Performance evaluation of layered double hydroxides containing benzotriazole and nitrogen oxides as additives in automotive primer for corrosion protection

Corrosion of metals comprises its deterioration due to the interaction with environment, what presents an economic associated aspect, once that resources are spent to repair these damaged materials. Organic coatings are commonly employed for metals protection; however, these coatings confer a physical protection barrier, which are prone to failures that may expose metal to the environment. Thus, insertion of particles which are capable to promote active protection against corrosion in these coatings is a relevant approach. Layered Double Hydroxides (LDH), which consists of inorganic hydrotalcite-type particles and are able to trap anions between its layers, have been studied as corrosion inhibitors anions carriers to promote active protection. These LDH show double functionality: 1) promote controlled release of corrosion inhibitors and 2) entrap corrosive anions, decreasing the medium aggressiveness. In this work, two commercial LDH containing different corrosion inhibitors (nitrogen oxides and benzotriazole) were evaluated on its ability to ion exchange and anticorrosion performance of carbon steel. Regarding to nitrogen oxide-loaded LDH, FourierTransform Infrared Spectroscopy (FTIR) and X-Ray Diffraction (XRD) results showed that nitrogen oxides were successfully intercalated, which were released in presence of chloride media. OCP results showed that the extract obtained from this LDH shifted OCP to nobler values, indicating the protection of metal. For benzotriazole-loaded LDH, FTIR and XRD results indicated the presence of benzotriazole in the structure, but its release was not observed. OCP results showed no significant increase of steel protection, corroborating with the conclusion that benzotriazole ions did not migrate to metal surface. Considering these results, it was proceeded the insertion of nitrogen oxides-loaded LDH in an automotive primer, under three different concentrations (0.2, 1 and 3%). Electrochemical Impedance Spectroscopy (EIS) showed that the more effective concentration on corrosion delay was 0.2%, which better balanced protection level conferred by LDH with a possible loss on effectiveness of coating due to porosity increase.A corrosão de metais consiste na deterioração destes em decorrência de sua interação com o ambiente, o que apresenta um aspecto econômico associado, uma vez que são despendidos recursos para o reparo destes materiais. Comumente utilizam-se revestimentos orgânicos para a proteção de metais; entretanto, tais revestimentos conferem uma barreira física de proteção, a qual está sujeita a falhas que podem expor o metal ao meio externo. Assim, a inserção de partículas capazes de promover proteção ativa contra corrosão nestes revestimentos é uma abordagem pertinente. Hidróxidos Duplos Lamelares (HDLs), que consistem em partículas inorgânicas do tipo hidrotalcita e são capazes de aprisionar ânions entre suas lamelas, têm sido estudados como carreadores de ânions de inibidores de corrosão para promover tal proteção ativa. Estes HDLs apresentam dupla funcionalidade: 1) promovem a liberação controlada de inibidores de corrosão e (2) realizam a captura de ânions corrosivos, diminuindo a agressividade do meio. Neste trabalho dois HDLs comerciais contendo diferentes inibidores de corrosão (óxidos de nitrogênio e benzotriazol) foram avaliados em relação a seu poder de troca iônica e desempenho na proteção de aço carbono. Em relação aos HDLs contendo óxidos de nitrogênio, teve-se que os resultados de Espectroscopia no Infravermelho com Transformada de Fourier (FTIR) e Difração de Raios-X (DRX) mostraram que os óxidos de nitrogênio se encontravam satisfatoriamente intercalados nos HDLs, os quais foram liberados quando em presença de íons cloreto. Os resultados de Potencial de Circuito Aberto (OCP) mostraram que o extrato obtido deste HDL deslocou o potencial de circuito aberto do aço carbono para valores mais nobres, indicando a proteção do metal. Para o HDL contendo benzotriazol, os resultados de FTIR e DRX indicaram a presença de benzotriazol na estrutura, mas sua liberação não foi observada. Os resultados de OCP neste caso não apresentaram deslocamento significativo nos valores de potencial de circuito aberto, corroborando com a conclusão de que os íons benzotriazol não migraram para a superfície do metal. Considerando tais resultados, procedeu-se com a inserção apenas dos HDL contendo óxidos de nitrogênio num primer automotivo, em três diferentes concentrações (0,2, 1 e 3% (m/m)). Os resultados de Espectroscopia de Impedância Eletroquímica (EIS) mostraram que a concentração de HDL mais efetiva no retardo à corrosão foi de 0,2%, sendo esta a concentração que melhor balanceou o nível de proteção conferido pelos HDLs com uma possível perda da efetividade do revestimento pelo aumento da porosidade

Performance Evaluation of Layered Double Hydroxides Containing Benzotriazole and Nitrogen Oxides as Autonomic Protection Particles against Corrosion

Layered double hydroxides (LDH) are lamellar structures with positively charged laminates and charge-compensating interlayer anions. The ion-exchange capacity of LDHs makes them as promising hosts for corrosion inhibitor anions with stimulus-responsive release and self-healing anticorrosion. In the current work, LDHs loaded with two different corrosion inhibitors (nitrogen oxides and benzotriazole) were evaluated for their ion-exchange capacity and autonomic protection against corrosion on carbon steel. Studies on nitrogen oxide-loaded LDH (NOx-LDH) showed that nitrogen oxides were successfully intercalated in LDH structure, which were released in chloride media. Open Circuit Potential (OCP) results showed that NOx-LDH extract shifted OCP to nobler values, indicating the protection of metal. For benzotriazole-loaded LDH (BTZ-LDH), the results indicated the presence of benzotriazole in the structure, but its release was not observed. OCP results showed no significant increase of carbon steel protection, corroborating with the conclusion that benzotriazole ions did not migrate to metal surface. Considering these results, the insertion of NOx-LDH in an automotive primer was proceeded, under three different concentrations (0.2. 1.0, and 3.0%). Electrochemical impedance spectroscopy (EIS) showed that the more effective NOx-LDH concentration on corrosion delay was 0.2%, which better balanced protection level conferred by LDH with a possible loss on effectiveness of coating due to increase in porosity

Evaluation of Corrosion Protection of Self-Healing Coatings Containing Tung and Copaiba Oil Microcapsules

The objective of the current research is to evaluate and compare the corrosion protection efficiency of the microcapsules containing tung oil and copaiba oil using stereoscopic images, electrochemical tests, open circuit potential (OCP), and polarization curves (Tafel analysis). Carbon steel plates were painted with three different coating systems: (a) a coating system with an automotive primer which served as the control, (b) a coating system with microcapsules containing 3% tung oil, and (c) a coating system with microcapsules containing 3% copaiba oil. A crosscut was performed using a scalpel on the coating surfaces to promote the release of the oils, and after drying, electrochemical cells were assembled using electrolyte 3% NaCl. From OCP analyses, it was verified that the coating system containing tung oil loaded microcapsules obtained more positive final values than the control system and the coating system containing copaiba oil loaded microcapsules. The stereoscope images corroborate the OCP results, and the polarization curve analyses also indicated that the microcapsules containing tung oil offer better corrosion protection than the other systems studied