Kaolinite-Magnesite Based Ceramics. Part I: Surface Charge and Rheological Properties Optimization of the Suspensions for the Processing of Cordierite-Mullite Tapes

Abstract

The present study aimed at investigating the influence of the concentration of sodium silicate and sodium hexametaphosphate on the dispersion of an aqueous kaolinitic clay slurry regarding further use for the tape casting process. The zeta potential of the kaolinitic clay slurry matched the requirements for tape casting. The addition of magnesite in the kaolinitic slurries tended to increase the zeta potential towards the required limit values. Despite this, the further addition of surfactants allowed improving the zeta potential in agreement with the tape casting conditions. Accordingly, the rheological behavior, under continuous and oscillatory flow conditions, of various mixtures of magnesite and a kaolinitic clay was studied. Regarding the pH and the zeta potential measurements, the E–F attraction prevailed at low pH value, and F–F or E–E attraction was predominant at high pH value. All slurries exhibited a shear thinning behavior, which was well-correlated by the Herschel–Bulkley model. It appeared that the best stability for the kaolinitic clay slurries was obtained while using 0.4 mass% and 1.2 mass% of sodium hexametaphosphate and sodium silicate, respectively. An increase in the magnesite concentration above 6 mass% led to a complex behavior with low cohesion energy due to the occurrence of soluble complexes.

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

“…The latter samples exhibited higher apparent porosity, justifying the observed behavior. Moreover, for the sample containing magnesite (K94M6), the level of apparent porosity was higher due to the decarbonation during sintering that significantly contributed to increasing the remaining porosity [17,27]. Sintering at 1000 °C tended to promote the decrease in viscosity of the amorphous phase (Arrhenius type dependence of viscosity with temperature), and therefore, promoted the initiation of viscous flow sintering of the studied samples.…”

“…The dispersion and formulation optimization have been already described in our former paper (part I.) [17].…”

“…It is a layered clay mineral consisting of the pilling up of two Kaolinite has a 1:1 sheet structure with chemical formulae Al2Si2O5(OH)4 (39.8 mass% Al2O3, 46.38 mass% SiO2, and 13.9 mass% H2O). It is a layered clay mineral consisting of the pilling up of two sheets-one tetrahedral sheet of silica (SiO4) joined to one octahedral sheet of alumina (AlO6) [15][16][17][18]. Indeed, the morphology of kaolinite mineral is plate-like.…”

“…The crystalline structure of talc has a 2:1 or TOT layer type with one octahedral (O) magnesium layer sandwiched between two tetrahedral silica layers ( Figure 2) [21]. In our previous work [1,17], the effect of magnesite amount on the different properties of kaolinitic clay ceramics was studied. However, in this study, we aimed to compare the final characteristics of the kaolinitic clay from Algeria (KT2) mixed with 6 mass% of magnesite, with those resulting from the use of a commercial kaolin (kaolin BIP) mixed with talc (as the source of magnesium oxide).…”

Comparative Properties of Porous Phyllosilicate-Based Ceramics Shaped by Freeze-Tape Casting

“…Indeed, clays appear to be appropriate raw material resources for these applications. Clays are readily available raw materials, mainly constituted from clay minerals, that exhibit a layered structure and are classified as phyllosilicates [23][24][25]. In general, raw clays also include some secondary nonclay minerals such as quartz, mica, feldspar, iron oxides, and titanium oxides.…”