Skład mineralny a własności surowcowe pstrych iłów poznańskich

Ryszard Wyrwicki




The term variegated clay is used by the present author to denote multi-coloured clay sediments of the Poznań series that contain haematite. The clays predominate among the Pliocene sediments and occur in several depositional cycles. The individual cycles commence with sandy silts and terminate with fat clays, the thickness of one cycle being less than 1 to several metres.
Comprehensive studies were carried out on 13 samples that represent different parts of the depositional cycles and different parts of the depositional basin.
According to the present results the sediment is composed of clay minerals (3:1–85%), quartz and iron oxides (11–15%) chiefly haematite. Among the clay minerals beidellite always prevails, most often with exchangeable Ca2+ , Mg2+  and Fe3+ ions. It is accompanied by varying illite and kaolinite proportions and by the mixed-layered illite-beidellite phase. Muscovite and anatase occur in subordinate amounts. Locally epigenetic limy and gypsum concretions have been encountered in the, weathering zone.
The variegated clays of the Poznań series are low-melting, medium- to high plastic. They absorb considerable amounts of make up water (Tab. 2) and have a high shrinkage in drying dependent on the clay minerals content (Fig. lA).
The physical properties of the ceramic material and their dependence on firing temperature are presented in Figs. 2–6. The present studies indicate that, generally speaking, two phases can be distinguished in the course of changes of the physical properties; sintering and thermal swelling. During the first phase the absorption ability decreases with the increase of total shrinkage, compressive strength, and bulk density. This phase terminates with maximum sintering when the material attains its maximum bulk density and most often its maximum compressive strength and absorption ability. These properties are clearly controlled by the clay minerals and quartz sand content (Figs. 11–13).
In temperatures higher than the maximum sintering temperature the material swells and as a consequence the bulk density and strength drops, while the absorption ability increases
Two types of ceramic material are produced in the sintering phase: porous and sintered with the absorption ability 6 and 6–0% by weight respectively. The physical properties of the porous, sintered, and thermally swollen material are listed in Tabs. 8–6.


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