
[晶体] 异相成核
Stirring of substrates may accelerate the heterogeneous nucleation and growth of the melt.
衬底的搅拌可加速熔体的非自发成核和长大。
Effect of melting temperatures on heterogeneous nucleation of polypropylene (PP) nucleated with different nucleating agents was investigated by DSC.
用DSC研究了熔融温度对不同类型成核剂成核PP的异相成核作用的稳定性的影响。
Continuous nucleation model was used to describe heterogeneous nucleation of the liquid metal.
在模拟过程中,采用连续形核的方法处理液态金属的异质形核现象。
The results show:1)Formation scaling is formed in the repeated heterogeneous phase nucleation and crystal growth. The crystal can grow both in pores and at throats.
研究结果表明:1油层结垢是在多次的异相成核—晶体生长过程形成的,晶体生长在孔隙中和喉道处均可发生;
During the treatment process of flue gas, heavy metal was concentrated in fly ash by the way of homogeneous nucleation and heterogeneous deposition.
在尾气处理过程中,重金属以均匀核化、异相沉积等方式从烟气浓缩到飞灰中。
The coupling analyses by DSC and polarized light microscopy proved the nucleation in the multiple crystallization was heterogeneous.
DSC和偏光显微联用分析发现,所有峰对应的结晶都是异相成核。
It was found in the experiment that the glass fiber (GF) has the function of heterogeneous nucleation for polypropylene (PP) and improves the crystalline morphology of PP.
试验表明,玻璃纤维(GF)对聚丙烯(PP)起异相成核作用,改变聚丙烯的结晶形态;
Continuous nucleation model is applied to describe heterogeneous nucleation in liquid metal.
采用连续形核模型来描述液相中的自发形核。
Based on the cellular automata technique, the heterogeneous nucleation model, dendrite growth model and random nucleation model are used to simulate the formation of equiaxed and columnar dendrite.
通过引入异质形核模型、枝晶生长模型、几率形核基底模型,借鉴单元自动生长机制,仿真了等轴晶、柱状晶组织形成的过程。
A continuous nucleation model was used to deal with the heterogeneous nucleation of a liquid metal.
采用连续形核的方法处理液态金属的异质形核现象。
A small quantity of fly ash can play a role in the heterogeneous nucleation, but increasing the filled quantity can change the crystallization form of PP.
少量粉煤灰可起到异相成核的作用,填充量的增加会改变PP的结晶形态;
It was concluded that the synthesis process of the LDHs films was heterogeneous nucleation.
研究认为,该薄膜的生长是一个异相成核的过程。
The results showed the addition of zeolite resulted in heterogeneous nucleation crystallization of PP, and improved the crystallinity of PP;
结果表明,沸石的引入使PP产生了异相成核结晶,结晶度提高;沸石质量分数为3%时,复合材料体系结晶较为完善;
Heterogeneous nucleation may take place at significantly lower supersaturations than homogeneous nucleation.
多相成核能在比均相成核低很多的过饱和状态下发生。
异质形核(Heterogeneous Nucleation) 是指新相(如晶体、液滴等)在凝固、结晶或相变过程中,优先依附于系统中已存在的外来界面(如容器壁、杂质颗粒、气泡表面等)上成核的现象。与均质形核(在均匀母相内部自发成核)相比,异质形核所需的能量壁垒更低,因此在自然界和工业过程中更为常见。
能量壁垒降低
异质形核的核心优势在于降低了临界形核功。根据经典形核理论,新相在基底表面成核时,其临界形核能 (Delta G^) 可表示为: $$ Delta G^ = Delta G{text{hom}}^ cdot f(theta) $$ 其中 (Delta G{text{hom}}^) 是均质形核能垒,(f(theta) = frac{(2 + cos theta)(1 - cos theta)}{4}),(theta) 为新相与基底的接触角。当 (theta < 180^circ) 时,(f(theta) < 1),表明异质形核更易发生。
基底的关键作用
基底表面的化学成分、晶体结构及粗糙度直接影响形核效率。若基底与新相的晶格匹配度高(共格界面),或表面能较低,可显著促进形核。例如,金属凝固中常用钛、锆等添加剂作为异质形核剂,因其晶格常数与金属晶体接近。
广泛存在的现象
临界形核半径 (r^) 和形核功 (Delta G^) 的表达式为: $$ r^ = -frac{2 gamma_{text{SL}}}{Delta G_v}, quad Delta G^ = frac{16 pi gamma_{text{SL}}}{3 (Delta Gv)} cdot f(theta) $$ 其中 (gamma{text{SL}}) 为固-液界面能,(Delta Gv) 为单位体积相变自由能差。接触角 (theta) 满足杨氏方程:(gamma{text{LV}} cos theta = gamma{text{SV}} - gamma{text{SL}})((gamma{text{LV}})、(gamma{text{SV}}) 分别为液-气、固-气界面能)。
权威参考文献来源:
heterogeneous nucleation(异相成核)是材料科学和物理化学中的重要概念,指物质在相变过程中,晶核的形成依赖于外来杂质或界面作用的现象。以下是详细解释:
异相成核是指分子或原子在杂质表面、界面或预先存在的晶种上形成晶核的过程。与均质成核(homogeneous nucleation)不同,异相成核不需要在纯物质内部自发形成晶核,而是借助外部媒介降低能量壁垒,使相变更容易发生。
特征 | 异相成核 | 均质成核 |
---|---|---|
成核位置 | 杂质或界面 | 纯物质内部 |
能量壁垒 | 较低 | 较高 |
常见场景 | 自然水体结冰、合金凝固 | 超纯液体过冷/过热状态 |
如需进一步了解具体领域(如材料科学或气象学)中的应用,可参考相关学术文献或专业教材。
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