Micro-inhomogeneous structure of liquid Al-Fe alloys

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Crystal growth nucleation and Fermi energy equalization of intrinsic spherical nuclei in glass-forming melts

Abstract

The energy saving resulting from the equalization of Fermi energies of a crystal and its melt is added to the Gibbs free-energy change ΔG_2ls associated with a crystal formation in glass-forming melts. This negative contribution being a fraction ε _ls(T) of the fusion heat is created by the electrostatic potential energy ?U₀ resulting from the electron transfer from the crystal to the melt and is maximum at the melting temperature T_m in agreement with a thermodynamics constraint. The homogeneous nucleation critical temperature T₂, the nucleation critical barrier ΔG_2ls?/k_BT and the critical radius R?_2ls are determined as functions of ε_ls(T). In bulk metallic glass forming melts, ε_ls(T) and T₂ only depend on the free-volume disappearance temperature T_0l, and ε_ls(T_m) is larger than 1 (T_0l>T_m/3); in conventional undercooled melts ε_ls(T_m) is smaller than 1 (T_0l>T_m/3). Unmelted intrinsic crystals act as growth nuclei reducing ΔG_2ls?/k_BT and the nucleation time. The temperature-time transformation diagrams of Mg₆₅Y₁₀Cu₂₅, Zr_41.2Ti_13.8Cu_12.5Ni₁₀Be_22.5, Pd₄₃Cu₂₇ Ni₁₀P₂₀, Fe₈₃B₁₇ and Ni melts are predicted using classic nucleation models including time lags in transient nucleation, by varying the intrinsic nucleus contribution to the reduction of ΔG_2ls?/k_BT. The energy-saving coefficient ε _nm(T) of an unmelted crystal of radius R_nm is reduced when R_nm ?R?_2ls; ε_nm is quantified and corresponds to the first energy level of one s-electron moving in vacuum in the same spherical attractive potential ?U₀ despite the fact that the charge screening is built by many-body effects.     

A Chemical Approach of the Molecular Entity Vacancy Model to the CaO‐Al2O3‐SiO2 Ternary Silicate Melt

A chemical approach of the molecular entity vacancy model (MEVM) to the CaO‐Al₂O₃‐SiO₂ ternary silicate melts has been suggested. The activities of all components in the melts were simultaneously predicted by using only the binary parameters of its sub‐binary melts which were determined by fitting the activities of their two components. The results indicated that the predicted values of activity of SiO₂ were in good agreement with the experimental data at both temperatures 1823 K and 1873 K, and those of CaO and Al₂O₃ were in reasonable agreement with the experimental data at 1823 K and were smaller than the graphical integration data of the Gibbs‐Duhem equation at 1873 K. The approach may be extended to some solution systems with the chemical interaction.     

碳酸钙填充聚丙烯熔体的流变性质

本工作以轻质碳酸钙粒子填充聚丙烯熔体为体系,利用RMS-605和Instron3211流变仪测定各种物料函数,研究了粒子浓度和界面状态的影响。     

基于粒子群优化算法的熔融指数预报

针对丙烯聚合生产控制中聚丙烯熔融指数在线测量的控制要求,以及过程变量间相关性高的特点,提出一种实用高精度的软测量方法,以弥补传统的实验室分析严重滞后所导致的生产控制瓶颈问题。采用主元分析,提取少量主元反映多个变量的综合信息,以降低预报模型的复杂度。并在此基础上建立基于径向基函数神经网络的统计预报模型,提出利用粒子群优化算法优化神经网络的结构与参数,以减少人为因素对建模的影响,得到最优预报结果。通过对工厂实际生产过程进行详细的预报检测,并进一步与国内外相关研究报道进行比较,结果表明,所提出的预报方法具有更强的可靠性和更高的准确性。     

The structure factor of dense two-dimensional polymer solutions

According to the generalized Porod law the intramolecular structure factor F(q) of compact objects with surface dimension ds scales as F(q)/N≈1/(R(N)q)^2d−ds in the intermediate range of the wave vector q with d being the dimension of the embedding space, N the mass of the objects and R(N)∼N1/d their typical size. By means of molecular-dynamics simulations of a bead-spring model with chain lengths up to N=2048 it is shown that dense self-avoiding polymers in strictly two dimensions (d=2) adopt compact configurations of surface dimension ds=5/4. In agreement with the generalized Porod law the Kratky representation of F(q) thus reveals a nonmonotonous behavior with q²F(q)∼1/(N1/2q)^3/4. Using a similar data analysis we argue briefly that melts of non-concatenated rings in three dimensions become marginally compact with ds=d=3, i.e. q²F(q)∼N⁰/q, for asymptotically long chains.     

Self Diffusion in Na2O-Rb2O-SiO2 Glass Melts as Obtained by Microgravity Experiments

Sodium and rubidium self-diffusion in several melts of the system (1 − x )Na₂· x Rb₂O·3SiO₂ were studied at temperatures greater than 1150°C under microgravity conditions. The diffusion coefficients ( D *) may be considered as intrinsic data. At 1250°C, D *_Na in this system is nearly independent of Rb₂O concentration, whereas D *_Rb is more impeded the higher the Na₂O content. Furthermore, it can be confirmed that the Nernst-Planck model, which relates selfdiffusion and interdiffusion coefficients, is also reasonably well fulfilled for this high-temperature melt state.     

Comments on ‘Solidification modes and microstructure of Fe–Cr alloys solidified at different undercoolings’

The critical growth velocity for a planar solidification front in undercooled alloy melts is discussed on the basis of the absolute stability theory to reexamine the interpretation of a current analysis of the solidification modes in undercooled bulk Fe–Cr alloys contributed by Xuezhi Zhang. Theoretically, it is possible to produce a planar front in the solidification of undercooled bulk melts. But practically, it is imopssible for the undercooled bulk Fe–Cr melts to produce a planar front in the solidification. The dendritic growth theories as well as the calculations due to Zhang have been analyzed.     

LiCl-KCl共晶熔盐中氧离子的去除

采用NH₄Cl和HCl气体进行LiCl-KCl共晶熔盐中氧离子的去除。在使用NH₄Cl和HCl气体去除LiCl-KCl共晶熔盐中的氧离子过程中，用钇稳定氧化锆测氧电极对熔盐中的氧离子浓度变化进行测定。结果表明，HCl与熔盐中氧离子反应生成H₂O，并将反应产物水通过HCl载带出去。NH₄Cl去除氧离子的过程也是通过NH₄Cl分解的HCl与氧离子反应除去熔盐中氧离子。NH₄Cl和HCl均能有效地去除LiCl-KCl熔盐中的氧离子，使氧离子浓度降低至10^-5～10^-4 mol/kg。