Electrical contact materials are used to produce switch and instrument panel of electronic components. The task of the contacts is to connect current paths, to interrupt current, and to carry current. The properties of the materials themselves will directly restrict the reliability, precision and life performance.
Ag-SnO2 has been recognized for its environmental friendly property, especially the outstanding performance like resistance to arc erosion, ablation and contact welding. So the new developed nontoxic Ag-SnO2 have the potential to take place of the toxic Ag-CdO. The Ag-SnO2 contact materials preparation process includes internal oxidation method and powder metallurgic method. But both two methods have some defects. The former can’t oxidize alloys which contain more Sn, and need In to promote internal oxidation. Powder metallurgic method can’t product Ag-12SnO2 materials. The obvious limitation is the difficulty of molding process, which can’t satisfy with small dimensional and high reliable developing trend. According to this, this thesis is to bring out a new producing technique of Ag-SnO2 to improve the related mechanical properties.
1 The second chapter in this thesis is mainly concerning with high-energy technique to produce Ag-SnO2 followed by physical and mechanical estimation. 2 Then some researching work on internal oxidation behavior of Ag-xSn (x=2, 4, 5, 6 wt.%) at 600-800℃; 3 Ag-4Sn alloy is made into atomization powder and milling powder separately, which internal oxidation behaviors are investigated at 300-500℃. 4 In the last part of the thesis, by combing both high-energy milling and internal oxidation techniques, a new producing process is established.
1 The investigation results showed that Ag-SnO2 produced by high-energy milling technique presents better physical and mechanical behavior than the traditional powder metallurgy way. But there are still some defects like unacceptable rigidity, which has to be modified by multiple annealing. 2 For the Ag-Sn alloys containing Sn less than 4wt.%, the oxidation kinetic curves nearly coincide with Wagner parabola rule. Especially in some appropriate conditions, Sn can be oxidized thoroughly. For the Ag-Sn alloys containing Sn more than 5wt.%, just a few Sn can be oxidized company with transferring from internal to external oxidation process. 3 At 300-500℃ Ag-Sn powders are oxidized soon. Oxidation rate of milling powder is much faster than atomization powder. The reason is the particles are deformed during milling, which produce stress and strain; this behavior is corresponding to increase the internal energy of the particles and decrease the reaction barrier.
Ag-SnO2 alloys made by new technique present better mechanical properties. At the same time it also overcome the difficulty to oxidize Ag-Sn alloys containing Sn more than 5wt.%. What’s more, this technique possess the virtues both powder metallurgy and internal oxidation process. So this combing technique successfully investigated in the thesis will be more acceptable new process for Ag-SnO2 alloy producing.
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