Title of Invention

"AN IMPROVED PROCESS FOR PREPARATION OF MN-ZN FERRITES"

Abstract

An improved process for the preparation of Mn-Zn ferrites by preparing aqueous solutions of ferric chloride, zinc chloride and manganese chloride, by known methods adjusting the pH of the iron chloride to 9.0 to 9.5 so as to precipitate iron as hydroxide using 5-10% aqueous ammonia, washing the prepared iron hydroxide mass till free of chloride, mixing the iron hydroxide slurry with zinc and manganese chloride solutions, adjusting again the pH of the mixed contents to 10.0 with 5-10% ammonia solution to obtain a slurry, autoclaving the above said slurry at 150-210°C for 2 to 3 hours and recovering Mn-Zn ferrites by known methods.

Full Text

This invention relates to an improved process for preparation of Mn-Zn ferrites. Particularly this invention relates to an improved process for the production of Mn-Zn ferrites with varying magnetic and microstructural properties which are useful in various electronic appliances. Manganese-Zinc ferrites are important materials because of their high permeability and low core losses. These ferrites have been widely used in electronic applications such as transformer, choke cons, noise filters, recording heads etc. The world demand of soft ferrites towards 2000 AD is estimated to be 221,500 million tons per year. The conventional method for preparation of ferrites is through ceramic route involving high temperature solid state reaction between the constituent oxides / carbonates. But ultra fine particles with uniform size distribution cannot be produced easily by this method. The non-uniform particles on compacting result in the formation of voids or low density area in the green compacts and on sintering , non- reproducible products in terms of their magnetic properties are obtained. In order to overcome difficulties arising out of ceramic route, wet chemical methods like air oxidation (Sisk M., Kilbride I. and Barker A.J, J. Mater. Sci. Letts, 1995, vol 14 p. 153), co-precipitation (Pankov V.V., Fernet M., Germi P.andMolard P, J. Magn. Magn. Mater, 1993, vol 120, p 69 ; Ataie A., Piramoon M.R. , Harris I.R. and Ponton C.B., J. Mater.Sci.,1995, vol.30, p 5600 ;), hydrothermal processing ( Yamamoto Y., Makino J., Magn. Magn. Mater., 1994, vol. 133, p 500 ; Kumazawa H, Maeda Y an Sada E., J. Mater. Sci. Letts., 1995, vol. 14, p 68 ;) have been considered for the production of homogeneous and fine ferrites. The use of hydrothermal technique to produce pure , ultra fine, relatively strain free Mn-Zn ferrites with narrow size distribution has attracted much attention. Most of the work on wet chemical process for ferrite has been carried out using NaOH (Johnson M.T, Noordermeer A., Severin M.M.E. and Meeuwissen W.A.M., J. Magn. Magn. Mater., 1992, vol 116, p!69) and the major impurity in these materials is sodium which causes decrease in the initial permeability of ferrite matedrials. These processes comprise of preparation of iron salt solution followed by neutralization with sodium hydroxide to form gel. The gel so formed is treated for alkali removal and aging to obtain the ferrites. These ferrites invariably have sodium as the impurity. For high frequency applications ferrites require high permeability, which depends on the density, porosity and level of impurities. Porosity and impurity at the grain boundary and within the grains causes hindrance to the domain wall motion and reduce the initial permeability drastically. To avoid Na incorporation in ferrites several workers have tried to prepare Mn-Zn ferrites using ammonia but could not succeed due to formation of soluble Mn and Zn amines in the presence of ammonium chloride which is formed during neutralization of iron chloride/iron nitrate solutions. The main objective of the present invention is to prepare Mn-Zn ferrites without any Na+ ion impurity in the matrix. Another objective of the present invention is to prepare a variety of Mn-Zn ferrites with different particle sizes exhibiting different magnetic properties. Yet another objective is to prepare the ferrites using blue dust/steel scrap as a source of iron which forms a major constituent of the manganese-zinc ferrite so that cost of production of the ferrites is considerably reduced. Accordingly, the present invention provides an improved process for the preparation of Mn-Zn ferrites which comprises preparing aqueous solutions of ferric chloride, zinc chloride and manganese chloride, by known methods adjusting the pH of the ferric chloride to 9.0 to 9.5 so as to precipitate iron as hydroxide using 5-10% aqueous ammonia, washing the prepared ferric hydroxide mass till free of chloride, mixing the ferric hydroxide slurry with zinc and manganese chloride solutions, adjusting again the pH of the mixed contents to 10.0 with 5-10% ammonia solution to obtain a slurry, autoclaving the above said slurry at 150-210°C for 2 to 3 hours and recovering Mn-Zn ferrites by known methods. The following examples are given to illustrate how the process of the present invention is carried out in actual practice and should not be construed to limit the scope of the invention. Example-1 82 milliliters of ferric chloride solution containing 120 g/l iron was taken in a one liter beaker and diluted to 250 milliliters. Ferric chloride is used as the starting material as it can be obtained from the dissolution of iron scrap or as pickle liquor from steel industry. 10% ammonia solution is added to adjust the pH to 9. The iron hydroxide precipitate is thoroughly washed to remove chloride. 31.5 ml of manganese chloride solution containing 100 g/l manganese and 20.1 ml of zinc chloride solution containing 100 g/l zinc are added to the iron hydroxide slurry obtained above. The pH of the slurry is again adjusted to 10 with 10% ammonia. The volume of the total contents is made to 600 milliliters. The slurry obtained is heated to 180°C in an autoclave for a period of two hours. The contents are cooled to 70°C, discharged, filtered and washed till free of chloride and ammonium ions. Almost quantitative precipitation of iron, manganese and zinc takes place for the formation of Mn0.65ZnO.35Fe2O4 ferrite (~9.6 milligram ofn Zn and Mn remain in solution). Analysis of the powder X-ray diffraction patterns suggests the formation of pure ferrite phase and transmission electron micrographs of the product so prepared show the formation of very fine spherical shape particles (7-12 nanometer size). High degree of crystallinity is indicated in the patterns. The magnetic measurements give the following values : coercivity He 13.25 Oe, saturation magnetisation Ms 58.28 emu/gram and the remanent magnetisation Mr 1.97 emu/gram. Examples 2 : 82 milliliters of ferric chloride solution containing 120 g/1 iron was taken in a one liter beaker and diluted to 250 milliliters. Ferric chloride is used as the starting material as it can be obtained from the dissolution of iron scrap or as pickle liquor from steel industry. 10% ammonia solution is added to adjust the pH to 9. The iron hydroxide precipitate is thoroughly washed to remove chloride. 31.5 ml of manganese chloride solution containing 100 g/1 manganese and 20.1 ml of zinc chloride solution containing 100 g/1 zinc are added to the iron hydroxide slurry obtained above. The pH of the slurry is again adjusted to 10 with 10% ammonia. The volume of the total contents is made to 600 milliliters. The slurry so obtained is heated to 150°C. The magnetic measurements give the following values : coercivity He 13.75 Oe, saturation magnetisation Ms 46.89 emu/gram and the remanent magnetisation Mr 1.35 emu/gram. Example 3 : 82 milliliters of ferric chloride solution containing 120 g/1 iron was taken in a one liter beaker and diluted to 250 milliliters. Ferric chloride is used as the starting material as it can be obtained from the dissolution of iron scrap or as pickle liquor from steel industry. 10% ammonia solution is added to adjust the pH to 9. The iron hydroxide precipitate is thoroughly washed to remove chloride. 31.5 ml of manganese chloride solution containing 100 g/1 manganese and 20.1 ml of zinc chloride solution containing 100 g/1 zinc are added to the iron hydroxide slurry obtained above. The pH of the slurry is again adjusted to 10 with 10% ammonia. The volume of the total contents is made to 600 milliliters. The slurry so obtained is heated to 210°C. The magnetic measurements give the following values : coercivity He 19.0 Oe, saturation magnetisation Ms 59.25 emu/gram and the remanent magnetization Mr 2.16 emu/gram. Example 4 : Mn0.50Zn0.50Fe2O4 was prepared in the following manner: 82 milliliters of ferric chloride solution containing 120 g/1 iron was taken in a one liter beaker and diluted to 250 milliliters. 10% ammonia solution is added to adjust the pH to 9. The iron hydroxide precipitate is thoroughly washed to remove chloride. 24.0 ml of manganese chloride solution containing 100 g/1 manganese and 28.5 ml of zinc chloride solution containing 100 g/1 zinc are added to the iron hydroxide slurry obtained above. The pH of the slurry is again adjusted to 10 with 10% ammonia. The volume of the total contents is made to 600 milliliters. The slurry so obtained is heated to 180°C in an autoclave for a period of two hours. The contents are cooled to 70°C, discharged, filtered and washed till free of chloride and ammonium ions. Almost quantitative precipitation of iron, manganese and zinc takes place for the formation of Mn0.5Zn0.5Fe2O4 ferrite as 180°C. The magnetic measurements give the following values : coercivity He 13.0 Oe, saturation magnetisation Ms 35.7 emu/gram and the remanent magnetization Mr 1.125 emu/gram. Example 5 : Mn0.35Zn0.65Fe2O4 was prepared by the following method: 82 milliliters of ferric chloride solution containing 120 g/1 iron was taken in a one liter beaker and diluted to 250 milliliters. 10% ammonia solution is added to adjust the pH to 9. The iron hydroxide precipitate is thoroughly washed to remove chloride. 16.6 ml of manganese chloride solution containing 100 g/1 manganese and 36.7 ml of zinc chloride solution containing 100 g/1 zinc are added to the iron hydroxide slurry obtained above. The pH of the slurry is again adjusted to 10 with 10% ammonia. The volume of the total contents is made to 600 milliliters. The slurry so obtained is heated to 180°C in an autoclave for a period of two hours. The contents are cooled to 70°C, discharged, filtered and washed till free of chloride and ammonium ions. Almost quantitative precipitation of iron, manganese and zinc takes place for the formation of Mn0.35Zn0.65Fe2O4 ferrite as 180°C. The magnetic measurements give the following values : coercivity He 14.5 Oe, saturation magnetisation Ms 24.21 emu/gram and the remanent magnetization Mr 0.5 emu/gram. The main advantages of the process are : 1. All the process steps are easy comprising of precipitation and washing steps. 2. The concentration of ammonium chloride in the present process is reduced by separately precipitating the iron and washing the chloride followed by mixing with Mn-Zn chloride solutions and hydrothermal precipitation. The earlier attempts by various investigators to produce ferrites by this technique were not successful as part of zinc dissolves at all pH ranges due to high ammonium chloride concentration in the system and stoichiometric ferrites could not be produced. 3. Most of the chloride associated with ferric chloride is washed prior to hydrothermal treatment results in non corrosive slurry. Therefore, it is easy to chose the material of construction for the autoclave. S.S 316 will serve the purpose. 4. > The experimental conditions can be chosen to obtain Mn-Zn ferrites of different compositions showing difference in the magnetic parameters and particle size. 5. The technique can also be applied to utilize blue dust/ plain steel scrap as a raw material for iron. claim : 1. An improved process for the preparation of Mn-Zn ferrites which comprises preparing aqueous solutions of ferric chloride, zinc chloride and manganese chloride, by known methods adjusting the pH of the ferric chloride to 9.0 to 9.5 so as to precipitate iron as hydroxide using 5-10% aqueous ammonia, washing the prepared ferric hydroxide mass till free of chloride, mixing the ferric hydroxide slurry with zinc and manganese chloride solutions, adjusting again the pH of the mixed contents to 10.0 with 5-10% ammonia solution to obtain a slurry, autoclaving the above said slurry at 1 50-21 0°C for 2 to 3 hours and recovering Mn-Zn ferrites by known methods. 2. An improved process as claimed in claim 1 wherein the iron concentration of ferric chloride solution is 120 g/L. 3. An improved process as claimed in claims 1-2 wherein manganese concentration of manganese chloride solution is 100 g/L. 4. An improved process as claimed in claims 1-3 wherein the zinc concentration of zinc chloride solution is 100 g/L. 5. An improved process as claimed in claims 1-4 wherein the pH of precipitation of ferric chloride solution is maintained at 9.0. 6. An improved process as claimed in claims 1-5 wherein the heating of the slurry is effected at temperature of 180°C. 7. An improved process as claimed in claims 1-6 wherein the heating of the slurry is done for a period of 2 hours. 8. An improved process for the preparation of Mn-Zn ferrites substantially as herein described with reference to examples.

Documents:

811-del-1999-abstract.pdf

811-del-1999-claims.pdf

811-del-1999-correspondence-others.pdf

811-del-1999-correspondence-po.pdf

811-del-1999-description (complete).pdf

811-del-1999-form-1.pdf

811-del-1999-form-19.pdf

811-del-1999-form-2.pdf