Cu、Bi对AgSnO₂复合材料反应合成的组织与性能的影响

【作者】 江珍雅；

【导师】 陈敬超；

【作者基本信息】 昆明理工大学 ， 材料学， 2006， 硕士

【摘要】 本文通过对AgSn、AgSnCu和AgSnBi合金的内氧化实验，以及反应合成AgSnO₂CuO和AgSnO₂Bi₂O₃复合材料实验的研究。从热力学和动力学上分析了Cu、Bi添加对内氧化以及反应合成制备AgSnO₂材料的影响，并对反应合成的AgSnO₂CuO和AgSnO₂Bi₂O₃复合材料在不同工艺时期的组织结构和物理性能进行了分析。通过热力学计算得到：1)各金属与氧的亲合力Sn＞Bi＞Cu；2)在热力学上SnO₂比SnO更稳定，CuO比Cu₂O更稳定；3)在AgSnCu系统中的化学位Cu＞Ag＞Sn，在AgSnBi系统中的化学位Ag＞Sn＞Bi。AgSn合金内氧化的过程中，很容易发生外氧化。AgSnCu合金内氧化机理与AgSn类似，在反应的过程中未氧化的Sn又可以夺取CuO中的O，但这需要一定的温度来提供足够的能量，去克服能垒，所以在这个温度点之前，AgSnCu的内氧化增重曲线跟AgSn很接近，或者比AgSn的增重少，因为Sn是比Cu更容易氧化的。这个关键的温度点为350℃。AgSnBi合金中，Bi几乎不溶氧，Bi的存在，稀释了Sn的浓度，降低了Sn形成氧化膜的速率，随着反应的进行，Bi依附吸附了过量氧的Sn生成氧化物，但内层中未氧化的Sn又可以夺取已氧化的Bi的氧，这需要一定的温度来提供足够的能量去克服能垒，这关键温度点为250℃。反应合成AgSnO₂CuO（SnO₂7.42wt％，CuO6.21wt％）和AgSnO₂Bi₂O₃（SnO₂7.79wt％，Bi₂O₃5.44wt％）复合材料的过程中，AgSnBiO系统的反应激活能约为235KJ／mol，AgSnCuO系统约为229KJ／mol，在相同的加热条件下，AgSnCuO系统先发生化学脱附，反映在温度上，就是AgSnCuO的脱附温度比AgSnBiO的脱附温度低20℃左右，为350℃。反应合成过程中：1)AgSnCu合金系统吸附氧的能力比较强，合金中Cu浓度越高，则吸附氧的能力越强，AgSnBi合金系统吸附氧的能力就比较弱，并且合金中Bi浓度越高，吸附氧的能力就越弱；2)AgSnCuO系统先是发生明显的置换反应，生成数量较多的氧化物，其中CuO的大量生成使基体的密度明显下降，再是基体中未反应Sn、Cu与游离氧的反应，生成的混合氧化物（SnO₂和CuO混杂在一起）弥散分布于基体，在晶界处有明显聚集。3)AgSnBiO系统，Bi被浓缩在晶界上，脆化了晶界，SnO₂在大颗粒的界面处偏聚，由于生成Bi₂Sn₂O₇使基体的密度下降。更多还原

【Abstract】 In the present study, both the oxidation behavior of AgSn AgSnCu AgSnBi alloys and the reactive synthesis of AgSnO₂CuO and AgSnO₂Bi₂O₃ composites are investigated.Hence, the effect of Cu Bi additive to fabriacte the AgSnO₂ composites is analysed by means of thermodynamic and kinetics.Also, microstructure and physical property of AgSnO₂CuO and AgSnO₂Bi₂O₃ composites at the different stage of process are detail studied.In this case , three conclusions are concluded by thermodynamic computation: l)The chemical affinity （Oxygen potential） of tin is stronger than bismuth, and bismuth stronger than copper. 2) The SnO₂ is more stable than SnO, and CuO more stable than Cu₂O. 3)From high to low, the order of chemical potential is Cu, Ag, Sn, Bi.It’s easy to form thick external oxide layer for AgSn alloy during the internal oxidation process.The internal oxidation mechanism in AgSnCu alloy has much common with the AgSn alloys.When copper gets oxidation, tin captures the oxygen from the copper oxide.The key point temperatures for tin to overcome energy barrier to capture the Oxygen belong to copper oxide is 350℃ .Bismuth has low cohesive affinity to oxygen.So, at first, the present of bismuth decreases the oxidation rate of the tin in the AgSnBi alloy.Tin is easy to fix oxygen and makes excessive oxygen in the matrix.Later, bismuth depends on tin oxide to form new oxide, such as Bi₂Sn₂O₇.At last, tin snatches oxygen from this new bismuth oxide at the 250℃.During the reactive synthesis of AgSnO₂CuO（SnO₂7.42wt% , CuO6.21wt%） and AgSnO₂Bi₂O₃（SnO₂ 7.79wt% , Bi₂O₃5.44wt%） composites, the activation energy of AgSnBiO system is higher than the AgSnCuO system.The activation energy to decompose for AgSnCuO system is about 229kJ/mole, AgSnBiO system about 235kJ/mole.The decompose temperature for AgSnCuO system is 350℃ , which is lower than AgSnBiO system about 20℃.During the reactive synthesis process: 1) The higher concentration ofcopper is, the higher ability for AgSnCu alloy to absorb oxygen.As for the bismuth in the AgSnBi alloy, quite the reverse. 2) The chemical reaction in the AgSnCuO or AgSnBiO system can be divided into two parts: One is displacement reactions between alloys and Ag₂O.The other is alloys reacting with active oxygen.Displacement reaction happens at the low temperature（<352℃） for the AgSnCuO system.Because of large quantity of copper oxide apperance, the density of matrix obviously decreases. 3) Bismuth is condensed at the grain boundary and decreases the property of the boundary.The SnO₂ particle uniformly disperses at the matrix and segregates at the grain boundary. The appearance of Bi₂Sn₂O₇ decreases the density of matrix.更多还原