Naslov
Structural study of Cr-doped mulite derived from single-phase precursor

Autori
Gržeta, Biserka ; Tkalčec, Emilija

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
Book of Abstracts, Ninth Slovenian-Croatian Crystallographic Meeting / Lach, Nina ; Leban, Ivan - Ljubljana : Univerza v Ljubljani, 2000

Skup
Ninth Slovenian-Croatian Crystallographic Meeting

Mjesto i datum
Gozd Martuljek, Slovenija, 15.06.2000. - 17.06.2000

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
aluminum silicate. XRD.Rietveld refinement; mulite

Sažetak
Mullite is technologically important material for advanced ceramics applications. It is an aluminum silicate with the chemical formula AlVI2(AlIV2+2xSiIV2-2x)O10-x, where x denotes the number of oxygen atoms missing per average unit cell, and IV and VI are the coordination states of the cations (W. E. Cameron, Am. Mineral. 62 (1977) 747; I. A. Aksay and J. A. Pask, J. Am. Ceram. Soc. 58 (1975) 507(. Depending on the synthesis procedure, the mullite structure is able to incorporate considerable amounts of transition metal cations (H. Schneider, Ceramics Transactions 6 (1990) 135(. The structural distribution of Cr3+ in mullite is of special interest because the low thermal expansion of mullite can be further reduced by chromium incorporation. Our interest has been focused on mullite samples which were derived from single-phase precursors. The precursors were prepared by using tetraethoxysilane (TEOS), Al(NO3)3.9H2O and Cr(NO3)3.9H2O (R. Nass, E. Tkalčec and H. Ivanković, J. Am. Ceram. Soc. 78 (1995) 3097(. The samples of pure mullite and of mullite with 2 mol( Cr2O3 were calcined at 1200 (C for 2 hours, slowly cooled down to RT and examined by X-ray powder diffraction. Samples were orthorhombic, space group Pbam. The unit-cell parameters were determined using Si as internal standard, and refined by the whole pattern profile fitting (WPPF program, H. Toraya, J. Appl. Cryst. 19 (1986) 440(. Rietveld method was performed to refine the crystal structure of the samples (PFLS program, H. Toraya and F. Marumo, Rep. Res. Lab. Eng. Mater. Tokyo Inst. Technol. 5 (1980) 55(, using the starting structure model after results of T. Ban and K. Okada (J. Am. Ceram. Soc. 75 (1992) 227(. It was found that the sample of pure mullite contained 62.8(3) mol( Al2O3, and had the following refined unit-cell parameters: a=7.5591(4), b=7.6862(4), c=2.8829(1) A. Incorporation of chromium into mullite structure enlarged the unit-cell parameters to: a=7.5664(4), b=7.6920(4), c=2.8893(1) A. Large c, low a and even lower b expansion indicated that Cr3+ entered AlO6 octahedra, substituting for Al3+. Rietveld refinement using such model converged with Rwp=0.08572.

Izvorni jezik
Engleski

Znanstvena područja
Kemija

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