Method of preparing silver-based oxide electrical contact materials with fiber-like arrangement

A method of preparing silver-based oxide electrical contact materials with fiber-like arrangement, comprising the steps of:

• (A) uniformly mixing silver-metal-additive alloy powders with graphite powders, and then ball-milling after placing the mixed powders into a high-energy ball milling tank in such a manner that the alloy powders and the graphite powders are refined to form uniform and ultrafine composite powders, wherein the metal in the alloy powders is able to form alloy with Ag, a reducibility of the metal is better than a reducibility of Ag and the metal is spontaneously oxidizable, a weight ratio of Ag to other metals in the alloy powders is calculated according to a composition of the preparation material and subsequent processing requirements, a weight ratio of the alloy powders to the graphite powders is calculated according to a looseness of the silver-based oxide electric contact materials, a content of the additive is calculated according to a content of the metal and subsequent processing requirements, and the additive is selected from a group consisting of Bi, In, Cu and rare earth elements,
• wherein in step (A), a particle size of the alloy powders is in the range from 80 to 400 meshes;
• a weight ratio of Ag to metal in the alloy powders is in the range from 3 to 0.5;
• a content of the graphite powders in the mixed powders is in the range from 0.5% to 3%;
• a content of the additive metal is based on the requirement that a weight of the metal oxide thereof is no more than that of an reinforcing phase in a silver-based oxide;
• the additive is selected from a group consisting of Bi, In, Cu and rare earth elements, a ball-milling speed is 180 to 300 rev/min, a ball-milling time 5-10 hours and a ball-to-powder weight ratio 10-20;
• (B) internally oxidizing the powders obtained from the step (A) comprising firstly decarburizing in air atmosphere and then internally oxidizing in oxygen atmosphere,
• wherein in step (B), the internal oxidization comprises two steps of firstly oxidizing for 5-15 hours in air atmosphere at an oxidization temperature of 250-700° C., and then oxidizing for 5-15 hours in oxygen atmosphere at an oxidization temperature of 300-700° C. and an oxygen pressure of 0.5-3.5 MPa, in such a manner the graphite powders in air atmosphere are firstly oxidized to form CO2 gas, a structure of the powders becomes loose due to a discharge of the CO2 gas, the loose structure in oxygen atmosphere is beneficial to a further spread of oxygen to an internal of the powders for promoting a complete oxidation of the metal, and ultimately a silver oxide material with the loose structure is formed;
• (C) sieving the internally oxidized powders obtained from the step (B), ball-milling after placing large particle powders that fail to pass a sieve into a high-energy ball milling machine, and then sieving again,
• wherein in step (C), a speed of the high-energy ball milling is 180-280 rev/min, a milling time is 5-15 hours, a ball-to-powder weight ratio is between 10-20, and a sieve mesh is 100-400 meshes;
• (D) uniformly mixing after placing the composite powders obtained from step (C) and matrix silver powders into a powder mixer, wherein a weight ratio of the composite powders to the matrix silver powders is calculated according to a composition of the preparation material and a desired fiber size,
• wherein in step (D), a speed of the powder mixer is 20-40 rev/min, a mixing time is 2-6 hours, and a particle size of the matrix silver powders is 50-400 meshes;
• (E) cold-isostatically pressing the powders obtained from step (D), wherein in step (E), a cold isostatic pressure is 100-400 MPa;
• (F) sintering the body obtained by cold isostatic pressing, wherein in step (F), a sintering temperature is 600-900° C., and a sintering time is 5-10 hours;
• (G) hot-pressing the body obtained by sintering, wherein in step (G), a hot-pressing temperature is 600-850° C., a hot-pressing pressure is 200-700 MPa, and a hot-pressing time is 5-30 min;
• and
• (H) hot-extruding the body obtained by hot-pressing, thereby obtaining the fibrous structural silver-based oxide electrical contact material, wherein in step (H), a heating temperature of the body is 700-900° C., an extrusion ratio is 60-400, an extrusion speed is 5-15 cm/min, a preheating temperature of an extrusion mold is 300-500° C., and during the hot-extrusion process, due to a flow of the matrix silver powders, particles of the powders with the loose structure are slowly opened and directionally arranged along a hot-extrusion direction for forming the fibrous structure.