Effect of magnesia additive on the morphology and physico-mechanical properties of kaolinitic clays ceramics

Abstract

Nigeria is rich in various minerals, including crude oil and solid minerals. However, despite this abundance, effectively utilizing these resources remains a challenge. Kaolin, also known as white China clay, is a crucial raw material used in industries such as ceramics, paper, paint, plastic, and welding electrodes. Despite its plentiful availability in Nigeria, kaolin has not been adequately exploited. Consequently, Nigeria spends approximately 14.35 million USD annually to import refined kaolin to meet local demand, due to the lack of capacity to process it to the required industrial standards. This study investigates the effect of magnesia (MgO) on the morphology and physico-mechanical properties of kaolinitic clay ceramics using the slip-casting method. Various analytical techniques were employed to examine the kaolin, including X-ray fluorescence (XRF), X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier Transform Infrared Spectroscopy (FTIR), and Scanning Electron Microscopy (SEM). Also, compressive and flexural tests were conducted. The XRF analysis revealed that all samples contained SiO₂ (54.41%wt), Al₂O₃ (34.05%wt), and other trace elements. The main mineral phases identified were quartz, microcline, and orthoclase. Among the samples, 30–200 exhibited the highest compressive strength at 218 MPa, while the highest flexural rigidity was observed in sample 15–200. The results indicated that MgO significantly affected the properties of kaolin, as the control sample had a compressive strength of 59 MPa. The study also found that the quantities of additives should align with stoichiometric requirements. Results showed hypo-stoichiometry in samples 30–600 and 15–400, and hyper-stoichiometry in sample 60–200. XRF, XRD, and FTIR spectra confirmed the elemental and chemical compositions of the samples, while SEM analysis revealed the morphological structure. It was observed that increasing the magnesia content from 10% to 30% led to an increase in pore spaces within the samples. TGA analysis provided insights into the relationship between mass loss and temperature variation in the ceramic samples, While The DTG curves explain the endothermic phase changes over changes in temperature; at 50–150°C, loss of the water phase is complete, at 300–400°C burning of organic matter phase is achieved and at 500–700°C endothermic dihyroxylation phase begins forming armorphous meta-kaolin.