THE ROLE OF INTERMEDIATE CALCIUM ALUMINATE PHASES IN SOLID STATE SYNTHESIS OF MAYENITE (Ca₁₂Al₁₄O₃₃)

Abstract

Structural transformations during the synthesis of mayenite ( Ca 12 Al 14 O 33) were investigated. The samples were prepared by a solid–state reaction and the transformations were researched by means of XRD, Rietveld analysis, SEM, and Raman spectroscopy. The three key phases ( CaAl 2 O 4, Ca 3 Al 2 O 6, Ca 5 Al 6 O 14) were identified and their role in the mayenite formation was assigned. The optimal low temperature pathway of the mayenite synthesis involving Ca 5 Al 6 O 14 intermediate was proposed.

Steam reforming of biomass tar model compound at relatively low steam-to-carbon condition over CaO-doped nickel–iron alloy supported over iron–alumina catalysts

“…The absence of CaO and Ca-Al-O peaks, which should be formed after decomposition of respective nitrate precursors during calcination at 900 • C for 4 h, indicates that CaO and Ca-Al-O are amorphous or well mixed with other support phases. It is noteworthy to mention here that formation of various calcium aluminates (Ca-Al X ) and mayenite-like structures were reported by others [46,54,55] during the synthesis of Ca-Al materials. However, in Fig.…”

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“…The polycrystalline mayenite samples were obtained by conventional high temperature solid-state reaction between analytical grade CaCO 3 (Aldrich) and c-Al 2 O 3 (Aldrich) as described elsewhere [27,28]. Amorphous Nb 2 O 5 and ZrO 2 oxides were prepared by hydrolysis of the metal precursors (Nb(C 2 H 5 O) 4 and ZrOCl 2 ) in diluted aqueous ammonia solution.…”

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“…Furthermore, the only calcium aluminate mixed phase is In the sorbents synthesized for laboratory scale (C30L and MayL, not shown), CaAl 2 O 4 and Ca 5 Al 6 O 14 calcium aluminate mixed phases were detected. It is possible that the enlargement of the scale generates diffusion limitations during the solid state synthesis step and, as reported by Ruszac et al [21] , these mixed phases are formed at low temperature (750-10 0 0 °C) as a metastable phase, showing that probably neither temperature nor time was enough to synthesized a unique Ca-Al oxide. Fig.…”