Mechanical Performance of Quartz‐tempered Ceramics: Part I, Strength and Toughness*

Abstract

The effect of quartz temper on the physical and mechanical properties of clay ceramics and the elucidation of the underlying mechanisms that are responsible for these efsects are presented here. Characteristics studied included bulk density, open and closed porosity, density of impervious portion and fracture morphology. Mechanical behaviour was studied by measuring energy dissipation during fracture, Young's modulus, initial fracture toughness and strength in flexure. The signifcant increase in toughness with quartz volume fraction is explained by the development of a model that accounts for the crack distribution around the grains. The archaeological implications of the work are discussed on the basis of all the parameters that might affect the potter's choices of raw materials.V. Kilikoglou, G. Vekinis, Y. Maniatis and P. M. Day workability, reduces shrinkage, assists in even drying and promotes some mechanical properties at the expense of some others (Rice 1986; Rye 1976). The most common rock tempering materials can be classified in two groups: calcite-based materials that chemically react with the clay minerals during firing and materials that are essentially inert at the usual firing temperatures (quartz, feldspar, etc.). The effects of temper on the performance, including mechanical performance, of ceramics was first studied and discussed in the pioneering work of Shepard (1965). Since then several studies have been reported in the literature. Much attention has been given to the explanation of the beneficial effects of certain tempering materials used in the prehistoric New World, with particular reference to crushed shell in comparison to sand. The main shell-tempered pottery characteristics studied have been thermal shock resistance (Steponaitis 1984;Bronitsky and Hamer 1986), strength (Bronitsky and Hamer 1986;Feathers 1989) and toughness (Feathers and Scott 1989). It has been demonstrated generally, through simulation tests, that shell can produce stronger and tougher ceramics than sand, which was replaced as a temper during the Late Woodland period in eastern North America. The same applies to limestone, although it was not used systematically, compared to grit or grog (Hoard et al. 1995). Besides enhanced mechanical properties, there are further benefits in the use of calcite-based tempers, summarized by Hoard et al. (1995): increase of workability, similar thermal expansivity to clay and a plate-like structure that aids crack propagation arrest, in a similar way to modem fibre-reinforced ceramics. However, calcite can be problematic at high firing temperatures (Maniatis and Tite 1981; Rice 1986) and, therefore, it can only be used as temper at low-firing temperatures, less than c. 700"C, where ceramic bodies remain essentially unvitrified and the maximum strength they develop is, thus, close only to their green strength.On the other hand, there have been many cases of high-fired and quartz-based-tempered pottery. A typical example is that of Punic amphorae transported as containers whose specifica...

Strength of kaolinite-based ceramics: Comparison between limestone- and quartz-tempered bodies

“…It is apparent then that temper affects drastically the performance characteristics of the fired ceramic bodies, something which attracted substantial attention in the last three decades. The studies have mainly reference to archaeological pottery, trying to explain changes of tempering traditions with time and use (Steponatis, 1984;Sabrah and Ebied, 1985;Bronitsky and Hamer, 1986;Okongwu, 1988;Hoard et al, 1995;Kilikoglou et al, 1995Kilikoglou et al, , 1998Hein et al, 2008;Garcia-Ten et al, 2010a,b;Hein et al, 2013;Allegretta et al, 2014).…”

“Losanga” decorated imitations of italic late republican black gloss tableware from South-Western Iberia: A multi-analytical/microchemical characterization

“…The low firing temperature in the kiln used to produce the "Losanga" pottery under investigation is further confirmed by the absence of bright reaction rims formed by Ca-rich silicate phases (such as diopside, gehlenite and anorthitic plagioclases) which typically form in Ca-rich ceramics when fired at higher temperatures [2]. In terms of microfabric porosity in the temper, fissures at quartz grain boundaries as a result of shrinkage of clay minerals during drying and expansion of quartz crystals from α to β phases during firing [10,34] are present, particularly in samples from Andalucia where secondary porosity typically with rounded pores can also be seen. Illitic laths while maintaining their sheet-like typical habit, show separation along basal cleavage planes (Fig.…”

Relationship between Young's modulus and temperature in porcelain tiles

“…According to a previous research [13] the hysteresis observed in porcelain materials is attributed to microcracking on cooling and healing of the microcracks during heating, in the region around the - quartz transition. Moreover, as set out elsewhere [17][18], porosity and metakaolinite transformation in the 429-740°C temperature range, in the early firing stage, negatively affect the Young's modulus behavior. On the other hand, as reported [4] cristobalite formation on cooling in the 225-250°C temperature range and residual mullite may act as a microstructural reinforcing and so improving the mechanical strength of quartz porcelains.…”