Gaćanović, Mico

Javor, Vesna

Digitale Bibliothek Thüringen

   Information Technology and Electrical  Engineering - Devices and Systems, Materials  and Technologies for the Future        Faculty of Electrical Engineering and Information Technology    Startseite / Index:  http://www.db-thueringen.de/servlets/DocumentServlet?id=14089 54. IWK Internationales Wissenschaftliches Kolloquium International Scientific Colloquium 07 - 10 September 2009 PROCEEDINGS Impressum  Herausgeber: Der Rektor der Technischen Universität llmenau  Univ.-Prof. Dr. rer. nat. habil. Dr. h. c. Prof. h. c. Peter Scharff  Redaktion: Referat Marketing   Andrea Schneider   Fakultät für Elektrotechnik und Informationstechnik  Univ.-Prof. Dr.-Ing. Frank Berger  Redaktionsschluss: 17. August 2009  Technische Realisierung (USB-Flash-Ausgabe):  Institut für Medientechnik an der TU Ilmenau  Dipl.-Ing. Christian Weigel  Dipl.-Ing. Helge Drumm  Technische Realisierung (Online-Ausgabe):  Universitätsbibliothek Ilmenau    Postfach 10 05 65  98684 Ilmenau  Verlag:   Verlag ISLE, Betriebsstätte des ISLE e.V.  Werner-von-Siemens-Str. 16  98693 llmenau   © Technische Universität llmenau (Thür.) 2009   Diese Publikationen und alle in ihr enthaltenen Beiträge und Abbildungen sind urheberrechtlich geschützt.   ISBN (USB-Flash-Ausgabe): 978-3-938843-45-1 ISBN (Druckausgabe der Kurzfassungen): 978-3-938843-44-4  Startseite / Index: http://www.db-thueringen.de/servlets/DocumentServlet?id=14089  ELECTROSTATIC CHARACTERIZATION: DETERMINING THE ZETA POTENTIAL AND SURFACE CONDUCTIVITY  Mićo Gaćanović, Vesna Javor  Faculty of Electrical Engineering, University of Banja Luka, Bosnia&Herzegovina Faculty of Electronic Engineering, University of Nis, Serbia   ABSTRACT  In the procedures of preventing discharges and elimination of static electricity in a double-layer case the values of Zeta potential ( potential) and surface conductivity of the phases states contact are determined. For the liquid phases pH value of the liquid is also analyzed. This analysis is particularly important in the usage and work with dangerous and flammable liquids, so as with explosive dusts. In this paper the results of the conducted procedure are presented, obtained by the method of thermovision in the investigation of the minimum values of ignition energy. The application of the results is possible in pharmacy, chemical, petrol and gas industry. −ζ  Index Terms - Zeta potential, surface conductivity, electrostatic characterization  1. INTRODUCTION For the adequate approach to the elimination of static electricity produced by the contact of two phases states in a double-layer and for the safe solution of that problem it is necessary to know the value of potential. On the basis of this value static electric-ity can be eliminated in a passive way which enables safe technological process. Such approach leads to decreasing the value of minimum ignition energy or discharges that occur in a double-layer and can pro-duce undesirable effects as flames and explosions [1]. −ζ2. POTENTIAL DETERMINATION −ζDoes potential characterize a certain substance, i.e., is it a property of material? The answer is nega-tive, because if we describe a certain substance by the zeta potential value, indicating, for instance,  under predetermined conditions, we should know at least the following: its form (crystal-line, amorphous, particulate, dispersions, macro-bod-ies e.g. discs, rods, spheres, capillaries, etc.); size of particles and purity of the substance; electrolyte (purity, concentration, conductivity); pH value; tem-perature; type of electrokinetic measurement and the corresponding conditions. Even if all the mentioned conditions were requested and defined by a conven-tion, the absolute values of the zeta potential on most solid-liquid interfaces achieved in different laborato-ries are hardly reproducible. Also the comparison of absolute values of the zeta potential obtained by different techniques, e.g. micro electrophoresis or streaming potential or other, does not make much sense, even if the same class of substances (materials) is analyzed under the same basic conditions. On the other hand, in an isolated experiment, the zeta potential values obtained under the quite identical conditions could be highly reproducible and therefore very useful for the interpretation of the behavior of that particular investigated interface [1], [2].           −ζmV50ζ −=3. −ζ POTENTIAL MEASUREMENTS −ζ potential measurements were conducted by laser Doppler electrophoresis using the Nano-S ZetaSizer (Malvern Instruments Limited, Malvern, Worcester-shire, U.K.) equipped with a 2 mW Helium Neon la-ser with an output of 633 run. Zeta potential is a measure of the net charge on a particle and depends on the charge on the particle plus the charge associ-ated with any ions that move along with the particle in an electric field. The applied potential of 150V and the modulation frequency of 250Hz were used. The instrument was calibrated with a standard carboxyl modified polystyrene latex solution, with a surface potential of 55mV, provided by Malvern Instruments.  −ζ potential is calculated from the Helmholtz-Smoluchowski equation:                            μη/επ4ζ =                                  (1)  where μ  is the electrophoretic mobility or velocity at unit potential gradient,  is the viscosity of the liquid and  is the dielectric constant. The dielectric constant and viscosity of water at 25°C were taken as applied. Samples were measured 20 times. The sample count rate was generally 2000 times higher than the background count for distilled and deionized water (filtered). For ηε−ζ potential determination, the results are expressed in absolute values (mV) [1], [3]. © 2009 - 54th Internationales Wissenschaftliches Kolloquium4. RESULTS Using method of thermovision the events of dis-charges in double-layer phases states are registered with the discharge energies as noted (in Joules) and presented in Figs.1 and 2.    Figure 1 Typical IR thermograph images of impacted areas in 3D commingled laminates (40x32mm area) All the images acquired after 15 seconds transient[3].     Figure 2 Linear interpolation of a typical evolution of impact-damaged area inside a sample of 3D commin-gled laminate. Agéma Thermovision 900 SW thermo-graphic camera, thermo-electrically cooled), [3].  In the contact of phases states (in a double-layer) static electricity  is produced, which depends on the differential capacity , where U is the established potential difference at the contact of phases states and C is the established capacity of the contact of phases states in a double-layer, deter-mined per time unity. The value of the established differential capacity  at the interface of phases states in a double-layer can be determined from the expression )(tq( , ,dC f U C t= ∂ ∂ ∂ )dCdU CCC t∂ ∂= ∂ ∂  i.e. ζdCCt∂= ∂ . The term Ct∂∂  leads to the conclusion that at the interface of phases states there occurs the lifting of the charge  from one to another energetic level of the phases states, which is also the function of potential. The phases states are characterized by the values of sur-face conductivity so as volume conductivity. For the analysis of the electrostatic characteristic of states and the )(tq−ζ−ζ potential in this case is important the surface conductivity of the phases states examined together with the value of PH. Lifting of the charge  from one to another energetic level of the phases states occurs as an impulse for both positive and negative charge per time unit. The images presenting the process in the area of phases states contact are given in Fig.1. It is very important to determine critical values of the charge . Our investigations in petrol industry have given the following results [1]. Positive impulse discharges in a double-layer liquid/solid state (in the case of a partially filled reservoir with petrol) are denoted with  and negative with . We determined the discharge constant as , so for )(tq)(tq+V −V1550 10 [C/ mV]qk-= ×  [ ] [ ] [ ] [ ]12CmV 20 10 C 20 pCk k kqqV qk++ += = × = q + (2) and [ ][ ][ ] [ ]12CmV 20 10 C 20 pCk k kqqV qk-- -= = × = q - (3) the following is obtained:   ( ) [ ]{ } [ ]{ }1 exp 0,116 20 pC 1 exp 2,32 pCk kP q q q+ += - - × = - - × k+ (4)   ( ) [ ]{ } [ ]{ }1 exp 0,168 20 pC 1 exp 3,36 pCk kP q q q- -= - - × = - - × k- (5)  ( ) [ ]{ } [ ]{ }exp 0,116 20 pC exp 2,32 pCk kg kg kgP q q q q+ + + +> = - × = - × (6)   ( ) [ ]{ } [ ]{ }exp 0,168 20 pC exp 3,36 pCk kg k kP q q q q- - - -> = - × = - × (7)  where ( )kP q+  and ( )kP q+  represent the possibilities for the charges  or  to be found in the reservoir in the corresponding intervals  or kq+kq-(0, )kq q+ Î k+(0, )kq q- Î k- , so ( )k kgP q q+ +>  and ( )k kgP q q- ->  are the possibilities for the charges  and kq+kq-  to be less than of the given values  or +kgq−kgq . The results of the calculations are given in the following table (Table 1) and the graphics are given in Figs.3 and 4.    Figure 4 The possibility function obtained from the  Figure 3 The possibility function obtained from the experiment for the interior of the reservoir in the experimental model [1], . )()( +++ => kkik qfqqP experiment for the interior of the reservoir in the     experimental model [1], )(|)||(| −−− => kkik qfqqP .       Figure 5 Equilibration of the 3%vl zirconia slurry prepared with KCl with PH adjusted initially to 4. The equilibration takes about 2 hours, [3]. 210− Figure 6 Titration of the 10%wt silica Ludox using 1NHCl and KOH, [3].   Table 1 The classification of calculated values of the possibilities for the charges  and  to occur inside the area of the experimental model of the reservoir [1]. kq+kq-i 1 2 3 4 5 6 7 [ ]kiq pC+  14096 12048 11024 1512 1256 1128 164 ( k kiP q q+ +> ) 0,999 0,999 0,997 0,995 0,991 0,982 0,964 [ ]kiq pC-  14096 12048 11024 1512 1256 1128 164 ( k kiP q q- -> ) 0,999 0,998 0,997 0,993 0,987 0,974 0,949 i 8 9 10 11 12 13 14 [ ]kiq pC+  132 116 18 14 12 1 2 ( k kiP q q+ +> ) 0,930 0,865 0,748 0,560 0,313 0,098 0,010 [pC]kiq-  132 116 18 14 12 1 2 ( k kiP q q- -> ) 0,900 0,811 0,657 0,432 0,186 0,035 0,001  Table 2 Zeta potential, surface conductivity and PH values[1] for the petrol.  zeta  potential  [mV]  +30  +22  +12    0  -15  -35  -30  -38  -40   conductivity    [S/m]   500  380  380  380  380  380  380  400  680          pH    3    4    5    6    7    8    9   10   11   The results of the experimental investigation car-ried out for [1] are also numbers of positive impulse discharges of the static electricity registered with an oscilloscope , and the number of negative discharges , so the total number of im-pulses is then , registered with the duration time of one second during the in-terval of 15 minutes, i.e. in the total time period of 15 seconds. Thus, the average values of the impulse fre-quencies are: 297N + =181N - =478N N N+ -= + = [ ] [ ][ ]297 20 Hzs 15 ssrNft++ = = = ,  (8) [ ] [ ][ ]181 12 Hzs 15 ssrNft-- = = = ,  (9) and the corresponding time intervals srT+  and srT- :  1 50 [ms]srsrTf++= = ,  (10) 1 83 [ms]srsrTf--= = .  (11) For each positive voltage V  or negative voltage  impulse there are positive  or negative  charges determined by the discharge constant . The possibilities for the charges to occur are transformed into the possibilities for the voltages to occur, as the following: +V - kq+kq-1550 10 [C/ mV]qk-= × ( ) ( ) [ ] [ ], 0,116 mV 2,32 pC1 1 kV qkP V P q e e+ +- -+ += = - = - (12)  ( ) ( ) [ ] [ ]0,168 mV 3,36 pC1 1 kVkP V P q e e-- -- -= = - = - q-kgq,  (13)  ( ) ( ) mV pC0,116 2,32gVg k kgP V V P q g e e+ +- -+ + + +< = < = = ,  (14)  ( ) ( ) mV pC0,168 3,36gVg kg kgP V V P q g e e-- -- - - -< = < = = kgq- .  (15)  For the maximum values of amplitudes of the −ζ po-tential at the established differential capacity , as the consequence of the break-down voltage  in the reservoir [1] as the following  dCkVmax 1ku =mV173ζ maxmax === −+ VV ,  (16) so the following is obtained:  pC0,116 0,168173 173 8, 652, 32 3, 36k kq q+ -= = = = ,  (17) and  [ ] ( ) [ ]max max max max173 mV ( ) 8,56 pCk kV V q V q V+ - + + - -= ³ Ù = ³ ,  (18) so that  [ ]( ) [ ]( ) 9173 mV 8, 65 pC 1, 93 10kP V P q+ +³ = ³ = -×-×5,  (19)  [ ]( ) [ ]( ) 13| | 173 mV | | 8, 65 pC 2, 39 10kP V P q- -³ = ³ = .  (20)  For the conditions [1]:   ( ) ( ) 0, 5sr k ksrP V V P q q+ + + +³ = ³ = ,  (21)  ( ) ( )| | | | | | | | 0,sr k ksrP V V P q q- - - -³ = ³ = ,  (22) the following is obtained:  0,116 2,32 0, 5sr ksrV qe e+ +- -= = ,  (23)  0,118 2,32 0, 5sr ksrV qe e- -- -= = ,  (24) so afterwards the following values are obtained:  ( ) [ ]ln 0, 50, 5 5, 98 mV0,116srV P V+ += = = =-,  (25) ( ) [ ]ln 0, 50, 5 0, 299 pC2, 32k ksrq P q+ += = = =-,  (26) ( ) [ ]ln 0, 50, 5 4,13 mV0,168srV P V- -= = = =-,  (27) ( ) [ ]ln 0, 50, 5 0,206 pC3, 36k k srq P q- -= = = =-.  (28) From the graphics given in Figs. 3 and 4 it can be noticed that at the points  and  we obtain the fastest changes of possibilities ( )0, 5kq P+ =(| | 0, 5kq P- = )i( )k kP q q+ +³  and ( k ki )P q q+ +³ . As for each value of the charge  or  there is a value of the voltage V or , the same diagrams can be used for the determination of possibilities  or kq+kq-+ V -( )iP V V+ +³ ( )iP V V- -³  for the voltages, the distribution of the positive and negative impulse amplitudes, so as for the intervals of reliabilities  or ( )V P+ ( )V P-  of these impulse amplitudes [1]. If we suppose that the charged drops are condensing above thin film of the uncharged petrol at the metallic walls of the reservoir, whereas each of charged drops has an average charge equal to the  which is , than for the case of ignition of the charged petrol layer it is necessary to calculate the number of charges that is obtained as the ratio of the critical charge for the ignition ksrq( ) [0, 5 0, 299 pCksr kq q P= = = ][ ]0, 5 Ckrq = m] and the average value of generated charges . The in-vestigations carried out for analysis of the established value of the electrokinetic or the Zeta potential avail-able in literature [3] for other phases states, where the values of PH and conductivity are taken into account, are given in Figs. 5 and 6. ( ) [0, 5 0, 299 pCksr kq q P= = =The electroacoustic −ζ potential probe is a con-venient tool for determining the optimal surfactant concentration corresponding to the saturated surface. This characterization can be performed also in the intact concentrated dispersion eliminating dilution. The classical equation, relating the electrophoretic velocity v and the potential, ignores the retarda-tion and relaxation forces, and thus it is only ap-proximation in natural conditions, where  is the relative permittivity, E is the strength of the electrical field and  is the viscosity of the fluid.  −ζεηThe flow of a liquid through a capillary tube in-duces a convection current in the direction of flow. Conduction current is induced by the potential differ-ence at the ends of the capillary. At the stationary state, the conduction current is equal to the convec-tion. Evaluation of the currents gives  and ηπ4/ζεEv =wKPE π4ζε// = , where  the specific con-ductance of the liquid is and P is the applied pressure drop in the capillary per unit length. The results for the wK−ζ potential and surface conductivity obtained from measurements [1] are presented in Table 2. 5. CONCLUSION On the basis of −ζ potential the value of electrostatic field can be estimated, so as the charge per unit volume. There is also a relation of this potential to the differential capacity  of a double-layer and the conductivity of the cloud formed in the contact of the states phases.  dCResults for the −ζ potential and surface conduc-tivity obtained from measurements and presented in this paper can be applied in passive elimination of the static electricity [1] in different industrial processes in order to prevent fires and explosions.    6. REFERENCES [1] Gaćanović M.: “German Patent No. 699 14 225“ (2003), “European Patent EP 1 169 888“ (2003), “Canadian Patent No.2,401,517“ (2007), “European-Asian Patent & Patent Russia No.EA003411“ (2004).  [2] Erickson D., Dongqing Li, and Carsten Werner: “An Improved Method of Determining the Poten-tial and Surface Conductance”, Journal of Colloid and Interface Science 232, pp.186–197, 2000. −ζ[3] Dukhin, A. S., P. J. Goetz, “Surfactant Titration of Kaolin Slurries using −ζ Potential Probe,” Dispersion Technology Inc., Mount Kisco, NY USA, 2000.  

Electrostatic characterization: determining the zeta potential and surface conductivity

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Electrostatic characterization: determining the zeta potential and surface conductivity

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