Advances in Ceramic Science and Engineering Vol. 1 Iss. 1, November 2012 11 Use of Factorial Design in the Study of the Influence of Firing Cycle Parameters on the Technological Properties of a Brazilian Kaolinitic Material Gisele T. Saleiro, André Z. Destefani, José N.F. Holanda Group of Ceramic Materials, Laboratory of Advanced Materials, Northern Fluminense State University, Av. Alberto Lamego 2000, 28013-602 Campos dos Goytacazes-RJ, Brazil jose.holanda@pesquisador.cnpq.br Abstract The firing cycle is an important variable in the production of red ceramics, which contributes to high energy demand. In this work the simultaneous effects of the firing cycle parameters (firing temperature and heating rate) on the technological properties of a kaolinitic material were evaluated by using the factorial design. The specimens were prepared by extrusion and fired at temperatures ranging from 700 to 1100 ºC using different heating rates (1 ºC/min, 10 ºC/min, and 20 ºC/min). The following technological properties were determined: linear shrinkage, apparent density, water absorption, and flexural strength. By using 3 2 factorial designs, it was found that the firing temperature is the main controlling factor of the technological properties of the kaolinitic material. The results obtained by factorial design also indicated that the kaolinitic material could support the use of rapid heating rate (up to 20 ºC/min) in the production of red ceramics. Keywords Kaolinitic Material; Firing Cycle; Factorial Design Introduction The term red ceramic is used to designate the clay- based products with reddish colour [1]. The red ceramic industry is focused on the manufacturing of building materials such as bricks, ceramic blocks, roofing tiles, and tubes. In general, the common clays are the most widely used raw materials for red ceramics. Common clays are present in every country in the world. The mineral composition of these clays is quite variable, but usually illite, chorite and kaolinite are the most common clay minerals present. The technological properties of red ceramics are influenced by several factors such as: i) chemical, mineralogical and physical characteristics; and ii) processing operations such as shaping, drying, and firing [2]. In particular, the firing cycle parameters (temperature, time, and heating rate) have a marked influence on the technological properties [3]. Conventionally, red ceramics require a slow-firing cycle that can reach up to 60 h (cold to cold). As a result, the firing process of red ceramics requires high demand of energy. This situation is not desirable because of the serious economic and environmental constraints. The fast-firing process has been successfully used in the production of several ceramic materials [3-13]. The main advantages of this process are: i) increased energy efficiency; ii) higher productivity (less time to firing); and lower environmental impact. Despite its importance, few studies have been conducted on the fast-firing process in the field of the red ceramic. In particular, there is need for most studies on the fast- firing cycles applied in different common clays used in the red ceramic industry worldwide. The purpose of this study was to investigate the effects of firing cycle parameters (firing temperature and heating rate) on the technological properties of a Brazilian kaolinitic material used in red ceramics using factorial design. The factorial design approach has been used successfully in several fields [14-16], and is extremamely useful for measuring the effects (or influence) one or more variables on the response of a process. It allows a combination of all variables at all levels, thus obtaining an analysis of a variable, subject to all the other combinations.