**3.2 Corrosion potential**

Immediately after finishing the immersion of all coated panels in the electrolyte, the potential was inferior to -1.10 V, a value located in the range of protection of the electrode. It is worth mentioning that cathodic protection is considered finished when the corrosion potential of coated panel increased to more positive values (anodic ones) than -0.86 V (referring to SCE) since the characteristic corrosion points of the iron oxides were visually observed.

PVC Values: 57.5, 60.0, 62.5, 65.0, 67.5 and 70.0%

Immersion test in 0.1 M sodium chloride solution allowed to observe, particularly in those panels with X-cut, that coatings based on nano-structured film-forming material as binder showed greater amount of white products from corrosion of metallic zinc than in those panels protected with primers made with partially hydrolyzed ethyl silicate as binder. This performance would be supported in the less zinc dispersion ability that displays the first

On the other hand, primers that included fine zinc particles (4 µm) also showed a galvanic activity more important than those made from regular zinc particles (8 µm). A similar conclusion was reached with the primers based on microzinc/conducting reinforcement fibers (graphite and silicon nitride) with respect to those based just on spherical microzinc dusts and mixture with insulating reinforcement fiber (quartz). In turn, it was also observed a rise of the galvanic activity of metallic zinc when the amount of conducting fibers was

For the lower values of PVC studied, the incorporation of conductive reinforcing fibers in increasing levels led to primers with a galvanic activity also increasing (similar amount of

Immediately after finishing the immersion of all coated panels in the electrolyte, the potential was inferior to -1.10 V, a value located in the range of protection of the electrode. It is worth mentioning that cathodic protection is considered finished when the corrosion potential of coated panel increased to more positive values (anodic ones) than -0.86 V (referring to SCE) since the characteristic corrosion points of the iron oxides were visually

white salts than in primers formulated with PVC nearest to CPVC).

(A) Water-based nano lithium silicate of 7.5/1.0 silica/alkali molar ratio

(B) Solvent-based, partially hydrolyzed tetraethyl orthosilicate

(I) Spherical microzinc (fine), D 50/50 4 µm

(II) Spherical microzinc (regular), D 50/50 8 µm

Types: (1) Without, (2) Graphite, (3) Silicon nitride (4) Quartz

Level: (a) 1.0, (b) 1.5 and (c) 2.0% w/w on coating solids

Film-forming material

> Spherical microzinc

Reinforcement fibers

Table 1. Primer identification.

**3. Result and discussion** 

binder, which would generate films more porous.

**3.1 Visual observation** 

increasing in the film.

**3.2 Corrosion potential** 

observed.

The electrode potential measurements as a function of immersion time indicates that both types of binders had a significant influence on the electrode potential: in general, more negative values were obtained with nano-structured film-forming materials, which means that the primers based on lithium silicate showed better cathodic protection than those manufactured with ethyl silicate.

On the other hand, slight differences in electrode potential could also be attributed to the average diameter of zinc particles; it was observed greater galvanic activity in samples prepared with 4 μm than with 8 μm (values more negative of electrode potentials for the former than for the latter).

Fig. 3. Electrode potential vs. immersion time in 0.1 M sodium chloride solution at pH 7.0 and 25 °C for primers based on 7.5/1.0 nanosilica/lithium oxide molar ratio, fine microzinc and graphite fibers.

Reinforcement Fibers in Zinc-Rich Nano Lithiun Silicate Anticorrosive Coatings 167

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

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

**Primer**

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.

57.5 60.0 62.5 65.0 67.5 70.0

57.5 60.0 62.5 65.0 67.5 70.0

**Primer**

**Degree of rusting**

**Degree of rusting**

The experimental values indicate a significant shift towards more positive values of potential in those primers with decreasing amounts of conducting reinforcement fibers in their composition (2.0, 1.5 and 1.0% w/w ratio, in that order).

Considering the performance, the worst primers have been formulated both with microzinc dusts alone and mixed with insulation reinforcement fibers.

Finally, there was observed only a slightly decreasing efficiency to the lower values of PVC studied with the incorporation of conductive reinforcing fibers in increasing levels.

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 spelled out in the visual observation.
