metastable liquid state miscibility gap in undercooled Pd-ni-P melts.

• Other Authors: Lau, Man Tat.
• Format: Others
• Language: English; Chinese
• Published: 2012
• Subjects: Nonequilibrium thermodynamics; Solidification; Cooling
• Online Access: http://library.cuhk.edu.hk/record=b5549028; http://repository.lib.cuhk.edu.hk/en/item/cuhk-328588

在近期的研究結果中, 相分離被發現發生在具非晶結構的Pd₄₁.₂₅Ni₄₁.₂₅P₁₇.₅合金，而該合金的構成元素之間的有負值的混合焓。通過高分辨率透射電子顯微鏡的直接成像的方法，他們為Pd-Ni-P非晶系統相分離的發生提供了證據。 === 在這篇論文所論述的研究工作中，我們運用類似的技術來研究Pḍ₄₀₊₀₅{U+2093}Nị₄₀₊₀₅{U+2093}P₂₀₋{U+2093}的合金系統從 x = 0到3.5的非晶相分離。 === 實驗結果顯示，任何在空氣中冷卻到578 K再在613K退火一小時的樣品 (乙類樣本)，非晶相分離都沒有發生。然而，在613K退火一小時而沒有經過578K和613K溫度範圍的Pḍ₄₀₊₀₅{U+2093}Nị₄₀₊₀₅{U+2093}P₂₀₋{U+2093}大塊非晶金屬(丙類樣本)，卻在部分成分範圍中發生相分離。在丙類樣本中，當x>1，相分離發生；而當x≤1，相分離沒有發生。通過量度高角環形暗場影像中顯示的兩個相的平均波長，我們可得出其統計結果，而該統計結果與槓桿規則吻合。從此可見，在過冷的Pd-Ni-P熔合合金中存在著亞穩液態混溶間隙。並且這種出現在有負值混合焓的系統的亞穩液態混溶間隙，可以以短程有序的模型來解釋。 === Recently, the phase separation was found in the system of amorphous Pd₄₁.₂₅Ni₄₁.₂₅P₁₇.₅ alloys which has negative heat of mixing among the constituent elements. In their work, the directly imaging method by technique of high resolution TEM provided the evidence of phase separation in amorphous Pd-Ni-P system. === In this work, by applying the similar technique of that previous studies, the alloy systems of Pḍ₄₀₊₀₅{U+2093}Nị₄₀₊₀₅{U+2093}P₂₀₋{U+2093} for x = 0 to 3.5were studied for amorphous phase separation. === The experimental result showed that for any sample which was allowed to cool down in air to 578 K before thermal annealing (B-type), there was no amorphous phase separation. But for the Pḍ₄₀₊₀₅{U+2093}Nị₄₀₊₀₅{U+2093}P₂₀₋{U+2093} BMG that was annealed at 613K for one hour without bypassing the temperature range between 578K and 613K (C-type), phase separation occurred with x>1 but absented when x≤1. The result of average wavelength measurement of the two phases in the HAADF images of the sample with phase separation obeyed the lever rule. This result suggested that in undercooled molten Pd-Ni-P alloys, there is a metastable liquid state miscibility gap. The formation of such miscibility gap in a system with negative heat of mixing can be explained by the model of unique short range orders. === Detailed summary in vernacular field only. === Detailed summary in vernacular field only. === Detailed summary in vernacular field only. === Lau, Man Tat = 過冷鈀、鎳、磷熔化物中的亞穩液態互溶間隙 / 劉文達. === Thesis (M.Phil.)--Chinese University of Hong Kong, 2012. === Includes bibliographical references. === Abstracts also in Chinese. === Lau, Man Tat = Guo leng ba, nie, lin rong hua wu zhong de ya wen ye tai hu rong jian xi / Liu Wenda. === Abstract --- p.i === Acknowledgement --- p.iv === List of Tables --- p.vii === List of Figures --- p.viii === Chapter Chapter 1 --- : Introduction --- p.1 === Chapter 1.1 --- Amorphous metal --- p.1 === Chapter 1.2 --- Phase Separation --- p.3 === Chapter 1.3 --- Nucleation --- p.6 === Chapter 1.4 --- Spinodal Decomposition --- p.10 === Chapter 1.5 --- Objective of the project --- p.16 === Figures --- p.18 === References --- p.26 === Chapter Chapter 2 --- : Experiment --- p.27 === Chapter 2.1 --- Preparation of sample --- p.27 === Chapter 2.2 --- Differential scanning calorimetry --- p.30 === Chapter 2.3 --- Preparation of TEM sample --- p.31 === Chapter 2.4 --- Microstructural analysis --- p.33 === Figures --- p.36 === References --- p.39 === Chapter Chapter 3 --- : A metastable liquid state miscibility gap in undercooled Pd-Ni-P melts --- p.40 === Chapter 3.1 --- Introduction --- p.40 === Chapter 3.2 --- Materials and experimental --- p.41 === Chapter 3.3 --- Results --- p.44 === Chapter 3.4 --- Discussions --- p.49 === Chapter 3.5 --- Conclusions --- p.52 === Table --- p.53 === Figures --- p.54 === References --- p.75