TITLE:
High coercivity permanent magnet by Iron ore rejects doping (slime) and its
manufacturing process.
FIELD OF INVENTION:
This invention relates to high coercivity permanent magnet by Iron ore rejects
doping (slime) and its manufacturing process.
BACKGROUND OF THE INVENTION:
In the present scenario every industry is looking for energy efficient product at
low cost, like automobile sector is looking for technology which can reduce the
weight of car without compromising the efficiency and it leads to fuel economy.
Magnetic material with high energy product have linear relationship with fuel
economy. Car has many motors and electronic system having magnets
Reducing the weight of magnet will help in techno-economy of automobile
sector.
Hexaferrites as permanent magnets are best known for their moderate
magnetic properties with low cost. More than 3 lakh tones of BaM hexagonal
ferrites are produced yearly which is 50% of total magnetic materials globally.

Ferrite magnets are being used in magnetic recording, electronic devices and
storage materials. Hexagonal ferrites are the cheapest magnets with moderate
magnetic properties in the category of permanent magnetic materials.
Ceramic magnets are made of ferrites, which are crystalline minerals
composed of iron oxide in combination with some other metal. They are given the
general chemical formula M(FexOy), M representing other metallic elements
than iron. The most familiar ferrite is magnetite, a naturally occurring ferrous
ferrite (Fe [Fe2O4], or Fe3O4) commonly known as lodestone. The magnetic
properties of magnetite have been exploited in compasses since ancient
times. Three basic classes of ferrites are made into magnetic ceramic products.
Based upon their crystal structure, they are the spinels, the hexagonal ferrites,
and the garnets. Spinels have the formula M(Fe2O4), where M is usually a
divalent cation such as manganese (Mn2+), nickel (Ni2+), cobalt (Co2+), zinc
(Zn2+), copper (Cu2+), or magnesium (Mg2+). M can also represent the
monovalent lithium cation (Li+) or even vacancies, as long as these absences
of positive charge are compensated by additional trivalent iron cations (Fe3 +).
The hexagonal ferrites have the formula M(Fe12O19), where M is usually
barium (Ba), strontium (Sr), or lead (Pb). The crystal structure is complex, but it
can be described as hexagonal with a unique c axis, or vertical axis. This is the
easy axis of magnetization in the basic

structure. Because the direction of magnetization cannot be changed easily to
another axis, hexagonal ferrites are referred to as "hard." Garnet ferrites have
the structure of the silicate mineral garnet and the chemical formula
M3(Fe5O12), where M is yttrium or a rare-earth ion. In addition to tetrahedral
and octahedral sites, such as those seen in spinels, garnets have
dodecahedral sites. The net ferrimagnetism is thus a complex result of
antiparallel spin alignment among the three types of sites. Garnets are also
magnetically hard.
In contrast, permanent ferrite magnets are made of hard ferrites, which have a
high coercivity and high remanence after magnetization. Iron oxide and barium
or strontium carbonate are used in manufacturing of hard ferrite magnets. The
high coercivity means the materials are very resistant to becoming
demagnetized, an essential characteristic for a permanent magnet. They also
conduct magnetic flux well and have a high magnetic permeability. This enables
these so-called ceramic magnets to store stronger magnetic fields than iron
itself. They are cheap, and are widely used in household products such as
refrigerator magnets. The density of ferrite magnets is about 5 g/cm3. The most
common hard ferrites are: Strontium ferrite, SrFe12O19 (SrO•6Fe2O3), used in
micro-wave devices, recording media, magneto-optic media,

telecommunication and electronic industry. Barium ferrite, BaFe12O19
(BaO•6Fe2O3), a common material for permanent magnet applications. Barium
ferrites are robust ceramics that are generally stable to moisture and corrosion-
resistant. They are used in subwoofer magnets and as a medium for magnetic
recording, e.g. on magnetic stripe cards. Cobalt ferrite, CoFe2O4 (CoOFe2O3),
used in some media for magnetic recording.
In order to improve the coercivity of Barium ferrite magnets a low cost doping
manufacturing process and technology has been developed by utilization of
slime as a dopant material. The Slime is a byproduct of the steel industry
having constituents like Hematite, Magnetite, Goethite, Silica,
Managnese oxide and Alumina predominantly. The complete invention is
described in below sections of this application.
OBJECTS OF THE INVENTION:
An object of the present invention is to propose a slime doped ferrite magnet
having a chemical formula BaO•2(FeO).n(Fe2O3).
Another object of the present invention is to propose a method for producing slime
doped barium ferrite magnets.

Still another object of the present invention is to propose an economical method to
prepare the slime doped ferrite magnet.
Further, object of the present invention is to propose a high coercivity
characteristic which is more than 3500Oe.
Still further object of the present invention is to propose slime doped barium ferrite
magnetic with an average particle size of less than a micron.
BRIEF DESCRIPTION OF THE INVENTION:
This invention relates to slime doped barium ferrite magnets having chemical
formula as BaO-2(FeO)-n(Fe2O3) with an appropriate range of n-value in said
formula between 6 and 9; a sintered body of said formula furthermore having
an average particle size of less than 5um and the maximum coercivity, of more
than 3500Oe.
In accordance with this invention there is also provided the method for
producing slime doped barium ferrite magnets comprising the steps of:
preparing a mixture of powdered BaCO3 and Fe2O3 with a mol ratio in a range
of 5 and 9;

adding 10-50% of slime to the said mixture;
subjecting the mixture to the step of calcinations;
pulverizing the calcined mixture.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Fig 1: shows the sketch for process of preparing permanent magnets.
Fig 2: shows the hysteresis loop of the experiment 1
Fig. 3: shows the hysteresis loop of the experiment 2
Fig. 4: shows the hysteresis loop of the experiment 3
Fig 5: shows the hysteresis loop of the experiment 4
Fig 6: shows the hysteresis loop of experiment 5
Fig 7: shows the barium ferrite hysteresis loop of the experiment 6

Fig 8: shows XRD pattern of different phase of slime
Fig 9: shows XRD pattern of different phase of experiment 1
Fig 10: shows XRD pattern of different phase of experiment 2
Fig 11: shows XRD pattern of different phase of experiment 3
Fig 12: shows XRD pattern of different phase of experiment 4
Fig 13: shows XRD pattern of different phase of experiment .5
Fig 14: shows XRD pattern of experiment 6
DETAILED DESCRIPTION OF THE INVENTION:
In this invention, a process and method has been proposed to get high coercivity
slime doped barium ferrite magnetic material. The slime doped magnetic
materials has more than 80% improvement in coercivity of hysteresis loop. The
slime comprises hematite, magnetite, silica, alumina and goethite predominantly.
The phase evolution due to dopant is analyzed by XRD and change in
magnetic property by vibrating sample magnetometer.

According to the invention, one or more of these objectives may be achieved
by providing a method for producing slime doped barium ferrite magnets,
comprising the
steps of:
- providing a chemical composition of the initial homogenous pre calcined
material;
- calcination of above material by heat-treatment;
- crushing of calcined material
In an embodiment of the invention the further component in the method is mixing
and pulverization to reduce the size of particle and homogenous distribution.
A temperature of 1150°C is needed for complete calcination. The flow chart of
the process is mentioned below in fig 1.
Pulverising: A pulveriser is mechanical device for the grinding of many
different types of materials. Here in our work we have used pulveriser to grind
the slime, iron oxide and BaCO3. Also these grinding increases the surface
area of these materials so that interaction surface between these three
materials will be more in during heat treatment step. Also this step helps in
homogenous mixing of these three components.

Heat treatment (Calcination): The mixture is calcined in electric furnace at a
high temperature. In this process, chemical reaction takes place and a weight
loss of around 8-10% occurs and expelled in the form of CO2 from the system.
Calcination serves to convert the mix into the hexaferrite phase in the form of
crystals. The sample was calcined in static air, the formation of ferrite taking
place, indicating that the reaction was completed. The calcination temperature
has effect on the phase formation. The temperature for heat treatment was
1100-1300°C and residence time was 1 -4hr.
Grinding: This step is to done by motar and pestle to break bigger lumps or
sintered part to small size.
Pulveriser: This step needs to be done for converting the ferrite in to fine
particles for characterisation and further processing.
The present invention to provide the ferrite magnet, in the conventional
ferrite which is formulated as Ba0.2(FeO).n(Fe203), and the
manufacturing process thereof by which said magnet maintains cost-
performance and high coercivity characteristics recognized with the
conventional magnet and furthermore exhibits the maximum coercivity

products more than 3500Oe. In order to achieve the aforementioned
objective, slime is admixed to raw powder which is a previously prepared
mixture of BaCCb and Fe2O3 under a given condition such that n-value in the
above formula is in a range between 5 and 9. Before calcining the said
mixture is pulverized to have an average particle size less than a micron.
After pulverization the material is mixed well for homogenous distribution of
dopants and barium carbonate. After calcining the said mixture, is
furthermore mixed and pulverized to have an average particle size of less
than a micron. Hence, the high coercivity permanent ferrite, which has not
been realized before, can be produced easily and at low cost.
In this invention a process and method to get high coercivity slime doped
barium ferrite magnetic material has been proposed. The slime doped
magnetic material has more than 80% improvement in coercivity of hysteresis
loop. The slime comprises hematite, magnetite, silica, alumina and goethite
predominantly. The alumina, silica and calcium mainly contribute to enhance
the coercivity. The phase evolution due to dopant is analyzed by XRD and
change in magnetic property by vibrating sample magnetometer.

According to this invention there is provided an slime doped barium
ferrite composition of permanent magnet for higher coercivity:
Slime composition: 10-50% (slime composition is mentioned in Table 1)
iron oxide composition: 50-90%
barium Carbonate: 0-25
EXAMPLES:
The invention will now be further described by way of examples undertaken
with doping of slime in barium ferrite. The six experiments were performed as
per process chart given in Fig 1. The different experiment composition is given
in table 1 and their hysteresis loops are given in Fig 2-7. The XRD patterns of
experiments 1 to 6 and slime is given in Fig 8-14. The presence of barium
dodecairon(lll) oxide phase confirms the synthesis of hexa ferrite during
calcinations heat treatment.
In experiment 1 the dopant slime is used 50% with 50 gm of Iron oxide(alpha-
Fe2O3) the coercivity in this case is 1900 Gauss. The experiments are done in
reducing the concentration of slime in barium ferrite and in experiment 5
where the slime is used 10 gm gives exceptional coercivity of 3500 Gauss.

WE CLAIM:
1. Slime doped barium ferrite magnets haying chemical formula as BaO-
2(FeO)-n(Fe2O3) with an appropriate range of n-value in said formula
between 6 and 9; a sintered body of said formula furthermore having an
average particle size of less than 5um and the maximum cdercivity, of
more than 3500Oe.
2. The method for producing slime doped barium ferrite magnets
comprising the steps of:
preparing a mixture of powdered BaCO3 and Fe2O3 with a mol ratio in a
range of 5 and 9;
adding 10-50% of slime to the said mixture;
subjecting the mixture to the step of calcinations;
pulverizing the calcined mixture.
3. The method as claimed in claim 2, wherein the average particle size of
less than 5µm.

4. The method as claimed in claim 2, wherein preferably 10-15% of slime
is added having the following chemical composition:
Oxides - % dry
Fe3O4 - <0.1
Fe2O3 - 80.72
FeO - 3.0
Al2O3 - 6.65
SiO2 - 5.74
P2O5 - 0.35
K2O - 0.12
Na20 - 0.11
MgO - 0.10
CaO - 0.20
MnO - 0.10
TiO2 - 0.30
V2O5 - 0.10
5. The method as claimed in claim 2, wherein the temperature range for
calcinations is 1100 to 1300°C and the time taken is 1 to 4 hrs.
6. The method as claimed in claim 2, wherein the step of calcination
converts the mix into hexaferite phase in the form of crystals.

7. The method as claimed in claim 2, wherein the preferred temperature
range is 1150°C.