**3.3 Degree of rusting**

The performance of panels tested during 1500 hours in salt spraying (fog) chamber (35±1 ºC; pH 6.5-7.2; continuous spraying of 5±1% w/w of NaCl solution) are shown in Figure 4 and Figure 5. They include only the average values of the tests performed in the failure in X-cut (Method A) and over the general area of panel (Method B).

The results of Method A were evaluated according to the advance from the cutting area: the value 10 defines a failure of 0 mm while zero corresponds to 16 mm or more. Those results corresponding to Method B were measured taking into account the percentage of area corroded by the environment: the scale ranges from 10 to 0, which means respectively no failure and over 75% of the rusted area.

On the other hand, Figure 6 displays one of the primer with best performance in salt spraying (fog) chamber for 1500 hours: A.I.2.c; applying the Method A, this primer showed a degree of rusting 10 (no failure, which means 0 mm of advance from the cutting area).

To study the variables considered (main effects), a statistical interpretation was carried out. First, the variance was calculated and later the Fisher F test was done.

The results indicated that type of binder, average diameter of microzinc particles, type of reinforcement fibers, level of reinforcement fibers and finally PVC values displayed an important influence on the performance of the protective coatings.

According to results, it was considered desirable for the statistical analysis to take into account all values of PVC studied for allowing a certain margin of safety in the performance since it is possible the generation of heterogeneities in primer composition attributable to poor incorporation of metallic zinc and/or sedimentation in container before applying.

Fig. 4. Coatings based on binder A: Degree of rusting in salt spraying (fog) chamber; average values of failures in X-cut and in general area of panel.

The experimental values indicate a significant shift towards more positive values of potential in those primers with decreasing amounts of conducting reinforcement fibers in

Considering the performance, the worst primers have been formulated both with microzinc

Finally, there was observed only a slightly decreasing efficiency to the lower values of PVC

Figure 3 includes values of potential versus immersion time in 0.1 M sodium chloride solution at pH 7.0 and 25 °C for primers formulated with 57.5 and 70.0% PVC values and based on 7.5/1.0 nano silica/lithium oxide molar ratio as film-forming material, fine microzinc (D 50/50 4 µm) as pigment inhibiting and graphite as reinforcement fiber in the three levels studied. In addition, this figure displays the corresponding reference primers. There is a total correlation between conclusions of visual observation and results of the electrode potentials obtained during immersion in 0.1 M sodium chloride solution; therefore, the basis of the quantitative results of electrode potentials are the same that those

The performance of panels tested during 1500 hours in salt spraying (fog) chamber (35±1 ºC; pH 6.5-7.2; continuous spraying of 5±1% w/w of NaCl solution) are shown in Figure 4 and Figure 5. They include only the average values of the tests performed in the failure in X-cut

The results of Method A were evaluated according to the advance from the cutting area: the value 10 defines a failure of 0 mm while zero corresponds to 16 mm or more. Those results corresponding to Method B were measured taking into account the percentage of area corroded by the environment: the scale ranges from 10 to 0, which means respectively no

On the other hand, Figure 6 displays one of the primer with best performance in salt spraying (fog) chamber for 1500 hours: A.I.2.c; applying the Method A, this primer showed a degree of rusting 10 (no failure, which means 0 mm of advance from the cutting area).

To study the variables considered (main effects), a statistical interpretation was carried out.

The results indicated that type of binder, average diameter of microzinc particles, type of reinforcement fibers, level of reinforcement fibers and finally PVC values displayed an

According to results, it was considered desirable for the statistical analysis to take into account all values of PVC studied for allowing a certain margin of safety in the performance since it is possible the generation of heterogeneities in primer composition attributable to poor incorporation of metallic zinc and/or sedimentation in container

First, the variance was calculated and later the Fisher F test was done.

important influence on the performance of the protective coatings.

studied with the incorporation of conductive reinforcing fibers in increasing levels.

their composition (2.0, 1.5 and 1.0% w/w ratio, in that order).

dusts alone and mixed with insulation reinforcement fibers.

(Method A) and over the general area of panel (Method B).

spelled out in the visual observation.

failure and over 75% of the rusted area.

**3.3 Degree of rusting** 

before applying.

Reinforcement Fibers in Zinc-Rich Nano Lithiun Silicate Anticorrosive Coatings 169

With the purpose of establishing the efficiency of each protective coating from an anticorrosive point of view, the average value of degree of rusting was calculated for areas with and without cutting. The results of Table 2 confirm the superior performance of waterbased nano lithium silicate of 7.5/1.0 silica/alkali molar ratio in relation to solvent-based, partially hydrolyzed tetraethyl orthosilicate, the major efficiency of fine microzinc compared to regular one and the increasing efficiency of primers as the level of conducting reinforcement fibers increased (Ahmed et al., 2010). On this last variable of formulation, it is worth mentioning that primers with 2.0% conducting reinforcement fibers showed the best protective capacity, which would occur due to the improved electric contact between zinc particles and with metallic substrate. On the other hand, the quartz used as reinforcement fiber due to characteristic non-conductive showed a similar performance that the

> **Degree of rusting Average values of failures in X-cut and in general area of panel**

> > 7.1 6.2

> > 7.0 6.3

> > 5.8 7.2 7.2 5.8

> > 6.2 6.8 7.3

corresponding reference primer (without reinforcement fiber).

**effect** 

B

I II

a b c

Corresponding standard deviation values support this conclusion.

Table 2. Average values of the simultaneous statistical treatment of all variables.

On the other hand, Table 3 lists the average values and the standard deviations of statistical processing for each primer; in addition, it also displays the general average values for each type of reinforcement fiber taking into account both binders considered. In this table, the highest value also indicates the best performance in terms of the ability to control the metal corrosion. The analysis of the results obtained by using both types of binder displays that the primers based just on two spherical microzinc (reference primers) and non-conducting reinforcement fibers (quartz) in the three considered levels, formulated with reduced values of PVC, showed a sharp decline in corrosion performance. On the other hand, those that included conducting reinforcement fibers (graphite and silicon nitride), despite having been manufactured with a significantly lower level of pigmentation, maintained their efficiency.

These results would be based on the reduced electrical contact between particles of both types of microzinc and the metal substrate, regardless of the corrosion products could not only increase the electrical resistance of the film but also could decrease the amount of

**Nature of effect Type of** 

**Type of binder** <sup>A</sup>

**Microzinc D 50/50** 

**Type of reinforcement fibers** 

**Level of reinforcement fibers** 

available zinc.

Fig. 5. Coatings based on binder B: Degree of rusting in salt spraying (fog) chamber; average values of failures in X-cut and in general area of panel.

Fig. 6. Primer A.I.2.c, performance in salt spraying (fog) chamber, Method A, degree of rusting: 10.

57.5 60.0 62.5 65.0 67.5 70.0

57.5 60.0 62.5 65.0 67.5 70.0

B.I.1 B.I.2.a B.I.2.b B.I.2.c B.I.3.a B.I.3.b B.I.3.c B.I.4.a B.I.4.b B.I.4.c

B.II.1 B.II.2.a B.II.2.b B.II.2.c B.II.3.a B.II.3.b B.II.3.c B.II.4.a B.II.4.b B.II.4.c

**Primer**

Fig. 6. Primer A.I.2.c, performance in salt spraying (fog) chamber, Method A, degree of

values of failures in X-cut and in general area of panel.

Fig. 5. Coatings based on binder B: Degree of rusting in salt spraying (fog) chamber; average

**Primer**

rusting: 10.

**Degree of rusting**

**Degree of rusting**

With the purpose of establishing the efficiency of each protective coating from an anticorrosive point of view, the average value of degree of rusting was calculated for areas with and without cutting. The results of Table 2 confirm the superior performance of waterbased nano lithium silicate of 7.5/1.0 silica/alkali molar ratio in relation to solvent-based, partially hydrolyzed tetraethyl orthosilicate, the major efficiency of fine microzinc compared to regular one and the increasing efficiency of primers as the level of conducting reinforcement fibers increased (Ahmed et al., 2010). On this last variable of formulation, it is worth mentioning that primers with 2.0% conducting reinforcement fibers showed the best protective capacity, which would occur due to the improved electric contact between zinc particles and with metallic substrate. On the other hand, the quartz used as reinforcement fiber due to characteristic non-conductive showed a similar performance that the corresponding reference primer (without reinforcement fiber).


Table 2. Average values of the simultaneous statistical treatment of all variables.

On the other hand, Table 3 lists the average values and the standard deviations of statistical processing for each primer; in addition, it also displays the general average values for each type of reinforcement fiber taking into account both binders considered. In this table, the highest value also indicates the best performance in terms of the ability to control the metal corrosion. The analysis of the results obtained by using both types of binder displays that the primers based just on two spherical microzinc (reference primers) and non-conducting reinforcement fibers (quartz) in the three considered levels, formulated with reduced values of PVC, showed a sharp decline in corrosion performance. On the other hand, those that included conducting reinforcement fibers (graphite and silicon nitride), despite having been manufactured with a significantly lower level of pigmentation, maintained their efficiency. Corresponding standard deviation values support this conclusion.

These results would be based on the reduced electrical contact between particles of both types of microzinc and the metal substrate, regardless of the corrosion products could not only increase the electrical resistance of the film but also could decrease the amount of available zinc.

Reinforcement Fibers in Zinc-Rich Nano Lithiun Silicate Anticorrosive Coatings 171

**A.I.1** 6.6 1.16 6.6 **B.I.1** 5.6 1.07 5.6

**A.I.2.b** 8.2 0.41 **B.I.2.b** 7.2 0.82 7.1

**A.I.3.b** 8.0 0.44 **B.I.3.b** 7.1 0.86 7.1

**A.I.4.b** 6.7 1.13 **B.I.4.b** 5.7 1.08 5.7

**A.II.1** 6.0 1.34 6.0 **B.II.1** 4.8 1.33 4.8

**A.II.2.b** 7.3 0.52 **B.II.2.b** 6.7 0.82 6.6

**A.II.3.b** 7.2 0.42 **B.II.3.b** 6.6 0.86 6.6

**A.II.4.b** 6.1 1.24 **B.II.4.b** 4.8 1.21 4.8

To explain the great tendency of zinc particles to corrode at the film surface of water-based nano lithium silicate primers as comparing with those solvent-based, partially hydrolyzed tetraethyl orthosilicate, it is necessary to consider that the first ones are based on binders, as mentioned, with a higher superficial tension. The last one implies inferior wetting, that means lower adhesion, penetration and spreading during metal zinc incorporation previous to application; consequently, they wet with more difficult the zinc particles while the second

The above-mentioned characteristic explains the great porosity of zinc-rich nano lithium silicate films and their high cathodic protective activity as comparing with zinc-rich

With regard to average diameter of zinc particle, size diminution increases significantly the surface area for a given weight. Since all surfaces have a given level of free energy, the ratio of surface energy to mass in small particles is so great that the particles adhered strongly themselves. For this reason, a lower particle size in a poor dispersion originates a greater flocculates (a high number of unitary particles are associated), which lead to zinc-rich

**Primer Average** 

**value** 

**B.I.2.a** 6.2 0.94

**B.I.3.a** 6.3 0.93

**B.I.4.a** 5.6 0.97

**B.II.2.a** 5.8 0.93

**B.II.3.a** 5.7 0.98

**B.II.4.a** 4.8 1.29

**Standard deviation σ n-1**

**General average value** 

**General average values** 

8.0

**A.I.2.c** 8.9 0.38 **B.I.2.c** 8.0 0.55

7.9

**A.I.3.c** 8.8 0.42 **B.I.3.c** 8.0 0.55

6.5

**A.I.4.c** 6.4 1.28 **B.I.4.c** 5.8 1.17

7.2

**A.II.2.c** 7.8 0.49 **B.II.2.c** 7.4 0.53

7.3

**A.II.3.c** 8.2 0.41 **B.II.3.c** 7.2 0.66

6.1

**A.II.4.c** 6.1 1.16 **B.II.4.c** 4.9 1.24

**Primer Average** 

**values** 

**A.I.2.a** 6.9 0.58

**A.I.3.a** 7.0 0.63

**A.I.4.a** 6.4 1.20

**A.II.2.a** 6.5 0.55

**A.II.3.a** 6.5 0.55

**A.II.4.a** 6.1 1.28

**4. Final considerations** 

tetraethyl orthosilicate films.

Table 3. Average values and standard deviation.

ones do it in a better way (more reduced interfacial tension).

**Standard deviation σ n-1**

The incorporation of conducting reinforcement fibers seems to have favored the conductivity, which leads to reduction of the efficient PVC, according to the abundant amount of zinc corrosion products visually observed, the results of the electrode potentials and those obtained in the salt spraying (fog) chamber. Figures 7 and 8 display the primer films based on binder A (water-based nano lithium silicate of 7.5/1.0 silica/alkali molar ratio), microzinc I (fine, 4 µm) and fiber 2 (graphite) in level c (2.0% w/w) for 57.5% and 70.0% PVC values respectively, after finishing the accelerated aging test. The analysis of the cited figures reveals that despite having larger distance between the particles of microzinc in the case of 57.5% PVC compared with that formulated with 70.0% PVC, the galvanic activity in the two primers is significant in both cases (as evidenced by the amount of white zinc salts). In addition, results of figures show that the conductive reinforcement fibers linked electrically the microzinc particles each other, even in the primer of less PVC (all particles, despite having no direct contact between them, demonstrated activity like sacrificial anodes).

Fig. 7. SEM micrograph of primer A.I.2.c formulated with 57.5% PVC.

Fig. 8. SEM micrograph of primer A.I.2.c formulated with 70.0% PVC.


Table 3. Average values and standard deviation.
