A Study on the Investigation of Flame Retardancy and Anticorrosive Properties of Boron Oxide-Additive Paints

Summary

This study aimed to develop paints with advanced properties by utilizing the characteristics of boric oxide, one of the boron chemicals found in abundance in Turkey. For this purpose, a solvent-based paint containing boric oxide additive was prepared, applied to different metal plates, and surface properties were examined. TG/DTA (Thermogravimetric/Differential Thermal Analysis) was performed to determine the flame-retardant properties of the paints. It is anticipated that the paint containing boric oxide and consisting of different additives will find applications in various metal industries due to its flame-retardant and corrosion-inhibiting properties. Keywords: boric oxide, paint, corrosion, mineral

Introduction

With developing technology, in recent years there has been a rapid increase in demand for paints that provide properties such as self-cleaning, high impact resistance, flame retardancy and corrosion resistance in metal industries such as automotive, shipbuilding and aerospace. When paint is applied to a surface, it forms a layer that is not only decorative but also protective. For this reason, the desired properties on surfaces that can be coated with paint can be achieved by improving paint properties. Unprotected metals are slowly or rapidly converted to their oxides through the effects of factors such as air, water, light and carbon dioxide. Separating metals from their oxides is a challenging process and causes significant losses in energy, raw materials and labor. For these reasons, protecting materials against corrosion, extending service life and preventing energy loss are extremely important. Although an indefinitely effective anticorrosive system does not exist, it is known that corrosion effects can be largely prevented through properly selected paint or coating methods. In a study conducted by Alıcılar et al. (2015), boron compounds such as sodium tetraborate, calcium and potassium tetraborate, anhydrous and aqueous zinc borate were added to water-based styrene acrylic paint. The painting properties of the additive-containing paints, smoke suppression, flame retardancy and antibacterial activity against two bacteria (E. coli and S. aureus) were determined. Experiments were repeated with ammonium polyphosphate additive for comparison with borates. As a result of the experiments and analyses, it was observed that sodium tetraborate could be used in paints as a smoke suppressant and flame retardant, and zinc borate could be an effective reagent against S. aureus bacteria in addition to its flame-retardant property. It was suggested that the reduction in paint viscosity caused by sodium tetraborate addition could be overcome by using thickeners. In addition to the advantages provided by zinc borate and sodium tetraborate additives, it was observed that they did not adversely affect other properties of the paint such as viscosity, gloss and color intensity. Although other boron-containing compounds (calcium and potassium tetraborate) partially possessed smoke suppression and flame-retardant properties, they did not show resistance to the tested bacteria [1]. In a review by Adamsons (2000), the profiles and chemical surface characterization of automotive coating systems were investigated in detail. Various system components (for example, clearcoat, base coat or adhesion promoter with plastic undercoat) must be durable, compatible and mutually integrated to create systems with adequate service life. This study provides researchers with insights into applications for addressing their vehicles' characterization needs [2]. In a study conducted by El Nemr et al. (2014), the effect of halogenated additives working together in a basic solution containing paint on aluminum corrosion was examined. Quantum chemical calculations were performed on the studied paints to determine the relationship between their molecular structures and corrosion inhibition effectiveness [3]. In another study, magnesium borate synthesized by solid-state reaction was added to paint content through an appropriate binder. Magnesium borate was produced as a result of sintering reactions of Magnesium Oxide and Boric Oxide. Magnesium borates with the formulations Mg2(B2O5) and MgB4O7, when added to the paint structure and applied on zinc plates, were found to increase resistance to high temperatures. Additionally, the Limiting Oxygen Index also confirms that magnesium borate addition imparts flame-retardant properties to the paint [4]. The flame-retardant effect of zinc borate in chlorine-containing coatings was examined by Giúdice and Benitez (2001). In the study, zinc borate was used instead of antimony trioxide in coatings. Zinc borate 2ZnO.3B2O3.3.5H2O (2:3:3.5) showed high thermal stability in TGA. With approximately 85.5% mass fraction, it showed the highest mass loss at 800°C. It was confirmed that materials exhibit flame-retardant properties in connection with the Limiting Oxygen Index. As a result, since the number of hydrate water molecules released at high temperatures can absorb large amounts of heat, this heat increased flame resistance and delayed heat increase [5]. In a study conducted by Garba (1998), the effect of zinc borate as a flame-retardant formulation on certain tropical woods in a different area was examined. When examining the results of impregnation effect on zinc borate-impregnated tropical woods, thermal characteristics were also taken into account. As a result of this treatment, flame spread rate, afterglow time and flame temperature were substantially reduced. It was observed that zinc borate, through its acidification with HCl, functioned as a flame-retardant formulation in a complex process involving dehydration, condensed phase and vapor phase mechanisms [6]. In another study, zinc borate used as an additive was employed to provide flame-retardant properties in electrical cables. It was found that the added zinc borate additives could raise ignition temperatures up to 235°C [7]. In a study conducted by Yıldız et al. (2009), new polyurethane-zinc borate composites were prepared to improve the flame-retardant properties of polyurethane. According to the results observed with induction time tests and supported by tests in real air condition rooms, it was discovered that zinc borate has very important effects on the oxidative stability of the polymer, and it was observed that polyurethane filled with zinc borate has better performance. Mechanical tests, thermogravimetric analysis and scanning electron microscopy studies were performed to characterize the zinc borate additive-containing product that was proven to provide significant flame-retardant properties [8]. In this study, it was found that paint containing boric oxide as one of the boron chemicals and consisting of different additives can be evaluated in different metal industries due to its flame-retardant and corrosion-inhibiting properties.

Experimental Work

Materials with different properties in the range of 0-6% (w/w) by weight were added to a determined amount of solvent-based paint diluted with thinner. As additives, natural mineral, fluorine-based surfactant and boric oxide were added to solvent-based paint at different percentages by weight, and the resulting mixtures were stirred at 1000 rpm for 3 minutes. The obtained paints were applied to specially prepared 10x10 cm² metal plates with the aid of an applicator and left to dry for 24 hours. TG/DTA analysis was performed to examine flame-retardant properties. Salt spray test was performed to examine anticorrosive properties.

Results and Discussion

In the reference paint, 4.7% mass loss is observed up to 260°C, 19.4% between 260-450°C, 10% between 450-490°C, and 0.8% after 500°C. The 4.7% mass loss up to 260°C is thought to be due to evaporation of the solvent mixed with the paint, while it can be said that major structural degradation occurs largely in the 260-450°C temperature range where mass loss of 19.4% is observed. (Figure 1). In the boron oxide-additive paint; 1.0% mass loss is observed up to 70°C, 2.1% between 70-150°C, 5.8% between 150-326°C, 13.7% between 326-410°C, and 11.1% after 410°C. When the prepared paint mixture is compared with the reference paint, it can be said that the structural degradation temperature starts at higher temperature values (326°C). Accordingly, it can be stated that the added additives impart flame-retardant properties to the paint (Figure 2).       For corrosion testing, plates were exposed to 5% sodium chloride solution sprayed at 0.7-1.4 bar air pressure for 96 hours, and the paint film was visually inspected at regular intervals. The unpainted portions of iron-made plates underwent corrosion, and no corrosion emergence was observed from beneath the painted portions to the surface. This situation proves that the paint mixtures are resistant to corrosion. The marks visible on the paint surface are caused by rust flowing from the corroded portions to the paint surface (Figure 3).  

Conclusion

In the study conducted, with the additives added, the flame-retardant properties of the paint were improved and paints resistant to corrosion were obtained. It was found that paint mixtures with improved properties can find applications in various metal industries. It is believed that this study will shed light on future work in the paint field both in terms of improving paint properties and evaluating them according to the industry in which they will be used. Assoc.Prof. Nil Acaralı / Faculty of Chemistry and Metallurgy / Department of Chemical Engineering / Yıldız Technical University Gizem Toprakçı / Faculty of Chemistry and Metallurgy / Department of Chemical Engineering / Yıldız Technical University

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[3] El Nemr, A., Moneer, A. A., Khaled, A., El Sikaily, A. and El-Said, G. F. (2014). "Modeling of Synergistic Halide Additives' Effect on the Corrosion of Aluminum in Basic Solution Containing Dye", Materials Chemistry and Physics, 144(1): 139-154.

[4] Atalay, Ö., (2012). "Magnesium Borate Synthesis and Its Use as a Flame-Retardant Pigment", Master's Thesis, Gazi University, Institute of Science, Ankara.

[5] Giudice, C. A. and Benitez, J. C. (2001). "Zinc borates as flame-retardant pigments in chlorine-containing coatings", Progress in Organic Coatings, 42(1): 82-88.

[6] Garba, B. (1999). "Effect of Zinc Borate as Flame Retardant Formulation on Some Tropical Woods", Polymer Degradation and Stability, 64(3): 517-522.

[7] Miroğlu, C., (2005). "Zinc Borate Production from Domestic Sources and Its Use in Flame-Resistant Cable Manufacturing", Master's Thesis, Istanbul Technical University, Institute of Science, Istanbul.

[8] Yıldız, B., Seydibeyoğlu, M. Ö. and Güner, F. S. (2009). "Polyurethane–Zinc Borate Composites with High Oxidative Stability and Flame Retardancy". Polymer Degradation and Stability, 94(7): 1072-1075.