128 MATERIAL ENGINEERING, STRUCTURAL STUDIES, DIAGNOSTICS

MATERIAL ENGINEERING, STRUCTURAL STUDIES, DIAGNOSTICS

APPLICATION OF BULK ANALYTICAL TECHNIQUE – PGAA FOR STUDYING IRON METALLURGY SLAGS, ORE AND ARTEFACTS Zsolt Kasztovszky1/, Ewa Pańczyk, Władysława Weker2/ 1/ Institute of Isotope and Surface Chemistry, Chemical Research Centre, Budapest, Hungary 2/ National Archeological Museum, Warszawa, Poland

In the course of the archaeological research (exca- important for establishing the context and scale of vations) in Mazovia, to the west of Warsaw, a vast production of iron artefacts in ancient Poland [1]. ironmaking region was discovered in 1967. It is The art and technique of ancient iron smelting estimated that the total number of furnaces in the in slag-pit furnaces, man’s original method for win- region (area of 300 km2 – Brwinów, Pruszków, Pę- ning metallic iron from its ore, has been largely cice) probably numbered 100 000 – 150 000. Maxi- lost in recent centuries. Many reconstructions of this mum production was achieved in the Roman-Bar- technique have been attempted by archaeologists barian Period (1st to 2nd centuries AD). The slag-pit in the last 50 years [2]. These experimental smelts furnaces were fed with local bog ores. have tended to be rather disappointing in terms of The smelting of ores is almost invariably related the production of usable iron; nonetheless, many to the formation of slags, because slags act as col- conclusions have been drawn from this work. Table 1. Chemical composition of bog iron in Poland – analytical method PGAA.

lectors for impurities introduced into the smelting Our primary goal was to smelt iron of sufficient process. Slag analysis thus has the potential for re- quantity and quality, and to explore the process for vealing important information about the metallur- a deeper understanding of iron production and dis- gical technology. This technological information is tribution in antiquity. NUCLEAR TECHNOLOGIES AND METHODS 129 Table 2. Chemical composition of bog iron ore after sieving. 130 MATERIAL ENGINEERING, STRUCTURAL STUDIES, DIAGNOSTICS The evidence from the mines suggests that all There are good technical reasons for such a small available bog iron ore was taken and used. First, it size of the individual furnaces. Air supply was one would be beneficiated (crushed an concentrated) by of the major constraints; if the furnace volume was removing as much as possible of the gangue (waste larger then it was impossible to supply manually rock). This could be done either by washing swirl- enough air to maintain the necessary temperatures. ing the crushed material in water and letting the Thus the early historical production process dif- denser ore separate out or by simply picking out the fered from the blast-furnace process in use nowa- richest mineral manually. To smelt the metal, the days, as iron was produced in direct process in the ore would be first have been roasted within the tem- solid state and the slag liquified. perature range of 500-800oC to make it more friable Slag fulfills two physical functions in a furnace: and to convert any minerals (carbonates, sulphides protection and transportation. Molten slag coats or chlorides) to oxides. The enriched ore would then and protects reduced iron particles from reoxida- have been smelted in a bloomery furnace. tion and carbonisation. Both protection and trans- Iron was obtained directly from its ore within a portation require a liquid, free-running slag. The single metallurgical process in a heart by reduc- fluidity of the slag is a function both of its chem- tion of the ore with charcoal which simultaneously istry and temperature. Although the slags appear served as a fuel. amorphous and uninformative, they are in fact a The melting point of pure iron is 1540oC. Even complex interacting systems of various crystalline by Roman times bloomery furnaces were not pro- minerals and glassy phases. Many of the minerals ducing heat much over 1200oC. Bloomery iron did only form under quite specific conditions, and their not involve the iron turning to the liquid state. In- identification and analysis, principally by scanning stead, it was a solid state conversion requiring electron microscopy (SEM) and X-ray diffraction chemical reduction of the ore. Ore was placed in a (XRD), can reveal much of the temperature and pit and mixed in a hot charcoal fire. Air was forced reducing conditions within the furnace. The bulk into the dome covered structure via bellows through analysis of the slags, together with the identifica- a fireproof clay nozzle called a tuyere. After a sus- tion of the minerals present, enable the chemistry, tained temperature of 1100-1200oC, liquid slag (oxi- thermodynamics and efficiency of the process to dised non-metallics) penetrated the pores down and be reconstructed. fell to the bottom leaving the spongy mass contain- Our first trials provided us with a valuable ex- ing the iron. Holes forming the sponge texture were perience, but produced only the most pitiable ex- a result of the removal of the non-metallics impu- amples of iron lumps. We attempted to deal with rities when the slag melted out. these problems by reducing both the fuel:ore ra- The bloomery furnaces were always necessar- tio, and lowering the airflow and temperature, with ily quite small: typical dimensions would be about disappointing results. The ore in this trial was our 1.5 m tall with an internal diameter of about 50 cm. local bog ore with different iron contents from bog Table 3. Chemical composition of bog iron ore after washing and sieving. NUCLEAR TECHNOLOGIES AND METHODS 131

Table 4. Composition of experimental slags – method PGAA.

ore: Brwinów (28.6% Fe), Chorzele (43.7% Fe) and PGAA is based on the detection of gamma-ray Rakszawa (about 38% Fe). photons, which are emitted after the capture of ther- The ore must be dressed carefully by hand-pick- mal or subthermal neutrons into the atomic nuclei, ing and washing, leaving less iron – rich pieces Table 5. Composition of ancient slags – method PGAA aside. It was roasted in a fire, and then broken up (Brwinów). until the pieces ranged from 1-2 cm to fines. The next steps of dressing ore were sieving and flota- tion. After all these operations the results of smelt- ing process were still disappointing. The question is about ancient methods of enriched bog iron ore. The relationship between the chemical compo- sition (especially at trace levels) of elements present in metal finding and the period and the ore where these findings belong, would enable us to work out chronological groupings. The site provided enough material for an exten- sive analysis such as bog iron ore, slag, slagblocks and fragments of furnace. We carried out elemen- tal analysis by means of a PGAA (prompt gamma activation analysis) analytical method. PGAA is a multicomponent analytical method, i.e. all the chemical elements can be detected with different sensitivities. In principle, it is possible to determine both the major and the trace elements simultaneous- ly, though the detection limits are matrix-depen- dent. The measurements do not require sample preparation; they give prompt results. It allows for determining such elements as: H, B, N, Si, Ca, Cd, Gd, Pb and Bi, the analysis of which with the in- strumental neutron activation analysis (INAA) method is difficult or almost impossible. On the other hand, the sensitivity of the PGAA method is lower than the INAA method by a few orders of magnitude. Moreover, usually after some days of i.e. the (n,γ) reaction. The photons energies range cooling (i.e. decay of radioactive products) the same between 50 keV and 11 MeV and are characteris- identical sample can be returned to the user. tic of a given element. The element identification 132 MATERIAL ENGINEERING, STRUCTURAL STUDIES, DIAGNOSTICS is based on the precise determination of gamma presented in Tables 2 and 3. Composition of the photon energies and intensities. ancient slags and from our experiments is shown The PGAA measurements were performed at in Tables 4 and 5. the Institute of Isotope and Surface Chemistry, The Mn content of Chorzele and Rakszawa ores Chemical Research Center (Budapest, Hungary). varies from 0.37 to 14.2%, respectively. For PGAA analysis purposes, a guided cold neu- The Ca content is mainly below 10%. Si and Al tron beam, obtained from the 10 MW Budapest are comparable in the ores and the slags and range Research Reactor, was used [3]. The thermal neu- from 40 to 8.7% and 2.5 to 0.6%, respectively. The trons, which exit the reactor core, are cooled by a slags contain up to 80% Fe and up to 2% Mn. The liquid hydrogen cell down to 16 K. Consequently, percentage of Fe present in the slags is still quite the achieved thermal equivalent neutron flux was high, as could be expected from the mineralogical 5·107 cm–2s–1. The size of the neutron beam was re- composition of the main component. The Fe con- stricted to 1×1 cm2 area. The investigated samples tent of the ore found in the settlement is, how- ore, slags and iron artefacts were packed in thin ever, lower than of the slags (Tables 2-5). Because teflon (FEP) films, and were placed in a well-de- of the low Fe content in the ore, the analysed pieces fined position of the sample holder chamber. The cannot be characteristic of the ore used for the an- mass of the investigated samples varied between cient production. The main problem connected with 0.12-12 g. methods of enriching ores in ancient times still is The emitted gamma photons were detected with unresolved. The main focus of our work is to con- a complex HPGe-BGO detector system in Comp- tinue to obtain iron as thoroughly as possible. We ton-suppression mode; the signals were processed also hope to achieve more specific experiments in with a multichannel analyser. The spectra were enriched ore and to apply our experience to other evaluated with Hypermet-PC software; the element types of ore, including goethite and hematite. identification was performed on the basis of our prompt-gamma element library [4]. References The peaks of interest were fitted by Hyper- [1]. Weker W.: Proces dymarski – teoria i praktyka. Hutnic- met-PC and mass ratios were calculated. The com- two Świętokrzyskie oraz inne centra i ośrodki metalurgii bined standard uncertainties of the mass ratios de- żelaza na ziemiach polskich. Kielce 2002, pp.199-202, pend on the uncertainty of the counting statistics, in Polish. the uncertainty of efficiency function and the un- [2]. Tylecote R.F., Adams R.: Experiments on iron smelting. In: Archeologie Experimental T1 – Le Feu. Actes du certainty of k0 factors. The most dominating of them is the uncertainty of counting statistics. The mea- Colloque International “Experimentation en archeo- surement time for one individual coin varied be- logie: Bilan et perspectives”, Archeodrome de Beaune, France, 6-9 April 1988. Paris 1991, pp.123-128. tween 460 s-24 h. [3]. Révay Zs., Molnár G.L.: Radiochim. Acta, 91, 361-369 Chemical composition of bog iron ore, ancient (2003). iron products, and slags from Chorzele and Raksza- [4]. Révay Zs., Belgya T., Kasztovszky Zs., Weil J.L., Mol- wa are listed in Table 1. The results of the chemi- nár G.L.: Nucl. Instrum. Meth. Phys. Res. B, 213, 385 cal analysis of the ore after sieving and washing are (2004).

TITANIUM DIOXIDE AND OTHER MATERIALS COATED WITH SILICA-QUATERNARY ALKYLAMMONIUM COMPOUNDS FOR USING IN BUILDING INDUSTRY AND ENVIRONMENT PROTECTION Andrzej Łukasiewicz, Dagmara K. Chmielewska, Lech Waliś

Silica biocides based on water glass and quaternary Unfortunately, SiO2-QAC biocides, with and N-alkylammonium salts (SiO2-QAC) were elabo- without a carrier show a weak ability to disperse in rated previously [1,2], by precipitation them with commercial resins. This distinctly limits their prac-

H2SO4 from water glass (WG) and QAC. These tical use. water-insoluble biocides show fungicidal, bacteri- We elaborated, therefore, a modified technol- cidal and algae destroying activity when added to ogy for obtaining SiO2-QAC biocides, especially con- water, or mixed with paints or building mortars. Bio- taining TiO2 and other materials with good ability cides can contain structurally bonded carriers such to disperse in resins and building mortars. The tech- as, e.g. TiO2 or dolomite. Titanium dioxide is of spe- nology is based on the observed ability of WG-QAC cial interest because of its properties useful for the salts to coate under suitable conditions TiO2, dolo- building industry and environmental protection. mite and other materials. The salt is formed by ex- + + Its ability to kill bacteria by absorbed UV light is change of Na cation in Si(ONa)n salt by QAC cat- known. ion: – → We have found that SiO2-QAC materials ab- Si(ONa)n + QAC+Cl Si(ONa)n-1QAC sorb UV light similarly to TiO2. Combined with (+NaCl) TiO2 they can show a synergism of UV effects. Coated material is stabilised by adding H2SO4.