ARCH 1764 Under the Microscope 250 Years of Brown’s Material Past
Prof. Clyde Briant Office hours Wednesday 4:00-6:00 pm 220 Barus and Holley
Prof. Brett Kaufman Office Hours: Tuesdays, 2:00-4:00 pm Rhode Island Hall 007
TA Susan Herringer
This presentation and the images within are for educational purposes only, and are not to be distributed Metallurgical Slags
Metallurgical Slags
• Usually consist of SiO2 plus oxides such as CaO, Al2O3, P2O5, MnO, MgO2. • Slag is a mixture of phases. • Current technology depends on type of furnace but overall goal is to control the chemistry of the final metal through control of the chemistry of slag. • Great emphasis today on reuse of slag: added to cements, reused in additional slags, various filler materials.
• https://www.youtube.com/watch?v=hBqhGHf zQFQ - https://www.youtube.com/watch?v=hBqhGHf zQFQ • http://science.howstuffworks.com/blast- furnace-videos-playlist.htm - http://science.howstuffworks.com/blast- furnace-videos-playlist.htm
Archaeological Slag and Dross Slag is the byproduct of metallurgical activity resulting from the processing of metallic ores and is usually composed of a glassy mass of ore detritus that contains vitreous gangue, solid dross, and unsmelted metallic components.
http://antiquity.ac.uk/projgall/ben-yosef330/images/figure6big.jpg 25 meter high slag heap from Late Roman period in Cyprus Types of slag research involves reverse engineering to study:
►much research into slag has focused on analysis of phase microstructure and chemical composition in order to deduce whether this byproduct resulted from primary smelting, secondary smelting (blooming), crucible smelting, or melting activities. ► source of the ores based on elemental ratios ► determining furnace environment and temperatures achieved by use of ternary phase diagrams and microstructures ► efficiency of extractive metallurgy over time and fuel usage ► social organization and “technological traditions” of metalworking communities regional studies of the metalworking traditions that help reconstruct economic, technological, and ecological trends Glossary Direct process: iron ore is reduced in a bloomery furnace, in which granulated ore is mixed with fuel (wood or dung charcoal) to produce an unmelted iron bloom with slag flowing off Indirect process: granulated iron ore and fuel react in a bloomery furnace to produce molten pig iron with a carbon content around 4%. The pig iron is then oxidized in a fining process, melted little by little until it consolidates into a bloom which is hammered to free it from slag and other impurities. Cast iron leaves little iron in the calcium/aluminum/magnesium rich slags Primary smithing: Hammering the bloom into a cake or bar Secondary smithing: Forging the metal-rich cake or bar into a final product Gangue: undesired components of a metal ore Smelting: extraction of gangue from ore to leave metal and slag byproduct Bloom: An iron mass with ore, slag, and furnace environment impurities that is the intermediate product between smelting an ore and a finished product. Dross: A metal oxide that is the result of recycling or melting scrap metal Wüstite: Human-made mineral from metallurgical production, FeO Spinel group (spinels): Minerals in oxide form that can result from smelting or melting activities, with magnetite being a common one in the form of Fe3O4 Olivine: Magnesium iron silicates often found in slag with the most common being fayalite, Fe2SiO4 Flux: When an ore is smelted, fluxes are often added to reduce the temperatures necessary to isolate the iron, including calcium and manganese, in addition to naturally occurring silicon in the ore which would induce self-fluxing
Qualitative rule of thumb as established by Buchwald and Wivel 1998
Ferrous slags rich in iron oxide phases are qualitatively linked to the production of wrought iron (α-ferrite microstructure), and ferrous slags poor in iron oxide phases but rich in olivine and glassy phases are qualitatively linked to the production of steel (pearlite microstructure) Smelting and melting slags and dross It is notoriously difficult to tell the difference between copper smelting and melting slags as the phases can be very similar and even in a melting slag (dross) the molten metal can react with the ceramic crucible to create slag phases, but there are some clear signs such as a fairly pure metal-oxide matrix.
Frozen rivers of molten copper in green/blue in a matrix of spinels, Jerusalem ~1000 BC Smelting copper slags
Schematic of smelting a copper sulphide ore (Tylecote, Ghaznavi, Boydell 1977) Melting copper dross
Copper oxide phases in dross, Jerusalem ~1000 BC Melting copper dross
Crucible slag or dross with cassiterite (tin oxide) crystals embedded in a dross or copper oxide matrix, Jerusalem ~1000 BC Melting copper dross
Ceramic crucible reacts with copper dross to produce slag phases Primary wüstite Primary wüstite or magnetite yellow blobs with white pure iron prill in a slag, 7th century BC Carthage Secondary wüstite in butterfly like formations, Carthage 800-600 BC Primary (blob) and secondary (dendritic) wüstite and fayalite laths, Carthage 800-600 BC Secondary wüstite in glassy matrix, Carthage ~600 BC Primary and secondary wüstite in fayalitic and glassy matrix, Carthage 800-600 BC Spinels of magnetite in geometric forms connected to delafossite
CuFeO2plant-like laths in a bronze recycling slag, Carthage Iron hammerscales collected with a magnet during excavations Hammerscales and flux, 800-600 BC Carthage
Iron hammerscales in calcium rich flux matrix Hammerscales and flux, 750-600 BC Carthage
Shell (calcium rich) likely as flux trapped in furnace detritus Crystalline fayalite in iron oxide poor slag, ~675 BC Carthage Fuel pseudomorphs in slag, iron rich phases that have taken the shape of heat- deformed wood anatomy Bloomery slag microstructure is comprised of two eutectics in the FeO/SiO2 system with adjacent secondary wüstite and fayalite phases wüstite-rich slag inclusion in ferrite matrix with lamellar pearlite and carbides, Crusader nail 13th century AD References Bachmann, H. G. 1982. The Identification of Slags from Archaeological Sites, Occasional Publication No. 6. London: Institute of Archaeology. Blakelock, Eleanor, Marcos Martinón-Torres, Harald A. Veldhuijzen, and Tim Young. 2009. Slag Inclusions in Iron Objects and the Quest for Provenance: An Experiment and a Case Study. Journal of Archaeological Science 36:1745-1757. Buchwald, Vagn Fabritius, and Helle Wivel. 1998. Slag Analysis as a Method for the Characterization and Provenancing of Ancient Iron Objects. Materials Characterization 40:73-96. Charlton, Michael F., Peter Crew, Thilo Rehren, and Stephen J. Shennan. 2010. Explaining the evolution of ironmaking recipes - an example from northwest Wales. Journal of Anthropological Archaeology 29:352-367. Craddock, P. T. 1995. Early Metal Mining and Production. Washington, D.C.: Smithsonian Institution Press. Eliyahu-Behar, A., S. Shilstein, N. Raban-Gerstel, Y. Goren, A. Gilboa, I. Sharon, and S. Weiner. 2008. An Integrated Approach to Reconstructing Primary Activities from Pit Deposits: Iron Smithing and Other Activities at Tel Dor under Neo-Assyrian Domination. Journal of Archaeological Science 35 (11):2895-2908. Eliyahu-Behar, Adi, Naama Yahalom-Mack, Sana Shilstein, Alexander Zukerman, Cynthia Shafer-Elliott, Aren M. Maeir, Elisabetta Boaretto, Israel Finkelstein, and Steve Weiner. 2012. Iron and Bronze Production in Iron Age IIA Philistia: New Evidence from Tell es- Safi/Gath, Israel. Journal of Archaeological Science 39:255-267. Fouzai, Boutheina, Lluís Casas, Néjia Laridhi Ouazaa, and Aureli Álvarez. 2012. Archaeomagnetic Data from Four Roman Sites in Tunisia. Journal of Archaeological Science 39:1871-1882. Gordon, Robert B., and David J. Killick. 1993. Adaptation of Technology to Culture and Environment: Bloomery Iron Smelting in America and Africa. Technology and Culture 34 (2):243-270. Hedges, R.E.M., and C.J. Salter. 1979. Source Determination of Iron Currency Bars through Analysis of the Slag Inclusions. Archaeometry 21 (2):161-175. Humphris, Jane, Marcos Martinón-Torres, Thilo Rehren, and Andrew Reid. 2009. Variability in Single Smelting Episodes - A Pilot Study Using Iron Slag from Uganda. Journal of Archaeological Science 36:359-369. Iles, Louise. 2009. Impressions of Banana Pseudostem in Iron Slag from Eastern Africa. Ethnobotany Research & Applications 7:283-291. Ingo, G.M., S. Mazzoni, G. Bultrini, S. Fontana, G. Padeletti, G. Chiozzini, and L. Scoppio. 1994. Small-area XPS and XAES Study of the Iron Ore Smelting Process. Surface and Interface Analysis 22:614-619. Killick, David, Nikolaas J. van der Merwe, Robert B. Gordon, and Danilo Grébénart. 1988. Reassessment of the Evidence for Early Metallurgy in Niger, West Africa. Journal of Archaeological Science 15:367-394. Paynter, S. 2006. Regional Variations in Bloomery Smelting Slag of the Iron Age and Romano-British periods. Archaeometry 48 (2):271-292. Radivojević, Miljana, Thilo Rehren, Ernst Pernicka, Dušan Šljivar, Michael Brauns, and Dušan Borić. 2010. On the Origins of Extractive Metallurgy: New Evidence from Europe. Journal of Archaeological Science 37:2775-2787. Shalev, S., S.Sh. Shilstein, and Yu. Yekutieli. 2006. XRF Study of Archaeological and Metallurgical Material from an Ancient Copper-Smelting Site near Ein-Yahav, Israel. Talanta 70:909-913. Tylecote, R. F., H.A. Ghaznavi, and P.J. Boydell. 1977. Partitioning of Trace Elements between the Ores, Fluxes, Slags and Metal during the Smelting of Copper. Journal of Archaeological Science 4:305-333. Veldhuijzen, H.A. 2003. 'Slag_Fun' - A New Tool for Archaeometallurgy: Development of an Analytical (P)ED-XRF Method for Iron-Rich Materials. Papers from the Institute of Archaeology 14:102-118.