Magnetic Nanoparticles: Ferrofluids - Lab Report Example

Name: Lab Assistant: Course: Date Experiment 2 MAGNETIC NANOPARTICLES: FERROFLUIDS AIM The aim of this lab was to prepare a magnetic fluid, observe its properties and then characterize the properties. Introduction Magnetism Magnetism is a material property that make an object to respond to an applied magnetic field at a sub-atomic or atomic level. The basic principle of magnetism is defined by the interactions between electrons during their orbital and spin motions. There are three different classes of magnetism: diamagnetism, paramagnetism and ferromagnetism. Diamagnetism can be described as a very small magnetic effect that is produced by electron orbital motions around the nucleus in the presence of a magnetic field. A diamagnetic force for any atom can be approximated, even though it is very negligible compared to paramagnetic and other effects. Thus, it may be ignore red in the total magnetic susceptibility. Paramagnetism arises in a material due to spinning and orbital motion of unpaired electrons in partially filled orbitals, which causes atoms or ions to exhibit a magnetic moment. Both electron spin and orbital motion contribute to the resulting paramagnetism, with the former having a greater magnitude. When the magnetic field is withdrawn, magnetization runs to zero, meaning that there is no magnetic interaction of atomic and molecular magnetic dipoles at individual level. The magnitisation process of paramagnetic materials is dependent on the randomized effect of temperature according to Curie law. Ferromagnetism arises as a result of electronic exchange forces that cause alignment of magnetic domains in a material (Charles). The magnetic moments experience very strong interactions due to these forces, and the alignment may be parallel or antiparallel. In addition, quantum mechanical phenomenon is involved because of relative orientation of two spinning electrons. Ferromagnetic materials remain magnetized permanently even though some hysteresis occur on application of a magnetic field. Ferrofluids A ferrofluid can be described as a stable colloidal liquid dispersion consisting of nanoscale ferromagnetic particles (Odenbach). In the presence of a magnetic field, a ferrofluid becomes strongly magnetized. This is as a result of a delicate balance of repulsive and attractive forces between the particles in the fluid. In specific, magnetic moments in the neighbouring panicles interact to produce magnetic forces, and also surfactant molecules that are attached on their surface. Ferrofluid was discovered in 1960s by NASA in an experiment to manipulate liquid rocket fuel to be drawn to a pump inlet in the weightless atmosphere by application of a magnetic field. Ferrofluids respond in the presence of a magnetic field, making it possible to control the location of the solution. Since then, ferrofluid has found several applications in electronic devices, mechanical engineering, material science, spacecraft propulsion, analytical instrumentation and medical applications. This lab experiment involved a synthesis reaction of iron (II) and iron (III) ions in a solution of aqueous ammonia to form Fe3O4 magnetite. Mixing Fe (II) and Fe (III) salts in a basic solution produces Fe3O4 magnetite nanoparticles. The magnetic nanoparticles are extremely small in size so that they cannot fully settle on to the bottom, but just hung within the fluid as if they were fully dissolved. The actual reaction that occurs is illustrated by the chemical equation below: 2 FeCl3 + FeCl2 + 8NH3 + 4H2O  Fe3O4 + 8NH4Cl Figure 1: Formation of Fe3O4 magnetite nanoparticles from the reaction between Fe (II) and Fe (III) in an aqueous ammonia solution. The magnetite was then mixed with an aqueous solution of tetramethylammonium hydroxide to create an aqueous environment with electrostatic inter-particle repulsion. The resulting ferrofluid was then tested for its spiking properties, X-ray powder diffraction (XRD) and magnetic susceptibility. Experimental Procedure Refer to the lab manual “Experiment 2: MAGNETIC NANOPARTICLES: FERROFLUIDS”, page 4-8. Results and Discussion Question 1. This is the balanced chemical equation for the synthesis of iron (II) and iron (III) ions in the presence of aqueous ammonia to form magnetite. 2 FeCl3 + FeCl2 + 8NH3 + 4H2O  Fe3O4 + 8NH4Cl From the balanced chemical equation, mole ratio of FeCl3:FeCl2 is 2:1 Molar mass of hydrated FeCl2 = 198.81g/mol Prepare 1 ml of 2M FeCl2 in 2M HCl: 1 ml of hydrated FeCl2 = (0.0012) = 0.002 moles From the mole ratio, moles of FeCl3 = (0.002 2) = 0.004 moles. The mass of FeCl3 equivalent to 0.004 moles = (0.004/270.3) = 1.08 g Question 2. Spiking Test This test was done by raising a magnet to the base of the boat with the ferrofluid to observe the spiking properties of the fluid. The figure below shows the spiking pattern that was obtained. Figure 2: Spiking pattern of the ferrofluid near a magnet Table 1: Results of spiking test Distance between the boat and the magnet (cm) Height of the spikes (mm) Relaxation time of spikes (sec) 1 2.5 1.5 0.5 7 2.5 0 4 3.0 Average = 2.3 sec. The largest distance between the boat and the magnet was 1.0 cm, while the highest spike was at 7 mm. The average relaxation time on withdrawal of the magnet was 2.3 sec. The height of the spikes increase as the distance between the magnet and the boat reduces, but drops as the distance reduces to zero. A similar trend is observed with the relaxation time. This means that the alignment of ferrofluid particles increases as the distance between the magnet and the sample reduces up to some point, beyond which the effect on the particles reduces. This results show that the ferrofluid has a good spiking effect. The spiking effect is as a result of a dynamic interaction between varous forces including surface tension, magnetic force, gravity force and Van der Waals force (Tabuchi, Ado and Sakaebe). The ferrofluid contains small magnetic compounds that act separately when induced by a magnetic field to form the pattern in figure 2 above. In the presence of the magnetic field, the ferrofluid particles tend to align themselves along the magnetic field lines. The adjacent magnetic fluid particles farther away from the magnet are magnetically attracted, while adjacent particles closer to the magnet are repelled. An accurate estimation of spike size can be done by using TEM or XRD. Question 3 The main difference between ferrofluids and commercial magnetite is the size of the particles. In ferrofluids, the particles primarily consist of nanoparticles suspended by Brownian motion, and under normal conditions, these nanoparticles will not settle down. Commercial magnetite fluids consist of micro-metre particles which cannot be suspended by Brownian motion, but instead, will settle after some time due to difference in inherent density between the particles and the carrier fluid. The surfactant used overcomes the attractive magnetic and Van der Waals forces between particles in a ferrofluid (Pant, Rashmi and Krishna). Question 4 X-ray Diffraction Results When the X-ray Diffraction was performed to identify the structure of magnetite particles, the graphs presented below were obtained. Figure 3: X-ray Diffraction peaks for reference magnetite. Figure 4(a): Peak number 1 close-up (magnetite) Figure 4(b): Peak number 2 close-up (magnetite) Figure 4(c): Peak number 3 close-up (magnetite) Figure 4(d): Peak number 4 close-up (magnetite) Figure 5: X-ray Diffraction peaks for the ferrofluid. Figure 6(a): Peak number 1 close-up (ferrofluid) Figure 6(b): Peak number 2 close-up (ferrofluid) Figure 6©: Peak number 3 close-up (ferrofluid) Figure 6(d): Peak number 4 close-up (ferrofluid) The figures from 1 to 6 above were produced by a powder x-ray technique to analyze the structure of the magnetite and the ferrofluid. Figure 3 to 4(d) are for the magnetite, while figure 5 to 6(d) represent XRD figures for the ferrofluid. The d values and intensity (counts) of the diffraction peaks in figure 5 are in a good match with that of a single crystalline spinel of the nanoparticles of Fe3O4. The broad peaks in the X-ray diffraction indicates the ultrafine small crystal size of the ferrofluid particles. The table below shows a tabulated data of the XRD results shown in the graphs above. Table: XRD data analysis and d-spacing for reference magnetite Peak no. Angle 2 theta (deg) 2Theta/2(deg) Intensity (counts) 100 FWHM Sin (2Theta/2) d spacing wavelength/2sin(theta) 1 35.1 17.55 9.3 0.16 0.30 2.57 2 41.2 20.6 25 0.18 0.35 2.20 3 50.5 25.25 9.0 0.22 0.43 1.79 4 67.3 33.65 7.8 0.30 0.55 1.4 Table: XRD data analysis and d-spacing for the ferrofluide Peak no. Angle 2 theta (deg) 2Theta/2 Intensity (counts) 10 FWHM Sin (2Theta/2) d spacing =wavelength/2sin(theta) 1 35.1 17.55 19 0.16 0.30 2.57 2 41.5 20.75 32 0.18 0.35 2.20 3 30.8 15.4 17.5 0.14 0.27 2.85 4 21 10.5 7.1 0.09 0.18 4.28 Form the XRD data in the tables above, the ferrofluid has an XRD pattern with broader peaks compared to the commercial magnetite. Question 5 For reference magnetite Peak 3 = 25 100 counts FWHM = 0.22 x 3.14 /180 = 0.0038 For the ferrofluid: Peak 3 = 25 10 counts FWHM = 0.14 x 3.14 / 180 = 0.0024 Using the Warren formula, B2=B2 colloide sample – B2 Bulk material B2 t= 2.131 x 10-4 nm Question 6 Magnetic Susceptibility The table below shows the results obtained when a Guoy balance was used to measure the magnetic susceptibility of diluted samples of the ferrofluid and the magnetite: Table 1: Magnetic susceptibility Dilution Weight of tube (g) Weight of tube + sample (g) Weight of sample (g) Sample length (cm) Tube reading (Ro) Tube + sample reading (R) Ferrofluid: 1:1000 1.6 1.75 0.15 3.5 -56 660 1:100 1.76 1.86 0.1 3.2 -55 720 Magnetite: 1: 1000 1.55 1.70 0.15 3.2 -57 83 1: 100 1.60 1.73 0.16 3.0 -49 62 Hg{CO(BCS)} 1.6 1.76 0.16 3.1 -43 40 Calibration constant for the Hg {CO (BCS)} R= 40 R0= -43 M (sample + tube) =1.76g M (empty tube) =1.60g M=0.16 = = 38.79 units for magnate (dilation 1:1000): R= -83 R0= -57 M = 0.16 = = 3.39 x 10-5 units for magnate (dilation 1:100): R= 62 R0= -49 M= 0.16 g = = 2.69 x 10-5 units for ferrofluide (dilation 1:1000): R= 720 R0= -55 M=0.10 g = = 1.56 x10-4 units for ferrofluide (dilation 1:100): R= 1340 R0= -59 M=0.14 g = = 2.58 x 10-4 units From the calculations above, it can be noted that mass susceptibility values for dilutions of magnate are lower compared to the mass susceptibility of the ferrofluide. This shows that the ferrofluid is magnetically stronger than commercial magnetite. Conclusion The XRD study in this experiment is a confirmation of the nanocrystalline nature of Fe3O4 particles. The nanoparticles in the sample are well dispersed, with an average particle size of 2.131 x 10-4 nm. On the other hand, the magnetic susceptibility measurements verify the superparamagnetic nature of the ferrofluid, as well as a good spiking effect. The superparamagnitization is attributed to the fine crystalline nature of the ferrofluid. References Read More