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  • Küçük Resim
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    The effect of Al3+ concentration on the properties of alumina powders obtained by reaction between aluminium sulphate and urea in boiling aqueous solution
    (Elsevier Sci Ltd, 2002) Sarikaya, Y.; Ada, K.; Alemdaroğlu, T.; Bozdoğan, I.
    Homogeneous precipitation of alumina precursors was carried out in boiling aqueous solutions that contained excess urea and 0.010 0.200 M Al3+. The obtained precursor precipitates were dried for 2 h at 100 C to yield precursor powders and the precursor powders were calcined for 2 h at 1000 degreesC to yield alumina powders. Precursor powders and alumina powders were investigated by X-ray diffraction (XRD), electron microscopy (EM), particle size distribution (PSD) analysis and nitrogen adsorption-desorption techniques for characterisation. Inspection of the XRD data showed that the precursor powders were amorphous in nature and the final product was delta-Al2O3, Investigation of the EM and PSD data of the powders showed that they contained unequally sized spheres and agglomerates. It was determined that, as the Al3+ concentration in the boiling aqueous solution increased, the number of 0.3-1.0 mum sized independent particles decreased and the sizes of agglomerates grew between 1.00 100 mum while their volume percentages increased from 50 to 80%. It was also observed that the specific surface areas of the alumina powders decreased from 98 m(2) g(-1) to 54 m(2) g(-1) and their specific micropore-mesopore volumes decreased from 0.31 cm(3) g(-1) to 0.14 cm(3) g(-1) as the Al3+ concentration in the boiling aqueous solution increased. It was observed that it was possible to prepare alumina powders that have different particle size distributions and different porosities by changing the Al3+ concentration while keeping the [urea]/[Al3+] ratio constant at a value of 5.4 in the boiling aqueous solution. (C) 2002 Elsevier Science Ltd. All rights reserved.
  • Küçük Resim
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    The investigation of the pore structure of fine alumina powders prepared for ceramic production by the technique of precipitation from solution
    (2000) Ada, K.; Sarıkaya, Y.; Alemdaroğlu, T.; Önal, M.
    In this study, alumina precursors were prepared in three different ways and were converted into three different alumina powders (Al2O3) by calcination. The precipitation methods of the alumina precursors were as follows: i) Addition in excess of a 25% NH3 solution dropwise for two hours, to a boiling 0.08 M A12(SO4)3 solution which was already buffered by NH3 / NH4Cl. ii) Boiling for two hours a 0.006 M Al2(SO4)S solution which contains C2H4(COOH)2, NH4Cl and (NHi)2CO. iti) Boiling for two hours a 0.2 M Al2(SO4)S solution which contains excess (NHj)2CO. In order to find out the effect of the followed procedure on the pore structure, the following determinations were realized. The powder shapes and sizes were determined by electron microscopy. The specific surface areas and the adsorption heats of these powders were calculated from the adsorption data. The mesopore size distribution curves were plotted by using the desoiption data. The specific micropore, mesopore and micropore-mesopore volumes were determined by extrapolating these curves. Finally, the dependence of the pore structure on the procedure of preparation was discussed in detail.