Preservice Elementary Teachers' Ideas about Clays

Article excerpt

ABSTRACT

Clays are important industrial materials used for many purposes because of their plasticity and other unique properties. Clay science concepts can be used to effectively support learning of foundational science principles in elementary grades. Because preparation to teach science affects the quality of a teacher's instruction, this study examined preservice elementary teachers' ideas about clays before and after lessons on clay science that incorporated instructional approaches supported by the literature. These teaching methods included viewing a slide show of clay mineral structures and scanning electron photographs of clay minerals, along with explanations of the origin of clay minerals and their properties; matching clay products to cards that described the properties of clays employed by the products; and playing a game in which participants identified clay products in different rooms or a house. Before instruction, most participants were familiar only with ceramics as clay products, with less than half aware that clays were naturally occurring materials. Pre-instructional concepts of the geologic origin of clay were similar for preservice teachers who "guessed" or "reasoned" answers compared to those who said they had learned the information previously. Participants exhibited significant gains in knowledge of clay properties for use in various products from pretest to posttest.

INTRODUCTION

Economic Importance of Clay - From prehistoric times, people have used clays for agriculture, pottery, and building. Clay is an important component or soils, binding together other particles, retaining water and facilitating chemical reactions important to plant growth.

The largest industrial use of Kaolin clay is the paper industry. Pure white kaolin is used as filling and coating for almost all copy paper, books, magazines, and printed cardboard packaging because of its properties of opacity, brightness, gloss, smoothness, ink receptivity, manufacturing behavior, and relative low cost (Murray, 1997). Modern ceramics industries are also large users of kaolin, manufacturing brick, tile, pipe, and refractories; fine porcelain china, stoneware crockery, earthenware dishes, and terracotta flowerpots; and porcelain sanitaryware, such as sinks and toilets. Kaolin is also used as extender in paints, enamels, and inks, filler in rubber and plastics, and an important component of fiberglass, cement, plaster, roofing granules, linoleum, polishing compounds, desiccants, adhesives, sizing, textiles, fertilizers, cosmetics, pharmaceuticals, medicines, food additives, insecticide carriers, detergents, crayons, and pencil leads (Murray, 1997).

Smectite clays, because of high base exchange capacity, fine particle size, viscosity, and swelling ability, have many important industrial uses (Murray, 1997). Swelling clay from bentonite (rock formed from the weathering of volcanic ash) expands in volume more than ten times when mixed in water, producing a high viscosity, thixotropic fluid (liquid when agitated, gel when undisturbed) allowing its use as a well-drilling fluid. Another use is as a binder of quartz sand for foundry molds. Smectite clay is used in pelletizing iron ore powder and animal feeds for easier handling by machinery. Swelling clays are used in earthen dams, as pond liners, in basement foundations, and in landfills or toxic waste impoundments to impede water flow and to prevent toxic chemicals from traveling. Highly absorbent smectite clays are used in cat litter and cosmetics, for filtering petroleum, and for clarifying oils, water, and wine. The gel properties of smectites are exploited for producing thickeners for paints, liquid hand soaps, shampoos, and toothpaste.

Smectites may be used to produce two high-tech products: nanocomposites ana pillared clays. Some nanocomposites are strong heat-resistant plastics formed by delaminating sodium montmorillonite to produce thin, small particles that are treated with organic polymers and bound to plastic polymers. …