The effect of the interaction between the minority phase droplets on the nucleation behavior during the liquid-liquid phase transformation

The microstructure evolution during the liquid-liquid phase transformation of Al-Pb alloy was calculated. The numerical results indicate that the interaction between the minority phase droplets has effect on the nucleation process of the droplets, and the effect increases with the cooling rate and the content of Pb. Supported by the National Natural Science Foundation of China (Grant Nos 50395104, 50671111 and 50620130095)     

调幅分解及形核对相分离作用机理研究

以SCN-30wt%H₂O, SCN-50 wt%H₂O和SCN-80 wt%H₂O三组透明体系, 在恒温场下实现了形核和调幅分解两种过程; 在此基础上, 施加温度梯度, 研究了第二相液滴的迁移运动规律. 结果表明, 相分离在临界成分体系以调幅分解方式进行, 在另外两种体系中以形核长大方式进行; 调幅分解与形核过程相比, 反应进行得更快, 液滴长大到同一尺寸所需时间仅为形核所需时间的1/3—1/2. 且临界成分体系有更大的不混溶间隙, 所以第二相液滴具有更多迁移时间, 揭示了偏晶体系相分离过程中在临界成分处易获得壳-核组织的内在机理. 在单向温度场中, 测量了不同半径的液滴迁移速率, 并且与理论Marangoni迁移速率值作比较, 发现液滴迁移速率和Marangoni理论迁移速率符合较好. 说明了在较好地抑制自然对流条件下Marangoni迁移对于相分离过程起主要作用.     

Clusters,metastability, and nucleation: Kinetics of first-order phase transitions

We describe and interpret computer simulations of the time evolution of a binary alloy on a cubic lattice, with nearest neighbor interactions favoring like pairs of atoms. Initially the atoms are arranged at random; the time evolution proceeds by random interchanges of nearest neighbor pairs, using probabilities compatible with the equilibrium Gibbs distribution at temperatureT. For temperatures 0.59T_c, 0.81 T_c, and 0.89T _c, with density of A atoms equal to that in the B-rich phase at coexistence, the density C₁ of clusters ofl A atoms approximately satisfies the following empirical formulas: C₁ w(1 –)³ andC ₁, (1 –)⁴Q₁w¹ (2 l 10). Herew is a parameter and we defineQ _l = _K e ^–E(K) , where the sum goes over all translationally nonequivalentl-particle clusters andE(K) is the energy of formation of the clusterK. Forl > 10,Q ₁ is not known exactly; so we use an extrapolation formulaQ _l Aw _s ^–l l ^– exp(–bl ), wherew _s is the value ofw at coexistence. The same formula (withw > w _s) also fits the observed values of C, (for small values ofl) at densities greater than the coexistence density (forT=0.59T_c): When the supersaturation is small, the simulations show apparently metastable states, a theoretical estimate of whose lifetime is compatible with the observations. For higher supersaturation the system is observed to undergo a slow process of segregation into two coexisting phases (andw therefore changes slowly with time). These results may be interpreted as a more quantitative formulation (and confirmation) of ideas used in standard nucleation theory. No evidence for a spinodal transition is found.Supported by AFOSR Grant No. 73-2430D and by ERDA Contract No. EY-76-C-02-3077*000.     

掺金玻璃在电场热处理中的形核过程

利用电场热处理工艺,成功制备出含纳米尺寸金颗粒掺杂的硼硅酸盐玻璃，采用x射线衍射、扫描电子显微镜和吸收光谱分析了在不同工艺条件下制备得到的玻璃样品的相成分、微观形貌和光学性能.然后在理论上分析了外电场对掺杂玻璃热处理过程的影响，提出了适合掺金玻璃的电场热处理热力学模型.模型中的关键因素是电场能量变化量，对此采用两种方法计算，一种是在一定简化后的理论计算；另一种是利用计算机有限元方法计算.两种方法的结果比较相近，并且都能解释前面的实验现象. 关键词： 掺金玻璃 形核 电场     

The study of spallation reactions, neutron production, and transport in a thick lead target and a uranium blanket during 1.5 GeV proton irradiation

The Neutron Activation Analysis Method was used to study neutron field in a setup consisting of a thick lead target and a natural uranium blanket. This setup was exposed to 1.5 GeV proton beam from the Nuclotron accelerator. By means of gamma-ray spectroscopic measurements we determined the yields of various nuclear reactions induced in the radio-chemical sensors. The data obtained were then compared with the results of a MCNPX simulation.