Parkville, VIC, 3010, Australia 2 Department of Systems Innovation, Graduate School of Engineering

Size: px

Start display at page:

Download "Parkville, VIC, 3010, Australia 2 Department of Systems Innovation, Graduate School of Engineering"

Benjamin Wright
6 years ago
Views:

1 MEASUREMENTS OF PARTICLE SIZE DISTRIBUTION OF TITANIUM DIOXIDE SUBMICRON PARTICLES IN A NON- AQUEOUS SOLVENT BY INTERACTIVE FORCE APPARATUS UNDER AN ELECTRIC FIELD Akira Otsuki 1, Gjergj Dodbiba 2, Toyohisa Fujita 2 1 Chemical and Biomolecular Engineering, University of Melbourne Parkville, VIC, 3010, Australia akira.otsuki@unimelb.edu.au 2 Department of Systems Innovation, Graduate School of Engineering The University of Tokyo, Hongo, Bunkyo, Tokyo , Japan ABSTRACT This paper describes the measurement of size distribution of TiO 2 fine particles in a non-aqueous solvent by interactive force apparatus (IFA) under an electric field. The application of the apparatus to the measurement of particle size distribution in a nonaqueous solvent was suggested. The results were compared with results obtained from size measurement by SEM. They showed that the distribution measured by IFA was larger (D 50 > 350 nm) at less than 0.06 V and was smaller (D 50 = nm) at higher than 0.12 V, compared with the one measured by SEM (D 50 = 300 nm). The difference is mainly due to the increase in number of particles in fine size fraction with increasing supply voltages. Decrease in size indicated that the breakage of coagulated particles and/or disintegration of doublet particles possibly occur due to the electric breakdown. The electric breakdown was explained by monitoring the mean diameters and their standard deviation obtained from IFA measurements at different supply voltages. Keywords: Particle size distribution, titanium dioxide submicron particles, non-aqueous solvent, interactive force apparatus, electric field, electric breakdown 1

2 1. Introduction It is important to characterise and manipulate the degree of dispersion and coagulation of fine particles in various media for many industrial processes (Elimelech et al, 1998; Allen, 1997). Therefore, there is a significant need for understanding those characteristics of fine particles in the specific media. Many techniques are currently available for evaluating them by measuring size (Nguyen, George & Jameson, 2006), turbidity (Ata & Yates, 2006), contact angle (Kusaka et al, 1993), zeta potential (Mitchell, Nguyen & Evans, 2005), force between particle and plate (Butt, Cappella & Kappl, 2005; Derelich et al, 2006) as well as combination of these techniques (Yoon, Flinn & Rabinovich, 1997; Yates et al, 2005). However, these methods usually are not suitable in highly concentrated suspensions and non-transparent suspensions. On the other hand, these kinds of solutions are commonly used in the many industrial procedures, such as separation of mineral particles. In this study, we focused on particle size measurement for characterising fine particles. The conventional technologies can be divided in two categories, i.e. measurements in (i) dry conditions and (ii) wet conditions (Allen, 1997). In dry condition, scanning electron microscope (SEM) and transmission electron microscope (TEM) are the common technologies for size measurement of submicron to nanoparticles. In wet conditions, the technologies using laser source (i.e. the dynamic light scattering and laser diffraction) are the commonly used. Each of them has advantages, and some drawbacks. By definition, the technologies in dry conditions are not applicable for the measurement in solvents. The technologies in wet conditions are not usually suitable for measurement in high particle concentrations and/or the suspensions with no optical transparency. The interactive force apparatus (IFA) was designed for determining the degree of dispersion and coagulation of particles suspended in functional fluids under a magnetic or electric field (Miyazaki et al, 2002; Shibayama et al, 2005). The apparatus employs a direct measurement system, not depending on the particle concentration and optical transparency of the suspensions. Moreover, the measurement can be conducted in various solvents (e.g. aqueous solution (Otsuki, Dodbiba & Fujita, 2010) and organic solvent (Otsuki, Dodbiba & Fujita, 2007)). However, the results were not fully compared with other methods and particle size distribution in non-aqueous solvent was not calculated due to the limited number of data acquisition. In this study, IFA was used to measure the size distribution of TiO 2 fine particles in non-aqueous solvent with increasing the number of data acquisition in order to evaluate the availability of IFA for the size distribution measurement. The current experimental setup allows detection of primary particles and/or aggregates of particles in a sample suspension. The results were compared with results obtained by analysing a series of photographs taken by SEM. This study indicated the applicability of IFA to industrial uses, e.g. online measurements of fine particles in their processing plants. 2. Materials and methods 2.1 Materials Titanium dioxide particles provided by Ishihara Sangyo were used for the measurements. Median diameter (D 50 ) was about 300 nm determined by analysing a 2

3 series of photographs taken by SEM. Concentration of TiO 2 fine particles in ethanol was 2 vol. per cent. A 2 wt. per cent of polyethyleneimine was added to disperse particles in ethanol. The sample suspensions were sonicated prior to the measurements. 2.2 Experimental setup a) Interactive force apparatus The IFA consists of three parts: 1. A measurement cell which consists of an electric balance, hemisphere and flat plate. The IFA measures the interactive force between two surfaces, i.e. a goldcoated glass hemisphere and brass flat plate, (which is fixed at the bottom of the sample cell). The main part measures the weight of the hemisphere immersed in a sample suspension with decreasing the distance between the two surfaces at a certain speed. 2. In the control unit a personal computer, piezo-stage controller and voltage supplier are employed to adjust a supply voltage, regulate the movement of piezo-stage and collect data from the balance and the piezo-stage controller. 3. The contact analysis unit (i.e. a multi-meter and oscilloscope) measures the contact point where the hemisphere and flat plate attach. Figure 1 shows the measurement cell of the apparatus. The hemisphere is hung from the electric balance into the sample suspension. The weight of the hemisphere is measured by using the electric balance, and recorded by the personal computer. The flat plate moves toward the hemisphere, and the distance d (e.g. from 100 nm) decreases until the hemisphere makes point contact with the flat plate. Applying voltage to the piezo-stage and its subsequent movement is used to regulate the distance between the hemisphere and flat plate. The rate of movement is determined based on an initial separation distance between the hemisphere and flat plate when a measurement starts (e.g. 1 nm/s for 100 nm distance). The piezo stage is located on a z stage. Detecting the contact point of the hemisphere to the flat plate at the bottom of the cell (i.e. d = 0) is the important reference point for subsequent distance measurements. The measured weight is converted to the interactive force by using the Derjaguin equation (Derjaguin, 1934): F(D)sphere = 2πW(D) R plane (1) where W (D)plane is the interactive free energy, F (D)sphere is the interactive force between the hemisphere and the flat plate, and R is the curvature radius of the glass hemisphere, respectively. The interactive force was plotted as a function of the distance between the hemisphere and flat plate (i.e. force-distance curve). This data is the basis to determine the size of fine particles. Under an electric field generated between two parallel plates, pearl chains of dielectric particles form towards the direction of electric field (Jordan & Shaw, 1989). In terms of shape of the chains, linear chains form over triangular chain under the electric field due to the former being more stable in terms of potential energy (Otsuki, Dodbiba 3

4 & Fujita, 2009). During the measurement, an electric field is applied between the hemisphere and flat plate, and dielectric particles are arranged toward the direction of electric field in the area between plate and hemisphere. When the two plates are close to each other, two different forces (i.e. repulsive and attractive forces) are alternately measured due to changes in the arrangements of the particles (Fig. 3) (Otsuki, Dodbiba & Fujita, 2010, 2011). The repulsive force occurs when the particle chain structure is stretched by compressive force; whereas the attractive force occurs when the particle chain structure is broken. The cycle of repulsive and attractive forces is determined by the primary size of particle or size of aggregate, which depends on the degree of agglomeration. In order to determine the cycle precisely, the 1 st derivative of the force is plotted. The distance between points at zero value of 1 st derivative, where the value turns negative to positive, corresponds to the size of particles or aggregates, which is the same as the cycle of repulsive and attractive forces as shown in Fig. 4. Figure 4 shows a typical derivative curve as a function of surface distance when TiO 2 fine particles suspended in ethanol was measured by IFA under 0.24 V supply voltage. From the Fig. 4, the size of TiO 2 particles was determined in the range from 147 to 471 nm. The wide range of particle size is explained by poly-disperse particle size distribution as shown in Fig. 5. Five continuous measurements were conducted and then a particle size distribution was calculated based on the measurements. b) SEM measurements Size of titanium dioxide particles was also measured using FE-SEM (S-4300, Hitachi, Ltd.) to compare the results with the one obtained using IFA. The particles were placed on the SEM stage and gently pressed with a spatula. It was then loaded into the machine. In this study, SEM photographs were transformed into a size distribution using the equipped computer software with necessary manual modification of identifying particles prior to the particle counting. The number of particles counted was approximately five thousands. 3. Results and discussion Figure 5 shows the size distribution of TiO 2 particles in ethanol measured by IFA and the results in dry condition measured by SEM. IFA measurements were conducted at different supply voltages from 0.03 to 0.48 V in order to investigate the effect of electric field strength on the results of measurement. As shown in this graph, the distribution measured by IFA was larger (D 50 > 350 nm) at lower than 0.06 V and was smaller (D 50 = nm) at higher than 0.12 V, than the one measured by SEM (D 50 = 300 nm). The difference is mainly because number of particles in fine size fraction increased with increasing supply voltage. This trend indicated that breakage of coagulated particles possibly occur at higher than 0.12 V supply voltages due to the electric breakdown. In order to confirm the electric breakdown during the IFA measurement at higher than 0.12 V supply voltages, two different particle size distribution functions were fitted with the experimental data. This curve fitting method has been used to explain the electric breakdown in an aqueous suspension (Otsuki, Dodbiba & Fujita, 2010). The distribution functions were Log normal distribution and Rosin-Rammler distribution as described in Eqs. (2) and (3), respectively. Log normal distribution is usually fitted well 4

5 with particle size distribution of synthesised spherical particles while Rosin-Rammler distribution is usually fitted well with particle size distribution of ground non-spherical particles. Q( d) = 1 2π lnσ ln d 0 ( d d ) 2 0 exp d(ln d) 2ln 2 σ (2) d Q d) 1 exp ( ) d e = n ( (3) where d is diameter of particle, d 0 is mean diameter of particle, σ is standard deviation, d e is absolute size constant, n is distribution constant. Figure 6 shows the size distribution of TiO 2 fine particles measured by the interactive force apparatus under two different supply voltages, (a) 0.03 and (b) 0.48 V, fitted with two different particle size distribution functions. Under the both supply voltages, the difference between fitting the experimental data with both functions was small as shown in Fig. 6. It indicates the existence of non-spherical particles in fed sample powders made difficult to determine whether the generation of non-spherical particles by electric breakdown. Moreover, median diameters and their standard deviation as a function of supply voltage are calculated and shown in Fig. 7, in order to confirm the electric breakdown. The graph shows the maximum, minimum and average of median diameter obtained from five continuous measurements and standard deviation of the median diameter. As shown in Fig. 7, standard deviation is low, around 100 at 0.06 to 0.24 V and 40 at 0.48 V to indicate the good reproducibility of data, and decreased with increasing the supply voltage. On the other hand, standard deviation is little high around 260 at 0.03 V. This trend is agreed with the one found in aqueous-silica system (Otsuki, Dodbiba & Fujita, 2010). Therefore, the results indicated that small particles are coagulated under weak supply voltage (0.03 and 0.06 V) while they are dispersed to be primary particles under strong supply voltage (0.12 and 0.24 V). Aggregates are dispersed and/or even doublets are disintegrated under even stronger voltage of 0.48 V by electric breakdown between electrodes. When the high voltage is applied, electrical disintegration may occur at the points where materials are weakly bound, e.g. interface of two minerals (Andres, Timoshkin, Jirestig & Stallknecht, 2001). The results measured by IFA at 0.06 V (Fig. 5) and SEM photograph (Fig. 1) indicate that there are aggregates and doublets of titanium dioxide particles. These particles are dispersed due to the electric breakdown which creates large current at the interface of the aggregates to expand and contract the interface immediately followed by disintegration of the aggregates. As the electric breakdown generates ions that adsorb on particle surfaces, the force forming pearl chains also becomes weaken (Nakajima & Matsuyama, 2002). Electric breakdowns in ER fluid and aqueous suspension were also reported in a similar/same experimental setup by Shibayama et al. in 2005 and Otsuki et al. in 2010, respectively. 4. Conclusions In this study, the size distribution of TiO 2 fine particles was measured by the interactive force apparatus under different supply voltages. The results were compared 5

6 with the results obtained from the analysis of SEM photographs in order to evaluate the availability of the apparatus for size distribution measurement in a non-aqueous solvent. The results show the distribution measured by IFA was larger (D 50 > 350 nm) at lower than 0.06 V and was smaller (D 50 = nm) at higher than 0.12 V, compared with the one measured by SEM (D 50 = 300 nm). The difference is mainly because number of particles in fine fraction increased with increasing supply voltages. This trend indicated that breakage of coagulated particles possibly occur when supply voltage was higher than 0.12 V due to the electric breakdown. The results indicate that breakage of coagulated particles possibly occur due to the electric breakdown. The electric breakdown was explained by monitoring the mean diameters and their standard deviation calculated from the IFA measurements. They indicates that finer particles are coagulated under the weak supply voltages (0.03 and 0.06 V) while they are dispersed to be primary particles under the strong supply voltages (0.12 and 0.24 V) or even they are disintegrated under even stronger voltage of 0.48 V by the electric breakdown between the electrodes. ACKNOWLEDGMENT The authors would like to express appreciation to financial support from University of Melbourne for attending to the conference. REFERENCES Allen, T, Powder sampling and particle size measurement, in Particle Size Measurement, in Volume 1, Fifth edition, pp (Chapman and Hall: London). Andres, U., Timoshkin, I., Jirestig, J., & Stallknecht, H., (2001). Liberation of valuable inclusions in ores and slags by electric pulses, Powder Technology 114, Ata, S., & Yates, P.D., (2006). Stability and flotation behaviour of silica in the presence of a non-polar oil and cationic surfactant, Colloid. Surf. A 277, 1-7. Butt, H.J., Cappella, B., & Kappl, M., (2005). Force measurements with the atomic force microscope: Technique, interpretation and applications, Surface Science Reports, 59, Derjaguin, B.V., (1934). Untersuchungen über die Reibung und Adhäsion, IV, Kolloid Zeits. 69, Drelich, J., Long, J., Xu, Z., Masliyah, J., & White, C.L. (2006). Probing colloidal forces between a Si 3 N 4 AFM tip and single nanoparticles of silica and alumina, J. Colloid Interface Sci. 303, Elimelech, M., Gregory, J., Jia, X., & Williams, R.A., (1998). in Particle deposition and aggregation, pp. 4-8 (Butterworth-Heinemann: Woburn). Jordan, T.C., & Shaw, M.T., (1989). Electrorheology, IEEE Transactions on Electrical Insulation 24, Kusaka, E., Tamai, H., Nakahiro, Y., & Wakamatsu, T., (1993). Role of surface free energy in a solid surface during collectorless liquid-liquid extraction, Minerals Engineering 6,

7 Mitchell, T.K., Nguyen, A.N., & Evans, G.M., (2005). Heterocoagulation of chalcopyrite and pyrite minerals in flotation separation, Adv. Colloid Interface Sci , Miyazaki, T., Shibayama, A., Sato T., & Fujita, T., (2002). Measurement of interaction force between small distances sandwiched with magnetic fluid under magnetic field, Journal of Magnetism and Magnetic Materials 252, Nakajima, Y., & Matsuyama, T., (2002). Electrostatics field and force calculation for a chain of identical dielectric spheres aligned parallel to uniformly applied electric field, J. Electrostatics 55, Nguyen, A.N., George, P., & Jameson, G.J., (2006). Determination of a minimum in the recovery of nanoparticles by flotation: Theory and experiment, Chemical Engineering Science 61, Otsuki, A., Dodbiba, G., & Fujita, T., (2007). Two-Liquid Flotation: Heterocoagulation of Fine Particles in Polar Organic Solvent, Material Transactions 48, Otsuki, A., Dodbiba, G., & Fujita, T., (2009). Effect of particle size distribution on formation of linear configuration of dielectric fine particles under the electric field, J. Phys. Conf. Series 147, Otsuki, A., Dodbiba, G., & Fujita, T., (2010). Measurement of particle size distribution of silica nanoparticles by interactive force apparatus under an electric field, Adv. Powder Tech. 21, Otsuki, A. Dodbiba, G., & Fujita, T., Chapter 40. Particle Size Measurements of Dielectric Particles using Pearl Chain Formations of the Particles under an DC Electric Field, in Electrical Phenomena at Interfaces and Biointerfaces: Fundamentals and Applications in Nano-, Bio-, and Environmental Sciences, Ed. Hiroyuki Ohshima, John Wiley & Sons, Inc., Shibayama, A., Otomo, T., Shimada, & K., Fujita, T., (2005). Measurement of interactive surface force of suspended particles in ER and MR suspensions under electric and magnetic field, International Journal of Modern Physics B 19(7-9), Stratton-Crawly, R., (1979). Beneficiation of Mineral Fines - Problems and Research Needs, pp (AIME: New York). Yates, P.D., Franks, G.V., Biggs, S., & Jameson, G.J., (2005). Heteroaggregation with nanoparticles: effect of particle size ratio on optimum particle dose, Colloid. Surf. A 255, Yoon, R.H., Flinn, D.H., & Rabinovich, Y.I., (1997). Hydrophobic interactions between dissimilar surfaces, J. Colloid Interface Sci. 185,

8 Fig. 1. SEM Photograph of titanium dioxide submicron particles. (a) (b) (c) (h) d Direction of movement (f) (d) (e) (g) (a) Electric balance (b) Platinum wire (c) Sample solution (d) Hemisphere (Gold-coated) (e) Flat plate (Brass) (f) Piezo-stage (g) Z stage (h) Glass cell Fig. 2. Schematic diagram of main part of experimental setup for the interactive force apparatus. 8

9 Hemisphere y Electric field x (Step1) (Step2) (Step3) Repulsion Attraction (Step4) Attraction (Step5) (Step6) Repulsion d Flat plate Time Fig. 3. Behaviour of dielectric particles during the measurements under an electric field (Otsuki, Dodbiba & Fujita, 2010) st Derivative, ( (F/R))/ d /x10 7 N m Surface distance, d/nm Fig. 4. Derivative curve of F (D)sphere R -1 when titanium dioxide particles in ethanol was measured by the interactive force apparatus at 0.24 V supply voltage as a function of surface distance. 9

10 Cumulative size distribution ( ) V 0.24 V 0.12 V 0.06 V SEM Particle size, d / nm Fig. 5. Size distribution of titanium dioxide particles in ethanol measured by the interactive force apparatus at the different supply voltages from 0.06 V to 0.48 V and measured by SEM Cumulative size distribution ( ) R-R L-N (a) 0.03 V Particle size, d / nm Cumulative size distribution ( ) L-N R-R (b) 0.48 V Particle size, d / nm Fig. 6. Size distribution of titanium dioxide particles in ethanol measured by interactive force apparatus at the different supply voltage (a) 0.03 V and (b) 0.48 V, fitted with Log-normal distribution function (L-N) and Rosin-Rammler distribution function (R-R). 10

11 1200 Median diameter, d 50/nm Standard deviation, σ Aggregation Aggregation /Dispersion Dispersion /disintegration Supply voltage, V /V Fig. 7. Median diameters and their standard deviation of titanium dioxide particles as a function of supply voltage measured by the interactive force apparatus. 11

Dispersion-Flocculation Behavior of Fine Lead Particles in an Organic Solvent

Materials Transactions, Vol. 49, No. 9 (2) pp. 2119 to 2123 #2 The Mining and Materials Processing Institute of Japan Dispersion-Flocculation Behavior of Fine Lead Particles in an Organic Solvent Masami