Juxiang Shao

Entropy-scaling laws for diffusion coefficients in liquid metals under high pressures

Molecular dynamic simulations on the liquid copper and tungsten are used to investigate the empirical entropy-scaling laws D*=A exp(BSex), proposed independently by Rosenfeld and Dzugutov for diffusion coefficient, under high pressure conditions. We show that the scaling laws hold rather well for them under high pressure conditions. Furthermore, both the original diffusion coefficients and the reduced diffusion coefficients exhibit an Arrhenius relationship DM=DM0 exp(−EM/KBT), ( M=un,R,D) and the activation energy EM increases with increasing pressure, the diffusion pre-exponential factors ( DR0 and DD0) are nearly independent of the pressure and element. The pair correlation entropy, S2, depends linearly on the reciprocal temperature S2=−ES/T, and the activation energy, ES, increases with increasing pressure. In particular, the ratios of the activation energies (Eun, ER, and ED) obtained from diffusion coefficients to the activation energy, ES, obtained from the entropy keep constants in the whole press...

Structural and magnetic properties of Sr1−x La x Fe12−x (Cu0.5Co0.5) x O19 hexaferrites prepared by the solid-state reaction method

Hexaferrite Sr1−xLaxFe12−x(Cu0.5Co0.5)xO19 (0 ≤ x ≤ 0.50) magnetic powders and magnets were synthesized by the solid-state reaction method. The phase compositions of magnetic powders were investigated by X-ray diffraction. The single magnetoplumbite phase is obtained in magnetic powders with x from 0 to 0.40. At x = 0.50, CoFe2O4, and α-Fe2O3 were observed. The morphology of the materials was characterized by a field-emission scanning electron microscopy. The particles were hexagonal platelets. Magnetic properties of the materials were measured by a permanent magnetic measure equipment. The remanence of the materials increases with x from 0 to 0.50. However, the intrinsic coercivity and magnetic induction coercivity of the materials increase with x from 0 to 0.15, and decreases when x varies from 0.15 to 0.50. Accordingly, the maximum energy product of the materials first increases with x from 0 to 0.35, and then decreases when x exceeds 0.35.

Transport properties and entropy-scaling laws for diffusion coefficients in liquid Fe0.9Ni0.1 up to 350 GPa

Transport properties and entropy-scaling laws for diffusion coefficients in liquid Fe0.9Ni0.1 alloy under high pressure conditions have been studied by molecular dynamics simulations based upon the Quantum Sutton and Chen potential. We find that the entropy-scaling laws proposed independently by Rosenfeld and Dzugutov for diffusion coefficients under ambient pressure, approximating the excess entropy by the pair correlation entropy, can be fruitfully extended to liquid Fe–Ni alloy under high pressure conditions to understand and predict the transport properties of the Earths core. In addition, our results suggest that the temperature dependence of the self-diffusion coefficient and viscosity follow the Arrhenius-type relation, and the activity energies for diffusion and viscosity increase with increasing pressure. The viscosity of liquid Fe0.9Ni0.1 alloy is slightly greater than that of pure liquid Fe, and lower than that of pure liquid Ni, at a given temperature and pressure. This result indicates that Ni has a slightly positive influence on the viscosity of liquid Fe–Ni alloy.

Preparation of Al3+-Co2+ co-substituted M-type SrCaNd hexaferrites and their controlled magnetic properties

Al3+-Co2+ co-substituted M-type SrCaNd hexaferrites with cation compositions Sr0.5Ca0.2Nd0.3Fe12.0-x(Al0.5Co0.5)xO19 were synthesized using the traditional ceramic process by varying AlCo content (x) (0.0 ≤ x ≤ 0.5). The microstructures, morphologies and ferromagnetic properties of the samples were investigated as a function of AlCo content (x) by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), Fourier transformer infrared (FT-IR) spectroscopy and Hysteresis graph meter. The X-ray diffraction patterns show that the hexaferrites with AlCo content (x) of 0.0 ≤ x ≤ 0.2) exhibited M-type phase and α-Fe2O3 as impurity phase, while the hexaferrites with AlCo content (x) ≥ 0.3 exhibited the single M-type phase. XRD, along with FT-IR analysis confirmed the formation of M-type hexaferrites and the successful substitution of Al3+ and Co2+ ions in the hexaferrite lattice. The results of FE-SEM images proposed that all the particles with regular hexagonal platelet-like shape were homogeneous dispersed. The remanence (Br) first increased with AlCo content (x) from 0.0 to 0.3, and then decreased when AlCo content (x) ≥ 0.3. The intrinsic coercivity (Hcj) and magnetic induction coercivity (Hcb) first increased with AlCo content (x) from 0.0 to 0.2, and then decreased with AlCo content (x) from 0.2 to 0.3, and increased when AlCo content (x) ≥ 0.3. Maximum energy product [(BH)max] first increased with AlCo content (x) from 0.0 to 0.2, and then decreased at AlCo content (x) ≥ 0.2. Squareness ratio (Hk/Hcj) decreased with increasing AlCo content (x) from 0.0 to 0.5.Al3+-Co2+ co-substituted M-type SrCaNd hexaferrites with cation compositions Sr0.5Ca0.2Nd0.3Fe12.0-x(Al0.5Co0.5)xO19 were synthesized using the traditional ceramic process by varying AlCo content (x) (0.0 ≤ x ≤ 0.5). The microstructures, morphologies and ferromagnetic properties of the samples were investigated as a function of AlCo content (x) by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), Fourier transformer infrared (FT-IR) spectroscopy and Hysteresis graph meter. The X-ray diffraction patterns show that the hexaferrites with AlCo content (x) of 0.0 ≤ x ≤ 0.2) exhibited M-type phase and α-Fe2O3 as impurity phase, while the hexaferrites with AlCo content (x) ≥ 0.3 exhibited the single M-type phase. XRD, along with FT-IR analysis confirmed the formation of M-type hexaferrites and the successful substitution of Al3+ and Co2+ ions in the hexaferrite lattice. The results of FE-SEM images proposed that all the particles with regular hexagonal platelet-like shape were homoge...

Entropy and transport properties of liquid metals along the melting curve

Molecular dynamics simulations are performed for several monatomic metals and Fe0.9Ni0.1 metallic alloy to study the transport properties and entropy of liquids along melting curve. Our results show that the self-diffusion coefficients and viscosity of liquids increase with increasing pressure along the melting curves. Analysis suggests that, at high pressure conditions, the pair correlation entropy S2 of liquids along melting curve is bout −3.71kB, independent of the pressure and variety of liquids, which indicates that there is no obvious change in liquid structure along the melting curve. The Rosenfeld entropy-scaling laws with S2 = −3.71kB and the special values of scaling parameters can give reasonable estimates for the self-diffusion coefficients and viscosity of liquid metals along melting curves. The effect of pressure on transport coefficients can be quantified through its corresponding effect on the melting temperature and number density, and this result is in consistent with the Andrade’s model...

Melting properties of Pt and its transport coefficients in liquid states under high pressures

Molecular dynamics (MD) simulations of the melting and transport properties in liquid states of platinum for the pressure range (50–200 GPa) are reported. The melting curve of platinum is consistent with previous ab initio MD simulation results and the first-principles melting curve. Calculated results for the pressure dependence of fusion entropy and fusion volume show that the fusion entropy and the fusion volume decrease with increasing pressure, and the ratio of the fusion volume to fusion entropy roughly reproduces the melting slope, which has a moderate decrease along the melting line. The Arrhenius law well describes the temperature dependence of self-diffusion coefficients and viscosity under high pressure, and the diffusion activation energy decreases with increasing pressure, while the viscosity activation energy increases with increasing pressure. In addition, the entropy-scaling law, proposed by Rosenfeld under ambient pressure, still holds well for liquid Pt under high pressure conditions.