Manufacturing C

Journal of Radioanalytical and Nuclear Chemistry, Vol. 255, No. 2 (2003) 295 298

The clay wall of an ancient iron smelting furnace studied

by M ssbauer spectroscopy

A. Nakanishi,1* T. Kobayashi,1 N. Hagihara2

1

Department of Physics, Shiga University of Medical Science, Shiga 520-2192, Japan

2

Department of Physics, Osaka City University, Osaka 558-8585, Japan

(Received April 18, 2002)

For an investigation of the ancient iron manufacturing technique, a modern simulation experiment was carried out. The smelting furnaces were

built with clay. Charcoal and raw materials were installed from the top of the furnace. Magnetite was used as the raw material. In the furnace, iron

oxide was reduced to metallic iron. The reduction reaction was mainly controlled by temperature and oxygen fugacity in the furnace. In order to

investigate the possibility for the estimation of these parameters, 57Fe M ssbauer spectra were recorded of the furnace wall at room temperature.

Introduction reactions between (1) magnetite and haematite, (2)

w stite and magnetite, (3) metallic iron and w stite and

In ancient China, iron manufacturing has been (4) metallic iron, ilmenite and ulv spinel. Furthermore,

developed widely, where iron ore was used as a raw the quartz in the clay of the furnace wall also reacts with

material. This technique was introduced into Japan in the iron oxides and metallic iron:

the 4-5th century AD. Iron manufacturing was made

o 2Fe 3 O 4 3SiO 2

3Fe 2 SiO 4 O 2 m

suitable for Japan since the production of iron ore was (5)

very small and a large amount of iron sand was easy to

get. There are, however, many problems concerning the o Fe 2 SiO 4

2Fe SiO 2 O 2 m (6)

iron manufacturing in ancient Japan, which

archaeologists cannot answer well. For an investigation

The equations show that fayalite is produced from

of the ancient iron manufacturing, the Committee of

the reaction between magnetite, metallic iron and quartz.

Education in Katano City, Osaka Prefecture, carried out

The direction of these six chemical reactions depends on

a modern simulation experiment in 1997. In this

the conditions in the furnace, especially temperature and

experiment iron ore or iron sand was used as the raw

oxygen fugacity. In order to investigate the possibility

material. Since Japanese iron sand consists of a

for the estimation of these parameters, M ssbauer

magnetite-ulv spinel solid solution (titanomagnetite), it

spectra of the furnace wall were recorded at room

contains a large amount of titanium. On the contrary,

temperature.

iron ore used in this experiment consists of magnetite

The Committee of Education in Katano City built an

and does not contain titanium. When iron sand is used as

ancient type of iron smelting furnace with clay. Two

raw material, it is necessary to remove titanium during

smelting furnaces were constructed; iron sand was used

the smelting process.

as the raw material for one furnace, and iron ore was

In order to get the metallic iron from iron oxides, the

used for the other one. The top of the furnace was open

chemical reactions in the smelting furnace are described

to air. Charcoal and the raw material were fed from the

as:

top. After the charcoal was fired, air was blown into the

1 o 3Fe 2 O 3

2Fe 3 O 4 furnace from its lower part. The oxygen in air reacts

m (1)

O2

2 with the charcoal to form carbon monoxide which

reduces the iron oxides to metallic iron. The furnace was

1.5

x

O 2 o Fe 3 O 4

Fe1- x O + 2 m (2) operated for 10 hours. Throughout the operation, raw

1 x 1- x

1 - x Fe 1 O 2

material and charcoal were added intermittently.

o Fe1- x O Thermocouples were buried in the clay wall of the

m (3)

furnace where the iron ore was used, in order to measure

2

the temperature of the wall during the operation of the

1 o Fe 2 TiO 4

Fe FeTiO 3 m

O2 (4) furnace. Samples were taken from the clay wall of the

2

furnace where iron ore was used as raw material and

analyzed by 57Fe M ssbauer spectroscopy.

where x

* E-mail: ********@*****.*****-***.**.**

0236 5731/2003/USD 20.00 Akad miai Kiad, Budapest

2003 Akad miai Kiad, Budapest Kluwer Academic Publishers, Dordrecht

A. NAKANISHI et al.: THE CLAY WALL OF AN ANCIENT IRON SMELTING FURNACE

Experimental of the ferrous iron is observed. Furthermore one doublet

with broad line is noticed. From its isomer shift it is due

The furnace was about 120 cm in height and 60 cm to the ferric iron.

in width. Samples were taken at the lower, middle and Spectra of the clay samples are shown in Fig. 2. In

upper part of the clay wall corresponding to 23, 48 and all spectra, a ferric doublet is observed, but the

73 cm above the ground level, where the thermocouples M ssbauer parameters are slightly changed with

were buried. The section of the wall can be divided into samples when this doublet is fitted to a single doublet. In

several layers.1 The innermost layer of the wall looks as the spectra of clay layers AA and A, a weak sextet is

black glass, which indicates that almost all mineral in noticed. From the hyperfine field and the isomer shift,

clay has melted. The outer part of the wall can be this sextet is assigned to haematite.

divided into five layers by their color; dark brown layer

Discussion

(AA), reddish brown layer (A), brown layer (B), whitish

brown layer (C) and whitish red layer (D). The color of

the clay reflects the difference of the temperature of the Magnetite has an inverse spinel structure. Iron atoms

clay. The temperatures of these layers measured by the occupy both tetrahedral and octahedral, so-called A and

thermocouples are 1200-1350 C (AA), 1050-1150 C B sites. The A sites are occupied by ferric irons and the

(A), 900-1050 C (B), 630-900 C (C) and under 630 C B ones by both ferric and ferrous irons. In a spectrum of

(D). The black glass was taken at the lower, middle and stoichiometric magnetite, the area of the B site sextet is

two times larger than that of the A site one.4 The area

upper part, and five clay layers were taken at the lower

part of the wall and measured. The sample was crushed ratio A to B site sextets in a spectrum of magnetite used

carefully and the powder, passed through a 100-mesh as raw material is similar to that of stoichiometric

sieve, was used for the M ssbauer measurements. magnetite. As shown in Fig. 1b, the intensity of the B

M ssbauer spectra were recorded at room temperature in site sextet decreases as compared to the intensity of the

a transmission geometry. The velocity calibration was A site one in the spectrum of sample M. Furthermore, in

carried out with a natural iron foil. the spectrum of sample U, the intensity of the A site

sextet is larger than that of the B site sextet. These

results indicate that the magnetite in samples M and U is

Results partially oxidized and the oxidation degree of magnetite

in sample U is larger than that in sample M. Therefore,

The black glass layer was produced by the reaction in the middle and upper parts of the furnace the

with melted clay and magnetite. M ssbauer spectra of atmosphere was oxidative, and the environment of the

these glasses taken at the lower (sample L), middle upper part of the furnace was more oxidative than that of

(sample M) and upper (sample U) parts of the wall are the middle part. Haematite is observed in the spectra of

shown in Fig. 1. A large asymmetrical doublet is samples M and U. Since, there was no haematite in the

observed as shown in Fig. 1a. This doublet can be due to raw material, this haematite was produced by the

the ferrous iron from an isomer shift fitted to a single oxidation of magnetite. The intensity of haematite in the

doublet. It is also well known that a doublet of ferrous spectrum of sample U is larger than that in the spectrum

iron in the M ssbauer spectrum of silicate glass shows of sample M. This result is consistent with the results

asymmetry, with the low-velocity peak more intense and from magnetite. In the spectrum of sample L, a ferrous

narrower than the high-velocity component.2,3 doublet is observed and haematite is not noticed. The

This asymmetry of the ferrous doublet is described by reduction reaction, occurred therefore, at the lower part

the distribution of the quadrupole splitting and the of the furnace.

correlation between the isomer shift and the quadrupole In spectra of samples M and U, a ferric doublet is

splitting. The observed doublet is, therefore, assigned to observed. Since the ferric doublet in silicate glass does

not show asymmetry,2,3 this doublet can be assigned to

the ferrous iron in the silicate glass. In this spectrum,

weak sextets with broad line are noticed. Hyperfine the ferric iron in the silicate glass because in the middle

fields and isomer shifts suggest that they are due to and upper part of the furnace the atmosphere was

oxidative. HELGASON et al.5 showed that a ferrous/ferric

magnetite. As shown in Fig. 1b and c three sextets are

observed in the spectra of samples M and U. From the ratio of iron atoms in silicate glass correlates with the

hyperfine fields and the isomer shifts one sextet can be oxygen fugacity of the environment where the silicate

due to haematite (sextet A) and two sextets to magnetite glass was produced. According to their results,

the logarithm of the Fe2+/Fe3+ ratio correlates

(sextets B, C). In both spectra, an asymmetrical doublet

linearly with the logarithm of the oxygen fugacity.

296

A. NAKANISHI et al.: THE CLAY WALL OF AN ANCIENT IRON SMELTING FURNACE

Fig. 1. M ssbauer spectra of black glasses taken at the lower (a), middle (b) and upper (c) part of the furnace wall.

The sextets A-C are explained in the text

But this relationship depends on the chemical fired under an oxidizing atmosphere, haematite is

composition of the silicate glass. Thus, comparing with observed. Since haematite is observed in the spectra of

the results of the laboratory experiments where clay layers AA and A as shown in Fig. 2, both samples

M ssbauer spectra of silicate glasses produced under were fired under an oxidizing atmosphere. Though clay

different oxygen fugacities were measured, the oxygen samples were taken from the lower part of the furnace

fugacity in the furnace can be estimated from the wall, a reducing atmosphere in the furnace did not affect

Fe2+/Fe3+ ratio in the black glass at the innermost layer these layers. In the spectra of the clay samples,

of the furnace wall. M ssbauer parameters of the doubles slightly change in

Generally, clays contain a small amount of iron samples for which the doublet is fitted to a single

oxides and hydroxides. It is well known that the oxides, doublet, and that reflects the difference in the

temperature of the samples.6 The changes in M ssbauer

hydroxides and clay minerals undergo chemical

transformation by heating.6 When the clay is fired under parameters are shown in Fig. 3. The temperatures of the

a reducing atmosphere, magnetite is observed in its clay layers AA-D can be estimated from the changes of

M ssbauer spectrum.7 On the contrary, when the clay is the isomer shift and the quadrupole splitting when

297

A. NAKANISHI et al.: THE CLAY WALL OF AN ANCIENT IRON SMELTING FURNACE

compared with results of the laboratory experiments

where M ssbauer spectra were measured for the clay

fired at different temperatures. The temperature of the

innermost layer can be also estimated from the

temperature gradient of the furnace wall. Consequently,

it is possible to estimate the temperature and the oxygen

fugacity in the furnace from the M ssbauer spectra of

the furnace wall.

Fig. 3. Changes in M ssbauer parameters of the doublet

*

The authors are indebted to Mr. S. MANABE, from the Committee

of Education in Katano City, for offering the samples.

References

1. N. HAGIHARA, S. MIONO, S. MANABE, A. NAKANISHI, Quat. Sci.

Rev., 20 (2001) 987.

2. D. VIRGO, B. O. MYSEN, Phys. Chem. Mineral., 12 (1985) 65.

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N. AYRES DE CAMPOS, J. Non-Crystal. Solid., 194 (1996) 48.

4. E. MURAD, J. H. JOHNSTON, in: M ssbauer Spectroscopy Applied

Fig. 2. M ssbauer spectra of the clay layers AA-D to Inorganic Chemistry, Vol. 2, G. J. LONG (Ed.), Plenum Press,

New York, 1987, p. 507.

5. . HELGASON, S. STEINTHORSSON, S. M RUP, Hyperfine

Interactions, 45 (1989) 287.

6. Ch. JANOT, P. DELCROIX, J. Phys. (Paris), 35 (1974) C6-557.

7. R. CHEVALIER, J. M. D. COEY, R. BOUCHEZ, J. Phys. (Paris),

37 (1976) C6-861.

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