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Physio-Chemical Characterization of the brick clays of Njala in the southern province of Sierra leone
Authors: Mohamed Syed Fofanah
Number of views: 4
The traditional ceramic industry in Sierra Leone has been extremely slow in adopting the automation techniques developed in industrialized countries and did not make appreciable efforts in developing techniques of its own, mainly due to lack of research data and technological expertise. For the traditional ceramic industry to survive and to contribute positively to nation building, high quality and affordable products must be introduced into the market to compete with imported building materials. This work tried to redress the issue of unavailability of scientific data by extensively investigating the physical and chemical characteristics of the brick bodies produced from selected clays at Njala in the Southern Province of Sierra Leone. This is to justify their suitability for industrial application, especially in low cost building materials production and to develop data bank for further research. Clay samples were collected from four sites at Njala namely Makonda, Pelewahun and Bonganema inland valley swamps. The physical and chemical compositions of the brick bodies prepared from these clay samples were analyzed using standard laboratory procedures. The results obtained from both the physical and chemical properties analyzed are within the acceptable range to produce fired clay bricks. With the exception of Njala clay, which exhibits medium plasticity, the other three clay samples (Makonday, Pelewahun and bonganema have excellent plasticity that justifies their use in ceramic applications, especially in case of complex shape forming and as additives for non-plastic ceramic materials. Water absorption of these clays are comparatively high with low bulk densities at 10000C and permissible linear shrinkage and high crushing strength at firing temperatures above 10000 C. Typically, clay brick consists of silica (sand) – 50% to 60% by weight, alumina (clay) – 20% to 30% by weight, lime – 2 to 5% by weight and iron oxide – ≤ 7% by weight. The results of the chemical analysis of these clay samples fall within these ranges, hence suitable for fired bricks production. To produce high-quality porcelain, processing of these clays is required to improve on certain physical properties like porosity, density and eventually water absorption. This could be done by addition of one or more of the following materials such as limestone, feldspar, kaolin, sand, talc, wollastonite and pyrophyllite in the right proportion followed by efficient processing technique and optimization of the firing temperature.
Key Words: Ceramic industry, brick clays, fired clay bricks, firing temperature, bulk density, water absorption, shrinkage, crushing strength.