Synthesis of monoclinic Celsian from Coal Fly Ash by using a one-step solid-state reaction process

Abstract

Monoclinic (Celsian) and hexagonal (Hexacelsian) Ba 1 _ JC Sr JC Al 2 Si 2 0 8 solid solutions, where x = 0,0.25,0.375,0.5,0.75 or 1, were synthesized by using Coal Fly Ash (CFA) as main raw material, employing a simple one-step solid-state reaction process involving thermal treatment for 5 h at 850-1300 °C. Fully monoclinic Celsian was obtained at 1200 °C/5 h, for SrO contents of 0.25 < x < 0.75. However, an optimum SrO level of 0.25 < x < 0.375 was recommended for the stabilization of Celsian. These synthesis conditions represent a significant improvement over the higher temperatures, longer times and/or multi-step processes needed to obtain fully monoclinic Celsian, when other raw materials are used for this purpose, according to previous literature. These results were attributed to the role of the chemical and phase constitution of CFA as well as to a likely mineralizing effect of CaO and Ti0 2 present in it, which enhanced the Hexacelsian to Celsian conversion.

Influence of mechanical activation on the synthesis of Sr-Celsian employing a precursor mixture containing coal fly ash

“…Since mechanical activation is a well-known way to enhance the reactivity of materials that will participate in a posterior solid state reaction process (8), and coal fly ash (CFA) is an alternative raw material that seems to promote the Hexacelsian to Celsian conversion due to the presence in it of mineralizers such as CaO and TiO 2 (9)(10)(11), the influence of the combination of both factors on the synthesis of Sr-Celsian was studied in the present work.…”

Solid state reaction synthesis of Ba_0.75Sr_0.25AlSi₂O₈ - Al₂O<sub>3 ceramic composites from mechanically activated precursor mixtures

“…The efficiency of this method depends on the nature and amount of the added mineralizer. The stabilization of Celsian also depends on the nature of the employed initial raw materials (11)(12)(13)(14)(15), as well as on the conditions used for the synthesis of BAS (5,16,17). For instance, the formation of Hexacelsian is usually favored by a diminution in the particle size of the precursor materials.…”

“…The SBAS solid solutions can be potentially useful for environmental barrier coatings (EBCs) such as those employed for Si-based (SiC, Si 3 N 4 ) ceramic components in the hot section of advanced gas turbine engines (1), as well as for X-ray radiation-shielding applications (2) and for the fabrication of missile nose cones (radomes) (3), among other applications. These materials can be obtained by partial substitution of BaO by SrO in BaAl 2 Si 2 O 8 (BAS) (4,5), or alternatively from mixtures of BAS with SrAl 2 Si 2 O 8 (SAS) (6). The formation of SBAS obeys Vegard's law and it can take place over the entire concentration range (0 ≤ x ≤ 1) (5,7).…”

“…These materials can be obtained by partial substitution of BaO by SrO in BaAl 2 Si 2 O 8 (BAS) (4,5), or alternatively from mixtures of BAS with SrAl 2 Si 2 O 8 (SAS) (6). The formation of SBAS obeys Vegard's law and it can take place over the entire concentration range (0 ≤ x ≤ 1) (5,7). Both BAS and SBAS are denominated either as Celsian (or Monocelsian) when their crystalline structure is monoclinic, or as Hexacelsian when they have a hexagonal lattice structure.…”

Ceramic radiotransparent materials on the basis of BaO-Al2O3-SiO2 and SrO-Al2O3-SiO2 systems

“…Ceramic radiotransparent materials are mainly used for the manufacture of radomes protecting antennas against the environmental influences. Besides the above mentioned requirements radio-ceramic materials must have: a high value of thermal resistance, low coefficient of linear thermal expansion and at the same time should protect the equipment from external influences [1][2][3][4][5][6][7][8].…”