Preliminary Research On Furnace Materials Of Historical Ferrous Metallurgy In China

As core technical materials of pyrotechnology, furnace materials for historical ferrous metallurgy and processing--including smelting, melting, casting, forging, and heat treatment--remain in smelting and foundry sites in a large amount all around China. The furnace materials that were found not only provide structural stability, but also to keep thermal stability, as well as to matiain chemical stability of furnaces during the metallurgical processing. However, this kind refractory ceramic material has not been as well studied as other metallurgical ceramics, and the understanding of these materials is still sketchy. The aim of this research is to understand the development history of furnace materials through reference research, field investigation, scientific research and simulation experiment, and to understand the details of the microsture and properties of these materials, as well as from this perspective to examine the ancient Chinese iron industry, which will be instructive to show the splendid wisdom and creativity of Chinese people.There were mainly four kinds of furnace material productions:simple clay material (rammed caly or clay brick), sand brick, sandy clay (clay with sands and gravel sized rock fragments) and rock production. Local clay has been used as mainly raw material, and as joint material. Sand and rock fragments were used as key material in the sand brick, and as temper in the snady clay production. Not only the amounts of clay matrix, all inclusions and pores, but also the sizes of inclusions and pores in differnent materials were widely different. It might be caused huge diffetences on material properties.Clay has its advantage on shaping and jointing, but easily metlting in a high temperature. Sands and rock fragments in a mixture of fine particles of matrix, these compositions are self-correcting; as the temperature and firing time increase, more liquid forms, but more sands and rock fragments dissolves, make the larger amount of silicate liquid even stiffer. The wonderful body of sandy clay materials which have refractory grains dispersed in a viscous silicate liquid containing an extensive network of fine crystallites that stiffen the liquid and prevent excessive slumping. In addition, higher porosity which sandy materials always had, as well as materials have organic temper, can help to escape hot gas through pores, stop the expansion of cracks and prevent the failure of the whole structures. From the XRD and DTA results, it seemd that ancient furnace linings experienced the same temperature in the metallurgical process, which were about1000-1100℃, and the refractoriness were about1250-1350℃. These two temperatures were lower than the smelting temperature (approximately1400℃), which suggested that furnace lining might play the role of sacrificial material to protect the whole furnace.Through the chemical stuieds, it was known that ancient furnace amterials might have the same amounts of compositions, which demonstrated that special clay or other raw materials have not been used. The compositions of adhering slags were mainly from furnace materils, while tapping slag didn’t, and simple clay materials provided more silicate to tapping slag than other furnace materials.Through simulation experiment, the process of choosing raw materials, the manufacturing technique of making furnace maerials, the chemical corrosion of slag on the furnace lining, and the alteration and accretion of furnace wall was observed in detail, and had given a good understand on the role of furnace material played in the metallurgical process.The study showed that smelting furnace materials were developed from simple clay material to a stone and clay co-existing structure. Rammed clay or stacked clay bricks were used during4th C. BCE and3rd C. CE, while, from7th to13th C.CE, refractory material of clay with sands and gravel sized rock fragments was lined on the inner surface of stone wall. For melting furnaces, simple caly material was used in the early time, after that sandy clay was used for a very short time. Because of puddling and crucible steel techniques, melting furnaces were disappeared.The "development" was not only caused by different resources, manufacturing technologies, but also because of different style of organization, such as it gave us a clue to see the relationship between ceramic and metallurgy in ancient China, and the result showed that they were on a way to separate. Meanwhile, the late furnaces have many technological improvements, such as the sacrificial clay refractory lining was replaceable, and made the furnace easy to repair and may have a longer use life. All in all, easy work, small organization, better quality and economic advantage might cause the development happened.