Title of Invention


Abstract An improved process for the preparation of high surface area hausmannite (Mn3O4) powder for ferrite comprising of reacting Manganese nitrate with NH4OH at room temperature to obtain Mn(OH)2 precipitate, subjecting Mn (OH)2 slurry to the step of air oxidation, the precipitate was filtered, washed and dried at 120°C to obtain Mn3O4. A process as claimed in claim 1 wherein the precursor is reacted with NH4OH at an alkaline pH between 8-9.An improved process as claimed in claim 1 wherein the air oxidation is carried out in fluidized bed reactor. An improved process as claimed in claim 1 wherein air flow is maintained from 2-5 litre/min. An improved process for the preparation of Mn3O4 substantially as herein described.
This invention relates to an improved process for the preparation of high surface area hausmannite (Mn3 O4) powder.
A good quality of MH3O4 with high surface area is generally used in Mn-ferrites. Commercial grade of Mn3O4 is not suitable for ferrites because of shrinkage problem during sintering which affects the quality and life of ferrite. Pure Mn3O4 with high surface area is difficult to synthesize by the conventional high temperature method. To achieve high surface area it is very essential to produce Mn3O4 at low temperature.
Manganese Oxides are very important compounds generally used in magnetic materials as well as batteries. Since the manganese is having the multiple oxidation states used in many electronics materials. Because of its many easily convertible valency states, it forms one of the most complex oxide systems. The ready valency change of Mn leads to formation of large number of oxides of varying degrees of stability. The possible valency states of Mn gives rise to lower oxides such as Manganese sesquioxide (Mn3O4) & Hausmannite (Mn3O4 & higher oxides like MnO & MnO2. In general the research has been found focused on structural studies of MnO2 & Mn3O4 because of its commercial use in ferrite as well as in batteries.

Few worker (Kuledama et a.l. . Fak. Mosk Gos Univ. 1974, 10, 90-2 (Russ)? Leiat al, J. Solid State Chem., 1980 31(1) 81-93 (Eng)s Mulik et al. Environ. Sc i . Techno). . 1976, 10(7), 668-74 (Eng); Shobaky et,jal. J. Therm. Anal. Calorim, 1998, 51(2), 529-539 (Er»Q); Lagijdz'e et. al. Perekhodnykh Redk Met. .1.978, 3, 126-34
flu»s> have prepared the Mh 0 by thermal decomposition of
; 3 4
othyer mangjanese salts like MnO . Mn(OH) MnNO ) , Mn-a>;al ate
! 4 2, 3 2
using very ; high temperature, Mn 0 is generally prepared by
• 34
reduction qf higher manganese oxides or by thermal decompositon
of divalent Manganous salts (e^g. Nitrate, carbonate or oxalate)
; o in air at ar0und 1000 C. Generally Mn O oxide is a spinel with
• 34
a tetragonsil structure & an actual composition of 2MnO.MnO .
2 o Since Mn 0 is a stable compound up to 1000 C it is generally
34 used in ferrite manufacture. Considering the commercial
application many researches have studied the synethesis of
Hn 0 was hitherto prepared by thermal decompositon of Mn at

o 1100 C for ;68 hrs, in air where the particle size obtained
around 2—3 microns. The manganelse oxide (Mn 0 ) was also prepared
using manganese hydroxide i.e. thermal decomposition of manganese
hydroxide oxide. Few researches (Mulik et.al Environ. Sci Technol . 1976,, 10(7), 668-74 Eng">5 Shobaky et. al . J. Therm Anal. Calorin, 1998 51(2), J&29-539 (Eng.); Lagidze et.al.
Perekhodnykh Redk Met. 1978, 3, 126-34 Russ.) studied Mn 0
3 4
preparation iusing thermal decomposi tons of manganese salts like
manganese su,l, fate and carbonate at high temperature. In this process the pollution problem was indicated due to evolution of
SO and CO . Mn 0 was prepared by MnCl or MnSO H 0 as
2 : 2 34 2 4. 2
starting salts. .MnSO .H O (0.06M) aqueous solution was
4 2 neutralized with NH OH (0.02M) at room temperature under stirring
4 conditions to yield manganese hydroxide. The product was refluxed
for 30 hrs to get the required phase of hydrsted Mn O . The
product was further calcined at higher temperature. The process.
was found to be very time consuming and uneconomical.
The high temperature process is well known process used for the
preparation of Mn O . In this method the raw material used is
3 4 pyrolusite ore MnO contain 60-70%, Fe .11-12% and other heavy
2 metals) which generally purified by leaching and converted in to
respective salts. The Mn-™ salts further roasted in controlled
atmospherefor Mn O .
3 4
Preparation of Mn 0 following conventional high temperature and
3 4 hydrothermal procedure© are well known in the literature. Many
workers (Kenneth Pisarczyk "K'i rk-Othmer" 4th edition V-15 P- 1003;Ulmarms> Encyclopedia of Industrial Chemistry Vol. 16, 131; Yamaroura, «t al , jpn. Kokai Tokyo, Koho-jp 62,30,623 (8730),623) CC1 C01 045/02), 09 Feb. 1987, App1.85/170,890.02 Aug. 19855 S.Ardizzon*, et al Colloids arid Surfaces A i Physicochem. Eng. Aspects 134 (1998) P 305; have studied the conventional high
temperature process. This process is followed by MrtO reduction
at 650 C to obtain MnO and same was partially oxidized for MnQ .
2 o After long heat treatment at 1000 C to Mn 0 was formed Few
3 4 workers (Sheppard et.al. Cream, Bull. 1988, 67, 1656; Mingos et
a.l. Chem.Soc. Rev. ,1.991 20(1) have also prepared Mn O using
3 4 hydro-thermal route at various temperature and time. In this
process th? formation of Mn O via hydroxide with partial
3 4 oxidation. The reset-ion time was varied from S hrs to 72 hrs. at
different pressures. This process had limitations of scale up and consistent quality of the product.
Apart from these processes, the microwave assisted route is another novel method of synthesis (Mingos et.al. Br. Ceram. Ind. 1994, 596; K.J. Rao et.al. Bull. Mater. Sci. 1993,18,447jRichard A. Nyquist et al "Infrared Spectra Of Inorganic Compound."1971> and i gj a very rapidly developing area of research .Microwave assisted synthesis is much faster, cleaner and more economical than the conventional methods. A variety of materials such as carbide, nitride, sulphide complex oxides etc have synthesized by microwaves. Many of these are of industrial and technological importance. An understanding of the mcirowave interaction with materials has been based on the concepts of dielectric heating and the resonance absorption due to rotational excitation, (K.J. Rao et.al. Bull. Mater. Sci 1995,18.447) reviewed the preparation of inorganic: material using microwaves. Microwaves synthesis is still in academic interest & commercial aspects needs to be focused.
The main object of the present invention is to provide a process
for the preparation hsusmannite (Mn 0 ) at low temperature for
3 4 ferrite which obviate? the disadvantages of the prior art and SB
described as mentioned above.
Another object of the present, invention is to provide an improved
process for preparation of high surface area hausmannite (Mn 0 )
3 4 powder 5
Yet another object of the present invention is to provide an
improved p;rocess for preparation of (Mn 0 ) powder using a
3 4 fluidi;?ed bed type reactor.
Still another object of the present invention is to provide an
improved process for preparation of hausmannite (Mn 0 ) powder at
3 4 pH range 7 •»- .1(3.5.
A further object of the present invention is to provide an
imp?"-oved process for preparation of (Mn O ) powder using air
3 4 suspension method.
A still further object of the present invention is to provide an
improved process for preparation of (Mn O ) powder using
3 4 manganese nitrate as a precursor.
Yet a further object of the present invention is to provide an improved process for preparation of high surface area hausmannite
Hn 0 ) powder which is cost effective. 3 4
According to the present invention there is provided sn improved
process for the preparation Mn 0 for ferrite and varistors which
3 4 comprises in reacting a precursor with NH OH to obtain MnNOH)
4 2
precipitate, subjection Mn(OH) slurry to the step of oxidation
to obtain l%i O .
In accordance with the present invention, the low temperature
method hasi been introduced for the preparation of Mn 0 .
3 4 Manganese ritirate MnNG ) of purity about 40.2V; and density 1.99
32 9/cm3) diluted with water The solution was stirred well
and in same solution NH HO was added to get Mn(OH) precipitate.
4 2
MnOH) slurry was subjected to air oxidation in a glass column
provided with sintered disc. The air flow for suspension
mantained 2-5 lit./min. for 10 min. This precipitate was then
filtered and washed with sufficient distilled water. The Mn 0
3 4 0 precipitate was then dried in an oven at 120 C.
Since the Manganese is having many valency states it is very difficult to get particular pure manganese oxide. Controller oxidative and reductive atmosphere is required to produce desired product. The following reactions are involved in the process.
The Mn 0 sample is tested for. MnO by using standard chemical
3 4 ' method. 0.2 gm sample, 2gm sodium oxalste and 0,3 gm Na CO was
2 3 taken in 50 ml distilled water in conical flask. The digestion
was carrieid out; using .1.0XH SO . The same solution was titrated
2 4 against 0.1 N KMnO solution.Pure Mn 0 sample prepared from
4 3 4
conventional method has percent MnO up to 38-405C.
The reaction was carried out at different pH and subsequently the
MnO content were determined as per the above procedure
2 Table.l). It was observed that the MnO content was increased at
high pH whe/re as it was moderate at pH 8—9 which is matching with
the MnO content present in the Mn O i.e. 39. SX. At hie/her pH
2 3 4
the yield MirtO 0 is lower becuase of the oxidation. Table 1 shows
3 4 the effect of pH on the MnO Due to high pH there may be rapid
2 surface oxidation of Mn(OH) The excess- hydroxyl species
2 surrounded by MnOH) taking longer time for drying resulting in
2 to surf ace•oxidation. At lower pH the MnO content was observed
2 less because partial oxidation. Optimum pH was observed around
8-9 where the MnO content was matching with theoretical value.

2.4 Structural characterization of Mn3O4 powder by XRD
Structural characterization of MnsO4 powder was performed by XRD. Table. 2 contains standard reflection parameters for both the presently considered oxides. XRD pattern with: relative intensities of Mn3O4 peaks is being agreement with standard values with pure phase of MnaO4 . From the XRD ( Fig. la & Ib ), it was observed that there was fto presence of Mn (OH)2 peak which was observed in commercial sample prepared by high temperature method.
2.5 Characterization of Powder using SEM.
of the present invention
Fig. 2a and;2b reveals the SEM picture of the standard and - Mn3O4 sample/ respectively. Most of the particles are spherical in shape & having uniform size. The particle size {observed is within the range of 190-200 nm which is less as compare to std. Sample. the clearly shows the higher surface area of MnaO4 which has been confirmed by BET analysis. BET surface area analysis of each sample was carried out and observed 40fli2/gm. This is the first tirne we are reporting the high surface area Mn304 process.
Invention of the present application will be more fully understood by reference to the following examples.

(Table Removed)

The reaction conditions were maintained in the reactor as per the above conditions. The MnOj contefit observed was 39.27%.
Example. 2 :

Sr. No

JOOgm. Mn(NO3)2 + 100 ml. Distilled watier + i80 ml NH3 Soln.

Reaction Conditions
Room Temperature
• pH = 10 TO
• Air =2-5 LPM
• Height of the bed :
• Dia. Of column=
• Time : 10 min


Yield (g)

From these observations it was clear that at slightly alkaline pH (7.5 to 8) yield of the product was low and at highly alkaline pH (10 to 10.5) yield of the product was observed more. At high pH the MnO2 content was observed was more than 40 % which shows the change in phase of Mn3O4. On the basis of these studies the continuous runs were performed between 8 to 9 pH. Example.3-6 reveals the results of the runs carried out at pH 8-9.
Example. 3

(Table Removed)
Example.r-3 reveals that the MnO2content observed was 39.27% and yield was 92 48% at 7.5 - 8 pH where as yield has been enhanced at pH 8-9. At higher pH the MnO2 content observed was more than theoretical value which may be because of oxidation during drying . The product obtained at higher pH required more drying temperature and time which resulting in to MnO2 . Table.2 contains the standard reflection parameters for Mn-oxides. XRD pattern shows that the relative intensities as well as hkl vialues of the Mn-oxide peaks are being in agreement with the standard values. The broadness of the peaks of the samples indicates a low degree of crystallanity . Since the reaction is proceeding through Mn(OH)2, we were suspecting the presence of Mn(OH2 in the product but XRD shows the absence of the same. From the d values and respective intensities major peak is observed at 2.50 (211) which clearly shows the presence of tetragonal structure of the product. Figure 2a ,b,and shows the shape and size of the particles of standard Mn3 O4and prepared by low temperature air suspension method respectively. The standard sample shows the mixed particles with different shapes. Many elongated particles of 3-5 microns in the length and 200-500 nm in diameter were observed in standard sample. Many other shapes of the particles were observed in SEM picture. Fig. 2 b shows uniform pattern of particles where the particles are spherical in shape. The particle size observed was in the range of 190-200 nm which is far less as compared to the standard sample prepared by conventional high temperature method. This clearly shows higher surface area and higher activity of the Mn3O4.
The BET surface area of the samples observed 40 m2/gm where as standard sample of conventional route showed 3 m2/gm. Considering the characteristic of Mn3O4 prepared by conventional high temperature method is entirely different than the present low temperature method. Since Mn is having the variety of possible oxidation states the temperature control becomes critical. Slight variation in temperature leads in to the formation of mixed oxides (Mn2O3, MnO etc.). It is very difficult to achieve

consistency in the product. Due to high temperature the process becomes uneconomical and uneasy to handle where as the present low temperature method gives consistent good quality product with high surfate area and activity. Due to the low temperature, there are less chances of formation of mixed oxides. The process is very simple and easy to handle all parameters to get required
Mri 0 . The process is much cheaper than the conventional high
3 4 temperature* method.
In view ;of the above important aspects of the present investigation the claim® are as follows.

1. An improved process for the preparation of high surface area
hausmannite (Mn304) powder for ferrite comprising of reacting
precursor manganese nitrate with NH40H at room temperature
maintaining pH between 8-9 to obtain Mn (OH)2 precipitate,
subjecting Mn(OH)2 slurry to the step of air oxidation in fluidized
bed reactor, the precipitate was filtered, washed and dried at
120°C to obtain Mn304.
2. An improved process as claimed in claim 1 wherein air flow is
maintained from 2-5 litre/min.
3. An improved process for the preparation Mn304 substantially as
herein described.












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Patent Number 248285
Indian Patent Application Number 942/DEL/2002
PG Journal Number 27/2011
Publication Date 08-Jul-2011
Grant Date 01-Jul-2011
Date of Filing 16-Sep-2002
# Inventor's Name Inventor's Address
PCT International Classification Number C12P 3/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA