Evaluation of the anticorrosive properties of environmental friendly inorganic corrosion inhibitors pigments

Anticorrosive properties of the following environmental friendly inorganic pigments were evaluated: zinc phosphate (ZP), zinc molybdate (ZM), zinc calcium molybdate (ZCM), zinc phosphomolybdate (ZPM) and zinc calcium phosphomolybdate (ZCPM). AISI 1010 steel samples were immersed in 10-2 mol dm-3 NaCl aqueous solution saturated with one of the pigments, followed by mass loss measurements, by monitoring the open circuit potential with immersion time and by potentiodynamic linear polarization at 1 mV s-1. The corrosion products on the steel surface were characterized by Scanning Electron Microscopy, Energy Dispersive X-ray and X-rays Diffraction analyses. All the pigments inhibited the corrosion of steel. The films formed on the steel surface protect the substrate against corrosion. The results suggest a synergic effect of phosphate and molybdate compounds in the phosphomolybdate-based pigments, improving the corrosion resistance of steel. The ZMP and ZCPM decreased the corrosion rate by a factor of 2.15 and 3.50, respectively.Neste trabalho foram estudadas as propriedades anticorrosivas de cinco pigmentos inorgânicos comerciais considerados ecologicamente corretos: fosfato de zinco (ZP), molibdato de zinco (ZM), molibdato de zinco e cálcio (ZCM), fosforomolibdato de zinco (ZPM) e fosforomolibdato de zinco e cálcio (ZCPM). Amostras de aço AISI 1010 foram imersas em solução aquosa de NaCl 10-2 mol dm-3 saturada com um dos pigmentos, seguido de medidas de perda de massa, monitoramento do potencial de circuito aberto com o tempo de imersão e polarização linear potenciodinâmica a 1 mV s-1. Os produtos de corrosão foram caracterizados por Microscopia Eletrônica de Varredura, Energia Dispersiva da raios-X e Difração de raios-X. Todos os pigmentos inibiram a corrosão do aço. Os filmes formados na superfície protegem o aço contra corrosão. Os resultados sugerem efeito sinérgico entre os compostos de fosfato e molibdato nos pigmentos a base de fosforomolibdato. Os pigmentos ZMP e ZCPM diminuíram a taxa de corrosão por um fator de 2,15 e 3,50, respectivamente