Sintering Behavior of Gehlenite. Part I: Self‐Forming, Macro‐/Mesoporous Gehlenite—Pore‐Forming Mechanism, Microstructure, Mechanical, and Physical Properties

Abstract

A novel kind of pore self-forming macro-/mesoporous gehlenite (2CaO . Al 2 O 3 . SiO 2 ) ceramic (abbreviated C 2 AS) having a highest porosity of 80% corresponding to a volume expansion of 134% during sintering has been developed. The pore selfforming ability, microstructure, mechanical, and thermal physical properties of the porous ceramic are related to the sintering temperature. The gehlenite ceramic shows a very good pore selfforming ability over a very wide range of temperature from 9001 to 14501C. No vesicant is required and no hydrothermal treatment is needed, as is generally the case for other kinds of porous ceramics or glasses. The pore self-forming ability of the C 2 AS porous ceramic can be attributed to the escape of the adsorbed water vapor during the sintering process, due to automatic hydration of the fine, amorphous, flakey-shaped starting C 2 AS powder particles synthesized by the organic steric entrapment (PVA) method, as well as to their fine, porous microstructure. The pores of the ceramics can be either open or closed, and the average pore size ranges from 0.6 to 1.1 lm, corresponding to a porosity of 75%-80%, respectively. The porous ceramic can preserve nanometer-sized (26-50 nm) crystallites up to 10001C. Sintered or thermally treated under different conditions, the porous ceramics exhibit relatively high flexural strengths ranging from 9.1 to 15.4 MPa, with a standard deviation of 0.3 and 4.2 MPa, respectively. Thermal properties of the porous ceramic up to 10001C, including thermal expansion coefficient, thermal diffusivity, specific heat, and thermal conductivity, were investigated, and the stability of the porous ceramic in boiling water was also studied.

Firing behavior of argillites from northern Tunisia as raw materials for ceramic applications

“…According to Zouaoui and Bouaziz 42 and Traoré et al, 43 anorthite is the main crystalline phase contributing to the improvement of the mechanical strength; however, the gehlenite phase is known by its pore self-formation, which causes a reduction in the mechanical strength. 44,45 This is confirmed by the X-ray pattern, which indicate at 1100°C an increase in reflections relative to the mullite and anorthite phases while gehlenite drop to develop. Zhou et al 46 behavior and the ceramic properties of these clays particularly in the Sejnène region, northwest Tunisia.…”

“…The amounts of some constituents like iron, calcium, magnesium, and alkali oxides in sample composition 11 influence the densification of fired clay materials causing a decrease in porosity and increasing strength. According to Zouaoui and Bouaziz 42 and Traoré et al, 43 anorthite is the main crystalline phase contributing to the improvement of the mechanical strength; however, the gehlenite phase is known by its pore self‐formation, which causes a reduction in the mechanical strength 44,45 . This is confirmed by the X‐ray pattern, which indicate at 1100°C an increase in reflections relative to the mullite and anorthite phases while gehlenite drop to develop.…”

Processing and Characterization of Multiphase Ceramic Composites Part II: Triplex Composites with a Wide Sintering Temperature Range

“…Equivolumetric, triplex, 33 vol% Al 2 O 3 –33 vol% yttrium aluminum garnet (YAG)–33 vol% ZrO 2 composite powder was synthesized using the organic, steric entrapment method 32–48 . Aluminum nitrate nonahydrate [Al(NO 3 ) 3 ·9H 2 O, 98+%, Aldrich Chemical Inc.], zirconium (IV) propoxide [Aldrich Chemical Inc., Milwaukee, WI, 70 wt% solution in 1‐propanol], and yttrium nitrate hexahydrate [Y(NO 3 ) 3 ·6H 2 O, 99%, Aldrich Chemical Inc.], were used as Al +3 , Zr +4 , and Y +3 sources, respectively.…”

Fabrication and electrical properties of porous BS–0.64PT high temperature piezoceramics using polystyrene microsphere

“…The PZT porous ceramics with 50 vol% PMMA had HFOM and g h of 3306 Â 10 À 15 /Pa and 0.057, respectively. The formation of the pores in BURPS process can be controlled by many factors, such as the shape [18], size [19][20][21] and volume [22,23] of PFA and sintering temperature [24][25][26]. All the influence factors can be used to control the properties of the pores, thus optimizing electrical properties of the porous piezoceramics.…”