
[晶體] 異相成核
Stirring of substrates may accelerate the heterogeneous nucleation and growth of the melt.
襯底的攪拌可加速熔體的非自發成核和長大。
Effect of melting temperatures on heterogeneous nucleation of polypropylene (PP) nucleated with different nucleating agents was investigated by DSC.
用DSC研究了熔融溫度對不同類型成核劑成核PP的異相成核作用的穩定性的影響。
Continuous nucleation model was used to describe heterogeneous nucleation of the liquid metal.
在模拟過程中,采用連續形核的方法處理液态金屬的異質形核現象。
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.
研究結果表明:1油層結垢是在多次的異相成核—晶體生長過程形成的,晶體生長在孔隙中和喉道處均可發生;
During the treatment process of flue gas, heavy metal was concentrated in fly ash by the way of homogeneous nucleation and heterogeneous deposition.
在尾氣處理過程中,重金屬以均勻核化、異相沉積等方式從煙氣濃縮到飛灰中。
The coupling analyses by DSC and polarized light microscopy proved the nucleation in the multiple crystallization was heterogeneous.
DSC和偏光顯微聯用分析發現,所有峰對應的結晶都是異相成核。
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.
試驗表明,玻璃纖維(GF)對聚丙烯(PP)起異相成核作用,改變聚丙烯的結晶形态;
Continuous nucleation model is applied to describe heterogeneous nucleation in liquid metal.
采用連續形核模型來描述液相中的自發形核。
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.
通過引入異質形核模型、枝晶生長模型、幾率形核基底模型,借鑒單元自動生長機制,仿真了等軸晶、柱狀晶組織形成的過程。
A continuous nucleation model was used to deal with the heterogeneous nucleation of a liquid metal.
采用連續形核的方法處理液态金屬的異質形核現象。
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.
少量粉煤灰可起到異相成核的作用,填充量的增加會改變PP的結晶形态;
It was concluded that the synthesis process of the LDHs films was heterogeneous nucleation.
研究認為,該薄膜的生長是一個異相成核的過程。
The results showed the addition of zeolite resulted in heterogeneous nucleation crystallization of PP, and improved the crystallinity of PP;
結果表明,沸石的引入使PP産生了異相成核結晶,結晶度提高;沸石質量分數為3%時,複合材料體系結晶較為完善;
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過飽和狀态下發生。
異質形核(Heterogeneous Nucleation) 是指新相(如晶體、液滴等)在凝固、結晶或相變過程中,優先依附于系統中已存在的外來界面(如容器壁、雜質顆粒、氣泡表面等)上成核的現象。與均質形核(在均勻母相内部自發成核)相比,異質形核所需的能量壁壘更低,因此在自然界和工業過程中更為常見。
能量壁壘降低
異質形核的核心優勢在于降低了臨界形核功。根據經典形核理論,新相在基底表面成核時,其臨界形核能 (Delta G^) 可表示為: $$ Delta G^ = Delta G{text{hom}}^ cdot f(theta) $$ 其中 (Delta G{text{hom}}^) 是均質形核能壘,(f(theta) = frac{(2 + cos theta)(1 - cos theta)}{4}),(theta) 為新相與基底的接觸角。當 (theta < 180^circ) 時,(f(theta) < 1),表明異質形核更易發生。
基底的關鍵作用
基底表面的化學成分、晶體結構及粗糙度直接影響形核效率。若基底與新相的晶格匹配度高(共格界面),或表面能較低,可顯著促進形核。例如,金屬凝固中常用钛、锆等添加劑作為異質形核劑,因其晶格常數與金屬晶體接近。
廣泛存在的現象
臨界形核半徑 (r^) 和形核功 (Delta G^) 的表達式為: $$ r^ = -frac{2 gamma_{text{SL}}}{Delta G_v}, quad Delta G^ = frac{16 pi gamma_{text{SL}}}{3 (Delta Gv)} cdot f(theta) $$ 其中 (gamma{text{SL}}) 為固-液界面能,(Delta Gv) 為單位體積相變自由能差。接觸角 (theta) 滿足楊氏方程:(gamma{text{LV}} cos theta = gamma{text{SV}} - gamma{text{SL}})((gamma{text{LV}})、(gamma{text{SV}}) 分别為液-氣、固-氣界面能)。
權威參考文獻來源:
heterogeneous nucleation(異相成核)是材料科學和物理化學中的重要概念,指物質在相變過程中,晶核的形成依賴于外來雜質或界面作用的現象。以下是詳細解釋:
異相成核是指分子或原子在雜質表面、界面或預先存在的晶種上形成晶核的過程。與均質成核(homogeneous nucleation)不同,異相成核不需要在純物質内部自發形成晶核,而是借助外部媒介降低能量壁壘,使相變更容易發生。
特征 | 異相成核 | 均質成核 |
---|---|---|
成核位置 | 雜質或界面 | 純物質内部 |
能量壁壘 | 較低 | 較高 |
常見場景 | 自然水體結冰、合金凝固 | 超純液體過冷/過熱狀态 |
如需進一步了解具體領域(如材料科學或氣象學)中的應用,可參考相關學術文獻或專業教材。
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