Abstract
This study evaluated the potential of raw clays from the Mukondeni region for structural ceramics and pottery based on traditional firing techniques. Physical properties were identified by particle size distribution, consistency limits, and clay activity. Mineralogical and chemical properties were investigated by X-ray diffraction (XRD) and X-ray fluorescence (XRF). Extruded clay bodies were fired at 900 °C. Technological characteristics were measured by weight loss (WL), bulk density (BD), dry linear shrinkage (DLS), fired linear shrinkage (FLS), water absorption (WA), and flexural strength (FS). The clays were low in <2 µm fractions (≤19%) and of medium to high plasticity with a clayey silt texture. Smectite was the dominant clay mineral while quartz and feldspar were major non clay minerals. The most abundant oxides were SiO2 (63.57–68.73%), Al2O3 (13.9–15.61%), and Fe2O3 (4.86–6.18%), whereas K2O, CaO, MgO, Na2O, TiO2, and P2O5 were depleted. Characterization based on the clay workability chart, Winkler’s diagram, and compositional ternary diagrams revealed acceptable extrusion properties and suitability for structural ceramics and earthenware. The clays showed acceptable WL, BD, LS, and WA, but unsatisfactory FS (≤1.08 MPa). Low mechanical strength was attributed to presence of smectites and inert nature of feldspar at 900 °C. Beneficiation through mixing with carbonate-rich raw materials is recommended.
Highlights
Natural clay is the main raw material in the manufacture of traditional ceramics [1,2,3,4]
The pits in the study (PSD) is important for determining suitability for various ceramic applications
Based on the PSD, MK 1 and Mk 2 were suitable raw materials for common bricks. This observation is consistent with grain size classification of raw ceramic materials from Cameroon [6,14,22], Morocco [16,30], and Turkey [4,31]
Summary
Natural clay (comprising clay minerals, silica, feldspar, and iron oxide) is the main raw material in the manufacture of traditional ceramics [1,2,3,4]. According to Teixera et al [5] and Serra et al [2], the exploitation of natural clays for various end-products, such as structural ceramics (bricks, roofing tile and blocks), and earthenware (household ceramics), is based on their availability, accessibility, and comparatively low to intermediate firing temperatures. Sintering temperature is considered one of the most important processing variables that influences final product costs [15]. The clay body undergoes chemical and structural modifications that deeply transform the inherent characteristics of raw ceramic material
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