A Novel Co-Precipitation Route for the Synthesis of Fine Mixed-Oxide Powders
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A NOVEL CO-PRECIPITATION ROUTE FOR THE SYNTHESIS OF FINE MIXED-OXIDE POWDERS
AMITA PATHAK AND P PRAMANIKO Department of chemistry, Indian Institute of Technology,
721 302,
Kharagpur
INDIA
ABSTRACT A new co-precipitation technique for the preparation of fine ceramic mixed-oxide povders using a mixture of (NH4 )HCO 3 , triethylamine and formaline in presence of soluble polymers, like polyvinyl alcohol (PVA). The mixture is chemically equivalent to one mole of triethylamnroniumcarbonate (TEAC). The mixed-oxide ccmpositions synthesized and characterized are - MN2 0 [Spinels; where M = Ni(II), Cu(II), Zn(II), Co(II) and N = Fe(III), tr(III)]; M3Fe50•2 [Garnets; where M = Y(III), 0 Gd(III)] and RBa 2 Cu 3 7+ [Ceramic superc~nductors; where R = rare-earths]. The final product is characterized by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy for microanalysis (EDX) and scanning electron microscopy (S2E4).
INTRODUCTION The preparation of high purity semiconductor grade ceramic mixedoxides has received wide attention due to the materials' great potential applicability in the electronic and electrical industries. Conventionally, the technical ceramics are made out of powders prepared by classical mixing-calcining-milling methods i.e. by the solid-
state reaction method. requires
high
melting/partial
reaction
melting
This method besides being painfully time-consuming tenperatures
of
the
which
enhance
constituting
solids
the
possibility
resulting
in
of
the
formation of additional undesirable phases. Moreover, such processes are affected by serious limitations of large inter-grain diffusion, a broad distribution in grain-size with minimal grain inter-growth. Hence, morphological control of the desired cconpound, using such techniques becomes difficult and ccrnplex. But high performance ceramics need chemically prepared po'Aders which are monophasic and possess higher density and improved chemical hamogeneity. Sane of these chemical routes are chemical co-precipitation using oxalates, citrates etc. (1-5). The present chemical technique is a simple and cost effective coprecipitation process for the synthesis of high performance semiconductor grade fine ceramic mixed-oxide povders. This work is a modification of our earlier reported work on the preparation of fine mixed-oxides by the co-precipitation technique using triethylamnonium-carbonate (organic carbonate) (6). The present report describes efforts to prepare mixed-oxide powders, such as, NiFe.0, ZnFe O, CoFe O, CuFe O, NiCr O, ZnCrO O,1 ' YBa 2, tu 33O_+c 2 , GdFe g-,,- Y3Fe.50 12' 2.3. 5~e; 7+. in presence of solu . ble. polymers . like YVA, using a precipitaling mixture consisting of anr•onium bicarbonate (1 mole), triethylamine (2.2 moles) and formaline (2 moles). The mixture is chemically equivalent to I mole of triethylarrrnoniumcarbonate (TEAC). Thus the tedious process of preparing TEAC is simplified by the use of ccrmnon, easily purificable laboratory reagents. The co-precipitated carbonates decomnpose/dissociate ccnpletely int
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