**2.1.3 Reinforcement fibers**

Nowadays reinforcement fibers are used in many materials to improve their physical and chemical properties (Huang et al., 2009 & Amir et al., 2010). A composite (FRP, fiberreinforced polymer) is formulated and manufactured with the purpose of obtaining a unique combination of properties; the incorporation of reinforcement fibers to coatings forms a hybrid structure. Fiber is defined as any material that has a minimum ratio of length to average transverse dimension of 10 to 1; in addition, the transverse dimension should not exceed 250 µm.

In anticorrosive coating formulations with hybrid structures, the following reinforcing fibrous materials were used: graphite, silicon nitride and quartz. The levels selected for the experiment were 1.0, 1.5 and 2.0% w/w on coating solids.

*Graphite.* It is an allotropic form of carbon (hexagonally crystallized). It displays black color with metallic brightness and it is non-magnetic; it has 2.267 g.cm-3 density at 25 °C. Usually, it is used as pigment in coatings to give conductive properties to the film. Graphite is formed by flakes or crystalline plates attached to each other, which are easily exfoliated. The electrons that are between layers are those that conduct electricity, and these are what give the quoted brightness (the light is reflected on the electron cloud) (Yoshida et al., 2009 & Abanilla et al., 2005). In perpendicular direction to the layers, it has a low electrical conductivity, which increases with the temperature (it behaves like a semiconductor); on the other hand, throughout the layers, the conductivity is greater and it is increased with the temperature, behaving like a semi-metallic conductor. In this work, graphite in fiber form was used with average values of 1020 μm and 82 μm for length and transverse dimension, respectively (Figure 2.A).

stage of tetraethyl orthosilicate that leads to the silicic acid formation, the absence of alcohol would generate the polycondensation of mentioned acid with silica precipitation and the null capacity to conform a polymeric silicic acid (Wang et al., 2009 & Yang et al., 2008).

In a first stage, the pure tetraethyl silicate and the isopropyl alcohol were mixed under agitation. Later, the water and the hydrochloric acid solution selected as catalyst were added (the final pH of the solution was slightly acid, 0.01% w/v, expressed as hydrochloric acid);

The conclusions from the experiences indicate that: an excessive amount of water (higher than calculated) generates a rapid gelling in the package, a high pH leads to a fast silica precipitation that reduces the capacity of formation of an inorganic polymer of elevated molecular weight and, in addition, a large quantity of acid retards the condensing reaction

In this study, two samples of commercial spherical zinc dust were used; the D 50/50 average particle diameters were 4 μm (fine) and 8 μm (regular), Figure 1. The main features were respectively 98.1 and 98.3% of total zinc and 94.1 and 94.2% of metal zinc, which means 5.0 and 5.1% of zinc oxide; in addition, metal corrosion inhibitors displayed

Nowadays reinforcement fibers are used in many materials to improve their physical and chemical properties (Huang et al., 2009 & Amir et al., 2010). A composite (FRP, fiberreinforced polymer) is formulated and manufactured with the purpose of obtaining a unique combination of properties; the incorporation of reinforcement fibers to coatings forms a hybrid structure. Fiber is defined as any material that has a minimum ratio of length to average transverse dimension of 10 to 1; in addition, the transverse dimension should not

In anticorrosive coating formulations with hybrid structures, the following reinforcing fibrous materials were used: graphite, silicon nitride and quartz. The levels selected for the

*Graphite.* It is an allotropic form of carbon (hexagonally crystallized). It displays black color with metallic brightness and it is non-magnetic; it has 2.267 g.cm-3 density at 25 °C. Usually, it is used as pigment in coatings to give conductive properties to the film. Graphite is formed by flakes or crystalline plates attached to each other, which are easily exfoliated. The electrons that are between layers are those that conduct electricity, and these are what give the quoted brightness (the light is reflected on the electron cloud) (Yoshida et al., 2009 & Abanilla et al., 2005). In perpendicular direction to the layers, it has a low electrical conductivity, which increases with the temperature (it behaves like a semiconductor); on the other hand, throughout the layers, the conductivity is greater and it is increased with the temperature, behaving like a semi-metallic conductor. In this work, graphite in fiber form was used with average values of 1020 μm and 82 μm for length and transverse dimension,

agitation continued until the end of the dissipation of heat (exothermic reaction).

due to the repulsion of protonated hydroxyl groups (Giudice et al., 2007).

respectively 2282 and 1162 cm2.g-1 values of specific area (BET).

experiment were 1.0, 1.5 and 2.0% w/w on coating solids.

**2.1.2 Pigmentation** 

**2.1.3 Reinforcement fibers** 

exceed 250 µm.

respectively (Figure 2.A).

Fig. 1. Commercial spherical zinc dusts. D 50/50 average particle diameters: 4 μm (fine) and 8 μm (regular).

*Silicon nitride (Si3N4).* It displays three different crystal structures (α, β and γ). It is industrially obtained by direct reaction between silicon and nitrogen at temperatures between 1300 and 1400 ºC. Silicon nitride is a material frequently used in the manufacture of structural ceramics with high requests of mechanical stress and wear resistance; it displays a moderately high modulus of elasticity and an exceptionally high tensile strength, which makes it attractive for its use in the form of fiber as reinforcement material for coatings films. It behaves like a semiconductor and it has 3.443 g.cm-3 density at 25 °C. For this experience, hexagonal β phase in the form of fiber has been selected, with average values of 1205 μm and 102 μm for length and transverse dimension, respectively (Figure 2.B).

*Quartz.* It is rhombohedral crystalline silica reason why it is not susceptible of exfoliation; chemically it is silicon dioxide (SiO2). Usually it appears colorless (pure), but it can adopt numerous tonalities if it has impurities; its hardness is such that it can scratch the common steels. It is often used in coatings as extender after being crushed and classified by size (average diameter between 1.5 and 9.0 μm). It is an insulating material from the electrical point of view; it has 2.650 g.cm-3 density at 25 °C (Chen et al., 2010 & Lekka et al., 2009). In this experience, quartz fibers were used with average values of 1118 μm and 95 μm for length and transverse dimension, respectively (Figure 2.C).

These reinforcements cannot be classified as nano materials since they no have at least one of the dimensions inferior to 100 nm (Aluru et al., 2003; Radhakrishnan et al., 2009; Behler et al., 2009 & Li & Panigrahi 2006).

Reinforcement Fibers in Zinc-Rich Nano Lithiun Silicate Anticorrosive Coatings 163

In this paper, the manufacture of hybrid coatings was made by ultrasonic dispersion in the vehicle. The efficiency of the fiber dispersion in the polymeric matrix was rheological monitored (viscosity of the system, measured at 10-3 sec-1, decreased during the sonification process until reaching a stationary value); the SEM observation corroborated both the

Finally, it should also be mentioned that this type of compositions is provided in two packages with the purpose of avoiding the reaction of metallic zinc with any vestige of moisture in some of the components, which would lead to the formation of gaseous hydrogen. In addition, the system could form a gel because of the reaction between silicic acids and zinc cations. Accordingly, prior to the primer application, the metallic zinc was

SAE 1010 steel panels were previously degreased with solvent in vapor phase; then they were sandblasted to ASa 2½ grade (SIS Specification 05 59 00/67) obtaining 25 µm maximum roughness Rm. The application was made in a single layer reaching a dry film thickness between 75 and 80 µm. In all cases, and to ensure the film curing before beginning the tests, the specimens were kept in controlled laboratory conditions (25±2 ºC and 65±5%

The study was statistically treated according to the following factorial design: 2 (type of binder) x 2 (average diameter of spherical microzinc particles) x 3 (type of reinforcement fibers) x 3 (level of reinforcement fibers) x 6 (PVC values), which make 216 combinations. In addition, reference primers (without reinforcement fiber) based on both binders and both spherical microzinc particles for the six mentioned PVC values were also considered, which means in total 24 reference primers. All panels were prepared in duplicate; primer

After curing process, panels of 150 x 80 x 2 mm were immersed in 0.1 M sodium chloride solution for 90 days at 25 °C and pH 7.0. A *visual inspection* was realized throughout the experience; in addition, the *electrode potential* was determined as a function of exposure time;

The tube size was 10 cm long and 5 cm diameter, with the lower edge flattened; the geometric area of the cell was 20 cm2. A graphite rod axially placed into the tubes and a saturated calomel electrode (SCE) were selected respectively as auxiliary and reference electrodes. The potential was measured with a digital electrometer of high input

Similar panels were tested in salt spraying (fog) chamber (1500 hours) under the operating conditions specified in ASTM B 117. After finishing the tests, the panels were evaluated according to ASTM D 1654 (Method A, in X-cut and Method B, in the rest of the surface) to

two clear acrylic cylindrical tubes were fixed on each plate (results were averaged).

efficiency of fiber dispersion and its stability after 3 months in can.

dispersed for 180 seconds at 1400 rpm in high-speed disperser.

**2.3 Manufacture of coatings** 

**2.4 Preparation of panels** 

relative humidity) for seven days.

identification is displayed in Table 1.

**2.5 Laboratory tests** 

impedance.

establish the *degree of rusting*.

Fig. 2. SEM micrograph of reinforcement fibers: A. Graphite, B. Silicon nitride and C. Quartz.
