Effect for molybdenum discs by the Fe and Ni content in molybdenum ingot
Because of its high strength, good thermal conductivity and electrical conductivity, as well as the similar expansion coefficient and good processing performance with silicon, molybdenum is used as the substrate material of silicon rectifying elements and silicon controlled silicon elements (the support of silicon wafer-molybdenum wafer).With the continuous progress of science and technology, the quality requirements of silicon controlled silicon manufacturers for molybdenum discs are constantly improved. In particular, the number of black spots on the surface of molybdenum discs with diameter larger than 70 mm becomes the main factor affecting the quality of molybdenum discs. Due to the existence of black spots, the conductivity and corrosion resistance of molybdenum discs become poor, which affects the service performance and service life of silicon rectifier elements. Therefore, to reduce and eliminate the black spots on the molybdenum disc is an urgent problem to be solved. Through the systematic tracking inspection and analysis of the technological process of producing molybdenum disc with molybdenum ingto with different impurity contents of Fe and Ni, the law and reason of producing molybdenum disc black spot are found out, which provides the basis for reducing or eliminating molybdenum disc black spot.
Molybdenum powder with different contents of Fe, Ni and other impurities was pressed and sintered to form a 80 mm molybdenum disc. The process route is as follows: molybdenum powder → pressing → sintering → molybdenum ingot → heating → rolling → heating → punching → edge rolling → grinding → washing → inspection → finished products.
(1） The number of black spots formed on the surface of molybdenum disc has nothing to do with the rolling process of molybdenum circle, which is mainly determined by the impurity content of Fe and Ni in molybdenum powder.
(2） There is a nonlinear relationship between the content of Fe and Ni and the distribution of round black spots. When the content of Fe and Ni is more than 0.0095 w% and 0.004 w%, the black spots increase suddenly. Less than this value, the number of black spots reduced to 2-4. Therefore, controlling the enrichment of Fe and Ni impurities in raw molybdenum powder is the fundamental way to reduce or eliminate molybdenum round black spots.
