Ján Ondruška

Thermoanalytical investigation of ancient pottery

Ceramic potsherds excavated in Biskupice (Banovce County, Slovakia) dated to the Hallstatt culture (8th to 6th centuries BC) were investigated by TGA, thermodilatometry (TDA) and XRD analysis. It was found that the samples consisted of illite/muscovite, feldspar and quartz. Their thermal behavior was typical for ceramics buried in soil for a long time: the mass loss (∼3 mass%) due to escaping the physically bound water (from room temperature to 300 °C) was followed by a gradual mass loss from dehydroxylation (∼3 mass%) as a consequence of the former rehydroxylation. Above the temperature 800 °C a rapid shrinkage of samples was observed in TDA curves. As follows from these results, maximal firing temperatures did not exceed 800 °C.

Influence of milling on physical properties of illite

Raw illitic clay (80 % illite, 4 % montmorillonite, 4 % orthoclase, and 12 % quartz) was milled in a planetary ball mill for 0, 60, 120, and 180 min in air. From milled clay, samples for XRD, granulometry, thermogravimetry, DTA, and dilatometry measurements were prepared. It was found that 1) the phase composition is almost unchanged by milling; 2) the distribution of grain sizes shows two distinct maxima; the ratio of their areas depends on the milling time – longer milling leads to larger agglomerates; 3) the dehydroxylation of illite is a two-step process: the first step is shifted to lower temperatures with the milling time; the temperature of the second step decreases only slightly with the milling time; 4) the mass loss during both steps of the dehydroxylation slightly decreases with the milling time; 5) the onset temperature of sintering sharply decreases at the longest milling time.