Nano-sized ferrite atoms are extensively studied in the last several decennaries for its electrical and magnetic belongingss in broad scope of technological applications 1,2. Nano-particles are defined as the stuff atoms holding characteristic dimensional length less than 100nm 3. The belongingss of nano-sized ferrite atoms are rather unusual as compared with bulk stuffs. The surface to volume ratio of nano-sized atom is big which greatly alters the belongingss of stuffs i.e. coercivity ( Hc ) , impregnation magnetisation ( I?s ) , Anisotropy energy ( EA ) 3.
Ferrites or passage metal oxides are brickle and stiff ceramic stuff, available in different colourss ( silver grey, brown black etc.
) . Magnetite ferrite is one of the oldest known magnetic stuffs as loadstone. Magnetic ferrites are low conducting or electrically insulating magnetic stuffs. Neel in 1948 first clip reported ferrimagnetic nature of ferrite stuff. In ferrimagnetic stuff the magnetic minutes originating from different lattice atoms are unequal and oppositely aligned therefore give a net magnetic minute 4. Ferrites do non bring forth any eddy current like other metal magnets.
Thus they are more suited stuff to utilize in high frequence jumping magnetic field.
1.2 Ferrites Structure
Ferrites received tremendous scientific attractive force due to its magnetic and dielectric features. These belongingss depend on the construction of ferrite. On the footing of their construction they are classified as follow:
1.2.1 Spinal Ferrites ( SF )
Spinel ferrites are one of the earliest known magnetic stuffs. Magnetite ( Fe3O4 ) was known many hundred old ages ago as loadstone. Its composing is FeOFe2O3. The general expression of spinal ferrite is XFe2O4, where Ten is a bivalent metal such as Fe, Co, nickel Zn, Cu, manganese ion or mixture of bivalent ions such that on mean two cornice electronic provinces are present 4,5. The accommodating possibility of figure of bivalent ions on same place in crystal has led ferrite to the topic of extended research and technological applications.
Spinal crystal is a close wadding of 32 O ions arranged in face centered three-dimensional ( FCC ) construction. This agreement of anions gives two types interstices sites for cations, tetrahedral A-sites and octahedral B-sites. The metal cations are distributed among the tetrahedral A- site surrounded by four O ions and octahedral B-sites surrounded by six O ions as shown in figure1.
Figure: Unit cell of spinal ferrite construction 5
In a unit cell there are a entire 64 tetrahedral sites ( A ) and 32 octahedral ( B ) sites available for cations. In instance if all A-sites and B-sites are filled with bivalent ions and trivalent ions severally, there would be 224 positive charges due to 64 divalent and 32 trivalent ions in comparing of 64 negative charges due to 32 anions, and the construction would non be electrically impersonal. However, merely 8 tetrahedral and 16 octahedral sites are occupied by cation. The net positive and negative charges therefore become equal and give an electrically insulating construction.
The construction shown in the fig.1 is an octant, which contains eight subcells, four tetrahedral and four octahedral constructions severally. Magnetic minutes of ions are represented by pointers and clearly indicate that magnetic minute of ion at octahedral B-site is antiparallel to the magnetic minute of ion at tetrahedral A-site. Since ions at both sites have unequal magnetic minute, therefore it gives rise to the net magnetic minute and illustrates ferrimagnetic nature 4.
In spinal ferrites ratio of the cations at A-site and B-site greatly alter the construction and belongingss of spinal ferrites, and depend on size, electronic constellation and electronic energy of the metal ion. Spinal ferrites are farther divided into three groups i.e. normal, reverse and assorted spinal ferrites 6.
In normal spinal construction eight tetrahedral A-sites are occupied by divalent atoms and the 16 octahedral B-sites are occupied by trivalent atoms. They are represented by chemical expression. A typical illustration of normal spinal ferrite is ZnFe2O4 7.
In reverse spinal ferrites, divalent atoms make full B-sites where as the trivalent atoms are every bit distributed among A and B-sites. Their chemical expression is. Example of reverse spinal ferrite is cobalt ferrite ( CoFe2O4 ) 6.
In mix spinal construction both tetrahedral ( A ) and octahedral ( B ) sites are partly filled by each sort of ions. Mixed spinal ferrites are represented by expression is, where is the inversion factor or inversion parametric quantity. Value of depends on the method of readying and the components of ferrites. For spinal construction and for reverse spinal construction x while for assorted spinal construction its value varies between 0 and1. MnFe2O4 is an illustration of assorted spinal ferrite 8.
1.2.2 Hexagonal Ferrite ( HF )
Hexangular ferrites construction is really much composite in comparing to that of spinal construction. The general expression is where X is normally Strontium ( Sr ) , Barium ( Ba ) or Lead ( Pb ) . The Ten and O-2 ions form a close jammed construction and give rise to three different interstices sites for the metal ions i.e. Tetrahedral, Octahedral and Trigonal bi-pyramid. The rhombohedral bi-pyramid interstices site is surrounded by 5 O atoms. The lattice parametric quantities of unit cell are and. Unit cell of hexaferrite contain 64 ions including 12 Fe+3 ions. These Fe+3 ions are distributed among the different interstices sites such that nine ions occupy octahedral B-Site, two on tetrahedral A-site and one occupy rhombohedral bi-pyramid site, surrounded by five co-ordinate sites. The agreement of spins at different sites is such that we get four odd spins form a unit cell lending to the magnetic minute of hexa ferrites 4.
1.2.3 Magnetic Rare Earth Garnets
Minerals like grossularite ( 3CaO. Al2O3.3SiO2 ) , andradite ( 3CaO.Fe2O3.SiO2 ) , spessarite ( 3MnO.Al2O3.3SiO2 ) have similar construction and are jointly called Garnet. Magnetic garnets crystallize in the same construction. The general expression of garnet is, where R is Yttrium or the rare Earth ions ( Gd, and Dy ) in instance of magnetic garnet. Garnets have dodecahedral or 12 sided crystal construction. Yttrium Fe garnet ( YIG ) has unit cell incorporating 160 atoms and peculiarly of import for the microwave applications. In the crystal construction of Garnets a new cation site dodecahedral site is available in add-on to the tetrahedral and octahedral sites 4.
Ferrites with absorbing magnetic and electrical belongingss are really of import due to their technological application.
1.3.1 Magnetic Properties
Ferrites are ferrimagnetic in nature as discussed earlier. On the bases of magnetic belongingss, ferrites can be divided into two groups: soft ferrites and difficult ferrites.
Soft ferrites were green goodss by J. L. Snoek and his colleagues before 1950. Soft ferrites have high permeableness, high electrical electric resistance and impregnation magnetisation. They offer low conduction, low magneto crystalline anisotropy and coercivity 9. Low coercivity consequences in easy magnetisation and demagnetisation of soft ferrites without dispersing much energy. Where the low conduction prevent undesired eddy current.
Hard ferrites are characterized by high coercivity, high permeableness, high electrical electric resistance and really high magneto crystalline anisotropy. High coercivity prevents the demagnetisation of difficult ferrites material and therefore makes it suited for the broad usage as lasting magnet 10.
1.3.2 Electrical Properties
Ferrites are electrically insulator or semiconducting stuff. Conduction of charges in ferrites is rather different than semiconducting material. Charge mobility is independent of the temperature fluctuations in ferrites, and electron associated with any peculiar ion remains stray. Presence of Iron ions in the ferrite construction with different cornice province can impact the conduction of the stuff ; nevertheless the construction as a whole is nonconductive. Ferrites do non offer eddy current in jumping field. They are potentially good campaigner in state of affairss where electrical conduction is undesired. They are peculiarly used as nucleuss of initiation spirals runing at high frequences because of their high permeableness, impregnation magnetisation and low electrical conduction 11.
1.3.3 Microwave Properties of Ferrites
Ferrites are extensively used in the complex microwaves communicating, satellite Communication, pilotage, radio detection and ranging engineering and spectrometry. Most common devices used in the microwave communicating are isolators, circulators, resonating chambers and stage shifter. These devices are made of ferrites holding low coercivity and high remanence and moderate permeableness. Permeability of ferrite depends on biasing magnetic field. Biasing field of ferrites is the amount of internal and external alternation field. In the absence of jumping field the magnetic minute of the negatron is aligned along the easy axis where possible energy of the system is low. When ferrites are placed in the in external alternating field or microwave field, this external biasing field reinforces the internal magnetic field. This alteration will significantly impact the permeableness of the ferrite. Magnetic minute of negatron will be under the action of internal and external microwave field which consequences in precessional gesture of magnetic minute about equilibrium place. This precessional gesture of magnetic minute is opposed by the forces like opposition of the stuff, and the negatron minute will precess in equilibrium precessional orbit under the action of external jumping field and internal damping. In this mechanism energy is transferred from the jumping field to the precessional gesture of negatron. This energy is dissipated by internal frication and consequences in warming of the stuff. This phenomenon is called resonance soaking up. Microwave soaking up as a consequence of resonance makes ferrites highly valuable tool for their application in the stealing engineering as microwave absorber. Stealth engineering is the modern technique in which aircrafts and missiles are made unseeable by surfacing them with microwave absorber ferrite pigment 4,11.
In early ages of course happening ferrites ( Magnetite ) were used as magnetic acerate leafs to happen North and South. However the applications of magnetic ferrites were limited due to the hapless cognition of magnetic stuffs and their applications. In the last century research workers have discovered and produced ferrites with some absorbing belongingss.
Nowadays ferrites have found their applications in high denseness storage devices and magnetic inks12. As the atom size lessenings, the figure of magnetic spheres in atoms besides decreases and the atom with size 5nm service as the individual sphere atom. This 5nm individual sphere atom can be used to make storage denseness of 10Gbits/cm 3,13. Ferrites are nonconductive ceramic stuffs. Ferrites are extensively used in the state of affairs where the electrical conduction of stuff is undesired. They offer no eddy current in the A.C. field. Ferrites are peculiarly used in the high frequence applications. They are peculiarly used as nucleuss of initiation spirals runing at high frequences because of their high permeableness, impregnation magnetisation and low electrical conduction. Ferrites are besides used for the contact action of different organic compounds 14. Ferro fluid is presently the most promising stuff with legion applications. Ferrites are dispersed in bearer liquid 15. They are used for heat exchange16. Ferro fluid can be used in a assortment of applications. They are used in the diagnosings of the malignant neoplastic disease in magnetic resonance imagination ( MRI ) device and magneto cytolysis for devastation of cancerous cells. Ferro fluid is besides used as bearer for the targeted drug bringing 17.
Cobalt Ferrite ( CoFe2O4 ) is good known difficult magnetic stuff with reverse spinal structureA , in which Co+2 ions are localized at B-site where Fe+3 ions are present in both A-site and B-site 18. The unit cell is characterized by lattice parametric quantities 8.38 A A and the interaction distances are b = 2.963 A , u = 0.2714 A , P = 2.963 A , q = 0.3106A , R = 38.336 A and s = 3.127 A 8,19. CoFe2O4 nanoparticles possess high chemical stableness and mechanical hardness. It has a really high magnetostriction value, low electric loss, high coercivity 5.3kOe ( Kilo Oersted ) , sensible magnetisation 80.8emu/g ( Electromagnetic Unit per Gram ) 20 and really high uniaxial magnetocrystalline anisotropy along regular hexahedron axis [ 1 0 0 ] 18,21,10. Cobalt ferrite show superparamagnetic behaviour at room temperature nevertheless at low temperature it behaves ferrimagnetically.
These belongingss are temperature dependent and show fluctuation with alteration in temperature. These belongingss make it a perfect stuff for usage in emphasis detector, precursors for doing ferro-fluids, magnetic infrigidation 22. It exhibit superparamagnet 23 behaviour at room temperature which is of import for the enhanced contrast magnetic resonance imagination ( MRI ) . The higher anisotropy and high coercivity make it a good campaigner for the magnetic recording devices such as audio and video tape and high-density digital recording discs or computing machine memory 21,24. Cobalt ferrite is used in medical field for devastation of malignant neoplastic disease cells by magnetic fluid hyperthermy 25, and targeted drug bringing 16. It is used as accelerator in the hydrolysis of different chemicals 26. CoFe2O4 has been used as microwaves absorber in different devices for stealing engineering 27.
Nano-particles are by and large defined as the atoms holding size less than 100 nanometre ( nm ) . In nano-particles surface to volume ratio is really big and the big figure of atoms at the surface enhances the surface energy and wider set gape which plays a dominate function in betterment of many belongingss. The quantum parturiency of negatron for the nano-particles has effects on the electrical conduction and magnetic susceptibleness of the stuff. Higher surface energy enhances the chemical activity accelerator field.
2.2 Brief Background of Nanoparticles
Fabrication and application of nano-particles have attracted great involvement in last several decayed. Nanostructured stuffs had its beginning from the big-Bang. All affair is formed by the condensation of atoms into larger multitudes under the action of gravitation. However the importance of the nano atoms were foremost realized in 19th century. Nanoparticles of metal colloids were foremost reported by Faraday in 1857 while working with metal all right atoms. He observed that the colour of the glass is effected with doped atom size 28. In 1959 Richard Feynman gave a talk “ There ‘s Plenty of Room at the Bottom ” at the one-year meeting of the American Physical Society ( APS ) at Caltech. In his talk he discussed the possibility of holding nano-sized public-service corporations and argued that the behaviour of the stuff at such a little size will be wholly different from bulk stuffs. He said “ As we go down and shirk around with the atoms down at that place, we are working with different Torahs, and we can anticipate to make different things. We can fabricate in different ways. We can utilize, non merely circuits, but some system affecting the quantal energy degrees, or the interactions of quantal spins. At the atomic degree, we have new sorts of forces and new sorts of possibilities, new sorts of effects ” 8. His article provides the counsel for work on the nano-materials and was regarded as the foundation of nanotechnology.
In 1962 Kubo 30 at Tokyo University gave theoretical preparation for the quantum parturiency of negatron. He suggested that the negatron in the nano sized atoms with size less than 10nm do non obey Fermi statistics. Kubo noted that the nano-sized atoms had strong inclination to stay electrically impersonal which effects specific heat, magnetisation, and superconductivity. This consequence is now called Kubo consequence. Ohshima et al.31 synthesis all right atom of aluminum oxide, carbonate and studied its crystal construction and morphologies with the aid of negatron microscope and negatron diffraction technique.
Field of nano stuffs has the potency for the theoretical every bit good as for experimental surveies. In last several decennaries of twentieth century, research workers have published big figure of documents on synthesis, word picture and theoretical preparation of the belongingss of nanoparticles. Key factors that attracted scientists are the belongingss of nanoparticles which are tremendously different than that of majority stuffs.
Size of atom has effects on surface tenseness, vapor force per unit area and stage passage which is called thermodynamic size consequence. Another exclusive belongings of the nanocrystals is defects in crystal. The denseness of crystal defects are so big that the spacing of two defect sites is of the order of the interatomic distance and it can drastically impact electrical, optical and mechanical belongingss of the stuffs. The size dependent crisp fluctuation in the belongingss of nanoparticles is termed as quantum size effect32. Nanoparticles have big surface to volume ratio. Most of the atoms of atom prevarications on the surface and can aggressively react to fluctuations of external electric and magnetic Fieldss.
2.3 Magnetic Nano-Particles
The magnetic behaviour of the nanoparticles is the alone character of the nano-particles. The beginning of magnetic attraction in atoms is the spin and orbital gesture of negatron. Magnetic dipole minutes originating from spin and orbital gesture are coupled to each other in different stuffs.
In diamagnetic stuffs the net magnetic dipole minute originating from the gesture of negatrons of different atoms naturals each other. In diamagnetic stuffs outermost shell of atom is wholly filled, and when placed in magnetic field it magnetized in the way antonym to the applied field. In paramagnetic stuffs outer most shell is partly filled, nevertheless the magnetic minutes of all odd negatrons are indiscriminately oriented. Paramagnetic stuffs magnetized in the way of applied field. Diamagnetic and paramagnetic magnetisation is really weak and observed merely in strong magnetic field. Other types of magnetic stuffs are ferromagnetic, ferrimagnetic and antiferromagnetic. In Ferromagnetic stuffs there is a strong interaction between the minutes of odd negatrons and consequence in a net magnetic minute and can be magnetized in weak magnetic field. In antiferromagnetic stuffs the magnetic minute arises from different lattice sites are equal and opposite. Therefore the net magnetic minute is zero. In 1940, Neel ‘s discover Ferrimagnetism. In ferrimagnetic stuff the magnetic minutes originating from different lattice atoms are unequal and oppositely aligned therefore give a net magnetic minute 4.
Lodestone or magnetite ( Fe3O4 ) is one of the oldest know ferrimagnetic stuff. It is of course happening mineral and known to the worlds from several centuries. Elmore 33 in 1938 prepare magnetic iron-ore for the first clip by precipitation of ferric chloride ( FeCl2 ) and ferrous chloride ( FeCl3 ) . Magnetite by and large falls in group of magnetic spinal ferrites. Ferrites of different composing and constructions have been the topic of major involvement in all over the universe in last century. There is ever a demand of ideal ferrite which is suited for usage in every set of needed application.
The wonder of research worker to hold an ideal ferrite merchandise with optimal public presentation, led them to the find of big figure of different ferrites. Those with amended mechanical, chemical and physical belongingss have been achieved through different synthesis techniques.
2.4 Cobalt Ferrite nano-Particles
Cobalt ferrite ( CoFe2O4 ) is one of the most of import ferrite which has assortment of technological applications. CoFe2O4 possess high chemical stableness and mechanical hardness. Cobalt ferrite behave superparamagnetically at room temperature and frrimagnetically at temperature below 260oC 34,35. It has a really high magnetostriction. Magnetostriction is defined as the alteration in the form or dimension of the lattice caused by the orientation of magnetic spheres in the external magnetic field. Spin and orbital minute of negatrons are strongly coupled in lattice. The orientation of the orbital magnetic minute is restricted. When way of spin alterations due to external magnetic field, it causes alteration in the orientation of the orbits. It produce a little fluctuation in the dimension of the lattice 5. In such stuffs magnetisation is produced when subjected to external emphasis. CoFe2O4 has high DC electric resistance and really little Eddy losingss. These belongingss make it a promising stuff for the emphasis detector applications 36. It is used in the motors, transducers and actuators37. CoFe2O4 is used in microwaves communicating, satellite Communication, pilotage, and radio detection and ranging engineering 27.
CoFe2O4 has really high uniaxial magnetocrystalline anisotropy.18,21. Some stuff preferred to magnetise in some peculiar way. This belongings is called magnetocrystalline anisotropy of stuff. Magnetic minute of CoFe2O4 prefers to point along the [ 1 0 0 ] axis of crystal. Magnetocrystalline anisotropy depend on temperature. Relation of anisotropy invariable with temperature is 10:
Magnetocrystalline anisotropy energy is given by Wohlfarth theory:
Where K is the anisotropy invariable, V is volume of grain and ?Y is the angle between way of magnetisation and easy axis. Magnetocrystalline anisotropy energy serves as a barrier for the superparamagnetic behaviour of the CoFe2O4 nanoparticles. When become comparable to thermal activation energy, particles show superparamagnetic behaviour 38. At room temperature becomes equal to and CoFe2O4 nanoparticles show superparamagnetic behaviour.
Cobalt ferrite ( CoFe2O4 ) has high coercivity 39. It requires big coercive force to demagnetise after impregnation magnetisation 40,41. The coercivity of CoFe2O4 varies with temperature. At room temperature its value is 5.3 kOe and increases to 25.2 kOe at temperature -268oC. Cobalt ferrite has sensible magnetisation because it contains Cobalt ( Co ) and Iron ( Fe ) which strongly respond to magnetic field because of their big magnetic minutes. Saturation magnetisation of CoFe2O4 has a value of 80.8emu/g at room temperature and it increases to 93.9emu/g at -268oC 10. This high anisotropy and coercivity are really of import belongings for magnetic informations recording. In magnetic informations recording, information is stored by magnetising stuffs. This magnetisation can be reversed by thermic energy. In order to forestall informations loss, either volume or anisotropy is increased to maintain the magnetic energy of the grain above the thermic reversal energy 42. If volume of the grain is increased, its anisotropy and coercivity will diminish or frailty versa. Therefore the high anisotropic and high coercive stuffs are peculiarly of import for the magnetic informations entering 18,24,43.
These belongingss make Co ferrite a perfect stuff for usage in emphasis detector, precursors for doing ferro-fluids, magnetic infrigidation 22. It exhibits superparamagnetic 23 behaviour which is of import for the enhanced contrast magnetic resonance imagination ( MRI ) . The higher anisotropy makes it a good campaigner for the magnetic recording devices such as audio and video tape and high-density digital recording discs or computing machine memory 21,24. Cobalt ferrite is used in medical field for devastation of malignant neoplastic disease cells by magnetic fluid hyperthermia25, and targeted drug delivery16. It is used as accelerator in the hydrolysis of different chemicals26. CoFe2O4 has been used as microwaves absorber in different devices for stealing technology27
All these belongingss were found to be strongly size dependant. It is observed that with decrease in size of atom below a finite value, CoFe2O4 exhibits superparamagnetic behaviour. Anisotropy, coercivity ( Hc ) of the CoFe2O4 additions and impregnation magnetisation ( I?s ) decreases with lessening in size 32,44. Grigorova et Al. ( 1998 ) reported that size of the atom depends on tempering temperature and showed that atom size additions with addition of tempering temperature 10.Maaz et Al. ( 2007 ) besides verified the same behaviour 21. However the literature suggests that the magnetic belongingss of Co ferrite are non merely size dependant but besides depend on the method of readying.
2.4.1 Synthesis techniques of Cobalt Ferrite Nano-Particles
To accomplish the smallest size of atoms, assorted techniques were developed for the synthesis of nano-sized Co ferrite. They include sonochemical reaction8, mechanical debasing 45, spray-drying, freeze-drying, hot-spraying, evaporation-condensation, matrix isolation, laser-induced vapour stage reactions and aerosols 25, precipitation 10,44, Coparticipation21, normal micelle and change by reversal micelle methods 46, micro emulsion method22, sol-gel, and glass crystallization47.
These synthesis techniques of the Co ferrites can be loosely divided into two chief classs viz. chemical and physical methods.
Chemical methods are really normally used for the synthesis of the ferrites. In this method chemicals are dissolved in proper dissolvers like H2O, ethyl alcohol, propyl alcohol and propanone etc. to do precursors. Precursors are assorted in definite molar ratios and converted to solid nano stage by precipitation at room temperature or higher temperature. Other methods are chemical vapor deposition or chemical bluess condensation. In these methods precursors are converted into gaseous province at high temperature and low force per unit area. This gas is allowed to lodge on substrate and condensed to organize nanoparticles 48,49,50. Sol-gel 20 is besides one of the wet chemical mob for the synthesis of Co nanoparticles.
In chemical methods belongingss of nano-crystal such as crystal construction, atom size, atom size distribution, and electrical, magnetic and mechanical belongingss are varied with different parametric quantities of chemical reaction involved in synthesis. Temperature, pH and reactants concentration are those parametric quantities.
Other group of synthesis techniques is Physical method of synthesis. There are several physical methods which are utilised to fix nano-crystalline stuffs. Among them most widely used is mechanical distortion or mechanical alloying. In this method precursors are subjected to high energy ball milling or high energy shear emphasis. Precursors are so annealed at high temperature to obtain nano-crystals23,45,51. Other physical methods like microwave decomposition 52 and laser extirpation 5 etc. are besides in pattern for the synthesis.
2.5 Literature Review
These readying techniques greatly alter the size and belongingss of the atoms. For the first clip it was reported by Schuele 53 et Al. ( 1961 ) that the size and belongingss of the atom are greatly dependent upon the method of readying. Schuele and his colleagues synthesized nanoparticles of CoFe2O4 with size 16nm by hydrothermal procedure. The impregnation magnetisation ( I?s ) of the CoFe2O4 atoms was observed to be 70emu/g ( electromagnetic units/grams ) while coercivity ( Hc ) about 0.75kOe ( kilo oersted ) . Dinging 45 et Al. ( 1995 ) prepared CoFe2O4 with 30nm atoms size by mechanical debasing method. Sample was annealed supra 700oC. The impregnation magnetisation ( I?s ) and coercivity ( Hc ) values were reported to be 77emu/g and 2-2.7kOe severally. In 1995 Moumen 54 and colleagues published their work sing the readying of CoFe2O4 nanoparticles. They prepared 2-5nm atom by chemical micelle method with I?s 50emu/g and Hc 8.8kOe and besides reported that the atom size varies with reactant and surfactant concentration. Blaskov 34 et Al. ( 1996 ) reported the size of atom as 5nm by chemical coprecipitation method followed by low temperature calcination. They observed I?s value 15emu/g and Hc value 13kOe. Muller 47 et Al. ( 1996 ) showed that tempering temperature has consequence on size and magnetic belongingss of atoms. They prepared atom of size 26-210nm by glass crystallisation method with assorted tempering temperatures and ascertained impregnation magnetisation ( I?s ) 74-88emu/g and coercivity ( Hc ) 0.51-0.89kOe. Pillai and Shah 24 ( 1996 ) prepared nano-particles holding size about 50nm utilizing H2O in oil micro emulsion technique. They observed coercivity 1.44kOe and impregnation magnetisation 65emu/g. Grigorova 10 et Al. in 1998 achieved 4.7-59nm atom size by coprecipitation method followed by tempering at assorted temperatures. They measured values of I?s 5.4-47.5emu/g and Hc 10-14kOe. In twelvemonth 1998 shafi 8 et Al. reported synthesis of Co ferrite nano-particles of size less than 5nm by sonochemical method and reported the ascertained value of magnetisation about 45emu/g. They besides reported that surface country of sample reduces with crystallisation and its value decreases to 52m2/g for sample heated at 700 oC. Yan 55 et Al. ( 1999 ) prepared cobalt ferrite nanoparticles by burning method utilizing glycine as fuel. The magnetic belongingss were observed to be strongly dependent on glycine ratio. The surface country they observed was 29m2/g which is much larger so observed for bulk sample. Shi and Ding 51 used combination of coprecipitation and mechanical alloying to bring forth all right atoms of size about 10nm. They observed fluctuation in impregnation magnetisation and coercivity value with addition of tempering temperature. Giri 56 et Al. ( 2000 ) reported first clip photomagnetism in Co ferrite prepared by coprecipitation method. . Ahn 26 et Al. in 2000 prepared nano-particles of size 4.9nm by micro emulsion method. The ascertained coercivity and magnetisation values were 15.1kOe and 15.2emu/g severally at 5K. Chinnasamy 57 et Al. develop a modified coprecipitation mob called seed mediated growing dominated coprecipitation. They produced 40nm atoms and achieved a high coercivity value 4.3kOe stopping point to the theoretical value 5.3kOe. Further they besides showed that atom size in the conventional co-precipitation method varies with molar ratio and flow rate of Na hydrated oxide ( NaOH ) . Kim 2 et Al. in twelvemonth 2003 reported synthesis of CoFe2O4 atom at assorted temperatures by coprecipitation method, and besides reported that size and magnetic belongingss depend on temperature of the precipitates. They synthesized CoFe2O4 nano-particle with size runing from 2-15nm. Kim et Al. observed magnetisation and coerecivity value 2-58.3emu/g and 0-193Oe. Cao and Gu 35 in 2005 utilize coprecipitation method to fix CoFe2O4 nanoparticles of atom size 22nm. They observed that Co ferrite behave superparamagnetically at room temperature. In twelvemonth 2005, Cannas 58 et Al. prepared nanoparticle of size runing from 15-58nm by thermic decomposition method and demo that size of atoms varies with pH value. They besides observed that the coercivity and impregnation magnetisation value decreased with addition of pH. Maaz 21 et Al. ( 2007 ) synthesized 15-48nm atoms by coprecipitation method and observed that Hc value to be10.5kOe at low temperature of -198oC. Kumar 59 et Al. in 2008 studied temperature dependance on atom size, surface country coercivity and magnetisation. They prepared Co ferrite by precipitation method and annealed sample at assorted temperature from 100-900oC. They observed that surface country of the sample decreases where atom size, magnetisation and coercivity of the sample additions with addition of tempering temperature. In twelvemonth 2012 Zalite 50 et Al. prepared CoFe2O4 nano atoms by sol-gel self-combustion method and by high frequence plasma technique and ascertained atom size of 10-20nm and 38-40nm and surface country of 37-43m2/g and 28-30m2/g severally. They besides studied magnetic belongingss of the stuff and ascertained impregnation magnetisation value53.4emu/g and 75.4emu/g and coercivity value 1.17kOe and 780Oe severally for the sample prepared by sol-gel self-combustion and high frequence plasma method.
This reappraisal reveals that the belongingss of CoFe2O4 nanoparticles show sensible fluctuation with readying techniques. Each technique has its ain advantages and disadvantages. Some jobs are besides associated with these techniques. If one technique enhances a belongings it may besides impact other belongingss. The measure of CoFe2O4 nanoparticle pulverization produced by these techniques is limited. No individual method can be adapted to accomplish big scale production with enhanced magnetic belongingss, smallest atom size and minimal size scattering.
There is ever a demand for the development of a method, which can get the better of these jobs. Comparative surveies of different readying techniques can play a critical function in detecting a readying technique to get the better of the above stated jobs. However in the past no attending was paid to such probe of the synthesis techniques. Grigorova et Al. ( 1997 ) gave some informations about the belongingss of CoFe2O4 synthesized through different paths. That information was collected from the work of different peoples. In last few decennaries no individual undertaking, based on the comparative surveies of these techniques is reported. The intent of present undertaking is to utilize different methods for the production of CoFe2O4 nanoparticle pulverization, and to choose out of these methods, the most suited one to get the better of the above stated short approachs.
In past Co ferrite has been investigated extensively ; nevertheless a really small attending has been given to the big scale production of Co ferrite and comparative surveies of the different synthesis techniques. Keeping in position the industrial importance of the big scale production of the Cobalt ferrite nanoparticles, the major purpose of the present undertaking is the comparative survey of different synthesis techniques, like co-precipitation and sol-gel. The dependance of construction and morphology of CoFe2O4 nanoparticles on the method of readying will be studied. The consequence of heat intervention on the belongingss of CoFe2O4 prepared by different methods will besides be investigated. This comparative survey will assist us to place the most suited method for the big scale production of CoFe2O4, and besides to minimise the production cost.
Synthesis and Characterization Techniques
The big scale synthesis of mano-dispersed nano atoms of is one of our basic purposes of this undertaking. Choice of the proper chemicals is really of import for this intent. Reagent grade chemicals of Ferric Chloride Hexahydrate ( FeCl36H2O ) , Cobalt Chloride Hexahydrate ( CoCl26H2O ) Sodium Hydroxide ( NaOH ) , Ethyl Alcohol ( C2H6O ) , Oleic Acid and Propylene Oxide were used for the synthesis. Oleic Acid and Propylene Oxides were used as wetting agent for the atom coating. Chemicals were used without farther purification. All these chemicals were supplied by Scharlu ( Germany ) which are listed in table 3.1 along with their specification.
Name of Chemicals
Name of Company
Ferric Chloride Hexahydrate
Cobalt Chloride Hexahydrate
Our chief aims were to fix the same required sample by two different paths from the same natural chemicals. The stuffs readying is a spot different, so we will discourse them individually.
Solid chemicals are weighed on sartorious G.M.B.H analytical balance and transportation to clean and dry flasks. Liquid samples were measured with class B volumetric flasks, burettes and measuring/transferring pipettes. All the glasswork used for the synthesis is best quality borosilicate glass.
3.2 Washing of glasswork
The most of import undertaking in synthesis of any sample is rinsing of the glasswork. To cut down the unsought drosss glasswork should be decently washed. It can be done by utilizing concentrated Nitric acid ( NH3 ) or Hydrochloric acid ( HCl ) . Glassware is foremost washed with acid and so it is rinsed with H2O for several times so that all acid is removed. Glassware is so rinsed with dual distill H2O for few times to take all the unsought drosss and so dried in oven.
3.3 Material Preparation for Coprecipitation
For the coprecipitation method precursors are made by fade outing proper sum of chemicals in dual distilled H2O. A specific ratio of these precursor solutions are mixed in a clean flask or beaker and are intensively stirred to acquire a homogeneous solution of the precursors.
3.3.1 Preparation of Ferric Chloride Hexahydrate ( FeCl36H2O ) solution
To fix 0.4M solution of ferrous chloride hexahydrate ( FeCl36H2O ) , 108.12g of FeCl36H2O is dissolved in one litre of dual distilled H2O. The solution was shaken for some clip so that all the FeCl36H2O are dissolved homogenously in dual distilled H2O.
3.3.2 Preparation of Cobalt Chloride Hexahydrate ( CoCl26H2O ) solution
0.2M solution of Cobalt chloride hexahydrate ( CoCl26H2O ) is prepared by fade outing 47.6g of CoCl26H2O in one litre of dual distilled H2O. The solution was shaken for some clip to obtain homogeneous solution.
3.3.3 Preparation of Sodium Hydroxide ( NaOH ) solution
3M solution of Na hydrated oxide ( NaOH ) was prepared by adding 120g of NaOH in a clean litre volumetric flask. Doubly distilled H2O is added till the solution is up to the grade. The flask is smartly shaken to obtain homogenously dissolved solution of NaOH.
3.3.4 Sample readying by Coprecipitation method
For the sample readying by coprecipitation method, foremost equal sum of Co chloride hexahydrate ( CoCl26H2O ) 0.2M solution and ferrous chloride hexahydrate ( FeCl36H2O ) 0.4M solution was put in a big level underside flask placed at hot home base and smartly stirred for one hr. At the same clip Na hydrated oxide ( NaOH ) solution was added bead wise at rate of 4ml/min into the solution boulder clay pH value rise to12.11.
At this phase a little sum of Oleic acid ( C2H6O ) was added to the solution. Oleic acerb Acts of the Apostless as wetting agent for coating of nanoparticles and to optimise the collection of the nano atoms at the clip of synthesis. That solution was heated at reaction temperature 80oC and smartly stirred for another 2 hour. Solution turned into dark brown or black precipitates of Co ferrite ( CoFe2O4 ) . The merchandise was so cooled at room temperature. To take drosss like Cl and Na, precipitates were washed several times with dual distilled H2O and so with ethyl alcohol. After rinsing precipitates were dried in oven at 100oC and left for 24hrs. Sample was so grinded into all right pulverization of CoFe2O4. The XRD of the sample show that it is formless stage of CoFe2O4 which contain 10 % H2O.
3.4 Material readying for Sol-gel method
Sol-gel method is the most widely used technique for the synthesis of Co ferrite. This technique is less complicated than any other synthesis method. For this a proper proportion of chemicals are dissolved in the ethyl alcohol and stirred for some tim so that gel is obtained and so this gel is dried harmonizing the demands of concluding merchandise.
3.4.1 Ferric chloride hexahydrate ( FeCl36H2O ) and ethanol solution
To fix 0.4M solution 72.08g of ferrous chloride hexahydrate ( FeCl36H2O ) of was added in 600ml of ethyl alcohol. Flask is good shaken so to that FeCl36H2O is dissolved in ethyl alcohol.
3.4.2 Cobalt chloride hexahydrate ( CoCl26H2O ) and ethanol solution
Molar solution of 0.2M is obtained by fade outing 31.7g of CoCl26H2O into 600ml of ethyl alcohol. A good dissolved and homogeneous solution is obtained.
3.4.3 Sample readying by sol-gel method
Both 0.4M solution of FeCl36H2O and 0.2M solution of CoCl26H2O are mixed in a big beaker under intensive stirring so that a homogeneous mixture is obtained. Then I added 280ml of propene oxide into the mixture and left for the stirring for 6hrs. However the mixture turned into dark gel in 30minutes merely. The mixture was so boiled at 80oC for 12hrs and black or dark brown pulverization of CoFe2O4 was obtained. The sample obtained was grinned into all right pulverization with aid of motor and Piston. The XRD of the sample show that construction was formless and no extremum was obtained in consequence.
3.5 Heat intervention
The procedure of heat intervention can be used to modify mechanical strength and physical belongingss of the stuffs. Sample warming and chilling rates can besides impact the belongingss of the stuffs. Materials are annealed at higher temperature to live over internal emphasis, which improve the microstructure and mechanical belongingss like tensile strength, hardness, ductileness and stamina etc.
The microstructure of the stuffs is greatly affected by the heat intervention. Majority of stuffs transform from formless to crystalline stuffs at temperature higher than room temperature. Cobalt ferrite shows crystallisation at temperature higher than 200oC. The crystallinity of CoFe2O4 additions with addition in temperature and extremely crystalline CoFe2O4 stuff is achieved at temperature higher than 600oC 60.
Samples prepared by coprecipitation method and sol-gel method were formless. They were filled in separate melting pots and heated to 800oC with heating rate of 10oC per minute. Samples were annealed for 8 hours at 800oC and so they were cooled at chilling rate of 10oC per minute. At this high temperature sample turn from formless to crystalline signifier and its colour alterations from brown to dark black. Sample was removed from the furnace and grinned to ticket pulverization and filled in separate bottles.
Heating and tempering of sample was carried with aid of furnace ( theoretical account no. LHT04/18 ) made by Naberthem Germany, and installed in Material Research Laboratory ( MRL ) , University of Peshawar. Furnace warming and chilling rates can be automatically adjusted. Maximal heating scope of the furnace is from 30oC to 1800oC.
3.6 Word picture techniques
Following techniques were used to qualify the samples:
Differential Thermal Analysis ( DTA ) was used to find stage transmutation temperature.
Thermogravenmatric Analysis ( TGA ) was used to happen out alterations in mass with temperature.
X-ray Dirractometer ( XRD ) was used for stage analysis and crystallite size finding
Scaning Electron Microscope ( SEM ) was used for the form, size and morphology of the atom.
Energy Dispersive X-ray Spectrometer ( EDX ) was used to find the chemical composing.
Atomic Force Microscope was used to analyze the surface of the atoms
Surface Area Analyzer was used to find surface country and pour size distribution
Fourier Transform Infrared Spectroscopy was used to find group of stuffs.
3.6.1 Differential Thermal Analysis ( DTA )
Differential thermic analysis ( DTA ) is a well-established tool to analyze the stage transmutation temperature of different stuffs. In this technique we study fluctuation in a belongings as map of externally applied and programed temperature. The term besides stands for assortment of techniques that used the survey of temperature dependant reactions which cause fluctuation in physical and chemical belongingss of substance. These dependent reactions are either endothermal or exothermal. Endothermic reactions are boiling, runing, vaporisation, sublimation, desolvation, chemical debasement, solid-solid stage passage, etc. and exothermal are crystallisation, oxidative decomposition and etc. These reactions either rise or lower the temperature of the specimen. The differential alterations in temperature of the specimen are plotted against the temperature. The curve obtained is called thermogram 61,62.
In this technique temperature fluctuation of the material specimen and an appropriate mention stuff is measured under controlled status as a map of temperature. Different reaction i.e. exothermal and endothermal reaction will do fluctuation in the temperature of the stuff where the temperature of the specimen remains the same. These temperature fluctuation cause alteration in the heat content ( I”H ) which is positive for endothermal reaction and negative for exothermal reaction 62.
Material specimen and mention stuff are placed in a furnace, whose temperature is controlled with computing machine package. Temperature fluctuation are detected with thermocouples and displayed in the computing machine package which record the informations electronically. If the temperature of the specimen leads the temperature of the mention stuff it will be an exothermal reaction. On other manus if the sample temperature lags behind the mention temperature it will be an endothermal reaction.
DTA analysis was carried at Centralized Research Laboratory ( CRL ) university of Peshawar. Both sample and reference stuff were placed in the aluminium pan and heated at heating in Diamond TG/DTA made by Perkin Elmer, USA. The heating rate of the furnace was 10 degree centigrade per minute ( 10oC/min ) in temperature runing from 30-1300oC.
Figure 3.1: Schematic of Differential Thermal Analyzer 62
3.6.2 Thermal hydrometric Analysis ( TGA )
Thermal hydrometric analysis ( TG ) is the technique which records the alteration in the weight or mass of stuffs as a map of clip, either at a finite and fixed temperature or over a scope of temperature at fixed heating rate. The thermic hydrometric analysis is the procedure in which material specimen is heated at high adequate temperature so that a constituent of the stuff decomposed into gas and evaporates. It is normally used to find features of the stuffs like debasement temperature, captive wet contents, oxidization temperature etc 61,62. The curve besides indicate the temperature at which sample should be treated to obtain heat resistive and stable stuff.
In TG analysis specimen is placed on an aluminum oxide or Pt pan. The pan mass is measured by a sensitive balance which detect really little fluctuation in the mass. The Cahn balance design is shown in Figure 3.2
Figure 3.2: Example of TG design 63
The balance is designed such that it can command the ambiance which is accomplished by gases released by the specimen. For this intent a thermocouple mounted really near to the pan. The chamber incorporating the balance is frequently tight air or inert gas, which help to protect the balance chamber and its associated electronic circuitry from gas diffusion 61-63.
TG analysis was carried out utilizing Diamond TG/DTA made by Parkin Elmer, USA. Sample were heated in aluminum oxide pan at heating rate of 10 degree centigrade per minute ( 10oC/min ) in temperature runing from 30-1300oC.
3.6.3 X-ray Diffraction and Crystal Structure Analysis
X raies are by and large defined as the electromagnetic radiation with wavelength in scope of 0.1-1A . These radiations are more energetic than UV ( UV ) radiations. Its energy scopes from 10-100keV. These radiations were accidently discovered by Wilhelm Conrad Rontgen in Germany in 1895. This find brings revolution in modern natural philosophies. X raies are of two types, Continuous and characteristic X raies. The ulterior one is used for the word picture of the stuffs. In twelvemonth 1912 Von Laue discovered the phenomenon of x-rays diffraction by crystal.
When a beam of X-ray encroaches a crystalline solid stuff and interact with negatrons or ions of the stuffs, the beams of the beam are scattered in all waies. Figure 3.1 shows way of X raies by different atomic planes of crystal as shown.
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Figure 3.3: Diffraction of X raies by atomic Airplanes of crystal 64
Two beams of incident beam are shown in the figure, which are scattered from two different planes. Lawrence Bragg provides a simple mathematical signifier of diffraction status. This is known as Bragg ‘s Law. Harmonizing to Bragg ‘s Law these beams will bring forth Bragg ‘s extremum if they interfere constructively. For the constructive intervention their way difference must be built-in multiple of wavelength of the radiation 65.
In this equation is the wavelength of the incident beam, N is the order of contemplation and an whole number, is the angle between incident and scattered beams where is inter planing machine spacing.
Bragg ‘s jurisprudence allows a precise measuring of inter-planer distance which can be used to find the lattice parametric quantities. For three-dimensional crystal cell lattice parametric quantities are equal and lattice angle are 90o.
Most of solid stuffs have crystalline construction. When they are capable to X raies, at some peculiar angles X raies are reflected with maximal strengths. This gives a form in which strengths of the reflected X raies are plotted against the 2I? value. The extremums observed in this form correspond to assorted crystal planes. Harmonizing to Bragg ‘s jurisprudence, extremums for big d-spacing is observed at little angles where for little d-values extremums are observed at big dispersing angles 65.
126.96.36.199 Phase Identification or Qualitative Analysis by XRD
The informations recorded from the x-rays diffraction can be used to place different stages of the stuffs. A stage of stuff can be defined as the part in which chemical composing and physical belongingss are unvarying. Most of crystalline stuffs have individual or multi stages. Each stage have alone diffraction form which is used to place it.
Since early decennaries of twentieth century, scientists had recorded big figure of standard diffraction forms. That database includes more than 550,000 forms of different stuffs. International Center for Diffraction Data ( ICDD ) founded Joint Committee for pulverization Diffraction Studies ( JSPDS ) in 1941. It gives a comprehensive set of database with name of Powder Diffraction File ( PDF ) which is updated yearly and includes information about d-spacing, comparative strengths, lattice margin etc 66.
For the stage designation of stuffs, its x-rays diffraction informations sample is compared with the JSPDS ( Joint Committee for Powder Diffraction surveies ) informations. The values of d-spacing and strengths obtained are compared with d-value and strengths given in JCPDS card. Therefore different stages of stuffs are identified on the footing of well-matched values of pulverization form and cards.
188.8.131.52 Crystallite Size Determination
The informations obtained from the x-rays diffraction of the stuff can besides be used to find the size of crystallite. For the atom holding crystallite size less than 10A give broaden diffraction extremums are observed. The term atom size is normally used for the crystallite size in this scope. The crystallite size is given by scherrer equation 65,67:
where I» is the wavelength of X raies, I? is the full breadth at half maximal ( FWHM ) of the extremum in radians, I? is the Bragg angle, C is a changeless with value runing from 0.9-1.0 depending on crystallite form and vitamin D is the crystallite size.
X-ray analysis was carried by JEOL-JDX-3532 Diffractometer with Cu KI±-radiations ( I»=1.54A ) beginning fitted with Ni-filtered. X ray tubing was operated at 30kV with tube current 30mA. Sample was scanned in the scope of 10o-70o at measure angle of 0.02o and scanning velocity of 1o per minute. The clip taken by each measure was 1.2sec. X ray was supported with computing machine plan loaded with ICDD x-rays diffraction files PDF-2. Phases were identified utilizing full informations hunt lucifer package.
3.6.4 Scaning Electron Microscope ( SEM )
Scaning negatron microscope is one of the most sophisticated instruments available for the microstructural word picture and analysis of the stuffs. It uses high energy negatrons instead than ordinary visible radiation to organize an image. When high energy negatron interacts with specimen it generates assortment of different signals. Such as X raies, Auger negatron, secondary negatrons, back scattered negatrons and cathode luminescence. These signals are used to analyze morphology, topography ( Surface surveies ) and compositional analysis. SEM has high declaration, big deepness of focal point field and provides three dimensional imagination. It has high magnification which makes the instrument utile for the stuff research 68.
The cardinal rules of Scaning Electron Microscope ( SEM ) were developed in the 1930. In 1938, Von Ardenne built first instrument which was later developed by Zwerykinetal in 1942 with declaration of 500A . The modern type of the instrument has been constructed in Cambridge by Otale and Mc Muller ( England 1948 ) . Nixon and his co-worker, extanded and work of Otale in 1959 and developed electron microscope with better contrast. In 1966, Cambrige Science Instrument Co. announced the word ‘s first commercial SEM 69.
Scaning Electron Microscope has many sophisticated constituents. All these constituents should be in proper map for accurate analysis of the sample under probe. Control console and electron optical column are the two chief parts of the SEM.
Control console is the chief unit of SEM to command maps of assorted constituents e.g. magnification, declaration, negatron gun, electromagnetic lenses and image contrast. In modern SEM most of the maps of constituents are controlled through computing machine package.
An negatron optical column for the SEM consists of negatron gun and electromagnetic lenses and scan spirals. Two common types of the negatron guns used in SEM to bring forth negatrons are thermionic Emission Gun and Field Emission Gun. In thermionic emanation negatron are generated by go throughing high curnt through fibril. These negatrons are accelerated from cathode to the specimen by application of high electromotive force runing from 1kV to 30kV 68. The fibril is surrounded by a grid cap, or wehnelt cylinder with round aperature centered at the fibril vertex. The grid cap is biased negatively between 0-500 Vs with regard to the cathode. The electric field produced in such agreement converge the emitted negatrons. While in field emanation gun, negatrons are generated by using high negative electromotive force to cathode about 3000V across the fibril.
Figure 3.4: Scaning Electron Microscope 70
Electron beam is converged by go throughing through electromagnetic lenses ( made of two electromagnetic pole pieces ) similar to optical lenses used to meet beam of visible radiation. This converged negatron beam is so allowed to interact with material specimen placed at the underside of the column. Air of the column is removed by a powerful vacuity pump.
The negatron beam scans across the specimen surface and bring forth different signals as discussed earlier. These signals are detected by different sensors and converted to electrical signals. These electrical signals are amplified and electronically recorded as image of the specimen. The electron barrage can do warming and extra negative charge on the specimen which affects the image quality peculiarly in instance of nonconducting stuffs. In instance of nonconducting stuff, extra negative charges and heat is removed by conductive coating of specimen. Coating besides increase mechanical strength of specimen and increase back scattered negatrons 68.
Scaning Electron Microscope ( SEM ) JSM5910 made by JEOL was used for SEM images. Its operating electromotive force is 30kV and maximal magnification is 300000X and declaration of 2.3nm.
3.6.5 Chemical Analysis of Surface Composition by EDX
The most of import portion of stuff word picture is the chemical analysis. Micro-constituent of the stuff are identified through different word picture techniques. Such as by X-ray scanning of the stuffs, atomic soaking up spectrometry, optical emanation spectrometry, infrared spectrometry, Reman spectrometry, Electron spin resonance spectrometry, fluorescence spectrometry and Rutherford back sprinkling, photoelectron spectrometry, Auger electron spectrometry and secondary ion mass spectrometry. The above mentioned techniques are widely used in the Fieldss of solid province stuff and surface scientific disciplines.
Energy diffusing X raies spectrometry ( EDX ) is the most normally used technique for the elemental analysis or qualitative analysis of the stuffs. Materials are subjected to high energy charge atoms like negatron, proton or high energy X raies. These incident radiations knockouts the inner shell negatrons or excite it to the higher energy degrees, go forthing a hole in the inner shell. The negatron passage to make full this hole from higher degree gives an x-ray photon of definite energy. These x-rays photon or characteristic X raies are used to place the component nowadays in stuff for the qualitative analysis. This technique is besides used to transport the quantitative analysis of the material specimen. The figure of photon of peculiar wavelength crossponds to the figure of atoms of a peculiar component nowadays in specimen 68,69.
The microstructure of samples was studied with aid of X-rays Energy Dispersive Spectrometer ( EDX-INCA 200, Oxford Instrument, U.K ) installed in Centralized Resource Laboratory ( CRL ) , Department of Physics, University of Peshawar. The EDX is capable to analyse elements runing from Boron to Uranium on periodic tabular array. In footings of Energy, declaration of EDX is 133eV.
3.6.6 Atomic Force Microscope ( AFM )
Atomic force microscopy is the topographical surveies of the surface of the material specimen. In this technique a crisp tip of cantilever is brought near to the surface of specimen so that it touches it and can feel the interatomic forces moving near the surface. Tip of AFM observe abhorrent force it touches the sample but at little distance it senses attractive force due to the Van-der-Walls attractive forces.
It was foremost designed to mensurate the raggedness of the sample. A beam of optical maser is focused on the brooding cantilever, which deflect the beam into a place sensitive array of photodiodes sensor. The cantilever tip gesture on the surface of the sample consequence the reflected angle and place of the optical maser beam. This assembly is used to scan the surface of sample and a computing machine package chalk out the image of the specimen.
Figure 3.5: Atomic Force Microscope 69
AFM has advantage over the SEM that is does non necessitate any conductive coating of the sample. It has high declaration and low cost in comparing of SEM69.
3.6.7 Surface Area Analyzer
Surface country of the solid is really of import to understand the behaviour of the solids. It can impact accelerator activity, surface assimilation capacity and processing of most pulverization and porous stuffs. Surface country chiefly increases with lessening in atom size. Some physical and chemical alterations such as disintegration or decomposition create pores in the atom. It can besides increase the surface country 71.
When solid atoms is exposed to a gas, the gas molecules adsorbed on the solid atoms. The adsorbed sum depends on the nature of absorbent and force per unit area. This surface assimilation can be physical or chemical. In physical surface assimilation gas molecules connect their egos due to some physical phenomena while in chemical surface assimilation ; molecule attached their ego with atom through chemical reaction. The physical surface assimilation in which gas molecules made a bed around the atom is more of import to find surface country of the atom.
The graph obtained by plotting the gas adsorbed at changeless temperature against the force per unit area is called surface assimilation isotherm and depends merely on form of the atom. A figure of theories are developed to explicate the surface assimilation procedure and isotherms. The first effort was made by Langmuir for monolayer adsorption71.
Two methods are developed for ciphering surface country and pore size. These methods are Brunauer-Emmett-Teller ( BET ) and Barret-Jouner-Halenda ( BJH ) .
184.108.40.206 Brunauer-Emmett-Teller ( BET )
Langmuir theory was further developed by Brunauer, Emmett and Teller by consideration of multilayer surface assimilation. The multilayer surface assimilation theory is known as Multilayer BET theory. Harmonizing to BET foremost layer attached itself with the atom by dipole interaction. The orientation of the first bed dipoles provides a base for the 2nd bed surface assimilation. In this manner multilayers adsorption take topographic point. It is most widely used technique for the finding of the surface country and pore size71,72.
220.127.116.11 Barret-Jouner-Halenda ( BJH )
This theoretical account was developed by Barret, Joyner and Halenda to cipher pore volume and radius. They assume that thickness of the residuary bed on the plane surface and the pores is the same. Thickness of the bed can be change with force per unit area of the specimen which help to find the volume of the pore 71,72.
Surface country analyser ( Model No: NOVA2200e ) installed in CRL, UOP, made by Quantachrome, USA, was used to find the surface country and pore size of the specimen under vacuity warming and nitrogen surface assimilation 73.
3.6.8 Fourier Transform Infrared Spectroscopy ( FTIR )
Fourier transform infrared spectrometry ( FTIR ) is a powerful technique to see inside the construction of the stuff molecules and atoms. It can be used to place molecules and atoms by the captive resonating frequences matching to different rotational and vibrational energy degrees. The crook of frequences absorbed by the stuff are clearly indicated as absent or in the spectrum. For the all right nanoparticles broadening is observed in the losing set 63,74.
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