Advanced Ceramic Processing 1st Edition Adel Mohamed Updated 2025
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ISBN-10: 953-51-2203-7
ISBN-13: 978-953-51-2203-6
Preface
http://dx.doi.org/10.5772/61026
Abstract
The book chapter mainly deals with the microwave sintering of high quality crystals
of La2MMnO6 (M = Ni or Co) ceramics. Double perovskite La2MMnO6 (M = Ni or Co)
ceramics with average particle size of ~65 nm were manufactured using microwave
sintering at 90°C for 10 min in N2 atmosphere for the first time. The morphology,
structure, composition, and magnetic properties of the prepared compacts were
characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM),
transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy
(EDX), infrared spectroscopy (IR and FTIR), and physical properties measurement
system (PPMS). The corresponding dielectric property was tested in the frequency
range of 1 kHz–1 MHz and in the temperature range of 300–600 K, and the ceramics
exhibited a relaxation-like dielectric behavior.
1. Introduction
Microwave sintering (MWS) is emerging and an innovative sintering technology for process‐
ing of ceramic materials and is commonly related with volumetric and uniform heating. MWS
is one of the exciting new fields in material science with vast potential for preparation of novel
and/or nanostructured ceramics/materials. Microwave heating has some important benefits
2 Advanced Ceramic Processing
over normal heating for ceramic processing, including reduced processing time, higher energy
efficiency, selective and controlled heating, environmental friendliness, and improved product
uniformity and yields. Microwave processing of materials is a relatively new technology that
can be used in wide range of different materials such as ceramics, ferroelectrics, oxides, metals,
and composites [1–10].
The effect of microwave radiation on the processing of several ceramic materials such as
magnetic materials, superconducting materials, dielectric materials, metals, polymers,
ceramics, and composite materials offers numerous benefits over conventional heating
techniques. These benefits include time and energy savings, volumetric and uniform heating,
considerably reduced processing time and temperature, improved product yield, fine micro‐
structures, improved mechanical properties, lower environmental impact, reduction in
manufacturing cost, and synthesis of new materials [11].
Microwave sintering has developed in recent years as a promising technology for faster,
cheapest and most environmental-friendly processing of a wide variety of materials, which
are regarded as significant advantages over conventional sintering procedures. Microwave
radiation/heating for sintering of ceramic constituents has recently appeared as a newly
motivated scientific approach [5].
Microwave sintering approach has unique advantages over conventional sintering methods
in many respects. The essential difference in the conventional and microwave sintering
processes is in the heating mechanism (Figure 1). In microwave heating, the materials them‐
selves absorb microwave energy and then transform it into heat within the sample volume
and sintering can be completed in shorter times. In microwave sintering, the heat is generated
internally within the test sample due to the rapid oscillation of dipoles at microwave frequen‐
cies [12]. The contribution of diffusion from external sources is lesser. The internal and
volumetric heating makes the sintering rapidly and uniformly. The heat generated through
conventional heating is generally transferred to the sample via radiation, conduction, and
convention [13]. This process takes longer duration for sintering the materials and causes some
of the constituents to evaporate. This may lead to modify the desired stoichiometry and grain.
Due to the energy efficient nature of microwave heating, there is a great opportunity for the
application of microwaves to process metal based materials to couple the many gains of
microwave heating. Recently, microwaves energy has been successfully used in different
composites, metal, ceramics, melting of metals and metal ores, joining or brazing of metals,
and heat treatment of metals [17].
The microwave energy is highly versatile in its application in the field of communication, and
it still dominates almost all communications in space and mobile or cordless phone technology
involves microwave frequencies. However, other than this communication, microwave energy
has found its use for a variety of applications including rubber products industry, food
processing, wood/paper/textile/ceramic drying, pharmaceuticals, polymers, printing materi‐
als, and biomedical fields over the past 50 years. These applications involve low temperature
(<500°C) utilization of microwaves. The high temperature (> 800°C) applications of micro‐
waves are a rather recent phenomenon.
Many researchers have reported that microwave heating is relatively faster than the conven‐
tional heating processes. This faster speed is manifested as a reduction in the densification time
of ceramic powder compacts, often allied to lower sintering temperatures [7]. Generally, the
synthesis kinetics and sintering materials are apparently upgraded by two or three orders of
magnitude or even more when conventional heating is switched for microwave heating [18].
Microwaves are electromagnetic waves with the electromagnetic radiations in the frequency
band of 300 MHz to 300 GHz, and their corresponding wavelength between 1 m and 1 mm
can be used successfully to heat many ceramic materials. Since most of the microwave band
is used for communication purpose, the Federal Communications Commission has allocated
only very few specific frequencies for industrial, scientific, and medical applications. A major
portion of these microwave used in the communication sector and only certain frequencies,
viz., 0.915, 2.45, 5.85, and 21.2 GHz, are chosen for medical and industrial applications. Among
these allowed frequencies, 2.45 GHz is the most common microwave frequency used for
industrial and scientific applications. The interaction and heating generation of ceramics under
microwave field depends on the dielectric, magnetic, and conductive loss of the material and
temperature dependent parameters.
The ability of a material to be heated in microwave field depends on its dielectric properties,
characterized by the dielectric complex constant ε*:
4 Advanced Ceramic Processing
Dielectric permittivity ε′ represents the material capacity to store electromagnetic energy and
loss factor ε″ to dissipate it.
The dielectric constant of a material varies with its temperature, frequency, and composition.
The power P absorbed in the material is proportional to the loss factor ε″, the frequency f [Hz],
and the electric field intensity E [V/m]:
P = 2 Pf e 0e '' E2 (2)
(or)
e ''
tan d = , (4)
e'
Eq. (3) shows that for a fixed value of electric field (E), the power in microwave absorbed in
the material mass is proportional to the frequency (f) (which is practically 2.45 GHz), the
dielectric permittivity (ε′), and loss factor (ε″) (through the loss tangent tan δ), which vary
with the materials temperature and humidity in their turn.
The diffusion of electromagnetic power into the absorber is characterized by skin depth (D)
and expressed as
D = (p f ms )
-1/ 2
(5)
where μ and σ are magnetic permeability and electrical conductivity and f is the frequency,
respectively.
The effective penetration depth decreases with increase in frequency which in turn causes less
heating. Hence, a suitable combination of parameters in Eqs. (2) and (4) is required for
achieving optimum coupling. It can be inferred from this discussion that low dielectric loss
materials take longer time and high dielectric loss materials take shorter duration in the
microwave sintering.
On a microscopic scale, the phenomenon of dielectric heating is the effect of impurity dipolar
relaxation in the microwave frequency region. When the vacancy jumps around the impurity
Microwave Fast Sintering of Double Perovskite Ceramic Materials 5
http://dx.doi.org/10.5772/61026
ion to align its dipole moment with the electric field the internal friction of the rapidly
oscillating dipole cause a homogeneous (volumetric) heating. Where the maximum absorption
of microwave energy at the frequency or temperature at which the loss factor (tan δ) attains
its maximum. This is equivalent to an elastic relaxation resulting in damping of mechanical
vibrations in solids.
The efficiency of the microwave dielectric heating is dependent on the ability of a specific
material (powder, solvent, or reagent or anything else) to absorb microwave energy and
convert it into heat. The heat is generated by the electric component of the electromagnetic
field through two main mechanisms, i.e., dipolar polarization and ionic contribution [19].
According to the electromagnetism, the effect of a material upon heat transfer rates is often
expressed as
-10 '' 2
DT 0.56 ´ 10 e eff fE
= (6)
t r Cp
where εeff'' is the effective relative dielectric loss factor, f is the frequency of microwave, E is the
magnetic fields of microwave within the material, ρ is the mass density of the sample, and CP
is the isotonic specific heat capacity [19]. In this case, the energy efficiency can easily reach 80–
90% utilization and higher than the conventional heating methods [20, 21]. However, the
essential nature of the interaction between microwaves and reactant molecules during the
preparation of materials is fairly uncertain and speculative.
In recent years, microwave sintering has shown significant advantages against conventional
sintering for the synthesis of ceramic materials. Microwave sintering has attained worldwide
attention due to its major advantages against conventional sintering methods, especially in
ceramic materials.
Microwave sintering can significantly shorten the sintering time leading to consume much
lower energy than conventional sintering.
There are major potential and real advantages using microwave energy for material processing
over conventional heating. These include the following:
Now microwave processing has been found that this technique can also be applied as effi‐
ciently and effectively to powdered metals as to many ceramics. Finally, The MWS operational
expenses are less than 50–80% to the conventional sintering techniques. The MWS technique
works 20 times faster than the conventional sintering method and takes only few minutes for
processing than the conventional ones (takes hours).
Multiferroic materials exhibits both ferroelectric and magnetic in nature and have much
attracted research interest due to their potential application in multistate data storage and
electric field controlled spintronics. Among all the studies related to the materials, transition
metal oxides with perovskite structure are noteworthy [22, 26].
Multiferroic materials with double-perovskite structure ( AA ' BB 'O6) are solid solutions of two
perovskites: ( ABO3) and ( A ' B 'O3). In ( AA ' BB 'O6), A and A’ represent alkaline rare earth cations
(La, Y, and Ce), while B and B’ are transition metal cations (Ni and Co). If A and A′ represent
the same chemical element, the double perovskite has the general formula ( A2 BB 'O6) and the
crystal structure of A2 BB 'O6 -type perovskite, as shown in Figure 2. Alkali-earth and lanthanide
(smaller ion) ions are alone usually occupied in the A site [27, 28]. If the A ion is too small, the
common expected distortions are cation displacement with BO6 and octahedral ones [29].
The most representative ( A2 BB 'O6) ferromagnetic double perovskites are La2NiMnO6 [30–33],
La2CoMnO6 [5, 34, 35], La2BMnO6 [36–48], and La2FeMnO6 [41, 42].
Figure 2. Crystal structure of A2BB’O6 type perovskite. The spheres at A and A′-site are for La and at B′-site are for Ni,
Co. The network of corner-sharing BO6 octahedra isare shown where oxygen atoms are in the corner of octahedra.
Microwave Fast Sintering of Double Perovskite Ceramic Materials 7
http://dx.doi.org/10.5772/61026
La2NiMnO6 (LNMO) has gained more attention as a rare example of a single-material platform
with multiple functions, such as ferromagnetic (FM) semiconducting properties up to room
temperature, magnetocapacitance, and magnetoresistance effects. The spin lattice coupling
characteristics of LNMO exhibits a larger magnetodielectric (MD) effect close to room tem‐
perature. It has been well documented that the spins, electric charge, and dielectric functions
in LNMO are turned by magnetic or electric fields. LNMO is considered as an FM semicon‐
ductor and shows Curie transition temperature (Tc) very close to room temperature. This
property in LNMO makes the Ni2+ and Mn4 ions ordered and occupied the centers of BO6
(corner shared) and B′O6 structures respectively. This arrangement leads to the distribution of
ideal double perovskite.
Among them, double perovskite La2NiMnO6 (LNMO) and La2CoMnO6 (LCMO) ceramics are
attractive due to their impressive properties and potential on industrial applications [30–33,
42, 43]. LNMO is a ferromagnetic semiconductor with high critical temperature of Tc~280 K,
which may be used in commercial solid-state thermoelectric (Peltier) coolers [42]. LCMO is
also a ferromagnetic semiconductor with critical temperature of Tc ~230 K [35–37]. Several
crystal structures have been identified, and it is confirmed that the ferromagnetic semicon‐
2
ductors LNMO and LCMO with high Tc are P1/n monoclinic structure, in which octahedra with
Ni (or Co) and Mn centers alternately stacking along (111). Recent reports indicate LNMO and
LCMO have considerable magnetodielectric effects at room temperature, which is very useful
for future electronic device [29, 35, 44, 45].
The double perovskites La2MMnO6 (M = Co and Ni) are one of the most commonly occurring
and important in all of materials science because they can exhibit novel magnetic, electric, and
optical properties [28–44]. La2MMnO6 crystallizes in a double perovskite structure with rock
salt configuration of MO6 and MnO6 octahedra. The ordering of M2+ and Mn4+ gives rise to 180°
super exchange interactions based on Goodenough–Kanamori rules and consequently high
ferromagnetic Curie transition temperature [43].
It is familiar that the properties of double perovskite compounds are strongly influenced by
the materials composition and microstructure, which are sensitive to the preparation technique
employed for their synthesis [46]. Various synthesis techniques such as sol–gel [30, 32, 35],
coprecipitation [31], solid-state reaction method [33, 34], microwave sintering process [5],
molten-salt synthetic process [26, 27] sol-gel autocombustion [41], and chemical solution
deposition method [47] have been reported in the preparation of double perovskite com‐
pounds. Each of the techniques has its own merits and limitations. For instance, conventional
sintering is a simple and relatively cheap method with a long holding time (several hours),
formation of lots of undesirable intermetallic compounds, and nonhomogeneous pore-size
distribution. In the recent years, microwave sintering has emerged as a new sintering method
for ceramics, semiconductors, metals, and composites.
8 Advanced Ceramic Processing
Microwave sintering (MWS) technique has gained a lot of significance in recent times for
materials (metals, composites, ceramics/nanoparticles) synthesis and sintering mainly because
of its intrinsic advantages [5] such as rapid heating rates, reduced processing times, substantial
energy savings novel and improved properties, finer microstructures, and being environmen‐
tally more clean. Therefore, it is viewed as one of the most advanced sintering techniques in
material processing [5, 48] and improved physical and mechanical properties [7]. It has been
shown that microwave sintering technique may provide enhanced densification in sintering
of metal, oxides and non-oxide ceramics [5, 48, 49, 50].
However, to the best of our knowledge in the open literature, there have been only a few reports
so far on the fabrication of double perovskite nanoparticles by microwave sintering approach
[5, 51]. The purpose of the current chapter will focus on fabrication of the double perovskite
La2MMnO6 (M = Ni, Co) ceramics and in order to further improve their magnetic and dielectric
properties for practical spintronic applications through microwave sintering approach.
2. Experimental procedure
2.1. Materials
All the chemical reagents were of analytical pure grade (99.99%) and used without further
purification. The versatile chemical coprecipitation–microwave sintering process [15] em‐
ployed in present investigation is two-step process which consists of coprecipitation method
is the first step of synthesis followed by microwave sintering in second half of experiment.
High-purity La(NO3)3.5H2O (Merck), Ni(NO3)2.6H2O (Sigma-Aldrich), Co(NO3)2.6H2O
(Sigma-Aldrich), and Mn(NO3)3.4H2O (Sigma-Aldrich) were used as starting materials. In a
typical experimental process, the high purity stoichiometric amounts of La(NO3)3.5H2O, Ni/
CO(NO3)2.6H2O, and Mn(NO3)3.4H2O were dissolved in appropriate amounts of deionized
water and magnetically stared vigorously for 2 h at 80°C. The ammonia solution was used
until to get 8.5 PH value. The stirring will continue for about 30 min, and the suspension was
ball milled for about 24 h with ethanol as a milling media. The reactants were to be mixed well
and then dried at 80°C in a cabinet drier for 24 h to obtain precursor powder sample. Then the
powder was subjected to microwave sintering under uniform heating to get dense ceramics.
Further, In order to achieve pure double perovskite phases, the precursor samples were put
into 2.45 GHz, 6 kW continuously adjustable microwave equipment (HAMiLab-HV3, Syno-
Therm), the maximum operating temperature up to 1400°C, and 0.5–3 kW. The multimode
Microwave Fast Sintering of Double Perovskite Ceramic Materials 9
http://dx.doi.org/10.5772/61026
microwave furnace consists of a cubical stainless steel chamber with a side of 30 cm. Two
magnetrons (microwave source), each with a maximum rated power of 1100 watts, are situated
opposite to each other. A box made of alumina, zirconia, and silica mixed cardboard is used
as a thermal insulator. The material is positioned in the center of box and is surrounded by
silicon carbide (susceptor) plates.
Figure 3. Experimental setup of multimode microwave furnace [3] (a) and Ssusceptor (b).
Figure 3. Experimental setup of multimode microwave furnace (a) and Susceptor (b).
During the sintering process, the microwave sintering chamber was filled with high purity
nitrogen gas flow (99.999%). An adjustable programmed electrical control system was used to
During the sintering process, the microwave sintering chamber was filled with high purity
deliver the required energy to the sample. The employed heating chamber was made up with
nitrogen gas flow (99.999%). An adjustable electrical control system was used to control the
stainless steel double walled tubular cavity with water-cooled facility, and the maintained
energy to be delivered to the sample at a programmed rate. The heating chamber was a
processing temperature is about 1400°C. A high purity quartz crystal cylinder arrangement is
available inside
double the stainless
walled, chamber,steel,
where thecooled
water samples werecavity
tubular loadedthatfor processing;
stayed the temperature
cool to touch, even
of the sample was measured
when processing usingwas
temperature infrared pyrometer
∼1400°C. during
Inside the the MW
chamber was asintering. The
high purity SiC plates
quartz
surrounded
crystal in the crucible
cylinder were served
where samples as susceptors
were loaded and provide
for processing. During initial
the MW heating to of
sintering bethe
compact
disc samples.
samples, Once the materials
temperature receivedusing
was measured absorb ansufficient MW heat including
infrared pyrometer. The crucible thewas
core and
will get uniform heating.
surrounded The secondary
by SiC plates, which act aspurpose of SiC
susceptors is to maintain
to provide the surface
initial heating temperature.
of the compact
The crucible was positioned at the center of the furnace so it provides strong MW radiation.
disk samples. Once the materials are sufficiently hot they will couple/absorb MW effectively
The green compacted disks for heated at 900°C for 10 min in atmospheric N2 ambient temper‐
and will get heated directly, including the core. The secondary purpose of SiC is to maintain
ature and heating rate of 20°C/min is maintained by varying magnetron power between 1000
the surface temperature. The crucible was positioned at the center of the furnace, where the
and 2500 W followed by normal frequency cooling.
MW radiation is the strongest. The green compacted disks were heated in atmospheric N2
2.3. Characterization and property
ambient at temperature of 900°C measurements of La2MMnO6
for 10 min at a heating (M = Ni,
rate of 20°C/min byCo) ceramics
varying the
magnetron power between 1000 and 2500 W followed by normal furnace cooling.
The crystal structure of the microwave sintered products was characterized by X-ray diffrac‐
Characterization and property measurements of La2MMnO6 (M = Ni, Co) ceramics
tion (XRD) using a Shimadzu X-ray diffractometer with Cu-Kα radiation 2θ range of 20 to 80°.
Raman spectra were carried out on an RM-1000 micro-Raman spectrometer with the 514.53
11
10 Advanced Ceramic Processing
nm line of an argon laser under ambient conditions. The composition, morphology, and
microstructures of the products were characterized by transmission electron microscope (TEM
FEI Tecnai F20 microscope, Japan) and field emission scanning electron microscope (FESEM,
Hitachi S-4800, Japan) equipped with an energy-dispersive X-ray spectrometer (EDS). Fourier
transform infrared spectroscopy (FTIR) was performed on a Nicolet 5700 spectrometer in the
wave number range of 400–4000 cm–1. The spectroscopic grade KBr pellets were used for
collecting the spectra with a resolution of 4 cm–1 performing 32 scans. X-ray photoelectron
spectroscopy (XPS) was performed on an ESCA-UK XPS system with an Mg Kα excitation
source (hν = 1486.6 eV), where the binding energies were referenced to the C1s peak at 284.6
eV of the surface adventitious carbon. The magnetic properties were measured using a physical
property measurement system (PPMS-9, Quantum Design, Inc., San Diego, CA, USA) at room
temperature under a maximum field of 20 kOe. Silver paste was applied on both sides of the
pellet for the electrical measurements. The variation of dielectric constant and dielectric loss
as a function of frequency at room temperature and as a function of temperature at different
frequencies was measured using computer interfaced HIOKI 3532-50 LCR-HITESTER.
The phase structure of the microwave sintered LNMO and LCMO nanoparticles was charac‐
terized by X-ray diffraction (XRD). As shown in Figure 4, no extra reflection peaks other than
those of pure perovskite phase are detected, indicating the high purity of nanoparticles can be
obtained in 10 min by this microwave sintering approach, which confirms the formation of
single phase compositions of LNMO and LCMO double perovskites [30].
The crystallite size was calculated from XRD patterns using the Debye–Scherrer formula [7],
described by the Eq. (7):
0.94 ´ l
D= (7)
b 1 ´ cos q
2
where D = crystallite size, λ = radiation wavelength (1.5405 Å), β1/2 = half-width of diffraction
profile, and θ = diffraction angle.
The average crystal size was found to be 23 nm for LNMO and 28 nm for LCMO, which are
2–3 times smaller than the particle/grain sizes measured by TEM as shown in below section.
Raman spectroscopy is one of the most important tools to attain the information about the
structure of the samples. The Raman spectra of microwave sintered LNMO and LCMO
ceramics are shown in Figure 5. The Raman spectra display two characteristics peaks at around
514, 653 cm–1 for LNMO and 488, 670 cm–1 for LCMO ceramics, corresponding to the well-
documented A band and B band, respectively. Martín–Carron et al. have assign the two peaks
where: D = crystallite size, λ = radiation wavelength (1.5405 Å), β1/2 = half-width of
diffraction profile, and θ = diffraction angle.
Microwave Fast Sintering of Double Perovskite Ceramic Materials 11
The average crystal size was found to be 23 nm for LNMO and 28 nm for LCMO, which are
http://dx.doi.org/10.5772/61026
2–3 times smaller than the particle/grain sizes measured by TEM as shown in below section.
(110)
LCMO
(b)
(200)
(211)
(100)
(111)
(431)
(220)
(211)
(113)
Intensity (a.u.)
(a) LNMO
20 30 40 50 60 70 80
2-Theta (degrees)
Figure 4. XRD patterns of the microwave sintered (a) LNMO and (b) LCMO ceramics.
Figure 4. XRD patterns of the microwave sintered (a) LNMO and (b) LCMO ceramics.
to the Ag antisymmetric stretching (or Jahn–Teller stretching mode) and Bg symmetric
stretching vibrations of the MnO
Raman spectroscopy octahedra,
is6 one respectively
of the most [34–36,
important tools 52–54].
to attain It is wellabout
the information known that
the Ag band is usually
the structure assigned
of the toThe
samples. antisymmetric
Raman spectrastretching
of microwave(orsintered
Jahn–Teller
LNMO stretching
and LCMO mode),
while theceramics
Bg band aredistributed to symmetric
shown in Figure stretching
5. The Raman vibrations.
spectra display A noticeable
two characteristics difference
peaks at is
–1 –1
seen between
aroundour LNMO/LCMO
514, ceramics
653 cm for LNMO and 488, and the for
670 cm bulk sample:
LCMO ceramics, Ag and Bg peaks
thecorresponding to the for the
well-documented
nanoparticles A bandbinding
shift to higher and B band, respectively.
energy, 13 andMartín–Carron et al. have assign
25 cm–1, respectively, whenthecompared
two to
the bulk crystal.
peaks toThe theshifting may occur stretching
A antisymmetric due to surface strain of the
(or Jahn–Teller crystal mode)
stretching structure
and[55].
g
The microstructure and morphology of microwave sintered LNMO and LCMO ceramics were
investigated by FESEM
B g symmetric and TEM
stretching techniques.
vibrations Typical
of the MnO SEMrespectively
6 octahedra, images of[52–54].
La2MMnO34–36
It 6is(M
well= Ni, Co)
nanoparticles are shown in Figure 6, the average grain size is about 52 nm and 58 nm for
La2NiMnO6 and La2CoMnO6, respectively. The grain size of La2CoMnO6 is bigger than that of
La2NiMnO6, which obeys the rule that relatively 13 large ionic radius id benefit to the diffusion
in the microwave sintering process.
From the morphologies of both samples, the grains seem to be homogeneous and form a group
of cluster phenomenon. The perovskite material has better microwave absorption capability
[5, 51] and leads to fine grain growth during the sintering process.
The EDX spectra (inset of 6a and 6b) and their corresponding tables confirm the presence of
the constituent elements (La, Ni, Co, Mn, and O), the composition being nearly the same as
that of stoichiometric La2NiMnO6 and La2CoMnO6, respectively.
As shown in Figures 7a and 7b, transmission electron microscopy (TEM) was applied for all
samples to determine particle size and confirmed that the particle sizes are about 53 ± 12 and
60 ± 15 nm for LNMO and LCMO, respectively, which agrees good agreement with the SEM
12 Advanced Ceramic Processing
-1
670 cm
-1
488 cm
Intensity (a.u.)
(b) LCMO
Bg
-1
653 cm
Ag
-1
514 cm
(a) LNMO
Figure 5. Raman of the microwave sintered (a) LNMO and (b) LCMO ceramics.
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Exploring the Variety of Random
Documents with Different Content
Technology - Course Outline
Third 2025 - Academy
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