Title of Invention

"AN IMPROVED PROCESS OF MAKING SODIUM ZIRCONIUM PHOSPHATE POWDER"

Abstract

The invention relates to an improved process of making sodium zirconium phosphate powder. The process steps are: preparing a batch containing 7.55 to 9.45wt% of Na2CO3, 35.0 to 40.0wt.% of ZrO2 and 49.0 to 55.0 wt.% of NH4H2PO4, mixing and grinding the batch for a period in the range of 6-8 hrs., heat treating the mixed batch at a temperature in the range of 160°-200°C for a period in the range of 12-18 hrs., regrinding the material in an organic solvent for a period in the range of 6-8 hrs., drying the reground material, heat treating the dried material at a temperature in the range of 500-650°C for a period in the range of 3 to 6 hrs., further raising the temperature in the range of 750 to 950°C for a period in the range of 12-18 hrs., grinding the heat treated material in an organic solvent medium for a period in the range of 6-8 hrs., drying the ground material, by known methods, sintering at a temperature in the range of 1300-1400°C for 24 to 48 hrs., grinding and milling the fired shapes by known methods.

Full Text

The present invention relates to an improved process of making sodium zirconium phosphate powder. The material has received much attention in recent times because of their ultra low coefficient of thermal expansion, high temperature stability, fast ionic conductivity, and as a host material for immobilisation of radioactive wastes. It also has great potential in additional application such as catalyst supports, auto engine components, heat exchangers and mirror blank for space technology. The present day method of making Sodium Zirconium Phosphate powder by solid state method for which references may be made to D.K. Agrawal, C.Y. Huang and H.A. Mckinstry in International Jour, of Thermophysics, Vol. 12, No. 4, 1991 and R. Roy, D.K. Agrawal, J. Almao and R.A. Roy in Mat. Res. Bull., Vol. 19, pp 471-477, 1984, wherein sodium carbonate, ZrO2 and NH4H2PO4 are mixed in stoichiometric amounts in acetone with hand grinding, air dried, sometimes ball milled, heat treated at 175°C overnight and then calcined to remove the volatiles, such as CO2, NH3 at 600°C for 4 hrs. and at 900°C for 16 hrs with intermediate grinding and mixing operations to ensure complete homogenisation of the powder, the calcined powder subjected to consolidation into disks and final sintering at 1000°C to 1400°C for 48 hrs to obtain NaZr2(PO4)3 and often free ZrO2 and ZrP2O7 as minor secondary phases. For sol-gel synthesis of NaZr2(PO4)3 reference may be made to D.K. Agrawal and J.H. Adair, J. Am. Ceram. Soc.,Vol. 73, No. 7, 2153-55, 1990, wherein starting components NaNO3, ZrO(NO3)2 or ZrO2(nitrate stabilised), NH4H2PO4 made into solutions, mixed in stoichiometric amounts, the order of mixing being critical for the formation of a single phase material and ensuring the homogeneity of the mixture, firstly NaNO3 and ZrO2 solutions are mixed, then an appropriate amount of H3PO4 was added slowly with constant stirring, maintaining the pH of the mixture at about 1.3, the highly viscous slurry formed at room temperature was heated at 80°C for 24 hrs. for gelation, gel dried at 120°C for 24 hrs., calcined between 300°C and 500°C , hand ground and then finally heat treated between 600°C and 1000°C for 24 hrs. to produce phase pure NaZr2(PO4)3. For synthesis of NaZr2(PO4)3 by hydrothermal method reference may be made to S. Komarneni in Int. Jour. High. Tech. Ceram., Vol. 4, No. 31, 1988, wherein stoichiometric amount of NaCl or NaNO3 is dissolved in 0.5 M ZrOCl2 solution and then H3PO4 is added dropwise under constant stirring, the gel obtained is dried at 70°C, ground, rehydrated and redried, the dried gel and water are loaded in Teflon lined Parr acid digestion bombs, heated between 170°C to 230°C for 1 to 3 days. The process of D.K.Agarwal et al consists of three calcination treatments viz ; 175° C overnight, 600 ° C for 4 hours and 900 ° C for hours, before final sintering, each calcination treatment being followed by a grinding and mixing operation. But the present process is a two atep calcination process before final sintering. The first calcination is done at 600 ° - 200 ° C for 12 - 18 hours. In the second calcination, temperature is first raised to 500 ° - 650 ° C, continuously agitated for 3-6 hours at the same temperature finally is raised to 750 ° - 950 ° C for a period of 12 - 18 hours, calcination treatment is followed by a grinding and mixing operation . Thus a firing upto 500 ° - 650 ° C and a mixing and grinding operation could be eliminated. The drawbacks of the above process are listed below : i) Attainment of homogeneity in solid state method is difficult. ii) Temperature of calcination of the mixture is somewhat higher in a solid state method. iii) Temperature of formation of sodium zirconium phosphate is high in a solid state method. iv) Multiple numbers of calcination steps make the solid state method complicated, v) Sol-gel processing leads to homogeneous products but the yield with respect to solid to reactant volume is very low. vi) Hydrothermal processing decreases the temperature of formation but is expensive. The main object of the present invention is to provide an improved process of making sodium zirconium phosphate powder which obviates the draw backs as detailed above. Another object of the present invention is to make the process simpler by elimination of one calcination step along with the subsequent grinding operation. Still another object of the present invention is to achieve increased homogeneity of mixed reactants in the slurry state method. Yet another object of the present invention is to increase the reactivity of the reactants in slurry state method. Still another object of the present invention is to lowering the calcination temperature of the mixture. Yet another object of the present invention is to make the process economic by recycling the alcohol added as milling medium. Accordingly the present invention provides an improved process of making sodium zirconium phosphate powder which comprises; characterised in that preparing a batch containing 7.55 to 9.45wt% of Na2CO3, 35.0 to 40.0wt.% of ZrO2 and 49.0 to 55.0 wt.% of NH4H2PO4, mixing and grinding the batch for a period in the range of 6-8 hrs., heat treating the mixed batch at a temperature in the range of 160°-200°C for a period in the range of 12-18 hrs., regrinding the material in an organic solvent for a period in the range of 6-8 hrs., drying the reground material, heat treating the dried material at a temperature in the range of 500-650°C for a period in the range of 3 to 6 hrs., further raising the temperature in the range of 750 to 950°C for a period in the range of 12-18 hrs., grinding the heat treated material in an organic solvent medium for a period in the range of 6-8 hrs., drying the ground material, by known methods, sintering at a temperature in the range of 1300-1400°C for 24 to 48 hrs., grinding and milling the fired shapes by known methods. In an embodiment of the present invention the homogenization may be performed in a mill such as planetary, ball, attrition. In still another embodiment of the present invention organic media may be isopropyl alcohol, ethanol, methanol, and acetone. The details of the process of the present ivneiton are given below: a) 7.55 to 9.45 wt. % of Na2CO3, 35.0 to 40.0 wt. % of ZrO2 and 49.0 to 55.0 wt. % of NH4H2PO4 are mixed for 6-8 hrs. in ball mill. b) The mass is heat treated at 160-200°C for 12-18 hrs. c) The fused mass is ground in a ball mill for 6-8 hrs. d) The ground mass is calcined at 500-650°C for 3 to 6 hrs. With constant agitation. e) The temperature is raised to 750-950°C for 12 to 18 hrs. f) The calcined mass is ground as in step 'c'. g) The ground mass is compacted into disks by hydraulic pressing. h) The compacted disks obtained in step 'g' are fired in the temperature range 1300-1400°C for 6 to 10 hrs. Preheating of mixture of Na2CO3, ZrO2 and NH4H2PO4 helps to drive off water and NHs, at 600°C remove most of the crystalline water and finally at 900°C remove CO2 form carbonates. Each of the calcinations steps is followed by a grinding operation to break the agglomerate and reduce the particle size for improved reactivity. The final product consists of dry cake of partially reacted pure oxides, calcined mass after grinding mixed with 15% PVA solution, compacted into disks and sintered at 1300°C for 8 hrs. The product obtained is single phase NaZr2(PO4)3 material. The novelty of the present invention lies in preparing NaZr2(PO4)3 powder by (i) eliminating one calcination step along with intermediate grinding and mixing operation (ii) increasing the reactivity of the calcined mass by the process of de-agglomeration of the same before going for the final calcination. The following examples are given by way of illustration and therefore should not be construed to limit the scope of the present invention. Example - 1 7.58 gms of Na2CO3, 35.33 gms of ZrO2 and 49.58 gms of NH4H2PO4 are mixed in a planetary mill with isopropyl alcohol in 1:1 for 8 hrs. The mixture is heat treated at 200°C for 12 hrs. The fused mass after grinding in the planetary mill for 8 hrs. in 1:1 ratio of solid : alcohol, is calcined at 650°C for 3 hrs. with continuous mechanical agitation. The temperature is raised to 800°C for 18 hrs. The calcined mass is subsequently ground in the planetary mill for 8 hrs. in 1:1 ratio of solid and alcohol. The ground mass is mixed with 15% PVA solution and compacted into disks and sintered at 1350°C for 4 hrs. The phase is identified as NaZr2(P04)3. Example - 2 7.79 gms of Na2CO3, 36.29 gms of ZrO2 and 50.92 gms of NH4H2PO4 are mixed in a planetary mill for 7.5 hrs. with isopropyle alcohol in 1:1 ratio. The mixture is heat treated at 185°C for 14 hrs. The fused mass after grinding as before is calcined at 600°C for 4 hrs. with continuous mechanical agitation. The temperature is raised to 850°C for 16 hrs. The calcined mass is again ground as before. The ground mass is mixed up with 15% PVA solution, compacted into disks and sintered at 1325°C for 6 hrs. The phase is identified as NaZr2(PO4)3. Example - 3 7.99 gms of Na2CO3, 37.24 gms of ZrO2 and 52.26 gms of NH4H2PO4are mixed in a planetary mill for 7 hrs. with isopropyl alcohol in 1:1.5 ratio. The mixture is heat treated at 175°C for 16 hrs. The fused mass after grinding as before is calcined at 550°C for 5 hrs. with continuous mechanical agitation. The temperature is raised to 900°C for 14 hrs. The calcined mass is again ground as before. The ground mass is mixed up with 15% PVA solution, compacted into disks and sintered at 130Q°C for 6 hrs. The phase is identified as NaZr2(PO4)3. Example - 4 8.40 gms of Na2CO3, 39.15 gms of ZrO2 and 54.94 gms of NH4H2PO4are mixed in a planetary mill for 6 hrs. with isopropyl alcohol in 1: 2 ratio. The mixture is heat treated at 160°C for 18 hrs. The fused mass after grinding as before is calcined at 500°C for 6 hrs. with continuous mechanical agitation. The temperature is raised to 950°C for 12 hrs. The calcined mass is again ground as before. The ground mass is mixed up with 15% PVA solution, compacted into disks and sintered at 1300°C for 8 hrs. The phase is identified as NaZr2(PO4)3. The main advantages of the present invention are : 1. The process is made simpler by eliminating one calcination step. 2. The homogeneity of the mixed reactants is increased. 3. The reactivity of the reactants is increased. 4. The formation temperature is reduced. We Claim: 1. An improved process of making sodium zirconium phosphate powder which comprises; characterised in that preparing a batch containing 7.55 to 9.45wt% of Na2CO3, 35.0 to 40.0wt.% of ZrO2 and 49.0 to 55.0 wt.% of NH4H2PO4, mixing and grinding the batch for a period in the range of 6-8 hrs., heat treating the mixed batch at a temperature in the range of 160°-200°C for a period in the range of 12-18 hrs., regrinding the material in an organic solvent for a period in the range of 6-8 hrs., drying the reground material, heat treating the dried material at a temperature in the range of 500-650°C for a period in the range of 3 to 6 hrs., further raising the temperature in the range of 750 to 950°C for a period in the range of 12-18 hrs., grinding the heat treated material in an organic solvent medium for a period in the range of 6-8 hrs., drying the ground material, by known methods, sintering at a temperature in the range of 1300-1400°C for 24 to 48 hrs., grinding and milling the fired shapes by known methods. 2. An improved process as claimed in Claim 1, wherein organic solvent used is isopropyl alcohol, ethanol, methanol, acetone. 3. An improved process of making sodium zirconium phosphate powder substantially as herein described with reference to the examples.

Documents:

203-del-2001-abstract.pdf

203-del-2001-claims.pdf

203-del-2001-correspondence-others.pdf

203-del-2001-correspondence-po.pdf

203-del-2001-description (complete).pdf

203-del-2001-form-1.pdf

203-del-2001-form-19.pdf

203-del-2001-form-2.pdf

203-del-2001-form-3.pdf