Title of Invention

"AN IMPROVED PROCESS FOR THE PREPARATION OF CERAMICS"

Abstract

This invention relates to an improved process for the preparation of lead zirconate titanate / lead lanthanum zirconate titanate ceramics. Particularly it relates to the preparation of (PZT / PLZT) ceramics at low temperature. Process steps are: dissolving titanium hydroxide and zirconium hydroxide in oxides acid solution wherein metal: oxides acid is in the range of 1:1 to 1:3 to obtain titanium oxalate and zirconium oblate, preparing water soluble ethylene diamante tetra acidic acids complex of the constitute metals such as lead, lanthanum, mixing thoroughly titanium and zirconium oxalates and EDTA metal complex, evaporating the said mixture rapidly at 200°C to produce processor powder, heating the said processor at 500 -600°C for 1 to 3 hrs to obtain lead zircon ate titanate (PZT) lead lanthanum zirunate titanate (PLZT) ceramics.

Full Text

This invention relates to an improved process for the preparation of ceramics. Particularly it relates to the preparation of Lead Zirconate-titanate / Lead lanthanum zirconate-titanate (PZT / PLZT) ceramics at low temperature. Piezoelectric ceramics are prepared for fabrication the electrochemical transducers used in mechanical frequency filters that find application in long-haul communications system. [Piezoelectricity - Edited by G. W. Taylor et. Al. ( ferrowelectric and related phenomena ) vol. 4, section II : first edition -printed on 1992( Gordon & Breach Science Publisher)] Piezoelectric materials have superior stability, smaller bulk and lower fabrication cost. Moreover, only mechanical filters are of sufficiently high quality to allow the frequency by premodulation to the internally specified FDM (Frequency-division multiplex) base group between 60 KHz to 108 KHz. This presents the enormous advantage that only single type of channel filter is required. Piezoelectric materials also being used in computer for getting signal (Sensor application). The general method of preparation of piezoelectric ceramics is through solid state reaction where TiO2, ZrO2 & PbO etc. are stoichiometrically mixed together and ball milled for at least 2 hr. to make them homogeneous. The mixture then on heating to 800°C give the single phasic PZT. The main object of the present invention is to provide 'Low temperature PZT & PLZT ceramics synthesis from the solution comprising oxalate complexes of Zr4+, Ti4+ and EDTA complexes of Pb and other constituent metals ( Bi, La, Sr, Ba, etc) which obiates the drawbacks as detailed above. Still another object of the present invention is to maintain homogeniety throughout the reaction. Yet another object of the present invention, no possibility of contamination which may occur in solid sate process during ball milling. Accordingly the present invention provides an improved process for the preparation of lead zirconate titanate / lead lanthanum zirconate titanate ceramics which comprises; a) dissolving titanium hydroxide and zirconium hydroxide in oxalic acid solution wherein metal: oxides acid is in the range of 1:1 to 1:3 to obtain titanium oxalate and zirconium oxalate, b) preparing water soluble ethylene diamine tetra acidic acids (EDTA)complex of the constituents metals such as lead, lanthanum, c) characterized in that mixing thoroughly titanium and zirconium oxalates obtained in step a) and EDTA metal complex obtained in step b), d) evaporating the said mixture rapidly at 200°C to produce precursor powder, e) heating the said precursor at 500 - 600°C for 1 to 3 hrs to obtain lead zirconate titanate (PZT) / lead lanthanum zirconate titanate (PLZT) ceramics. In an embodiments of the present invention simple technique with low fabrication cost. In another embodiments of the present invention atomic scale mixing of the constituent metal atoms through out the reaction which prevent the formation of impure phases of constituent metal oxides. The process of this invention is elucidated by the following examples however this should not limit the scope of the invention. Example 1 TiO2 on treatment with HF & NH4F produced a water soluble complex (NH4)2TiF6, which on treatment with dilute NH4OH produced Titanium hydroxide. Similarly zirconium hydroxide was prepared from zirconyl oxychloride solution using NH4OH. Both hydroxides were assayed at 900°C/3h to get the percentage of TiO2 and ZrO2 in the corresponding hydroxide. Titanium hydroxide and zirconium hydroxide were dissolved in oxalic acid solution (metal : oxalic acid = 1:2). Now stoichiometric amounts of titanium oxalate, zirconium oxalate solution and constituent metal EDTA ( Pb, La ) complex solution, which were being prepared by adding metal nitrate solution to ammonical EDTA solution, were mixed and the mix ture was rapidly evaporaed on hot plate (~200°C) to produce precursor powder'. The precursor on pyrolysis to 600°C/2h produces single phasic PZT, PLZT ceramics. The high stability of Pb-EDTA complex prevent the precipitation of Pb-oxalate and thus homogeneity is maintained throughout the reaction. Example 2 Preparation of Lead Zirconate-titanate Pb(Zr.6Ti.4)O3 termed as PZT TiO2 oxide on treatment with HF & NH4F on water bath for 72 hrs produced a water soluble complex (NH4)2TiF6, which on treatment with dilute ammonium hydroxide produced titanium hydroxide. Zirconium hydroxide precipitated from aqueous zirconyl oxychloride solution using ammonium hydroxide. Both hydroxides were assayed at 900°C/3h to get the content of TiO2 & ZrO2 in the corresponding titanium and zirconium hydroxides. Lead nitrate solution slowly dissolve in ammonical EDTA solution to produce Pb(EDTA) solution with a metal ion : EDTA mole ratio 1:1. The hydroxides of titanium and zirconium were dissolved in oxalic acid solution (metal:oxalic acid = 1:2). Now the stoichiometric amount titanium oxalate solution, zirconium oxalate solution were mixed with Pb-EDTA solution and the mixture was rapidly evaporated on hot plate (~200°C). A fluppy organic based powder was obtained which is termed as precursor powder. The precursor on heating to 600°C/2h give single phasic PZT. The main advantages of the present inventions are 1. The process is technically simple. 2. Raw materials are cheaper. Because we can also get low temperature PZT starting from titanium-isopropoxide, zirconium isopropoxide appears to be lacking advantage for commercialization. 3. It is also a low temperature synthesis compare to solid state method. 4. It can be used as mechanical filter. 5. It can also be used in sensor application. We Claim: 1. An improved process for the preparation of lead zirconate titanate / lead lanthanum zirconate titanate ceramics which comprises; a) dissolving titanium hydroxide and zirconium hydroxide in oxalic acid solution wherein metal: oxides acid is in the range of 1:1 to 1:3 to obtain titanium oxalate and zirconium oxalate, b) preparing water soluble ethylene diamine tetra acidic acids (EDTA)complex of the constituents metals such as lead, lanthanum, c) characterized in that mixing thoroughly titanium and zirconium oxalates obtained in step a) and EDTA metal complex obtained in step b), d) evaporating the said mixture rapidly at 200°C to produce precursor powder, e) heating the said precursor at 500 - 600°C for 1 to 3 hrs to obtain lead zirconate titanate (PZT) / lead lanthanum zirconate titanate (PLZT) ceramics. 2. An improved process as claimed in claim 1 wherein the amount of EDTA complex of constituent metal is >-1 mole. 3. An improved process for the preparation of lead zirconate titanate / lead lanthanum zirconate titanate ceramics substantially as herein described with reference to the examples.

Documents:

126-del-2000-abstract.pdf

126-del-2000-claims.pdf

126-del-2000-correspondence-others.pdf

126-del-2000-correspondence-po.pdf

126-del-2000-description (complete).pdf

126-del-2000-form-1.pdf

126-del-2000-form-19.pdf

126-del-2000-form-2.pdf