| AgCdO with good incorrodibility to arc erosion, high resistance to fusion welding and lower contact resistance, has been regard as the best contact material for long time. It widely used in low-voltage from several voltages up to kilos voltages, was called universal contact point. Metal Cadmium and its compounds are toxic for organism. Biological half period is about 10 - 30 years in human bodies. Aggregation, in kidney, skeleton and blood, easily lead to some diseases such as liver cancer, prostate cancer and lung cancer.Recently, with the enhancement on environmental protection consciousness, AgCdO material has been restricted to be used in some countries. In Feb.2003, two environmental protection injunctions were publicized in EU. According to ?Vorschlag fur eine Richtline des europischen Parlaments und des Rates zur Beschrnkung der Verwendung bestimmter gefhrlicher Stoffe in elektrischen und elektrronischen Geraten ? such as Pb, Hg, Cd and Cr6+ etc, six matter are prohibited to use in electrical information products, which will be carried out on July 1st, 2006.Therefore, development and exploitation of the new material, with friendly-environment function and high electric contact property, has been a hot topic in its field. Fortunately, AgSnO2 is mostly researched and the most prospective material. At present, lots of production are developed in native and abroad, including the processes of alloy oxidization, powder-sintering extrusion, alloy powder pre-oxidization and coprecipitation. But, in productive process, most of them have some problems, such as high material intensity, hardness and low rate of hardening etc, which bring about some hard difficulties for the following cold-forming process.According to metallurgical thermodynamics theory, the reaction mechanism of reaction synthesis preparation for Ag-basic contact materials is researched in this thesis. The material AgSnO2(10) was prepared successfully through reaction synthesis method. And it is studied that the preparation process, the microscopic structure, mechanical behavior, electricity property and surface topography after burning loss of thematerial AgSnO2( 10).In our research, the better-structural AgSnO2(10) is yielded on the condition: 45 taper die, 750C ingot, 500C mode and 0.1 mm/s to 0.2 mm/s extrusion speed. The conclusions show: through reaction synthesis process, element Sn diffuses outside from the AgSn alloy particle and combines to produce SnO2 with element O around the AgSn particle, which lead to the development of aggregation band. SnO2 particles are produced by reaction grow in the ground mass and have small size and hardness on material mechanical property. TEM diagram shows SnO2 particle diameter is about 50nm, several small particles to possibly compound chemical structure similar to (Sn, Ag)O2, which can increase interfacial energy between the SnO2 particle surface and the Ag matrix and improve plasticity and malleability of the material AgSnO2(10). Ultimate elongation, on annealing condition, is up to 22%. Through press work, the Ag matrix is elongated and attenuated to form fibrous structure and banded structure. SnO2 particles, distributed on boundary layer, flow and rotate, with the Ag matrix done, and the unite SnO2 particles and big particles be crushed and begin to adjust their positions and form fibrous structure or banded structure along extrusion deforming direction. With the deformation of the Ag matrix, Sn2 particles can insert continuously into the Ag matrix and finally accomplish the homogenous dispersion. The characteristic, of reaction synthesis preparation for AgSnO2, is "reaction synthesis, particle refinement, matrix coarseness, press dispersion".On the aspect electric property, the material AgSnO2, Prepared through reaction synthesis method, has the lower resistance much less than related national standards. And experimental measured data are consistent with the result of theoretical calculation. At the same time, it has high resistance to transfer, long electrical life and low consu... |
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