Kaolinite-Magnesite or Kaolinite–Talc-Based Ceramics. Part II: Microstructure and the Final Properties Related Sintered Tapes

Abstract

In recent decades, talc and kaolinite have been widely used as raw materials for the ceramic industry. In this study, the final characteristics of kaolinitic clay mixed with 6 mass% of magnesite obtained in our previous work were compared with those obtained with mixtures of kaolin (kaolin BIP) and talc (as the source of magnesium oxide). However, different amounts of talc in the kaolin powder were studied, namely 10, 30, and 50 mass% of added talc (with respect to kaolin + talc). The tape casting process was used during this work in order to manufacture the green tapes in an aqueous system with 0.2 mass% of dispersant. Subsequently, the green tapes were heated to 1000 and 1100 °C with a dwelling time of 12 min. The green and sintering tapes were characterized using the following techniques: DTA/TG, X-ray diffraction, porosity, and flexural strength analyses. The results obtained from our previous work indicate that the specimen with 6 mass% of MgCO3 sintered at 1200 °C for 3 h exhibited the best performances, with high flexural strength and weak porosity value—117 MPa and 27%—respectively. As results from this study, the optimal mechanical and thermal properties of sintering tapes were obtained for the specimen with 10 mass% of added talc sintered at 1100 °C. Indeed, this specimen exhibited 50 MPa and 43% of stress to rupture and apparent porosity, respectively.

Study of a Waste Kaolin as Raw Material for Mullite Ceramics and Mullite Refractories by Reaction Sintering

“…However, quartz and microcline do not present any weight loss after thermal treatment [53]. For pure kaolinite, 13.9 wt % of structural water is lost after thermal treatment at 1000 • C [1][2][3][4]. From the results of Table 2, it can be observed that the sample with higher kaolinite content (Burela with 85 wt %), the LOI is 11.90 wt %.…”

“…Assuming that all the LOI is a consequence of the kaolinite content as single clay mineral, being dehydroxylated by thermal treatment, it is possible to estimate the percentage of kaolinite in the samples. Taking into account that pure kaolinite lost 13.9 wt % (i.e., the LOI of a pure kaolinite is this value) as structural water [1][2][3][4], the contents of kaolinite for the raw kaolin sample and its fraction under 63 µm are calculated as ~19 wt % and ~47 wt %, respectively (Table 2). Thus, the washing process of the raw kaolin produced an increase of the kaolinite percentage in the sample, although it was assumed in this estimation that kaolinite is the only clay mineral present.…”

“…Kaolinite is a dioctahedral phyllosilicate with a theoretical formula Al 2 O 3 •2SiO 2 •2H 2 O or Al 2 Si 2 O 5 (OH) 4 with a 1:1 layered structure of [(Si 2 O 5 )] 2− and [Al 2 (OH) 4 ] 2+ molecular sheets and composition of 39.5 wt % Al 2 O 3 , 46.5 wt % SiO 2 and 14 wt % H 2 O [1][2][3][4]. According to Murray [5], kaolinite can be formed by hydrothermal alteration or weathering reactions or by a combination of both processes.…”

“…It has been mentioned that if potassium ions are not properly removed (following the weathering process), illitic clays (2:1 layered structure silicates) are formed instead of kaolinite [3]. Kaolin ores, with a relative high proportion of kaolinite, are a very interesting raw materials, with important and wide applications due to the properties of kaolinite layer silicate: low surface area (compared to other clay minerals, such as smectites), layered appearance, white or almost white colour, chemically inert in a wide range of pH (4)(5)(6)(7)(8)(9), with low heat and electricity conductivity, refractoriness (high-temperature resistance of ~1550 • C) and non-abrasive [1,3,[9][10][11][12][13][14]. Consequently, powdered and processed raw kaolin materials with a relatively high-proportion of kaolinite can be technologically applied in several industries, such as porcelain manufacture, ceramics, refractories, paper, paints, composite materials, polymers, and many more [1,3,[9][10][11][12][13][14].…”

Characterization of the Flux System: Lithium-Aluminum Silicate (Li)–Alkali Feldspars (Na,K); Magnesium (Mg) and Calcium (Ca)–Silicates

“…The influence of magnesium is interesting when using a silicate such as talc, as materials of increased densification and mechanical properties are obtained. However, studies on the effect of a heating cycle (heating rate and heating time), purity of talc materials (including calcination) and related thermal properties are very important [ 18 , 19 ]. In glass-ceramic materials using talc, mineral bridges and nanocrystallites have been found to cause crack deflection, which strengthens the grain boundary and improves the mechanical properties of the ceramics [ 20 , 21 ].…”