Synthesis of Celsian (BaAl₂Si₂O₈) from Solid Ba‐Al‐Al₂O₃‐SiO₂ Precursors: I, XRD and SEM/EDX Analyses of Phase Evolution

Abstract

An intimate Ba-Al-Al 2 O 3 -SiO 2 powder mixture, produced by high-energy milling, was pressed to 3 mm thick cylinders (10 mm diameter) and hexagonal plates (6 mm edgeto-edge width). Heat treatments conducted from 300°to 1650°C in pure oxygen or air were used to transform these solid-metal/oxide precursors into BaAl 2 Si 2 O 8 . Barium oxidation was completed, and a binary silicate compound, J ournal 3109 Prior work has revealed that novel reaction paths to Ba-CeO 3 , 62 BaFe 12 O 19 , 66 BaTiO 3 , 67,68 and YBa 2 Cu 3 O y 64 can be accessed by the oxidation of solid, alkaline-earth-metal-bearing precursors. The purpose of the present paper is to identify the reaction path(s) to celsian from a Ba-Al-Al 2 O 3 -SiO 2 precursor. Knowledge of the reaction path to celsian is considered an important first step in the processing of celsian-based composites. Before discussing the results of such work, prior analyses of phase evolution to celsian from mixed salt and metallic precursors is reviewed. II. Reaction Paths to Celsian (1) Mixed Salt PrecursorsSeveral authors have examined the formation of celsian from powder mixtures containing BaCO 3 and kaolin. [39][40][41][42][43]49 Heating such precursors at 6°-10°C/min in the temperature range ∼400°-665°C results in appreciable weight loss because of the dehydroxylation of kaolinite. 40,42,49 Weight-loss measurements also have indicated the onset of BaCO 3 decomposition above ∼600°C. 40,42,49 Further annealing in the temperature range 650°-800°C has yielded an amorphous oxide. 2,[41][42][43]49 Hexacelsian had been reported to form during annealing at Ն825°C, whereas the onset of monoclinic celsian formation has required further heat treatment at ∼1130°-1200°C. 2,39,[41][42][43]49 Based on infrared spectroscopy and X-ray diffraction (XRD) analyses, Planz and Muller-Hesse 39 have reported that the loss of H 2 O from kaolin leads to the formation of the metakaolin structure described by Brindley and Nakahira, 81 in which a layer of corner-sharing and edge-sharing AlO 4 tetrahedra is joined to a layer of SiO 4 tetrahedra. This metakaolin precursor is believed to yield an ordered form of hexacelsian with a layer of cornersharing AlO 4 tetrahedra joined to a layer of SiO 4 tetrahedra (as opposed to a ␤-hexacelsian structure with aluminum and silicon distributed in a more random fashion within a double layer of corner-sharing tetrahedra 33 ).

Synthesis of Al6Si2O13-BaAl2Si2O8-ZrO2-based composites and their wettability by molten Al and an Al-Si alloy

“…The melting point of BaAl 2 Si 2 O 8 is $ 1760 1C and it is chemically compatible with Al 2 O 3 under 1720 1C and with Al 6 Si 2 O 13 (mullite) under 1554 1C [24][25][26][27][28][29][30][31][32].…”

Development of celsian ceramics from fly ash useful for X-ray radiation-shielding application

“…The micrographs of shielding sample clearly show the compacted and continued integrated morphological characteristics. The micrograph 16,43 of fly ash clearly reveals (cf. Fig.…”

“…barium aluminosilicate (BAS) is well known for its applications in refractories, porcelains, glass ceramics and electrical insulators. 1,2 Recently, the application spectrum of BAS has further extended for potential application: (a) as a ceramic matrix for high temperature composites 3,4 and (b) in making cast prostheses for biomedical application because of their radiopacity and better strength in comparison to conventional feldspathic porcelains and ease of imparting desired shape by adopting glass ceramic processing route of fabrication. 5 Silica glasses containing barium, e.g.…”

Preparation and dielectric properties of celsian ceramics based on hexagonal BaAl2Si2O8

“…To obtain BaAl 2 Si 2 O 8 under laboratory conditions, researchers either introduce trace levels of additives that are present in small amounts in natural celsian, or use sol-gel processing, or fire starting mixtures in a reducing atmosphere (5% H 2 + 95% N 2 ) [7][8][9].…”