Effect of Some Metal Elements on the Oxidation Rate in Ag-Sn Alloy

The use of fine particles based on certain oxides in the replacement of toxic Ag-CdO electrical contact materials, Ag-Sn2 performance is relatively good, but it is difficult to use the conventional internal oxidation process Sn = 65 ~ 10w% The study of internal oxidation of Ag-Sn alloy wire shows that adding 5% or more of In or high pressure oxygen (10 MPa) can oxidize the Ag-Sn alloy, and the microstructure of the Ag-Sn alloy also improves. However, the addition of rare metals, indium, raises the cost. Oxidation of high pressure oxygen causes difficulty in the manufacture of equipment. SEM and scanning electron microscopy have studied the microstructure of the inner oxide layer of Ag-6.5Sn-1.lBi-0.6Cu alloy. In the high-frequency furnace, the alumina was used to smelt the alloy under Q-vacuum, and the sample was processed to a thickness of 3mm. Samples were oxidized and oxidized at different times using oxygen pressures of 0 to 4 to 0.6 MPa, 500°C, and 700°C, respectively. A metallographic sample was formed, the thickness of the oxide layer was measured with an optical microscope, and the microstructure was observed. The surface distribution of metal elements in the oxide layer of Ag-6 6Cu alloy was observed by scanning electron microscopy.

2 Experimental results 21 Effect of addition of metal elements on the oxidation rate in Ag-Sn alloys The influence of the same content of BiSbCu and Zn on the internal oxidation rate of Ag-65Sn alloys was investigated at 500 °C and 0.4-0.6 MPa oxygen pressure for each alloy. The relationship between the thickness of the inner oxide layer and the internal oxidation time (ignoring the oxide layer of the outermost layer) From the observation, under the same conditions, each alloy can be internally oxidized, but the internal oxidation rate is not the same. The order of influence of the addition of metal elements on the internal oxidation rate of Ag-65Sn alloy in this study is Bi>Sb>Cu>Zn It is also seen that the internal oxidation rate of Ag-6.5Sn-1.1Bi-0.6Cu alloy is greater than that of Ag-6.5. The internal oxidation rate of the Sn-1.5In alloy can be seen that adding 1.5% of In in the Ag-6.5Sn alloy does not accelerate the internal oxidation rate of the Ag-Sn alloy. The inner oxide layer thickness of the Ag-6. 5Sn-3Sb at 700C and The relationship of time. Comparing and observing the temperature dependence of the internal oxidation rate of the alloy as a rejection of the microstructure of the alloy in order to understand the internal oxidation of Ag-Sn alloys with added metal elements, optical microscopy and the microstructure of the post-oxidation layer . It is the microstructure observed with an optical microscope. A is an oxidized metal and B is an unoxidized metal. Seen from A, there are large grains with one grain. The observed cracks are due to the increase in volume caused by internal oxidation. Scanning Electron Microscope Topography Comparison 5 and 7 It can be seen that more Sn is distributed at grain boundaries. In other words, there is an aggregation of Sn2 and Bi oxides at the grain boundary. Discussion According to the thermodynamic theory, the oxidation reaction of all metal elements is spontaneous, and the oxidation reaction ability depends on the outermost layer and the outer layer of the metal element. The electronic structure of the layer and the generation of oxides from the special study Fromhold studied the metal oxidation theory, that the metal oxide thickness growth is a diffusion process, and diffusion is generated by the concentration gradient, and deduced that the thickness of the metal oxide layer increased The theoretical mathematical formula with time is a parabolic relationship. And shows that, in the 0.4-0.6MPa oxygen pressure, 500 °C and 70C under the internal oxidation, the thickness of the oxide layer within the alloy and the relationship between the time is a parabolic relationship. However, the added metal elements are different, and the internal oxidation rate of the Ag-Sn alloy is different. When the temperature is different, the internal oxidation rate is also different. It is difficult for the Ag-Sn alloy to form a dense protective film of Sn2 so that the diffusion of oxygen into the interior of the alloy is difficult. The addition of an easily oxidizable BiSb element destroys the dense layer of Sn2, thereby creating a condition for oxygen diffusion. The results show that it is feasible to replace In with Bi and Sb elements as additive elements of Ag-Sn alloy to accelerate the internal oxidation of Ag-Sn alloy.

The analysis of the microstructure shows that more Sn and Bi elements are accumulated at the grain boundary of the alloy oxide layer. Under the Sn component studied, the Ag-Sn alloy is solid solution. Therefore, the aggregation of Sn element is produced during the internal oxidation.

The internal oxidation process of the 0.6Cu alloy is: at the oxide layer thickness X, at the higher oxygen concentration and temperature, the Bi particles at the higher-order grain boundary positions are first oxidized, destroying the dense layer of Sn2 that has been formed, creating The oxygen-diffused channel oxygen surrounds the Sn and Cu particles at the grain boundary and promotes their oxidation. This results in a high concentration of oxygen and a low concentration of Sn in the oxidized region, and a low concentration of oxygen in the adjacent crystal grains. High concentration of Sn, so formed a large concentration gradient, to promote the diffusion of oxygen into the crystal, Sn to the grain boundary diffusion, so that the oxidation of the entire grain within the oxidation process is repeated in this way, to promote the thickness of the oxide layer which is also the grain boundary There are more reasons for Sn2. The higher the pressure of oxygen and the higher the temperature, the higher the oxidation rate in the Ag-Sn alloy. 4 Conclusions The results show that the increase of the thickness of the inner oxide layer of a Ag-Sn alloy added with a metal element has a parabolic relationship with the time. The rate of oxidation in the alloy depends on the properties of the added metal and the internal oxidation temperature Both Bi and Sb in this study can accelerate the internal oxidation rate of the Ag-Sn alloy.