interface in the ternary mixtures. Furthermore, our findings show that with increasing volume fraction of A-b-B diblock copolymer(фC), copolymer profiles broaden while фC≥ 0.4, a lamellar phase is formed and by further increasing фC, more thinner layers are observed. Moreover, the results show that, with the increase of фC, the phase interface first gradually transforms from plane to a curved surface rather than micelle or lamellar phase while with the increase of the interaction between A and B segments(ε_(AB)), the copolymer chains not only get stretched in the direction perpendicular to the interface, but also are oriented. The simulations also revealthat the difference between symmetric and asymmetric copolymers is negligible in statistics if the lengths of two blocksare comparable.     

稀土三元催化剂作用下正辛酸缩水甘油酯-二氧化碳-环氧丙烷的三元共聚合研究

本工作研究了稀土三元催化剂(三氯乙酸稀土配合物/二乙基锌/甘油)催化下的正辛酸缩水甘油酯、二氧化碳和环氧丙烷三元共聚合。红外光谱、核磁共振和差示扫描结果表明所获得的聚合物是一种新型的三元共聚物。随着反应单体中正辛酸缩水甘油酯比例的增加,所得聚合物在20℃下的断裂伸长率由二氧化碳－环氧丙烷共聚物的31.0%增大到二氧化碳－正辛酸缩水甘油酯共聚物的983.9%,相应的玻璃化转变温度由39.6℃降低至-12.3℃。所得三元共聚物中长碳链侧基单元含量为5.6%时,其断裂伸长率就已经达到481.1％,而拉伸强度仍然维持在24.9MPa的较高水平。     

分子动力学模拟研究[Bmim][PF_6]+水+醇三元体系的微观结构和分子间相互作用(英文)

研究离子液体体系的微观结构和分子间相互作用具有重要意义.本文对1-丁基-3-甲基咪唑六氟磷酸盐([Bmim][PF6])+水+乙醇和[Bmim][PF6]+水+异丙醇三元体系进行了分子模拟研究,计算了径向分布函数和不同组成的水-醇混合溶剂与离子液体阴阳离子间的相互作用能,并将其分解为库仑相互作用能和Lennard-Jones(LJ)势能.在此基础上,研究了溶液体系的微观结构、分子间相互作用和相行为.结果表明,水倾向于与离子液体阴离子和阳离子极性部分作用,醇倾向于与阴离子和阳离子非极性部分作用;库仑力主导阴离子-溶剂相互作用,色散力主导阳离子-溶剂相互作用,阴阳离子的缔合状态对色散力影响较小,对库仑力的影响非常显著.