|Title of Invention||
AN IMPROVED PROCESS FOR THE PREPARATION OF GAMMA FERRICOXIDE
|Abstract||An improved process for the preparation of gamma-ferric oxide by heating the Fe3O4 having nano-meter particle size of 8 to 20 nm in presence of air at a temperature of 80°C to 125°C for a period of 2 to 10 hours till brown coloured gamma-ferric oxide is obtained.|
|Full Text||This invention relates to an improved process for the preparation of gamma ferric oxide (γ-Fe2O3). The γ-Fe2O3 thus prepared has tetragonal structure. Gamma ferric oxide is widely used in magnetic recording materials in audio and video applications for tape recorders, cassette records as well as for video tapes.
Gamma ferric oxide (γ-Fe2O3) is conventionally prepared starting from FeSO4.7H20 and sodium hydroxide. FeSO4.7H2O is dissolved in water. Sodium hydroxide solution and ferrous sulphate solutions are mixed and agitated to provide new surface of the mixture exposed to the atmosphere. At the same time FeSO4.7H20 and scrap iron are agitated in enough quantity of water at 60°C which form a green mass. This is added to the above material and air is bubbled through the resulting mass at 60°C. A chemical analysis shows Fe2O3.H20 product showing 86% Fe2O3 and 12% H2O. This is further filtered, washed and dried at 100°C. Filter cake is crushed and hydrogen is passed through the crushed material at 399°C. The amount of water vapour released in large volume drops of substantially giving a black coloured powder of chemical formula Fe3O4.
It is converted to gamma ferric oxide by passing air continuously at a temperature of 150 to 315°C. The gamma ferric oxide made by the above process has the familiar tan colour of tape coating. Its coercivity is about 2750e.
There are various other processes other than that mentioned above, given in the literature for the preparation of gamma ferric oxide (γ-Fe2O3)
starting from a-Fe2O3/a-FeO(OH) with a solution of phosphoric acid ester, drying at 100°C, reducing to Fe3O4 in H2 atmosphere at 380 to 500°C and finally oxidizing in a
N-atmosphere at 250°C. (Ger. Patent 2,250,643, 18th Nov. 1976) or by reducing acicular goethite (a-FeO(OH)) at 300 to 700°C and further oxidizing it to gamma ferric oxide (Jap. Patent 05,335,126 (93,335,126) (CI. Ho. 1F1/11), 17th Dec 1993) or by using ferrous oxalate and ferric oxalate in the ratio of Fe3O4 and thermally decomposing to form γ-Fe2O3 (Mater Letter 1994, 20(3-4), 143) or by the decomposition of ammonium ferric oxalate hydrate at 275°C to form γ-Fe2O3 (J. Anal. Appl. Pyrolysis 1995,31,157) or by the decomposition of N2H5Fe(N2H3COO)3. H20 (Hydrazinium iron hydrazino carboxylate) at the temperature of approximately 200°C or by the decomposition of (N2H3COO)2(N2H4)2 (Iron hydrazino carboxylate hydrazinate) at approx. 200°C (J. Mater. Sci. Lett. 5 (1986) 221).
The synthesis of the complexes given in the last reference involves many steps (Proc. Ind. Acad. Sci. (Chemical Sciences), 95, No. 4, Oct 1985, 345). The above mentioned processes have the following disadvantages. The above processes, in general, involve the synthesis of ferrosoferric oxide which needs the temperature of approximately 400 to 500°C. The next step involves the oxidation of Fe3O4 at around 250°C in air/nitrogen atmosphere to form (-ferric oxide. Other methods mentioned above require the formation of organo metallic complexes necessitating various steps to get the desired complex compounds.
The main objective of the present invention is to prepare γ-Fe2O3 by avoiding the drawbacks of hitherto known processes described above.
Another objective of the present invention is to get designed γ-Fe2O3 at low temperature of 80°C as compared to higher temperatures indicated in the hitherto process.
Still another object of the present invention is to use Fe3O4 having characteristics such as particle size in the range of nanometers and higher surface area. More particularly Fe3O4 employed in the process of the present invention is prepared by the process disclosed in our co-patent application No. 3695/Del/98 "An Improved Process For The Synthesis Of Ferrosoferric Oxide (Fe3O4)". This process involves the reaction of iron salts such as chlorides, nitrates and sulphates with hydrazine hydrate at room temperature.
Accordingly the present invention provides an improved process for the preparation of gamma-ferric oxide (γ-Fe2O3) which comprises heating the Fe3O4 having nano-meter particle size of 8 to 20 nm in presence of air at a temperature of 80°C to 125°C for a period of 2 to 10 hours till brown coloured γ-Fe2O3 is obtained.
The process for the preparation Fe3O4 involves following steps:
Ferric chloride anhydrous is dissolved in distilled or deionised water with a concentration 0.01 M to 5 M.
Hydrazine hydrate is diluted to various required percentages varying from 50 to 90%.
Hydrazine hydrate solution is added to ferric chloride solution drop by drop.
The mixture is stirred continously with mechanical stirrer to mix hydrazine hydrate uniformly in the solution.
Required amount of hydrazine hydrate is added to get the pH from 7 to 10.
Pure jet black precipitate of Fe3O4 is observed in the solution.
Solution is filtered and washed with hot water to remove chloride/ sulphate ions and excess hydrazine hydrate.
Precipitate is dried under vacuum or sun dried. Approximately 92 to 96% yeild was obtained by this method.
The above procedure was used to prepare ferrosoferric oxide with ferrous chloride, ferrous sulphate and ferric sulphate solution with above mentioned concentration.
The process of the present invention comprises of following steps:
Ferrosoferric oxide prepared as above is heated at 100 to 150°C by passing air in a suitable container such that the fresh surface comes in contact with air inturn producing gamma ferric oxide. Gamma ferric oxide obtained by the above method is characterized by XRD, Moessbauer spectroscopy, IR and magnetic measurements indicating the formation of y-
XRD studies indicated the total formation of γ-Fe2O3 with particle sizes of 8 to 20 nm with different concentrations of salt solutions and hydrazine hydrate with different dilutions.
The process of this invention is illustrated by the following examples. However, this should limit the scope of the invention.
EXAMPLE : 1
This example illustrates the process for the preparation of Fe3O4 to be used in the present invention.A solution of 0.5 M concentration of FeCI3 solution was prepared by dissolving 21.02g of anhydrous FeCI3 in 260 ml of distilled water. 80%
Hydrazine hydrate was prepared by diluting 99% of hydrazine hydrate. Approximately 35 ml of 80% of hydrazine hydrate was added drop by drop to the above FeCI3 solution. The solution was stirred contineously by a mechanical stirrer till 80% hydrazine hydrate is added completely. Black precipitate of Fe3O4 is formed during addition. The said solution was filtered through Whatman filter paper No. 42. The precipitate was washed thoroughly with hot water number of times for the total removal of chloride ions and excess hydrazine hydrate.
The precipitate is dried in vacuum dessicator at room temperature or sun dried in a petri dish to get Fe3O4 which converts to γ-Fe2O3 on further heating at 125°C. Roughly 96 to 98% product yield is obtained by this method. XRD indicated only the presence of γ-Fe2O3. Particle size was of the order of 13 nm. IR & moessbauer spectra confirmed the formation of γ-Fe2O3. Saturation magnetization determined by oscillation pendulum method gave the value of 60 Gauss cm3/g at room temperature (~30°C) and coercivity 1570e. The value is slightly less compared to the literature value due to the very fine particle size of gamma ferric oxide.
EXAMPLE : 2
The precipitate of Fe3O4 thus obtained in Example 1 is subjected to further heating at 125°C. Roughly 83% product yield is obtained by this method. XRD indicated only the presence of γ-Fe2O3. Particle size was of the order of 10 nm. IR & moessbauer spectra confirmed the formation of γ-Fe2O3. Saturation magnetization determined by oscillation pendulum method gave the value of 62.2Gausscm3/g at room temperature (~30°C) and coercivity 183.40e. The value is slightly less compared to the literature value due to the very fine particle size of the gamma ferric oxide.
EXAMPLE : 3
The precipitate of Fe3O4 obtained as in Example 1 is converted to y-Fe2O3 by further heating at 125°C. XRD indicated only the presence of y-Fe2O3. Particle size was of the order of 13nm. IR & moessbauer spectra confirmed the formation of γ-Fe2O3. Saturation magnetization determined by oscillation pendulum method gave the value of 62Gausscm3/g at room temperature (~30°C) coercivity 211 60e. The value is slightly less compared to the literature value due to the very fine particle size of the gamma ferric oxide.
Thus the improved process given under this invention has the following advantages.
Synthesis of Fe3O4 as a first step is carriedout at room temperature, which is converted to gamma ferric oxide by just drying in air atmosphere at a suitable temperature of at least 80°C.
We claim :
1. An improved process for the preparation of gamma-ferric oxide (-Fe2O3)
which comprises heating the Fe3O4 having nano-meter particle size of 8 to 20
nm in presence of air at a temperature of 80°C to 125°C for a period of 2 to
10 hours till brown coloured -Fe2O3 is obtained.
2. An improved process for the preparation of gamma-ferric oxide (-Fe2O3)
substancially as herein described with reference to the examples.
|Indian Patent Application Number||3695/DEL/1998|
|PG Journal Number||38/2012|
|Date of Filing||09-Dec-1998|
|Name of Patentee||COUNCIL OF SCIENTIFIC & INDUSTRIAL RESEARCH|
|Applicant Address||RAFI MARG, NEW DELHI-110001, INDIA.|
|PCT International Classification Number||C07C|
|PCT International Application Number||N/A|
|PCT International Filing date|