Study of the Adhesion Force of Asphaltene Aggregates to Metallic

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Study of the adhesion force of asphaltene aggregates to metallic surfaces of Fe and Al Alejandro Ortega Rodriguez, Salvador A. Cruz, Isidoro Garcia-Cruz, and Carlos Lira-Galeana Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.5b02065 • Publication Date (Web): 13 Nov 2015 Downloaded from http://pubs.acs.org on November 14, 2015

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Study of the adhesion force of asphaltene aggregates to metallic surfaces of Fe and Al *

A. Ortega-Rodriguez1, S. A. Cruz2, I. Garcia-Cruz1 and C. Lira-Galeana1

1

Instituto Mexicano del Petroleo, Eje Central Lazaro Cardenas 152, Mexico 07730, Mexico 2

Departamento de Física, Universidad Autonoma Metropolitana - Iztapalapa P.O, Box 55534, Mexico 09340, Mexico

* Corresponding Author: Phone number: (+5255) 9175 6757, E-mail: [email protected]

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Abstract

Atomic force microscopy (AFM) was used to measure the adhesion force of asphaltene aggregates to metallic surfaces of Aluminum (Al) and Iron (Fe) at room temperature and atmospheric pressure.

A simple analytical expression based on Lindhard’s

Continuum Planar Potential (CPP) approximation that incorporates the effect of the surrounding fluid (a solvent), and has no fitting parameters, was developed and tested with the experimental results. This expression provided predictions in good agreement with measured data.

KEYWORDS: Asphaltene adhesion to metals, interaction potentials, flow assurance


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1. Introduction Asphaltenes are a class of compounds whose precipitation and deposition behavior cause significant problems in both the upstream and downstream sectors of the oil industry. Blockage in producing wells, transport lines and processing equipment, are high-cost issues reported in typical field cases1. The great diversity and complex structure of asphaltene molecules has been a long-standing challenge to understand their role in physical and chemical oil processing. Structure-elucidation studies propose that asphaltenes may consist of stacks of fused aromatic rings in planar regions, with appended aliphatic side chains2-6. This dominant structural characteristic has been experimentally confirmed in recent studies by Schuler et al.,7 after careful analysis of a wide range of individual asphaltene structures using atomic resolution imaging techniques by combining atomic force microscopy (AFM) and scanning tunneling microscopy (STM). Although more complex structures are found in the latter report indicating the wide range of asphaltene architectures – the aforementioned common structural characteristic is preserved. We also consider that the presence of heteroatoms like sulphur and nitrogen make nucleophilic or electrophilic reactions also available, with probable effects on asphaltene adhesion to metallic equipment. Various methods to represent the organic substrate/metal interaction do exist. Among them there are the long-range, organic/metal van der Waals interactions, or the one using first principles at a molecular level8,9. In this work, we have rather chosen to consider a CCP and further validate it through the use of AFM measurements. Production impairment from asphaltenes in producing wells is a topic of continued research in both industry and academy. In modern simulators10-11 the multi-phase flow equations are solved numerically for a given pipeline geometry, metallic properties, and 3 ACS Paragon Plus Environment

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oil rate. The iterative process includes the initial and updated stages of asphaltene deposition. Deposition of asphaltenes may be thus result, in a general way, from a balance between dragging and adhesion forces within the pipe. However, to the best of our knowledge, a phenomenological expression to account for asphaltene adhesion to different metallic surfaces has not yet been reported in literature. Such an expression may be helpful in describing the likelihood of asphaltenes to deposit in the field under typical processing conditions. On the other hand, AFM is a method to measure nano-forces between a probe tip and a given material surface. It is thus possible to use AFM to study nano-topographical surfaces, and measure adhesion and electrostatic forces12-13. AFM measurements involve a fixed tip at the end of a flexible cantilever, which scans the surface of the sample. Deflections of the cantilever are recorded, and used to build-up the surface topography. Surface images are obtained by plotting the deflection of the cantilever with its position, while its height is controlled by a feedback loop, which maintains a constant force between tip and sample14-15. This work describes the development of a simple analytical expression for the adhesion force of spherical asphaltene particles with two different metallic surfaces (Al and Fe). Our expression, based on the framework of the continuous planar potential (CPP) approximation16 is tested and compared favorably with the force measurements using AFM.

2. Model


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The model for particle-surface interaction proposed in this work relies on two main assumptions: i) the validity of pairwise superposition of atom-molecule interactions and ii) the neglect of contributions of image forces and polarization effects in the case of metallic surfaces. These two simplifying assumptions characterize our model as a first order approximation for the estimate of the particle-surface interaction. In spite of this, we deem the relevant features of the interaction are preserved providing important clues to explain the experimental observation of particle-surface adhesion forces. We now proceed to the details of the model. Let us consider a spherical particle of radius R composed by n asphaltene molecular aggregates per unit volume. The particle center is further assumed to be located a distance z 0 from a metallic surface, which is characterized by an atomic areal density of

ν atoms per unit surface as shown in Figure 1. Let dN = ndV denote the number of asphaltene aggregates within a differential volume element dV forming the particle and d N ′ = ν dS

the number of surface atoms in the differential surface element dS.

Considering validity of assumption (i), the differential contribution to the total interaction potential acting on dN due to the surface atoms is given as: dU =ν dN ∫ V (r ′) dS

(1)

S

where S in the integral symbol means summation of all surface-atom contributions. Thus, after integrating Eq. (1) over the particle volume the total particle-surface potential becomes:

U ( z 0 , R) =

∫ dU = nν ∫ dV ∫ V (r ′)dS V

(2)

S


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Note that a central quantity to consider in Eq. (2) is the interaction potential V (r ′) between one asphaltene molecule and a surface atom. This binary potential is associated to van der Waals forces which, in this work, are assumed to be the most significant factor to define the interaction between the asphaltene particle (zero net charge) and a mono-layer of metal atoms considered here (although a multilayer of metal atoms provides a more rigorous representation, as described elsewhere17). The generation of analytical forms for the asphaltene molecule- atom interaction has been previously discussed17 through use of specific Molecular Mechanics (MM) numerical estimates of the interaction potential between Fe, Al and Cr atoms and a known asphaltene molecular structure18, as an example, using the COMPASS- force field. Recently,19-22 it has also been pointed out that the use of COMPASS– force field to model interactions in organic molecules/metal systems is adequate. In those calculations17, an average interaction potential was built after considering different relative asphaltene-atom positions and orientations. The resulting average potential was then adjusted by a physically well-fundamented analytical expression23-25 given as:

V (r ′) =

(

)

4 Z 1 Z 2 −αr ′ C e + Ar ′εe − βr ′ − 2 6 e −γ / r ′ εr ′ ε r′

(3)

where in this case, Z 1 is the number of atoms in the asphaltene species and Z2 =1 (one metallic atom). The parameters A, C, α, β, γ are obtained after fitting Eq. (3) to the corresponding MM numerical values26. The effect of a surrounding medium (e.g a host


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solvent) on the interaction energy is accounted for through its effective dielectric constant, ε , as indicated in Eq. (3). The interested reader is kindly addressed to Refs. 23 and 27 for a more detailed description of this aspect. Although Eq. (3) may be used to evaluate the particle-surface interaction as prescribed in Eq. (2), an analytical expression for the total potential becomes too intricate due to the complex nature of the integrals involved. Since a simple analytical expression for the particle-surface interaction is desirable for practical calculations, we decided to use a simpler Lennard-Jones-type (LJ) analytical function to represent Eq. (3) as:

V (r ′) =

C12 C6 − , r ′12 r ′ 6

(4)

where the coefficients C12 and C6 are obtained from the fitting of Eq. (4) to the average MM calculations expressed by Eq. (3). Using Eq. (4) for the molecule-atom interaction, the particle-surface interaction potential is constructed as follows. Let ρ denote the radius of the annular surface element dS = 2πρ dρ measured from the intersection point of the normal line joining the particle´s volume element dV and the surface (see Figure 1). Then, the distance from this volume element to an atom sitting on the surface is given by:

r′ =

z2 + ρ 2 .

(5)


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Adding all binary contributions V ( z 2 + ρ 2 ) from surface atoms to the interaction potential with the dN = n dV asphaltene molecules contained in dV, leads to the surface integration implied by Eq. (1) as: ∞ C   C 2 2 dU = ν dN ∫ V ( r ′) dS = ν dN ∫ V ( z + ρ ) 2πρ dρ = 2πν dN  1210 − 64  0 4z  10 z

(6)

The particle-surface interaction is then readily obtained after adding all contributions from the volume elements dV within the particle indicated by Eq.(2) as:

C   C U ( z 0 , R) = ∫ dU = 2πν n∫  1210 − 64  dV 4z  10 z  C  8R − z 0 8R + z 0  C6 = π 2 nν  12  + − 8 ( z 0 + R) 8  6 1260  ( z 0 − R )

 2R − z0 2 R + z 0   +   2 ( R + z 0 ) 2    ( z 0 − R)

(7)

where dV = r 2 sin ϑ dr dϑ dϕ and the relation z = z 0 + r cosϑ (see Figure 1) , have been used to evaluate all integrals in terms of z . Note that Eq. (7) depends only on the relevant quantities defining the type of interacting systems through the C12 and C6 coefficients; the asphaltene volume density, n ; metallic atomic surface density, ν ; particle size R and central distance to the surface z 0 . Moreover, the features of the model discussed so far are applicable to any molecular asphaltene structure as far as the corresponding average molecule-atom interaction potential is available. We believe that Eq. (7) may be used as an approximate expression to describe particle-surface interactions in pipeline simulations involving asphaltenecontaining petroleum fluids.


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Finally, the particle-surface adhesion force may now be estimated through differentiation of the interaction potential given by Eq. (7), relative to the particlesurface separation z 0 :

C  1 2(2R − z0 ) 2(2R + z0 ) 1 Fz0 = π 2 nν  6  − − − − 2 2 (z0 − R)3 (z0 + R)3   6  (R + z0 ) ( z0 − R) −

8(8R − z0 ) 8(8R + z0 ) C12  1 1 − − −   8 8 1260 (R + z0 ) (z0 − R) (z0 − R)9 (z0 + R)9 

(8)

3. Results and Discussion

3.1. Model predictions for the Interaction potential between an asphaltene particle and a metallic substrate.

As a sample calculation to test the validity of the particle-surface interaction scheme proposed in this work, we have calculated the interaction energy between a fullerene C60 particle and a graphite plane, to compare with available corresponding calculations28-30. In this case, the volume integral implied by Eq. (2) is reduced to a surface integral over the fullerene particle with fixed radius R. Using a LJ 12-6 potential as in Eq. (4) for the C-C interaction, the C60-graphite surface potential becomes:

U C60 =

N2 R3

 C12   C6    1 1 1 1 − − −    9 9  3 3  ( z 0 + R )  48  ( z 0 − R ) ( z 0 + R )    360  ( z 0 − R )

(9)


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where N is the number of carbon atoms (N=60) on the fullerene surface and a similar graphitic surface atomic density ν = N / 4πR 2 is assumed. Eq. (9) is exactly the same as that obtained in Ref. 26, thus confirming the correctness of our Eq. (2). Interestingly, the MM calculations for the C60-graphitic plane interaction show very good quantitative agreement with the predictions of Eq. (9) as may be verified from Figure 2. In this case, the fullerene radius R= 3.55 Å and the C12 and C6 LJ-parameters for C-C have been taken from Ref. 28. The previous example points to the adequacy of the treatment leading to Eqs. (7) and (8) to estimate the asphaltene particle- surface interaction and force, respectively. We now turn our attention to the main aspects defining the relevant quantities required in Eqs (7) and (8) to define the particle-surface interaction potential and force. Following the results reported in Refs. 17 and 27 for the asphaltene/Fe (Al) interaction potential in vacuum ( ε = 1) , the corresponding interaction potentials for an airsurrounding environment ( ε = 1.1 ) have been re-scaled according to Eq. (3) to correspond to the experimental particle-surface force measurements of this work. The resulting interaction curves were further adjusted to a LJ (12-6) potential according to Eq. (4) with the C12 and C6 coefficients given in Table 1 for each metallic atom. Figure 3 shows the resulting LJ curves as compared with the ones corresponding to Eq. (3) in each case. As may be gathered from this figure, the position and depth of the potential minimum is well reproduced, although its width and range is only approximately reproduced. This is particularly noticeable for the Fe atom. These are common features associated to the inherent rigidity of the LJ potential as compared with the more realistic potential expressed by Eq. (3). However, we deem the LJ interaction potential curves provide relevant information on the binary interaction to yield the total particle-surface 10 ACS Paragon Plus Environment

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potential and force values considering the simple analytic expressions given by Eqs. (7) and (8). In this work we have considered only a single metal layer representing the substrate (Fig. 1). Certainly, inclusion of more metallic layers would lead to an enhanced contribution to the interaction potential and force, as previously reported in the case of asphaltene molecule- metallic surface interactions17. However, our primary goal here is to test the capability of Eq.(8) to provide a simple and reasonable approximation of the particle-surface adhesion force when compared with experiment. According to this approximate treatment, Figure 4 shows the asphaltene particle- Fe and Al metallic surface adhesion forces calculated from Eq. (8), where the corresponding asphaltene and metal parameters given in Appendix A have been used.

Table 1. Best-fit LJ parameters used in Eq. (4) for the asphaltene molecule-atom interaction.

Type of atom

C12 ( kcal / mole × 10 6 A12 )

C6 ( kcal / mole × 10 3 A 6 )

Fe

2 .61

8.61

Al

3.39

7.12

o

o

3.2. AFM measurement of the adhesion force between an asphaltene particle and a metallic surface.

The Iron and Aluminum substrates used in our experiments had surfaces with dimensions of 10 mm. x 10 mm. x 1 mm. of industrial quality31. The asphaltene sample was isolated from a Maya-type crude oil sample with a molecular weight of 794.47 g/gmol18,27.

Measured

SARA

compositions

(sequential

IP

143

and

HPLC


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chromatographic technics32) of this oil are: 21.98 wt. % saturates, 35.85 wt. % aromatics, 28.59 wt. % resins and 13.58 wt. % asphaltenes. Force curves between the AFM probe and metallic surfaces were measured by recording the cantilever deflection in the force displacement curve using an AFM NanoScope IV33 apparatus, equipped with the NanoMc software which calculates the hardness in samples of Iron and Aluminum having an asphaltene film34-35. A cantilever with an Si ultra-sharp tip of 25 nm diameter, 15-20 µm height, spring constant k of 5 N/m and resonant frequency f of 300 KHz was used (Figs 5a,b). First, the metals were washed with pure chloroform, and pure toluene, five times, and then with acetone three times in a sonicator bath for 30 minutes, to remove any dirt and grease. The washed materials were placed for overnight in a vacuum oven at 80°C to remove any liquid still present in the metals. Following drying, the metals were placed in a moisture-free environment to ensure minimal water adsorption. Later, the tip in the cantilever was immersed in an asphaltene solution in toluene (2 wt. %), were an asphaltene drop (semi-spherical agglomerate) was then trapped on the tip (see Figure 6). The attached asphaltene drop to the cantilever tip shown in Fig. 6 was merely the result of the sinkage of the drop/tip system into the asphaltene-in-toluene suspension, from which no control of the (randomly attached) size of the asphaltene drop (macro cluster) was made. Although our model assumes a fully-evaporated solvent situation for the drop (partly because the 25°C test temperature provides some evaporation), our experiments did not measure the amount of solvent which truly remains within the test asphaltene drop settled on the tip. Figure 5a,b shows this setup. According to geometrical characteristics of the tip in the cantilever, we can assume that the asphaltene particle has a diameter larger than the TSB parameter (15 microns) and higher than the tip height (15-30 micron (see Fig. 5a,b and 6). Force measurements were performed in different locations on the metallic 12 ACS Paragon Plus Environment

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substrate at 25o C. Taking into account this argument, our calculated results are in reasonable agreement with results from similar systems36-39. Results obtained from force curves between asphaltene particles stuck on the tip and metallic substrates (iron and aluminum) are shown in Fig. 7 a,b. Fig. 5 HERE Fig. 6 HERE Fig. 7 HERE Figure 7 a,b shows the force of adhesion between the cantilever/tip/attached asphaltene particle and metal surfaces of Fe and Al. The test is carried out by bringing the tip of the cantilever with the attached asphaltene to the surface, and recording the intensity of the attracting force at each distance, to the point of contact with the surface. From Fig. 7 a,b it is evident that the maximum force is attained when the attached asphaltene drop on the tip of the touches the metal surface at zero distance between each other. For the square and circle symbols (zones 1 and 2 in the figure), no such a touching situation was made. Although ten different force measurements on different metal locations where made, only three of these measurements are shown in the figure (spheres, squares and triangle patterns, respectively). For the case of Fe, it is seen that the force of adhesion (roughly 100 nN, zone 3 of triangles patterns) is larger than the one measured for an Al region (roughly 75 nN, zone 3). Similarly, for Fe the force (about 7 nN, zone 1 of spheres patterns), is slightly higher than the force measured for a location on the Al surface (6 nN, zone 1). Due to the highly heterogeneous surface-morphology of the metallic substrates used in our AFM experiments (which were obtained from “coupon” samples of industrial metal pipes for sales, which may eventually have traces of oxide), it is evident that significant surface irregularities are present in these kind of industrial13 ACS Paragon Plus Environment

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type of metal samples, making the repeatability of this kind of measurements very difficult. Interaction potentials for the α-hematite-asphaltene interacting system, which may be useful for the system studied in this work in the case of metal oxidation, have been theoretically derived previously

36

. From Figure 7a, it is apparent that a sharp

decrease at distances higher than 0.9 nm is seen for the attractive curve of zone 3 (see above), at a value of approximately 0.8 nm. This behavior shows an increase on the attractive force between the asphaltene and the Fe surface at distance close to that of the contact one between these two materials. This happens when the increase of attractive forces gets higher than the spring’s constant of the cantilever. For the case of the Al surface (see Figure 7b), it is observed that a smooth increase for the adhesion force is observed, until the contact point between the two materials is reached (about 0.5 nm); intermolecular forces are the source of the attractive force between asphaltene molecules and the atoms of the metallic surfaces, when they are in contact. Aromatic regions in asphaltenes play an important role to increase the attractive force6,38. Also, the adhesion is associated with the molecules’ adhesive mechanical-properties, where the energy is dissipated through visco-elastic or elastic deformations while adhesion takes place.40. Figure 7a,b also imply that, depending on the zone of measurement, more repulsive rather than attractive forces domain these interactions. For instance, in the case of Fe, Fig 7a shows that the slope of zone 3 implies a taller (0.8 nm height) repulsive interaction as compared to the much shorter heights of interactions for zones 1 and 2, for zone 3, a distance range of more repulsive rather than attractive forces can be found. Figure 8 a,b shows the adhesion curves obtained by equation 8 and by AFM experiments for each metallic system. 14 ACS Paragon Plus Environment

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Fig. 8 HERE Figure 8a demonstrates that the adhesion force calculated by Eq. 8a in the case of Fe is in good agreement with the experiment AFM measurements for zones 1 and 2. To illustrate the contrasting effect of surface heterogeneity on the force calculations by our model, figure 8a shows that at distances of 0.8 nm between the cantilever and the metallic surface, a difference between calculated and experimental force measurements is large (calculated value = 20 nN; measurement value= 102 nN, zone 3). The calculated and measured force values are however very much agreeable if zones 2 and 1 of the same metal are scanned. This means that the model developed in this work provides an average estimation of the realistic force values for this kind of systems. Finally, for the Al case (Figure 8b), the force value calculated by Eq. 8 is about 10 nN. It differs in approximately 0.4 nm as compared to the 70 nN value as dictated by AFM on zone 3. As occur in the case of the Fe substrates, in this case, the result obtained by Eq. 8 represents an average force value among the screened zones of the Al surface. In spite of these differences and by the simplicity of our model of spherical particle, the observed overall correlation between well depth in AFM experiments and our analytical adhesion force model seem to be reasonable. Moreover, this adhesion force model takes into account the effect of the surrounding medium by means of an effective dielectric constant i.e. air (ε=1.1), and it considers superposition in each substrate layer to calculate the total adhesion force. Finally, to confirm that asphaltene aggregates adhere stronger to an Fe surface rather than to an Al surface (as Fig. 7a,b so infer), a set of Berkovich hardness tests41 were carried out. Details of a typical test procedure can be found in Ref.41. The tests were performed with the NanoMc module33 of an AFM NanoScope IV35 apparatus, using an 15 ACS Paragon Plus Environment

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ultra-high force cantilever for Nanoindenting. The tip is designed to be ultra-high strength made of stainless steel (Veeco Probe) of about 13 µm of thickness, spring constant k of 150 N/m and resonant frequency f of 50 kHz. In Fig. 9a,b, both surfaces were scanned and show the topographic measurements for each metallic substrate coated with an asphaltene deposit. Different kinds of three-dimensional surface profiles can be seen. Fig. 9 HERE On Figs. 10 and 11, the contact depth, projected area and pile-up dimensions are shown. The NanoMc module in AFM Nano Scope instrument was used to determine the hardness, which is tabulated in Table 2. Fig. 10 HERE Fig. 11 HERE

Table 2. Hardness of asphaltene deposits on metallic substrates. Type of substrate Fe Al

Hardness Berkovich, MPa Vickers 1604 151.6 842 80

Berkovich and Vickers hardness grades are higher in the Fe substrate case than Al case. These results indicate that asphaltene deposit is more compact and harder on iron surface than on aluminum surface.

4. Conclusions


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A calculation method for the force of adhesion and interaction between spherical asphaltene particles and metallic surfaces of Fe and Al has been developed and tested with experimental data. The proposed method is simple and provides an algebraic analytical expression for both the interaction potential and adhesion force (Eqs, 7 and 8) in these materials. Simple physical-property data of the asphaltene / metal materials are required. The proposed force expression takes into account both the short and long-range interactions through an effective dielectric constant. This approach provides a way to account for the effect of a surrounding media on asphaltene – metal interactions (including any oil solvent) AFM experiments have shown that, when industrial – grade metals are used, the topology of the force – distance plots show slightly different trends owing to the varying topography of these surfaces. When compared to the force measurements of Fe and Al surfaces, the proposed model is able to capture the essential features of the measured interactions, using no fitting parameters, with reasonable good agreement. Since our treatment is based on interaction forces between ideal metallic surfaces/spherical asphaltene particles, anisotropic effects are omitted. By considering that the proposed analytical expression does not account for imperfection and impurities of the industrial-grade metals used, the results obtained are remarkable. For petroleum-engineering applications, we deem our adhesion force model provides a reasonable approximate expression to account for asphaltene adhesion forces to Fe and Al metals as required in an oil-well numerical simulator with asphaltene precipitation and plugging.


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Acknowledgments The authors thank the Mexican Institute. of Petroleum’s authorities for granting permission to publish this work.


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References 1. J. G. Speight, J.G. . The Chemistry and Technology of Petroleum, Marcel Dekker, Inc. New York, 1991; pp 412-463. 2. Ruiz-Morales, Y. Energy & Fuels 2007, 21, 256. 3. García-Cruz, I.; Martínez-Magadán, J. M.; Guadarrama,P.; Salcedo, R.; Illas, F. J. Phys. Chem. A 2003, 107,1597 4. García-Cruz, I.; Martínez-Magadán, J. M.; Salcedo, R.; Illas, F. Energy & Fuels 2005, 19, 998. 5. T. F. Yen, J. G. Erdmann, W.E. Hanson. J. Chem. Eng. Data. 1961,6 6. Murgich, J., J. A. Abanero and O. P. Strauzs. Energy & Fuels. 1999, 13, 278. 7. Schuler, B., Meyer, G., Peña, D., Mullins, O.C. and Gross, O. Journal of the American Chemical Society. 2015, 137, 9870. 8. Zoppi, L., Martin-Samos, L. Baldridge, K. K. Acc. Chem. Res. 2014, 47, 33103320 9. Aradya, S. V., Frei, M., Hybertsen, M. S., Venkataraman, L. Nature Materials, 2012, 11, 872. 10. Ramirez-Jaramillo, E, C. Lira-Galeana and O. Manero. Energy & Fuels. 2006, 20, 1184 11. Vargas, F.M., Creek, J.L. and W. Chapman. Energy and Fuels, 2010, 24, 22942299. 12. Zahabi, A. and Gray, M.R. Energy & Fuels, 2012, 26, 2891 13. Wang, S., Liu, J., Zhang, L., Xu, Z. and Masliyah, J. Energy & Fuels, 2009, 23, 862 14. Cleveland, J.P. ,S. Manne, D. Bocek, P. K. Hansma. Rev. Sci. Instrumen. 1993, 64, 403. 15. Hutter J.L. and J. Bechhoefer. Rev. Sci. Instrum. 1993, 64, 1868 16. Lindhard, J., K. Dan. Vidensk. Selsk. Mat. Fys. Medd. 1965, 34, 4. 17. Ortega-Rodriguez, A., F. Alvarez-Ramirez, S.A. Cruz. and C. Lira-Galeana. J. Colloid Interface Sci.. 2006, 301, 352. 18. Zajac, G. W., N.K. Sethi, and J.T. Joseph. Scanning Microscopy. 1994, 8, 463. 19. Taylor, C.D. and Marcus, P. Molecular Modeling of Corrosion Processes Scientific Developent and Engineering Application. John Wiley. NJ, USA. 2015 20. Wei, D., Xu, Q., Zhao, T. and Dai, H. Advanced in Structural Bioinformatics. Springer, China. 2014. 21. Musa, A.Y., Jalgham, T. and Mohamad, B. Corrosion Science. 2014, 56, 176. 22. Obot, I.B. and Gazem, M. Corrosion Science. 2014, 83, 359. 23. Ortega-Rodriguez, A, C. Lira-Galeana, Y. Ruiz-Morales and S.A. Cruz. Petrol. Sci. Tech. 2001, 19, 245. 24. Ortega-Rodriguez, A. Thermodynamics of Asphaltene Precipitation in Petroleum Mixtures, PhD, thesis, Nacional University of Mexico, Mexico. 2004 25. Barthelat, J.C., I. Ortega-Blake, S.A. Cruz, C.Vargas-Aburto and L. T. Chadderton. Physical Review A. 1985, 31, 1382. 26. Accelrys. Insight II and Docking Modules. User’s Manuel. Molecular Simulation Inc. San Diego, 1996. 19 ACS Paragon Plus Environment

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27. Ortega-Rodriguez, A., Cruz, S.A., Gil-Villegas, A., Guevara-Rodriguez, F and Lira-Galeana, C. Energy & Fuels, 2003, 17, 1100. 28. Ruoff, R.S. and A.P. Hickman. J. Phys. Chem. 1993, 97, 2494. 29. Girifalco, L.A. J. Phys. Chem. 1992, 96, 858. 30. Girifalco, L.A., M. Hodak and S.L. Roland. Phys. Rev. B 2000, 62, 13104. 31. ASTM A 53 Standard for Iron, and ASTM B 345 Standard for Aluminum. 32. IP 143 Procedure. Asphaltenes precipitation with normal heptane. 1971. British Standard BS 4696. 33. Digital Instruments, Inc. 797 Sheridan Drive Buffalo, NY 14150 34. Kittel, C. Introduction to Solid State Physics. 17 th. Edition. John Wiley & Sons. N-Y 1996. Chapter 1. 35. Shuman, D. Microsc. Ana. 2005, 19, 21. 36. Ortega-Rodriguez, A., Cruz, S.A. and Lira-Galeana, C. Paper A23 presented at The First International Conference on Heavy Organic Depositions (HOD 2002) 2002. Puerto Vallarta, Jal. Mexico. 37. Alboudwarej, H., D. Pole, W.Y. Svrcek and H.W. Yarranton. Ind. Eng. Chem. Res. 2005, 44, 5585. 38. Murgich, J., E. Rogel and R. Leon. Petrol. Sci. Tech. 2001, 19, 437. 39. Alvarez-Ramirez, F., I. Garcia-Cruz, G. Tavizon and J.M. Martinez-Magadan. Petrol. Sci. Tech. 2004, 22, 915. 40. Israelachvili, J. Intermolecular and Surface Forces. Academic Press, San Diego, Cal. USA. 1992. 41. M.M. Khrushchov & E.S. Berkovich, Industrial Diamond Review. 1951, 11 42


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Figure 1.


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Figure 2.


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Figure 3.


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Figure 4.


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a)

b)

Tip Geometry: Tip Height (h):

Anisotropic 15um - 20um

Front Angle (FA):

15°

Back Angle (BA):

25°

SideAngle (SA):

17.5°

Tip Radius (Nom.):

Study of the Adhesion Force of Asphaltene Aggregates to Metallic

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