Recently, under the leadership of Professors Wang Linjun and Xu Run from the PI (Pure Iron) project team, jointly formed by Shanghai University, Hebei Longfengshan Foundry Co., Ltd. (Longfengshan Foundry), the Metallurgical Economic Research and Development Center (Economic Research Center), and the High-end Equipment Basic Component Material Research Institute of Shanghai University (Zhejiang) (Shangshan Institute), the team successfully produced ultra-pure iron with a purity of 5N2 (5N~6N). This marks a significant scientific breakthrough following the team’s achievement of producing 4N7 high-purity iron in 2021 and realizing the industrialization of 4N electrolytic iron in 2023.
Pure iron is an important industrial raw material, and the technology for purifying pure iron reflects a country’s level of industrial development. 5N-grade ultra-pure iron is of great significance for material science research, technological innovation, and engineering applications. Its production process has been a world-class scientific challenge, with only developed countries like Japan and the United States having previously achieved laboratory production of 5N-grade ultra-pure iron. China’s successful production of 5N-grade ultra-pure iron signifies that it has joined the forefront of the world in iron purification.
Currently, the purity of pure iron produced on a large scale in China is 99.0~%99.9% (2N3N). To overcome the technical difficulties of producing 5N-grade ultra-pure iron, in April 2022, Wang Linjun proposed a scheme for purifying ultra-pure iron using the zone melting method by combining existing semiconductor material purification technology with iron ultra-purification. Xu Run led the team through two years of continuous and arduous scientific research, designing and manufacturing the first ultra-high vacuum vertical floating zone induction zone furnace in China. Through extensive and meticulous scientific work, they further understood the rules and mechanisms of iron purification, forming a systematic technology for purifying ultra-pure iron. The PI project team continued to carry out experimental work and in September 2023, for the first time, produced 5N ultra-pure iron using a combination of electrolysis, vacuum melting, and vacuum vertical zone melting. After more than six months of continuous efforts, the team mastered a consistently excellent, stable, and repeatable purification process in March 2024. Third-party testing confirmed that the purity of the ultra-pure iron samples reached 5N2 (99.9992%), with gas impurity elements (carbon, nitrogen, oxygen, hydrogen) content at only 4.5ppm, and the total content of other elements at 3.2ppm (including all 73 impurity elements accurately measurable by GDMS).
It is reported that based on carbon content, iron is classified into pig iron, steel, and pure iron, with iron containing less than 0.0218% carbon being called pure iron. Unlike the properties of pig iron and steel, high-purity iron and ultra-pure iron above 4N grade possess excellent soft magnetic properties, corrosion resistance, ductility, thermal properties, and electrical conductivity. Using them as raw materials can significantly enhance the performance and quality of special alloys, high-end special steel, semiconductors, and amorphous materials, thereby promoting the development of industries such as aviation, aerospace, electronics, energy, and semiconductors.
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