Electrochemical Determination of Oxidic Melt Diffusion Coefficients

The chemical diffusion coefficient of electroactive species such as Fe³⁺ and Ce⁴⁺ in silicate melts have been measured using an electrochemical technique: square wave voltametry. The experiments are conducted in an induction furnace in which three electrodes (made of platinum or iridium) are inserted in the crucible containing the melt. The technique has been improved to reduce the uncertainties due to the presence of a meniscus on the electrodes. Experimental results have been obtained at temperatures up to 1560 °C. The technique has proven its ability to analyze melts containing several electroactive species. These experimental results are compared to data from the literature. Paper presented at the Seventh International Workshop on Subsecond Thermophysics, October 6–8, 2004, Orléans, France.     

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.     

铁磷和硼硅酸盐熔体对耐火材料的腐蚀性能

耐火材料的选择对放射性核废料的玻璃化过程是至关重要的 ,本文采用动态耐火材料腐蚀速度技术比较了铁磷模拟放射性核废料熔体和硼硅酸盐熔体DWPF的腐蚀性质 ,测量在10 0 0至 130 0℃之间进行。在铁磷熔体中 ,致密氧化铝和氧化铬耐火材料有最低的熔线腐蚀速度 ,二氧化硅、锆英石和AZS耐火材料的腐蚀速度比较高。同时 ,氧化铝和氧化铬耐火材料在铁磷熔体中的腐蚀速度小于它们在硼硅酸盐熔体DWPF中的腐蚀速度。对氧化铬耐火材料来说 ,其在三种含有模拟HLW废料的铁磷熔体中的熔线腐蚀速度小于 0 1mm day。按照DWPF熔化器的设计标准 ,Alumina和Zircon商品耐火材料可以用来熔化多种HLW废料。     

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。     

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.     

Specific heat of superheated Al-10Sr alloy melts

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Internal Nucleation of Highly Undercooled Magnesium Metasilicate Melts

Crystallization and vitrification in undercooled, fine magnesium silicate droplets, with compositions ranging from 34.5 ≤ wt% MgO ≤ 39.9, were examined following containerless drop tube processing. From an initial phase assemblage of a mixture of the metasilicate (MgSiO₃) polymorphs orthoenstatite and clinoenstatite, three morphological powder types were observed following processing: unmelted shards, glass spheres, and melted/recrystallized spheres. The primary phase in the powders processed at a maximum temperature of ∼1650°C is the high-temperature metasilicate polymorph protoenstatite, with metastable forsterite (Mg₂SiO₄) also appearing. The melted/recrystallized spheres have the uniform, submicrometer texture of a glass ceramic, decisively different from the surface crystallization textures normally seen for melts/glasses of these compositions. Transmission electron microscopy results indicate that the glass-ceramic texture occurs because the process technique allows a liquid-phase immiscibility to precede crystallization. The phases and textures developed during containerless solidification processing of these metsilicate compositions are analyzed thermodynamically; the minimum amount of undercooling required for amorphous phase separation is evaluated using the metastable extensions of the forsterite + liquid and the silica-rich, twoliquid miscibility phase boundaries. The application of metastable phase diagram analysis is demonstrated as an effective guide for identifying potential compositions for development of novel glass-ceramics.