The firing temperature of a Persian-period kiln excavated at Tel Michal (Makmish), on the Mediterranean coast north of Tel
Aviv, Israel, is estimated from the composition of its pottery, using X-ray diffraction and IR spectroscopy methods. The kiln
was built with two chambers: an upper one where the vessels were fired and a lower one for the burning. Storage jars that
had been fired and remained inside the kiln are composed of lime tempers and quartz sand in a fired clay matrix that contains
amorphous material and the high-temperature Ca-silicates gehlenite and anorthite. The tempers are composed of re-formed calcite.
Thermal simulation indicates that the composition is compatible with a heating temperature of 800–900°C, which represents
the firing temperature in the upper chamber of the kiln.
The formation of carnallite type double salts by grinding mixtures of hydrated magnesium halide and alkali halides with the
same anions was investigated by X-ray diffraction, infrared spectroscopy and thermal analysis. Carnallite (KMgCl3·6H2O), cesium-carnallite (CsMgCl3·6H2O), bromo-carnallite (KMgBr3·6H2O) and cesium-bromo-carnallite (CsMgBr3·6H2O) were formed by grinding mixtures of MgCl2·6H2O with KCl or CsCl and MgBr2·6H2O with KBr or CsBr, respectively. Hydrated solid solutions of magnesium in potassium or cesium halides were obtained from
that portion of potassium and cesium halides which did not take part in the formation of the double salt.
The Iron Age ceramic technology used in the manufacturing of cooking pots was studied by thermo-FTIR spectroscopy analysis.
The pottery was excavated at Tel Hadar on the eastern shore of the Sea of Galilee. The results demonstrate that the cooking
pots were manufactured using noncalcareous or slightly calcareous raw material proceeds from soil. The firing was at about
750-850C and the cementation to ceramic was obtained by low temperature sintering of the clay. The use of soil raw material
composed of smectitic (montmorillonitic) clay enabled the low temperature sintering. The clay from soil is relatively poorly
crystallized and rich in natural iron oxide, both of which induce earlier sintering. Most of the cooking pots were tempered
with broken pieces of large calcite crystals that were added to the clayey raw material from an additional source. Alternative
tempering with limestone particles composed of polycrystalline calcite is inappropriate as it brings about earlier and intense
decarbonation during the firing, which causes defects in the pots.
Oil shale ashes from the PAMA demonstration power plant in the Negev region of Israel are produced by fluidized bed combustion
(700–850C) under short residence time. The FED is organic-rich calcareous raw material rich in carbonate rather than clays.
Thus it is important to ascertain whether the calcite in the ashes is original natural calcite from the raw material or the
product of recarbonation of lime. Three groups of ashes from the power plant, Ash Cooler (AC), Fly Ash (FAS) and Boiler Bank
(BB) were examined using XRD, FT-IR, SEM and isotope analysis methods. The recarbonated calcite is distinguished from the
natural original by smaller crystal size, lower degree of crystallinity and the presence of impurities. High negative δ13C values in oil shale ashes are explained by assuming recarbonation of lime with CO2 originating from the combustion of the organic matter of the raw oil shale. Fly Ash, FAS, and BB, produced from organically-rich
FED, contain more recarbonated calcite than bottom ash, AC. This observation can be explained by the larger grains of the
AC, which do not reach the highest temperature area, and thus most of the original calcite does not decompose.
The quartz-cristobalite transformation in heated natural chert (flint) rock composed of micro- and ŗypto-quartz was investigated
in the temperature interval of 1000–1300°C by micro-Raman spectroscopy, FT-IR spectroscopy, X-ray diffraction and Scanning
Electron Microscopy. A small amount of crystobalite was first observed in the chert after heating at 1000°C for 1 h and the
transformation was almost completed after heating at 1300°C for 24 h. On the other hand, cristobalite was not detected in
well-crystallized pure quartz after heating under the same conditions. The transformation occurs as a solid state nucleation
and crystal growth of cristobalite replacing quartz at high-temperatures. The chert rock is naturally rich in crystal defects
and boundaries which serve as nucleation sites and enable an earlier quartz-cristobalite transformation.
Limestone and monocrystalline calcite tempers (grains) are abundant in ancient pottery. In pottery from the Canaan area the
former is common in Iron Age storage and table-ware vessels and the latter is present in cooking pots. Limestone is much more
widespread than monocrystalline calcite and the potters used it often as tempers when manufacturing pottery vessels, but usually
not for cooking pots. While defects appear frequently around limestone tempers, they do not appear around monocrystalline
calcite ones. This study examines the reason for using the latter tempers rather than the former ones.
Raw materials of carbonate tempers in a clay matrix were fired and the decarbonation process was followed by quantitative
IR thermospectrometry. The results indicate that the monocrystalline calcite tempers prevent formation of defects in the cooking
pots during firing or during use. The reasons for this are higher thermostability at elevated temperatures, lower intensity
of decarbonation, and retention of grain shape, as compared to limestone tempers.
Authors:R. Knubovets, Y. Nathan, S. Shoval, and J. Rabinowitz
The thermal transformations in phosphorites during flash calcination were investigated by FT-IR spectroscopy, X-ray diffraction
and chemical analyses. During flash calcination changes occur, both in the composition of the phosphorite and in the crystallochemistry
of the fluor-carbonate-apatite (francolite). The former changes include: decomposition of a great part of the calcite in the
rock and oxidation of organic matter. The latter changes include: partial removal of the structural carbonate; partial relocation
of the remaining carbonate ions in the apatite structure; a new arrangement of hydroxyl groups and fluorine on the hexagonal
axis; partial condensation of the orthophosphate groups and increase of crystallite sizes. Isomorphous substitution of PO4−3 in apatite by SO4−2 and SiO4−4 may take place.
Authors:S. Shoval, K. Michaelian, M. Boudeulle, G. Panczer, I. Lapides, and S. Yariv
The products of dickite heated in air at 1000 to 1300°C were studied using curve-fitting of transmission and photoacoustic infrared and micro-Raman spectra. The spectra were compared with those of mullite, Al-spinel, corundum, cristobalite, amorphous silica and meta-dickite. Bands that characterize crystalline phases appeared at 1100°C and became stronger with increasing temperature. Mullite, Al-spinel, corundum and amorphous silica were identified by their characteristic bands. The characteristic IR bands of cristobalite overlap those of mullite and amorphous silica, and its presence was therefore established from intensity ratios of the appropriate bands. The research clearly demonstrated the advantage of using curve-fitting for the identification of high temperature phases in the study of the thermal treatment of kaolin-like minerals by infrared and Raman spectroscopy. This technique seems to be a useful method for materials analysis in the ceramic industry.