Article pubs.acs.org/EF
Characteristics of Vapor Condensation on Coal-Fired Fine Particles Junchao Xu, Jun Zhang,* Yan Yu, Qiang Meng, and Hui Zhong Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education, Southeast University, Nanjing 210096, Jiangsu Province, China ABSTRACT: Heterogeneous condensation of water vapor on coal-fired fine particles was investigated in a growth tube. The influence of operating parameters and wetting agent addition on vapor condensation enlargement for three coal-fired fine particles from different power plants were tested. The results show that all the three coal-fired fine particles induce heterogeneous condensation and the process is favored by increasing the water temperature and residence time and decreasing particles initial number concentration; wetting agent addition highly facilitates the effect of vapor condensation on fine particles and the performance is increased with the increase of wetting agent addition. It is also found that excessive addition encourages the performance of final mean size of particles but discourages the performance of finer particles enlargement. With wetting agent addition, the mean diameter of fine particles can be enlarged above 3 μm while the mean diameter can only be enlarged above 2 μm without wetting agent addition (the original mean diameter of particles is about 0.15 μm).
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nucleation ability. Chen et al.15−17 investigated the heterogeneous condensation on submicrometer particles of SiC, SiO2, TiO2, Al2O3, carbon black, and naphthalene in a flow cloud chamber through the measurement of removal efficiency. The results showed that particle removal efficiency increased with increase of supersaturation and the chemical composition of the aerosols played an important role on the nucleation process. Hogrefe18 and Sharoichenko19 studied vapor condensation on individual micron-sized clean glass particles by combining an upward thermal diffusion with an electrostatic levitation and an optical CCD in a visible way. They found that heterogeneous nucleation was sensitive to the surface properties of the individual particles. Though many particles that induce heterogeneous condensation under water vapor were studied, the coal-fired particles size, chemical composition, and surface properties are different from the particles listed above. Furthermore, Fan et al.20 enabled heterogeneous condensation into application in a scrubber for coal-fired fine particles removal. High efficiency removal of fine particles from coalfired flue gas with conventional dust removal facilities was achieved through using heterogeneous condensation of water vapor on fine particles as a preconditioning technique. Moreover, a novel process to remove fine particles with high efficiency by heterogeneous condensation in a wet flue gas desulfurization (WFGD) system was developed.21,22 The results showed that the removal efficiency of coal-fired fine particles increased with increasing amount of added steam. These experimental data were obtained by measuring removal efficiency as a function of supersaturation. In addition, wetting agent addition greatly improved the particles removal efficiency in the WFGD system.23 In spite of the large amount work on heterogeneous condensation for particle enlargement that has
INTRODUCTION The emissions of particulate matter entrained in flue gas from industrial and vehicles are considered as major health and environmental concerns.1,2 Source apportionment of PM2.5 shows that coal-fired fine particles from power plants are one of the main sources of fine particles in ambient air, especially in China.3,4 However, the traditional dust removal equipment (like electrostatic precipitators, cyclones, wet scrubbers, etc.) is far less efficient in collecting submicrometric particles, especially in the range of 0.1−1 μm, called the Greenfield Gap.5 Obviously, it would be much easier for their removal if one could manage to enlarge the particles size before they enter into the collection devices. So some technologies of enlarging particles size, such as electrostatic agglomeration,6 acoustic wave agglomeration,7 chemical agglomeration,8 and vapor condensation,9 have been put forward. In these technologies, particles growth by vapor condensation is one of the most promising preconditioning techniques for industrial dust collection.10,11 The pilot experiment of Bao et al. showed that the improvement of fine particles number concentration removal efficiency of at least 40−60% could be attained by the vapor condensation in which the supersaturated field was constructed by adding 0.08 kg of steam per N m3 of flue gas.12 Vapor condensation on particles is a process of heterogeneous condensation. For understanding the characteristics of vapor condensation on fine particles, Porstendorfer et al.13 studied the heterogeneous condensation of vapor on Ag and NaCl particles in a size-analyzing nuclei counter and observed the process significantly depends on the particle size and chemical composition. For the NaCl aerosol, however, the measured critical supersaturation was much lower than predicted by Kelvin’s equation. Lammel et al.14 studied the water vapor condensation on carbon black and chemically modified carbonaceous particles by simultaneous measurement of condensation nuclei (CN) and cloud condensation nuclei (CCN), and the results showed that the nucleation ability of particles increased with increasing soluble mass fraction but the soluble fraction was not the only characteristic affecting the © 2016 American Chemical Society
Special Issue: 5th Sino-Australian Symposium on Advanced Coal and Biomass Utilisation Technologies Received: September 24, 2015 Revised: January 3, 2016 Published: January 4, 2016 1822
DOI: 10.1021/acs.energyfuels.5b02200 Energy Fuels 2016, 30, 1822−1828
Article
Energy & Fuels Table 1. Chemical Composition of Different Particles chemical composition (%)
Na2O
MgO
Al2O3
SiO2
P2O5
SO3
CaO
K2O
Fe2O3
Cl
TiO2
Jiaxing Nanjing Inner Mongolia
0 0.4 1.3
0.38 1.04 1.33
50.11 30.6 23.2
40.32 51.5 55.6
0.78 1.08 0.75
0.63 1.148 0.61
3.63 7.0 5.1
0.35 1.2 2.4
1.99 5.4 7.3
0 0 0
1.75 0.63 0.53
adhesion of water with the tube walls. In the experiment, the liquid temperature was kept at the desired value, Th, by means of a thermostatic bath. The cooling unit cooled the aerosol gas into dew point, and then the cooled and saturated gas was sent into the growth tube and encountered the hot water supplied by the thermostatic bath. The water vapor was transferred from the tube wall into the cooled gas which generated a supersaturation environment for the mass diffusivity is bigger than the heat diffusivity of water vapor. The measurement part consists of a laser droplet measuring instrument (model OMEC-DP-02, China), an optical measurement window, and a hot wind fan. The laser instrument allows the measurement of PSD in the range between 0.05 and 1500 μm. The optical measurement window, which was made of optical glass, is closed to the outlet of the growth tube avoiding the evaporation of droplets containing particles. The hot wind fan provides a hot airflow around the optical window to avoid droplets evaporating and condensing on the window. Temperature of the thermostat was set at 303, 313, and 323 K to study the influence of water temperature. Otherwise, two initial number concentrations 1.7 × 106/cm3 and 3.4 × 106/cm3 and two residence time, 1.2 s and 2.12 s, were tested to understand their influence. Wetting agents are compounds that lower the surface tension (or interfacial tension) between two liquids or between a liquid and a solid. Here a polysorbate surfactant, Tween 20, was used as the wet agent and was introduced into the system with the hot water at the concentration 10 g/L, 20 g/L, 30 g/L, respectively (for Inner Mongolia particles an extra concentration 40 g/L was set because its higher contact angle than other particles). Blank tests were taken only with hot water and clean air inlet to detect the homogeneous condensation at different temperature Th. The results showed that no homogeneous condensation occurred in the growth tube at any temperature Th (303−323 K) setup in our experiments.
been done, the characteristics of vapor condensation on the particles from coal combustion have not been directly investigated. This is because the droplet contains particles that are easily evaporated from the particle surface, and there is no good way to analyze the particle size distribution (PSD) of the droplet. However, direct measurement of PSD after its growth is necessary for research of water condensation on particles. In addition, though it has been known wetting agent addition could improve the performance of particle removal, the mechanism is uncertain. In this paper, a direct measurement was developed to research the characteristics of coal-fired fine particles growth under the supersaturation vapor which was never done before and to explore how the wetting agent addition improves the performance of particles’ enlargement.
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EXPERIMENTAL SECTION
The coal-fired fine particles were collected from the power plants’ ash container of Nanjing, Jiaxing, and Inner Mongolia, respectively, and separated by a cyclone separator to obtain particles less than 10 μm in diameter (the experiment of heterogeneous condensation on coal-fired particles is for a mechanistic research, so the way to get particles is applicable). More than 95.2% (all the percentage based on the particles number in this paper) particles is less than 0.2 μm and 96.6% less than 1 μm after separation. The chemical composition was analyzed by XRF technique and the results are shown in the Table 1. The initial particles number concentration was measured by means of an electrical low pressure impactor (ELPI, Finland). As illustrated in Figure 1, the experimental apparatus includes three parts as follow, aerosol generation part, the particles growth part, and the measurement part.
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RESULTS AND DISCUSSION
Influence of Water Temperature. The supersaturation profiles throughout the growth tube were described by employing a heat and mass transfer modeling,24 and the result is shown in Figure 2. It can be seen that the supersaturation in
Figure 1. Diagram of experimental apparatus. The aerosol generation part consists of an aerosol generator (model SAG-410, Germany) and an air compressor which supplies pure air as the carrier gas. The particles growth part consists of a growth tube, a cooling unit, and a hot water thermostat. The growth tube was made of glass with an internal diameter of 1.5 cm and a length of 40 cm. The hot water inlet to the growth tube was designed as tangential to ensure a perfect
Figure 2. Profile of supersaturation in the axis of the growth tube. 1823
DOI: 10.1021/acs.energyfuels.5b02200 Energy Fuels 2016, 30, 1822−1828
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the growth tube which activates more small size particles as nucleation cores. Second, the water temperature increase makes the gas temperature increase which is favored to the nucleation rate of heterogeneous condensation on particles according to eq 1 in the classical heterogeneous condensation theory.25,26
the growth tube increases with an increase of the water temperature. Also, the location of maximum supersaturation moves toward an inlet of the growth tube with the water temperature increase (when the water temperature is 303, 313, and 323 K, the maximum supersaturation is 1.032, 1.143, and 1.324, and the corresponding location is 33.44, 28.00, and 24.24 cm distance from the inlet of growth tube, respectively). The PSD with or without water in the growth tube is exhibited in Figure 3. It could be seen that the PSD is almost
J = K exp( −ΔG*/kT )
(1)
where J is the nucleation rate, K is a kinetic constant, ΔG* is the free energy of formation of the critical embryo on the foreign particle, k is the Boltzmann constant, and T is the gas temperature. Lastly, the location of maximum supersaturation moves toward the inlet of the growth tube, which extends the length for the activated particles growth. It is worth noting that when the water temperature is 323 K, more than 70% particles could be enlarged up to 1 μm in diameter, which is large enough to be collected by some conventional separators. So the following studies of our experiments were tested at the water temperature of 323 K. The mean size of initial particles and after growth particles was calculated, and the results are shown in Table 2. It could be Table 2. Arithmetic Average Size of Particles under Different Water Temperaturesa sources Jiaxing Nanjing Inner Mongolia a
original 0.156 μm 0.146 μm 0.143 μm
water temperature 303 K 0.146 μm 0.141 μm 0.145 μm
313 K 0.616 μm 0.669 μm 0.617 μm
323 K 2.301 μm 2.170 μm 2.043 μm
t = 1.2 s, N = 1.7 × 106/cm3.
seen all the particles can be enlarged from about 0.140 to 0.140, 0.600, and 2.000 μm at the water temperatures 303, 313, and 323 K, respectively. This clearly indicates that the final mean size of particles is sensitive to water temperature. Influence of Initial Particles Number Concentration. Figure 4 reports the influence of initial particles number concentration on heterogeneous condensation on the coal-fired fine particles. The comparison of the two PSD after growth clearly points out that the higher number concentration, the worse performance for particles enlargement, which corresponds with the results of simulation in a particle size magnifier.27 In fact, the higher number concentration of particles would decrease the opportunity for small particles being activated because there is vapor competition among them when the particles number is above 104/cm3.27 Moreover, the more particles exist, the more vapor condensation is needed for the activated particles growth, which leads to a poor vapor environment. This phenomenon could be seen in the small size particles range from 0.15 to 0.2 μm particularly. The percentage of this range particles increase approximately 10% when the initial particles number concentration increases from 1.7 × 106/ cm3 up to 3.4 × 106/cm3. However, in the big size range of particles, the influence of particles initial number concentration is mild. In fact, the concentration of particles rising will decrease the maximum supersaturation in the growth tube.28 In addition, the smaller the particle, the higher the supersaturation required activating condensation growth according to the Kelvin equation. Hence, the vapor is more easily condensed on bigger size particles and the number of big size particles increase affects the small size particles enlargement. Table 3 gives the mean size of particles with or without the water inlet. About a decrease of 0.2 μm in mean size of particles
Figure 3. Influence of water temperature (t = 1.2 s, N = 1.7 × 106/ cm3).
coincident with each other at the temperature of 303 K suggesting that the supersaturation is too small to activate the particles to become nucleation cores. As shown in Figure 2, the maximum of the supersaturation distribution in the growth tube is 1.03 at 303 K. Considering all the PSD after enlargement, the PSD moves to bigger size with the increasing of water temperature. It can be explained as follows. First, the increase of water temperature results in a higher supersaturation profile in 1824
DOI: 10.1021/acs.energyfuels.5b02200 Energy Fuels 2016, 30, 1822−1828
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Energy & Fuels
one. It suggests that the number increase affect the finer particles growth significantly. Influence of Residence Time. Figure 5 gives the influence of residence time on particle enlargement under vapor
Figure 4. Influence of initial particles number concentration (Th = 323 K, t = 1.2 s).
is presented when double the particles initial number concentration. Therefore, the final mean size of particles is slightly affected by the initial particles number concentration even though higher initial particles number concentrations leads to vapor competition. However, it could also be found that the mean size of small particles at 1.7 × 106/cm3 range from 0.05 to 1 μm and is nearly 120% of the higher number
Figure 5. Influence of residence time (Th = 323 K, N = 1.7 × 106/ cm3).
condensation. The results show that particle enlargement is favored by higher residence time for all three particles, especially in the small size range. The particles ranging from
Table 3. Arithmetic Average Size of Particles under Different Initial Particles Number Concentrationsa Jiaxing
a
Nanjing
Inner Mongolia
sources
D̅ 0.05−10
D̅ 0.05−1
D̅ 0.05−10
D̅ 0.05−1
D̅ 0.05−10
D̅ 0.05−1
original N = 1.7 × 106/cm3 N = 3.4 × 106/cm3
0.156 μm 2.301 μm 1.942 μm
0.095 μm 0.417 μm 0.351 μm
0.148 μm 2.170 μm 1.976 μm
0.093 μm 0.400 μm 0.351 μm
0.147 μm 2.043 μm 1.807 μm
0.088 μm 0.405 μm 0.313 μm
Th = 323 K, t = 1.2 s. 1825
DOI: 10.1021/acs.energyfuels.5b02200 Energy Fuels 2016, 30, 1822−1828
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Energy & Fuels 0.15 to 0.2 μm are totally enlarged for Jiaxing and Nanjing particles when the residence time extends from 1.2 to 2.12 s, but there is still some particles in the range from 0.15 to 0.2 μm for Inner Mongolia particles, which perhaps is due to the bigger contact angle of particles. (The contact angle of particles with water was measured by employing the sessile drop method, and for the particles of Jiaxing, Nanjing, and Inner Mongolia, the contact angle is 35.7°, 38.5°, and 40.1°, respectively). Results15 showed that the higher contact angle of particles, the higher critical supersaturation was needed for particles activated. In the growth tube, the supersaturation increases with the increase of the distance from inlet before supersaturation reaches the maximum value. So the small particles with bigger contact angle get activated later than those with a smaller contact angle in the growth tube, and then the effective length (the length from the location of particles be activated to the outlet of growth tube) for bigger contact angle particles decrease and more small particles cannot be enlarged into a bigger size. The same results are also found in Figure 3 (the peak of small size particles is 11.53%, 14.05%, and 15.85% at the temperature of 323 K for Jiaxing, Nanjing, and Inner Mongolia particles, respectively) and Figure 4 (the peak of small size particles is 20.75%, 22.27%, and 28.79% at the concentration of 3.4 × 106/cm3 for Jiaxing, Nanjing, and Inner Mongolia particles, respectively). Both of them indicate that much more percentage of small particles cannot be enlarged for higher contact angle particles, which suggests the dependence of particles growth on the contact angle. The influence of residence time can be explained from the following two factors. On one hand, residence time extension means the more time under the district of higher supersaturation for particles, the more chance for small particles to be activated. On the other hand, the more residence time for particles staying in the growth tube, the more vapor can be condensed on the activated particles. Data in Table 4 show that the mean size of particles slightly increases with the residence time extension, which is seems to Table 4. Arithmetic Average Size of Particles under Different Residence Timesa
a
sources
Jiaxing
Nanjing
Inner Mongolia
original t = 1.2 s t = 2.12 s
0.156 μm 2.301 μm 2.597 μm
0.148 μm 2.170 μm 2.352 μm
0.147 μm 2.043 μm 2.290 μm
Figure 6. Influence of wetting agent addition (Th = 323 K, t = 1.2 s, N = 1.7 × 106/cm3).
Th = 323 K, N = 1.7 × 106/cm3.
reducing the critical diameter of small particles. Comparing with no wetting agent addition, the wetting agent addition greatly improves the enlargement performance of small size particles ranging from 0.1 to 1 μm. Though the mean size of particles increases with the wet agent concentration increase as illustrated in Table 5, the enlargement performance of small size particles of Jiaxing and Nanjing with 20 g/L wetting agent addition is better than with
be quite less influenced by residence time. Nevertheless, with the residence time increase from 1.2 to 2.12 s, the percentage of the small particles less than 1 μm decrease 16.50%, 17.34%, and 10.91% for Jiaxing, Nanjing, and Inner Mongolia particles, respectively, from Figure 5. That is to say, higher residence time is necessary for particles enlargement even though it lightly affects the final mean size of particles, especially for the small size particles growth. Influence of Wetting Agent Addition. Figure 6 shows the results of the influence of wetting agent addition. As it can be seen, the performance of the entire three particles enlargement is favored by the wetting agent addition. This can be explained that the agent wetting addition decreases the contact angle of particles (for Nanjing particles, the contact angle decrease to 28.7° with 20 g/L wetting agent addition from the original contact angle is 38.5°) and, consequently,
Table 5. Arithmetic Average Size of Particles with Different Concentrations of Wetting Agenta
a
1826
sources
original
n = 0 g/L
n = 20 g/L
n = 30 g/L
Jiaxing Nanjing Inner Mongolia
0.156 μm 0.146 μm 0.143 μm
2.301 μm 2.170 μm 2.043 μm
2.970 μm 2.947 μm 2.650 μm
3.360 μm 3.279 μm 3.186 μm
Th = 323 K, t = 1.2 s, N = 1.7 × 106/cm3. DOI: 10.1021/acs.energyfuels.5b02200 Energy Fuels 2016, 30, 1822−1828
Article
Energy & Fuels
case-crossover study. J. Toxicol. Environ. Health, Part A 2008, 71 (8), 512−520. (2) Biswas, S.; Verma, V.; Schauer, J. J.; Sioutas, C. Chemical speciation of PM emissions from heavy-duty diesel vehicles equipped with diesel particulate filter (DPF) and selective catalytic reduction (SCR) retrofits. Atmos. Environ. 2009, 43 (11), 1917−1925. (3) Song, Y.; Zhang, Y. H.; Xie, S. D.; Zeng, L. M.; Zheng, M.; Salmon, L. G.; Shao, M.; Slanina, S. Source apportionment of PM2.5 in Beijing by positive matrix factorization. Atmos. Environ. 2006, 40 (8), 1526−1537. (4) Wu, S.; Deng, F.; Wei, H.; Huang, J.; Wang, X.; Hao, Y.; Zheng, C.; Qin, Y.; Lv, H.; Shima, M.; Guo, X. Association of cardiopulmonary health effects with source-Appointed ambient fine particulate in Beijing, China: A combined analysis from the healthy volunteer natural relocation (HVNR) study. Environ. Sci. Technol. 2014, 48 (6), 3438−3448. (5) Seinfeld, J H.; Pandis, S N. Atmospheric Chemistry and Physics; John Wiley: Hoboken, NJ, 1998; p 1326. (6) Ji, J.; Hwang, J.; Bae, G.; Kim, Y. Particle charging and agglomeration in DC and AC electric fields. J. Electrost. 2004, 61 (1), 57−68. (7) Riera-Franco de Sarabia, E.; Gallego-Juárez, J. A.; AcostaAparicio, V. M.; Rodríguez-Maroto, J. J.; Dorronsoro, J. L.; SanzRivera, D.; Gómez-Moreno, F. J.; Martín-Espigares, M. Acoustic Agglomeration of submicron particles in diesel exhausts: First results of the influence of humidity at two acoustic frequencies. J. Aerosol Sci. 2000, 31, 827−828. (8) Rajniak, P.; Mancinelli, C.; Chern, R. T.; Stepanek, F.; Farber, L.; Hill, B. T. Experimental study of wet granulation in fluidized bed: Impact of the binder properties on the granule morphology. Int. J. Pharm. 2007, 334 (1), 92−102. (9) Cozzolino, G. Water condensation for submicronic particles abatement. Ph.D. Dissertation, University of Naples Federico II, Naples, Italy, 2013. (10) Yoshida, T.; Kousaka, Y.; Okuyama, K. Growth of aerosol particles by condensation. Ind. Eng. Chem. Fundam. 1976, 15 (1), 37− 41. (11) Yoshida, T.; Kousaka, Y.; Okuyama, K.; Nomura, F. Application of particle enlargement by condensation to industrial dust collection. J. Chem. Eng. Jpn. 1978, 11 (6), 469. (12) Jingjing, B.; Linjun, Y.; Jinpei, Y.; et al. Experimental study of fine particles removal in the desulfurated scrubbed flue gas. Fuel 2013, 108, 73−79. (13) Porstendorfer, J.; Scheibel, H. G.; Pohl, F. G.; Preining, O.; Reischl, G.; Wagner, P. E. Heterogeneous nucleation of water vapor on monodispersed Ag and NaCl particles with diameters between 6 and 18 nm. Aerosol Sci. Technol. 1985, 4 (1), 65−79. (14) Lammel, G.; Novakov, T. Water nucleation properties of carbon black and diesel soot particles. Atmos. Environ. 1995, 29 (7), 813−823. (15) Chen, C.-C.; Guo, M.-S.; Tsai, Y.-J.; Huang, C.-C. Hetergeneous nucleation of water vapor on submicrometer particles of SiC, SiO2 and Naphthalene. J. Colloid Interface Sci. 1998, 198, 354−367. (16) Chen, C.; Tao, C. Condensation of supersaturated water vapor on submicrometer particles of SiO2 and TiO2. J. Chem. Phys. 2000, 112 (22), 9967. (17) Chen, C.; Hung, L.; Hsu, H. Heterogeneous nucleation of water vapor on particles of SiO2, Al2O3, TiO2, and Carbon Black. J. Colloid Interface Sci. 1993, 157 (2), 465−477. (18) Hogrefe, O. V.; Keesee, R. G. Heterogeneous vapor-to-liquid nucleation of water on individual glass particles. Aerosol Sci. Technol. 2002, 36 (2), 239−247. (19) Sharoichenko, O. V. A New Apparatus for Study of Heterogeneous Nucleation on Single Micron-Sized Insoluble Particles. Ph.D. Dissertation, State University of New York, Albany, NY, 2000. (20) Fan, F. X.; Yang, L. J.; Yan, J. P.; Bao, J. J.; Shen, X. L. Experimental investigation on removal of coal-fired fine particles by a condensation scrubber. Chem. Eng. Process. 2009, 48 (8), 1353−1360.
30 g/L wetting agent addition, as it could be seen from Figure 6, the percentage of particle size lower than 2 μm with 30 g/L is higher than with 20 g/L wetting agent addition (it appears when the wetting agent addition concentration is 40 g/L for Inner Mongolia particles, which perhaps is caused by the bigger contact angle of particles). The wetting agent addition cannot only reduce the contact angle of small size particles but also reduce the contact angle of big size particles, thus more vapor condenses on big size particles under certain supersaturation, resulting in this unexpected consequence. The mean size of particles increases with more wetting agent addition also evidences this assumption. Besides, with wetting agent addition, the mean size particles can be enlarged above 3 μm under the condition of initial diameter about 0.15 μm while the fine particles can only be enlarged above 2 μm without wetting agent addition. Therefore, as illustrated above, suitable wetting agent addition is beneficial to the particles enlargement. Otherwise, excessive wetting agent addition encourages the mean size of particles enlargement but discourages the small size particles growth.
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CONCLUSION Characteristics of vapor condensation on three coal-fired particles were investigated in the growth tube by a direct measurement of PSD. The mechanism of wetting agent addition facilitating the enlargement performance of small particles is also presented. The results show that the particles enlargement is quite sensitive to water temperature. The increase of number concentration is negative for particles enlargement, and it is also found the vapor competition is strongly occurring among small size particles and the big size particles increase affects the small size particles growth. Higher residence time is necessary for particle enlargement even though it has little impact on the mean size of particles, especially for the small size particles growth. The addition of wetting highly improves the performance of particles enlargement, especially for the particles size ranging from 0.1 to 1 μm. Excessive wetting agent addition encourages the mean size of particles enlargement while discourages the small size particles growth, suggesting suitable wetting agent addition should be applied for the particles enlargement and the amount of addition is various for different particles, depending on the particles contact angle.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The support of this research by the National Natural Science Foundation of China (Grant No. 51576043) and the Major State Basic Research Development Program of China (973 Program Grant No. 2013CB228504) is gratefully acknowledged.
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REFERENCES
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