VISCOUS FLOW SINTERING OF LARGE CERAMIC SLABS
| Reference | Presenter | Authors (Institution) | Abstract |
|---|---|---|---|
| 16-007 | Michele Dondi | Dondi, M.(CNR-ISTEC); Zanelli, C.(CNR-ISTEC); Conte, S.(CNR-ISTEC); Soldati, R.(CNR-ISTEC); Cruciani, G.(University of Ferrara); Ardit, M.(University of Ferrara); | The production of porcelain
stoneware tiles is moving towards ever-larger size, from 320x160 to 480x180
cm (from 5.1 to 8.6 m2) and thickness from 3 to 20 mm (up to 400 kg each slab). The driving force of this product-process innovation is
twice: gain in efficiency and productivity from highly standardized
manufacturing plants as well as commercial
return from value added, versatility and new application fields (e.g. façades, furniture, alternative
to ornamental stones and wood slabs). Nevertheless, this technological advancement
is stressing the requirements of uniform densification and minimal deformations
during firing. It is a hard task, since porcelain stoneware is sintered by partial
vitrification, through viscous flow of an abundant liquid phase formed at high
temperature. Such a process must be kept under strict control to achieve the
desired properties of final products and prevent defects induced by
pyroplasticity. The present contribution will overview the evolution of
microstructure and phase composition of porcelain stoneware with temperature
and soaking time. Industrial firing schedules let feldspars to melt quickly
(K-feldspar>plagioclase) while quartz is only partially dissolved at the
highest temperature. Once formed, mullite is gradually dissolved, though by a
decreasing rate, making the melt increasingly peraluminous. The melt viscosity
lowers rapidly up to 1200°C, but tends to increase slowly during soaking. These
physical and mineralogical features affect both sintering kinetics and
pyroplasticity, which depends on both the melt viscosity and the amount of
crystals suspended in the liquid phase. In fact, firing deformation could scale
with crystals shape and size distribution, which in turn reflect in a complex
way the dissolution rate of mullite and quartz into the melt (buffered by
silica oversaturation and strong peraluminous character).<!--[if gte mso 9]> |